Cubane-Type Mo3FeS44+,5+ Complexes Containing Outer Diphosphane Ligands: Ligand Substitution Reactions, Spectroscopic Studies, and Electronic Structure

A general protocol to access Mo3FeS44+ clusters selectively modified at the Fe coordination site is presented starting from the all-chlorine Mo3(FeCl)­S4(dmpe)3Cl3 (1) [dmpe = 1,2-bis­(dimethylphosphane-ethane)] cluster and tetrabutylammonium salts (n-Bu4NX) (X = CN–, N3–, and PhS–). Clusters Mo3(FeX)­S4(dmpe)3Cl3 [X = CN– (2), N3– (3), and PhS– (4)] are prepared in high yield, and comparison of geometric and redox features upon modification of the coordination environment at the Fe site at parity of ligands at the Mo sites is also presented. The existence of the cubane-type Mo3FeS44+,5+ redox couple is demonstrated by cyclic voltammetry and for compound 1 by cluster synthesis and X-ray structure determinations. Ground states for the 1/1+ redox couple are evaluated on the basis of magnetic susceptibility measurements, electron paramagnetic resonance, and 57Fe Mössbauer spectroscopy aimed at providing an input of experimental data for electronic structure determination based on density functional theory calculations.