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New ruthenium complexes of two tridentate ligands 2,6-bis( benzimidazol-2-yl)pyridine ( L7) and 2,6bis( 1 -methylbenzimidazol-2-yl)pyridine (La) have been synthesised. Proton and 13C NM R spectroscopy served well for their characterization, and the observed change. Proton chemical shift yields information about the electron distribution accompanying deprotonation of the ligands. The [ RuL7Jn+ chelate acts as a tetrabasic acid, with pK, ranging from 2.5 to 10.7, depending on the ruthenium oxidation state. The absorption spectra and oxidation potentials are consequently sensitive to solution pH and to solvent. The proton-coupled oxidative electron-transfer reactions of the complexes afford stable higher oxidation states such as Ru'". The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate 1igand)ruthenium compounds.

A facile synthesis method or ruthenium(II) polypyridine complexes by microwave irradiation has been developed. This method greatly reduces reaction time from 4 hours to 20 minutes with better yield(60–90%). The procedures are simple and may be used for synthesis of a variety of metal polypyridine complexes.

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The preparation and spectroscopic and electrochemical properties of new 2,2'-bibenzimidazolate-(BiBzIm-) bridged binuclear complexes of the general formula [(bpy)2M(BiBzIm)M'(bpy)2]"+ (M = Ru, Os; M' = Ru, Os, Co, Ni) are reported. The Os(II)-Os(III) mixed-valence complex shows multiple intervalence-transfer (IT) absorption bands at 4800 and 8180 cm'1 in the near-infrared region, which can be attributed to the orbital splitting of optically prepared Os(III) site by tetragonal distortion and spin-orbit coupling. The Ru(II)-Os(III) and Ru(II)-Ru(III) mixed-valence complexes also exhibit multiple IT bands. The bandwidths at half-intensity for IT bands are narrower than those expected from Hush's theoretical treatment. These new mixed-valence complexes belong to Robin and Day's class II. The comproportionation constant Kmm for the complex = M' = Ru greater than that foe the complex = M' = Os is observed. This result, contrary to the trends reported so far, is discussed in terms of the orbital mixing between metal sites and BiBzIm. The anionic BiBzIm bridging ligand can cause stabilization of the mixed-valence complex by reducing the positive charge on the complex. The comparison of a BiBzIm-bridged complex with a bpm-bridged one is also discussed in terms of the donor-acceptor property of the ligand.