Coordination cages as permanently porous ionic liquids


Porous materials are widely used in industry for applications that include chemical separations and gas scrubbing. These materials are typically porous solids, although the liquid state can be easier to manipulate in industrial settings. The idea of combining the size and shape selectivity of porous domains with the fluidity of liquids is a promising one and porous liquids composed of functionalized organic cages have recently attracted attention. Here we describe an ionic-liquid, porous, tetrahedral coordination cage. Complementing the gas binding observed in other porous liquids, this material also encapsulates non-gaseous guests—shape and size selectivity was observed for a series of isomeric alcohols. Three gaseous chlorofluorocarbon guests, trichlorofluoromethane, dichlorodifluoromethane and chlorotrifluoromethane, were also shown to be taken up by the liquid coordination cage with an affinity that increased with their size. We hope that these findings will lead to the synthesis of other porous liquids whose guest-uptake properties may be tailored to fulfil specific functions.

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Fig. 1: Preparation and rheology of cages 1–3.
Fig. 2: Shape selectivity in the encapsulation of isomers of propanol and butanol by cage 2.
Fig. 3: Uptake of three gaseous CFC guests in cage 2 as a neat liquid.

Data availability

The authors declare that all data supporting the findings of this study are included within the article and its Supplementary Information, and are also available from the authors upon request.


  1. 1.

    O’Reilly, N., Giri, N. & James, S. L. Porous liquids. Chem. Eur. J. 13, 3020–3025 (2007).

    PubMed  Google Scholar 

  2. 2.

    Zhang, J. et al. Porous liquids: a promising class of media for gas separation. Angew. Chem. Int. Ed. 54, 932–936 (2015).

    CAS  Google Scholar 

  3. 3.

    Li, P. et al. Electrostatic-assisted liquefaction of porous carbons. Angew. Chem. Int. Ed. 56, 14958–14962 (2017).

    CAS  Google Scholar 

  4. 4.

    Costa Gomes, M., Pison, L., Červinka, C. & Padua, A. Porous ionic liquids or liquid metal–organic frameworks? Angew. Chem. Int. Ed. 57, 11909–11912 (2018).

    CAS  Google Scholar 

  5. 5.

    Giri, N. et al. Liquids with permanent porosity. Nature 527, 216–220 (2015).

    CAS  PubMed  Google Scholar 

  6. 6.

    Shan, W. et al. New class of type III porous liquids: a promising platform for rational adjustment of gas sorption behavior. ACS Appl. Mater. Inter. 10, 32–36 (2018).

    CAS  Google Scholar 

  7. 7.

    Liu, H. et al. A hybrid absorption–adsorption method to efficiently capture carbon. Nat. Commun. 5, 5147 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  8. 8.

    Gaillac, R. et al. Liquid metal–organic frameworks. Nat. Mater. 16, 1149–1155 (2017).

    CAS  PubMed  Google Scholar 

  9. 9.

    Bennett, T. D. & Horike, S. Liquid, glass and amorphous solid states of coordination polymers and metal–organic frameworks. Nat. Rev. Mater. 3, 431–440 (2018).

    Google Scholar 

  10. 10.

    Jie, K. et al. Transforming porous organic cages into porous ionic liquids via a supramolecular complexation strategy. Angew. Chem. Int. Ed. (2020).

    CAS  PubMed  Google Scholar 

  11. 11.

    Greenaway, R. L. et al. Understanding gas capacity, guest selectivity, and diffusion in porous liquids. Chem. Sci. 8, 2640–2651 (2017).

    CAS  PubMed  PubMed Central  Google Scholar 

  12. 12.

    Zhang, F. et al. Thermodynamics and kinetics of gas storage in porous liquids. J. Phys. Chem. B 120, 7195–7200 (2016).

    CAS  PubMed  Google Scholar 

  13. 13.

    Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard (WBCSD and WRI, 2012).

  14. 14.

    Castilla, A. M., Ronson, T. K. & Nitschke, J. R. Sequence-dependent guest release triggered by orthogonal chemical signals. J. Am. Chem. Soc. 138, 2342–2351 (2016).

    CAS  PubMed  Google Scholar 

  15. 15.

    Tao, S. J. Positronium annihilation in molecular substances. J. Chem. Phys. 56, 5499–5510 (1972).

    CAS  Google Scholar 

  16. 16.

    Kleywegt, G. J. & Alwyn Jones, T. Detection, delineation, measurement and display of cavities in macromolecular structures. Acta Crystallogr. D 50, 178–185 (1994).

    CAS  PubMed  Google Scholar 

  17. 17.

    Montzka, S. A. et al. An unexpected and persistent increase in global emissions of ozone-depleting CFC-11. Nature 557, 413–417 (2018).

    CAS  PubMed  Google Scholar 

  18. 18.

    Rigby, M. et al. Increase in CFC-11 emissions from eastern China based on atmospheric observations. Nature 569, 546–550 (2019).

    CAS  PubMed  Google Scholar 

  19. 19.

    Chen, T. H. et al. Mesoporous fluorinated metal–organic frameworks with exceptional adsorption of fluorocarbons and CFCs. Angew. Chem. Int. Ed. 54, 13902–13906 (2015).

    CAS  Google Scholar 

  20. 20.

    Shiflett, M. B. & Yokozeki, A. Hydrogen substitution effect on the solubility of perhalogenated compounds in ionic liquid [bmim][PF6]. Fluid Phase Equilib. 259, 210–217 (2007).

    CAS  Google Scholar 

  21. 21.

    Yang, D. et al. Encapsulation of halocarbons in a tetrahedral anion cage. Angew. Chem. Int. Ed. 54, 8658–8661 (2015).

    CAS  Google Scholar 

  22. 22.

    Heinz, T., Rudkevich, D. M. & Rebek, J. Pairwise selection of guests in a cylindrical molecular capsule of nanometre dimensions. Nature 394, 764–766 (1998).

    CAS  Google Scholar 

  23. 23.

    Akine, S., Miyashita, M. & Nabeshima, T. A metallo-molecular cage that can close the apertures with coordination bonds. J. Am. Chem. Soc. 139, 4631–4634 (2017).

    CAS  PubMed  Google Scholar 

  24. 24.

    Käseborn, M., Holstein, J. J., Clever, G. H. & Lützen, A. A rotaxane-like cage-in-ring structural motif for a metallosupramolecular Pd6L12 aggregate. Angew. Chem. Int. Ed. 57, 12171–12175 (2018).

    Google Scholar 

  25. 25.

    Hof, F., Nuckolls, C. & Rebek, J. Diversity and selection in self-assembled tetrameric capsules. J. Am. Chem. Soc. 122, 4251–4252 (2000).

    CAS  Google Scholar 

  26. 26.

    Yan, Y. et al. Smart self-assemblies based on a surfactant-encapsulated photoresponsive polyoxometalate complex. Angew. Chem. Int. Ed. 49, 9233–9236 (2010).

    CAS  Google Scholar 

  27. 27.

    Wang, M., Zheng, Y.-R., Ghosh, K. & Stang, P. J. Metallosupramolecular tetragonal prisms via multicomponent coordination-driven template free self-assembly. J. Am. Chem. Soc. 132, 1–9 (2010).

    Google Scholar 

  28. 28.

    Mondal, B. & Mukherjee, P. S. Cage encapsulated gold nanoparticles as heterogeneous photocatalyst for facile and selective reduction of nitroarenes to azo compounds. J. Am. Chem. Soc. 140, 12592–12601 (2018).

    CAS  PubMed  Google Scholar 

  29. 29.

    Bondy, C. R., Gale, P. A. & Loeb, S. J. Metal–organic anion receptors: arranging urea hydrogen-bond donors to encapsulate sulfate ions. J. Am. Chem. Soc. 126, 5030–5031 (2004).

    CAS  PubMed  Google Scholar 

  30. 30.

    Scherer, M., Caulder, D. L., Johnson, D. W. & Raymond, K. N. Triple helicate–tetrahedral cluster interconversion controlled by host–guest interactions. Angew. Chem. Int. Ed. 38, 1588–1592 (1999).

    CAS  Google Scholar 

  31. 31.

    Liu, Y., Hu, C., Comotti, A. & Ward, M. D. Supramolecular Archimedean cages assembled with 72 hydrogen bonds. Science 333, 436–440 (2011).

    CAS  PubMed  Google Scholar 

  32. 32.

    Ajami, D. & Rebek, J. Compressed alkanes in reversible encapsulation complexes. Nat. Chem. 1, 87–90 (2009).

    CAS  PubMed  Google Scholar 

  33. 33.

    Roy, X. et al. Prussian blue nanocontainers: selectively permeable hollow metal–organic capsules from block ionomer emulsion-induced assembly. J. Am. Chem. Soc. 133, 8420–8423 (2011).

    CAS  PubMed  Google Scholar 

  34. 34.

    Campos-Fernández, C. S. et al. Anion template effect on the self-assembly and interconversion of metallacyclophanes. J. Am. Chem. Soc. 127, 12909–12923 (2005).

    PubMed  Google Scholar 

  35. 35.

    Turunen, L., Warzok, U., Schalley, C. A. & Rissanen, K. Nano-sized I12L6 molecular capsules based on the [NI+N] halogen bond. Chem 3, 861–869 (2017).

    CAS  Google Scholar 

  36. 36.

    Sun, L. Y. et al. Template synthesis of three-dimensional hexakisimidazolium cages. Angew. Chem. Int. Ed. 57, 5161–5165 (2018).

    CAS  Google Scholar 

  37. 37.

    Markiewicz, G. et al. Selective C70 encapsulation by a robust octameric nanospheroid held together by 48 cooperative hydrogen bonds. Nat. Commun. 8, 15109 (2017).

    PubMed  PubMed Central  Google Scholar 

  38. 38.

    Jie, K. et al. Linear positional isomer sorting in nonporous adaptive crystals of a pillar[5]arene. J. Am. Chem. Soc. 140, 3190–3193 (2018).

    CAS  PubMed  Google Scholar 

  39. 39.

    Jia, C. et al. Selective binding of choline by a phosphate-coordination-based triple helicate featuring an aromatic box. Nat. Commun. 8, 938 (2017).

    PubMed  PubMed Central  Google Scholar 

  40. 40.

    Brachvogel, R. C., Hampel, F. & Von Delius, M. Self-assembly of dynamic orthoester cryptates. Nat. Commun. 6, 7129 (2015).

    PubMed  PubMed Central  Google Scholar 

  41. 41.

    Ozores, H. L., Amorín, M. & Granja, J. R. Self-assembling molecular capsules based on α,γ-cyclic peptides. J. Am. Chem. Soc. 139, 776–784 (2017).

    CAS  PubMed  Google Scholar 

  42. 42.

    Xuan, W. et al. A chiral quadruple-stranded helicate cage for enantioselective recognition and separation. J. Am. Chem. Soc. 134, 6904–6907 (2012).

    CAS  PubMed  Google Scholar 

  43. 43.

    Preston, D., Sutton, J. J., Gordon, K. C. & Crowley, J. D. A nona-nuclear heterometallic Pd3Pt6 ‘donut’-shaped cage: molecular recognition and photocatalysis. Angew. Chem. Int. Ed. 57, 8659–8663 (2018).

    CAS  Google Scholar 

  44. 44.

    Chepelin, O. et al. Luminescent, enantiopure, phenylatopyridine iridium-based coordination capsules. J. Am. Chem. Soc. 134, 19334–19337 (2012).

    CAS  PubMed  Google Scholar 

  45. 45.

    Krieg, E. et al. A recyclable supramolecular membrane for size-selective separation of nanoparticles. Nat. Nanotechnol. 6, 141–146 (2011).

    CAS  PubMed  Google Scholar 

  46. 46.

    Lee, D. W. et al. Supramolecular fishing for plasma membrane proteins using an ultrastable synthetic host–guest binding pair. Nat. Chem. 3, 154–159 (2011).

    CAS  PubMed  Google Scholar 

  47. 47.

    Yoshizawa, M., Tamura, M. & Fujita, M. Diels–Alder in aqueous molecular hosts: unusual regioselectivity and efficient catalysis. Science 312, 251–254 (2006).

    CAS  PubMed  Google Scholar 

  48. 48.

    Cullen, W. et al. Highly efficient catalysis of the Kemp elimination in the cavity of a cubic coordination cage. Nat. Chem. 8, 231–236 (2016).

    CAS  PubMed  Google Scholar 

  49. 49.

    Zhang, Q., Catti, L., Pleiss, J. & Tiefenbacher, K. Terpene cyclizations inside a supramolecular catalyst: leaving-group-controlled product selectivity and mechanistic studies. J. Am. Chem. Soc. 139, 11482–11492 (2017).

    CAS  PubMed  Google Scholar 

  50. 50.

    Fukui, T. Control over differentiation of a metastable supramolecular assembly in one and two dimensions. Nat. Chem. 9, 493–499 (2017).

    CAS  PubMed  Google Scholar 

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L.M., A.B.G., C.J.E.H. and A.T. acknowledge support from the UK Engineering and Physical Sciences Research Council (EPSRC EP/P027067/1) and the European Research Council (ERC 695009). C.C.P. acknowledges the Engineering and Physical Sciences Research Council for funding (EPSRC DTP grant EP/M508007/1). L.L. acknowledges an EPSRC Departmental Studentship. A.W. and A.R.S. acknowledge the National Centre for Research and Development (LIDER/024/391/L-5/13/NCBR/2014) and National Science Centre in Poland (PRELUDIUM UMO-2016/21/N/ST5/00851) for funding). T.D.B. thanks the Royal Society for a University Research Fellowship (UF150021), and for a Research Grant (RSG\R1\180395). C.M.D. acknowledges the Veski Inspiring Women Fellowship for support. We acknowledge Z. Wu and O. Planes for preliminary work done on this project, as well as D. S. Robson for videography. Additionally, we thank the NMR facility at the University of Cambridge Chemistry Department and the EPSRC UK National Mass Spectrometry Facility at Swansea University for characterization.

Author information




L.M., A.B.G, C.J.E.H. and J.R.N. conceived and designed the experiments. A.T. designed the ligand synthesis. L.M., C.J.E.H. and A.W. performed the synthetic work. C.C.P. conducted and analysed all the rheological measurements. T.D.B. and L.L. performed and analysed the DSC and TGA measurements. L.M. led the project overall. C.M.D. performed and analysed the PALS measurements. All the authors contributed to the manuscript preparation.

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Correspondence to Thomas D. Bennett or Jonathan R. Nitschke.

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Supplementary information

Supplementary Information

Synthesis and characterization of materials, characterization data, porosity measurements on cage 2, guest uptake experiments and computational modelling.

Supplementary video 1

Flow of the neat-liquid cage 2 material in a 3 mm NMR tube on pushing a reference capillary into the sample.

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Ma, L., Haynes, C.J.E., Grommet, A.B. et al. Coordination cages as permanently porous ionic liquids. Nat. Chem. 12, 270–275 (2020).

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