Preparation and characterization of triangular clusters [M3Q4(acac)3(py)3]+ (M=Mo, W; Q=S, Se)

Reactions of [M3Q4(H2O)9]4+ with acetylacetone (Hacac) and pyridine (py) in weakly alkaline solutions (pH 8–9) give mixed-ligand complexes [M3Q4(acac)3(py)3]+ (M=Mo, W; Q=S, Se), isolated as hexafluorophosphate salts. For M=Mo, Q=S and for M=W, Q=both S and Se, X-ray structural analysis has been carried out. The three compounds are isostructural and crystallize as [M3Q4(acac)3(py)3]PF6·CHCl3. Each M is attached to one capping (μ3) and two bridging (μ2) chalcogen atoms, one pyridine ligand and one chelating acetylacetonate ligand. The latter are coordinated symmetrically in positions trans to the μ2-Q bridges to give cluster cations with crystallographic threefold rotation symmetry (point group 3m or C3v). The structure is preserved in solution. CV experiments show two almost reversible waves due to consecutive one electron reductions with the ease of reduction decreasing in the order, Mo3S4>Mo3Se4>W3Se4>W3S4. FAB MS data are also discussed.