Valence tautomerism in a cobalt-dioxolene complex containing an imidazolic ancillary ligand.

This work reports the synthesis, structural, spectroscopic and magnetic investigation of two complexes, [Co(bmimapy)(3,5-DTBCat)]PF·HO (1) and [Co(bmimapy)(TCCat)]PF·HO (2), where bmimapy is an imidazolic tetradentate ancillary ligand and 3,5-DTBCat and TCCat are the 3,5-di--butyl-catecholate and tetrachlorocatecholate anions, respectively. Their structures have been elucidated using single crystal X-ray diffraction, showing a pseudo-octahedral cobalt ion bound to a chelating dioxolene ligand and the ancillary bmimapy ligand in a folded conformation. Magnetometry displayed an entropy-driven, incomplete, Valence Tautomeric (VT) process for 1 in the 300-380 K temperature range, while 2 displayed a temperature independent, diamagnetic low-spin cobalt(iii)-catecholate charge distribution.