Networked molecular cages as crystalline sponges for fullerenes and other guests

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 M(6)L(4) 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 M(12)L(8) and M(12)L(24) cuboctahedral molecular cages and these large cages absorb up to 35 weight per cent of C(60) or C(70) by simply soaking the crystals in a toluene solution of the fullerene. When the crystals are immersed in fullerene mixtures, C(70) is preferentially absorbed.