Synthesis, characterization and crystal structure of a new unsymmetric tetranuclear copper-carbonate complex: reversible CO2 fixation

A novel tetranuclear unsymmetric copper(II) complex [Cu4II(TPPNOL)2(CO3)2](ClO4)2·6H2O (1), (HTPPNOL=N,N,N′-tris-(2-pyridylmethyl)-1,3-diaminopropan-2-ol), was obtained by the reaction between copper(II) perchlorate hexahydrate and the ligand HTPPNOL, under a CO2 atmosphere, in a basic medium. The synthesis, X-ray crystal structure and spectroscopic properties of (1) are presented. The reversibility of the CO2 fixation process was monitored by UV–Vis spectroscopy in an aqueous medium (NaOH/HClO4), and a nucleophilic CO2 fixation mechanism through the intermediate hydroxo [Cu2(HTPPNOL)(OH)2]+ complex is proposed.