Unprecedented Tuning of Structures and Gas Sorption Properties of Two 2D Nickel Metal−Organic Frameworks via Altering the Positions of Fluorine Atoms in Azamacrocyclic Ligands

Abstract

Two 2D metal−organic frameworks (MOFs) of [NiL1]3[BTC]2·7H2O·6DMF (1) and [NiL2]3[BTC]2·H2O·3DMF (2) have been constructed using macrocyclic Ni(II) complexes ([NiL1](ClO4)2/[NiL2](ClO4)2) and BTC3- as building blocks [L1 = 3,10-bis(4- fluorobenzyl)-1,3,5,8,10,12-hexaazacyclotetradecane, L2 = 3,10-bis(2-fluorobenzyl)-1,3,5,8,10,12-hexaazacyclotetradecane, and BTC3- = 1,3,5-benzenetricarboxylate]. The results of X-ray diffraction analyses indicate that 1 shows a 2D brick wall structure with BTC3- bridging three [NiL1]2+ via C1 symmetry, while 2 displays a 2D honeycomb-like structure with BTC3- bridging three [NiL2]2+ via C3 symmetry. The results of gas sorption measurements indicate that desolvated 1 can selectively adsorb CO2 rather than N2 and H2, while desolvated 2 cannot adsorb any of these gases under the same condition. More interestingly, the sorption isotherm of CO2 for desolvated 1 shows a large hysteresis. The different sorption properties of desolvated 1 and 2 can be attributed to their different structures tuned by the positions of the fluorine atoms in the macrocyclic ligands.