Zinc(ii) and cadmium(ii) metal–organic frameworks with 4-imidazole containing tripodal ligand: sorption and anion exchange properties

Abstract

The use of a 4-imidazole containing tripodal ligand 1,3,5-tri(1H-imidazol-4-yl)benzene (H₃L) enabled isolation of two three-dimensional (3D) porous metal–organic frameworks (MOFs) [Zn(HL)]·solvent (1) and [Cd(H₃L)₂](ClO₄)₂·10.5H₂O (2) featuring 4,4- and 3,6-connected nets related to the structures of ecl and pyrite, respectively. Framework 1 has 3D channels based on Zn–Im⁻ (Im⁻ = imidazolate) moieties due to partial deprotonation of the 1H-imidazol-4-yl groups of H₃L while porous framework 2 is constructed by the coordination of neutral H₃L ligands with Cd(II). Desolvated solid 1′ showed remarkable uptake for CO₂, N₂, H₂, CH₄ gases as well as the volatile organic vapor of MeOH, EtOH, i-PrOH and C₆H₆, significantly, exhibiting temperature dependent selective gas sorption for CO₂ over N₂. Grand Canonical Monte Carlo (GCMC) simulations were performed to elucidate the mechanism of the selective gas adsorption. Cage-like motifs are found in pyrite-net 2, in which ClO₄⁻ anions are hosted, and the results of IR, elemental analysis and PXRD measurements confirm that 2 has a reversible anion exchange property among perchlorate, nitrate and nitrite anions.