Molybdenum Dithiolene Complexes: Trinuclear Mixed-Valence Complexes and Geometrical Isomers of Dinuclear Complexes

Abstract

Abstract The reaction of an oxygen- and sulfur-bridged incomplete cubane-type molybdenum complex [Mo3(µ3-S)(µ-S)2(µ-O)(dtp)3(µ-dtp)(CH3CN)] (3) (dtp, diethyl dithiophosphate) with methyl propiolate (HC≡CCOOCH3, MP) and phenyl acetylene (HC≡CC6H5, PA) yields trinuclear mixed-valence Mo3(IV, V, V) complexes [Mo3(O)2(µ3-S)(µ3-SCH=C(COOCH3)S)(dtp)3(µ-OAc)] (3MP) and [Mo3(O)2(µ3-S)(µ3-SCH=C(C6H5)S)(dtp)3(µ-OAc)] (3PA), respectively, and also dinuclear Mo2(V, V) complexes [Mo2(O)2(µ-S)(µ-SCH=C(COOCH3)S)(dtp)2] (2aMP and 2bMP (a geometrical isomer of 2aMP)) and [Mo2(O)2(µ-S)(µ-SCH=C(C6H5)S)(dtp)2] (2aPA and 2bPA (a geometrical isomer of 2aPA)), respectively. The origin of the geometrical isomerism of the dimers comes from the unsymmetric nature of the acetylene derivatives. All of the structures were determined by X-ray crystallography, which revealed that each complex has two carbon-sulfur (µ-S) bonds arising from the adduct formation reaction between complex 3 and an acetylene derivative MP or PA. 1H NMR spectroscopy has proven that the dinuclear complexes are formed via the trinuclear complexes. The XPS spectra of 3MP show that the peaks of Mo 3d3/2 and Mo 3d5/2 are clearly split into two in the ratio of two to one, respectively, while those of 3 show no splitting, which indicates that 3MP is a mixed-valence complex with Mo3(IV, V, V) oxidation states. Cyclic voltammograms of 3MP and 3PA show chemically reversible one-electron oxidation processes at E1/2 = 0.21 V and E1/2 = 0.15 V vs. Ag/Ag+, respectively, and irreversible reduction peaks at −0.92 V and −1.00 V vs. Ag/Ag+, respectively. The dinuclear complexes, especially 2aPA and 2bPA having phenyl groups, are photosensitive to give their isomeric counter parts.