The redox series [Ru(bpy)2(L)]n, n =+3,+2,+1, 0, with L = bipyridine, click derived pyridyl-triazole or bis-triazole: a combined structural, electrochemical, spectroelectrochemical and DFT investigation

The compounds [Ru(bpy)(2)(L-1)](ClO4)(2) (1(ClO4)(2)), [Ru(bpy)(2)(L-2)](ClO4)(2) (2(ClO4)(2)), [Ru(bpy)(2)(L-3)](ClO4)(2) (3(ClO4)(2)), [Ru(bpy)(2)(L-4)](ClO4)(2) (4(ClO4)(2)), [Ru(bpy)(2)(L-5)](ClO4)(2) (5(ClO4)(2)), and [Ru(bpy)(2)(L-6)](ClO4)(2) 6(ClO4)(2) (bpy = 2,2'-bipyridine, L-1 = 1-(4-isopropyl-phenyl)-4-(2-pyridyl)-1,2,3-triazole, L-2 = 1-(4-butoxy-phenyl)-4-(2-pyridyl)-1,2,3-triazole, L-3 = 1-(2-trifluoromethyl-phenyl)-4-(2-pyridyl)-1,2,3-triazole, L-4 = 4,4'-bis-{1-(2,6-diisopropyl-phenyl)}-1,2,3-triazole, L-5 = 4,4'-bis-{(1-phenyl)}-1,2,3-triazole, L-6 = 4,4'-bis-{1-(2-trifluoromethyl-phenyl)}-1,2,3-triazole) were synthesized from [Ru(bpy)(2)(EtOH)(2)]-(ClO4)(2) and the corresponding click-derived pyridyl-triazole or bis-triazole ligands, and characterized by H-1-NMR spectroscopy, elemental analysis, mass spectrometry and X-ray crystallography. Structural analysis showed a distorted octahedral coordination environment about the Ru(II) centers, and shorter Ru-N-(triazole) bond distances compared to Ru-N(pyridine) distances in complexes of mixed-donor ligands. All the complexes were subjected to cyclic voltammetric studies, and the results were compared to the well-known [Ru(bpy)(3)](2+) compound. The oxidation and reduction potentials were found to be largely uninfluenced by ligand changes, with all the investigated complexes showing their oxidation and reduction steps at rather similar potentials. A combined UV-vis-NIR and EPR spectroelectrochemical investigation, together with DFT calculations, was used to determine the site of electron transfer in these complexes. These results provided insights into their electronic structures in the various investigated redox states, showed subtle differences in the spectroscopic signatures of these complexes despite their similar electrochemical properties, and provided clues to the unperturbed redox potentials in these complexes with respect to ligand substitutions. The reduced forms of the complexes display structured absorption bands in the NIR region. Additionally, we also present new synthetic routes for the ligands presented here using Cu-abnormal carbene catalysts.