Article | Published:

Molecular shape sorting using molecular organic cages

Nature Chemistry volume 5, pages 276281 (2013) | Download Citation

Abstract

The energy-efficient separation of chemical feedstocks is a major sustainability challenge. Porous extended frameworks such as zeolites or metal–organic frameworks are one potential solution to this problem. Here, we show that organic molecules, rather than frameworks, can separate other organic molecules by size and shape. A molecular organic cage is shown to separate a common aromatic feedstock (mesitylene) from its structural isomer (4-ethyltoluene) with an unprecedented perfect specificity for the latter. This specificity stems from the structure of the intrinsically porous cage molecule, which is itself synthesized from a derivative of mesitylene. In other words, crystalline organic molecules are used to separate other organic molecules. The specificity is defined by the cage structure alone, so this solid-state ‘shape sorting’ is, uniquely, mirrored for cage molecules in solution. The behaviour can be understood from a combination of atomistic simulations for individual cage molecules and solid-state molecular dynamics simulations.

  • Compound C48H48N12

    Ethylenediamine/triformylbenzene cage

  • Compound C72H84N12

    trans-1,2-Diaminocyclohexane/triformylbenzene cage

  • Compound C114H108N16

    trans-1,2-Diaminocyclopentane/tris(4-formylphenyl)amine cage

  • Compound C9H12

    Mesitylene

  • Compound C9H12

    4-Ethyltoluene

  • Compound C9H12

    3-Ethyltoluene

  • Compound C9H12

    2-Ethyltoluene

  • Compound C8H10

    ortho-Xylene

  • Compound C8H10

    para-Xylene

  • Compound C8H10

    meta-Xylene

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Acknowledgements

The authors acknowledge funding from the EPSRC (EP/H000925/1) and the Leverhulme Trust (F/00025/Al). A.C. is a Royal Society Wolfson award holder. The authors thank J.T.A. Jones for assistance with NMR measurements.

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Affiliations

  1. Department of Chemistry and Centre for Materials Discovery, University of Liverpool, Brownlow Hill, Liverpool, Merseyside L69 3BX, UK

    • Tamoghna Mitra
    • , Kim E. Jelfs
    • , Marc Schmidtmann
    • , Adham Ahmed
    • , Samantha Y. Chong
    • , Dave J. Adams
    •  & Andrew I. Cooper

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Contributions

A.C. conceived the project. T.M., D.A. and A.C. designed the experiments. T.M. prepared the cages and carried out the sorption experiments. K.J. conceived the modelling strategy and performed the molecular simulations. M.S. solved the single-crystal structures and S.C. refined the powder X-ray diffraction data. T.M. and A.A. performed the breakthrough experiments.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Andrew I. Cooper.

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Crystallographic information files

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    Supplementary information

    Crystallographic data for the complex between mesitylene and compound CC3

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    Supplementary information

    Crystallographic data for the complex between meta-xylene and compound CC3

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    Supplementary information

    Crystallographic data for the complex between para-xylene and compound CC3 at 100K

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    Supplementary information

    Crystallographic data for the complex between para-xylene and compound CC3 at 295K

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DOI

https://doi.org/10.1038/nchem.1550

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