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What is the IPCC AR6 synthesis report and why does it matter?

Summary report by world’s leading climate scientists sets out actions to stave off climate breakdown

• Samoa PM urges world to save Pacific people from climate crisis obliteration

What is the IPCC AR6 synthesis report?

The fourth and final instalment of the sixth assessment report (AR6) by the Intergovernmental Panel on Climate Change , the body of the world’s leading climate scientists, is the synthesis report, so called because it draws together the key findings of the preceding three main sections. Together, they make a comprehensive review of global knowledge of the climate.

The first three sections covered the physical science of the climate crisis, including observations and projections of global heating, the impacts of the climate crisis and how to adapt to them, and ways of reducing greenhouse gas emissions. They were published in August 2021, February and April 2022 respectively.

The synthesis report also includes three other shorter IPCC reports published since 2018, on the impacts of global heating of more than 1.5C above pre-industrial levels, climate change and land , and climate change and the oceans and cryosphere (the ice caps and glaciers).

What will the key findings be?

There is no new science in the synthesis report, just a recap of the main findings of the previous publications. Those include warnings that the world was approaching “irreversible” levels of global heating, with catastrophic impacts rapidly becoming inevitable ; and that it was “now or never” to take drastic action to avoid disaster.

Much of the synthesis report is likely to focus on the future, setting out the possible policies and actions that will stave off the worst ravages of climate breakdown and warning of the impacts of further heating.

If the main findings have already been published, why is this report needed?

Its purpose is to reduce the thousands of pages of science to a shorter format, which is further condensed into a “summary for policymakers”, to provide scientific underpinning for global climate action. It is written by scientists but haggled over by representatives of the UN’s nearly 200 governments, so some argue it is subject to watering down by regimes that do not like its messages .

The report is supposed to inform the next UN climate summit, Cop28 , which will be hosted by the United Arab Emirates in Dubai from 30 November. There, nations’ progress on cutting greenhouse gas emissions since the Paris climate agreement of 2015 will be assessed. It is certain to find that governments are well off track on their emissions-cutting goals.

Will this report change anything?

This is the sixth IPCC report since the body was set up in 1988, with each comprehensive assessment taking roughly six to eight years to compile. As the reports have grown in size and urgency, so have global greenhouse gas emissions. In 2018, the IPCC warned that emissions must be halved by 2030, compared with 2010 levels, to have a good chance of limiting temperature rises to 1.5C. Yet emissions continue to climb. Last year, they rose by a little under 1% , according to the International Energy Agency. That leaves a rapidly diminishing “carbon budget” for the world to stay within the IPCC’s advised limits.

What should governments do?

Reduce emissions sharply and give up fossil fuels, through investments in renewable energy and other low-carbon technologies, increase energy efficiency, rethink agriculture and restore forests and degraded natural landscapes. It may also be necessary to develop technologies that suck carbon dioxide from the air, called “direct air capture” , or explore other means of “climate repair” .

When is the next IPCC report?

Not until about 2030. That means AR6 is effectively the last IPCC report while it is still feasible – only just – to stay within 1.5C.

Now that the impacts of the climate crisis are highly visible, and the underlying science well understood , some argue that the reporting cycles should be shortened, so that policymakers can receive clearer scientific advice throughout this crucial decade.

The IPCC can also be ordered to compile shorter reports on specific subjects, in between its mammoth comprehensive assessments. The increasingly urgent question of what to do if the world overshoots 1.5C of heating could well be a candidate for such treatment.

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Synthesis report of the ipcc sixth assessment report (ar6), attachments.

Urgent climate action can secure a liveable future for all [EN/AR/RU/ZH]

INTERLAKEN, Switzerland, March 20, 2023 — There are multiple, feasible and effective options to reduce greenhouse gas emissions and adapt to human-caused climate change, and they are available now, said scientists in the latest Intergovernmental Panel on Climate Change (IPCC) report released today.

“Mainstreaming effective and equitable climate action will not only reduce losses and damages for nature and people, it will also provide wider benefits,” said IPCC Chair Hoesung Lee. “This Synthesis Report underscores the urgency of taking more ambitious action and shows that, if we act now, we can still secure a liveable sustainable future for all.”

In 2018, IPCC highlighted the unprecedented scale of the challenge required to keep warming to 1.5°C. Five years later, that challenge has become even greater due to a continued increase in greenhouse gas emissions. The pace and scale of what has been done so far, and current plans, are insufficient to tackle climate change.

More than a century of burning fossil fuels as well as unequal and unsustainable energy and land use has led to global warming of 1.1°C above pre-industrial levels. This has resulted in more frequent and more intense extreme weather events that have caused increasingly dangerous impacts on nature and people in every region of the world.

Every increment of warming results in rapidly escalating hazards. More intense heatwaves, heavier rainfall and other weather extremes further increase risks for human health and ecosystems. In every region, people are dying from extreme heat. Climate-driven food and water insecurity is expected to increase with increased warming. When the risks combine with other adverse events, such as pandemics or conflicts, they become even more difficult to manage.

Losses and damages in sharp focus

The report, approved during a week-long session in Interlaken, brings in to sharp focus the losses and damages we are already experiencing and will continue into the future, hitting the most vulnerable people and ecosystems especially hard. Taking the right action now could result in the transformational change essential for a sustainable, equitable world.

“Climate justice is crucial because those who have contributed least to climate change are being disproportionately affected,” said Aditi Mukherji, one of the 93 authors of this Synthesis Report, the closing chapter of the Panel’s sixth assessment.

“Almost half of the world’s population lives in regions that are highly vulnerable to climate change. In the last decade, deaths from floods, droughts and storms were 15 times higher in highly vulnerable regions,“ she added.

In this decade, accelerated action to adapt to climate change is essential to close the gap between existing adaptation and what is needed. Meanwhile, keeping warming to 1.5°C above pre-industrial levels requires deep, rapid and sustained greenhouse gas emissions reductions in all sectors. Emissions should be decreasing by now and will need to be cut by almost half by 2030, if warming is to be limited to 1.5°C.

Clear way ahead

The solution lies in climate resilient development. This involves integrating measures to adapt to climate change with actions to reduce or avoid greenhouse gas emissions in ways that provide wider benefits.

For example: access to clean energy and technologies improves health, especially for women and children; low-carbon electrification, walking, cycling and public transport enhance air quality, improve health, employment opportunities and deliver equity. The economic benefits for people’s health from air quality improvements alone would be roughly the same, or possibly even larger than the costs of reducing or avoiding emissions.

Climate resilient development becomes progressively more challenging with every increment of warming. This is why the choices made in the next few years will play a critical role in deciding our future and that of generations to come.

To be effective, these choices need to be rooted in our diverse values, worldviews and knowledges, including scientific knowledge, Indigenous Knowledge and local knowledge. This approach will facilitate climate resilient development and allow locally appropriate, socially acceptable solutions.

“The greatest gains in wellbeing could come from prioritizing climate risk reduction for low-income and marginalised communities, including people living in informal settlements,” said Christopher Trisos, one of the report’s authors. “Accelerated climate action will only come about if there is a many-fold increase in finance. Insufficient and misaligned finance is holding back progress.”

Enabling sustainable development

There is sufficient global capital to rapidly reduce greenhouse gas emissions if existing barriers are reduced. Increasing finance to climate investments is important to achieve global climate goals. Governments, through public funding and clear signals to investors, are key in reducing these barriers. Investors, central banks and financial regulators can also play their part.

There are tried and tested policy measures that can work to achieve deep emissions reductions and climate resilience if they are scaled up and applied more widely. Political commitment, coordinated policies, international cooperation, ecosystem stewardship and inclusive governance are all important for effective and equitable climate action.

If technology, know-how and suitable policy measures are shared, and adequate finance is made available now, every community can reduce or avoid carbon-intensive consumption. At the same time, with significant investment in adaptation, we can avert rising risks, especially for vulnerable groups and regions.

Climate, ecosystems and society are interconnected. Effective and equitable conservation of approximately 30-50% of the Earth’s land, freshwater and ocean will help ensure a healthy planet. Urban areas offer a global scale opportunity for ambitious climate action that contributes to sustainable development.

Changes in the food sector, electricity, transport, industry, buildings and land-use can reduce greenhouse gas emissions. At the same time, they can make it easier for people to lead low-carbon lifestyles, which will also improve health and wellbeing. A better understanding of the consequences of overconsumption can help people make more informed choices.

“Transformational changes are more likely to succeed where there is trust, where everyone works together to prioritise risk reduction, and where benefits and burdens are shared equitably,” Lee said. “We live in a diverse world in which everyone has different responsibilities and different opportunities to bring about change. Some can do a lot while others will need support to help them manage the change.”

Temperature-Scale Equivalents 1.1C = 2.0F 1.5C = 2.7F

For more information, please contact:

IPCC Press Office: [email protected] Lance Ignon, SYR Communications Specialist: [email protected]

Notes to editors

AR6 Synthesis Report in Numbers

Review comments: 6841

• Governments: 47 (21 Developed, 2 Economies in transition, 22 Developing, 2 SIDS)
• Government Comments: 6636 (1814 Figures, 4822 Text)
• Observers: 5
• Observer Comments: 205

Core Writing Team members: 49 Review Editors: 9 Extended Writing Team Authors: 7 Contributing Authors: 28 Women: 41 Men: 52 Developing Country Authors: 37 Developed Country Authors: 56

About the IPCC

The Intergovernmental Panel on Climate Change (IPCC) is the United Nations body for assessing the science related to climate change. It was established by the United Nations Environmental Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide political leaders with periodic scientific assessments about climate change. The IPCC has 195 member states that are members of the UN or WMO.

Thousands of people from all over the world contribute to the work of the IPCC. For the assessment reports, experts volunteer their time as IPCC authors to assess the thousands of scientific papers published each year to provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks. An open and transparent review by experts and member governments is an essential part of the IPCC process to ensure an objective and complete assessment and to reflect a diverse range of views and expertise.

The IPCC has three working groups: Working Group I, which addresses with the physical science of climate change; Working Group II, which focuses on the impact, adaptation and vulnerability associated with climate change; and Working Group III, which deals with the mitigation of climate change. It also has a Task Force on Greenhouse Gas Inventories that develops methodologies for measuring emissions and removals.

IPCC assessments provide governments, at all levels, with scientific information they can use to develop climate policies. IPCC assessments are a key input into the international negotiations to tackle climate change. IPCC reports are drafted and reviewed in several stages to guarantee accuracy, objectivity and transparency.

About the Sixth Assessment Cycle

The IPCC publishes comprehensive scientific assessments every six to seven years. The previous one, the Fifth Assessment Report , was completed in 2014 and provided the main scientific input to The Paris Agreement.

At its 41nd Session in February 2015, the IPCC decided to produce a Sixth Assessment Report (AR6). At its 42nd Session in October 2015, it elected a new Bureau, which is composed of the IPCC Chair, the IPCC Vice-Chairs, the Co-Chairs and Vice-Chairs of the Working Groups, and the Co-Chairs of the Task Force. At its 43rd Session in April 2016, the IPCC decided to produce three Special Reports, a Methodology Report and AR6.

The Working Group I contribution to AR6, Climate Change 2021: the Physical Science Basis , was released on 9 August 2021. The Working Group II contribution, Climate Change 2022: Impacts, Adaptation and Vulnerability , was released on 28 February 2022. The Working Group III contribution, Climate Change 2022: Mitigation of Climate Change , was released on 4 April 2022.

The IPCC also published the following special reports on more specific issues during the Sixth Assessment Cycle:

Global Warming of 1.5°C (2.7°F) in October 2018; Climate Change and Land in August 2019; and Special Report on the Ocean and Cryosphere in a Changing Climate in September 2019

In May 2019, the IPCC released the 2019 Refinement to the 2006 IPCC Guidelines on National Greenhouse Gas Inventories .

For more information, please visit www.ipcc.ch . Most videos published by the IPCC can be found on its YouTube channel.

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10 Big Findings from the 2023 IPCC Report on Climate Change

• climate change
• Climate Resilience
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• climatewatch-pinned

March 20 marked the release of the final installment of the Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6) , an eight-year long undertaking from the world’s most authoritative scientific body on climate change. Drawing on the findings of 234 scientists on the  physical science of climate change , 270 scientists on  impacts, adaptation and vulnerability to climate change , and 278 scientists on  climate change mitigation , this  IPCC synthesis report  provides the most comprehensive, best available scientific assessment of climate change.

It also makes for grim reading. Across nearly 8,000 pages, the AR6 details the devastating consequences of rising greenhouse gas (GHG) emissions around the world — the destruction of homes, the loss of livelihoods and the fragmentation of communities, for example — as well as the increasingly dangerous and irreversible risks should we fail to change course.

But the IPCC also offers hope, highlighting pathways to avoid these intensifying risks. It identifies readily available, and in some cases, highly cost-effective actions that can be undertaken now to reduce GHG emissions, scale up carbon removal and build resilience. While the window to address the climate crisis is rapidly closing, the IPCC affirms that we can still secure a safe, livable future.

Here are 10 key findings you need to know:

1. Human-induced global warming of 1.1 degrees C has spurred changes to the Earth’s climate that are unprecedented in recent human history.

Already, with 1.1 degrees C (2 degrees F) of global temperature rise, changes to the climate system that are unparalleled over centuries to millennia are now occurring in every region of the world, from rising sea levels to more extreme weather events to rapidly disappearing sea ice.

Additional warming will increase the magnitude of these changes. Every 0.5 degree C (0.9 degrees F) of global temperature rise, for example, will cause clearly discernible increases in the frequency and severity of heat extremes, heavy rainfall events and regional droughts. Similarly, heatwaves that, on average, arose once every 10 years in a climate with little human influence will likely occur 4.1 times more frequently with 1.5 degrees C (2.7 degrees F) of warming, 5.6 times with 2 degrees C (3.6 degrees F) and 9.4 times with 4 degrees C (7.2 degrees F) — and the intensity of these heatwaves will also increase by 1.9 degrees C (3.4 degrees F), 2.6 degrees C (4.7 degrees F) and 5.1 degrees C (9.2 degrees F) respectively.

Rising global temperatures also heighten the probability of reaching dangerous tipping points in the climate system that, once crossed, can trigger self-amplifying feedbacks that further increase global warming, such as thawing permafrost or massive forest dieback. Setting such reinforcing feedbacks in motion can also lead to other substantial, abrupt and irreversible changes to the climate system. Should warming reach between 2 degrees C (3.6 degrees F) and 3 degrees C (5.4 degrees F), for example, the West Antarctic and Greenland ice sheets could melt almost completely and irreversibly over many thousands of years, causing sea levels to rise by several meters.

2. Climate impacts on people and ecosystems are more widespread and severe than expected, and future risks will escalate rapidly with every fraction of a degree of warming.

Described as an “an atlas of human suffering and a damning indictment of failed climate leadership” by United Nations Secretary-General António Guterres, one of AR6’s most alarming conclusions is that adverse climate impacts are already more far-reaching and extreme than anticipated. About half of the global population currently contends with severe water scarcity for at least one month per year, while higher temperatures are enabling the spread of vector-borne diseases, such as malaria, West Nile virus and Lyme disease. Climate change has also slowed improvements in agricultural productivity in middle and low latitudes, with crop productivity growth shrinking by a third in Africa since 1961. And since 2008, extreme floods and storms have forced over 20 million people from their homes every year.

Every fraction of a degree of warming will intensify these threats, and even limiting global temperature rise to 1.5 degree C is not safe for all. At this level of warming, for example, 950 million people across the world’s drylands will experience water stress, heat stress and desertification, while the share of the global population exposed to flooding will rise by 24%.

Similarly, overshooting 1.5 degrees C (2.7 degrees F), even temporarily, will lead to much more severe, oftentimes irreversible impacts, from local species extinctions to the complete drowning of salt marshes to loss of human lives from increased heat stress. Limiting the magnitude and duration of overshooting 1.5 degrees C (2.7 degrees F), then, will prove critical in ensuring a safe, livable future, as will holding warming to as close to 1.5 degrees C (2.7 degrees F) or below as possible. Even if this temperature limit is exceeded by the end of the century, the imperative to rapidly curb GHG emissions to avoid higher levels of warming and associated impacts remains unchanged.

3. Adaptation measures can effectively build resilience, but more finance is needed to scale solutions.

Climate policies in at least 170 countries now consider adaptation, but in many nations, these efforts have yet to progress from planning to implementation. Measures to build resilience are still largely small-scale, reactive and incremental, with most focusing on immediate impacts or near-term risks. This disparity between today’s levels of adaptation and those required persists in large part due to limited finance. According to the IPCC, developing countries alone will need $127 billion per year by 2030 and $295 billion per year by 2050 to adapt to climate change. But funds for adaptation reached just $23 billion to $46 billion from 2017 to 2018, accounting for only 4% to 8% of tracked climate finance.

The good news is that the IPCC finds that, with sufficient support, proven and readily available adaptation solutions can build resilience to climate risks and, in many cases, simultaneously deliver broader sustainable development benefits.

Ecosystem-based adaptation, for example, can help communities adapt to impacts that are already devastating their lives and livelihoods, while also safeguarding biodiversity, improving health outcomes, bolstering food security, delivering economic benefits and enhancing carbon sequestration. Many ecosystem-based adaptation measures — including the protection, restoration and sustainable management of ecosystems, as well as more sustainable agricultural practices like integrating trees into farmlands and increasing crop diversity — can be implemented at relatively low costs today. Meaningful collaboration with Indigenous Peoples and local communities is critical to the success of this approach, as is ensuring that ecosystem-based adaptation strategies are designed to account for how future global temperature rise will impact ecosystems.

4. Some climate impacts are already so severe they cannot be adapted to, leading to losses and damages.

Around the world, highly vulnerable people and ecosystems are already struggling to adapt to climate change impacts. For some, these limits are “soft” — effective adaptation measures exist, but economic, political and social obstacles constrain implementation, such as lack of technical support or inadequate funding that does not reach the communities where it’s needed most. But in other regions, people and ecosystems already face or are fast approaching “hard” limits to adaptation, where climate impacts from 1.1 degrees C (2 degrees F) of global warming are becoming so frequent and severe that no existing adaptation strategies can fully avoid losses and damages. Coastal communities in the tropics, for example, have seen entire coral reef systems that once supported their livelihoods and food security experience widespread mortality, while rising sea levels have forced other low-lying neighborhoods to move to higher ground and abandon cultural sites. 

Whether grappling with soft or hard limits to adaptation, the result for vulnerable communities is oftentimes irreversible and devastating. Such losses and damages will only escalate as the world warms. Beyond 1.5 degrees C (2.7 degrees F) of global temperature rise, for example, regions reliant on snow and glacial melt will likely experience water shortages to which they cannot adapt. At 2 degrees C (3.6 degrees F), the risk of concurrent maize production failures across important growing regions will rise dramatically. And above 3 degrees C (5.4 degrees F), dangerously high summertime heat will threaten the health of communities in parts of southern Europe.

Urgent action is needed to avert, minimize and address these losses and damages. At COP27, countries took a critical step forward by agreeing to establish funding arrangements for loss and damage, including a dedicated fund. While this represents  a historic breakthrough  in the climate negotiations, countries must now figure out the details of what these funding arrangements, as well as the new fund , will look like in practice — and it’s these details that will ultimately determine the adequacy, accessibility, additionality and predictability of these financial flows to those experiencing loss and damage.

5. Global GHG emissions peak before 2025 in 1.5 degrees C-aligned pathways.

The IPCC finds that there is a more than 50% chance that global temperature rise will reach or surpass 1.5 degrees C (2.7 degrees F) between 2021 and 2040 across studied scenarios, and under a high-emissions pathway, specifically, the world may hit this threshold even sooner — between 2018 and 2037. Global temperature rise in such a carbon-intensive scenario could also increase to 3.3 degrees C to 5.7 degrees C (5.9 degrees F to 10.3 degrees F) by 2100. To put this projected amount of warming into perspective, the last time global temperatures exceeded 2.5 degrees C (4.5 degrees F) above pre-industrial levels was more than 3 million years ago.

Changing course to limit global warming to 1.5 degrees C (2.7 degrees F) — with no or limited overshoot — will instead require deep GHG emissions reductions in the near-term. In modelled pathways that limit global warming to this goal, GHG emissions peak immediately and before 2025 at the latest. They then drop rapidly, declining 43% by 2030 and 60% by 2035, relative to 2019 levels.

While there are some bright spots — the annual growth rate of GHG emissions slowed from an average of 2.1% per year between 2000 and 2009 to 1.3% per year between 2010 and 2019, for example — global progress in mitigating climate change remains woefully off track. GHG emissions have climbed steadily over the past decade, reaching 59 gigatonnes of carbon dioxide equivalent (GtCO2e) in 2019 — approximately 12% higher than in 2010 and 54% greater than in 1990.

Even if countries achieved their climate pledges (also known as nationally determined contributions or NDCs),  WRI research  finds that they would reduce GHG emissions by just 7% from 2019 levels by 2030, in contrast to the 43% associated with limiting temperature rise to 1.5 degrees C (2.7 degrees F). And while handful of countries have submitted  new or enhanced NDCs  since the IPCC’s cut-off date,  more recent analysis  that takes these submissions into account finds that these commitments collectively still fall short of closing this emissions gap.

6. The world must rapidly shift away from burning fossil fuels — the number one cause of the climate crisis.

In pathways limiting warming to 1.5 degrees C (2.7 degrees F) with no or limited overshoot just a net 510 GtCO2 can be emitted before carbon dioxide emissions reach net zero in the early 2050s. Yet future carbon dioxide emissions from existing and planned fossil fuel infrastructure alone could surpass that limit by 340 GtCO2, reaching 850 GtCO2.

A mix of strategies can help avoid  locking in  these emissions, including retiring existing fossil fuel infrastructure, canceling new projects, retrofitting fossil-fueled power plants with carbon capture and storage (CCS) technologies and scaling up renewable energy sources like solar and wind (which are now cheaper than fossil fuels in many regions).

In pathways that limit warming to 1.5 degrees C (2.7 degrees F) — with no or limited overshoot — for example, global use of coal falls by 95% by 2050, oil declines by about 60% and gas by about 45%. These figures assume significant use of abatement technologies like CCS, and without them, these same pathways show much steeper declines by mid-century. Global use of coal without CCS, for example, is virtually phased out by 2050.

Although coal-fired power plants are starting to be retired across Europe and the United States, some multilateral development banks continue to invest in new coal capacity. Failure to change course risks stranding assets worth trillions of dollars.

7. We also need urgent, systemwide transformations to secure a net-zero, climate-resilient future.

While fossil fuels are the number one source of GHG emissions, deep emission cuts are necessary across all of society to combat the climate crisis. Power generation, buildings, industry, and transport are responsible for close to 80% of global emissions while agriculture, forestry and other land uses account for the remainder.

Take the  transport system , for instance. Drastically cutting emissions will require urban planning that minimizes the need for travel, as well as the build-out of shared, public and nonmotorized transport, such as rapid transit and bicycling in cities. Such a transformation will also entail increasing the supply of electric passenger vehicles, commercial vehicles and buses, coupled with wide-scale installation of rapid-charging infrastructure, investments in zero-carbon fuels for shipping and aviation and more.

Policy measures that make these changes less disruptive can help accelerate needed transitions, such as subsidizing zero-carbon technologies and taxing high-emissions technologies like fossil-fueled cars. Infrastructure design — like reallocating street space for sidewalks or bike lanes — can help people transition to lower-emissions lifestyles. It is important to note there are many co-benefits that accompany these transformations, too. Minimizing the number of passenger vehicles on the road, in this example, reduces harmful local air pollution and cuts traffic-related crashes and deaths.

Systems Change Lab  monitors, learns from and mobilizes action to achieve the far-reaching transformational shifts needed to limit global warming to 1.5 degrees C, halt biodiversity loss and build a just and equitable economy.

Transformative adaptation measures, too, are critical for securing a more prosperous future. The IPCC emphasizes the importance of ensuring that adaptation measures drive systemic change, cut across sectors and are distributed equitably across at-risk regions. The good news is that there are oftentimes strong synergies between transformational mitigation and adaptation. For example, in the global food system, climate-smart agriculture practices like shifting to  agroforestry  can improve resilience to climate impacts, while simultaneously advancing mitigation.  

8. Carbon removal is now essential to limit global temperature rise to 1.5 degrees C.

Deep decarbonization across all systems while building resilience won’t be enough to achieve global climate goals, though. The IPCC finds that all pathways that limit warming to 1.5 degrees C (2.7 degrees F) — with no or limited overshoot — depend on some quantity of  carbon removal . These approaches encompass both natural solutions, such as sequestering and storing carbon in trees and soil, as well as more nascent technologies that pull carbon dioxide directly from the air.

Hover over each carbon removal approach to learn more:

Note: This figure includes carbon removal approaches mentioned in countries' long-term climate strategies as well as other leading proposed approaches. Note: The natural vs. technological categorization shown here is illustrative rather than definitive and will vary depending on how approaches are applied, particularly for carbon removal approaches in the ocean.

The amount of carbon removal required depends on how quickly we reduce GHG emissions across other systems and the extent to which climate targets are overshot, with estimates ranging from between 5 GtCO2 to 16 GtCO2 per year needed by mid-century.

All carbon removal approaches have merits and drawbacks. Reforestation, for instance, represents a readily available, relatively low-cost strategy that, when implemented appropriately, can deliver a wide range of benefits to communities. Yet the carbon stored within these ecosystems is also vulnerable to disturbances like wildfires, which may increase in frequency and severity with additional warming. And, while technologies like bioenergy with carbon capture and storage (BECCS) may offer a more permanent solution, such approaches also risk displacing croplands, and in doing so, threatening food security. Responsibly researching, developing and deploying emerging carbon removal technologies, alongside existing natural approaches, will therefore require careful understanding of each solution’s unique benefits, costs and risks.

9. Climate finance for both mitigation and adaptation must increase dramatically this decade.

The IPCC finds that public and private finance flows for fossil fuels today far surpass those directed toward climate mitigation and adaptation. Thus, while annual public and private climate finance has risen by upwards of 60% since the IPCC’s Fifth Assessment Report, much more is still required to achieve global climate change goals. For instance, climate finance will need to increase between 3 and 6 times by 2030 to achieve mitigation goals, alone.

This gap is widest in developing countries, particularly those already struggling with debt, poor credit ratings and economic burdens from the COVID-19 pandemic. Recent mitigation investments, for example, need to increase by at least sixfold in Southeast Asia and developing countries in the Pacific, fivefold in Africa and fourteenfold in the Middle East by 2030 to hold warming below 2 degrees C (3.6 degrees F). And across sectors, this shortfall is most pronounced for agriculture, forestry and other land use, where recent financial flows are 10 to 31 times below what is required to achieve the Paris Agreement’s goals.

Finance for adaptation, as well as loss and damage, will also need to rise dramatically. Developing countries, for example, will need $127 billion per year by 2030 and $295 billion per year by 2050. While AR6 does not assess countries’ needs for finance to avert, minimize and address losses and damages,  recent estimates  suggest that they will be substantial in the coming decades. Current funds for both fall well below estimated needs, with the highest estimates of adaptation finance totaling under $50 billion per year.

10. Climate change — as well as our collective efforts to adapt to and mitigate it — will exacerbate inequity should we fail to ensure a just transition.  

Households with incomes in the top 10%, including a relatively large share in developed countries, emit upwards of 45% of the world's GHGs, while those families earning in the bottom 50% account for 15% at most. Yet the effects of climate change already — and will continue to — hit poorer, historically marginalized communities the hardest.

Today, between 3.3 billion and 3.6 billion people live in countries that are highly vulnerable to climate impacts, with global hotspots concentrated in the Arctic, Central and South America, Small Island Developing states, South Asia and much of sub-Saharan Africa. Across many countries in these regions, conflict, existing inequalities and development challenges (e.g., poverty and limited access to basic services like clean water) not only heighten sensitivity to climate hazards, but also limit communities’ capacity to adapt.  Mortality from storms, floods and droughts, for instance, was 15 times higher in countries with high vulnerability to climate change than in those with very low vulnerability from 2010 to 2020.

At the same time, efforts to mitigate climate change also risk disruptive changes and exacerbating inequity. Retiring coal-fired power plants, for instance, may displace workers, harm local economies and reconfigure the social fabric of communities, while inappropriately implemented efforts to halt deforestation could heighten poverty and intensify food insecurity. And certain climate policies, such as  carbon taxes  that raise the cost of emissions-intensive goods like gasoline, can also prove to be regressive, absent of efforts to recycle the revenues raised from these taxes back into programs that benefit low-income communities.

Fortunately, the IPCC identifies a range of measures that can support a just transition and help ensure that no one is left behind as the world moves toward a net-zero-emissions, climate-resilient future. Reconfiguring social protection programs (e.g., cash transfers, public works programs and social safety nets) to include adaptation, for example, can reduce communities’ vulnerability to a wide range of future climate impacts, while strengthening justice and equity. Such programs are particularly effective when paired with efforts to expand access to infrastructure and basic services.

Similarly, policymakers can design mitigation strategies to better distribute the costs and benefits of reducing GHG emissions. Governments can pair efforts to phase out coal-fired electricity generation, for instance, with subsidized job retraining programs that support workers in developing the skills needed to secure new, high-quality jobs. Or, in another example, officials can couple policy interventions dedicated to expanding access to public transit with interventions to improve access to nearby, affordable housing.

Across both mitigation and adaptation measures, inclusive, transparent and participatory decision-making processes will play a central role in ensuring a just transition. More specifically, these forums can help cultivate public trust, deepen public support for transformative climate action and avoid unintended consequences.

Looking Ahead

The IPCC’s AR6 makes clear that risks of inaction on climate are immense and the way ahead requires change at a scale not seen before. However, this report also serves as a reminder that we have never had more information about the gravity of the climate emergency and its cascading impacts — or about what needs to be done to reduce intensifying risks.

Limiting global temperature rise to 1.5 degrees C (2.7 degrees F) is still possible, but only if we act immediately. As the IPCC makes clear, the world needs to peak GHG emissions before 2025 at the very latest, nearly halve GHG emissions by 2030 and reach net-zero CO2 emissions around mid-century, while also ensuring a just and equitable transition. We’ll also need an all-hands-on-deck approach to guarantee that communities experiencing increasingly harmful impacts of the climate crisis have the resources they need to adapt to this new world. Governments, the private sector, civil society and individuals must all step up to keep the future we desire in sight. A narrow window of opportunity is still open, but there’s not one second to waste.

Note: In addition to showcasing findings from the IPCC’s AR6 Synthesis Report, this article also draws on previous articles detailing the IPCC’s findings on  the physical science of climate change ,  impacts, adaption and vulnerability ,  and  climate change mitigation .

Relevant Work

6 takeaways from the 2022 ipcc climate change mitigation report, 6 big findings from the ipcc 2022 report on climate impacts, adaptation and vulnerability, 5 big findings from the ipcc’s 2021 climate report, 8 things you need to know about the ipcc 1.5˚c report.

Join us on March 23 for a high-level webinar featuring IPCC authors, government representatives and leading carbon removal experts to discuss how carbon removal is a critical tool in our toolbox to address the climate crisis.

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How to Synthesize Written Information from Multiple Sources

Shona McCombes

Content Manager

B.A., English Literature, University of Glasgow

Shona McCombes is the content manager at Scribbr, Netherlands.

Learn about our Editorial Process

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

On This Page:

When you write a literature review or essay, you have to go beyond just summarizing the articles you’ve read – you need to synthesize the literature to show how it all fits together (and how your own research fits in).

Synthesizing simply means combining. Instead of summarizing the main points of each source in turn, you put together the ideas and findings of multiple sources in order to make an overall point.

At the most basic level, this involves looking for similarities and differences between your sources. Your synthesis should show the reader where the sources overlap and where they diverge.

Unsynthesized Example

Franz (2008) studied undergraduate online students. He looked at 17 females and 18 males and found that none of them liked APA. According to Franz, the evidence suggested that all students are reluctant to learn citations style. Perez (2010) also studies undergraduate students. She looked at 42 females and 50 males and found that males were significantly more inclined to use citation software ( p < .05). Findings suggest that females might graduate sooner. Goldstein (2012) looked at British undergraduates. Among a sample of 50, all females, all confident in their abilities to cite and were eager to write their dissertations.

Synthesized Example

Studies of undergraduate students reveal conflicting conclusions regarding relationships between advanced scholarly study and citation efficacy. Although Franz (2008) found that no participants enjoyed learning citation style, Goldstein (2012) determined in a larger study that all participants watched felt comfortable citing sources, suggesting that variables among participant and control group populations must be examined more closely. Although Perez (2010) expanded on Franz’s original study with a larger, more diverse sample…

Step 1: Organize your sources

After collecting the relevant literature, you’ve got a lot of information to work through, and no clear idea of how it all fits together.

Before you can start writing, you need to organize your notes in a way that allows you to see the relationships between sources.

One way to begin synthesizing the literature is to put your notes into a table. Depending on your topic and the type of literature you’re dealing with, there are a couple of different ways you can organize this.

Summary table

A summary table collates the key points of each source under consistent headings. This is a good approach if your sources tend to have a similar structure – for instance, if they’re all empirical papers.

Each row in the table lists one source, and each column identifies a specific part of the source. You can decide which headings to include based on what’s most relevant to the literature you’re dealing with.

For example, you might include columns for things like aims, methods, variables, population, sample size, and conclusion.

For each study, you briefly summarize each of these aspects. You can also include columns for your own evaluation and analysis.

The summary table gives you a quick overview of the key points of each source. This allows you to group sources by relevant similarities, as well as noticing important differences or contradictions in their findings.

Synthesis matrix

A synthesis matrix is useful when your sources are more varied in their purpose and structure – for example, when you’re dealing with books and essays making various different arguments about a topic.

Each column in the table lists one source. Each row is labeled with a specific concept, topic or theme that recurs across all or most of the sources.

Then, for each source, you summarize the main points or arguments related to the theme.

The purposes of the table is to identify the common points that connect the sources, as well as identifying points where they diverge or disagree.

Step 2: Outline your structure

Now you should have a clear overview of the main connections and differences between the sources you’ve read. Next, you need to decide how you’ll group them together and the order in which you’ll discuss them.

For shorter papers, your outline can just identify the focus of each paragraph; for longer papers, you might want to divide it into sections with headings.

There are a few different approaches you can take to help you structure your synthesis.

If your sources cover a broad time period, and you found patterns in how researchers approached the topic over time, you can organize your discussion chronologically .

That doesn’t mean you just summarize each paper in chronological order; instead, you should group articles into time periods and identify what they have in common, as well as signalling important turning points or developments in the literature.

If the literature covers various different topics, you can organize it thematically .

That means that each paragraph or section focuses on a specific theme and explains how that theme is approached in the literature.

Source Used with Permission: The Chicago School

If you’re drawing on literature from various different fields or they use a wide variety of research methods, you can organize your sources methodologically .

That means grouping together studies based on the type of research they did and discussing the findings that emerged from each method.

If your topic involves a debate between different schools of thought, you can organize it theoretically .

That means comparing the different theories that have been developed and grouping together papers based on the position or perspective they take on the topic, as well as evaluating which arguments are most convincing.

Step 3: Write paragraphs with topic sentences

What sets a synthesis apart from a summary is that it combines various sources. The easiest way to think about this is that each paragraph should discuss a few different sources, and you should be able to condense the overall point of the paragraph into one sentence.

This is called a topic sentence , and it usually appears at the start of the paragraph. The topic sentence signals what the whole paragraph is about; every sentence in the paragraph should be clearly related to it.

A topic sentence can be a simple summary of the paragraph’s content:

“Early research on [x] focused heavily on [y].”

For an effective synthesis, you can use topic sentences to link back to the previous paragraph, highlighting a point of debate or critique:

“Several scholars have pointed out the flaws in this approach.” “While recent research has attempted to address the problem, many of these studies have methodological flaws that limit their validity.”

By using topic sentences, you can ensure that your paragraphs are coherent and clearly show the connections between the articles you are discussing.

As you write your paragraphs, avoid quoting directly from sources: use your own words to explain the commonalities and differences that you found in the literature.

Don’t try to cover every single point from every single source – the key to synthesizing is to extract the most important and relevant information and combine it to give your reader an overall picture of the state of knowledge on your topic.

Step 4: Revise, edit and proofread

Like any other piece of academic writing, synthesizing literature doesn’t happen all in one go – it involves redrafting, revising, editing and proofreading your work.

Checklist for Synthesis

•   Do I introduce the paragraph with a clear, focused topic sentence?
•   Do I discuss more than one source in the paragraph?
•   Do I mention only the most relevant findings, rather than describing every part of the studies?
•   Do I discuss the similarities or differences between the sources, rather than summarizing each source in turn?
•   Do I put the findings or arguments of the sources in my own words?
•   Is the paragraph organized around a single idea?
•   Is the paragraph directly relevant to my research question or topic?
•   Is there a logical transition from this paragraph to the next one?

Further Information

How to Synthesise: a Step-by-Step Approach

Help…I”ve Been Asked to Synthesize!

Learn how to Synthesise (combine information from sources)

How to write a Psychology Essay

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Flash Flood Guidance System Community: Member-to-Member Innovation for Operation

In late March, 42 operational forecasters from NMHSs from Southeast Europe, the Black Sea, and the Middle East regions gathered in Bucharest for a 3-day Flash Flood Guidance System (FFGS) User Training workshop hosted by the National Meteorological Administration of Romania and technically supported by the Turkish State Meteorological Service (TSMS).  

Floods are the deadliest natural hazards, striking numerous regions in the world each year. The projected increase in the intensity of extreme precipitation translates to an increase in the frequency and magnitude of pluvial floods – surface water and flash floods ( IPCC AR6 Synthesis Report: Climate Change 2023 ). This, combined with land use changes and increased population, negatively impacts flood-prone areas. 

WMO, with financial support from the USAID Bureau for Humanitarian Assistance (BHA) and the active involvement of 73 National Meteorological and Hydrological Services (NMHSs) is leading the Flash Forecasting Guidance System (FFGS) with Global Coverage project.  

The project entered its “Sustainability Phase”, which includes upscaling FFGS coverage to 31 more countries in support of Early Warnings for All. In addition, in the Sustainability Phase, the responsibility for management and enhancement of the system and capacities will be handed over to global, regional, and national centers. As part of this journey, Members are developing tools for enhancing the effectiveness of flash flood forecasts and warning messages. 

The FFGS User Training Workshop 

During the workshop, TSMS introduced a suite of innovative tools designed to advance flash flood response and preparedness. The first one, a life-saving automated email warning system, alerts forecasters of potential flash floods, ensuring they receive alerts from FFGS anywhere in the world. The second tool offers a detailed visualization of flash flood threats on Google Maps. Lastly, a specialized application developed for Türkiye monitors Snow Water Potential, crucial for managing water resources and anticipating flood risks due to rapid snowmelt. This application supports sectors like energy, agriculture, and water management with enhanced preparedness and informed decision-making capabilities. 

The primary objective of the Workshop was to train forecasters on the use of the post-processing tools developed by the TSMS to: 

• monitor FFGS products more precisely, 
• issue flash flood early warnings more effectively, 
• provide forecasters with timely and effective data and products. 

Furthermore, the workshop included practical training and hands-on sessions on the effective usage and operation of the new tools. 

Enhancing collaboration and knowledge exchange 

One of the main focuses of the workshop was member-to-member (m2m) learning and technology transfer. Participants hailed from countries with diverse meteorological backgrounds, each facing unique challenges in flash flood forecasting.  

Tatjana Vujnovic from the Croatian Meteorological and Hydrological Service underscored the importance of sharing effective practices and tools among colleagues. 

Member-to-member learning and the transfer of technology are crucial. If a member has developed an effective practice or a new tool - or "subtool" - it can be of great significance. Additionally, with varying levels of experience within our team, newer colleagues can gain deeper insights from more experienced colleagues, offering a broader perspective. We are eagerly anticipating the operationalization of these tools, such as warning emails with maps. We also look forward to the possibility of entering addresses to send warnings ourselves, adapting to changes within the forecasting teams. This flexibility and speed are key to improving our response to weather-related emergencies.

This sentiment was echoed by Abed El Rahman Zawawy from the Lebanese Meteorological Department, who highlighted the value of collaboration in improving flash flood warning systems across borders.  

Meeting peers who speak the same scientific language, share the same meteorological challenges, and have similar concerns undoubtedly expands my professional network and enhances my skills. Cooperation between meteorological services, especially among neighboring countries, is a logical step toward improving flash flood warning systems. This approach is vital because clouds do not recognize borders, and rivers are not confined to a single country. This particular workshop will improve my work methodologies and interactions with colleagues, positively impacting our collective forecasting abilities.

Bridging technological and knowledge gaps 

Amalya Misakyan of the Hydrometeorology and Monitoring Center SNCO in Armenia shed light on the challenges faced by her country and praised the tools developed by TSMS for their ability to simplify tasks and save time.  

In our country, the primary challenges we face in issuing timely flash flood warnings include the lack of nowcasting/radars and NWP (Numerical Weather Prediction) models. Our meteorological forecasts rely mainly on global or regional models, which often do not perform well in mountainous regions. For flash flood forecasting, in addition to our own products, we primarily utilize FFGS (Flash Flood Guidance System) products . The developed tools simplify the work of hydrological forecasters, facilitate their tasks, and help save time.

Ertan Turgu from the TSMS emphasized the importance of internal training to ensure the successful transfer of knowledge acquired during workshops.  

The new enhancements introduced by members, such as those demonstrated by TSMS, significantly contribute to the overall operations of forecasters and hydrologists. Knowledge and technology used here make the forecaster's task more manageable, encouraging greater effectiveness in their work. Organizing internal training within the country could enable the transfer of knowledge and skills acquired in these workshops to other staff members and contribute to providing better and more accurate Early Warning forecasts.

Marius Matreata from the National Institute of Hydrology and Water Management in Romania outlined key enhancements needed to advance flash flood forecasting capabilities. Matreata's vision included the development of a unified "FFG Client application" to integrate functionalities from the tools developed by TSMS and others, paving the way for more efficient and accurate early warnings on a national level. 

There's also a critical need to enhance monitoring capabilities with new sensor technologies, provide continuous training for forecasters, ensure team stability by reducing personnel changes, and continue to improve model capabilities. Implementing these enhancements could significantly reduce the time needed to evaluate the severity of a situation and elaborate warning messages. It highlights the likely need to develop a local "FFG Client application" for national level forecasters, integrating selected functionalities from tools developed by TSMS and others from different regions.

The FFGS User Training workshop marked a significant milestone in the ongoing efforts to enhance flash flood forecasting and early warning systems. Through member-to-member learning and collaboration, operational forecasters from diverse regions came together to exchange knowledge, share effective practices, and explore innovative tools developed by the TSMS. The workshop not only addressed the challenges faced by participating countries but also paved the way for future advancements in flash flood forecasting capabilities. 

As countries move forward in the Sustainability Phase of the FFGS project, continued collaboration, internal training, and technological advancements will be essential in ensuring the effective management of flood risks and the protection of vulnerable communities worldwide. 

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• Open access
• Published: 26 April 2024

Computationally guided synthesis of a hierarchical [4[2+3]+6] porous organic ‘cage of cages’

• Qiang Zhu   ORCID: orcid.org/0000-0001-6462-9340 1 , 2 ,
• Hang Qu   ORCID: orcid.org/0000-0001-8726-3062 1 ,
• Gokay Avci 3 ,
• Roohollah Hafizi 4 ,
• Chengxi Zhao 1 , 5 ,
• Graeme M. Day   ORCID: orcid.org/0000-0001-8396-2771 4 ,
• Kim E. Jelfs   ORCID: orcid.org/0000-0001-7683-7630 3 ,
• Marc A. Little   ORCID: orcid.org/0000-0002-1994-0591 6 &
• Andrew I. Cooper   ORCID: orcid.org/0000-0003-0201-1021 1 , 2  

Nature Synthesis ( 2024 ) Cite this article

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• Computational chemistry
• Computational methods
• Materials chemistry
• Molecular capsules
• Self-assembly

Here we report a two-step, hierarchical synthesis that assembles a trigonal prismatic organic cage into a more symmetric, higher-order tetrahedral cage, or ‘cage of cages’. Both the preformed [2+3] trigonal prismatic cage building blocks and the resultant tetrahedral [4[2+3]+6]cage molecule are constructed using ether bridges. This strategy affords the [4[2+3]+6]cage molecule excellent hydrolytic stability that is not a feature of more common dynamic cage linkers, such as imines. Despite its relatively high molar mass (3,001 g mol −1 ), [4[2+3]+6]cage exhibits good solubility and crystallizes into a porous superstructure with a surface area of 1,056 m 2  g −1 . By contrast, the [2+3] building block is not porous. The [4[2+3]+6]cage molecule shows high CO 2 and SF 6 uptakes due to its polar skeleton. The preference for the [4[2+3]+6]cage molecule over other cage products can be predicted by computational modelling, as can its porous crystal packing, suggesting a broader design strategy for the hierarchical assembly of organic cages with synthetically engineered functions.

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A class of organic cages featuring twin cavities

Self-assembled conjoined-cages

Non-statistical assembly of multicomponent [Pd2ABCD] cages

The chemical synthesis of complex organic molecules is part of our toolkit to access materials with unique structures and functions 1 , 2 , 3 , 4 , 5 . Supramolecular self-assembly is a powerful strategy to synthesize molecules comprising a number of separate precursors 6 , 7 , 8 ; these assemblies can also be nanometres in size 9 , 10 or chemically interlocked 11 , 12 . However, obtaining the desired self-assembly outcomes for more complex molecules quickly becomes synthetically challenging, particularly when the bond-forming chemistry has low reversibility. This creates a dichotomy: the more successful supramolecular reactions often lead to labile, unstable products, and this can limit the scope for applications. This challenge can be tackled by careful tuning of precursor structure and functionality, such as molecular geometry, or by iterative optimization of the synthetic procedures, but the best reaction conditions are often not intuitively obvious.

Some of the earliest supramolecular systems were synthesized by condensing simple bidentate building blocks, such as ethylenediamine and triethylene glycol, to form cryptands and crown ethers, respectively 13 . These molecules inspired the synthesis of larger and more complex architectures. For example, Fujita and co-workers introduced the concept of emergent behaviour in the assembly of large self-assembled macrocyclic products using carefully designed precursors 14 . Such supramolecular design strategies have allowed us to synthesize more complex self-assembled structures and, hence, to unlock new applications 2 , 15 , 16 . However, high structural complexity is often accompanied by increased synthetic challenges and lower predictability because of sensitivity to parameters such as the precise bond angles in the precursors 9 , 14 , 17 .

Postsynthetic modifications have been used previously to enhance the porosity of organic cages 18 , 19 , such as by hooping parts of the cage together 20 . More recently, we and others have used hierarchical assembly strategies to form topologically complex hydrogen-bonded organic frameworks 21 , 22 and covalently bonded materials, such as covalent organic frameworks 23 , 24 , 25 , 26 , using three-dimensional organic cages as the building blocks 27 . These studies have shown that cage-based building blocks can assemble into higher-order structures and increase the complexity of the resulting materials, for instance, by controlling network topology and interpenetration, while still offering a degree of structural predictability. In turn, this has afforded cage-based hydrogen-bonded organic frameworks and three-dimensional cage-based covalent organic frameworks with properties such as guest-responsive structural flexibility 23 and self-healing behaviour 28 . However, this hierarchical structuring approach does not appear to have been extended to the preparation of porous organic cage molecules 18 , 29 : that is, to synthesize larger porous cages from smaller organic cage precursors.

The use of organic cages as precursors to synthesize higher-order porous structures is attractive because it embeds cage molecules, with their own chemical complexity, into larger, hierarchical cages with the potential to create new functions while retaining useful properties such as solution processability 19 , 27 , 30 . For example, this strategy might produce porous materials with more sophisticated hierarchical porosities. To tackle this goal, we considered three criteria: (1) geometry—the cage precursors need geometries that can be arranged into a higher-order structure in a useful yield; (2) chemical stability—the chemical bonding in the cages must not be too labile, both to impart stability for applications and also to avoid the dynamic scrambling that might occur, for example, in trying to construct an imine cage from another imine cage 31 ; (3) rigidity—the precursors need sufficient rigidity to direct chemical reactivity to the desired product and to ensure that the resultant hierarchical cage is shape persistent and retains its porous structure after removal of solvent from the voids.

To meet these three criteria, we chose a trigonal prismatic [2+3] ether-bridged cage molecule, Cage-3-Cl , as the polyhedral building block to construct a hierarchical ‘cage of cages’ (Fig. 1 ). The preconfigured rigid geometry and excellent chemical stability of Cage-3-Cl allowed this [2+3] cage to assemble with tetrafluorohydroquinone ( TFHQ ) into the hierarchically structured organic ‘cage of cages’ compound, [4[2 + 3] + 6]cage .

The [ 4[2 + 3] + 6]cage molecule was synthesized via the S N Ar reaction between Cage-3-Cl and TFHQ in the presence of DIPEA. The triangular prism and the yellow sticks in the lower figure scheme represent Cage-3-Cl and TFHQ , respectively.

Results and discussion

Nucleophilic aromatic substitution (S N Ar) reactions have been reported to undergo reversible covalent bond formation when using electron-poor aromatic compounds 32 , 33 , 34 , while still leading to stable molecular products. Reversible error-correction is important for the formation of complex molecules that must self-sort during the reaction from a variety of possible products. Although the S N Ar reaction has been used in the synthesis of ether-bridged cages, most tend to be [2+3] or [2+4] cage products with small intrinsic cavities 35 , 36 , 37 , with the exception of a larger [4+6] ether-linked cage reported by Santos and co-workers 32 . One possible reason for the lack of larger cages synthesized via S N Ar chemistry is the less predictable orientation of the ether bridges compared to the imines and boronate esters for which larger cages are more commonplace 10 , 38 , 39 , 40 , 41 , 42 .

Previous investigations by our group and others have demonstrated that Cage-3-Cl has a highly symmetric and rigid triangular prism geometry both in solution and in the solid state 21 , 36 . This geometry makes Cage-3-Cl an ideal building block for forming higher-order cage molecules, such as molecular barrels 20 . The three residual chlorine atoms exhibit high reactivity 43 , 44 , which is essential for forming ether bridges. We selected TFHQ as the linear bridge between Cage-3-Cl molecules because the fluorine atoms might afford extra barriers to restrict the rotation of the ether bridges, and might improve the solubility of the resulting cage–cage molecules 36 , 45 .

To explore the available bond angles and the relative flexibility of the ether bridges in possible hierarchical cage products, we performed molecular dynamics (MD) and density functional theory (DFT) calculations. Models were constructed with the supramolecular toolkit (stk) software 46 to predict the most likely reaction products. As shown in Fig. 2 , the [4[2+3]+6] stoichiometry is predicted to form a stable, shape-persistent cage structure that exhibits a much lower energy than alternative [2[2+3]+3] and [8[2+3]+12] topologies. The [2[2+3]+3] topology has by far the highest relative energy (660.8 kJ mol −1 ) due to its highly strained geometry. The [8[2+3]+12] topology has higher relative energy (24.04 kJ mol −1 ) than the [4[2+3]+6] cage, which suggests that the [4[2+3]+6] topology is the thermodynamically favoured product, although we stress that these calculations do not include any solvent effects. As such, the [8[2+3]+12] topology might also be accessible under other synthesis conditions, whereas we predict that the [2[2+3]+3] topology is not. The cis – trans configurations of the ether bridges in the hypothetical [8[2+3]+12]cage can result in various positional configurations; all of these structural conformers were predicted to have relative energies that were between 24.0 and 229.1 kJ mol −1 higher than the [4[2+3]+6]cage, indicating a strong preference for the [4[2+3]+6] product (Supplementary Information Section 1 and Supplementary Figs. 1 – 4 ).

x  = number of Cage-3-Cl cages, y  = number of TFHQ linkers. Atom colours: carbon, grey; nitrogen, blue; oxygen, red; fluorine, green. Hydrogen atoms are omitted for clarity. Note the break in the energy scale for the highly strained [2[2+3]+3]cage, which has by far the highest relative energy (660.8 kJ mol −1 ). The DFT energies indicate that the [4[2+3]+6] stoichiometry is predicted to form a stable, shape-persistent cage structure that has a lower relative energy (24.04 kJ mol −1 ) than the alternative [8[2+3]+12] topology.

These simulation results suggested that it might be possible to synthesize [4[2 + 3] + 6]cage via the S N Ar reaction between Cage-3-Cl and TFHQ (Fig. 1 ). We therefore attempted the reaction experimentally, and screened a range of conditions in which we varied the reagent concentration, solvent and base (Supplementary Table 1 ). From these experiments, we found that the reaction in acetone in the presence of the acid scavenger N , N -diisopropylethylamine (DIPEA) afforded a new product with the highest yield of 53% after purification. The 1 H NMR spectrum for the purified reaction product from the acetone reaction with DIPEA showed two singlets at 7.09 and 6.85 ppm, which we assigned to the two aromatic protons in the [2+3] cage (H a and H b ; Fig. 3a and Supplementary Fig. 5 ). The presence of two singlets indicates different environments, which we attribute to one of the protons being more shielded. However, apart from this splitting of the aromatic proton singlet in Cage-3-Cl , the NMR spectroscopy data indicated that the resulting product had high symmetry in solution. In the 13 C NMR spectrum, we observed three signals in the 174.5–173.1 ppm range (Fig. 3b and Supplementary Fig. 6 ), which we assigned to the triazine ring carbon atoms. We attribute the characteristic splitting, observed at 142.5 and 140.0 ppm with a coupling constant of 250 MHz, to the coupling between the carbon and fluorine atoms in the TFHQ linker (Fig. 3b and Supplementary Fig. 6 ). We also confirmed the presence of these fluorinated aromatic rings by 19 F NMR spectroscopy, observing a singlet at −155.62 ppm (Supplementary Fig. 7 ), indicating that the fluorine atoms were symmetrically equivalent in solution. We also used high-resolution matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to analyse the reaction product. We found an ion with a mass-to-charge ( m / z ) ratio of 3,002.0756 (Fig. 3c and Supplementary Figs. 8 and 9 ), which matched well with the theoretical value of [ [4[2 + 3] + 6]cage  + H] + (3002.0871), indicating the formation of [4[2 + 3] + 6]cage .

a , 1 H NMR (400 MHz, acetone- d 6 ) spectra of Cage-3-Cl (green, bottom) and [4[2 + 3] + 6]cage (blue, top). b , 13 C NMR (100 MHz, dioxane- d 8 ) spectra: TFHQ (yellow, bottom), Cage-3-Cl (green, middle) and [4[2 + 3] + 6]cage (blue, top). Insets: zoom-ins of the boxed regions. The NMR spectra highlight the splitting of peaks due to the formation of a hierarchical ‘cage of cages’ structure. c , High-resolution MALDI-TOF spectrum of [4[2 + 3] + 6]cage , showing an ion with an m / z ratio of 3,002.0756 assigned to [ [4[2 + 3] + 6]cage  + H] + . Two internal calibrants (Spherical) with m / z ratios of 2,979 and 3,423 that bracketed the ion of interest were used to limit the m / z error to ±5 ppm.

Source data

We next grew crystals for single-crystal X-ray diffraction analysis to confirm the structure of the [4[2 + 3] + 6]cage molecule. Slow evaporation of a mixture of acetone/ethanol afforded single crystals suitable for X-ray analysis using synchrotron radiation (Supplementary Fig. 10 and Supplementary Table 2 ). The synchrotron single-crystal structure, which we refined in the monoclinic P 2 1 space group, revealed that the [4[2 + 3] + 6]cage molecule adopts a tetrahedral topology, where four Cage-3-Cl cage molecules serve as the vertices and six TFHQ molecules are located as the edges (Fig. 4a ). The interior and the exterior aryl caps of the Cage-3-Cl cage molecules form a core–shell structure, defining an inner and outer truncated tetrahedron with edge lengths of 6.4 and 13.7 Å, respectively (Fig. 4b ). We also calculated the electrostatic potentials for the [4[2 + 3] + 6]cage molecule, which showed that the centre of the [4[2 + 3] + 6]cage molecule is surrounded by aromatic rings, affording π–π interactions for any guest molecules within the cage (Fig. 4c and Supplementary Information Section 1 ).

a , Structure of an individual [4[2 + 3] + 6]cage molecule. Atom colours: carbon, grey; hydrogen, white; nitrogen, blue; oxygen, red; fluorine, green. b , Representation of the [4[2 + 3] + 6]cage molecule using two truncated tetrahedra on the inner and outer aryl caps of the [2+3] Cage-3-Cl cage molecules. For clarity, all atoms here are coloured grey. c , Electrostatic potential maps of the [4[2 + 3] + 6]cage molecule. The red and blue surfaces represent negative and positive regions of potential, respectively. Colour bar, −31.4 to 94.1 kcal mol −1 . d , e , Pore channels in the extended [4[2 + 3] + 6]cage crystal structure as viewed along the a axis ( d ) and the b axis ( e ). For clarity, hydrogen atoms are omitted in b , e and f . The yellow surfaces in d and e represent the contact surface as measured using a 1.2 Å diameter probe. f , Scheme explaining the window splitting in the [4[2 + 3] + 6]cage crystal structure along the a axis; the window of the lower blue cage is partially occluded by the aryl face of the upper yellow cage.

The interior of the cage core exhibits an electron-poor character because of the V-shaped electron-deficient clefts formed by the triazine rings of Cage-3-Cl and the fluorine-decorated aromatic rings. This environment might be useful for selective guest molecule separation 47 , 48 , 49 . In the extended crystal structure of this cage of cages, the asymmetric cell contains one [4[2 + 3] + 6]cage molecule, which assembles into a porous supramolecular structure by interacting with 12 neighbouring [4[2 + 3] + 6]cage molecules through van der Waals forces (Supplementary Fig. 11 ). Two of the windows in the [4[2 + 3] + 6]cage molecule are narrowed into smaller channels by the Cage-3-Cl vertices from neighbouring cage molecules (Fig. 4d,f and Supplementary Fig. 12 ), yielding three-dimensional interconnected pore channels (Fig. 4d,e ). Using Zeo++ 50 , we calculated that the pore-limiting diameter of the [4[2 + 3] + 6]cage crystal structure was 6.4 Å and the largest cavity diameter was 8.9 Å (Supplementary Table 3 and Supplementary Figs. 13 – 15 ), suggesting that the structure is microporous. From these calculations, we also determined that voids in the [4[2 + 3] + 6]cage crystal structure that are accessible to a 1.65 Å CO 2 probe occupy 32.0% of the unit cell volume (Supplementary Table 3 ).

There was strong agreement between the predicted structure for the [4[2 + 3] + 6]cage molecule and the molecule observed in the crystal structure (Fig. 5 ). This validates the theoretical predictions, and the close match between the crystal structure prediction (CSP)-predicted structure and experimental crystal structure adds confidence in the crystal structure refinement (Supplementary Fig. 17 ). The root mean squared displacement (r.m.s.d.) was calculated as 0.5 Å with a maximum distance between atoms of 1.4 Å. However, the experimental displacement parameters are large due to disorder in the crystal structure (Supplementary Fig. 11a ). Further attempts to synthesize the larger [8[2+3]+12] product by varying the reaction conditions were unsuccessful, based on MALDI-TOF analysis of the resulting products (Supplementary Table 1 and Supplementary Fig. 8 ), in line with the molecular stability predictions (Fig. 2 ).

a – c , The predicted structure (red) overlaid with the single-crystal X-ray diffraction structure (blue) is shown as viewed along the a ( a ), b ( b ) and c ( c ) crystallographic axes. The r.m.s.d. was calculated as 0.5 Å with a maximum distance between atoms of 1.4 Å, highlighting the close structural similarity between the predicted and experimental structures.

In principle, catenation of this cage is possible, given its large intrinsic voids (>10 Å diameter), as observed for considerably smaller imine cages 11 . However, we saw no evidence for catenated cage side-products, either by NMR or by MALDI-TOF characterization.

We next used CSP to explore the solid-state packing of these hierarchical cages. The lattice energy landscape was explored using quasi-random sampling of the crystal packing space with the Global Lattice Energy Explorer (GLEE) 51 . Initial trial structures were generated from rigid molecules and subjected to lattice energy minimization using an empirically parameterized potential with atomic multipole electrostatics 52 (see Supplementary Information Section 4 , Supplementary Tables 4 and 5 , and Supplementary Figs. 16 – 25 for full details).

Surprisingly, the CSP landscape for [4[2 + 3] + 6]cage (Fig. 6 ) showed catenated structures, along with the non-catenated cage that was observed experimentally, even though the discrete [4[2 + 3] + 6]cage molecule was used for the CSP calculations. Three distinct catenations were identified in the predicted crystal structures: triply interlocked cage dimers (Fig. 6c ), singly interlocked cage dimers (Fig. 6d ) and singly interlocked one-dimensional (1D) cage chains 12 , 53 (Fig. 6e ). The details of the methods used for catenation detection are provided in Supplementary Information Section 4 and Supplementary Figs. 18 ‒ 20 . All sampled structures within a 197 kJ mol −1 energy window from the global energy minimum were found to be catenanes (Supplementary Figs. 21 and 22 ), indicating a strong thermodynamic preference over the non-catenated cages observed by experiment. To verify the relative energies calculated using the rigid-molecule, force-field approach, a selection of catenated and non-catenated predicted structures were re-evaluated using periodic DFT, which confirmed this greater thermodynamic stability (see Supplementary Information Section 4 for full details).

a , Computational crystal energy landscape of [4[2 + 3] + 6]cage with colour-coded categorization based on catenation type: discrete, non-catenated cages (uncoloured circles), triply interlocked cage dimers (green circles), singly interlocked cage dimers (blue) and singly interlocked 1D cage chains (orange). The yellow star and blue cross represent the predicted structures matching the experimentally observed [4[2 + 3] + 6]cage crystal structure and [4[2 + 3] + 6]cage·acetone solvated structure, respectively. b , Energy landscape after removal of the catenated structures, with colour coding based on the diameter of the largest sphere ( D f ) capable of freely moving within the crystal structure’s channel(s). Channels are found based on their ability to accommodate a CO 2 molecule. D f  = 0 corresponds to no channel being found. c – e , Atomic structures depicted for examples of a triply interlocked cage dimer ( c ), a singly interlocked cage dimer ( d ) and a singly interlocked 1D cage chain ( e ).

While the CSP study did not explicitly target catenated structures, the sampled catenated configurations suggest that triply interlocked catenanes (green points, Fig. 6a ), in particular, might be much more thermodynamically stable in the solid state. This echoes previous findings for [4+6] imine cages, in which discrete cages were found to transform into triply interlocked catenanes upon exposure to acid, suggesting that the individual cages were the kinetic rather than the thermodynamic product 11 . The absence of catenanes in our experiments might be explained by the much lower reversibility of the ether bonding in the [4[2 + 3] + 6]cage molecule, which is not accounted for in the CSP calculations. Prompted by these solid-state CSP results, we also explored the relative thermodynamic stability of catenanes at the molecular level. DFT calculations of catenane dimers showed that the energy difference between the molecular equivalent non-catenated [4[2 + 3] + 6]cage dimer and trimer fragments retrieved from the global lowest-energy CSP, and the corresponding triply interlocked catenane molecular fragment was 373.7 kJ mol −1 and 324.7 kJ mol −1 , respectively, reaffirming strong thermodynamic favour towards the catenane structures.

When we remove the catenated structures from the CSP plot (Fig. 6b and Supplementary Fig. 23 ), this reveals the observed experimental structure positioned at the bottom of a low-density ‘spike’ in the energy landscape, approximately 13.6 kJ mol −1 higher than the global energy minimum for non-catenated cages. The predicted crystal structure reproduces the geometry of the experimentally determined [4[2 + 3] + 6]cage crystal structure accurately (Supplementary Fig. 17 ), confirming that the crystal structure determined by X-ray diffraction corresponds to a low-energy local minimum in lattice energy. The colour coding in this ‘non-catenated’ crystal structure landscape represents the diameter of the largest sphere capable of unrestricted movement within the crystal structure channels. Channel dimensions are determined based on their capacity to accommodate a CO 2 molecule with a kinetic radius of 1.65 Å (Supplementary Figs. 24 and 25 ). In the landscape depicted in Fig. 6b , void analysis has been restricted to structures within 20 kJ mol −1 of the low-energy edge of the energy-density distribution of structures. Except for a very small number of predicted structures (purple points, Fig. 6b ), all investigated structures, including the synthesized structure, show potential for CO 2 uptake. That is, CSP suggests that [4[2 + 3] + 6]cage has an intrinsic propensity to be porous in the majority of its potential crystalline packing modes.

Molecular crystals exhibiting permanent porosity in the solid state are attractive for applications such as gas capture, separation and catalysis 18 , 54 . One successful approach that we and others have developed is to form porous organic crystals by synthesizing cages with prefabricated shape-persistent cavities that are retained after solvents are removed during activation 18 , 50 , 54 . Our calculations revealed that the ether bridges in the [4[2 + 3] + 6]cage skeleton appeared to be relatively rigid, suggesting shape persistence. We therefore investigated the porosity in the [4[2 + 3] + 6]cage crystals using gas sorption analysis. We activated the [4[2 + 3] + 6]cage crystals by first exchanging the ethanol and acetone crystallization solvents with diethyl ether or n -pentane, which we chose because of their low surface tensions. Then, we removed any residual solvent from the crystals under a dynamic vacuum at room temperature. Subsequent powder X-ray diffraction (PXRD) analysis revealed that the [4[2 + 3] + 6]cage crystals retained some crystallinity after being activated using these conditions (Supplementary Fig. 26 ). The [4[2 + 3] + 6]cage crystals activated via the diethyl ether solvent exchange route appeared more crystalline, and this sample was used for the subsequent gas sorption experiments described here.

Nitrogen sorption isotherms recorded at 77 K revealed that the crystalline [4[2 + 3] + 6]cage exhibits a type I N 2 sorption isotherm with a relatively high Brunauer–Emmett–Teller surface of 1,056 m 2  g −1 (Fig. 6a and Supplementary Figs. 27 ‒ 29 ), consistent with a microporous solid and the pore size distribution plot calculated using Zeo++ 51 (Supplementary Table 3 and Supplementary Fig. 13 ). We found that crystalline [4[2 + 3] + 6]cage has a CO 2 uptake capacity of 3.98 mmol g −1 at 1 bar and 273 K (Fig. 7b and Supplementary Fig. 30 ). This CO 2 uptake is high compared with other porous organic crystalline materials, such as covalent organic frameworks 55 , at comparable temperatures and pressures, and is one of the highest CO 2 uptakes reported to date for a porous organic cage (Supplementary Table 6 ) 56 , 57 . The calculated isosteric heat of adsorption of CO 2 on crystalline [4[2 + 3] + 6]cage ranges between 21.1 and 23.2 kJ mol −1 (Supplementary Fig. 31 ), which indicates a strong affinity between the adsorbed CO 2 gas and polar [4[2 + 3] + 6]cage crystal pores, rationalizing this high uptake capacity. In addition, we found that crystalline [4[2 + 3] + 6]cage has a high SF 6 uptake capacity of 3.21 mmol g −1 at 1 bar and 273 K (Supplementary Fig. 32 ). The calculated isosteric heat of adsorption of SF 6 on crystalline [4[2 + 3] + 6]cage ranges between 29.2 and 29.5 kJ mol −1 , which again indicates a strong affinity between adsorbed SF 6 gas molecules and the [4[2 + 3] + 6]cage crystal pores (Supplementary Fig. 33 ). Analysis of the [4[2 + 3] + 6]cage powder after the gas sorption isotherms by PXRD analysis indicated that the material remained crystalline during these measurements (Supplementary Fig. 34 ).

a , N 2 sorption isotherms recorded at 77 K showing hysteresis in the desorption isotherm. b , CO 2 gas sorption isotherms recorded at 273 K (cyan) and 298 K (orange) showing an uptake capacity of 3.98 mmol g −1 at 1 bar and 273 K. Closed and open symbols represent the adsorption and desorption isotherms, respectively.

We also uncovered a second crystal structure of the [4[2 + 3] + 6]cage molecule during this study, referred to as [4[2 + 3] + 6]cage·acetone , which crystallized from slow evaporation of an acetone- d 6 solution (Supplementary Fig. 35 ). [4[2 + 3] + 6]cage·acetone crystallized in the cubic space group \(I\bar{4}3m\) ( a  = 23.2901(15) Å, V  = 12633(2) Å 3 , Supplementary Table 7 ) with the ether-bridged cage adopting a perfect tetrahedral geometry in the structure (Supplementary Fig. 36 ). The [4[2 + 3] + 6]cage·acetone lost crystallinity rapidly after being removed from the acetone- d 6 solvent and cracked (Supplementary Fig. 35 ). We therefore performed single-crystal analysis by sealing a solvated crystal in a borosilicate capillary containing residual acetone- d 6 solvent. However, due to the poorer crystal stability of 4[2 + 3] + 6]cage·acetone , we did not investigate its solid-state properties further. The instability of this form was further investigated through computational geometry optimization of the crystal structure. Employing the same energy model as used in the CSP study, rigid-molecule geometry optimization of the structure after solvent removal resulted in considerable structural distortion from the original cubic lattice, adopting a monoclinic form, in keeping with the observed experimental instability. Details can be found in Supplementary Information Section 8 . The relaxed structure, denoted by a blue cross in the landscape of Fig. 6a , is situated 103 kJ mol −1 above the global energy minimum on the landscape of non-catenated structures. This energy difference underscores the crucial role of solvent stabilization in the synthesis of this solvated structure, and can also help to rationalize why this tetrahedral molecular structure was not predicted using gas-phase (that is, solvent-free) DFT calculations (Fig. 5 ).

For practical applications, gas sorption capacity is not the only criterion. For example, most CO 2 capture applications involve wet or humid gas streams, and hence water stability is important. Many porous organic cage materials, such as imine cages and (particularly) boronate ester cages, are unstable to water. We therefore explored the hydrolytic stability of the [4[2 + 3] + 6]cage molecule by immersing the synthesized crystals in water for 12 days. Subsequent analysis of the sample by 1 H NMR spectroscopy revealed that [4[2 + 3] + 6]cage remained chemically intact under these conditions (Supplementary Fig. 38 ). PXRD analysis of the same sample also revealed that the [4[2 + 3] + 6]cage crystals retained their crystallinity under these conditions (Supplementary Fig. 39 ). Hence, both the chemical and crystal structure of [4[2 + 3] + 6]cage molecule appear to have good hydrolytic stability.

We report the assembly of a more complex type of porous organic cage—a ‘cage of cages’—that was synthesized using a two-step hierarchical self-assembly strategy. In this study, we demonstrate the strategy by assembling four trigonal cages into a larger tetrahedral cage. The resulting [4[2 + 3] + 6]cage molecule exhibits excellent stability in water, and crystals of the [4[2 + 3] + 6]cage show permanent porosity and a high surface area of 1,056 m 2  g −1 . The abundance of polar atoms in the cage cavity endows it with high CO 2 and SF 6 uptake capacity. The good solubility of [4[2 + 3] + 6]cage in acetone indicates it has the potential to be used as a building block for even more complex structures, such as porous cage co-crystals. More broadly, this illustrates a strategy for hierarchical molecular assembly using computation as a guide to assess the most likely reaction products. For example, it might be possible in the future to design analogous systems where the [2+3] cages contribute discrete, prefabricated porosity into a higher-order, hierarchically porous crystal.

This study also showcases the use of computational design in supramolecular synthesis, both at the molecular level (Fig. 5 ) and in the solid state (Fig. 6 ). It is notable that triply interlocked cage catenane dimers emerged as the most stable predicted crystal packings (Fig. 6a ). Such catenanes were not observed in experiments, most likely because they are kinetically disfavoured, but they are nonetheless synthetically plausible because analogous structures have been formed using more reversible [4+6] imine cage-forming reactions 11 . Less obviously, infinite 1D catenated cage chains are also produced in these simulations (Fig. 6e ), and in some cases these structures are predicted to have similar lattice energies to the experimentally observed non-catenated cage (Fig. 6a ). This highlights how a priori structure predictions have the power to suggest non-intuitive new materials, although it is unclear how one might design a kinetic pathway to these chain structures, even though analogous structures have been observed for less complex macrocycles 53 .

Molecular simulations

Both Cage-3-Cl and cage-of-cages models were constructed in Tri2Di3, Tri4Di6 and Tri8Di12 topologies using the stk software 46 . All cages were annealed with an MD simulation at 700 K for 50 ns with a time step of 0.5 fs after a 100 ps equilibration time with the OPLS4 force field as implemented in the Macromodel Suite 58 . Five hundred random configurations from the total MD duration were sampled and energy minimized, with the lowest energy configuration selected for DFT calculations. DFT calculations were performed with CP2K v.2023.1 (ref. 59 ) software using the generalized gradient approximation theory with the Perdew–Burke–Ernzerhof functional 60 and def2-TZVP basis sets 61 . A planewave cut-off value of 400 Ry and a relative cut-off value of 100 Ry were parameterized to obtain converged energy levels and dispersion interactions were accounted for with Grimme’s DFT-D3 approach 62 .

The geometries of the [4[2 + 3] + 6]cage were then fully optimized by means of the hybrid M06-2X functional in Gaussian16 (ref. 63 ). The def2-SVP basis set 64 , 65 was applied for all atoms. No symmetry or geometry constraint was imposed during optimizations. The optimized geometries were verified as local minima on the potential energy surface by frequency computations at the same theoretical level 63 .

Synthesis of [4[2+3]+6]cage

To synthesize [4[2 + 3] + 6]cage , DIPEA (61 µl, 0.35 mmol) was dissolved in acetone (25 ml) and purged with N 2 for 10 min. To the acetone solution, a mixture of Cage-3-Cl (58.7 mg, 0.1 mmol) and TFHQ (27.3 mg, 0.15 mmol) in acetone (6 ml) was added dropwise over 3 h under a N 2 atmosphere. After the addition was complete, the reaction was stirred at room temperature for 36 h. The solvent was then removed by rotary evaporation, and the crude product was purified by column chromatography using acetone/CH 2 Cl 2 (10% vol/vol acetone) as eluent to afford [4[2 + 3] + 6]cage as a white solid in 53% isolated yield: 40 mg (0.013 mmol). 1 H NMR (400 MHz, acetone- d 6 ): δ (ppm) 7.09 (s, 12H, H b ), 6.85 (s, 12H, H a ); 19 F NMR (376 MHz, acetone- d 6 ): δ (ppm) −155.62; 13 C NMR (100 MHz, dioxane- d 8 ): δ (ppm) 174.5, 173.5, 173.1, 153.2, 152.8, 142.5, 140.1, 140.0, 128.3, 115.2, 114.8. MALDI-TOF [M + H] + , [C 120 H 24 F 24 N 36 O 36  + H] + : calculated, 3002.0871; found, 3002.0756.

CSP involves the following general steps: (1) molecular geometry optimization; (2) trial crystal structure generation; (3) local lattice energy minimization of trial structures; and (4) duplicate removal.

The geometry of the molecular cage was optimized at the B3LYP/6-311 G(d,p) level using Gaussian09 software 66 , and the resulting geometry was kept fixed throughout the subsequent steps. Trial crystal structures are generated using the Global Lattice Energy Explorer (GLEE) code 51 . Subsequently, these trial structures undergo lattice optimization while preserving the rigidity of the molecular cage. For this task, we employ an empirically parameterized intermolecular atom–atom exp-6 potential coupled with atomic multipole electrostatics. The force-field parameters are acquired from the FIT force field 67 , 68 . Atom-centred multipoles up to hexadecapole on each atom were derived from the electron density through DMA, and partial charges (used in early stages of optimization) were fitted to the molecular electrostatic potential generated by these multipoles 69 , 70 . The overall model is denoted as FIT + DMA.

The search for space groups involves sampling the ten most common space groups for organic crystals along with four trigonal space groups (143, 144, 145 and 146), each with one molecule in the asymmetric unit. A quasi-random method is used to search these selected space groups separately, and valid structures are lattice energy minimized using DMACRYS software 52 in a two-stage protocol. The first stage involves FIT + DMA with partial charges, followed by the second stage with multipole electrostatics. More details can be found in Supplementary Information .

Data availability

The authors declare that the data supporting the findings of this study are available within the paper, its Supplementary Information files, and the Cambridge Crystallographic Data Centre (deposition numbers 2303319 for [4[2 + 3] + 6]cage and 2326368 for [4[2 + 3] + 6]cage·acetone ). The crystal structures and structure factor data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif . The CSP data are available at the University of Southampton Institutional Research Repository at https://doi.org/10.5258/SOTON/D2929 (ref. 71 ).

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Acknowledgements

A.I.C. thanks the Royal Society for a Research Professorship (RSRP\S2\232003). C.Z. acknowledges the China Scholarship Council for financial support (202106745008). R.H. acknowledges the Iridis 5 High Performance Computing facility, and associated support services at the University of Southampton. Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by the Engineering and Physical Sciences Research Council (EPSRC) (EP/R029431 and EP/X035859), this work used the Archer2 HPC facility. We acknowledge A. Hunter for performing the MALDI-TOF analysis at the National Mass Spectrometry Facility (NMSF) at Swansea University, and Diamond Light Source for access to beamlines I19 (CY30461). We received funding from the EPSRC (EP/V026887/1) and the Leverhulme Trust via the Leverhulme Research Centre for Functional Materials Design. This project has received funding from the European Research Council under the European Union’s Horizon 2020 Research and Innovation programme (grant CoMMaD number 758370).

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Authors and affiliations.

Materials Innovation Factory and Department of Chemistry, University of Liverpool, Liverpool, UK

Qiang Zhu, Hang Qu, Chengxi Zhao & Andrew I. Cooper

Leverhulme Research Centre for Functional Materials Design, University of Liverpool, Liverpool, UK

Qiang Zhu & Andrew I. Cooper

Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, London, UK

Gokay Avci & Kim E. Jelfs

Computational Systems Chemistry, School of Chemistry, University of Southampton, Southampton, UK

Roohollah Hafizi & Graeme M. Day

Key Laboratory for Advanced Materials and Joint International Research Laboratory of Precision Chemistry and Molecular Engineering, Feringa Nobel Prize Scientist Joint Research Center, Frontiers Science Center for Materiobiology and Dynamic Chemistry, Institute of Fine Chemicals, School of Chemistry and Molecular Engineering East China University of Science and Technology, Shanghai, China

Chengxi Zhao

Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, UK

Marc A. Little

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Contributions

Q.Z. led the experimental work and the synthesis and characterization of the materials. A.I.C., K.E.J. and M.A.L. conceived the idea and modelling strategy with Q.Z. and supervised the project. H.Q. and M.A.L. conducted the single-crystal X-ray diffraction analysis and solved the structure. G.A., K.E.J. and C.Z. performed the molecular simulations. R.H. and G.M.D. performed the CSP, and G.M.D. supervised this part of the project. Q.Z., G.A., R.H., G.M.D., K.E.J., M.A.L. and A.I.C. analysed the data and prepared the paper. All authors discussed the results and contributed to the paper.

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Correspondence to Marc A. Little or Andrew I. Cooper .

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Peer review information.

Nature Synthesis thanks Chenfeng Ke, Bernhard Schmidt and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Alison Stoddart, in collaboration with the Nature Synthesis team.

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Supplementary information

Supplementary information.

Supplementary Figs. 1–9, Tables 1–8, Scheme 1, synthetic procedures and methods, molecular simulation, NMR, MALDI-TOF, powder X-ray diffraction, single-crystal X-ray diffraction, crystal structure prediction and gas sorption analysis.

Supplementary Data 1

Simulated structures of [2[2 + 3] + 3]cage.xyz, 4[2 + 3] + 6]cage.xyz, [8[2 + 3] + 12]cage.xyz, [8[2 + 3] + 12]cage_1.xyz, [8[2 + 3] + 12]cage_2.xyz, and [8[2 + 3] + 12]cage_3.xyz.

Supplementary Data 2

X-ray crystallographic data of [4[2 + 3] + 6]cage, CCDC 2303319.

Supplementary Data 3

Crystallographic data of [4[2 + 3] + 6]cage·acetone, CCDC 2326368.

Supplementary Video 1

Video showing the single crystal structure of [4[2 + 3] + 6]cage.

Supplementary Data 4

Tabulated source data used to prepare Supplementary Figs. 1–2, 8, 13, 14, 26–34 and 39.

Supplementary Data 5

Raw NMR spectroscopy data used to prepare Supplementary Figs. 5, 7 and 38.

Source Data Fig. 3

Raw NMR spectroscopy data and MALDI-TOF data.

Source Data Fig. 7

Source data for carbon dioxide gas sorption isotherms recorded at 273 and 298 K in Fig. 7.

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Zhu, Q., Qu, H., Avci, G. et al. Computationally guided synthesis of a hierarchical [4[2+3]+6] porous organic ‘cage of cages’. Nat. Synth (2024). https://doi.org/10.1038/s44160-024-00531-7

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Received : 25 October 2023

Accepted : 26 March 2024

Published : 26 April 2024

DOI : https://doi.org/10.1038/s44160-024-00531-7

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