Formation (and properties) of palladium derivatives of [Mo3Q4(H2O)9]4+: absence of similar derivatives of [W3Q4(H2O)9]4+ (Q = S, Se)
Abstract
The reaction of Pd black with [Mo3Se4(H2O)9]4+ in 2 M HCl gives the single cube [Mo3(PdCl)Se4(H2O)9]3+, which on removal of Cl− forms the edge-linked double cube [{Mo3PdSe4(H2O)9}2]8+. No similar reactions of [W3S4(H2O)9]4+ and [W3Se4(H2O)9]4+ are observed, and in no case is Pt black incorporated into the trinuclear species. The crystal structure of [{Mo3PdSe4(H2O)9}2](pts)8·18H2O has been determined (pts− = p-toluenesulfonate), and is consistent with Mo–Mo and Mo–Pd bonding. Properties of the Pd derivatives of both [Mo3Q4(H2O)9]4+ (Q = S, Se) are considered. No heteroatom transfer is observed on mixing [Mo3(PdCl)Se4(H2O)9]3+ with [Mo3S4 (H2O)9]4+ as is the case of [Mo3SnSe4(H2O)12]6+ with [Mo3S4 (H2O)9]4+. The single cubes [Mo3(PdCl)Q4 (H2O)9]3+ (Q = S, Se), react 1 ∶ 1 with SnCl3− to give [Mo3(PdSnCl3)Q4(H2O)9]3+ with Pd–Sn bonding. Formation constants K (25 °C) are 1.15 × 103 M−1 (Q = S) and 9.5 × 103 M−1 (Q = Se). On mixing the heterometal cubes [Mo3PdS4(H2O)10]4+ and [Mo3SnS4(H2O)12]6+ in 2 M HCl no Pd–Sn bonding occurs. With [Pd(H2O)4]2+ and [Mo3SnS4(H2O)12]6+ in 2.0 M HClO4, reaction steps Mo3SnS46+ → Mo3S44+ + SnII, followed by SnII + PdII → SnIV + Pd0 are observed, and Pd0 is precipitated. Rate constants for the oxidation of [Mo3(PdCl)S4(H2O)9]4+ and [{Mo3PdS4(H2O)9}2]8+ with [Co(dipic)2]− (dipic = 2,6-pyridinedicarboxylate) are within a factor of 2, indicating no significant change in redox properties. This contrasts with the behaviour of single and corner-shared double cubes e.g. M′ = Sn.