Tripodal imidazole frameworks: Reversible vapour sorption both with and without significant structural changes

Abstract

A series of tripodal imidazole frameworks (TIFs) are reported based on a tripodal, cavity-containing tris(imidazole) derivative. In the case of [Co₃Cl₆(1)₂]·n(solvent) (TIF-1) which possesses a doubly interpenetrated framework structure, the material exhibits rigid, permanent porosity and selectively absorbs CO₂. The non-interpenetrated [Co(1)₂(H₂O)₂]Cl₂·4H₂O (TIF-2) also absorbs gases and vapours fully reversibly exhibiting a reversible phase change in the process and considerable conditioning and hysteresis. The very highly hydrated [Co(1)₂]Cl₂·22H₂O (TIF-3) irreversibly dehydrates to the layered structure [Co(1)₂]Cl₂·H₂O (TIF-4). A nickel analogue [Ni(1)₂]Cl₂·22H₂O (TIF-5) closely related to TIF-3 is also reported along with two isostructural, non-porous materials [MCl₂(1)] (M = Mn, TIF-6; M = Cd, TIF-7) based on d⁵ and d¹⁰Mn(II) and Cd(II). Some of the materials may be prepared by mechanochemical as well as solution based methods. We liken TIF-1 to a gas cylinder, TIF-2 to a sponge and TIF-3 to a fragile soda can that is crushed on emptying to give TIF-4.