Rhodium Ions Research Articles

Microstructural and oxygen-handling characteristics of CeO2with M3+promoters. Part 1.—Characterization of calcined powders by XRD and oxygen-isotope exchange

Comparisons of the oxygen-handling properties of calcined CeO2, CeO2–Al2O3, RhOx–CeO2, RhOx–CeO2/Al2O3 and La2O3–CeO2 materials are made on the basis of their experimentally observed abilities to bring about R0-type homophase oxygen isotope equilibration of an equimolar (16O2+18O2) mixture at room temperature, and/or to induce low onsettemperatures (ca. 550 K) for pairwise heterophase oxygen isotope-exchange between gas-phase 18O2 and oxygen-16 species from the oxide. Those oxygen equilibration/exchange processes were enhanced over precalcined RhOx–CeO2 materials prepared from chloride-free precursors, but not over La2O3–CeO2. That difference contrasted with expectations for similar concentrations of dopant-related, anion vacancy creation in each material, based upon XRD observations of the incorporation of each dopant into a slightly expanded CeO2(fluorite) lattice. Consideration is given not only to conventional contribution to oxygen equilibration/exchange by residual RhOX species at the RhOX–CeO2 surfaces, but also to ways in which bulk-incorporated, variable-valency rhodium ions can indirectly facilitate those processes.

On the binding strength of surface metal atoms in a high electric field—face-specific appearance energy measurements of field evaporated rhodium ions

To examine the effect of a high external electrostatic field on the strength of atomic binding at metal surfaces, we carried out absolute appearance energy measurements of rhodium ions field evaporated at 103 K from the relatively open Rh(100) plane and from the close packed Rh(111) plane. The crystal facets were characterized in a probe hole field ion microscope equipped with an external gimbal system for manipulation of the emitter apex with five degrees of freedom. Using a newly developed retarding potential technique, absolute values for rhodium field ion appearance energies were derived from measurements of the high energy onset of ion retardation curves. Appearance energies of ions field evaporated from Rh(100) were 0.6 eV greater than for field evaporation from Rh(111). Applying a thermionic cycle, the binding energy for Rh was 7.0 eV at Rh(100) step sites, and 6.4 eV at Rh(111) step sites, in both cases being greater than the cohesive energy for rhodium (5.75 eV). Conclusively, the external electric field of, in our case, approximately 41 V nm −1 enhances the binding strength of Rh surface atoms especially at less densely packed rhodium surfaces. The data are discussed within the framework of an earlier reported model involving the short-range, field-induced diffusion of a kink site atom prior to field evaporation.

Photoinduced intramolecular electron transfer reactions within donor-acceptor linked compounds in solution and within donor-acceptor ion-pairs in crystal

Intramolecular electron transfer (ET) processes within donor-acceptor linked compounds in solution and donor-acceptor ion-pairs in crystal have been investigated by means of laser photolysis kinetic spectroscopy. An excited Ru(II)-moiety of donor-acceptor compounds undergoes intramolecular electron-transfer to either ruthenium(III) ion, rhodium(III) ion or a cobalt(III) ion, followed by back ET to regenerate the original reactant. An Arrhenius plot of the ET rate gave a straight line with an intercept (frequency factor) and a slope (activation energy) for the photoinduced ET and the back ET. Mixed-valence isomer states produced via photoinitiated ET rapidly decayed via back ET. A common and large frequency factor observed for Ru(II)-Rh(III) compounds is accounted for in terms of solvent-relaxation dynamics. For the back ET in the Ru(II)-Co(III) compounds, the frequency factors are reduced because of negative entropy change. ET within donor-acceptor ion-pair of Ru(bpy)23 and Co(CN)36 in crystal took place very rapidly compared with in water.

Photoinduced ET and back-ET in bimetallated compounds of Ru(II)-Rh(III) and Ru(II)-Co(III)

Intramolecular electron transfer processes in bimetallated donor-acceptor compounds have been investigated by means of laser photolysis kinetic spectroscopy. An excited Ru(II)-moiety of donor-acceptor compounds undergoes intramolecular electrontransfer to either a rhodium(III) ion or a cobalt(III) ion, followed by back-electron transfer, an Arrhenius plot of the electron-transfer-rate gave a straight line of intercept (frequency factor) and slope (activation energy) for the photoinduced electron transfers and the back electron transfers. A common and large frequency factor observed for Ru(H)-Rh(III) compounds is accounted for in terms of solvent-relaxation dynamics. The activation energy observed consists of outersphere rearrangement energy depending on the metal ion-metal ion distance. For the photoinduced electron transfers and subsequent back-electron transfers in the Ru(II)-Co(III) compounds, the electron-transfer-rates are reduced because of weak electronic coupling, large rearrangement energy and negative entropy change.

Electrochemical Reduction of Nicotinamide Coenzyme (NAD<sup>+</sup>) Mediated with Rhodium Ion Immobilized in Polymer Modified Electrodes

Electrochemical Reduction of Nicotinamide Coenzyme (NAD<sup>+</sup>) Mediated with Rhodium Ion Immobilized in Polymer Modified Electrodes

Preparation and characterization of some complexes of chromium(III), cobalt(III) and rhodium(III) ions containing 1,4,8,12-tetra-azacyclopentadecane

Some new complexes of chromium(III), cobalt(III) and rhodium(III) containing 1,4,8,12-tetra-azacyclopentadecane and imido ligands have been prepared and characterized by elemental analyses, conductometric, magnetic, IR and electronic spectral studies. The complexes have the general formula trans-[ML(im) 2]ClO 4 [where M = chromium(III), cobalt(III) or rhodium(III); L = 1,4,8,12-tetra-azacyclopentadecane; im = anion of succinimide (sim − or phthalimide (pim −)]. A proposed trans configuration for the complexes is supported by spectral data.

Oxidants containing rhodium. X-ray photoelectroc spectra of dicaesium hexachlororhodate(iv), claus' blue and model compounds

The X-ray photoeletron spectra of dicaesium hexachlororhodate(IV), tricaesium hexachlororhodate(III), a hydrated rhodium(III) oxide, and the barium salt of Claus' blue—previously formulated as a rhodate(VI)—suggest that the latter has rhodium(III) ions in an oxygen environment. ESR and Raman spectra of this blue solid confirm that the superoxide moiety is present. Prior work on higher oxidation states of rhodium in various environments is critically re-assessed. The compounds Cs 2[MCl 6] (M = Rh, Pt and Ir) are isomorphous by X-ray powder diffraction.

Kinetics and mechanism of the reaction of thiocyanate ion with hexaaquo rhodium(III) ion

The kinetics of replacement of aqua ligands of hexaaquorhodium(III) ion by thiocyanate ion in aqueous media have been studied spectrophotometrically. The reaction rate is pH-dependent in the pH 1–3 range and is independent of the incoming ligand concentration. Activation parameters, calculated by studying the reaction in the 45°–60°C range, suggest a primary H2O dissociation-controlled process and are comparable to the activation parameters of an H2O exchange process.

COT1, a Gene Involved in Cobalt Accumulation in Saccharomyces cerevisiae

The COT1 gene of Saccharomyces cerevisiae has been isolated as a dosage-dependent suppressor of cobalt toxicity. Overexpression of the COT1 gene confers increased tolerance to cobalt and rhodium ions but not other divalent cations. Strains containing null alleles of COT1 are viable yet more sensitive to cobalt than are wild-type strains. Transcription of COT1 responds minimally to the extracellular cobalt concentration. Addition of cobalt ions to growth media results in a twofold increase in COT1 mRNA abundance. The gene encodes a 48-kDa protein which is found in mitochondrial membrane fractions of cells. The protein contains six possible membrane-spanning domains and several potential metal-binding amino acid residues. The COT1 protein shares 60% identity with the ZRC1 gene product, which confers resistance to zinc and cadmium ions. Cobalt transport studies indicate that the COT1 product is involved in the uptake of cobalt ions yet is not solely responsible for it. The increased tolerance of strains containing multiple copies of the COT1 gene is probably due to increased compartmentalization or sequestration of the ion within mitochondria.

COT1, a gene involved in cobalt accumulation in Saccharomyces cerevisiae.

The COT1 gene of Saccharomyces cerevisiae has been isolated as a dosage-dependent suppressor of cobalt toxicity. Overexpression of the COT1 gene confers increased tolerance to cobalt and rhodium ions but not other divalent cations. Strains containing null alleles of COT1 are viable yet more sensitive to cobalt than are wild-type strains. Transcription of COT1 responds minimally to the extracellular cobalt concentration. Addition of cobalt ions to growth media results in a twofold increase in COT1 mRNA abundance. The gene encodes a 48-kDa protein which is found in mitochondrial membrane fractions of cells. The protein contains six possible membrane-spanning domains and several potential metal-binding amino acid residues. The COT1 protein shares 60% identity with the ZRC1 gene product, which confers resistance to zinc and cadmium ions. Cobalt transport studies indicate that the COT1 product is involved in the uptake of cobalt ions yet is not solely responsible for it. The increased tolerance of strains containing multiple copies of the COT1 gene is probably due to increased compartmentalization or sequestration of the ion within mitochondria.

Polarisation of selenium and tellerium in compounds containing mixed metal clusters: Crystallographic and tellurium-125 Mössbauer spectroscopic evidence

Compounds of composition Mo 6− x M x X 8 (X = Se, Te) are composed of units in which the Mo 6− x M x trigonal antiprismatic metallic cluster is surrounded by eight chalcogens in a distorted cubic array. The cluster-metal to chalcogen intra cluster separations in the Mo 6− x M x X 8 compounds are shorter than those in the binary compounds Mo 6Se 8 and Mo 6Te 8 whereas similar distances in the closely related Chevrel phase compounds M x Mo 6X 8 are longer. The 125Te Mössbauer spectra recorded from compounds of the type Mo 6− x Ru x Te 8 and Mo 5.5Rh 0.5Te 8 show that the shorter metal to chalcogen intra cluster distances result from the polarisation of tellurium 5 p electrons by high oxidation state ruthenium or rhodium ions. Polarisation is enhanced by the incorporation of larger concentrations of ruthenium into the metal cluster.

Structure of the anti-cancer drug complex tetrakis(μ-acetato)-bis(1-methyladenosine)dirhodium(II) monohydrate

[Rh2(C2H3O2)4(C11H16N5O4)2].H2O, Mr = 1024.6, triclinic, P1, a = 7.808 (3), b = 11.469 (4), c = 12.091 (2) A, alpha = 69.55 (2), beta = 79.46 (2), gamma = 76.61 (3) degrees, V = 980.7 (6) A3, Z = 1, Dx = 1.735 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu = 77.6 cm-1, F(000) = 522, room temperature, R = 0.053 for 3638 unique reflections. Structure consists of two rhodium(II) ions in a metal--metal bond bridged by four acetate groups. The remaining axial coordination sites on the rhodium ions are coordinated to the N(7) positions of two 1-methyladenosine molecules.

Crown thioether chemistry. The rhodium complexes of 1,4,7-trithiacyclononane (9S3) and 1,5,9-trithiacyclododecane (12S3) and the conformational factors that stabilize monomeric rhodium(II) ions

Crown thioether chemistry. The rhodium complexes of 1,4,7-trithiacyclononane (9S3) and 1,5,9-trithiacyclododecane (12S3) and the conformational factors that stabilize monomeric rhodium(II) ions

Synthesis and Reaction of trans-Dichlorobis(o-phenylenediamine)rhodium(III) Perchlorate with Some Oxidizing Agents

Abstract A new rhodium(III) complex with o-phenylenediamine, trans-[RhCl2{C6H4(NH2)2}2]ClO4 was synthesized and the reaction with oxidizing agents studied. Due to coordination with the rhodium(III) ion the o-phenylenediamine (opd) was greatly stabilized against oxidation and the complex was oxidized slowly by periodate via intermediate radical complex to bis(o-benzoquinone diimine)dichlororhodium(III) complex which decomposed to the final products.

Kinetic studies of the complexation of oxalate to the t2g 6 hexaaqua ions of ruthenium(II) and rhodium(III)

A kinetic study on the reactions of oxalate with the isoelectronic t2g6 hexaaqua ions of ruthenium(II) and rhodium(III) reveals vastly differing mechanisms occurring for the two ions. For hexaaquaruthenium(II) equilibration kinetics is relevant giving a 1:1 oxalato complex, which is presumably chelated. For the forward reaction the dependence on [H+] indicates a rate-determining reaction of [Ru(OH2)6]2+ with the monoanion of oxalic acid. A comparison of rate constants and activation parameters for HC2O4– with those obtained for H2O, Cl–, Br– or I– as incoming ligands on [Ru(OH2)6]2+ suggests the presence of an interchange reaction largely controlled by the rate of water exchange. For hexaaquarhodium(III) a two-stage process occurs ultimately giving rise to tris(oxalato) products. In the first stage, a single rate-determining anation reaction proceeds to completion giving mainly cis-[Rh(OH2)2(C2O4)2]–(≈90%) with a smaller amount (≈10%) of the trans product. Rate-determining entry of the first oxalate ligand is believed to be involved. The dependence of the observed rate constants (kobs) for the first stage with both temperature and [H+] is discussed as indicating involvement of a mechanism where in interaction of H2C2O4 occurs with both [Rh(OH2)6]3+ and [Rh(OH2)5(OH)]2+ in a process involving retention of the Rh–OH(OH2) bond during the activation step. Rate constants are not only observed to be far in excess (>103×) of those for water exchange on the two aqua rhodium(III) ions but also found to be extremely close to those re-evaluated with respect to the corresponding reaction on [Ir(OH2)6]3+ in support of the existence of a metal independent C–O bond-breaking process. Possible reasons behind the differing behaviour observed for Ru2+ and Rh3+ are considered.

Rhodium-niobia interaction in niobia-promoted Rh/SiO 2 catalysts: formation of RhNbO 4 on SiO 2

Rhodium-niobia interaction in both Nb 2O 5-promoted Rh/SiO 2 catalysts and rhodium double oxide (RhNbO 4) catalysts has been studied by XRD, XPS, EXAFS and FT-IR, and catalytic properties were examined in relation to the catalyst structures. The extent of Rh-Nb 2O 5 interaction in Nb 2O 5-promoted Rh catalysts was sensitive to preparation variables such as the Nb/Rh ratio, the SiO 2 used, and the calcination temperature (the formation of RhNbO 4). Fine particles of RhNbO 4 supported on SiO 2 showed considerably high catalytic activity in ethane hydrogenolysis reaction, and this result was discussed in terms of an important role of a highly-oxidized state of rhodium ion.

Photoreduction of Rhodium(III) Ions in Water with Ultraviolet Light Aiming to Prepare the Dispersions of Ultrafine Particles

Abstract Rhodium(III) ions in an aqueous solution were successfully photoreduced by ultraviolet light irradiation. In the presence of a soluble polymer or a surfactant as a protective agent, the stable dispersions of ultrafine metal particles of rhodium were prepared. Besides, the photoreduction proceeded on irradiation with visible light in the presence of ethanol or 2-propanol.

ChemInform Abstract: Formation of Racemic and Meso Isomers of Mono‐ and Dihydroxo‐Bridged Dinuclear Ions by Hydrolysis of the cis‐Aquahydroxobis(1,2‐ethanediamine)rhodium(III) Ion.

AbstractThe hydrolysis of the racemic title complex ion at 60, 80 and 100 °C is studied by HPLC, and it is shown that the equilibrium solutions contain the meso (Δ,Λ) and the racemic (Δ,Δ/Λ,Λ) isomers of the species (I) and (II) together with the mononuclear parent compound.

Formation of racemic and meso isomers of mono- and dihydroxo-bridged dinuclear ions by hydrolysis of the cis-aquahydroxobis(1,2-ethanediamine)rhodium(III) ion

Etude cinetique et mecanisme de formation d'isomeres des especes [(H 2 O)(en) 2 Rh(OH) Rh(en) 2 (OH)] 4+ et [(en) 2 Rh(OH) 2 Rh(en) 2 ] 4+ a partir de l'hydrolyse du complexe mononucleaire du titre, en=ethylenediamine. Etudes quantitatives au moyen de la chromatographie HPLC et de la spectrophotometrie. Constantes d'equilibre entre les isomeres racemiques, parametres thermodynamiques

Reactions of Rh 2(O 2CCH 3) 2{Ph 2P(C 6H 4)} 2 with monothiocarboxylic acids: facile synthesis of Rh 2(OSCR) 4·2PPh 3 molecules and X-ray crystal structure of Rh 2(OSCC(CH 3) 3) 4·2PPh 3

The reaction of Rh 2(O 2CCH 3) 2(Ph 2P(C 6H 4)) 2·2THF with an excess of the monothio acids HOSCR (RCH 3, C 6H 5,-C(CH 3) 3) gives a series of products Rh 2(OSCR) 4·2PPh 3 in which the initially bridging orthometallated triphenylphosphine ligands have been protonated and are now coordinated as neutral ligands to the rhodium(II) ions. In addition the two bridging acetate groups are displaced and the rhodium-to-rhodium bond is bridged by four monothiocarboxylate groups in the final product. The reaction products were characterized by elemental analyses, infrared and 1H NMR spectroscopy. The structure of Rh 2(OSCC(CH 3) 3) 4·2PPh 3 was unequivocally established by a single crystal X-ray diffraction experiment. This compound crystallizes in the monoclinic space group P2 1/ n with one half of the dimer constituting the asymmetric unit. The cell dimensions are: a=12.508(8), b=12.976(7), c=17.582(5) Å, β=92.31(3)°, V=2851(2) Å 3 and Z=2. The structure was refined to R=0.086 ( R′=0.070). The Rh-Rh distance is 2.584(1) Å and the Rh-P distance 2.475(2) Å. The length of this metal-metal bond is appreciably greater than that observed for Rh 2(OSCCH 3) 4·2HOSCCH 3 (2.550(3) Å), the only other tetramonothiocarboxylato complex of rhodium(II) to have been structurally characterized. The electron transfer behaviour of these compounds has been studied by cyclic voltammetry in several solvents. The potential at which the dinuclear molecule undergoes oxidation was found to be dependent on the identity of the substituent group on the monothiocarboxylate ligands, with the oxidation becoming easier as the electron-donating power of the substituent group was increased.