Two solvent-dependent zinc(ii) supramolecular isomers: structure analysis, reversible and nonreversible crystal-to-crystal transformation, highly selective CO2 gas adsorption, and photoluminescence behaviors

Abstract

Two new zinc(II) microporous metal–organic frameworks (MOFs), [Zn(dcpy)(bpe)_0.5]·3H₂O (1) and [Zn(dcpy)(bpe)_0.5]·(CH₃OH)_0.5·(H₂O)_0.5 (2) constructed from the same initial materials 3-(2',5'-dicarboxylphenyl)pyridine (H₂dcpy), 1,2-di(4-pyridyl)ethylene (bpe) and Zn(NO₃)₂·6H₂O, exhibiting varying architectures from a 2-fold parallel interpenetrated structure to a 4-fold parallel interpenetrated framework were synthesized by changing the reaction solvents. Complexes 1 and 2 are supramolecular isomeric and both show 2-nodal (3,4)-connected networks, which represent rare dmc and coe topology styles, respectively. Interestingly, 1 presents reversible crystal structural transformation upon dehydration and rehydration, whereas 2 transforms into a new crystal phase 2a after desolvated. When dipping 2a into a DMF/CH₃OH/H₂O mixed solvent, another new crystal phase 2b can be formed, moreover, 2a and 2b could convert to each other through desolvation and solvation. In particular, the dehydrated 1a shows a high selective gas sorption for H₂ over N₂ at 77 K and high selectivity for CO₂ over N₂ at 293 K. The photoluminescence behaviors of 1 and 2 are also discussed.