Ruthenium nitrosyl complexes [Ru(trpy)(L1-4)(NO)]3+ (13−16) [trpy = 2,2‘:6‘,2‘ ‘-terpyridine, L1 = 2-(2-pyridyl)benzoxazole, L2 = 2-(2-pyridyl)benzthiazole, L3 = 2-(2-pyridyl)benzimidazole, L4 = 1-methyl-2-(2-pyridyl)-1H-benzimidazole] were obtained in a stepwise manner starting from [RuII(trpy)(L1-4)(Cl)]ClO4 (1−4) → [RuII(trpy)(L1-4)(H2O)](ClO4)2 (5−8) → [RuII(trpy)(L1-4) (NO2)]ClO4 (9−12) → [RuII(trpy)(L1,2,4)(NO)](ClO4)3 (13, 14, 16)/[RuII(trpy)(L3)(NO)](ClO4)2(NO3) (15). Crystal structures of 1, 2, 4, 9, 12, 13, 15, and 16 established the stereoretentive nature of the transformation processes. Though the complexes of L1, L3, and L4 were isolated in the isomeric form A (π-acceptor trpy and azole ring in the equatorial plane and the pyridine and chloride donors in the axial positions), complexes of L2 preferentially stabilized in form B (trpy and pyridine in the equatorial plane and the azole ring and chloride donors in the axial positions). The ν(NO) stretching frequency varied in the range of 1957−19...

Effect of 2-(2-Pyridyl)azole-based ancillary ligands (L1-4) on the electrophilicity of the nitrosyl function in [RuII(trpy)(L1-)4)(NO)]3+ [trpy = 2,2':6',2' '-Terpyridine]. synthesis, structures, and spectroscopic, electrochemical, and kinetic aspects.

A series of mono- and dinuclear Ru complexes containing a bridging ligand, L-diimide-L (L = 2-(2-pyridyl)benzimidazole; diimide = benzene-1,2:4,5-bis(dicarboximide) (bdi; pyromellitimide) or naphthalene-1,8:4,5-bis(dicarboximide) (ndi), with either propane or xylene group as linkers, have been prepared. The mono- and dinuclear Ru complexes containing the bdi or ndi ligand, exhibit characteristic metal-to-ligand charge transfer (MLCT) transition at 458 nm. The mono- and dinuclear Ru/Os complexes exhibit a rich redox chemistry arising from both M(II) to M(III) oxidation and ligand-based consecutive reduction of diimide and 2,2'-bipyridine (bpy) ligands. The emission decays fit well with double- or triple-exponential decay models. The non-exponential decay curve reveals the existence of several conformers in solution due to the flexible propane or p -xylene linker. The much shorter emission lifetimes of the [M(bpy) 2 (L-diimide-L)] complexes compared with the parent [M(bpy) 2 L] indicates the intramolecular electron-transfer from the excited M(bpy) 2 moiety to the diimide. The fastest rates of electron transfer (3 · 10 10 s -1 ) are attributable to the folded conformers suitable for the electron donor/acceptor through-space interaction. A time-resolved absorption spectroscopic study of the dinuclear bdi and ndi complexes revealed appearance of the electron-transfer products, M(III) and the diimide radical anion, and their rapid disappearance. The effect of the linkers of the ligand L-diimide-L on the rates of electron transfer and the back electron transfer is also discussed.

Syntheses, Spectroelectrochemistry and Photoinduced Electron-Transfer Processes of Novel Ru and Os Dyad and Triad Complexes with Functionalized Diimide Ligands

The energy transfer of a charge−transfer triplet excited state (3CT) in [Ru(bpy)3](PF6)2 (bpy = 2,2‘-bipyridine) crystals doped with [Os(bpy)3](PF6)2 was studied by a time-correlated single-photon counting method, where the excited Ru(II) moiety and the Os(II) moiety act as energy donor (D) and acceptor (A), respectively. 3CT of Ru2+ in the [OsxRu1-x(bpy)3](PF6)2 (x > 0.0099) exhibited multiexponential decay, which is ascribed to direct energy transfer to Os2+ at various rates depending on the D−A distances. Hopping of 3CT to the closest Ru2+ (Ikeda et al., J. Phys. Chem. A, 2000) changed the D−A distances and made the decay faster at a later time. The complex emission decay was analyzed by a Monte Carlo simulation. The rates of energy transfer to Os2+ at 0.82 and 1.08 nm were determined to be 1.7 × 1011 and 7 × 109 s-1, respectively. The distance dependence of the rates of energy transfer through space and its mechanism are discussed.

Fast Energy Transfer of Charge−Transfer Triplet Excited State (3CT) of [Ru(bpy)3](PF6)2 to Os2+ at Short Distances in the Crystal

The charge separated(CS) state was efficiently formed as a result of stepwise electron transfer reactions in a novel Ru(II)(bpy)2-diimide-Os(III)(bpy)2 triad system (efficiency > 0.7); the rate of electron transfer and the charge separation yield were determined from picosecond time-resolved absorption spectra.

T. Ohno

Papers

Reversible intramolecular electron transfer between ru(ii) complexes in the charge-transfer excited states