Exo-iron centres linked to MoFeS clusters

Monocubane clusters with exo-iron atoms were synthesized from the iron-bridged dicubane [NEt4](3)[Mo2Fe7S8(SEt)(12)] by reactions with pi-acid ligands. The structures of two derivatives, [NEt4][MoFe3S4X3(mu-SEt)(3)Fe((CNBu)-Bu-t)(3)], X = Cl or PhS, have been established by X-ray crystallography. Electrochemical and Mossbauer data showed that the cubane core retains the {MoFe3S4}(3+) redox level of the parent material and that the exo-iron centre is in the low-spin iron(II) state. Infrared and electrochemical data showed that there is little electronic interaction between the cubane and exo-iron centres. The parent complex possesses a low-spin bridging iron(III) centre. This centre undergoes slow electron transfer which is ascribed to spin-state reorganisation to high-spin Fe-II. Reduction of the cubane units leads to reversible deco-ordination of a bridging thiolate group from a molybdenum centre.