Synthesis and Characterization of Strongly Solvatochromic Molybdenum(III) Complexes.

A series of seven molybdenum(III) complexes with the general formula of [Mo(diimine)Cl4]- were synthesized and characterized by X-ray diffraction, IR, cyclic voltammetry (CV), and UV-vis. The complexes were discovered to be highly solvatochromic, showing shifts in λmax between ∼120 and 170 nm in solvents ranging from water to acetone. Varying the substituents on the diimine ligand influenced the absorption energy such that electron-withdrawing groups induced a red shift while electron-donating groups exhibited the opposite effect. The complexes were surprisingly stable in both acidic and basic solutions, and in the case where carboxylic acid substituents were present, additional shifts in the absorption maxima were observed, corresponding to the state of protonation of these groups. Both the MoIV/III and MoIII/II redox couples were observed in CV experiments and were complemented with density functional theory (DFT) calculations.