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

The new binucleating ligand 3,5-bis(1'-(4'-(2 " -pyridyl)-2'-thiabutyl))pyr azo (BLEPH) forms dinuclear Cu-II complexes which are able to bind one addi tional 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)(C l)(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 brid ged by the central pyrazolyl group of the BLEP and one azide (in 1), one ch loro (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 (CuC uII)-Cu-I/(CuCuI)-Cu-I couples, and -291 mV for 1 corresponding to the (CuC uII)-Cu-II/(CuCuI)-Cu-I process, respectively. The intramolecular magnetic exchange coupling (J = -46.6 cm(-1)) in the bromo-bridged complex shows wea ker antiferromagnetic interaction than the N-3-bridged complex. The exchang e coupling process through mu (2)-N-3 ligand enhances the net antiferromagn etic interaction. Electronic spectra covering the 12 500-50 000 cm(-1) regi on are also reported for these complexes. (C) 2000 Elsevier Science B.V. Al l rights reserved.