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

Centrosymmetric [Cu2(μ-X)­(μ-Lm*)2]­(ClO4)3 (X = F–, Cl–, Br–, OH–, Lm* = m-bis­[bis­(3,5-dimethyl-1-pyrazolyl)­methyl]­benzene)],
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) dz2 orbital.