Preparation and properties of the corner-shared double cube [Mo6PbS8(H2O)18]8+ as a derivative of [Mo3S4(H2O)9]4+

Abstract

The heterometallic corner-shared double-cuboidal cluster [Mo₆PbS₈(H₂O)₁₈]⁸⁺, with the lead atom common to both cubes, has been prepared for the first time by the reaction of [Mo₃S₄(H₂O)₉]⁴⁺ with lead shot, which requires up to 1 h to reach completion, and by addition of a solution mix of [Mo₃S₄(H₂O)₉]⁴⁺ and Pb^II to an excess of BH₄^–, when reaction is rapid. The air-sensitive blue-green product has UV/VIS absorbance bands at 387 and 757 nm in 2.0 M HClO₄. Inductively coupled plasma atomic emission spectroscopy confirmed the Mo : Pb : S ratio as 6 : 1 : 8. It was eluted from a cation-exchange column with 4 M Hpts (toluene-p-sulfonic acid), but not 2 M Hpts (or 4 M HClO₄), consistent with a high charge, confirmed as 8 + from the 2 : 1 stoichiometries for the oxidation reactions with e.g.[Co(dipic)₂]^–(dipic = pyridine-2,6-dicarboxylate) or [Fe(H₂O)₆]³⁺, which yield [Mo₃S₄(H₂O)₉]⁴⁺. Kinetic studies on the oxidations with [Co(dipic)₂]^– and [Fe(H₂O)₆]³⁺ were also carried out as part of an overall appraisal of the reactivity of the heterometallic clusters.