Templated syntheses of heterometal tungsten–cobalt–sulfur clusters with different nuclearities

Abstract

A series of new W–Co–S clusters have been synthesized utilizing the complex [Et₄N][(Tp*)WS₃] (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate(1-)) as the synthetic template, by rational control of the stoichiometry of reactants and by employment of a reductant or precipitant as an auxiliary reagent. By solubility control or addition of a precipitant to avoid the involvement of Cl^– in the reaction, the cluster [(Tp*)WS₃]₂Co (2) could be obtained. With different ratios of the Co source to the template, together with the use of an appropriate amount of reducing reagent, clusters [{(Tp*)WS₃}₂Co]¹⁻ (3) and [{(Tp*)WS₃}₂Co₂Cl]¹⁻ (4) could be synthesized as their Et₄N⁺ salts, and [{(Tp*)WS₃}₂Co₄Cl₂(DMF)]¹⁻ (5) could be isolated as its [Co(DMF)₆]²⁺ salt. A common structural feature of these clusters is that they all have a pair of [(Tp*)WS₃] templates chelating different numbers of Co atoms to form W–Co–S clusters with distinct nuclearities. The clusters [(Tp*)WS₃]₂Co (2) and [{(Tp*)WS₃}₂Co]¹⁻ (3) both have one Co atom chelated by two [(Tp*)WS₃] templates, and the difference lies in not only the oxidation states but also the fact that the Co atom in 2 adopts an octahedral coordination environment while that in 3 bears a tetrahedral coordination sphere, which means that the [(Tp*)WS₃] template is tri-dentate in 2 and bi-dentate in 3. The cluster [{(Tp*)WS₃}₂Co₂Cl]¹⁻ (4) has two Co atoms chelated by a pair of [(Tp*)WS₃] templates, in which one of the Co atoms is also terminally bound by a Cl^– ligand. There are four Co atoms chelated by two [(Tp*)WS₃] templates in the cluster [{(Tp*)WS₃}₂Co₄Cl₂(DMF)]¹⁻ (5), two of which are bound terminally by the Cl^– ligands. Studies of redox properties by cyclic voltammetry indicate the existence of two reversible redox pairs related to clusters 2 and 3, respectively.