Preparation and properties of heterometallic cube derivatives Mo3M′S4 from [Mo3S4(H2O)9]4+ with M′ = Pt, Rh and Re, and [W3S4(H2O)9]4+ analogues

Abstract

Three heterometallic Mo₃M′S₄ derivatives (M′ = Pt, Rh, Re) of the incomplete single-metal depleted cube [Mo₃S₄(H₂O)₉]⁴⁺ have been prepared by reactions with [PtCl₄]²⁻ (+ H₃PO₂ reductant), RhCl₃ and [Re(CO)₅Br], respectively. With [PtCl₄]²⁻, the initial product gives, on standing for 2–3 days, the edge-linked double cube [{Mo₃PtS₄(H₂O)₉}₂]⁸⁺, which is difficult to elute in Dowex cation-exchange chromatography. In the reaction with RhCl₃, chloro products, e.g. [Mo₃RhCl₃S₄(H₂O)₉]⁴⁺, precede formation of [Mo₃RhS₄(H₂O)₁₂]⁷⁺, which is also difficult to elute, and with [Re(CO)₅Br], the product [Mo₃Re(CO)₃S₄(H₂O)₉]⁵⁺ is obtained. Analyses are consistent with oxidation state assignments Pt⁰, Rh^III and Re^I, where the reactions proceed by addition of these forms to [Mo₃S₄(H₂O)₉]⁴⁺. The analyses and X-ray crystal structure of (Mo₂NH₂)[Mo₃Re(CO)₃S₄(NCS)₄] are consistent with the formation of an Mo₃ReS₄ single cube. Yields are high in the first two cases, but much lower in the Re case. Alternative preparations are described in the case of Rh and Re. All three products decay on heating, with reformation of trinuclear [Mo₃S₄ (H₂O)₉]⁴⁺, which can be recovered by Dowex chromatography. As compared to heterometallic derivatives so far considered, those with M′ = Pt, Rh, Re are much more substitution (and redox) inert, and are air stable. Analogues from [W₃S₄(H₂O)₉]⁴⁺ with M′ = Pt, Rh have been prepared using similar procedures.