Ionothermal Synthesis of a Novel 3D Cobalt Coordination Polymer with a Uniquely Reported Framework: [BMI]2[Co2(BTC)2(H2O)2]

Abstract

The framework of [RMI]2[Co2(BTC)2(H2O)2] (RMI = 1-alkyl-3-methylimidazolium, alkyl; ethyl (EMI); propyl (PMI); butyl (BMI)), which has uniquely occurred in ionothermal reactions of metal salts and H3BTC (1,3,5-benzenetricarboxylic acid), an organic ligand, reappeared in this work. Ionothermal reaction of cobalt acetate and H3BTC with [BMI]Br ionic liquid as the reaction medium yielded the novel coordination polymer [BMI]2[Co2(BTC)2(H2O)2] (compound B2). Similar ionothermal reactions with different [EMI]Br and [PMI]Br as the reaction media have been previously reported to produce [EMI]2[Co3(BTC)2(OAc)2] (compound A1) and [PMI]2[Co2(BTC)2(H2O)2] (compound B1), respectively. In contrast with the trinuclear secondary building unit of A1, the framework structure of B1 and B2 consists of dinuclear secondary building units in common, but with subtle distinction posed by the different size of the incorporated cations. These structural differences amidst the frameworks showed interesting aspects, including guest and void volume, and were used to explain the chemical trend observed in the system. Moreover, the physicochemical properties of the newly synthesized compound have been briefly discussed.