Azo dyes sulphur-bridged ruthenium–molybdenum complexes: Synthesis, spectroscopic and electrochemical characterization of [(α/β-NaiR′)2Ru(μ-S)2Mo(OH)2]

The reaction of azo dye complexes ctc-[Ru(α/β-NaiR′)2Cl2] (1) [α/β-NaiR′ = 1-alkyl-2-α/β-(naphthylazo)imidazole, C10H7–NN–C3H2NN(1)–R′, R′ = Me (2), Et (3), Bz (4)] with (NH4)2MoS4 in aqueous MeOH afforded reddish violet colour mixed ligand complexes of the type [(α/β-NaiR′)2Ru(μ-S)2Mo(OH)2] (2–4). In complexes 2–4 the terminal MoS bonds of the MoS42− unit become hydroxylated and the molybdenum ion is reduced from the starting MoVI in MoS42− to MoIV in the final product (2–4). The solution electronic spectra exhibit a strong MLCT band at 550–570 nm in DCM. Cyclic voltammograms show a Ru(III)/Ru(II) couple at 1.10–1.4 V, irreversible Mo(IV)/Mo(V) oxidations in the 1.66–1.72 V range, along with four successive reversible ligand reductions in the range −0.45 to −0.67 V (one electron), −0.82 to −1.12 V (one electron), and −1.44 to −1.90 V (simultaneously two electrons).