Showing papers by "T. N. Guru Row published in 2002"

Structure determination at room temperature and phase transition studies aboveT c in ABi4Ti4O15 (A = Ba, Sr or Pb)

Abstract: The room temperature structure of three compounds belonging to the Aurivillius family (n = 4), ABi4Ti4O15 (A = Ba, Sr or Pb) has been analysed. BaBi4Ti4O15 crystallizes in a tetragonalI4/mmm space group whereas SrBi4Ti4O15 and PbBi4Ti4O15 crystallize in the orthorhombic space group A21am. The starting model for the Sr and Pb analogues was derived fromab initio methods and refined using the Rietveld method. The cations Ba and Sr are disordered over the Bi sites while the Pb cation is found exclusively in the [Bi2O2]2+ layers. The TiO6 octahedra are tilted with the Ti-O bonds forming zigzag chains along the “c” axis. The displacement of Bi atoms along the “a” axis might be responsible for ferroelectricity in these compounds. The high temperature X-ray data aboveT c indicate no structural transition for A = Ba and Pb while A = Sr transforms to the tetragonal structure.

Electron density study of 2H-chromene-2-thione.

Abstract: The charge-density distribution in 2H-chromene-2-thione (2-thiocoumarin), C9H6OS, has been determined from X-ray diffraction data measured at 90 K using a CCD detector, to a resolution of sinθ/λ 2σ(I) [R(F) = 0.021, wR(F) = 0.022, goodness of fit = 1.81] in order to generate the difference Fourier maps. The topological properties of the molecular electron density in terms of the bond critical points and the evaluation of the dipole moment show that the molecular dipole moment in the crystal is higher than the corresponding value derived from theoretical calculations.

Variable Temperature X-ray Crystal Structure Analysis of a Type I Langbeinite: Rb2Cd2 (SO4) 3

Abstract: The structure of a type I langbeinite, Rb2Cd2(SO4)3, displays three different phases, cubic with a = 10.378(5) A (space group P213) at room temperature, monoclinic at 120 K with a = 10.328(3), b = ...

4-Chloro­benzohydrazide

Abstract: The crystal structure of the title compound, C7H7N2OCl, has been determined in the monoclinic space group P21/c at room temperature. The structure is stabilized by intermolecular N—H⋯O and N—H⋯N hydrogen bonds.

3-Nitro­acetanilide

Abstract: The title compound, also known as N-(3-nitro­phenyl)­acet­amide, C8H8N2O3, is an organic non-linear optical material. It crystallizes in the monoclinic system in the chiral space group P21, and there are four independent mol­ecules in the asymmetric unit.

2,4,5-Trichloroacetanilide

Abstract: The title compound, C8H6Cl3NO, also known as N-(2,4,5- trichlorophenyl)acetamide, is an organic non-linear optical material. It crystallizes in the monoclinic system, in the noncentrosymmetric space group Pn.

2H-Thiochromen-2-one

Abstract: The crystal structure of the title compound, C$_{9}$H$_{6}$OS, also known as 2H-thiochromen-2-one, has been determined as monoclinic in the space group Pc at room temperature. The molecule is essentially planar and the crystal is a candidate for second harmonic generation (SHG) effects.

Comment on "Structure of $NaBi_3V_2O_{10}$ and Implications for Ionic Conductivity"

Abstract: The recent publication in this journal by Sleight’s group1 describing the structure and ionic conductivity prompts us to comment on their observations in light of our earlier published work. Our publication clearly brought out the existence of two polymorphic modifications of $NaBi{_3}V{_2}O_{10}$ and we were the first to establish the structure of the R form from the ab initio powder X-ray diffraction technique. It may be pointed out that the work published by Sinclair’s group was ambiguous as the structure reported in ref 4 (\beta-form) was entirely different from the one reported in ref 3 for which the conductivity data were provided.

2,4,6-Tri­methyl­acetanilide

Abstract: The title compound, C11H15NO, also known as N-(2,4,6-tri­methyl­phenyl)­acet­amide, is an organic non-linear optical material. It crystallizes in the monoclinic system, in a non-centrosymmetric space group Pn.

2-Amino-5-propyl-1,3,4-thiadiazole

Abstract: The title compound, C5H9N3S, which exhibits a hypoglycemic effect, crystallizes in space group P21/c. The structure is held together by a network of intermolecular N—H⋯N hydrogen bonds.

(3-Methoxy­phenyl)­acetic acid

Abstract: The title compound, C9H10O3, also known as (m-methoxy­phenyl)­acetic acid, has been found to crystallize in the monoclinic space group P21/c at room temperature. It is the starting material for the synthesis of a large number of 1,2,3,4-tetra­hydro­iso­quinoline compounds [Nagarajan et al. (1985). Indian J. Chem. Sect. B, 24, 83–97]. The compound forms dimers in the crystalline state, with O—H⋯O hydrogen bonds between the carboxyl groups, across a crystallographic centre of symmetry.

Ethyl N-(5-bromo-3-phenyl­indol-2-yl)­carbamate

Abstract: The crystal structure of the title compound, C17H15BrN2O2, has been determined at room temperature The indole moiety is essentially planar and the structure is stabilized by intra- and intermolecular N-HO hydrogen bonds

Ab initio Structure Determination via Powder X-Ray Diffraction

Abstract: Structure determination by powder X-ray diffraction data has gone through a recent surge since it has become important to get to the structural information of materials which do not yield good quality single crystals. Although the method of structure completion when once the starting model is provided is facile through the Rietveld refinement technique, the structure solution ab initio is still not push-button technology. In this article a survey of the recent development in this area is provided with an illustration of the structure determination of alpha-NaBi3V2O10.