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Nakhon Ratchasima, Thailand

Gaur A.,Karlsruhe Institute of Technology | Klysubun W.,111 University Ave | Joshi S.K.,P.A. College | Soni B.,Vikram University | And 3 more authors.
Journal of Physics: Conference Series | Year: 2016

XAFS of three Cu(II) diethylenetriamine complexes (in crystalline form) having different coordination geometries have been investigated. First complex has distorted tetragonal pyramidal, second has distorted square planar and third has distorted square pyramidal geometry. The difference in coordination geometries has been inferred from the differences in pre-edge peak, rising part of edge and in shape of white line, which are seen clearly in the derivative XANES spectra. The distortion in geometry has been correlated with the intensity of peaks in derivative spectra. These inferences have been corroborated from EXAFS analysis where the different paths have been used in the theoretical fits in R space to show contributions of different scatterers at different distances. Source

Gaur A.,Karlsruhe Institute of Technology | Klysubun W.,111 University Ave | Soni B.,Vikram University | Shrivastava B.D.,Vikram University | And 2 more authors.
Journal of Molecular Structure | Year: 2016

X-ray absorption spectroscopy (XAS) is very useful in revealing the information about geometric and electronic structure of a transition-metal absorber and thus commonly used for determination of metal-ligand coordination. But XAFS analysis becomes difficult if differently coordinated metal centers are present in a system. In the present investigation, existence of distinct coordination geometries around metal centres have been studied by XAFS in a series of trimesic acid Cu(II) complexes. The complexes studied are: Cu3(tma)2(im)6 8H2O (1), Cu3(tma)2(mim)6 17H2O (2), Cu3(tma)2(tmen)3 8.5H2O (3), Cu3(tma) (pmd)3 6H2O (ClO4)3 (4) and Cu3(tma)2 3H2O (5). These complexes have not only Cu metal centres with different coordination but in complexes 1-3, there are multiple coordination geometries present around Cu centres. Using XANES spectra, different coordination geometries present in these complexes have been identified. The variation observed in the pre-edge features and edge features have been correlated with the distortion of the specific coordination environment around Cu centres in the complexes. XANES spectra have been calculated for the distinct metal centres present in the complexes by employing ab-initio calculations. These individual spectra have been used to resolve the spectral contribution of the Cu centres to the particular XANES features exhibited by the experimental spectra of the multinuclear complexes. Also, the variation in the 4p density of states have been calculated for the different Cu centres and then correlated with the features originated from corresponding coordination of Cu. Thus, these spectral features have been successfully utilized to detect the presence of the discrete metal centres in a system. The inferences about the coordination geometry have been supported by EXAFS analysis which has been used to determine the structural parameters for these complexes. © 2016 Elsevier B.V. All rights reserved. Source

Hormes J.,University of Bonn | Hormes J.,Louisiana State University | Diekamp A.,University of Innsbruck | Klysubun W.,111 University Ave | And 2 more authors.
Microchemical Journal | Year: 2016

Three mortar samples from different construction phases of the Cathedral of Paderborn (Germany) between ~ and ~1220AC have been investigated using three different and partly complementary techniques: conventional X-ray diffraction (XRD), synchrotron radiation based X-ray fluorescence (SR-XRF), and X-ray absorption near edge structure (XANES) spectroscopy. Samples were sieved and then investigated according to size: smaller and larger than 75μm. For the small samples XRD detected CaCO3 (calcite) and SiO2 (quartz) as the most abundant compounds and Na(AlSi3O8) (albite) as a minor component. No compounds containing transition metals (e.g. Fe) were observed by XRD. XRF results indicate just a marginal enrichment of binder compounds in the small samples as compared to the large ones. By XRF, in all samples Fe was observed at a very high concentration together with Ti and Zn at high concentrations and some other metals with lower concentration indicating that these metals are in an amorphous form and thus "invisible" for XRD. XANES spectra confirm the XRD result that most Ca exists as calcite, however at least in one sample (the "youngest" one) where the S-concentration is quite high also Ca(SO4) was detected via Ca-K and S-K-XANES spectra. Fe-K-XANES spectra indicated that Fe exists in the mortar samples with valency +3 as Fe2O3. Most likely, the SiO2 grains are coated with iron oxides that have a high adsorption capability for trace metals explaining in this way the XRF detection of several metals at low concentration. © 2015. Source

Klysubun W.,111 University Ave | Hauzenberger C.A.,University of Graz | Ravel B.,U.S. National Institute of Standards and Technology | Klysubun P.,111 University Ave | And 3 more authors.
X-Ray Spectrometry | Year: 2015

Two samples of the blue glass produced in the middle 19th century from the Temple of the Emerald Buddha in Bangkok, Thailand, were studied in order to understand the origin of its blue color. The oxide components and trace elements are quantitatively determined by scanning electron microscopy coupled with energy-dispersive and wavelength-dispersive spectrometry and laser ablation inductively coupled plasma mass spectroscopy techniques. The results identify the glass type as soda-lime-silica glass with high lead content. The 3d transition elements detected include iron, manganese, cobalt, and copper. Combined analyses of X-ray absorption near edge structures and optical absorbance lead to a conclusion that the antique glass is primarily colored in blue by the divalent cobalt with additional yellow coloration as a result of the trivalent iron. The tetrahedral coordination geometry of these two species was deduced from the XANES pre-edge intensity and the optical absorption bands of their d-d transitions. The redox ratios of Fe2+/Fe3+, Mn2+/Mn3+, and Cu1+/Cu2+ in the original blue glass and the reference glasses were determined by the K-edge XANES analysis. The blue color of the antique glass can be reproduced in a laboratory glass on the basis of composition and melting conditions. © 2015 John Wiley & Sons, Ltd. Source

Klysubun W.,111 University Ave | Ravel B.,U.S. National Institute of Standards and Technology | Klysubun P.,111 University Ave | Sombunchoo P.,111 University Ave | Deenan W.,111 University Ave
Applied Physics A: Materials Science and Processing | Year: 2013

Yellow and colorless ancient glasses, which were once used to decorate the Temple of the Emerald Buddha, Bangkok, Thailand, around 150 years ago, are studied to unravel the long-lost glass-making recipes and manufacturing techniques. Analyses of chemical compositions, using synchrotron x-ray fluorescence (SRXRF), indicate that the Thai ancient glasses are soda lime silica glasses (60 % SiO2; 10 % Na2O; 10 % CaO) bearing lead oxide between 2-16 %. Iron (1.5-9.4 % Fe2O3) and manganese (1.7 % MnO) are present in larger abundance than the other 3d transition metals detected (0.04-0.2 %). K-edge x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure spectroscopy (EXAFS) provide conclusive evidence on the oxidation states of Fe being 3+ and Mn being 2+ and on short-length tetrahedral structures around the cations. This suggests that iron is used as a yellow colorant with manganese as a decolorant. L 3-edge XANES results reveal the oxidation states of lead as 2+. The results from this work provide information crucial for replicating these decorative glasses for the future restoration of the Temple of the Emerald Buddha. © 2013 Springer-Verlag Berlin Heidelberg. Source

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