Preparation and aqueous solution properties of the heterometallic cuboidal complex [W3CuS4(H2O)10]5+

The first heterometallic derivative of the trinuclear WIV3 incomplete cuboidal cluster [W3S4(H2O)9]4+ has been prepared by reaction with (i) Cu metal, and (ii) Cu+ or CuCl(solid). In both cases the product is the cuboidal [W3CuS4(H2O)10]5+ ion. The corresponding reactions of [Mo3S4(H2O)9]4+ yield [Mo3Cu-S4(H2O)10]4+ and [Mo3CuS4(H2O)10]5+ respectively. The observation that the reaction of [W3S4(H2O)9]4+ with copper yields the 5+ and not the 4+ product suggests that the 4+ cluster is less stable in the tungsten case. Rate constants (25 °C) for the reaction of Cu+ with [W3S4(H2O)9]4+(1.82 × 103 M–1 s–1) and [Mo3S4(H2O)9]4+(980 M–1 s–1) suggest a similar addition process. The 1:1 stoichiometries for the oxidation of [W3CuS4(H2O)9]5+ with [Co(dipic)2]–(dipic = pyridine-2,6-dicarboxylate) and [Fe(H2O)6]3+ giving [W3S4(H2O)9]4+ and Cu2+ as products, further support the 5+ overall charge assignment. Rate constants have been determined and mechanisms assigned to these reactions. At 25°C, I= 2.00 M (LiClO4), the [Co(dipic)2]– reaction is outer-sphere with a rate constant of 17.7 × 103 M–1 s–1, while outer-sphere [Fe(H2O)6]3+(2.68 × 102 M–1 s–1) and inner-sphere [Fe(H2O)5(OH)]2+(5.0 × 105 M–1 s–1) reactions are observed for the FeIII oxidant. Rate constants are of the same order of magnitude to those for the corresponding reactions of [Mo3CuS4(H2O)10]5+, suggesting that a common electron-transfer process involving the copper centre may be relevant in both cases.