Kristallstruktur und thermische Phasenumwandlung von Tetramethylammoniumcyanid, (CH3)4N+CN- / Crystal Structure and Thermal Phase Transition of Tetramethylammonium Cyanide, (CH3)4N+CN-

1999 ◽  
Vol 54 (3) ◽  
pp. 372-376 ◽  
Author(s):  
Andreas Komath ◽  
Oliver Blecher
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Room Temperature ◽  
Temperature Phase ◽  
Cyanide Ion ◽  
Space Group ◽  
Disorder Transition ◽  
Thermal Phase Transition ◽  
Cell Dimensions ◽  
Thermal Phase

Tetramethylammonium cyanide crystallizes in the tetragonal space group P4/nmm, Z = 2, with cell dimensions a = 773.6(1), c = 546.8(1) pm. The cyanide ion is disordered in the plane perpendicular to the c-axis indicating a rotation. The room temperature phase undergoes a thermal phase transition at -59.9°C probably caused by an order-disorder transition of the cyanide ion.

Structure at 200 and 298 K and X-ray investigations of the phase transition at 242 K of [NH2(CH3)2]3Sb2Cl9 (DMACA)

1996 ◽  
Vol 52 (2) ◽  
pp. 287-295 ◽  
Author(s):  
J. Zaleski ◽  
A. Pietraszko
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Temperature Phase ◽  
Space Group ◽  
X Ray ◽  
Low Temperature Phase

[NH2(CH3)2]3Sb2Cl9 (dimethylammonium nonachlorodiantimonate, DMACA) has, at 200 K, a monoclinic Pc space group, with a = 9.470 (3), b = 9.034 (3), c = 14.080 (4) Å, β = 95.81 (3)°, V = 1198.4 (4) Å3, Z = 2 [R = 0.024, wR = 0.025 for 4613 independent reflections with F > 4σ(F)]. At 298 K DMACA has P21/c space group with a = 9.686 (3), b = 9.037 (3), c = 14.066 (4) Å, β = 95.57 (3)°, V = 1225.3 (5) Å3, Z = 2 [R = 0.034, wR = 0.035 for 2736 reflections with F > 4σ(F)]. The anionic sublattice of DMACA consists of polyanionic (Sb2Cl9 3−), layers. In the low-temperature phase there are three crystallographically non-equivalent dimethylammonium cations in the crystal structure. One of the cations is located inside the polyanionic layers, two others – one ordered and one disordered – between the polyanionic layers. In the room-temperature phase there are two non-equivalent cations – both disordered – in the crystal structure. Temperature dependencies of lattice parameters between 200 and 300 K were determined. The occurrence of a second-order phase transition at T = 242 K was confirmed. The dependence of lengths of Sb—Cl contacts on the presence and strength of N—H...CI hydrogen bonds was discussed. It was found that lengths of Sb—Cl bonds may differ from each other by as much as 0.3 Å, because of the presence of N—H...Cl hydrogen bonds. These differences were attributed to distortion of the lone-electron pair on antimony(Ill).

Betaine arsenate, (CH3)3NCH2COO · D3AsO4: structure refinement using multiple-wavelength synchrotron radiation data

1997 ◽  
Vol 212 (9) ◽  
Author(s):  
S. Kek ◽  
M. Grotepaß-Deuter ◽  
K. Fischer ◽  
K. Eichhorn
Keyword(s):  
Crystal Structure ◽  
Synchrotron Radiation ◽  
Room Temperature ◽  
Structure Refinement ◽  
Temperature Phase ◽  
Space Group ◽  
Radiation Data ◽  
Multiple Wavelength

AbstractThe crystal structure of deuterated betaine arsenate, (CHThe both paraelectric and ferroelastic room-temperature phase of betaine arsenate crystallizes in space group

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 127I NQR and Crystal Structure Studies of [N(CH3)4]2 CdI4

2000 ◽  
Vol 55 (1-2) ◽  
pp. 225-229 ◽  
Author(s):  
Hideta Ishihara ◽  
Keizo Horiuchi ◽  
Thorsten M. Gesing ◽  
Shi-qi Dou ◽  
J.-Christian Buhl ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Order Phase Transition ◽  
Intensity Ratio ◽  
Room Temperature ◽  
Liquid Nitrogen Temperature ◽  
Temperature Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

The temperature dependence of 127I NQR and DSC as well as the crystal structure at room temperature of the title compound were determined. This compound shows a first-order phase transition of an order-disorder type at 245 K. Eight 127I(v1:m = ±1/2 ↔ ±3/2) NQR lines of 79.57, 81.86, 82.56, 83.36, 84.68, 87.72, 88.34, and 88.86 MHz, and corresponding eight 127I(v2: m = ±3/2 ↔±5/2) NQR lines were observed at liquid nitrogen temperature. Three 127I(υi) NQR lines wfth an intensity ratio of 1:1:2 in the order of decreasing frequency were observed just above the transition point and two NQR lines except for the middle-frequency line disappeared around room temperature. This temperature behavior of NQR lines is very similar to that observed in [N(CH3)4]2Hgl4. Another first-order phase transition takes place at 527 K. The structure of the room-temperature phase was redetermined: orthorhombic, Pnma, Z = 4, a = 1342.8(3), b = 975.7(2), c = 1696.5(3) pm. The NQR result of three lines with an intensity ratio of 1:1:2 is in agreement with this structure. The thermal displacement parameters of atoms in both cations and anions are large.

Isotope Effect in TlH2PO4 and TlD2PO4

1998 ◽  
Vol 54 (6) ◽  
pp. 790-797 ◽  
Author(s):  
S. Ríos ◽  
W. Paulus ◽  
A. Cousson ◽  
M. Quilichini ◽  
G. Heger
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Room Temperature ◽  
Point Of View ◽  
Temperature Phase ◽  
Neutron Diffraction Data ◽  
Antiferroelectric Phase ◽  
Low Temperature Phase ◽  
Structural Point ◽  
Prototype Phase

The crystal structure of the antiferroelectric phase of TlD2PO4, deuterated thallium dihydrogenphosphate, has been determined from single-crystal neutron diffraction data collected at room temperature. The para-antiferroelectric transition (T_c^d = 353 K) of TlD2PO4 is analysed from a structural point of view and compared with the phase transition of TlH2PO4 at TI = 357 K, already characterized. The distinct phase sequences observed in the two compounds when decreasing temperature from that of the high-temperature prototype phase (prototype phase/room-temperature phase/low-temperature phase) are discussed and associated with the different ordering of the two crystallographically inequivalent H (D) atoms existing in the prototype phase.

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.

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 Structure and pseudosymmetry of cholesterol at 310 K

2002 ◽  
Vol 58 (2) ◽  
pp. 260-264 ◽  
Author(s):  
Leh-Yeh Hsu ◽  
Jeff W. Kampf ◽  
Christer E. Nordman
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Unit Cell ◽  
The Other ◽  
Temperature Phase ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form [Hsu & Nordman (1983). Science, 220, 604–606], has been fully refined using augmented X-ray data. The crystals are triclinic, space group P1, with (reassigned) cell parameters a = 27.565 (10), b = 38.624 (16), c = 10.748 (4) Å, α = 93.49 (3), β = 90.90 (3), γ = 117.15 (3)°, and V = 10151 (7) Å3. The unit cell contains Z = 16 molecules, of which eight are related to the other eight by unusual twofold rotational pseudosymmetry. The structure is related to the room-temperature phase, with Z = 8, by a rearrangement of some of the molecules, and by a doubling of the a axis.

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

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