The cubanes, which we shall define in this paper as complexes with a M4X4core in which the metal ions occupy four nonneighbouring vertices of a cube, and the triply bridging X units the four others (Scheme 2), are a particularly interesting family .The Fe4S4cubanes are well known in biology as electron transferagents.5,6Very recently, a heteronuclear Mn3CaO4cubane was shown to be present at the active site of the oxygen evolving centre of photosystem II,7and a Fe3MoS4cubane has been identified at the active site of nitrogenase.8M4O4units show interesting magnetic exchange properties and may under certain circumstances act as single molecule magnets.