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

Abstract

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 H₂L1 was prepared from piperazine in three steps and good yield. A structure containing the deprotonated form K₂L1·2H₂O was determined and consists of a three-dimensional coordination polymer containing inorganic K₂(COO)₂(OH₂) layers separated by the long organic bridging linker. The free compound H₂L1 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 [Zn₃(L1)₂(OH)₂]·2DMF·0.5H₂O 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 N₂ and H₂.