Oxidation State Of Ruthenium Research Articles

Enhanced Electrocatalytic Activity for Nitrate Reduction to Ammonia by Tuning a Ruthenium Oxidation State of Ruthenium-Based Nanotubes

Enhanced Electrocatalytic Activity for Nitrate Reduction to Ammonia by Tuning a Ruthenium Oxidation State of Ruthenium-Based Nanotubes

Ruthenium supported on silicate and aluminosilicate mesoporous materials applied to selective sugar hydrogenation: Xylose to xylitol

A series of ruthenium-based catalysts supported on a set of silicate and aluminosilicate mesoporous molecular sieves was synthesized and tested in xylose hydrogenation. The materials were characterized in terms of morphology, textural properties, acidity, as well as ruthenium loading, dispersion, and oxidation state. In general, the aluminosilicates-based catalysts displayed a higher activity compared to their respective silicate supports, which can be ascribed to a higher Ru content and dispersion, enhanced by a higher acidity. The most active synthesized catalyst (Ru/Al-MCM-4) displayed an improved performance compared to a commercial Ru/C catalyst due to a better xylitol selectivity. Two modelling approaches were implemented to describe the kinetic rate. The first model was based on the hypothesis that xylose molecules and hydrogen are adsorbed in different active sites on the catalyst surface, while the second model supposes the formation of an intermediate on the catalyst surface that reacts to form xylitol. Both models gave a very good description of the experimental data.

Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions.

Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. The aim of this study is to evaluate the control that such a photoassisted method can exert on the properties of ruthenium nanoparticles supported on TiO2 by means of the variation of the incident irradiance and hence of the photodeposition rate. For that purpose, different Ru/TiO2 systems with the same metal load have been prepared under varying irradiance and characterized by means of elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the so-obtained materials has been evaluated by using the degradation of formic acid in water under UV-A light. Particles with size around or below one nanometer were obtained, depending on the irradiance employed in the synthesis, with narrow size distribution and homogeneous dispersion over the titania support. The relation between neutral and positive oxidation states of ruthenium could also be controlled by the variation of the irradiance. The obtained photocatalytic activities for formic acid oxidation were in all cases higher than that of undecorated titania, with the sample obtained with the lowest irradiation giving rise to the highest oxidation rate. According to the catalysts characterization, photocatalytic activity is influenced by both Ru size and Ru0/Ruδ+ ratio.

Two Simple and Highly Efficient Variants of the Griffith‐Ley Oxidation of Alcohols

AbstractThe Griffith‐Ley oxidation of alcohols to aldehydes and ketones is performed with either RuCl3 ⋅ (H2O)x or a highly stable, well‐defined ruthenium catalyst and with cheap trimethylamine N‐oxide (TMAO) as the oxygen source. The use of n‐heptane as the solvent, which forms a second phase with TMAO and a part of the alcohol, allows the reactions to be performed with a minimum amount of catalyst. This results in high local concentrations and thus to very rapid conversions. Detailed quantum chemical calculations suggest, that the Griffith‐Ley oxidation not necessarily requires high oxidation states of ruthenium but can also proceed with RuII/RuIV species.

Structural, spectroscopic and electronic properties of a family of face-shared bi-octahedral Ru25+/6+ complexes with a bridging 2,5-di(2-pyridyl)pyrrolide ligand.

A family of Ru2 dimers, [Ru2(μ-κ2N,N':κ2N',N''-dpp)2(μ-X)(X)2]q+ (X = Cl, Br, q = 0 and X = I, q = 1) is synthesized from a [Ru2(OAc)4Cl] paddlewheel starting material. The neutral products are mixed-valence Ru25+ dimers with a Ru-Ru bond order of 0.5, while the cationic iodide is a Ru26+ dimer with formal bond order of 1.0. The Ru-Ru distance is strikingly independent of the identity of the halide and the oxidation state of ruthenium, most likely a consequence of the small bridging nitrogen which constrains the geometry. The spectroscopic properties (EPR, UV/Vis) of the Br complex are consistent with a large σ-σ* splitting in [Ru2(μ-κ2N,N':κ2N',N''-dpp)2(μ-Br)(Br)2].

Ruthenium Oxide Nanosheets for Enhanced Oxygen Evolution Catalysis in Acidic Medium

AbstractThe fabrication of highly active and robust hexagonal ruthenium oxide nanosheets for the electrocatalytic oxygen evolution reaction (OER) in an acidic environment is reported. The ruthenate nanosheets exhibit the best OER activity of all solution‐processed acid medium electrocatalysts reported to date, reaching 10 mA cm−2 at an overpotential of only ≈255 mV. The nanosheets also demonstrate robustness under harsh oxidizing conditions. Theoretical calculations give insights into the OER mechanism and reveal that the edges are the origin of the high OER activity of the nanosheets. Moreover, the post OER analyses indicate, apart from coarsening, no observable change in the morphology of the nanosheets or oxidation states of ruthenium during the electrocatalytic process. Therefore, the present investigation suggests that ruthenate nanosheets are a promising acid medium OER catalyst with application potential in proton exchange membrane electrolyzers and beyond.

Proton-Rocking-Chair-Type Redox Capacitors Based on Indium Tin Oxide Electrodes with Multilayer Films Containing Ru Complexes.

A rechargeable proton-rocking-chair-type redox capacitor was fabricated using scalable layer-by-layer-(LbL)-assembled films composed of two dinuclear Ru complexes that exhibit proton-coupled electron-transfer (PCET) reactions with different Ru(II/III) redox potentials (RuNH-OH and RuCH-OH). RuNH-OH and RuCH-OH contain different coordination environments that involve two phosphonate linker ligands at both ends and bridging 2,6,2',6'-tetrakis(benzimidazol-2-yl)-4,4'-bipyridine or 1,3,1',3'-tetrakis(benzimidazol-2-yl)-5,5'-biphenyl ligands, respectively. The molecular units were assembled onto indium tin oxide (ITO) electrodes by complexation between the phosphonate groups and zirconium(IV) ions. The LbL growing process of these multilayer films was monitored by electrochemical or UV-vis spectroscopic measurements. The thus obtained LbL films on the ITO electrodes showed PCET reactions at different potentials, depending on the bridging ligands. The introduction of cyclometalated Ru-C bonds in the bridging ligand of RuCH-OH led to the stabilization of the ruthenium(III) oxidation state, and therefore, RuCH-OH exhibited lower p Ka values for the imino N-H protons in the bridging benzimidazole groups compared to those of the corresponding RuNH-OH complex. The proton movements that accompany the redox reaction in the Ru multilayer films on the ITO electrode were confirmed using a pH indicator probe. For the performance test of a proton-rocking-chair-type redox capacitor, a two-electrode system composed of RuNH-OH and RuCH-OH multilayer films on ITO electrodes was examined in an aqueous solution of NaClO4. Under galvanostatic conditions, stable, reversible, and repeatable charging/discharging processes occurred. The capacitance increased with an increasing number of LbL layers. For comparison, a similar redox capacitor composed of two RuNMe-OH and RuCMe-OH analogues, in which all four imino N-H protons on the benzimidazole moieties are protected by N-Me groups, was constructed and examined. In these complexes, the capacitance decreased by 77% compared to the PCET-type capacitor composed of a cell containing RuNH-OH and RuCH-OH; this result strongly suggests that the proton movement plays a more important role for the charge storage than the anion movement. In such LbL films composed of Ru complexes that exhibit PCET-type redox reactions, the capacitance is drastically improved with an increasing number of layers and using protons as charge carriers.

Synthesis and Biological Evaluations of Organoruthenium Scaffolds: A Comprehensive Update

Background: Currently ruthenium complexes are immerging as effective anticancer agents due to their less toxicity, better antiproliferative and antimetastatic activity, better stability in cellular environment and most importantly variable oxidation and co-ordination states of ruthenium allows binding this molecule with a variety of ligands. So in past few years researchers have shifted their interest towards organoruthenium complexes having good fluorescent profile that may be applicable for cancer theranostics. Nowadays, photodynamic therapy has become more acceptable because of its easy and effective approach towards killing cancer cells. Objective: Objective of this review article is to shed light on synthesis, characterization, stability and fluorescence studies of various ruthenium [Ru(II) and Ru(III)] complexes and different bioactivity studies conducted with the synthesized compounds to test their candidacy as potent chemotherapeutic agents. Methods: Various heterocyclic ligands containing N,O and S as heteroatom mainly were prepared and subjected to complexation with ruthenium-p-cymene moiety. In most cases [Ru(η6-p-cymene)(µ-Cl)Cl]2 was used as ruthenium precursor and the reactions were conducted in various alcohol medium such as methanol, ethanol or propanol. The synthesized complexes were characterized by 1H NMR and 13C NMR spectroscopy, GC-MS, ESI-MS, elemental analysis and single crystal X-ray crystallography methods. Fluorescence study and stability study were conducted accordingly using water, PBS buffer or DMSO. Stable compounds were considered for cell viability studies. To study the efficacy of the compounds in ROS generation as photosensitizers, in few cases, singlet oxygen quantum yields in presence of light were calculated. Suitable compounds were selected for in vitro & in vivo antiproliferative, anti-invasive activity studies. Result: Many newly synthesized compounds were found to have less IC50 compared to a standard drug cysplatin. Those compounds were also stable preferably in physiological conditions. Good fluorescence profile and ROS generation ability were observed for few compounds. Conclusion: Numerous ruthenium complexes were developed which can be used as cancer theranostic agents. Few molecules were synthesized as photosensitizers which were supposed to generate reactive singlet oxygen species in targeted cellular environment in presence of a particular type of light and thereby ceasing cancer cell growth.

Systematic Study of Pt-Ru/C Catalysts Prepared by Chemical Deposition for Direct Methanol Fuel Cells

In this research, the activity and stability for methanol electro-oxidation on Pt-Ru/C catalysts was increased by optimising the catalyst preparation method. The Pt-Ru/C catalysts were synthesised using Pt(acac)2 and Ru(acac)3 precursors for chemical deposition of the metals. Performance of the catalyst was examined by cyclic voltammetry and chronoamperometry in a methanol-containing electrolyte. TEM, EDS, X-ray photoelectron spectroscopy and XRD were used to physically characterise the catalysts. The parameters investigated were precursor decomposition phase, synthesis temperature and Pt/Ru ratio. Precursor deposition from the liquid phase was more active for methanol electro-oxidation, predominantly due to particle size and degree of alloying achieved during this precursor decomposition phase. Synthesis temperature affected the particle size, active surface area, ruthenium oxidation state and degree of alloying which in turn affected catalyst stability and activity for methanol electro-oxidation. The Pt/Ru ratio greatly affects the performance of the catalyst. The catalyst with the highest activity for methanol electro-oxidation was the catalyst synthesised at 350 °C with a Pt/Ru ratio of 50:50.Graphical

Correlation Between Calcination Temperature and Bifunctional Catalytic Activity for Oxygen Electrode Reaction of Pyrochlore Type Metal Oxide Containing Bi and Ru

Several types of rechargeable air battery with higher energy density have been intensively investigated and we focus on metal hydride/air (MH/air) battery. There are several issues to realize this type of battery and especially, we investigate to develop an active air electrode to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an alkaline solution. To the best of our knowledge, some perovskite and pyrochlore type metal oxides are promised as bifunctional catalyst corresponding to the purpose. In particular, catalytic activity of pyrochlore type metal oxides such as Pb2Ru2O7 and Bi2Ir2O7 have been reported. On the other hand, we focus on Bi2Ru2O7, pyrochlore type metal oxide, owing to its higher OER activity. Then, we prepared Bi2Ru2O7 by so-called precipitation method and investigated correlation between the calcination temperature and the bifunctional catalytic activity. Bi(NO3)3 and RuCl3 aqueous solutions were separately prepared and well mixed at 1:1 in molar ratio. The mixture solution was heated up to 75oC with stirring and subsequently NaOH aqueous solution was added. Then, oxygen was flowed into the solution for 72 h. The precipitate was obtained by evaporation of the solvent and finally, it was heated under atmospheric air at 500, 600 and 700oC for 3 h to obtain final products. X-ray diffraction (XRD) and X-ray absorption near edge structure spectroscopy (XANES) were used to characterize the product. In particular, electric state of ruthenium was investigated by the latter. Oxygen contents of the products were estimated by temperature-programmed reduction technique (TPR). ORR and OER activity were evaluated in 0.1 mol dm-3 KOH solution by a rotating ring disk electrode (RRDE). The disk and ring electrodes were made by glassy carbon (GC) and Pt, respectively. The product was dispersed on GC and fixed with a thin film of anion-exchange-membrane (corresponding ionomer solution: AS-4, TOKUYAMA K.K.). A three-electrode cell, Hg|HgO reference electrode and a Ni mesh counter electrode were used. Figure 1 shows XRD patterns of the products. The diffraction peaks assigned to Bi2Ru2O7 were observed for the products obtained at 500 and 600oC; on the other hand, several peaks assigned to the impurity phase were recognized in the case of 700oC. The lattice constant calculated for the products obtained at 500 oC was very close to the theoretical value of Bi2Ru2O7. XANES spectra suggest that the oxidation state of ruthenium in the product depends on the calcination temperature. This tendency is similar to the TPR results in which oxygen contents were decreased with increasing the calcination temperature from 500oC to 600oC. The onset potentials estimated for ORR and OER were roughly 0.9 V and 1.39 V and it is irrespective to the calcination temperature; on the other hand, Tafel slope strongly depended on the calcination temperature. Typically, the slope for both ORR and OER dramatically decrease when the calcination temperature was increased from 500oC to 600oC. Therefore, we assumed that oxygen vacancy as well as electric state of ruthenium, which could be controlled by the calcination temperature, strongly influences on the bifunctional catalytic behavior and the rate determining steps for ORR and OER. This work was supported by “Advanced Low Carbon Technology Research and Development Program (ALCA)” of Japan Science and Technology Agency (JST). The authors express gratitude to Tokuyama Corporation for supplying AS-4. Figure 1

Kinetics of ruthenium(III) catalyzed and uncatalyzed oxidation of monoethanolamine by N-bromosuccinimide

Kinetics of uncatalyzed and ruthenium(III) catalyzed oxidation of monoethanolamine by N-bromosuccinimide (NBS) has been studied in an aqueous acetic acid medium in the presence of sodium acetate and perchloric acid, respectively. In the uncatalyzed oxidation the kinetic orders are: the first order in NBS, a fractional order in the substrate. The rate of the reaction increased with an increase in the sodium acetate concentration and decreased with an increase in the perchloric acid concentration. This indicates that free amine molecules are the reactive species. Addition of halide ions results in a decrease in the kinetic rate, which is noteworthy. Both in absence and presence of a catalyst, a decrease in the dielectric constant of the medium decreases the kinetic rate pointing out that these are dipole—dipole reactions. A relatively higher oxidation state of ruthenium i.e., Ru(V) was found to be the active species in Ru(III) catalyzed reactions. A suitable mechanism consistent with the observations has been proposed and a rate law has been derived to explain the kinetic orders.

Supercritical water reforming of glycerol: Performance of Ru and Ni catalysts on Al2O3 support

Supercritical water reforming of glycerol was studied in a tubular fixed-bed reactor using a Ru/Al2O3 catalyst, and was compared with our previous study using a Ni-based catalyst, with the aim of enhancing the performance of a global process designed under energy self-sufficient conditions. Relatively high glycerol concentrations of up to 25 wt.% and temperatures from 500 to 800 °C were tested. Glycerol conversion was very high (>99%) at temperatures of 600 °C and above, but low at 500 and 550 °C (<50%) using the Ru/Al2O3 catalyst. The gas product (dry basis) was mainly CH4 and CO2, while H2 production was quite low, against expectations. Under the same operating conditions, the behavior of the catalysts is quite different as the Ni catalyst promotes H2 production much more than the Ru catalyst. A detailed discussion is provided on our results and those of previous studies using the Ru/Al2O3 catalyst, thus acquiring more insight into the catalyst behavior. The Ru catalyst showed a large increase in its crystalline phase after testing, although the oxidation state of ruthenium did not change.

Diminished photoisomerization of active ruthenium water oxidation catalyst by anchoring to metal oxide electrodes

Surface-binding of molecular water oxidation catalysts through phosphonated ligands offers a promising strategy for attaching homogeneous catalysts onto conductive or semiconductive oxide surfaces for heterogeneous catalysis. In this work, the highly active [Ru(tpy)(pynap)OH2]2+ (tpy=2,2′:6′,2″-terpyridine; pynap=2-(pyrid-2′-yl)-1,8-naphthyridine) water oxidation catalyst is attached onto metal oxide electrodes through a phosphate group. Electrochemical and photoelectrochemical results confirm that ruthenium oxidation chemistries and water oxidation proficiency remain largely unaffected by phosphonation. Surface-binding reveals minimal photoisomerization of the active d-form and allows us to evaluate photoelectrochemical and mechanistic properties of the catalyst. Spectroelectrochemical experiments support the evolution of multiple ruthenium oxidation states in agreement with Pourbaix diagrams. Although photoisomerization of d-[Ru(H2PO3-tpy)(pynap)OH2]2+ is considerably hindered when the catalyst is attached onto a rigid oxide electrode, surface desorption remains a major challenge.

New rock salt-related oxides Li3M2RuO6 (M=Co, Ni): Synthesis, structure, magnetism and electrochemistry

We describe the synthesis, crystal structure, magnetic and electrochemical characterization of new rock salt-related oxides of formula, Li 3 M 2 RuO 6 ( M =Co, Ni). The M =Co oxide adopts the LiCoO 2 ( R- 3 m ) structure, where sheets of LiO 6 and (Co 2 /Ru)O 6 octahedra are alternately stacked along the c -direction. The M =Ni oxide also adopts a similar layered structure related to Li 2 TiO 3 , where partial mixing of Li and Ni/Ru atoms lowers the symmetry to monoclinic ( C 2 /c ). Magnetic susceptibility measurements reveal that in Li 3 Co 2 RuO 6 , the oxidation states of transition metal ions are Co 3+ (S=0), Co 2+ (S=1/2) and Ru 4+ (S=1), all of them in low-spin configuration and at 10 K, the material orders antiferromagnetically. Analogous Li 3 Ni 2 RuO 6 presents a ferrimagnetic behavior with a Curie temperature of 100 K. The differences in the magnetic behavior have been explained in terms of differences in the crystal structure. Electrochemical studies correlate well with both magnetic properties and crystal structure. Li-transition metal intermixing may be at the origin of the more impeded oxidation of Li 3 Ni 2 RuO 6 when compared to Li 3 Co 2 RuO 6 . Interestingly high first charge capacities (between ca. 160 and 180 mAh g −1 ) corresponding to ca. 2/3 of theoretical capacity are reached albeit, in both cases, capacity retention and cyclability are not satisfactory enough to consider these materials as alternatives to LiCoO 2 . Two new rock salt related oxides of formula, Li 3 M 2 RuO 6 , ( M =Co, Ni) have been prepared. The M =Co oxide adopts the LiCoO 2 ( R- 3 m ) structure and the M =Ni oxide adopts a similar layered structure related to Li 2 TiO 3, monoclinic ( C 2 /c ), with partial mixing of Li and Ni/Ru atoms. For Li 3 Co 2 RuO 6 , oxidation state for Ru is 4+ and antiferromagnetic (AFM) order is found below 10 K while for the analogous Li 3 Ni 2 RuO 6 , Ru oxidation state is 5+ and a ferrimagnetic (FM) behavior with a Curie temperature of 100 K is found. Electrochemical studies correlate well with both magnetic properties and crystal structure. • New Ruthenium rock salt-related oxides of formula, Li 3 M 2 RuO 6 ( M =Co, Ni) were studied. • Structurally different: rhombohedral α-NaFeO 2 -type (Co) and monoclinic Li 2 TiO 3 -type (Ni) • Magnetic behavior is different: the Co sample is AFM while the Ni one is ferrimagnetic. • Ruthenium oxidation states are different: 4+ in the Co sample and 5+ in the Ni one. • Electrochemical studies correlate well with magnetic properties and crystal structures.

Problems with the thermogravimetric determination of oxygen stoichiometries in pure and rare-earth substituted La2RuO5

The oxygen stoichiometries of pure and rare-earth substituted La2RuO5 have been investigated by thermogravimetry (TG) in reducing atmosphere. Assuming that the observed total weight loss is caused by the reduction of Ru4+ to Ru-metal, remarkable oxygen deficiencies were calculated. These would correspond to ruthenium oxidation states significantly lower than the ones experimentally observed by XANES. To explain this discrepancy we investigated the reduction products by X-ray absorption spectroscopy (XAS). EXAFS measurements at the Ru–K edge revealed the presence of an X-ray amorphous ruthenium oxide, indicating an incomplete reduction. The apparent oxygen deficiencies obtained for pure and rare-earth substituted samples correlate with the amount of remaining ruthenium oxide. The presence of a ruthenium oxide species was furthermore verified by Ru–LIII XANES investigations. Our results show that the determination of oxygen contents by thermogravimetry might fail even for the easily reducable nobel metal oxides and therefore has to be applied with caution if the reaction products cannot be identified unambiguously.

Topochemical Fluorination of Sr3(M0.5Ru0.5)2O7 (M = Ti, Mn, Fe), n = 2, Ruddlesden–Popper Phases

Reaction of the appropriate Sr3(M(0.5)Ru(0.5))2O7 (M = Ti, Mn, Fe), n = 2, Ruddlesden-Popper oxide with CuF2 under flowing oxygen results in formation of the oxide-fluoride phases Sr3(Ti(0.5)Ru(0.5))2O7F2, Sr3(Mn(0.5)Ru(0.5))2O7F2, and Sr3(Fe(0.5)Ru(0.5))2O(5.5)F(3.5) via a topochemical anion insertion/substitution process. Analysis indicates the titanium and manganese phases have Ti(4+), Ru(6+) and Mn(4+), Ru(6+) oxidation state combinations, respectively, while Mössbauer spectra indicate an Fe(3+), Ru(5.5+) combination for the iron phase. Thus, it can be seen that the soft fluorination conditions employed lead to formation of highly oxidized Ru(6+) centers in all three oxide-fluoride phases, while oxidation states of the other transition metal M cations remain unchanged. Fluorination of Sr3(Ti(0.5)Ru(0.5))2O7 to Sr3(Ti(0.5)Ru(0.5))2O7F2 leads to suppression of magnetic order as the fluorinated material approaches metallic behavior. In contrast, fluorination of Sr3(Mn(0.5)Ru(0.5))2O7 and Sr3(Fe(0.5)Ru(0.5))2O7 lifts the magnetic frustration present in the oxide phases, resulting in observation of long-range antiferromagnetic order at low temperature in Sr3(Mn(0.5)Ru(0.5))2O7F2 and Sr3(Fe(0.5)Ru(0.5))2O(5.5)F(3.5). The influence of the topochemical fluorination on the magnetic behavior of the Sr3(M(0.5)Ru(0.5))2O(x)F(y) phases is discussed on the basis of changes to the ruthenium oxidation state and structural distortions.

Oxidation states and redox behavior of ruthenium ammine complexes with redox-active dioxolene ligands

Synthesis of ruthenium-dioxolene complexes with ammines [Ru(NH3)4(diox-R)]n+, where diox-R is a dioxolene with substituent R=3,5-di-tert-butyl, H, tetrachloro, and 4-nitro, was carried out. These complexes were characterized by spectroscopy, magnetic susceptibility measurements, and cyclic voltammetry. The oxidation states of ruthenium and the redox-active dioxolene ligand in the complexes varied depending on the nature of the dioxolene substituents. [Ru(NH3)4(diox-R)]n+ (R=3,5-di-tert-butyl and H) has a divalent ruthenium and dioxolene in the quinone oxidation state with a minor amount of the complex in Ru(III)-semiquinonato oxidation state. The complexes exhibited valence tautomerism depending on the donor number of solvents. However, [Ru(NH3)4(diox-R)]n+ (R=tetrachloro and 4-nitro) has a trivalent ruthenium and dioxolene in the catecholate oxidation state. Electrochemical and spectroelectrochemical investigation of these complexes revealed that their electrochemical behavior depended on not only the oxidation state of the prepared complex but also the nature of the dioxolene substituent in the complex. Their redox reaction was found to proceed by the EC mechanism involving valence tautomerism.

Role of Ruthenium Oxidation States in Ligand-to-Ligand Charge Transfer Processes

We describe in this paper the properties of [Ru(II/III)(bpy)(2)ClL](+1/+2) and [Ru(II/III)(bpy)(2)L(2)](+2/+3). L = ditolyl-3-pyridylamine (dt3pya) is a redox active ligand related to triarylamines, which is very similar to 3-aminopyridine except for the reversible redox behavior. The monosubstituted complex shows a metal-to-ligand charge-transfer (MLCT) at 502 nm, and reversible waves in acetonitrile at E(0)(Ru(III/II)) = 1.07 V, E(0)(L(+/0)) = 1.46 V (NHE). The disubstituted complex shows an MLCT at 461 nm, a photorelease of dt3pya with quantum yield of 0.11 at 473 nm, and two reversible one-electron overlapped waves at 1.39 V associated with one of the ligands (1.37 V) and Ru(III/II) (1.41 V). Further oxidation of the second ligand at 1.80 V forms a 2,2'-bipiridine derivative, in an irreversible reaction similar to dimerization of triphenylamine to yield tetraphenylbenzidine. In the dioxidized state, the spectroelectrochemistry of the disubstituted complex shows a ligand-to-ligand charge transfer at 1425 nm, with a transition moment of 1.25 Å and an effective two-state coupling of 1200 cm(-1). No charge transfer between ligands was observed when Ru was in a 2+ oxidation state. We propose that a superexchange process would be involved in ligand-metal-ligand charge transfer, when ligands and metals are engaged in complementary π interactions, as in metal-ligand-metal complexes. Best orbital matching occurs when metallic donor fragments are combined with acceptor ligands and vice versa. In our case, Ru(III) bridge (an acceptor) and two dt3pya (donors, one of them being oxidized) made the complex a Robin-Day Class II system, while the Ru(II) bridge (a donor, reduced) was not able to couple two dt3pya (also donors, one oxidized).

Characterization and dissolution properties of ruthenium oxides

Ruthenium oxides (RuO2·1·10H2O and RuO2) have been synthesized by forced hydrolysis and oxidation of ruthenium chloride. The resulting materials were extensively characterized to determine the crystallinity, surface area, and ruthenium oxidation state. Surface charging experiments indicate a large quantity of reactive functional groups for both materials and a decrease in the acidity of the surface functional groups with crystallization of the hydrous oxide. Dissolution studies conducted in acidic and basic pH environments indicate Ru-oxides are insoluble in 0.1M HCl and slightly soluble in 0.1M NaOH. Oxalate and ascorbate (5mM) promoted dissolution of RuO2·1·10H2O demonstrated an increase in dissolution rates with decreasing pH and increasing ligand surface coverage. XPS analysis of the RuO2·1·10H2O surface after ligand promoted dissolution revealed the reduction of Ru(IV) to Ru(III) indicating that both ascorbate and oxalate reductively dissolve RuO2·1·10H2O. Dissolution experiments with RuO2 resulted in dissolution only for 5mM oxalate at pH 3. Dissolution rates calculated for RuO2·1·10H2O and RuO2 are compared with previously published dissolution rates for iron oxides, demonstrating an order of magnitude decrease in the oxalate and ascorbate promoted dissolution.

Investigation of electrochemical properties of RuO 2 thin films modified by e-beam irradiation

The influence of electron beam irradiation on the electrochemical properties of electrodeposited RuO 2 thin films was investigated using a 1 MeV electron beam. Crystallinity change before and after electron beam irradiation was investigated by X-ray diffraction, and the oxidation state of ruthenium was determined by X-ray photoelectron spectroscopy. Scanning electron microscopy was utilized to examine the morphology of the films. The results show that electron beam irradiation altered the oxidation state of ruthenium and increased crystallinity. Cyclic voltammetry was employed to evaluate the electrochemical properties of the synthesized RuO 2 films in terms of their application as electrodes of electrochemical capacitors. RuO 2 irradiated with 40 kGy showed 2.7 times higher capacitance (520 Fg −1) than the as-electrodeposited sample (190 Fg −1).