Far-infrared spectroelectrochemistry: a study of linear molybdenum/iron/sulfur clusters

The far-infrared spectroelectrochemistry of linear M/Fe/S (M=Mo, W) complexes was investigated in methylene chloride and dichloroethane. With CsI as spectral windows, bands above 200 cm⁻¹ can be observed in methylene chloride, except for a weak methylene chloride band at 450 cm⁻¹. Substitution of dichloroethane for methylene chloride, solvents of nearly identical electrochemical properties, allows one to observe solute bands in the 450-cm⁻¹ region. The far-infrared spectroelectrochemistry of [MoFe₂S₄Cl₄]²⁻ and its tungsten analogue was investigated. The disappearance of the oxidation bands and the appearance of bands due to the reduced product could be clearly observed. The origin of the vibrational bands could be clearly identified using ³⁴S-substituted complexes. In addition to the far-infrared bands, the resonance Raman spectroelectrochemistry of the oxidized and reduced complex, along with the ³⁴S-substituted complexes was obtained. Far-infrared and resonance Raman spectroelectrochemistry can be combined to understand the electrochemical mechanism of transition metal complexes.