Showing papers on "Oxidation state published in 1985"

IR Studies of NH3, Pyridine, CO, and NO Adsorbed on Transition Metal Oxides

Abstract: Chemisorption of small molecules is often used as a probe for By probing the surface properties of transition metal oxides the interaction of molecules with the surface, information is often obtained on the oxidation state, the coordination symmetry, the degree of coordination unsaturation of the surface cations, the acid-base properties of the surface hydroxyl groups, and the presence and the nature of surface Lewis acid and B rosnsted acid sites This information is deduced from experimental measurements of the adsorption isotherms, the heats of adsorption, the thermal desorption spectra, and the vibrational spectra of the adsorbate Until recently, when high resolution electron energy loss spectroscopy became available, vibrational spectra were obtained with infrared spectroscopy Laser Raman spectroscopy has seldom been used because of the low Raman scattering cross section of most molecules

Adsorption of CO, CO2, H2, and H2O on titania surfaces with different oxidation states

Abstract: The adsorptive properties of titania surfaces with different oxidation states were proved by temperature-programmed desorption (TPD) of CO, H2, CO2, and H2O. Auger electron spectroscopy and X-ray photoelectron spectroscopy revealed that vacuum annealing an oxidized titanium foil at temperatures from 300 to 800 K was an effective means of systematically varying the average surface oxidation state from TiU to TiS . Carbon monoxide weakly adsorbed (desorption energy of 44-49 kJ x mol ) in a carbonyl fashion on coordinatively unsaturated cation sites. Titania surfaces were inert with respect to H2 adsorption and dissociation. Carbon dioxide adsorbed in a linear molecular fashion. Water adsorbed both molecularly and dissociatively. Results are discussed in terms of the role of titania oxidation state in CO hydrogenation over titania-supported metal catalysts. 74 references, 7 figures.

Theory of 3d Transition Atom Impurities in Semiconductors

Abstract: The utility of semiconductors in many device applications, such as high­ speed logic circuits ( 1-2), optoelectronic devices (3-4), microwave devices (5), and solar cells (6), rests on the characteristics of the intentionally introduced impurities (dopants) as much as on the properties of trace amounts of unintentional contaminations. Transition atom (T A) impurities in semiconductors form a special class of such contaminants. They were studied experimentally in great detail (e.g. review articles in References 7-10) using a broad range of techniques, including optical absorption, luminescence, photocapacitance, photoconductivity, electron para­ magnetic resonance (EPR), electron nuclear double resonance (ENDOR), deep level transient spectroscopy (DLTS), and Hall effect. This review article is concerned with the theoretical understanding of the electronic properties of T A impurities in Si, III-V, and II-VI semiconductors. First, we establish the nomenclature. When a transition atom takes up a substitutional site, say on a cation, its formal oxidation state when neutral (labeled A 0) becomes that of the site it replaces, e.g. T A 3 + if it replaces a column III element. When the impurity captures an electron its charge state becomes negative (denoted A ), and the oxidation state is TA2+. Conversely, when the impurity loses an electron its charge state becomes positive (labeled A +), and the oxidation state becomes TA4+. The tenfold degenerate atomic d orbitals can split in the cubic environment into a

The radiation chemistry of some platinum-containing radiosensitizers and related compounds.

Abstract: Oxidation and reduction of cis- and trans-dichlorodiammine platinum II (cis- and trans-PDD), cis-dichlorobis(1-(2-hydroxyethyl)-2 methyl-5 nitroimidazole-N/sup 3/)-platinum II (cis-Flap), and cis-dichlorobis(isopropylamine)-trans-dihydroxyplatinum IV (Chip) have been studied using pulse radiolysis. Spectra corresponding to platinum in various oxidation states have been observed and several rate constants have been obtained. Reduction of all the compounds, except cis-Flap, produces species of a lower oxidation state of platinum which subsequently have both chloride ligands replaced. Ultimately, these products disproportionate. Oxidation of all four compounds consists of production of a higher oxidation state of platinum followed by replacement of chloride ligands and finally disproportionation of the products. Only cis-Flap and Chip could be reduced by oxidized DNA bases. The one-electron reduction potential of cis-Flap was found to be -370 +/- 10 mV. It was not possible to measure the potentials of the other compounds since their ligands were replaced rapidly but it is estimated that the one-electron reduction potentials decrease in the order cis- or trans-Flap > Chip > cis-PDD > trans-PDD.

High resolution photoemission investigation: The oxidation of W

Abstract: Surface‐sensitive core‐level photoelectron spectra excited by synchrotron radiation are presented for surface oxide phases of W in the monolayer range. Discrete chemically shifted core levels are observed and are shown to be associated with specific formal oxidation states by comparison with bulk reference compounds. Slight increases in the value of the core‐level shift for each oxidation state as the surface oxygen content increases are attributed to changes in the screening response of the system. Decomposition of the spectra into the separate contributions from each oxidation state provides specific and quantitative chemical information about the surface oxides. This and similar studies should be particularly useful for characterizing the disordered systems typical in applied surface physics where clarity of interpretation is very important.

Iodine chemistry in the +1 oxidation state. I. The electronic spectra of OI−, HOI, and H2OI+

Abstract: Electronic spectra are reported for the hypoiodite ion (OI−), hypoiodous acid (HOI), and its conjugate acid (H2OI+) in aqueous media. Iodine in the +1 oxidation state was produced by either of the ...

The Synthesis, Crystal and Molecular Structure, and Oxidation State of Iron Complex from Pyridoxal Isonicotinoyl Hydrazone and Ferrous Sulphate

Abstract: The reaction of isonicotinoyl hydrazone of pyridoxal (PIH), a biologically active iron-carrier, with FeSO4-7H20 at pH ∼ 6 generates the delta, lamda species of the N,N-trans-O,O-cis-cis coordination isomer of an iron(III) complex with iron-to-ligand ratio of 1:2. The dark red-brown crystals are monoclinic, space group C2/c, with unit-cell dimensions a = 14.487(2), b = 18.586(2), c = 27.508(4) A, β = 102.76(3)°, and Z = 8. The coordination around the metal is distorted octahedral and involves the protonated organic ligands, which are chelated through the phenolic oxygen [Fe-O1 1.941(6), Fe-O1′ 1.938(6)], an enolic form of the carbonyl oxygen [Fe-O3 2.017(6), Fe-O3′ 2.018(6)] and the azomethinic nitrogen [Fe-N2 2.133(8), Fe-N2′ 2.133(8)]. Packing is determined by systems of N-H….O and O-H….O hydrogen bonds involving the protonated pyridoxal nitrogens, the pyridoxal hydroxymethyl group, and the [SO4]2− group. The Mossbauer spectra at different temperatures (300 K, 88 K and 4.1 K) clearly prove that the iron atom in the complex is in a high-spin trivalent state.

Redox reactions in condensed oxide systems II. Variation of the structure of vanadium phosphate glasses in dependence on the oxidation state of vanadium

Abstract: The glass formation range in the systems V2O5VO2P2O5 and VO2V2O3P2O5 has been determined by melting V2O5 or VO2 together with P4O10 or utilizing H3PO4, respectively, in the series (VzOz/2)1−x(PO2.5)x with 0.2 < x < 0.8 in air taking care to realize equilibrium conditions.v Glass transition temperature, chemical durability and conductivity measurements indicate two distinct ranges which are discussed in terms of a structural model. The values are compared with data from the literature.

Binuclear Alkoxide Complexes of Niobium and Tantalum in Lower Oxidation States.

Abstract: Our knowledge of Nb and Ta complexes with RO/sup -/ and ROH ligands is almost exclusively limited to those in the highest oxidation state of the metals. Thus while extensive and multifaceted studies have been carried out for the M(V) species, there have been only a few reports dealing with such compounds involving tetravalent metals and none in lower oxidation states. In view of the very rich chemistry of Mo and W alkoxides and recent developments in the chemistry of low-valent Nb and Ta complexes, where interesting novel complexes and remarkable reactivity patterns have been found, there seems to be a considerable potential in the compounds of these two elements in oxidation states lower than +5 with alcohol-related ligands. Accordingly the authors have explored the reaction of the confacial bioactahedral Nb/sub 2/Cl/sub 6/(THT)/sub 3/ (1), THT = tetrahydrothiophene, with alcohols, ROH, for R = Me, Et and i-Pr. Three different types of compounds have been characterized by X-ray crystallography. A purple solution of 1 in toluene changes to brown within several hours upon addition of excess alcohol. For R = Et and i-Pr the removal of solvent under vacuum affords a compound of the formula Nb/sub 2/Cl/sub 5/-(OR)ROH)/sub 4/ (2)more » in the form of an orange or yellow-brown powder or a brown crystalline solid. 19 references, 3 figures.« less

Electronic spectra of transition metal ions in gel-derived and melt-derived glasses

Abstract: The absorption spectra of 3d transition elements Cr, Mn, Fe, Co, Ni and Cu were studied in SiO 2 R m O n compositions (R: a transition element), which were prepared at 500°C as coating films through the sol-gel process from a solution consisting of Si(OC 2 H 5 ) 4 , H 2 O, HCl and the nitrate of a transition metal. Generally speaking, the characteristic features of the peaks corresponding to a particular valence and coordination state of an element were similar to those reported for silica glass prepared at a high temperature of 1450°C, although the concentration of the particular valence and coordination state was not equal. This indicates that the SiO 2 network similar to that prepared at high temperatures is already constructed at low temperatures around 500°C. The oxidation state of copper in glasses prepared or treated in air atmosphere was studied with melt-derived silicate and gel-derived silica glasses by measuring the optical absorption due to Cu 2+ ions and making chemical analysis. It has been shown that the redox equilibrium of copper in glass shifts towards the higher valence state as the temperature decreases in the wide temperature range from about 1550°C to 500°C and that at least a portion of the copper is present as Cu 2+ ions in SiO 2 glass prepared at low temperatures up to about 500°C.

Coloring of iron surface controlled by Ti +O + double-ion implantations

Abstract: Ti + O + double-ion implantations in pure iron have been performed with 1 × 10 17 Ti + /cm 2 at 150 keV and with 1 × 10 17 and 2×10 17 O + /cm 2 at 50 or 35 keV at room temperature Oxidation state of pre-implanted titanium was investigated by means of X-ray photoelectron spectroscopy Colored surfaces were produced by the double-ion implantations combined with an electrochemical oxidation of the specimens Colors such as deep blue, purple, and brown appeared after the electrochemical oxidation with cyclic voltammetry in a 05 mol/dm 3 acetate buffer solution of pH 5 The mechanism of the coloring is discussed from analysis of the oxidation state of pre-implanted titanium and concentration-depth profiles of the titanium before and after the anodic oxidation of specimen electrodes These results showed that double-ion implantations are a useful technique to achieve the coloring with corrosion inhibition of iron surfaces

Kinetics of CO oxidation over Co3O4/γ-Al2O3. Part III: Mechanism

Abstract: Interpretations of a variety of transient experiments are combined with information from the literature to reveal the roles played by the Co/sub 3/O/sub 4/ catalyst surface and adsorbed species The reaction path depends on the oxidation state of the catalyst A rather coherent picture of oxidation-reduction catalysis by a metal oxide is obtained

A relation between oxidation state of sulfur and acidic property of iron oxide containing sulfur

Abstract: Five kinds of iron oxide catalysts promoted with sulfur were prepared by impregnating Fe(OH)3 with (NH4)2SO4 and by treating Fe2O3 and Fe(OH)3 with H2S and SO2. Changes in acidic properties of the catalysts with changes in oxidation states of sulfur were investigated by test reactions such as isomerization of cyclopropane and dehydration of 2-propanol over the oxidized or reduced catalysts. It has been found that the generation of acidic properties of the catalysts was independent of the kinds of the starting sulfur compounds, but dependent on the oxidation states of the sulfur. The sulfur in the highest oxidation state was responsible for the strongly acidic property of the catalyst.

N,N'-Dialkyl-pyrazinium and quinoxalinium salts. N-Heterocyclic redox systems with the radical cation intermediate as most persistent oxidation state

Abstract: Etude par voltammetrie cyclique du comportement redox des diethyl-1,4 pyrazinedium et diethyl-1,4 quinoxalinedium dans l'eau et dans le DMF

Transition metal containing plasma polymers

Abstract: The plasma polymerization of the C2 hydrocarbons in the presence of Fe(CO)5 vapor can lead to the formation of soluble cluster complexes (I) and/or high oxidation state iron both in the form of the oxide (II) and associated with the carboxylate or β‐diketonate ion (III). Analysis of the electron spectroscopy for chemical analysis (ESCA) spectra obtained yields information regarding the nature of I on the one hand, and regarding the prevalence of II relative to III, on the other. The relative yield of I with respect to (II+III) can be controlled, at will, by variation of W/F. This permits control of the coating’s morphology (continuity) as shown by the electrodeposition of Prussian blue on smooth surfaces coated with plasma polymer containing I+II+III.

Hydrogen absorption by lanthanide silicides

Abstract: The hydrogen absorption behaviour of Ln5Si3, (Ln ≡ Y, La, Nd, Ho) and related compounds is similar to that of the parent metal. This behaviour has been studied by gravimetric and volumetric methods. Particular attention was paid to the question of how strain in the host compound shifted the α → β phase transition temperature in Ho5Si3Hx. Only a minor affect was observed. XPS measurements showed that hydrogen changes the oxidation state of silicon from slightly negative to strongly positive.