Dinuclear Paddle-Wheel Copper(II) Carboxylates in the Catalytic Oxidation of Carboxylic Acids. Unusual Polymeric Chains Found in the Single-Crystal X-ray Structures of [Tetrakis(μ-1-phenylcyclopropane-1-carboxylato-<i>O</i>,<i>O‘</i>)bis(ethanol-<i>O</i>)dicopper(II)] and <i>catena</i>-Poly[[bis(μ-diphenylacetato-<i>O</i>:<i>O‘</i>)dicopper](μ₃-diphenylacetato-1-<i>O</i>:2-<i>O‘</i>:1‘-<i>O‘</i>)(μ₃-diphenylacetato-1-<i>O</i>:2-<i>O‘</i>:2‘-<i>O‘</i>)]

Abstract

The X-ray structures and spectroscopic and magnetic properties of [tetrakis(&mgr;-1-phenylcyclopropane-1-carboxylato-O,O')bis(ethanol-O)dicopper(II)], 1, and catena-poly[[bis(&mgr;-diphenylacetato-O:O')dicopper](&mgr;(3)-diphenylacetato-1-O:2-O':1'-O')(&mgr;(3)-diphenylacetato-1-O:2-O':2'-O')], 2, two extended-chain copper(II) carboxylates with dinuclear paddle-wheel subunits, are reported. 1 crystallizes in the triclinic space group P&onemacr;, with a = 6.8873(3) Å, b = 11.7367(6) Å, c = 13.7899(7) Å, alpha = 107.076(4) degrees, beta = 93.545(4) degrees, gamma = 103.967(4) degrees, Z = 1. The Cu.Cu distance is 2.6009(4) Å, and the Cu.carboxylate O distances are in the range 1.937(2)-1.962(2) Å. The ethanol at the apex forms an unsymmetrical bifurcated H bond to two carboxylate oxygens of another dinuclear unit with O.O distances 2.980(3) and 3.108(3) Å, thereby extending the structure along the a-axis. The magnetic structure consists of isolated antiferromagnetically coupled dinuclear copper units, with a -2J value of 242 cm(-)(1), in concurrence with the EPR parameters, viz., g(x)() = 2.03(1), g(y)() = 2.07(1), g(z)() = 2.35(1), A( parallel) = 0.064(2) cm(-)(1), D = 0.316(15) cm(-)(1), E = 0.005(1) cm(-)(1). The -2J value is the smallest value measured for dinuclear copper carboxylates with oxygen-donor ligands at the axial position and no electron-withdrawing carboxylate R groups. 2 crystallizes in the monoclinic space group P2(1)/c, with a = 15.953(2) Å, b = 5.385(6) Å, c = 28.322(10) Å, beta = 120.22(3) degrees, Z = 2. The compound contains tetrakis(diphenylacetato)dicopper(II) units, forming a polymeric structure along the b-axis by axial coordination of a carboxylate oxygen to copper of a subsequent dinuclear unit, at 2.323(11) Å. The intradimer Cu.Cu distance is 2.594(4) Å; the interdimer Cu.Cu distance is 3.425(5) Å. The -2J value of 321 cm(-)(1) was interpreted as originated from isolated antiferromagnetically coupled dinuclear copper units. The EPR parameters are g(x)() = 2.07(1), g(y)() = 2.02(1), g(z)() = 2.33(1), D = 0.347(10) cm(-)(1), E = 0.0034(5) cm(-)(1). The dinuclear subunits are likely candidates for the catalytically active Cu species in copper(II)-catalyzed oxidation of carboxylic acids.