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

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)]center dot solvent (1) and [Cd(H3L)(2)](ClO4)(2)center dot 10.5H(2)O (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, N-2, H-2, 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 N-2. 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.