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A series of cyclometalated diruthenium complexes with a redox-active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one-electron-oxidized state can be either in the form of a weakly or strongly coupled mixed-valence diruthenium complex, a fully charge-delocalized three-center system, or a bridge-biased electrophore. This transition among different electronic forms was supported by electrochemistry, near-infrared absorption, electron paramagnetic resonance, and density functional theory analysis. [ABSTRACT FROM AUTHOR]

Two series of linear ruthenium coordination oligomers, [(Ntpy)Ru n(tppz) n−1(tpy)]2 n+ (mono-Ntpy series, n=1-3) and [(Ntpy)2Ru n(tppz) n−1]2 n+ (bis-Ntpy series, n=1-3) have been prepared, where Ntpy is the capping ligand 4′-di- p-anisylamino-2,2′:6′,2′′-terpyridine, tppz is tetra-2-pyridylpyrazine, and tpy is 2,2′:6′,2′′-terpyridine. The electrochemical measurements evidence oxidation events from both the amine segments and the metal centers and reduction waves from tppz and the capping ligands. Both series complexes display much enhanced light absorption with respect to model complexes without terminal amine units. Density functional theory (DFT) calculations have been performed on both series and time-dependent DFT (TD-DFT) calculations have been performed on the bis-Ntpy-series compounds ( n=1-4) to characterize their electronic structures and excited states and predict the electronic properties of long-chain polymers. Upon one-electron oxidation, the mono-Ntpy-series monoruthenium and diruthenium complexes display N+-localized transitions and metal-to-nitrogen charge-transfer (MNCT) transitions in the near-infrared (NIR) region. DFT and TD-DFT computations on the one-electron-oxidized forms of the mono-Ntpy-series compounds ( n=1-4) provide insight into the nature of the MNCT transitions and the degree of charge delocalization. [ABSTRACT FROM AUTHOR]

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]

A new cydometalating bridging ligand 1,3,6,8-tetra(2-pyridyl)pyrene was designed acid synthesized through 4-told Suzuki couplings between 1,3,68-tetrabromopyrene and 2-pyridylboronate. A bis-cyclometalated bisruthenium complex bridged by this ligand showed the presence of an electronic coupling between individual metal centers, as indicated by electrochemical and spectroscopic studies. [ABSTRACT FROM AUTHOR]