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 (LH)-H-1 and 1,4-bis(1,2,4-triazolo-3-imino)benzene (LH2)-H-2, respectively. The well characterized Schiff bases were allowed to react with cis-Ru(bpy)(2)Cl-2 (center dot) 2H(2)O. Isomers of the mononuclear complexes Ru(bpy)(2)L-1]PF6 center dot NH4PF6 (1a, N4) and [Ru(bpy)(2)L-1]PF6 center dot 0.5NH(4)PF(6) (1b, N2), and the dinuclear Ru(II) complexes [Ru(bpy)(2)(LRu)-Ru-2(bpy)(2)](PF6)(2) center dot NH4PF6 (2a, N4N4), [Ru(bpy)(2)(LRu)-Ru-2(bpy)(2)](PF6)(2) center dot NH4PF6 center dot 2H(2)O (2b, N2N2) and [Ru(bpy)(2)L2-Ru(bpy)(2)](PF6)(3) center dot 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 d pi(Ru-II) -> pi*L transition. Highly intense ligand-based pi ->pi* transitions are observed in the UV region. A dual emission occurs from the N2 and N2N2 isomers. (C) 2008 Elsevier Ltd. All rights reserved.