Networked molecular cages as crystalline sponges for fullerenes and other guests

Abstract

Many molecular cages selectively bind guests in solution, but in the solid state close packing often prevents guest entry, which renders the cages inactive. We envisioned that coordination networks constructed from well-known molecular cages could transfer the richness of solution-state host–guest chemistry into the solid state. We report a crystalline coordination network generated from an infinite array of octahedral M6L4 cage subunits (M = metal, L = ligand). This coordination network is a ‘crystalline molecular sponge’ engineered on the molecular level and retains similar guest recognition properties to those found in solution. The network crystallinity is robust and thus X-ray diffraction analysis can be used to unambiguously observe single-crystal to single-crystal guest inclusion. The void spaces define alternating M12L8 and M12L24 cuboctahedral molecular cages and these large cages absorb up to 35 weight per cent of C60 or C70 by simply soaking the crystals in a toluene solution of the fullerene. When the crystals are immersed in fullerene mixtures, C70 is preferentially absorbed. The wealth of solution-chemistry properties of a well-known M6L4 coordination cage can be transferred into the solid state by networking the cage into a highly porous crystalline structure. The material behaves as a ‘fullerene sponge’, absorbing up to 35 wt% of C60 or C70 into the crystal, with a preference for C70 when exposed to mixtures of the two.

Cite this article

Inokuma, Y., Arai, T. & Fujita, M. Networked molecular cages as crystalline sponges for fullerenes and other guests. Nature Chem 2, 780–783 (2010). https://doi.org/10.1038/nchem.742

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