Porous organic cages


Porous materials are important in a wide range of applications including molecular separations and catalysis. We demonstrate that covalently bonded organic cages can assemble into crystalline microporous materials. The porosity is prefabricated and intrinsic to the molecular cage structure, as opposed to being formed by non-covalent self-assembly of non-porous sub-units. The three-dimensional connectivity between the cage windows is controlled by varying the chemical functionality such that either non-porous or permanently porous assemblies can be produced. Surface areas and gas uptakes for the latter exceed comparable molecular solids. One of the cages can be converted by recrystallization to produce either porous or non-porous polymorphs with apparent Brunauer–Emmett–Teller surface areas of 550 and 23 m2 g−1, respectively. These results suggest design principles for responsive porous organic solids and for the modular construction of extended materials from prefabricated molecular pores.

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Figure 1: Structures for cages 1–3 determined by X-ray crystallography for desolvated cages, as shown with one of the triangular pore windows facing.
Figure 2: Schematic of cage–cage packing in the crystal structures of 1–3.
Figure 3: Varying the vertex functionality for cages 1–3 leads to an evolution in pore structure and connectivity.
Figure 4: Gas-sorption isotherms for cages 1–3.
Figure 5: Molecular simulations suggest that the 0D cage volume contributes to N2 gas uptake for 2, despite being formally isolated from the 1D pore channels.
Figure 6: Recrystallization of 1 forms a permanently porous polymorph.


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We thank the Engineering and Physical Sciences Research Council (EPSRC) for financial support under grant EPSRC/C511794 and Kaneka Corporation, Japan, for financial supporting a research visit for T.T. We thank the STFC for access to Diamond and M.J. Rosseinsky for helpful advice. A.C. is a Royal Society Wolfson Research Merit Award holder.

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T.T., S.I.S., S.J., D.J.A. and S.S. synthesized cages 13, J.T.A.J. and R.C. carried out volumetric sorption measurements, D.B. carried out gravimetric sorption measurements, T.H. carried out microscopy, desolvation studies and TGA, A.T. constructed the molecular models and carried out the sorption simulations, J.B., A.M.Z.S., S.Y.C., C.T., S.T., J.P. and A.S. carried out the crystallography; in particular J.B. and A.S. solved the crucial first structure for the cage 1 ethyl acetate solvate. J.T.A.J. discovered the porous polymorph of 1. A.I.C. conceived the experiments; all authors contributed to writing the paper.

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Correspondence to Andrew I. Cooper.

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Tozawa, T., Jones, J., Swamy, S. et al. Porous organic cages. Nature Mater 8, 973–978 (2009). https://doi.org/10.1038/nmat2545

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