PREPARATION AND CHARACTERIZATION OF DINUCLEAR COPPER(II) COMPLEXES CONTAINING THE [CU2(MU-OAC)2]2+ CORE

Treatment of an aqueous slurry of known Cu2(OH)2(bpy)2(ClO4)2 (1) with an excess of MeCOOH led to rapid formation of the blue complex [Cu2(O2CMe)2(H2O)2 (bpy)2](ClO4)2.H2O (3). Complex 3 has also been prepared by slow crystallization from an H2O/MeCOOH reaction mixture containing the polymeric compound [Cu4(O2CMe)8 (bpy)2]n (5), bpy and NaClO4. A similar reaction system containing a lesser amount of H2O led to fast precipitation of the anhydrous compound [Cu2(O2CMe)2(OClO3)2(bpy)2] (4). The transformation of 1 to 3 is reversible; treatment of 3 with neat H2O led to high-yield isolation of 1. Using a significantly shorter reaction time and a a smaller volume of H2O, the procedure yielded the known complex [Cu2(OH)(H2O(O2CMe)(bpy)2](ClO4)2 (2). Similarly, complex 4 can be transformed to 2 in good yield. Complex 3 crystallizes in the monoclinic space group P2(1)/a with (at - 172-degrees-C) a = 17.037(3), b = 9.743(2), c = 18.357(4) angstrom, beta = 98.19(5)-degrees, Z = 4 and V =3016.05 angstrom 3. A total of 3651 unique data with F > 2.33-sigma(F) were refined to values of conventional indices R(R(w)) of 7.89 (8.74)%. Complex 4 crystallizes in the monoclinic space group C2/c with (at -172-degrees-C) a = 11.555(4), b = 15.231(5), c = 15.885(6) angstrom, beta = 100.27(2)-degrees, Z = 4 and V = 2750.76 angstrom 3. A total of 1456 unique data with F > 2.33-sigma(F) were refined to values of R and R(w) of 3.23 and 3.63% , respectively. The structure of 3 consists of the doubly-bridged [Cu2(O2CMe)2(H2O)2(bpy)2]2+ cation, two considerably disordered ClO4- anions and the disordered H2O solvate molecule. The two acetates are in the familiar eta(1):eta(1):mu(2) bridging mode; a terminal bpy molecule and one aqua ligand complete five-coordination at each metal atom. The molecule of 4 is very similar to the cation of 3; the aqua ligands of 3 are replaced by two terminal, axial monodentate perchlorato groups. In both 3 and 4, the dimers are stabilized by bpy-bpy stacking interactions, and the precise structural effects of these interactions are described.