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

Two 2D metal organic frameworks (MOFs) of [NiL1](3)[BTC](2)center dot 7H(2)O center dot 6DMF (1) and [NiL2](3)[BTC](2)center dot H2O center dot 3DMF (2) have been constructed using macrocyclic Ni(II) complexes ([NiL1](ClO4)(2)/[NiL2](ClO4)(2)) and BTC3- as building blocks (L-1 = 3,10-bis(4-fluorobenzyl)-1,3,5,8,10,12-hexaazacyclotetradecane, L-2 = 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 C-1 symmetry, while 2 displays a 2D honeycomb-like structure with BTC3- bridging three [NiL2](2+) via C-3 symmetry. The results of gas sorption measurements indicate that desolvated 1 can selectively adsorb CO2 rather than N-2 and H-2, 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.