Search results for "Oxidation state"
showing 10 items of 91 documents
Molecular materials with conducting and magnetic properties based on ET and [ M(tdas)2]x-dithiolenes
2004
Two hybrid molecular materials showing a combination of magnetic and conducting properties, the charge-transfer (ET) 2 [Fe(tdas) 2 ] (1) and (ET)Ni(tdas) 2 (2), (ET=bis(ethylenedithio) tetrathiafulvalene; M=Fe, Ni; tdas=l,2,5-thiadiazole-3,4-dithiolate) salts, are characterized by vibrational (IR and Raman) and UV-VIS-NIR spectroscopies. These studies have proved to be effective and diagnostic tools in identifying the oxidation state (partial or integer) and the packing pattern (dimers or segregated stacks) of the ET donor only, since no v(C=C) group vibration sensitive to the charge of M(tdas) 2 complexes has been observed. This is ascribed to the extensive electron-delocalization inside t…
Heterobimetallic complexes of cobalt(IV) porphyrin-corrole dyads. Synthesis, physicochemical properties, and X-ray structural characterization.
2005
The synthesis of a novel family of heterobinuclear cofacial biphenylene (B), anthracene (A), 9,9-dimethylxanthene (X), or dibenzofuran (O) bridged porphyrin-corrole complexes, (PCY)MClCoCl, is reported, M being either an iron(III) or manganese(III) ion. Each complex was characterized by electrochemistry, mass spectrometry, UV-vis, IR, and electron spin resonance spectroscopy. Unlike previously examined biscobalt porphyrin-corrole dyads, the cobalt ion of the corrole moiety is present in a high-valence +4 oxidation state, as proven by electrochemistry, spectroelectrochemistry, and an X-ray diffraction study of (PCB)FeClCoCl, which shows the presence of a bound Cl- anion on the cobalt corrole…
A comparative study of the surface and bulk properties of lanthanum-strontium-manganese oxides La1âxSrxMnO3±δ as a function of Sr-content, oxygen…
1999
Abstract The properties of the perovskite-type La 1− x Sr x MnO 3± δ oxides (0≤ x ≤1) are related to the reversible redox reaction of manganese ions Mn 3+ ↔Mn 4+ . This reaction plays an essential role both in the interfacial transfers and transport properties and depends on relative cation concentrations and experimental conditions. In this paper we present experimental investigations aiming to determine, to compare and to control some of the surface and bulk properties of these oxides. The bulk and surface Mn 4+ contents were investigated by thermogravimetry analysis (TGA) in hydrogen and X-ray photo-electron spectroscopy (XPS) respectively. With a finely divided La 0.8 Sr 0.2 MnO 3 powde…
Synthesis and crystal structure of novel Ruddlesden–Popper strontium niobium oxynitrides
2002
Abstract The family (SrO)(SrNbO 2-x N) n is the first example of Ruddlesden-Popper strontium niobium oxynitrides and provides layered structures to obtain mixed valence niobium compounds with a variety of oxidation states and transport properties. We have prepared members with n =1 (Sr 2 NbO 3 N) and n =2 (Sr 3 Nb 2 O 5 N 2 ) by solid state reaction of Nb 2 O 5 and SrCO 3 at 900–1050 °C under ammonia flow. These compounds crystallize in the I4/mmm space group and show a range of anionic stoichiometry that together with the N/O ratio determines the formal oxidation state for niobium and therefore the resultant physical properties. Samples of the n =1 member show mixed valence Nb 5+ /Nb 4+ an…
Oxidation State and Local Structure of Chromium Ions in LaOCl
2021
This research is funded by the Latvian Council of Science, project “Novel transparent nanocomposite oxyfluoride materials for optical applications”, project No. LZP-2018/1-0335. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017- TeamingPhase2 under grant agreement No. 739508, project CAMART2.
Comparison of Permeation Measurements and Hybrid Density Functional Calculations on Oxygen Vacancy Transport in Complex Perovskite Oxides
2014
The oxygen vacancy (VO••) formation enthalpy (ΔHF) was determined from the effective activation energies obtained in the permeation measurements on a series of solid solutions La0.98–xSrxCo0.2Fe0.8O3−δ (x = 0.125–0.8) and compared with the results of ab initio calculations at finite temperatures based on the hybrid (PBE0) and GGA+U calculations, as well as previous thermogravimetric experiments. The Mulliken atomic charges, magnetic moments, and the Fe-VO•• and Sr-VO•• distances are analyzed. The strong dependence of formation enthalpy of VO•• on the Fe oxidation state due to variation in Sr and VO•• concentrations is discussed.
Novel Ni(II) Mixed Ligand Complex Modified Electrode: Catalytic Effect on Anodic Oxidation of Phenol
2004
Cyclic voltammetry, using graphite paste electrode (GPE) and chemically modified GPE with Ni(II) mixed ligand complex (MGPE), is described for sensing and detoxification of phenol. A novel mixed ligand complex of nickel with 1,4,8,11-tetraaza cyclotetradecane (cyclam) and thiocyanate in the molar ratio of 1 : 2 : 5 is synthesized and characterized by spectroscopic and electrochemical studies. The Ni(II)-cyclam-thiocyanate complex behaves as a fast electron-transfer mediator, as nickel ions exist in higher oxidation state of Ni(III) on applying a potential of 1.25 V (vs. Ag/AgCl), which catalyses the oxidation of the target species. The mixed ligand complex, when incorporated in the graphite…
Correlation between oxidation states of transition metal ions and variation of the coercivity in mixed-valence defect spinel ferrites
1997
Abstract Due to the very high dispersion of mixed-valence spinel ferrites prepared by ‘soft chemistry’ it becomes possible to oxidize in the spinel lattice, not only ferrous ions but also different transition metal ions (Cr 3+ , Mn 2+ , Mn 3+ , Mo 3+ , Mo 4+ V 2+ , V 3+ , Cu + ), by ‘soft’ oxidation between 150 and 500°C, under formation of non-stoichiometric spinels cation vacancies. The oxidation state with the coordination and the oxidation temperature of the cations have been determined in coppermanganese ferrites by derivative thermogravimetry (DTG), based on the specific solid-state reactivity of cations in the redox reaction. For Co-modified non-stoichiometric spinels, which present…
Structural diversity in charge transfer salts based on Mo3S7 and Mo3S4Se3 clusters complexes and bis(ethylenedithio)tetrathiafulvalene (ET)
2007
Chemical modification of the trinuclear [Mo3(μ3-S)(μ2-S2)3Br6]2− cluster, at either the outer bromine or the disulfide ligands, allows the facile preparation of the dianions [Mo3(μ3-S)(μ2-S2)3(tdas)3]2− ([1]2−) (tdas = 1,2,5-thiadiazole-3,4-dithiol), [Mo3(μ3-S)(μ2-SSe)3Br6]2− ([2]2−) and [Mo3(μ3-S)(μ2-S2)3Cl6]2− ([3]2−). Electrocrystallization of bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of these dianions affords a series of charge transfer salts, namely (ETA)(ETB)[1], (ETA)(n-Bu4N)[2], (ETA)(ETB)[3]2·CH3CN, and ((ETA)(ETB)(ETC)(ETD))2{[3]2Cl}·CH3CN, where the ET subscripts denote crystallographically independent molecules. In all cases, the various cluster–cluster, cluster…
Intermediate valencies of vanadium cations appearing during oxidation of vanadium–iron spinels
2000
Abstract The oxidation state of vanadium cations in nanosized vanadium–iron spinels at stoichiometry and at oxidative nonstoichiometry has been investigated by associating X-ray diffraction, thermal analysis (DSC), infrared and X-ray photoelectron spectroscopies. It has been established that, during oxidation, the V3+ cations present several intermediate valencies before to realize the final oxidation state +5. A comparison was made with the oxidation of V2O3.