Synthesis and proton magnetic resonance properties of Fe3Ms4(M = Mo or W) cubane-like cluster dimers

Synthetic procedures leading to the preparation of the complexes [Fe6M2S8(SR)9]3–(where M = Mo and R = Ph, C6H4Cl-p, C6H4Me-p, or Et; or M = W and R = Et) and [Fe6M2S8(SPh)6(OMe)3]3–(where M = Mo or W) are detailed. 300 MHz 1H n.m.r. spectra have been recorded for these complexes and [Fe6Mo2S8Cl6(SR′)3]3–(where R′= Et or Ph) in [2H6]dimethyl sulphoxide at temperatures between ca. 20 and 80 °C. For all complexes, a clear distinction between bridging and terminal ligands is observed and, within each set of bridging and terminal ligands, only one resonance is observed for each chemically different proton. The bridging ligands exhibit much smaller isotropic shifts than those for the corresponding ligands in the terminal positions and all of the shifts decrease in magnitude with an increase in temperature. The isotropic shifts of the terminal ligands appear to be predominantly contact in origin via a π-(arylthiolato-groups) or σ-(alkylthiolato-groups) spin delocalisation mechanism; however, for the bridging region both contact and dipolar mechanisms seem to be operative, the latter being of particular importance for the µ2-methoxo-bridged complexes.