Dinuclear cobalt bis(dioxolene) complex exhibiting two sequential thermally induced valence tautomeric transitions

4,6-Di-2'-pyridylpyrimidine is employed as a bis( diimine) ligand bridging two cobalt bis( dioxolene) centers. The thermally induced valence tautomeric transitions of these two metal centers are coupled through the ligand. The result is that sequential switching from high-spin Co-II to low-spin Co-III of one center, followed by the onset of switching of the other center at lower temperature, is observed in a solid amorphous thin film by IR absorption spectroscopy.