Oxo-bridged Dinuclear Ruthenium Research Articles

Amphiphilic Oxo-Bridged Ruthenium "Green Dimer" for Water Oxidation.

SummaryIn 1982, an oxo-bridged dinuclear ruthenium(III) complex, known as “blue dimer,” was discovered to be active for water oxidation. In this work, a new amphiphilic ruthenium “green dimer” 2, obtained from an amphiphilic mononuclear Ru(bda) (N-OTEG) (L1) (1; N-OTEG = 4-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-pyridine; L1 = vinylpyridine) is reported. An array of mechanistic studies identifies “green dimer” 2 as a mixed valence of RuII-O-RuIII oxo-bridged structure. Bearing the same bda2- and amphiphilic axial ligands, monomer 1 and green dimer 2 can be reversibly converted by ascorbic acid and oxygen, respectively, in aqueous solution. More importantly, the oxo-bridged “green dimer” 2 was found to take water nucleophilic attack for oxygen evolution, in contrast to monomer 1 via radical coupling pathway for O-O bond formation. This is the first report of an amphiphilic oxo-bridged catalyst, which possesses a new oxygen evolution pathway of Ru-bda catalysts.

Molecular Self-Assembly in a Family of Oxo-Bridged Dinuclear Ruthenium(IV) Systems

A series of six novel RuIV compounds of formula (H2bpy)2[{RuCl5}2(μ-O)] (1), (PPh4)2[{RuCl4(H2O)}2(μ-O)]·4H2O (2), (PPh4)2[{RuCl4(MeCN)}2(μ-O)] (3), (PPh4)2[{RuCl4(dmf)}2(μ-O)] (4), (PPh4)2[{RuCl4(...

Possibility of Dielectric Material: Magnetic Resonance Study of Oxo‐Bridged Dinuclear Ruthenium Mixed‐Valence Complex

AbstractSolid‐state broad line 1H‐NMR (nuclear magnetic resonance) and ESR (electron spin resonance) were performed for an oxo‐bridged dinuclear ruthenium [RuORu]5+ (Ru3.5+ORu3.5+) mixed‐valence complex. The 1H‐NMR spin‐lattice relaxation rate T1−1 was significantly enhanced, to below 100 K with a peak at approximately 33 K. The T1−1 peak temperature was frequency‐independent, indicating that this anomaly is a possible phase transition. Below approximately 40 K, an abrupt decrease of 1H‐NMR spin‐spin relaxation time T2 provides evidence of the appearance of inequivalent 1H‐sites (sudden decrease in symmetry). ESR spectra suddenly disappeared above 35 K. The electronic properties and possible charge ordering (Ru3+ORu4+) states in this mixed‐valence compound are discussed from a microscopic point of view.

Evaluation of the Oxo-bridged Dinuclear Ruthenium Ammine Complex as Redox Mediator in an Electrochemical Biosensor

The mediation of electron-transfer by oxo-bridged dinuclear ruthenium ammine [(bpy)2(NH3)RuIII(µ-O)RuIII(NH3)(bpy)2]4+ for the oxidation of glucose was investigated by cyclic voltammetry. These ruthenium (III) complexes exhibit appropriate redox potentials of 0.131–0.09 V vs. SCE to act as electron-transfer mediators. The plot of anodic current vs. the glucose concentration was linear in the concentration range between 2.52×10−5 and 1.00×10−4 mol L−1. Moreover, the apparent Michaelis-Menten kinetic (KMapp) and the catalytic (Kcat) constants were 8.757×10−6 mol L−1 and 1,956 s−1, respectively, demonstrating the efficiency of the ruthenium dinuclear oxo-complex [(bpy)2(NH3)RuIII(µ-O)RuIII(NH3)(bpy)2]4+ as mediator of redox electron-transfer.

Three distinct redox states of an oxo-bridged dinuclear ruthenium complex.

A series of [{(terpy)(bpy)Ru}(μ-O){Ru(bpy)(terpy)}](n+) ([RuORu](n+), terpy=2,2';6',2''-terpyridine, bpy=2,2'-bipyridine) was systematically synthesized and characterized in three distinct redox states (n=3, 4, and 5 for Ru(II,III)2, Ru(III,III)2, and Ru(III,IV)2, respectively). The crystal structures of [RuORu](n+) (n=3, 4, 5) in all three redox states were successfully determined. X-ray crystallography showed that the Ru-O distances and the Ru-O-Ru angles are mainly regulated by the oxidation states of the ruthenium centers. X-ray crystallography and ESR spectra clearly revealed the detailed electronic structures of two mixed-valence complexes, [Ru(III)ORu(IV)](5+) and [Ru(II)ORu(III)](3+), in which each unpaired electron is completely delocalized across the oxo-bridged dinuclear core. These findings allow us to understand the systematic changes in structure and electronic state that accompany the changes in the redox state.

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Electrochemical behavior of oxo-bridged dinuclear ruthenium(III) complex ([(bpy)2(H 2O)Ru III-O-Ru III(H 2O)(bpy)2] 4+) has been studied in aqueous solution (KCl 0.5 mol L −1) by both cyclic and rotating disk electrode (RDE) voltammetry in order to identify and elucidate the reaction mechanism. Modified electrode containing the oxo-bridged ruthenium complex incorporated into a cation-exchange polymeric film deposited onto platinum electrode surface was studied. Cyclic voltammetry at the modified electrode in KCl solution showed a single-electron reduction/oxidation of the couple Ru III-O-Ru III/Ru III-O-Ru IV. The modified electrode exhibited electrocatalytic property toward hydrogen peroxide oxidation in KCl solution with a decrease of the overpotential of 340 mV compared with the platinum electrode. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the hydrogen peroxide oxidation. The first at low overpotential region there is no significant change in the Tafel slope (∼0.130 V dec −1) with varying peroxide concentration. The second region at higher overpotential the slope values (0.91–0.47 V dec −1) were depended on the peroxide concentration. The apparent reaction order for H 2O 2 varies from 0.16 to 0.50 in function of the applied potential. The apparent reaction order (at constant potential) with respect to H + concentration of 10 −5 to 10 −1 mol L −1 was 0.25. A plot of the anodic current vs. the H 2O 2 concentration for chronoamperometry (potential fixed = +0.61 V) at the modified electrode was linear in the 1.0 × 10 −5 to 2.5 × 10 −4 mol L −1 concentration range.

Oxo-linked diruthenium(III) complex with 2,2′-bipyridine in ortho-metalation

Oxo-bridged dinuclear ruthenium(III) complex [Ru 2(μ-O){η 2( N, N)-bpy} 2{μ-η 1(C),η 2( N, N)-bpy} 2](PF 6) 2 ( 1) with ortho-metalated 2,2′-bipyridine (bpy) was synthesized and characterized by X-ray crystallography. Electrochemical studies revealed that the Ru 2 III,III complex exhibits four reversible or quasi-reversible redox processes due to successive oxidation or reduction of the diruthenium centers.

Syntheses, crystal structures, susceptibility and EPR studies of oxo-bridged dinuclear ruthenium (III) complexes with linear Ru–O–Ru bonds: and [(Py) 3(C 2O 4)Ru IIIORu III(C 2O 4)(Py) 3] and [(4-MePy) 3(C 2O 4)Ru IIIORu III(C 2O 4)(4-MePy) 3]·2-Mebmz ·3H 2O (Py = pyridine; 4-MePy = 4-methylpyridine; 2-Mebmz = 2-methylbenzimidazole)

Two oxo-bridged dinuclear ruthenium(III) complexes, [(Py) 3(C 2O 4)Ru IIIORu III(C 2O 4)(Py) 3] ( 1) and [(4-MePy) 3(C 2O 4)Ru IIIORu III(C 2O 4)(4-MePy) 3]·2-Mebmz ·3H 2O ( 2) (Py = pyridine; 4-MePy = 4-Methylpyridine; 2-Mebmz = 2-methylbenzimidazole) were prepared by reacting RuCl 3 with K 2C 2O 4 and pyridine or 4-Methylpyridine and characterized by spectral data and X-ray crystallography. In both ( 1) and ( 2), the Ru–O–Ru bonds are linear, with the two C 2O 4 2− ions trans to each other at the terminal positions. The magnetic susceptibility of ( 1) was analyzed using a general isotropic exchange Hamiltonian H=−2JS 1·S 2 (S 1=S 2=1/2) , yielding an antiferro-magnetic spin coupling constant J=−53 cm −1 .

Inhibition of mitochondrial calcium ion transport by an oxo-bridged dinuclear ruthenium ammine complex

Ruthenium red is a well-known and effective inhibitor of the mitochondrial Ca2+ uniporter; however, Reed and Bygrave [(1974) FEBS Lett. 46, 109-114] tentatively attributed this inhibition to a colorless impurity present in commercial samples of ruthenium red (RR). This component has now been isolated and a derivative, (mu-O) [(HCO2)(NH3)4Ru]2Cl3, structurally characterized. The active species in solution appears to be the symmetrical oxo-bridged ion, [X(NH3)4Ru-O-Ru(NH3)4X]3+, where X = Cl- or OH-. Its absorption spectrum shows a maximum at 360 nm. The dinuclear ruthenium ammine complex inhibits Ca(2+)-stimulated respiration of rat liver mitochondria with an I50 of 3.5 pmol/mg of protein compared to the value of 60 pmol of RR/mg of protein. The inhibition by the dinuclear compound is noncompetitive with Ca2+. Respiration-linked swelling of mitochondria induced by Cd2+ also responds similarly to both the dinuclear complex and RR. A close correlation was observed between binding to mitochondria as monitored with 103Ru-labeled dinuclear complex and inhibition of Ca2+ transport. A Scatchard plot yielded estimates of maximum specific binding and dissociation constant of 7.5 pmol/mg of protein and 1.3 nM, respectively. The inhibitor has the characteristics of a satisfactory affinity ligand for purification of the uniporter.

Electrochemistry and stability studies of oxo-bridged dinuclear ruthenium(III) complexes for water oxidation

Electrochemical and water oxidation studies have been carried out for the bridged complexes (1) and (2). [graphic omitted] Three consecutive reversible two-electron processes were shown to occur. Repeated continuous cyclic scans of the redox processes, however, led to the decomposition of the dimers to the monomeric complex. Visible spectra showed that the decomposition leads to the formation of cis-[Ru(bpy)–2(H2O)2]2+. The dimer complexes are stable at a Nifion-coated graphite electrode in their adsorbed state even on repeated cyclic scans of the redox processes. It was shown by gas chromatography as well as by mass spectroscopy that oxygen was evolved by water oxidation on adding CeIV ion to an aqueous solution of the dinuclear complex. The turnover number showed that the complexes worked as catalysts for water oxidation, although they suffer partial decomposition during the catalysis. The nitrite complex was more stable than the water complex against decomposition.