Reactivity of triazolyl Schiff bases with Ru(II)-2,2′-bipyridyl: Synthesis, spectroscopic characterization of isomers and their photo-physical properties

The condensation of 3-amino-1H-1,2,4-triazole with benzaldehyde and terephthalaldehyde provides the bidentate and tetradentate Schiff bases 1,2,4-triazolo-3-imino-benzene L1H and 1,4-bis(1,2,4-triazolo-3-imino)benzene L2H2, respectively. The well characterized Schiff bases were allowed to react with cis-Ru(bpy)2Cl2 · 2H2O. Isomers of the mononuclear complexes Ru(bpy)2L1]PF6 · NH4PF6 (1a, N4) and [Ru(bpy)2L1]PF6 · 0.5NH4PF6 (1b, N2), and the dinuclear Ru(II) complexes [Ru(bpy)2L2Ru(bpy)2](PF6)2 · NH4PF6 (2a, N4N4), [Ru(bpy)2L2Ru(bpy)2](PF6)2 · NH4PF6 · 2H2O (2b, N2N2) and [Ru(bpy)2L2Ru(bpy)2](PF6)3 · NH4PF6 (2c, Ru(II)-Ru(III)) were separated by column chromatography and characterized by their elemental analysis, FAB mass and spectral (IR, NMR, UV–Vis) data. The data obtained suggest that the ligands are bound to the metal centre via the N4 and N2 atoms of the triazole moiety along with the N (imine) atom. The complexes display metal-to-ligand charge-transfer (MLCT) transitions in the visible region from the dπ(RuII) → π∗L transition. Highly intense ligand-based π→π∗ transitions are observed in the UV region. A dual emission occurs from the N2 and N2N2 isomers.

Trizolyl Schiff bases complexed with cis-[Ru(bpy)2Cl2] · 2H2O provide mononuclear (N2, N4) and dinuclear (N4N4, N2N2 and RuII–RuIII) isomers which are characterized spectroscopically. Out of all the isomers, the N2 and N2N2 isomers show dual emission at room temperature, whereas emission quenching is observed from the RuII–RuIII complex.Figure optionsDownload as PowerPoint slide