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A series of mononuclear cyclometalated ruthenium complexes with 1,2,4,5-tetrakis(N-methylbenzimidazolyl)benzene have been prepared, where two N-methylbenzimidazoles bind to the metal center and others remain intact. Electronic properties of these complexes were investigated by electrochemical and spectroscopic studies and DFT/TDDFT computations. The RuII/III redox potentials of theses complexes can be modulated by attaching substituents of various electronic natures on the non-cyclometalating ligand. These complexes display enhanced visible light absorption compared to those without two free-standing N-methylbenzimidazolyl units as a result of the three-chromophore effect. [ABSTRACT FROM AUTHOR]

The linear bis-cyclometalated Ru(II) complex [(ttpy)Ru(ttabp)Ru(ttpy)]2+was prepared from the oxidative coupling of the monometalliccomplex [(ttpy)Ru(dtab)]+in good yield, where ttpy is4′-tolyl-2,2′:6′,2″-terpyridine, ttabpis 3,3′,5,5′-tetrakis(1-butyl-1H-1,2,3-triazol-4-yl)biphenyl,and dtab is 1,3-bis(1-butyl-1H-1,2,3-triazol-4-yl)benzene.The electronic properties of these two complexes were studied andcompared by electrochemical and spectroscopic methods and DFT/TDDFTcalculations. The complex [(ttpy)Ru(ttabp)Ru(ttpy)]2+showedtwo consecutive RuII/IIIredox waves at +0.34 and +0.51V vs Ag/AgCl with a comproportionation constant Kcof 760. One-electron oxidation of [(ttpy)Ru(ttabp)Ru(ttpy)]2+by electrochemical methods produced the mixed-valent complex[(ttpy)Ru(ttabp)Ru(ttpy)]3+, which exhibited a symmetricintervalence charge transfer band at 1800 nm (νmax= 5550 cm–1, εmax= 5100 M–1cm–1, Δν1/2= 3580 cm–1). The energy and shape of this bandare very similar in the different solvents studied (CH3CN, DMF, CH2Cl2). [(ttpy)Ru(ttabp)Ru(ttpy)]3+was determined to be a class II/III borderline system withthe electronic coupling parameter Hab=530 cm–1. It displayed a metal-centered rhombicEPR signal at 77 K with an isotropic gfactor of2.109 and total ganisotropy of 0.256, which pointsto an appreciable spin distribution on the bridging ligand in additionto the metal centers. [ABSTRACT FROM AUTHOR]