Sulphur-bridged ruthenium–molybdenum complexes: [(R-aapm)2Ru(m-S)2 Mo(OH)2]. Synthesis, spectroscopic and electro-chemical characterization. R-aapm = 2-(arylazo)pyrimidine

The reaction of ctc-[Ru(R-aapm)2Cl2] (1) with (NH4)2MoS4 in aqueous MeOH afforded redviolet mixed ligand complexes of the type [(R-aapm)2Ru(m-S)2Mo(OH)2] (2a–2e) [R-aapm = 2-(arylazo) pyrimidine, p-R-C6H4-N=N-C4H3NN, R = H (2a), Me (2b), Cl (2c), OMe (2d), NO2 (2e)]. In complexes (2a–2e) the terminal Mo=S bonds of the MoS 4 2– unit get hydroxylated and the molybdenum ion is reduced from the starting MoVI in MoS 4 2– to MoIV in the final product. The solution electronic spectra exhibit a strong MLCT band at 550–570 nm in DCM. The 1H NMR spectra confirms the geometry of the complexes as being that of cis-trans-cis isomers. Cyclic voltammograms show a Ru(III)/Ru(II) couple at 1,10–1,40 V, irreversible Mo(IV)/Mo(V) oxidations in the 1,66–1,72^0 V range, along with four successive reversible ligand reductions in the range –0,45–0,67 V (one electron), –0,82–1,12 V (one electron), –1,44–1,90 V (simultaneously two electrons).).