Halide and Hydroxide Linearly Bridged Bimetallic Copper(II) Complexes: Trends in Strong Antiferromagnetic Superexchange Interactions

Centrosymmetric [Cu-2(mu-X) (mu-L-m*)(2)]. (ClO4)(3) (X = F-, Cl-, Br-, OH-, L-m* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzenen)], the first example of a series of bimetallic copper(II) complexes linked by a linearly bridging mononuclear anion, have been prepared and structurally characterized. Very strong antiferromagnetic exchange coupling between the copper(II) ions increases along the series F- < Cl- < OH- < Br-, where -J = 340, 720, 808, and 945 cm(-1). DFT calculations explain this trend by an increase in the energy along this series of the antibonding antisymmetric combination of the p orbital of the bridging anion interacting with the copper(II) d(z)(2) orbital.