Ruthenium-Decorated Lipid Vesicles: Light-Induced Release of [Ru(terpy)(bpy)(OH(2))](2+) and Thermal Back Coordination

Electrostatic forces play an important role in the interaction between large transition metal complexes and lipid bilayers. In this work, a thioether-cholestanol hybrid ligand (4) was synthesized, which coordinates to ruthenium(II) via its sulfur atom and intercalates into lipid bilayers via its apolar tail. By mixing its ruthenium complex [Ru(terpy)(bpy)(4)](2+) (terpy = 2,2';6',2'-terpyridine; bpy = 2,2'-bipyridine) with either the negatively charged lipid dimyristoylphosphatidylglycerol (DMPG) or with the zwitterionic lipid dimyristoylphosphatidylcholine (DMPC), large unilamellar vesicles decorated with ruthenium polypyridyl complexes are formed. Upon visible light irradiation the ruthenium-sulfur coordination bond is selectively broken, releasing the ruthenium fragment as the free aqua complex [Ru(terpy)(bpy)(OH(2))](2+). The photochemical quantum yield under blue light irradiation (452 nm) is 0.0074(8) for DMPG vesicles and 0.0073(8) for DMPC vesicles (at 25 °C), which is not significantly different from similar homogeneous systems. Dynamic light scattering and cryo-TEM pictures show that the size and shape of the vesicles are not perturbed by light irradiation. Depending on the charge of the lipids, the cationic aqua complex either strongly interacts with the membrane (DMPG) or diffuses away from it (DMPC). Back coordination of [Ru(terpy)(bpy)(OH(2))](2+) to the thioether-decorated vesicles takes place only at DMPG bilayers with high ligand concentrations (25 mol %) and elevated temperatures (70 °C). During this process, partial vesicle fusion was also observed. We discuss the potential of such ruthenium-decorated vesicles in the context of light-controlled molecular motion and light-triggered drug delivery.     

cis-Bis(bipyridine)ruthenium Imidazole Derivatives: A Spectroscopic, Kinetic, and Structural Study

The ruthenium bis(bipyridine) complexes cis-[Ru(bpy)(2)Im(OH(2))](2+), cis-[Ru(bpy)(2)(Im)(2)](2+), cis-[Ru(bpy)(2)(N-Im)(2)](2+), cis-[Ru(dmbpy)(2)Im(OH(2))](2+), cis-[Ru(dmbpy)(2)(N-Im)(OH(2))](2+)(bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, Im = imidazole, N-Im = N-methylimidazole), have been synthesized under ambient conditions in aqueous solution (pH 7). Their electrochemical and spectroscopic properties, absorption, emission, and lifetimes were determined and compared. The substitution kinetics of the cis-[Ru(bpy)(2)Im(OH(2))](2+) complexes show slower rates and have lower affinities for imidazole ligands than the corresponding cis-[Ru(NH(3))(4)Im(OH(2))](2+) complexes. The crystal structures of the monoclinic cis-[Ru(bpy)(2)(Im)(2)](BF(4))(2), space group = P2(1)/a, Z = 4, a = 11.344(1) ?, b = 17.499(3) ?, c = 15.114(3) ?, and beta = 100.17(1) degrees, and triclinic cis-[Ru(bpy)(2)(N-Im)(H(2)O)](CF(3)COO)(2).H(2)O, space group = P&onemacr;, Z = 2, a = 10.432(4) ?, b = 11.995(3) ?, c = 13.912(5) ?, alpha = 87.03(3) degrees, beta = 70.28(3) degrees, and gamma = 71.57(2) degrees, complexes show that these molecules crystallize as complexes of octahedral Ru(II) to two bidentate bipyridine ligands with two imidazole ligands or a water and an N-methylimidazole ligand cis to each other. The importance of these molecules is associated with their frequent use in the modification of proteins at histidine residues and in comparisons of the modified protein derivatives with these small molecule analogs.     

Proton-Induced Tuning of Electrochemical and Photophysical Properties in Mononuclear and Dinuclear Ruthenium Complexes Containing 2,2'-Bis(benzimidazol-2-yl)-4,4'-bipyridine: Synthesis, Molecular Structure, and Mixed-Valence State and Excited-State Properties

A series of mono- and dinuclear Ru(bpy)(2) complexes (bpy = 2,2'-bipyridine) containing 2,2'-bis(benzimidazol-2-yl)-4,4'-bipyridine (bbbpyH(2)) were prepared. The mononuclear complex [Ru(bpy)(2)(bbbpyH(2))](ClO(4))(2).CH(3)OH.4H(2)O was characterized by an X-ray structure determination. Crystal data are as follows: triclinic, space group P&onemacr;, a = 14.443(4) ?, b = 15.392(4) ?, c = 11.675(2)?, alpha = 101.44(2) degrees, beta = 107.85(2) degrees, gamma = 96.36(2) degrees, V = 2380(1) ?(3), Z = 2. The coordination geometry of the ruthenium(II) ion is approximately octahedral. The dihedral angle between the two pyridyl rings in bbbpyH(2) is 9.4(3) degrees, which is close to coplanar, in the complex. Mono- and dinuclear complexes exhibit broad charge-transfer absorption bands at 420-520 nm and emission at 660-720 nm in CH(3)CN solution with lifetimes of 200-800 ns at room temperature. Transient difference absorption spectra and resonance Raman (rR) spectra were used to assign the charge-transfer bands in the 420-520 nm region and to identify the lowest excited states. Both absorption and emission spectra are sensitive to solvent and solution pH. Deprotonation of the dinuclear complex raises the energies of the pi orbitals of the bbbpyH(2) ligand, so that they become closer in energy to the pi orbitals of bpy. The intervalence band of [(bpy)(2)Ru(bbbpyH(2))Ru(bpy)(2)](5+)()()is observed at 1200 nm ( epsilon = 170 M(-)(1) cm(-)(1)) in CH(3)CN. The value of the electronic coupling matrix element, H(AB), was determined as 120 cm(-)(1). Upon deprotonation, the IT band was not observed. It is therefore concluded that a superexchange pathway occurs predominantly via the Ru(II) dpi-bbbpyH(2) pi interaction, since deprotonation decreases the interaction. The role of the intervening fragments in the bridging ligand is discussed from the viewpoint of orbital energies and their orbital mixing with Ru dpi orbitals.     

Study of the ligand substitution reactions of cis,cis-[(bpy)(2)(L)RuORu(L')(bpy)(2)](n+) (L,L' = H(2)O,OH(-), NH(3)) using electrospray ionization mass spectrometry and (1)H NMR

We have successfully applied electrospray ionization mass spectrometry (ESI-MS) and (1)H NMR analyses to study ligand substitution reactions of mu-oxo ruthenium bipyridine dimers cis,cis-[(bpy)(2)(L)RuORu(L')(bpy)(2)](n+) (bpy = 2,2'-bipyridine; L and L' = NH(3), H(2)O, and HO(-)) with solvent molecules, that is, acetonitrile, methanol, and acetone. The results clearly show that the ammine ligand is very stable and was not substituted by any solvents, while the aqua ligand was rapidly substituted by all the solvents. In acetonitrile and acetone solutions, the substitution reaction of the aqua ligand(s) competed with a deprotonation reaction from the ligand. The hydroxyl ligand was not substituted by acetonitrile or acetone, but it exchanged slowly with CH(3)O(-) in methanol. The substitution reaction of the aqua ligands in [(bpy)(2)(H(2)O)Ru(III)ORu(III)(H(2)O)(bpy)(2)](4+) was more rapid than that of the hydroxyl ligand in [(bpy)(2)(H(2)O)Ru(III)ORu(IV)(OH)(bpy)(2)](4+). In methanol, slow reduction of Ru(III) to Ru(II) was observed in all the mu-oxo dimers, and the Ru-O-Ru bridge was then cleaved to give mononuclear Ru(II) complexes.     

Syntheses, characterization, and photochemical properties of amidate-bridged Pt(bpy) dimers tethered to Ru(bpy)3(2+) derivatives

Amidate-bridged diplatinum(II) entities [Pt(2)(bpy)(2)(μ-amidato)(2)](2+) (amidate = pivalamidate and/or benzamidate; bpy = 2,2'-bipyridine) were covalently linked to one or two Ru(bpy)(3)(2+)-type derivatives. An amide group was introduced at the periphery of Ru(bpy)(3)(2+) derivatives to give metalloamide precursors [Ru(bpy)(2)(BnH)](2+) (abbreviated as RuBnH, n = 1 and 2), where deprotonation of amide BnH affords the corresponding amidate Bn, B1H = 4-(4-carbamoylphenyl)-2,2'-bipyridine, and B2H = ethyl 4'-[N-(4-carbamoylphenyl)carbamoyl]-2,2'-bipyridine-4-carboxylate. From a 1:1:1 reaction of [Pt(2)(bpy)(2)(μ-OH)(2)](NO(3))(2), RuBnH, and pivalamide, trinuclear complexes [Pt(2)(bpy)(2)(μ-RuBn)(μ-pivalamidato)](4+) (abbreviated as RuBn-Pt(2)) were isolated and characterized. Tetranuclear complexes [Pt(2)(bpy)(2)(μ-RuBn)(2)](6+) (abbreviated as (RuBn)(2)-Pt(2)) were separately prepared and characterized in detail. The quenching of the triplet excited state of the Ru(bpy)(3)(2+) derivative (i.e., Ru*(bpy)(3)(2+)) upon tethering the Pt(2)(bpy)(2)(μ-amidato)(2)(2+) moiety is strongly enhanced in RuB1-Pt(2) and (RuB1)(2)-Pt(2), while it is only slightly enhanced in RuB2-Pt(2) and (RuB2)(2)-Pt(2). These are partly explained by the driving forces for the electron transfer from the Ru*(bpy)(3)(2+) moiety to the Pt(2)(bpy)(2)(μ-amidato)(2)(2+) moiety (ΔG°(ET)); the ΔG°(ET) values for RuB1-Pt(2), (RuB1)(2)-Pt(2), RuB2-Pt(2), and (RuB2)(2)-Pt(2) are estimated as -0.01, 0.00, +0.22, and +0.28 eV, respectively. The considerable difference in the photochemical properties of the B1- and B2-bridged systems were further examined based on the emission decay and transient absorption measurements, which gave results consistent with the above conclusions.     

Ru(bpy)2(5-cyanouracil)2]2+ as a potential light-activated dual-action therapeutic agent

The cation cis-[Ru(bpy)(2)(5CNU)(2)](2+) (bpy = 2,2'-bipyridine; 5CNU = 5-cyanouracil) was synthesized and investigated for use as a potential light-activated dual-action therapeutic agent. The complex undergoes efficient photoinduced 5CNU ligand exchange for solvent water molecules, thus simultaneously releasing biologically active 5CNU and generating [Ru(bpy)(2)(H(2)O)(2)](2+). The latter binds covalently to ds-DNA, such that photolysis results in the generation of 3 equiv of potential therapeutic agents from a single molecule.     

Changing the role of 2,2'-bipyridine from secondary ligand to protagonist in [Ru(bpy)2(N-N)]2+ complexes: low-energy, red emission from a ruthenium(II)-to-2,2'-bipyridine 3MLCT state

Two new bidentate ligands (1 and 2) with bicyclic guanidine moieties were synthesized and attached to a Ru(II)(bpy)(2) core (bpy = 2,2'-bipyridine) to afford complexes 3 and 4, which were characterized by spectroscopic and electrochemical methods. Complex 4 was further characterized by X-ray crystallography. In cyclic voltammetric studies, both complexes show a Ru(II/III) couple, which is 500 mV less positive than the Ru(II/III) couple of Ru(bpy)(3)(2+). The (1)MLCT and (3)MLCT states of 3 (560 nm/745 nm) and 4 (550 nm/740 nm) are significantly red-shifted with respect to Ru(bpy)(3)(2+) (440 nm/620 nm). Compounds 3 and 4 exhibit emission from a Ru(II)-to-bpy (3)MLCT state, which is rarely the emitting state at λ > 700 nm in [Ru(bpy)(2)(N-N)](2+) complexes.     

Effect of pH on the photophysical and redox properties of a ruthenium(II) mixed chelate derived from imidazole-4,5-dicarboxylic acid and 2,2'-bipyridine: an experimental and theoretical investigation

Combined experimental and DFT-TD-DFT computational studies were utilized to investigate the structural and electronic properties of mixed-ligand monometallic ruthenium(II) complexes of compositions [(bpy)(2)Ru(H(2)Imdc)](+) (1(+)), its N-H deprotonated form [(bpy)(2)Ru(HImdc)] (1), and COOH deprotonated form [(bpy)(2)Ru(Imdc)](-) (1(-)), where H(3)Imdc = imidazole-4,5-dicarboxylic acid and bpy = 2,2'-bipyridine. The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the previously reported X-ray data. The influence of pH on the absorption, emission, and redox properties of [(bpy)(2)Ru(H(2)Imdc)](+) (1(+)) has been thoroughly investigated. The absorption titration data were used to determine the ground state pK values, whereas the luminescence data were utilized for the determination of excited state acid dissociation constants. The proton-coupled redox activity of 1(+) has been studied over the pH range 2-12 in acetonitrile-water (3:2). From the E(1/2) versus pH profile, the equilibrium constants of the variously deprotonated complex species in Ru(II) and Ru(III) oxidation states have been determined. As compared to the protonated complex (1(+)), which undergoes reversible oxidation at 0.96 V (vs Ag/AgCl) in acetonitrile, the redox potential of the fully deprotonated complex (1(-)) is shifted to a much lower value, viz., 0.52 V. Density functional theory (DFT) and time-dependent DFT (TD-DFT) study provides insight into the nature of the ground and excited states with resulting detailed assignments of the orbitals involved in absorption and emission transitions. In particular, the red-shifts of the absorption and emission bands and the cathodic shift in the oxidation potential of 1(+) compared to 1 and 1(-) are also reproduced by our calculations.     

Synthesis and structural,electrochemical, and optical properties of Ru(II) complexes with azobis(2,2'-bipyridine)s

Two new ditopic ligands, 5,5"-azobis(2,2'-bipyridine) (5,5"-azo) and 5,5"-azoxybis(2,2'-bipyridine) (5,5"-azoxy), were prepared by the reduction of nitro precursors. Mononuclear and dinuclear Ru(II) complexes having one of these bridging ligands and 2,2'-bipyridine terminal ligands were also prepared, and their properties were compared with previously reported Ru(II) complexes having 4,4"-azobis(2,2'-bipyridine) (4,4"-azo). The X-ray crystal structure showed that 5,5"-azo adopts the trans conformation and a planar rodlike shape. The X-ray crystal structure of [(bpy)(2)Ru(5,5"-azo)Ru(bpy)(2)](PF(6))(4) (Ru(5,5"-azo)Ru) showed that the bridging ligand is in the trans conformation and nearly planar also in the complex and the metal-to-metal distance is 10.0 A. The azo or azoxy ligand in these complexes exhibits reduction processes at less negative potentials than the terminal bpy's due to the low-lying pi level. The electronic absorption spectra for the complexes having 5,5"-azo or 5,5"-azoxy exhibit an extended low-energy metal-to-ligand charge-transfer absorption. The ligands, 5,5"-azo and 5,5"-azoxy, and the mononuclear complex, [(bpy)(2)Ru(5,5"-azo)](2+), isomerize reversibly upon light irradiation. The low-energy MLCT state sensitizes the isomerization of the azo moiety in this complex. While [(bpy)(2)Ru(4,4"-azo)Ru(bpy)(2)](PF(6))(4) exhibits light switch properties, namely, significant electrochromism and a large luminescence enhancement, upon reduction, Ru(5,5"-azo)Ru does not show these properties. The radical anion formation upon reduction of these complexes has been confirmed by ESR spectroscopy.     

Luminescence of tris(2,2'-bipyridine)ruthenium(II) cations ([Ru(bpy)(3)]2+) adsorbed in mesoporous silicas modified with sulfonated phenethyl group

The adsorption of tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)]2+) complex cation into modified mesoporous silicas was investigated. In order to immobilize [Ru(bpy)(3)]2+, the mesopore surface was modified with sulfonic acid groups by the reactions between MCM-41 and phenethyl(dichloro)methylsilane and the subsequent sulfonation of the attached phenethyl groups with chlorosulfonic acid. The modified mesoporous silicas effectively adsorbed [Ru(bpy)(3)]2+ from ethanol solution. It was thought that the effective adsorption was the cause of the cooperative effects of the electrostatic interactions between [Ru(bpy)(3)]2+ cation and sulfonic acid group and the interactions between the phenyl rings on the mesopore surface and the bipyridine rings of the complex. The variation of the position and the intensity of the luminescence of [Ru(bpy)(3)]2+ suggested that the average distance between the adjacent [Ru(bpy)(3)]2+ changed with the loading amounts.     

Photoinitiated DNA Binding by cis-[Ru(bpy)2(NH3)2]2+

The ligand-loss photochemistry of cis-[Ru(bpy)(2)(NH(3))(2)](2+) (bpy = 2,2'-bipyridine) was investigated in water and in the presence of added ligands such as bipyridine and chloride. Irradiation of the complex results in the covalent binding to 9-methyl- and 9-ethylguanine, as well as to single-stranded and double-stranded DNA. This photoinduced DNA binding is not observed for the control complex [Ru(bpy)(2)(en)](2+) (en = ethylenediamine) under similar irradiation conditions. The results presented here show that octahedral Ru(II) complexes with photolabile ligands may prove useful as photoactivated cisplatin analogs.     

Electronic modification of the [Ru(II)(tpy)(bpy)(OH(2))](2+) scaffold: effects on catalytic water oxidation

The mechanistic details of the Ce(IV)-driven oxidation of water mediated by a series of structurally related catalysts formulated as [Ru(tpy)(L)(OH(2))](2+) [L = 2,2'-bipyridine (bpy), 1; 4,4'-dimethoxy-2,2'-bipyridine (bpy-OMe), 2; 4,4'-dicarboxy-2,2'-bipyridine (bpy-CO(2)H), 3; tpy = 2,2';6',2'-terpyridine] is reported. Cyclic voltammetry shows that each of these complexes undergo three successive (proton-coupled) electron-transfer reactions to generate the [Ru(V)(tpy)(L)O](3+) ([Ru(V)=O](3+)) motif; the relative positions of each of these redox couples reflects the nature of the electron-donating or withdrawing character of the substituents on the bpy ligands. The first two (proton-coupled) electron-transfer reaction steps (k(1) and k(2)) were determined by stopped-flow spectroscopic techniques to be faster for 3 than 1 and 2. The addition of one (or more) equivalents of the terminal electron-acceptor, (NH(4))(2)[Ce(NO(3))(6)] (CAN), to the [Ru(IV)(tpy)(L)O](2+) ([Ru(IV)=O](2+)) forms of each of the catalysts, however, leads to divergent reaction pathways. The addition of 1 eq of CAN to the [Ru(IV)=O](2+) form of 2 generates [Ru(V)=O](3+) (k(3) = 3.7 M(-1) s(-1)), which, in turn, undergoes slow O-O bond formation with the substrate (k(O-O) = 3 × 10(-5) s(-1)). The minimal (or negligible) thermodynamic driving force for the reaction between the [Ru(IV)=O](2+) form of 1 or 3 and 1 eq of CAN results in slow reactivity, but the rate-determining step is assigned as the liberation of dioxygen from the [Ru(IV)-OO](2+) level under catalytic conditions for each complex. Complex 2, however, passes through the [Ru(V)-OO](3+) level prior to the rapid loss of dioxygen. Evidence for a competing reaction pathway is provided for 3, where the [Ru(V)=O](3+) and [Ru(III)-OH](2+) redox levels can be generated by disproportionation of the [Ru(IV)=O](2+) form of the catalyst (k(d) = 1.2 M(-1) s(-1)). An auxiliary reaction pathway involving the abstraction of an O-atom from CAN is also implicated during catalysis. The variability of reactivity for 1-3, including the position of the RDS and potential for O-atom transfer from the terminal oxidant, is confirmed to be intimately sensitive to electron density at the metal site through extensive kinetic and isotopic labeling experiments. This study outlines the need to strike a balance between the reactivity of the [Ru═O](z) unit and the accessibility of higher redox levels in pursuit of robust and reactive water oxidation catalysts.     

Interaction between biimidazole complexes of ruthenium and acetate: hydrogen bonding and proton transfer

The hydrogen bonding and deprotonation processes between four ruthenium biimidazole complexes, namely [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1, bpy is bipyridine, BiimH(2) is 2,2'-biimidazole), [Ru(bpy)(2)-(BbimH(2))](PF(6))(2) (2, BbimH(2) is 2,2'-bibenzimidazole), and [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3, DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) and [Ru(bpy)(2)(TMBbimH(2))](2+) (4, TMBbimH(2) is 5,6,5',6'-tetramethyl-2,2'-bibenzimidazole), and acetate are investigated. Their hydrogen bonded adducts are indeed trapped and observed by absorption spectra and electrochemical experiments in acetonitrile solution in the presence of an excess of acetic acid for the first time. The binding constants log K(B) for these adducts are 6.74 for 1·OAc, 7.11 for 2·OAc, 7.26 for 3·OAc, and 6.99 for 4·OAc. A new approach to calculate the deprotonation constant is also developed by establishing a set of circular equilibria. The equilibrium constants for the first deprotonation step of the complexes log K(A) are 2.74 for 1, 5.19 for 2, 4.54 for 3, and 3.78 for 4. The pK(a1) values of the complexes in acetonitrile solution are calculated by subtracting log K(A) from pK(a) (HOAc in acetonitrile), giving 19.6 for 1, 17.1 for 2, 17.8 for 3, and 18.5 for 4. The degree of proton transfer (D(PT)) can be quantified by the calculation of absorption spectral and redox data, which is 0.41 for 1·OAc, 0.53 for 2·OAc, 0.57 for 3·OAc, and 0.47 for 4·OAc. Interestingly, the binding constant log K(B) (7.26) and D(PT) value (0.57) both reach their maxima at a critical point, where pK(a1) for the complex is 17.8 and ΔpK(a) for the adduct is 4.5 (ΔpK(a) = pK(a)(HOAc) - pK(a1), in acetonitrile solution). Moreover, the binding constant log K(B) shows linear correlation with the degree of proton transfer D(PT).     

Enantiospecific synthesis of delta and lambda [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine,ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate): (1)H and (13)C NMR studies and X-ray structure determination of rac-[Ru(bpy)(2)quo]PF(6)

In this paper, we describe the enantiospecific synthesis and the complete characterization of the two hexacoordinated ruthenium(II) monocations [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine, ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate) in their enantiomeric Delta and Lambda forms. The corresponding enantiomeric excesses (ee's) are determined by (1)H NMR using pure Delta-Trisphat (tris(tetrachlorobenzenedialato)phosphate(V) anion) as a chiral (1)H NMR shift reagent. A complete (1)H and (13)C NMR study has been carried out on rac-[Ru(bpy)(2)ppy]PF(6) and rac-[Ru(bpy)(2)quo]PF(6). Additionally, the X-ray molecular structure of rac-[Ru(bpy)(2)quo]PF(6) is reported; this latter species crystallizes in the monoclinic C2/c space group (a = 22.079 A, b = 16.874 A, c = 17.533 A, alpha = 90 degrees, beta = 109.08 degrees, gamma = 90 degrees ).     

An alternative synthesis method for [Os(NN)(CO)(2)X(2)] complexes (NN = 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine; X = Cl, Br, I). Electrochemical and photochemical properties and behavior

A novel synthesis method is introduced for the preparation of [Os(NN)(CO)(2)X(2)] complexes (X = Cl, Br, I, and NN = 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmbpy)). In the first step of this two-step synthesis, OsCl(3) is reduced in the presence of a sacrificial metal surface in an alcohol solution. The reduction reaction produces a mixture of trinuclear mixed metal complexes, which after the addition of bpy or dmbpy produce a trans(Cl)-[Os(NN)(CO)(2)Cl(2)] complex with a good 60-70% yield. The halide exchange of [Os(bpy)(CO)(2)Cl(2)] has been performed in a concentrated halidic acid (HI or HBr) solution in an autoclave, producing 30-50% of the corresponding complex. All of the synthesized trans(X)-[Os(bpy)(CO)(2)X(2)] (X = Cl, Br, I) complexes displayed a similar basic electrochemical behavior to that found in the ruthenium analog trans(Cl)-[Ru(bpy)(CO)(2)Cl(2)] studied previously, including the formation of an electroactive polymer [Os(bpy)(CO)(2)](n) during the two-electron electrochemical reduction. The absorption and emission properties of the osmium complexes were also studied. Compared to the ruthenium analogues, these osmium complexes display pronounced photoluminescence properties. The DFT calculations were made in order to determine the HOMO-LUMO gaps and to analyze the contribution of the individual osmium d-orbitals and halogen p-orbitals to the frontier orbitals of the molecules. The electrochemical and photochemical induced substitution reactions of carbonyl with the solvent molecule are also discussed.     

Mechanistic investigation of CO2 hydrogenation by Ru(II) and Ir(III) aqua complexes under acidic conditions: two catalytic systems differing in the nature of the rate determining step

Ruthenium aqua complexes [(eta(6)-C(6)Me(6))Ru(II)(L)(OH(2))](2+) {L = bpy (1) and 4,4'-OMe-bpy (2), bpy = 2,2'-bipyridine, 4,4'-OMe-bpy = 4,4'-dimethoxy-2,2'-bipyridine} and iridium aqua complexes [Cp*Ir(III)(L)(OH(2))](2+) {Cp* = eta(5)-C(5)Me(5), L = bpy (5) and 4,4'-OMe-bpy (6)} act as catalysts for hydrogenation of CO(2) into HCOOH at pH 3.0 in H(2)O. The active hydride catalysts cannot be observed in the hydrogenation of CO(2) with the ruthenium complexes, whereas the active hydride catalysts, [Cp*Ir(III)(L)(H)](+) {L = bpy (7) and 4,4'-OMe-bpy (8)}, have successfully been isolated after the hydrogenation of CO(2) with the iridium complexes. The key to the success of the isolation of the active hydride catalysts is the change in the rate-determining step in the catalytic hydrogenation of CO(2) from the formation of the active hydride catalysts, [(eta(6)-C(6)Me(6))Ru(II)(L)(H)](+), to the reactions of [Cp*Ir(III)(L)(H)](+) with CO(2), as indicated by the kinetic studies.     

Photolysis of (Diamine)bis(2,2'-bipyridine)ruthenium(II) Complexes Using On-Line Electrospray Mass Spectrometry

Photolysis of Ru(bpy)(2)(en)(2+) and Ru(bpy)(2)(tn)(2+), where bpy = 2,2'-bipyridine, en = ethylenediamine, and tn = 1,3-propylenediamine, was studied in acetonitrile using on-line electrospray mass spectrometry (ES-MS). These complexes are known to undergo a four-electron oxidation photochemically, giving the alpha,alpha'-diimine complexes. The monoimine complexes involved in this stepwise process were detectable after photoirradiation (lambda >420 nm). Also, new ligand-oxidized complexes Ru(bpy)(2)(en+14)(2+) and Ru(bpy)(2)(tn+14)(2+) were observed together with photosubstitution products such as Ru(bpy)(2)(AN)(2)(2+) and Ru(bpy)(2)(AN)(2)X(+) (AN = acetonitrile). The notation (en+14) and (tn+14) represents loss of two hydrogen atoms and addition of an oxygen atom to the en and tn ligands. Photosubstitution intermediates with the monodentate diamine, Ru(bpy)(2)(tn)(AN)(2+) and Ru(bpy)(2)(tn)(AN)X(+), were detected in the ES mass spectrum of the tn complex but not in that of the en complex. Other photosubstituted intermediates with the monodentate (en+14) and (tn+14) ligands were detected by on-line mass analysis. The electrospray technique combined with use of a flow-through photoreaction cell was shown to be a useful tool for studying photolysis of inorganic metal complexes.     

Multiple pathways for benzyl alcohol oxidation by Ru(V)═O3+ and Ru(IV)═O2+

Significant rate enhancements are found for benzyl alcohol oxidation by the Ru(V)═O(3+) form of the water oxidation catalyst [Ru(Mebimpy)(bpy)(OH(2))](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine] compared to Ru(IV)═O(2+) and for the Ru(IV)═O(2+) form with added bases due to a new pathway, concerted hydride proton transfer (HPT).     

Establishment of structure-conductivity relationship for tris(2,2'-bipyridine) ruthenium ionic C(60) salts

Three ionic C(60) salts with [Ru(bpy)(3)](m+) (bpy = 2,2'-bipyridine) as cations were synthesized. The UV-vis-NIR spectra, XPS spectra, and elemental analysis have demonstrated their compositions: [Ru(bpy)(3)](2)(C(60)) (1), [Ru(bpy)(3)](C(60)) (2), and [Ru(bpy)(3)](C(60))(2) (3). Single crystals of polycrystalline compounds 1 and 2 were obtained as solvates. At room temperature, all three salts are semiconducting with the highest four-probe conductivity observed for compound 1 at ～10 S m(-1). The electronic conduction mechanisms can be described appropriately by an electron hopping model in this immobilized polyvalent redox system.