Preparation and characterization of dinuclear copper(II) complexes containing the [Cu 2(μ-OAc) 2] 2+ core

Abstract

Treatment of an aqueous slurry of known Cu 2(OH) 2(bpy) 2(ClO 4) 2 ( 1) with an excess of MeCOOH led to rapid formation of the blue complex [Cu 2(O 2CMe) 2(H 2O) 2(bpy) 2](ClO 4) 2·H 2O ( 3). Complex 3 has also been prepared by slow crystallization from an H 2O/MeCOOH reaction mixture containing the polymeric compound [Cu 4(O 2CMe) 8 (bpy) 2] n ( 5), bpy and NaClO 4. A similar reaction system containing a lesser amount of H 2O led to fast precipitation of the anhydrous compound [Cu 2(O 2CMe) 2(OClO 3) 2(bpy) 2] ( 4). The transformation of 1 to 3 is reversible; treatment of 3 with neat H 2O led to high-yield isolation of 1. Using a significantly shorter reaction time and a smaller volume of H 2O, the procedure yielded the known complex [Cu 2(OH)(H 2O)(O 2CMe)(bpy) 2](ClO 4) 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°C) a = 17.037(3), b = 9.743(2), c = 18.357(4) Å, β = 98.19(5)°, Z = 4 and V = 3016.05 Å 3. A total of 3651 unique data with F > 2.33σ( 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°C) a = 11.555(4), b = 15.231(5), c = 15.885(6) Å, β = 100.27(2)°, Z = 4 and V = 2750.76 Å 3. A total of 1456 unique data with F > 2.33σ( 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 [Cu 2(O 2CMe) 2(H 2O) 2(bpy) 2] 2+ cation, two considerably disordered ClO 4 − anions and the disordered H 2O solvate molecule. The two acetates are in the familiar η 1:η 1:μ 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.