Monocubane clusters with exo-iron atoms were synthesized from the iron-bridged dicubane [NEt4]3[Mo2Fe7S 8(SEt)12] by reactions with π-acid ligands. The structures of two derivatives, [NEt4][MoFe3S4X3(μ-SEt) 3Fe(CNtBu)3], X = Cl or PhS, have been established by X-ray crystallography. Electrochemical and Mössbauer data showed that the cubane core retains the _MoFe3S4₃+ 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 FeII. Reduction of the cubane units leads to reversible deco-ordination of a bridging thiolate group from a molybdenum centre.