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Dordevic T.,University of Vienna | Gerger S.,University of Vienna | Karanovic L.,Laboratory of Crystallography
European Journal of Mineralogy | Year: 2017

During systematic research on the mineral-related arsenates in the system CdO-MO-As2O5-H2O (M2+ = Mg, Co, Ni, Cu, Zn), three new Cd-containing arsenates Cd4.65Ni0.35 (AsO4)2(HAsO4)24H2O (1), Cd0.75Co2.75 (H0.5AsO4)2(HAsO4) (2) and Cd1.25Zn0.75 (HAsO4)22H2O (3) have been synthesized under hydrothermal conditions, while the Zn-arsenate Zn9 (AsO4)64H2O (4) and again 2 have been prepared under ionothermal conditions using the ionic liquid 1-ethyl-3-methylimidazolium bromide, (C6H11N2)Br, as the solvent. Their crystal structures were determined using single-crystal X-ray diffraction data and refined to the reasonably low R-values: 1 - R1 = 0.030; 2 - R1 = 0.047; 3 - R1 = 0.029; 6 - R1 = 0.029. The compounds 1, 2 and 3 are structural analogues of three different arsenate mineral phases. Compound 4 was for the first time synthesized using ionic liquid as the solvent and the hydrogen atoms were found and refined. Infrared and Raman spectra were measured and evaluated in order to obtain further information on the anion groups and especially on the short hydrogen bonds. The OH stretching frequency is in good agreement with the observed O:::O distances. The different approaches in the synthesis of mineral-related arsenates, the temperature treatment as well as the role of added water in ionothermal synthesis are also discussed. © 2016 E. Schweizerbart'sche Verlagsbuchhandlung.


Hagemann H.,University of Geneva | D'Anna V.,University of Geneva | Rapin J.-P.,University of Geneva | Rapin J.-P.,Laboratory of Crystallography | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

Deuterium-hydrogen exchange in solid α-Mg(BH4)2 is demonstrated. Compared to the previously reported exchange reactions in the alkali borohydrides, the temperature at which isotope exchange starts to take place is significantly lower (132°C vs 200°C for LiBH4). The activation energy for the deuterium-hydrogen exchange reaction is estimated to be 51 ± 15 kJ/mol. Almost complete isotope exchange was observed by treating solid Mg(BH4)2 for 72 h at 172°C with 42 bar of D2. Preliminary experiments indicate that under these conditions Ca(BH4)2 also undergoes isotope exchange. © 2010 American Chemical Society.


Mitchell S.,Institute for Chemical and Bioengineering | Milina M.,Institute for Chemical and Bioengineering | Verel R.,Institute for Chemical and Bioengineering | Hernandez-Rodriguez M.,Institute for Chemical and Bioengineering | And 3 more authors.
Chemistry - A European Journal | Year: 2015

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends. Feel the heat: Changes in the aluminum coordination (see figure) and associated acidic character of hierarchical zeolites primarily result from a reduction of the thermal stability of framework aluminum with increasing mesoporous surface area. This finding highlights the critical impact of calcination, an integral step in the synthesis and regeneration of zeolite catalysts, on the protonic form. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Dordevic T.,University of Vienna | Karanovic L.,Laboratory of Crystallography
Journal of Solid State Chemistry | Year: 2010

A new monoclinic polymorph of Ba(AsO3OH) was synthesized under hydrothermal conditions. It represents a previously unknown structure type. Its crystal structure was determined from a racemic twin using single-crystal X-ray diffraction data collected at 120 and 293 K [space group P21, a=7.2149(14)/7.2370(2), b=7.7028(15)/7.7133(2), c=21.7385(43)/21.8079(5)Å, β=95.95(3)/96.073(1)°, V=1201.6(4)/1210.51(5) Å, Z=12]. The crystal structure of P21-Ba(AsO3OH) has a layered character and is built up of four types of regularly alternating layers parallel to (0 0 1). Every AsO3OH tetrahedron is chelating to two Ba atoms and bridged by another two Ba atoms. Each OH group acts as hydrogen bond donor toward the oxygen atoms positioned in the same or adjacent layers. Although the H atoms could not be located, no ambiguities are present in the hydrogen-bonding scheme. Single-crystal vibrational spectroscopy (FTIR and Raman) was used to describe the vibrational behavior of the hydrogen bond system; particularly the spectroscopic manifestation of the very short and short hydrogen bonds (2.462(7)2.575(7) Å). In order to complement spectroscopic data on protonated orthoarsenates, infrared spectra of triclinic F1̄-Sr(AsO 3OH) and the orthorhombic variety of Pbca-Ba(AsO3OH) were recorded and discussed. Furthermore, structural features of other alkaline earth hydrogen arsenates are discussed. © 2010 ElsevierInc. All rights reserved.


Dordevic T.,University of Vienna | Gerger S.,University of Vienna | Karanovic L.,Laboratory of Crystallography
Acta Crystallographica Section E: Crystallographic Communications | Year: 2016

Both unique Cd atoms in the tetragonal polymorph of bis(1-ethyl-3-methylimidazolium) tetrabromidocadmate, (C6H11N2)2[CdBr4], occupy special positions (site symmetry 4). The crystal structure consists of isolated tetrahedral [CdBr4]2- anions which are surrounded by 1-ethyl-3-methylimidazolium cations. The methyl and ethyl side chains of the cations show positional disorder in a 0.590 (11):0.410 (11) ratio. In the crystal, (C6H11N2)+ cations display three weak C-H⋯Br hydrogen-bond interactions through the imidazolium ring H atoms with the Br- ligands of the surrounding complex anions. The alkyl groups of the side chains are not involved in hydrogen bonding.


Dorevic T.,University of Vienna | Stojanovic J.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials | Karanovic L.,Laboratory of Crystallography
Acta Crystallographica Section E: Structure Reports Online | Year: 2010

The title compound, dizinc cadmium hydroxide tetraoxido-vanadate, Zn 1.86Cd0.14(OH)VO4, was prepared under low-temperature hydro-thermal conditions. It is isostructural with Zn 2(OH)VO4 and Cu2(OH)VO4. In the crystal structure, chains of edge-sharing [ZnO6] octahedra are inter-connected by VO4 tetra-hedra (site symmetries of both V atoms and their coordination polyhedra are.m.) to form a three-dimensional [Zn(OH)VO4]2- framework with channels occupied by Zn and Zn/Cd cations adopting trigonal-bipyramidal and distorted octa-hedral coordinations, respectively. Zn1.86Cd0.14(OH)VO 4 is topologically related to adamite-type phases, and descloizite- and tsumcorite-type structures.


Maiti S.,Laboratory of Crystallography | Steurer W.,Laboratory of Crystallography
TMS Annual Meeting | Year: 2014

Many exciting properties such as high hardness, high strength, wear resistance and oxidation resistance are generally observed due to the distorted lattice and slow diffusion rate in high-entropy alloys (HEAs). In this study, HEAs based on refractory metals like Hf Mo, Nb, Ta, Ti, W and Zr are studied with the goal to develop both ambient and high-temperature structural materials and understand their structure-property relationship. HEA compositions like MoNbTaW and TaNbHfZrTi have been studied for their phase-stability, local atomic displacement and hardness. The refractory HEAs form a body-centered cubic disordered phase in the as-cast and also in the homogenized (1600-1800°C) samples. X-ray diffractions on single crystals reveal some streak-like diffuse intensities adjacent to the (110) reflections, which might be due to a short-range order of one or more elements combined with atomic size differences. The hardness of the synthesized refractory HEAs can be 3-4 times that of the pure elements.


PubMed | University of Vienna and Laboratory of Crystallography
Type: Journal Article | Journal: Acta crystallographica. Section E, Crystallographic communications | Year: 2016

Both unique Cd atoms in the tetra-gonal polymorph of bis-(1-ethyl-3-methyl-imidazolium) tetra-bromido-cadmate, (C6H11N2)2[CdBr4], occupy special positions (site symmetry -4). The crystal structure consists of isolated tetra-hedral [CdBr4](2-) anions which are surrounded by 1-ethyl-3-methyl-imidazolium cations. The methyl and ethyl side chains of the cations show positional disorder in a 0.590(11):0.410(11) ratio. In the crystal, (C6H11N2)(+) cations display three weak C-HBr hydrogen-bond inter-actions through the imidazolium ring H atoms with the Br(-) ligands of the surrounding complex anions. The alkyl groups of the side chains are not involved in hydrogen bonding.


PubMed | Institute for Chemical and Bioengineering and Laboratory of Crystallography
Type: Journal Article | Journal: Chemistry (Weinheim an der Bergstrasse, Germany) | Year: 2015

A literature survey reveals a prominent reduction in the concentration of Brnsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends.


Subba Reddy B.V.,Natural Product Chemistry | Swathi V.,Natural Product Chemistry | Swathi V.,Center for Chemical Biology | Swain M.,Natural Product Chemistry | And 4 more authors.
Organic Letters | Year: 2014

A variety of aldehydes undergo smooth coupling with 4-hydroxy-N-methyl-2-methylene-N-phenylbutanamide in the presence of BF3·OEt2 under ambient conditions to produce the corresponding spiro-oxindole derivatives in good yields with excellent selectivity. It is an entirely new strategy to construct the spirocycles in a one-pot operation through a Prins cascade process. © 2014 American Chemical Society.

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