A series of quadruply bonded dimolybdenum compounds of form Mo2(EE′CC
CPh)4 (EE′ = {NPh}2, Mo22NN; {NPh}O, Mo22NO;{NPh}S, Mo22NS; OO, Mo22OO) have been synthesised by ligand exchange reactions of Mo2(O2CCH3)4 with the acid or alkali metal salt of {PhC
CCEE′}−. The compounds Mo22NO, Mo22NS and Mo22OO were structurally characterised by single crystal X-ray crystallography. The structures show that Mo22NO adopts a cis-2,2 arrangement of the ligands about the Mo24+ core, whereas Mo22NS adopts the trans-2,2 arrangement. The influence of heteroatom substitution on the electronic structure of the compounds was investigated using cyclic voltammetry and UV-Vis spectroscopy. Simple N for O for S substitution in the bridging ligands significantly alters the electronic structure, lowering the energy of the Mo2-δ HOMO and reducing the Mo24+/5+ oxidation potential by up to 0.9 V. A different trend is found in the optoelectronic properties, with the energy of the Mo2-δ-to-ligand-π* transition following the order Mo22OO > Mo22NO > Mo22NN > Mo22NS. Electronic structure calculations employing density functional theory were used to rationalise these observations.
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