PREPARATION AND CHARACTERIZATION OF TRIPLY-BRIDGED DINUCLEAR COPPER(II) COMPLEXES CONTAINING THE [CU2(MU-OH)(MU-X)(MU-OAC)]+ CORE (X = CL, BR), AND THE CRYSTAL-STRUCTURE OF [CU2(OH)CL(OAC)(BPY)2](CLO4).H2O

Synthetic procedures are described that allow access to complexes containing the cation [Cu2(mu-OH)(mu-X)(mu-O2CMe)(bpy)2]+ (X = Cl, Br). Reaction mixtures consisting of CuX2, bpy, OH-, MeCO2- and ClO4- (X = Cl-) in MeOH/H2O give blue solutions from which the products [Cu2(OH)Cl(O2CMe)(bpy)2](ClO4).H2O (1) and [Cu2(OH)Br(O2 CMe)(bpy)2]Br.H2O (4) can be obtained in good yield. Complex 1 may also be prepared from the known complexes [Cu2(OH)(H2O)(O2CMe)(bpy)2](ClO4)2 (2) and Cu2(OH)2(bpy)2 (ClO4)2 (3). Complex 1 crystallizes in monoclinic space group P2(1)/n with (at - 175-degrees-C) a = 8.434(1), b = 16.074(2), c = 9.430(1) angstrom, beta = 98.09(1)-degrees, Z = 2 and V = 1265.83 angstrom-3. The structure was solved by direct methods (MULTAN) and refined to values of conventional indices R(R(w)) of 3.38 (3.54)% using 1499 unique reflections with F > 2.33-sigma(F). The structure of the cation consists of a triply-bridged pair of five-coordinate copper(II) atoms. One of the bridging ligands is a syn,syn-eta-1:eta-1:mu-2 acetate group, the others being the Cl- and OH- ions; a terminal bpy molecule completes five-coordination at each metal. The Cu...Cu separation is 2.957(1) angstrom. The metal coordination geometry is best described as distorted square-pyramidal with the Cl- ligand occupying the apical site for each metal. The oxygen atom of the water molecule is hydrogen-bonded to the OH- hydrogen. Recrystallization of 1 from warm water yields 3 in 20% yield; addition of NaClO4 to the solution increases the yield to 40%. Complex 1 in warm water containing one equiv. of NaClO4 and one equiv. of NaOH also gives 3 (yield 73%). The thermal decomposition, room temperature mu-eff values, and electronic and IR spectra of 1 and 4 are discussed in terms of the nature of bonding and structure of 1.