The First Cobalt Metallacrowns:  Preparation and Characterization of Mixed-Valence Cobalt(II/III), Inverse 12-Metallacrown-4 Complexes

Aerobic reactions of Co(O₂CMe)₂·4H₂O with di-2-pyridyl ketone oxime (Hpko) in the presence of counterions (ClO₄^-, PF₆^-) give the tetranuclear, mixed-valence cobalt(II/III) clusters [Co^II₂Co^III₂(OR)₂(O₂CMe)₂(pko)₄S₂]X₂ [R = H, S = MeOH, X = ClO₄ (1); R = Me, S = EtOH, X = PF₆ (2)] depending on the solvent mixture. Complexes 1 and 2 are the first Co members in the family of metallacrowns adopting the extremely rare inverse 12-metallacrown-4 motif.