The preparations and properties of ruthenium(II) complexes containing the bidentate ligand l-(2-pyridyl)-3,5-dimethylpyrazole, L, are described. The tris complex RuL32+ is shown to readily undergo photosubstitution in acetonitrile solution to produce RuL2(CH3CN)22+, which in the presence of other bidentate ligands undergoes thermal substitution of the coordinated acetonitrile. , 13C, and "Ru NMR spectra are reported for all the complexes. Proton and carbon-13 NMR reveal the presence of geometrical isomerism, where it exists; proton and ruthenium-99 NMR allow the evaluation of the percentage of these isomers. Ruthenium-99 NMR proves to be an excellent probe of electron density at the metal and is possibly useful to evaluate the amount of x-back-bonding depending on the ligands. Electronic spectral data and oxidation potential measurements are given for comparison with those of the well-known Ru(bpy)32+ complex but do not lead to consistent results.
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