Preparation, electrochemical behavior, and variable-temperature magnetic properties of Co(3,5-DBSQ)2 complexes of imidazole- or pyrazole-substituted ligands

Herein we describe the preparation of four new Co(3,5-DBSQ)(2) containing known 2-(2-pyridyl) benzimidazole 1, 2,2'-bisbenzimidazole 2, or 2,2-(1H-pyrazole-3,5-diyl)dipyridine 3. We investigate the electronic and variable-temperature magnetic susceptibility properties of these complexes. Complexes containing 2 and 3 are bimetallic and variable-temperature magnetic susceptibility data suggest observation of a stable intermediate (high-spin and low-spin) state for the bimetallic complex with 3, which does undergo valence tautomerism. Complexes 4-6 containing imidazole-based ligands 1 and 2 feature high-spin ground states and no valence tautomerism is observed in these materials. This experimental finding is corroborated with density functional theory calculations, which support the existence of a stable high-spin ground state in these complexes.