Dinuclear copper(II) complexes incorporating a novel pyrazolo-based ligand with S- and N-rich coordination spheres

The new binucleating ligand 3,5-bis(1'-(4'-(2 " -pyridyl)-2'-thiabutyl))pyrazo (BLEPH) forms dinuclear Cu-II complexes which are able to bind one additional exogenous bridging molecule such as N-3(-), Cl-, Br- and OH-. Three of these complexes [Cu-2(BLEP)(mu -N-3)(N-3)(2)] (1); [Cu-2(BLEP)(mu -Cl)(Cl)(H2O)]Cl (2); and [Cu-2(BLEP)(mu -Br)(Br)(H2O)]Br (3) were characterized by X-ray single crystal structure analysis. The two copper centers are bridged by the central pyrazolyl group of the BLEP and one azide (in 1), one chloro (in 2) or bromo (in 3) and the side arm of BLEP coordinates to each of the coppers with one pyridyl N and one thia S. Electrochemical studies of these complexes reveal that the redox waves are -247 and 15 mV for 2; - 215 and 37 mV for 3 corresponding to the (CuCuII)-Cu-II/(CuCuII)-Cu-I and (CuCuII)-Cu-I/(CuCuI)-Cu-I couples, and -291 mV for 1 corresponding to the (CuCuII)-Cu-II/(CuCuI)-Cu-I process, respectively. The intramolecular magnetic exchange coupling (J = -46.6 cm(-1)) in the bromo-bridged complex shows weaker antiferromagnetic interaction than the N-3-bridged complex. The exchange coupling process through mu (2)-N-3 ligand enhances the net antiferromagnetic interaction. Electronic spectra covering the 12 500-50 000 cm(-1) region are also reported for these complexes. (C) 2000 Elsevier Science B.V. All rights reserved.