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

A series of mixed-valent, multinuclear cobalt-oxido clusters [Co^IIICo^II₂(mdea)₃(H₂mdea)]ClO₄ (<b>1</b>), [Co^III₂Co^II₂(mdea)₄(DAA)₂](BPh₄)₂ (<b>2</b>), [Co^III₃Co^II₄(mdea)₆(NO₃)₃](NO₃)₂ (<b>3</b>), [Co^III₃Co^II₄(mdea)₆(fa)₃](ClO₄)₂ (<b>4</b>), [Na₂Co^III₄Co^II₄(mdea)₆(CO₃)₄(OH)₂(H₂O)₂] (<b>5</b>), [Co^III₃Co^II₇(mdea)₆(fa)₅(OH)₄](ClO₄)₃ (<b>6</b>), and [Co^III₄Co^II₉(mdea)₈(NO₃)₄(OH)₈](NO₃)₂ (<b>7</b>) 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 <i>N</i>-methyldiethanolamine (H₂mdea) as a stabilizing ligand and feature Co₃O₄ (<b>1</b>), Co₄O₆ (<b>2</b>), Co₇O₁₂ (<b>3, 4</b>), Na₂Co₈O₁₈ (M₁₀O₁₈) (<b>5</b>), Co₁₀O₁₆ (<b>6</b>), and Co₁₃O₂₄ (<b>7</b>) scaffolds. The increasing number of Co cations in the cobalt-oxido cores of compounds <b>1</b>-<b>7</b> 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 Co^II/Co^III centers in the complexes were studied by cyclic voltammetry (CV), while their magnetic properties were investigated via temperature-dependent magnetic susceptibility.