The effect of bipyridine modifications on the electrochemical and electronic properties of Ru(II)–bipyridine carbonyls

The electrochemical properties of the Ru(II)–mono(bipyridine) complexes (4,4′-L2-2,2′-bpy)Ru(CO)2Cl2 (L=NH2, t-Bu, Me, H, Cl, Br, COOH, H2PO3, NO2) (L=1–9, respectively) were studied in CH3CN by means of cyclic voltammetry. The effect of the electronic nature of the ligand substituent on the experimental redox data, on the computational HOMO–LUMO energy differences, and on the ionization energies was investigated. The computational work was carried out using the density functional hybrid method. The positive shift of the Ru(II)/Ru(III) potential values, which was induced by increasing the electron-withdrawing nature of the substituent, was found to correlate with the decreasing HOMO–LUMO energy difference and with the increasing ionization energies. The ligand electrochemical parameter, EL(L), was derived from the experimental redox data for the 4,4′-L2-2,2′-bipyridine ligands (L=NH2, t-Bu, Cl, NO2). The ligand parameters followed the electron-donor or electron-acceptor nature of the ligands studied.