A structural analysis of {M4O4} cubanes where M = Mn and Fe

Abstract

The structures of the M₄O₄ units found in manganese and iron cubanes are analysed. The model used is that established previously for cobalt and nickel cubanes based on a distortion of the cube by compression of the oxygen atoms along a body diagonal. Further distortion which maintains a S₄ or, less frequently, a C₃ axis is generally seen. In spite of the distortion, average M–M distances in a cubane are quite constant for a given oxidation state and generally decrease as the metal is oxidised. The angles at the oxygen atoms increase from 90° for the ideal cube to around 97°. For metal oxidation states above or equal to +IIIµ₃-hydroxo ligands transform to µ₃-oxo ligands. Ligands such as carboxylates which can bridge diagonal faces of the cube are generally seen with higher oxidation states.