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-O,O‘)bis(ethanol-O)dicopper(II)] and catena-Poly[[bis(μ-diphenylacetato-O:O‘)dicopper](μ3-diphenylacetato-1-O:2-O‘:1‘-O‘)(μ3-diphenylacetato-1-O:2-O‘:2‘-O‘)]

Abstract

The X-ray structures and spectroscopic and magnetic properties of [tetrakis(μ-1-phenylcyclopropane-1-carboxylato-O,O‘)bis(ethanol-O)dicopper(II)], 1, and catena-poly[[bis(μ-diphenylacetato-O:O‘)dicopper](μ₃-diphenylacetato-1-O:2-O‘:1‘-O‘)(μ₃-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 P1̄, with a = 6.8873(3) Å, b = 11.7367(6) Å, c = 13.7899(7) Å, α = 107.076(4)°, β = 93.545(4)°, γ = 103.967(4)°, 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_∥ = 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 P2₁/c, with a = 15.953(2) Å, b = 5.385(6) Å, c = 28.322(10) Å, β = 120.22(3)°, 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.