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

A novel tetranuclear unsymmetric copper(II) complex [Cu-4(II)(TPPNOL)(2) (CO3)(2)](ClO4)(2). 6H(2)O (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 W-Vis spectroscopy in an aqueous medium (NaOH/HClO4), and a nucleophilic CO2 fixation mechanism through the intermediate hydroxo [Cu-2(HTPPNOL) (OH)(2)](+) complex is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.