Structural chemistry and selective CO2 uptake of a piperazine-derived porous coordination polymer

A new piperazine-derived ligand has been prepared and used to synthesise a porous coordination polymer which displays selective carbon dioxide uptake after solvent exchange and thermal activation. The ligand N, N'-bis.4-carboxyphenylmethylene) piperazine H(2)L1 was prepared from piperazine in three steps and good yield. A structure containing the deprotonated form K(2)L1 center dot 2H(2)O was determined and consists of a three-dimensional coordination polymer containing inorganic K-2(COO)(2)(OH2) layers separated by the long organic bridging linker. The free compound H(2)L1 displays a one-dimensional hydrogen-bonded polymeric structure in the solid state with hydrogen bonding interactions between carboxylic acids and piperazine groups tightly linking molecules together. The two-dimensional polymeric complex [Zn-3(L1)(2)-(OH)(2)]center dot 2DMF center dot 0.5H(2)O 1 was prepared and analysed in the solid state to reveal tubular one-dimensional channels which, when activated by solvent exchange and evacuation, displayed selective affinity for CO2 over N-2 and H-2.