Coordination cages as permanently porous ionic liquids

Abstract

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.

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Acknowledgements

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.

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

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Supplementary information

41557_2020_419_MOESM69_ESM.mov

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

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). https://doi.org/10.1038/s41557-020-0419-2

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