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.