Magnetic superexchange couplings in doubly bis(2-pyridyl)pyrazolato-bridged dinuclear copper(ii) complexes

The solvothermal reaction of CuCl₂·2H₂O with 3,5-bis(2-pyridyl)pyrazole (Hbpypz) in a methanol/water mixed solvent produces a dinuclear Cu^II complex, formulated as syn-[Cu₂(μ-bpypz)₂Cl_1.5(H₂O)_0.5]Cl_0.5·3H₂O. Single-crystal X-ray diffraction analysis revealed that the two Cu^II centres were in a distorted square-pyramidal coordination environment. The basal plane of each Cu^II centre was bridged by two unique bis-bidentate bpypz⁻ ligands. One of the apical coordination sites showed disorder and was occupied by chloride or water. In contrast, the other apical site was solely occupied by chloride with no disorder. The apical coordination sites of the two Cu^II centres adopted a syn-configuration across the Cu₂(μ-bpypz)₂ basal plane. Variable-temperature static magnetic susceptibility measurements indicated a strong antiferromagnetic interaction of −191.52 cm⁻¹ between the Cu^II centres, mediated by the doubly bpypz⁻ bridging ligands. Broken-symmetry DFT calculations were performed using various characteristic functionals with different basis sets to investigate magnetic superexchange couplings in detail. The global hybrid GGA PBE0 functional, combined with the def2-TZVP basis set and ZORA relativistic approximation, provided the most accurate results, closely reproducing the experimental magnetic exchange values. These computational approaches were validated by their successful application to related complexes.