| 1. |
- Zubkov, V. G., et al.
(författare)
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Structural, vibrational, electronic, and luminescence properties of the cyclotetravanadates A(2)M(VO3)(4) (A=Na,Ag; M=Ca,Sr)
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77, s. 174113-
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Tidskriftsartikel (refereegranskat)abstract
- The physical properties of the family of cyclotetravanadates A(2)M(VO3)(4), where A=Na,Ag and M=Ca,Sr, have been studied by means of x-ray powder diffraction, neutron diffraction, electron diffraction, infrared, Raman, NMR, photoexcitation and pulse cathode beam excitation, and x-ray photoelectron spectroscopies, and band structure calculations. The differences between the structural, vibrational, luminescence, and electronic properties of the alkali metal-containing [Na2Ca(VO3)(4) and Na2Sr(VO3)(4)] and the d metal-containing cyclotetravanadates [Ag2Ca(VO3)(4) and Ag2Sr(VO3)(4)] are analyzed. Na2Ca(VO3)(4), Ag2Ca(VO3)(4), Na2Sr(VO3)(4), and Ag2Sr(VO3)(4) have tetragonal structures, P4/nbm, with a=10.438 49(6), 10.445 24(5), 10.634 49(4), and 10.625 74(6), and c=4.938 73(5), 4.968 45(5), 4.962 05(4), and 4.979 30(4) angstrom, respectively. The main structural feature of A(2)M(VO3)(4) is the tetracyclic [V4O12] units. The hybridized O 2p-V 3d states of the tetracyclic [V4O12] units have a dominant influence on the electronic structure of these compounds. The compounds are semiconducting with a local density approximation band gap increasing, from 1.85 eV for Ag2Ca(VO3)(4) to 3.02 eV for Na2Ca(VO3)(4). The prospects of these compounds as advanced materials for detectors of photon and corpuscular radiation as well as for color correction of light emission sources such as lamp and light emitting diode sources are discussed.
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| 2. |
- Risberg, Emiliana, Damian, et al.
(författare)
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Sulfur X-ray absorption and vibrational spectroscopic study of sulfite, sulfur dioxide and sulfonate solutions, and of the substituted sulfonate ions X3CSO3- (X = H, Cl, F)
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 46:20, s. 8332-8348
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra have been recorded and the S(1s) electron excitations evaluated by means of density functional theory−transition potential (DFT−TP) calculations to provide insight into the coordination, bonding, and electronic structure. The XANES spectra for the various species in sulfur dioxide and aqueous sodium sulfite solutions show considerable differences at different pH values in the environmentally important sulfite(IV) system. In strongly acidic (pH < 1) aqueous sulfite solution the XANES spectra confirm that the hydrated sulfur dioxide molecule, SO2(aq), dominates. The theoretical spectra are consistent with an OSO angle of 119° in gas phase and acetonitrile solution, while in aqueous solution hydrogen bonding reduces the angle to 116°. The hydration affects the XANES spectra also for the sulfite ion, SO32-. At intermediate pH (4) the two coordination isomers, the sulfonate (HSO3-) and hydrogen sulfite (SO3H-) ions with the hydrogen atom coordinated to sulfur and oxygen, respectively, could be distinguished with the ratio HSO3-:SO3H- about 0.28:0.72 at 298 K. The relative amount of HSO3- increased with increasing temperature in the investigated range from 275 to 343 K. XANES spectra of sulfonate, methanesulfonate, trichloromethanesulfonate, and trifluoromethanesulfonate compounds, all with closely similar S−O bond distances in tetrahedral configuration around the sulfur atom, were interpreted by DFT−TP computations. The energy of their main electronic transition from the sulfur K-shell is about 2478 eV. The additional absorption features are similar when a hydrogen atom or an electron-donating methyl group is bonded to the −SO3 group. Significant changes occur for the electronegative trichloromethyl (Cl3C−) and trifluoromethyl (F3C−) groups, which strongly affect the distribution especially of the π electrons around the sulfur atom. The S−D bond distance 1.38(2) Å was obtained for the deuterated sulfonate (DSO3-) ion by Rietveld analysis of neutron powder diffraction data of CsDSO3. Raman and infrared absorption spectra of the CsHSO3, CsDSO3, H3CSO3Na, and Cl3CSO3Na·H2O compounds and Raman spectra of the sulfite solutions have been interpreted by normal coordinate calculations. The C−S stretching force constant for the trichloromethanesulfonate ion obtains an anomalously low value due to steric repulsion between the Cl3C− and −SO3 groups. The S−O stretching force constants were correlated with corresponding S−O bond distances for several oxosulfur species.
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| 3. |
- Tyutyunnik, A. P., et al.
(författare)
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CRYSTAL STRUCTURE AND VIBRATIONAL SPECTRA OF M[VO(2)(SeO(4))(H(2)O)(2)]center dot H(2)O (M = K, Rb, NH(4))
- 2011
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Ingår i: Journal of Structural Chemistry. - 0022-4766 .- 1573-8779. ; 52:2, s. 350-357
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Tidskriftsartikel (refereegranskat)abstract
- By the hydration of MVO(SeO(4))(2) with saturated water vapors at room temperature a series of isostructural complex compounds of vanadium(V) of the composition M[VO(2)(SeO(4))(H(2)O)(2)]center dot H(2)O (K, Rb, NH(4)) are synthesized and their physicochemical properties are studied. Based on the X-ray and neutron diffraction data, it is found that their crystal structure is composed of VO(6) octahedra linked in infinite chains by bridging SeO(4) tetrahedra. Each of the VO(6) octahedra has two short terminal V-O bonds forming a bent dioxovanadium group VO(2)(+). Two water molecules are coordinated by vanadium and one molecule is out of the first coordination sphere in the interchain space. The vibrational spectra of the studied compounds are completely consistent with their structural features.
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