XAS, ESR and potentiometric studies of three dinuclear N,N′-para-xylylenebis(tetraazamacrocycle)copper(II) complexes - X-ray crystal structure of [N,N′-p-xylylenebis(cyclen)]copper(II)

Abstract : Dicopper complexes with N,N′-p-xylylenebis(cyclam or cyclen) and with the heteroditopic N,N′-p-xylylenebis(cyclam-cyclen) were synthesized. An X-ray study of the N,N′- p-xylylenebis(cyclen)dicopper complex showed that the copper(II) ion is five-coordinate with an H2O molecule in apical position. With this ligand, a polymeric chain was also obtained in the presence of KSCN. The terminal donor atoms of the bridging NCS- anion are coordinated in apical position to the square-pyramidal copper(II) ion. Two alternating kinds of Cu2L4+ moieties are present in the chain, the first with two N4S chromophores and the second with two N5 chromophores. EXAFS and XANES results are in agreement with a five-coordinate copper ion in the cyclen unit and a six-coordinate copper ion in the cyclam unit. Thermodynamic constants were determined by potentiometry. The existence of dinuclear Cu2L4+ species (ligand/metal ratio < 1) and mononuclear CuLHn(2+n)+ species (ligand/metal ratio > 1) were confirmed by an ESR study at variable pH. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.