Influence of a 'Dangling' Co(ll) Ion Bound to a [MnCo_3O_4] Oxo Cubane

摘要

Cobalt(II), in the presence of acetate and nitrate, quantitatively adds to the manganese–cobalt oxido cubane Mn~(IV)Co~(III)_(3)O_(4)(OAc)_(5)(py)_(3) (1 ) to furnish the pentametallic dangler complex Mn~(IV)Co~(III)_(3)Co~(II)O_(4)(OAc)_(6)(NO_(3))(py)_(3) (2 ). Complex 2 is structurally reminiscent of photosystem II’s oxygen-evolving center, and is a rare example of a transition-metal “dangler” complex. Superconducting quantum interference device magnetometry and density functional theory calculations characterize 2 as having an S = 0 ground state arising from antiferromagnetic coupling between the Co~(II) and Mn~(IV) ions. At higher temperatures, an uncoupled state dominates. The voltammogram of 2 has four electrochemical events, two more than that of its parent cubane 1 , suggesting that addition of the dangler increases available redox states. Structural, electrochemical, and magnetic comparisons of complexes 1 and 2 allow a better understanding of the dangler’s influence on a cubane.