Multinuclear Mixed-Valent Co-Oxido Complexes: Synthesis, Structure, Magnetic, and Electrochemical Properties

A series of mixed-valent, multinuclear cobalt-oxido clusters [CoIIICoII₂(mdea)₃(H₂mdea)]ClO₄ (1), [CoIII₂CoII₂(mdea)₄(DAA)₂](BPh₄)₂ (2), [CoIII₃CoII₄(mdea)₆(NO₃)₃](NO₃)₂ (3), [CoIII₃CoII₄(mdea)₆(fa)₃](ClO₄)₂ (4), [Na₂CoIII₄CoII₄(mdea)₆(CO₃)₄(OH)₂(H₂O)₂] (5), [CoIII₃CoII₇(mdea)₆(fa)₅(OH)₄](ClO₄)₃ (6), and [CoIII₄CoII₉(mdea)₈(NO₃)₄(OH)₈](NO₃)₂ (7) containing up to 13 Co atoms were synthesized and structurally characterized using single-crystal X-ray diffraction as well as FT-IR and UV-vis spectroscopy. The cobalt-oxido clusters contain N-methyldiethanolamine (H₂mdea) as a stabilizing ligand and feature Co₃O₄ (1), Co₄O₆ (2), Co₇O₁₂ (3, 4), Na₂Co₈O₁₈ (M₁₀O₁₈) (5), Co₁₀O₁₆ (6), and Co₁₃O₂₄ (7) scaffolds. The increasing number of Co cations in the cobalt-oxido cores of compounds 1-7 results from the systematic addition of pseudocubane Co₃O₄ units and the progressive incorporation of hydroxide ligands. The water oxidation activity and electrochemical properties of the CoII/CoIII centers in the complexes were studied by cyclic voltammetry (CV), while their magnetic properties were investigated via temperature-dependent magnetic susceptibility.