Ru L2 Research Articles

Atomic distribution and structural evolution of mesostructured PtRu nanoparticles electrodeposited on a microemulsion lyotropic liquid-crystalline template probed using EXAFS and XANES

Mesostructured PtRu nanoparticles were electrochemically reduced from their metallic salts directed by a hexagonally packed microemulsion lyotropic liquid-crystalline (MLLC) template. We investigated the structural evolution and atomic distribution of the MLLC-templated mesoporous PtRu nanoparticles (NPs) after electroreduction for varied duration using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, complemented by energy-dispersive X-ray spectroscopy (EDS) and field-emission transmission electron microscopy (FE-TEM). The XANES data at the Ru L2,3 and Pt L3 edges show predominantly metallic states of Ru and Pt in the PtRu NPs upon electroreduction. The reduction of Ru(3+) ions in RuCl3 into Ru atoms involves intermediate RuCl-containing complexes. A more rapid reduction of Pt precursors and a release of Ru atoms from Ru precursors in two steps upon electroreduction resulted in aggregation into PtRu nanoparticles, featuring a Pt-rich core, a Ru-rich shell and a varied alloy extent of Ru, deduced from EXAFS data. The complementary results provide insight into the mechanism of growth and atomic distribution of mesostructured PtRu bimetallic nanoparticles from the use of the MLLC-type templates.

Synthesis and properties of novel crown ether-annelated 4′,5′-diaza-9′-(1,3-dithiole-2-ylidene)-fluorenes and their ruthenium(II) complexes

Two novel redox-active 1,3-dithiole (DT) ring-fused 4,5-diazafluorene ligands with crown ether moieties (L1 and L2) were synthesized and characterized. The crystal structure of L1 was studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding bis(bipyridine)ruthenium(II) complexes [4: Ru L1(bpy)2 and 5: Ru L2(bpy)2], were also been investigated.

L2,3-edge x-ray absorption near-edge spectroscopy analysis of photoisomerism in solid ruthenium–sulfur dioxide complexes

Ru L2,3 edge x-ray absorption near-edge spectroscopy spectra of four compounds [Ru(SO2)(NH3)4X]Y (X = water, Y = (±)-camphorsulfonate2; X =water, Y = tosylate2; X =isonicotinamide, Y = tosylate2; X =pyridine, Y = triflate2) are reported before and after optical excitation, which causes photoinduced linkage isomerism of the SO2 ligand. Principal component analysis reveals consistent changes in the spectra upon photoisomerization, suggesting a partial oxidation of the Ru ion. These results demonstrate that x-ray absorption near-edge spectroscopy is an effective means of probing photoinduced linkage isomerism.

Ru L2,3 XANES theoretical simulation with DFT: A test of the core-hole treatment

Density functional theory (DFT)-based relativistic calculations were performed to model the Ru L-edge X-ray absorption near edge structure (XANES) spectra of the hexaammineruthenium complex [Ru(NH3)6]3+ and “blue dimer” water oxidation catalyst, cis,cis- [(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ (bpy is 2,2-bipyridine). Two computational approaches were compared: simulations without the core-hole and by modeling of the core-hole within the Z+1 approximation. Good agreement between calculated and experimental XANES spectra is achieved without including the core-hole. Simulations with algorithms beyond the Z+1 approximation were only possible in a framework of the scalar relativistic treatment. Time-dependent DFT (TD-DFT) was used to compute the Ru L-edge spectrum for [Ru(NH3)6]3+ model compound. Three different core-hole treatments were compared in a real-space full multiple scattering XANES modeling within the Green function formalism (implemented in the FEFF9.5 package) for the [Ru(Mebimpy)(bpm)(H2O)]2+ complex. The latter approaches worked well in cases where spin–orbit treatment of relativistic effects is not required.

Density functional theory simulation of the L2,3 XANES spectra

A method for the theoretical simulation of X-ray absorption near edge structure (XANES) spectra at the Ru L2,3 edges has been developed using relativistic density functional theory (DFT) calculations. The effect of the parameters of DFT calculations on the shape of theoretical curves has been comparatively analyzed for XANES spectra of a water oxidation catalyst and hexaammineruthenium complexes. Recommendations for the choice of the best parameters ensuring good agreement with the experimental data, including the most correct exchange-correlation potential, have been made.

Double-exchange enhanced magnetoresistance in SrRu0.5Mn0.5O3

Magnetoresistance ratio (MR), Δρ/ρ0, in SrRu0.5Mn0.5O3 is enhanced by 20% near the Curie temperature (Tc=125 K) compared to the parent compound SrRuO3 (Tc=165 K) which is a super exchange mediated ferromagnetic metal. The enhancement in MR ratio in the equiatomic B site composition is due to the onset of double-exchange mediated ferromagnetic interaction. The Mn, Ru L2,3 edge of the x-ray absorption spectra of the SrRu0.5Mn0.5O3 phase shows the coexistence of ionic pairs involving Mn+3/Ru+5↔Mn+4/Ru+4. Mn+3 (t2g3eg1) recognizes both Mn+4/Ru+5 (t2g3eg0) as magnetically equivalent sites for eg electron hopping and for maintaining the eg hole carrier concentration.

X-ray Absorption Studies of Ruthenium Silicide

We have investigated the X-ray absorption fine structures (XAFS) of several ruthenium-silicon intermetallic compounds at the Ru L2,3, Ru K and Si K-edges. From the analysis of the Ru and Si K-edge XANES (X-Ray Absorption Near Edge Structures), particularly the relative intensity of the absorption feature just above the threshold, we found that ruthenium gains p-like electrons upon dilution in silicon. Likewise, compound formation of silicon with ruthenium results in the increase of p-like electrons at the silicon site. The Ru L2,3-edge also exhibits variation in the whiteline intensity for ruthenium silicide of different composition. This is used to infer d charge redistribution at the Ru site upon the formation of Ru-Si intermetallic compounds. The implications of the results are discussed.

Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO2 Films

AbstractA series of CN‐bridged trinuclear Ru complexes of the general structure [RuL2(μ‐(CN)Ru(CN)L2′)2] where L is 2,2′‐bipyridine‐4,4′‐dicarboxylic acid and L′ is 2,2′‐bipyridine (1)2,2′‐bipyridine‐4,4′‐dicarboxylic acid (2), 4,4′‐dimethyl‐2,2′‐bipyridine (3), 4,4′‐diphenyl‐2,2′‐bipyridine (4), 1,10‐phenanthroline (5), and bathophenanthrolinedisulfonic acid (6) have been synthesized, and their spectral and electrochemical properties investigated. The two carboxylic functions on the 2,2′‐bipyridine ligand L serve as interlocking groups through which the dye is attached at the surface of TiO2 films having a specific surface texture. The role of these interlocking groups is to provide strong electronic coupling between the π* orbital of the 2,2′‐bipyridine and the 3d‐wave‐function manifold of the conduction band of the TiO2, allowing the charge injection to proceed at quantum yields close to 100 %. The charge injection and recombination dynamics have been studied with colloidal TiO2, using laser photolysis technique in conjunction with time‐resolved optical spectroscopy. Photocurrent action spectra obtained from photo‐electrochemical experiments with these trinuclear complexes cover a very broad range in the visible, making them attractive candidates for solar light harvesting. Monochromatic incident photon‐to‐current conversion efficiencies are strikingly high exceeding 80% in some cases. Performance characteristics of regenerative cells operating with these trinuclear complexes and ethanolic triiodide/iodide redox electrolyte have been investigated. Optimal results were obtained with complex 1 which gave a fill factor of 75 % and a power conversion efficiency of 11.3% at 520 nm.

Ru L edge x-ray absorption studies of the electronic structure of Ru3(CO)12 adsorption and the formation of Ru–Cu bimetallics on Cu(111)

Ru L2,3 edge XANES (x-ray absorption near edge structure) together with AES (Auger electron spectroscopy) and LEED (low energy electron diffraction) studies of Ru3(CO)12 adsorbed on Cu(111) reveal the following: (a) Ru3(CO)12 adsorbs molecularly on Cu(111) at low temperature (≲−50°). (b) Upon electron bombardment, Ru3(CO)12 dissociates to form bare Ru aggregates which exhibit very broad Ru L2,3 white lines and featureless absorption in the XANES spectrum indicating that the Ru atoms are not well ordered on the Cu(111) surface. (c) Annealing of the bare Ru aggregates on Cu(111) at 450 °C results in the formation of Cu/Ru bimetallic clusters in which the Ru atoms are in the core and exhibit bulk-like Ru L2,3 XANES while the surface is covered with Cu atoms. Analysis of the Ru L3 white line intensity indicates that charge redistribution in the Ru d band occurs upon the transformation from the bare Ru aggregates to the bimetallic Cu/Ru clusters on Cu(111).

Synthesis of Bimetallic Cyano-Bridged Cations Containing Cyclopentadienyl Ruthenium(II)

Abstract The cyano complexes [Ru(Cp) L2 (CN)] (L=PPh3, AsPh3 or SbPh3; Cp=η5-C5H5) react with the corresponding chloro complexes [Ru(Cp)L2Cl] to give the diruthenium cyano-bridged cations [(Cp)L2Ru(μ-CN) RuL2(Cp)]+.