Investigation of the Cs x Rb1−x TiOAsO4 Series. I. Crystal Structure Analysis and Pseudo-symmetry

1998 ◽  
Vol 54 (5) ◽  
pp. 635-644 ◽  
Author(s):  
M. N. Womersley ◽  
P. A. Thomas ◽  
D. L. Corker
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Room Temperature ◽  
Structural Changes ◽  
Crystal Structure Analysis ◽  
Orthorhombic Space Group ◽  
Acta Cryst ◽  
Space Group ◽  
Structural Framework

Refinements of five crystals in the Cs2x Rb2−2x Ti2O2As2O8 series, caesium rubidium titanyl arsenate, with x = 0.07, 0.31, 0.58, 0.71 and 0.86, which are compositional analogues of KTiOPO4 (KTP), have been completed at 293 K and two (x = 0.71, 0.86) at low temperature. All the structures are found to be orthorhombic (space group Pna21) and are isostructural with KTP, although there is evidence of some Cs disorder over additional sites in the framework, particularly at the Cs-rich end of the series, as discussed in Part II [Thomas & Womersley (1998). Acta Cryst. B54, 645–651]. Unusually large U 33 parameters for shared Cs/Rb sites are observed and are shown to be the result of the existence of separate sites for Cs and Rb within the structural framework, although the coordinates of these sites cannot be resolved convincingly. The structural changes in the TiO6/AsO4 framework required to accommodate an increasing fraction of the larger Cs cation across the series and under cooling to 120 K are elucidated. Finally, the deviations of the room-temperature and low-temperature structures from the high-temperature prototypic structure (space group Pnan) are examined and suggest that the phase-transition temperature should increase linearly from CsTiOAsO4 to RbTiOAsO4.

scholarly journals A variable-temperature study of a phase transition in barbituric acid dihydrate

2005 ◽  
Vol 61 (4) ◽  
pp. 464-472 ◽  
Author(s):  
Gary S. Nichol ◽  
William Clegg
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Barbituric Acid ◽  
Crystal Packing ◽  
Variable Temperature ◽  
Mirror Plane ◽  
Monoclinic Space Group ◽  
Orthorhombic Space Group ◽  
Acta Cryst ◽  
Space Group

The crystal structure of barbituric acid dihydrate (C4H4N2O3·2H2O) has twice been reported as orthorhombic, space group Pnma, with all atoms (except for CH2 H atoms) lying on the mirror plane [Al-Karaghouli et al. (1977). Acta Cryst. B33, 1655–1660; Jeffrey et al. (1961). Acta Cryst. 14, 881–887]. The present study has found that at low temperatures, below 200 K, the crystal structure is no longer orthorhombic but is non-merohedrally twinned monoclinic, space group P21/n. This phase is stable down to 100 K. Above 220 K the crystal structure is orthorhombic, and between 200 and 220 K the structure undergoes a phase change, with the monoclinic-to-orthorhombic phase transition itself taking place at around 216–217 K. The size of the β angle in the monoclinic structure is temperature dependent; at 100 K β is around 94° and it decreases in magnitude towards 90° as the temperature increases. Although the hydrogen-bonding motifs are the same for both crystal systems, there are significant differences in the crystal packing, in particular the out-of-plane displacement of the two water molecules and the sp 3-hybridized C atom of barbituric acid.

Order-Disorder Phase Transition in NaBD4

2004 ◽  
Vol 443-444 ◽  
pp. 287-290 ◽  
Author(s):  
P. Fischer ◽  
Andreas Züttel
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Structure Model ◽  
Space Group ◽  
Disorder Phase Transition ◽  
Low Temperature Crystal Structure ◽  
Disorder Type

By means of neutron diffraction the low-temperature crystal structure of NaBD4 has been determined. At 10 K the lattice parameters are a = 4.332(1) Å and c = 5.869(1) Å. Deuterium is found in a tetrahedral arrangement [sites (8g)] around B. The symmetry corresponds to space group P42/nmc. For room temperature the structure model for NaBD4 of Davis and Kennard with disordered deuterium distributed over two sites has been revised to space group Fm-3 m. Thus the 190 K phase transition known from specific heat measurements is of order-disorder type, caused by reorientations of BD4 tetrahedra.

NQR and Crystal Structure of 4,5-Dichloroimidazole, C3H2N2Cl2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Unit Cell ◽  
Space Group ◽  
Temperature Range ◽  
Temperature Coefficients ◽  
Group D

AbstractThe two line 35Cl NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77≦ T/K ≦ 389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v ( 35Cl)= f(T). Also the temperature coefficients of the 35Cl NQR frequencies are "normal". At 77 K the 35Cl NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D44-P41212, Z = 8 molecules per unit cell; at 295 K : a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed.

scholarly journals Crystal structure of 8-hydroxyquinoline: a new monoclinic polymorph

2014 ◽  
Vol 70 (9) ◽  
pp. o924-o925 ◽  
Author(s):  
Raúl Castañeda ◽  
Sofia A. Antal ◽  
Sergiu Draguta ◽  
Tatiana V. Timofeeva ◽  
Victor N. Khrustalev
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Three Dimensional ◽  
Solvent Mixture ◽  
Acta Cryst ◽  
Space Group ◽  
Compound C ◽  
Centrosymmetric Dimers

In an attempt to grow 8-hydroxyquinoline–acetaminophen co-crystals from equimolar amounts of conformers in a chloroform–ethanol solvent mixture at room temperature, the title compound, C9H7NO, was obtained. The molecule is planar, with the hydroxy H atom forming an intramolecular O—H...N hydrogen bond. In the crystal, molecules form centrosymmetric dimersviatwo O—H...N hydrogen bonds. Thus, the hydroxy H atoms are involved in bifurcated O—H...N hydrogen bonds, leading to the formation of a central planar four-membered N2H2ring. The dimers are bound by intermolecular π–π stacking [the shortest C...C distance is 3.2997 (17) Å] and C—H...π interactions into a three-dimensional framework. The crystal grown represents a new monoclinic polymorph in the space groupP21/n. The molecular structure of the present monoclinic polymorph is very similar to that of the orthorhombic polymorph (space groupFdd2) studied previously [Roychowdhuryet al.(1978).Acta Cryst.B34, 1047–1048; Banerjee & Saha (1986).Acta Cryst.C42, 1408–1411]. The structures of the two polymorphs are distinguished by the different geometries of the hydrogen-bonded dimers, which in the crystal of the orthorhombic polymorph possess twofold axis symmetry, with the central N2H2ring adopting a butterfly conformation.

Spontaneous deformation of protocatechuic acid monohydrate crystals: crystallographic aspects

1983 ◽  
Vol 387 (1793) ◽  
pp. 311-330 ◽  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonding ◽  
Single Crystal ◽  
Protocatechuic Acid ◽  
Crystal Structure Analysis ◽  
Stable Phase ◽  
Space Group ◽  
Molecular Arrangement ◽  
Two Phases

Remarkable aspects of the crystallization of 3,4-dihydroxybenzoic acid (protocatechuic acid, PCA) from water as described by R. W. Wood ( Proc. R. Soc. Lond . A 197,283-294 (1949)) are confirmed. This compound crystallizes as the monohydrate in four different polymorphic phases: three are triclinic (oblique needles, needles and rhombs) and belong to one subgroup, while the fourth, monoclinic, phase constitutes a separate subgroup. It is probable that the triclinic rhombs are the stable phase at 25° C, with the other phases monotropically related to it. Crystal data for the triclinic needles are a = 9.926(9), b = 9.532(9), c = 8.131(8)Å, α = 100.8(1), β = 90.7(1), γ = 102.4(1)°, Z = 4, space group P1 - ; and for th e triclinic rhombs a = 12.693(9), b = 8.011(6), c = 8.121(6) Å, α = 72.2(1), β = 108.5(1), γ = 103.2(1)°, Z = 4, space group P1 - . Both crystals can be described in terms of a unit cell containing eight formula units, with dimensions a ≈ 12.7, b ≈ 9.5, c ≈ 13.0 Å, α ≈ 88, β ≈ 101, γ ≈ 107°; the space group for the triclinic needles is B1 - and for the triclinic rhombs A1 - . Crystal structure analyses (four-circle diffractometer, MoKα) of these two phases (triclinic needles, 1287 reflexions used in the final refinement cycle, R F = 11.1%; triclinic rhombs, 1761 reflexions, R F = 6.9%) show that both contain essentially similar layer pairs of PCA and H 2 O molecules, with hydrogen bonding both within each layer and, apparently, between them; however, the stacking of the layer pairs in the two phases differs. The crystals of the oblique needles are so small and unstable to stress that crystal structure analysis was not possible. The crystal structure of the monoclinic needles ( a = 12.32(1), b = 3.64(1), c = 17.60(2) Å, β = 107.7(2)°, Z = 4, space group P2 1 / n was determined (CuK α , 787 reflexions, R F = 6.8%); the overall molecular arrangement differs from that in the triclinic phases in an absence of PCA•H 2 O layers although there are distinct resemblances between the hydrogen bonding schemes. The phase transition ‘oblique needles → triclinic needles’ is ‘single crystal to single crystal’ and is a topotaxic transition. The phase transition ‘triclinic needles → triclinic rhombs’ is ‘single crystal to oriented polycrystal’ and is described as partially topotaxic, there being preservation of layer arrangement but not of complete three-dimensional orientation.

Die Kristallstruktur von 2,4-Diaminovinamidinium-bis-tetrachloroferrat(III), (C9H16N4) [FeCl4]2 / The Crystal Structure of 2,4-Diaminovinamidinium Bis-tetrachloroferrate(III), (C9H16N4)[FeCl4]

1996 ◽  
Vol 51 (8) ◽  
pp. 1137-1140 ◽  
Author(s):  
Michael Feist ◽  
Sergej Trojanov ◽  
Erhard Kemnitz
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Aqueous Solutions ◽  
Room Temperature ◽  
Orthorhombic Space Group ◽  
Interatomic Distances ◽  
Space Group

(davaH2)[FeCl4]2 crystallizes at room temperature from aqueous solutions of 2,4-diaminovinamidinium hydrochloride, (davaH)Cl, and FeCl3 in 3M HCl in the orthorhombic space group Pca21 with a=14.108(3), b = 16.502(3), c = 18.919(4) Å, Z=8. The structure consists of diprotonated tricyclic (davaH2)2+ cations and slightly distorted tetrahedral [FeCl4]- anions. The cations are bent around the central heptacycle forming boat-like units. One of the two independent cations is disordered between two positions. Some interatomic distances N···Cl are interpreted in terms of N-H···Cl hydrogen bonds.

Low-temperature crystal structure of RS-thiocamphor

2004 ◽  
Vol 219 (9) ◽  
Author(s):  
E. Louise R. Robins ◽  
Michela Brunelli ◽  
Asiloé J. Mora ◽  
Andrew N. Fitch
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Low Temperature ◽  
Room Temperature ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Two Phase ◽  
X Ray ◽  
Low Temperature Crystal Structure

AbstractDSC and high-resolution powder X-ray diffraction measurements in the range 295 K–100 K show that RS-thiocamphor undergoes two phase transitions. The first, at around 260 K on cooling, is from the room-temperature body-centred-cubic phase to a short-lived intermediate. At 258 K the low-temperature form starts to appear. The crystal structure of the latter is orthorhombic, space group

Polysulfonylamine, CIII [1] Ein Hydroxylamin mit bemerkenswert kurzer O-N-B Bindung: Kristall- und Molekülstruktur von MeO-N(SO2Me)2 / Polysulfonylamines, C III [1] A Hydroxylamine with a Remarkably Short O-N Bond: Crystal and Molecular Structure of MeO-N(SO2Me)2

1998 ◽  
Vol 53 (5-6) ◽  
pp. 634-636 ◽  
Author(s):  
Martina Näveke ◽  
Armand Blaschette ◽  
Peter G. Jones
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Low Temperature ◽  
Title Compound ◽  
Crystal And Molecular Structure ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Bond Angles

Abstract The crystal structure of the known title compound was determined by low-temperature X-ray diffraction (orthorhombic, space group Pbcn, Z = 4). The molecule displays an unusually short O-N bond, a relatively long C-O bond and a moderately pyramidal O-NS2 skeleton (O-N 133.1, C-O 148.5 pm, sum of bond angles at N: 347.4°).

A New Allotropic Form of Bi2O3

1998 ◽  
Vol 547 ◽  
Author(s):  
N. Kumada ◽  
N. Kinomura
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Single Crystals ◽  
Bismuth Oxide ◽  
Hydrothermal Reaction ◽  
Starting Material ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Allotropic Form ◽  
R Factors

AbstractSingle crystals of a new allotropic form of bismuth sesquioxide, Bi2O3 were prepared by low temperature hydrothermal reaction using hydrated sodium bismuth oxide, NaBiO3·nH2O, as a starting material. This bismuth oxide crystallized in the orthorhombic space group Pccn with a=12.732(2), b=4.955(2) and c=5.582(2)Å, z=4, and the R-factors were R=0.030 and Rw=0.030 for 1702 unique reflections. The crystal structure is built up by corner- and edge-sharing of irregular BiO5 polyhedra and the tunnel is running along the c-axis.

scholarly journals The low-temperature triclinic crystal structure of silver 3-sulfobenzoic acid

2020 ◽  
Vol 76 (8) ◽  
pp. 1275-1278
Author(s):  
Reuben T. Bettinger ◽  
Philip J. Squattrito ◽  
Darpandeep Aulakh
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Room Temperature ◽  
Monoclinic Structure ◽  
Structure Space ◽  
Reversible Phase Transition ◽  
Triclinic Structure ◽  
Reversible Phase ◽  
Acidic Hydrogen

Poly[(μ4-3-carboxybenzenesulfonato)silver(I)], Ag(O3SC6H4CO2H) or [Ag(C7H5O5S)] n , has been found to undergo a reversible phase transition from monoclinic to triclinic between 160 and 150 K. The low-temperature triclinic structure (space group P\overline{1}) has been determined at 100 K. In contrast to the reported room temperature monoclinic structure, in which the nearly equivalent carboxylate C—O distances indicate that the acidic hydrogen is randomly distributed between the O atoms, at 100 K the C—O (protonated) and C=O (unprotonated) bonds are clearly resolved, resulting in the reduction in symmetry from C2/c to P\overline{1}.

Sign in / Sign up

Export Citation Format

Share Document