Preperation, structure and properties of thre MoW cuboidal complexes
...s, with red selenium deposits noticed upon decomposition. 18 Many cuboidal cluster complexes have also been prepared and characterised. About twenty (Group 6-15) heteroatom (M’) derivatives of [Mo3S4(H2O)9]4+ having single Mo3M’S4 or related double cube core structures are well known.4 A lesser number of heteroatom derivatives of [W3S4(H2O)9]4+ have also been studied but tend to be more susceptible to oxidation, and therefore less stable. Only one of these heterometallic cuboidal clusters Mo3CuS4 is known to show any reversible electrochemistry, and the remainder all show only one oxidation state. Almost all the complexes show a degree of air sensitivity, and all revert to the trinuclear starting product [M3S4(H2O)9]4+ (M = Mo or W) upon oxidation. 4 The [Mo4S4(H2O)12]5+ can be prepared, interestingly, by a number of routes, often with the purple double cube [Mo7S8(H2O)18]8+ as a biproduct. 1, 11-13 The cuboidal complex [Mo4S4(H2O)12]5+ has some distinctive properties which set it apart from the Mo3M’S4 heterometallic clusters. The all molybdenum aqueous complex shows well defined redox chemistry, with three oxidation states existing. These can be accessed by both cyclic voltammetry and controlled redox interconversions. The orange [Mo4S4(H2O)12]4+ has twelve framework electrons (need to be able to justify this 12 electrons counting. If you can write a short justification here it would be good), sufficient for six metal-metal bonds, but is unstable and easily oxidised to the [Mo4S4(H2O)12]5+ cluster. The red [Mo4S4(H2O)12]6+ cube has only ten electrons and has a tendency to fragment due to it’s high charge and/or low electron count. Somewhat surprisingly the green [Mo4S4(H2O)12]5+ is the most stable of the three oxidation states (I find it a bit strange to talk about oxidation states of the cluster since oxidation state usually refers to a single element for a cluster. Better to refer to this as the redox state of the cluster), having only eleven framework electrons, one less than required for six metal-metal bonds. The double cube complex [Mo7S8(H2O)18]8+ also shows a high degree of stability, although the...