A templated synthesis of tetranuclear polyoxoalkoxymolybdates(v). Bromo coordinated oxomolybdenum(v) clusters: known core structure with new ligands. Oxidation to the Lindquist anion

Abstract

Reactions of (PyH)₂[MoOCl₅] and (PyH)[MoOBr₄] with alcohols in the presence of tetramethylpyrazine have inadvertently resulted in a series of tetranuclear polyoxoalkoxymolybdates(V) with the general formula (PyH)₂[Mo₄O₈(OR)₂(HOR)₂X₄] (1a: R = Me, X = Cl; 1b: R = Et, X = Cl; 1c: R = Et, X = Br). Reaction with the nitrogen donor ligand pyridine (Py = C₅H₅N), run under similar conditions, afforded neutral cluster [Mo₄O₈(OEt)₂Br₂Py₄] 2a, which also crystallizes as an acetonitrile solvate, [Mo₄O₈(OEt)₂Br₂Py₄]·2CH₃CN 2b. The compounds were characterized by single crystal X-ray diffraction studies. All five tetranuclear clusters contain as a common feature the {Mo₄O₄(μ₃-O)₂(μ-O)₂(μ-OR)₂}²⁺ core onto whose periphery different terminal ligands are attached. The core structure may be viewed as the fusion of two well-defined {Mo₂O₄}²⁺ building blocks bridged through oxo groups. The {Mo₂O₄}²⁺ clusters with coordinated bromo ligands are the first of this type to be structurally characterized. Introduction of water resulted in a fully oxidized [LH₂][Mo₆O₁₉]·L·2EtOH 3 (L = tetramethylpyrazine) whose structure consists of Lindquist anions trapped in the vacancies between the intertwined organic chains with the LH₂²⁺⋯ethanol⋯L repeating unit.