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

Centrosymmetric [Cu₂(μ-X)­(μ-<b>L</b>_{<i><b>m</b></i>}*)₂]­(ClO₄)₃ (X = F^–, Cl^–, Br^–, OH^–, <b>L</b>_{<i><b>m</b></i>}* = <i>m</i>-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 −<i>J</i> = 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_<i>z</i>² orbital