Controlling Valence Tautomerism of Cobalt Complexes Containing the Benzosemiquinone Anion as Ligand

The transformation from Co II to Co III (e.g., 1 → 2 ) is displayed by the compounds of type 1 in solution when the temperature is lowered (L is a bidentate N‐donor ligand with a diimine structure, 3,5‐dtbsq − the 3,5‐di‐ tert ‐butylbenzosemiquinone anion, and 3,5‐dtbcat − the corresponding catecholate ion). In the process one electron is transferred from the Co center to one of the 3,5‐dtbsq − ligands to form the catecholate ligand. Microcrystalline samples in which L is phenanthroline undergo the transformation abruptly at about 240 K. equation image