Gas-induced transformation and expansion of a non-porous organic solid

Organic solids composed by weak van der Waals forces are attracting considerable attention owing to their potential applications in gas storage, separation and sensor applications. Herein we report a gas-induced transformation that remarkably converts the high-density guest-free form of a well-known organic host (p-tert-butylcalix[4]arene) to a low-density form and vice versa, a process that would be expected to involve surmounting a considerable energy barrier. This transformation occurs despite the fact that the high-density form is devoid of channels or pores. Gas molecules seem to diffuse through the non-porous solid into small lattice voids, and initiate the transition to the low-density kinetic form with 10 expansion of the crystalline organic lattice, which corresponds to absorption of CO"2 and N"2O (refs4,5). This suggests the possibility of a more general phenomenon that can be exploited to find more porous materials from non-porous organic and metal-organic frameworks that possess void space large enough to accommodate the gas molecules. © 2008 Nature Publishing Group.