Coordination preferred open metal sites containing porous coordination polymers for selective gas/solvent adsorption

Abstract

Three isostructural PCPs with molecular formula, Zn2M2(μ3-OH)2(BTMB)2 ⊃ Guest (M = Zn (1), Co (2) and Ni (3)) (BTMB3− = 1,3,5-benzenetris(m-benzoate)) were synthesized by refluxed conditions at 125 °C. The obtained products were characterized by PXRD, TGA, and FTIR. These PCPs synthesized by this new synthetic method containing unique mono-metallic, [Zn4(μ3-OH)2]6+ and bimetallic cluster cores [Zn2M2(μ3-OH)2]6+ (M = Zn, Co or Ni) with coordination-free open metal sites (OMSs). They also exhibited specific adsorption isotherms with varying surface areas using CO2 gas adsorption study. This might be due to the different metal ions present in the framework along with their different number of open metal Lewis acidic sites in the degassed state. The CO2 gas adsorption BET surface areas found to be 295, 317 and 272 m2 g−1 and their CO2 gas adsorption Langmuir surface areas found to be 570, 662 and 560 m2 g−1, respectively for 1, 2 and 3 analogs. By utilizing this coordination preferred OMSs, we carried out various gas and solvent adsorption study for these three PCPS. The gas adsorption profiles of these PCPs indicated that the adsorption profile is type 1 and also the amount of gas adsorbed was different for three different metals ions used in these PCPs. Whereas, the solvents adsorption isotherms showed type-V of isotherm with aromatic solvents exhibited a unique gate-opening profile and aliphatic solvent molecules shown gate closing behavior.