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.

X-ray powder diffraction data of anilinium trimolybdate tetrahydrate and anilinium trimolybdate dihydrate

1999 ◽  
Vol 14 (4) ◽  
pp. 280-283 ◽  
Author(s):  
A. Rafalska-Łasocha ◽  
W. Łasocha ◽  
M. Michalec
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Room Temperature ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns

The X-ray powder diffraction patterns of anilinium trimolybdate tetrahydrate, (C6H5NH3)2Mo3O10·4H2O, and anilinium trimolybdate dihyhydrate, (C6H5NH3)2Mo3O10·2H2O, have been measured in room temperature. The unit cell parameters were refined to a=11.0670(7) Å, b=7.6116(8) Å, c=25.554(3) Å, space group Pnma(62) and a=17.560(2) Å, b=7.5621(6) Å, c=16.284(2) Å, β=108.54(1)°, space group P21(4) or P21/m(11) for orthorhombic anilinium trimolybdate tetrahydrate and monoclinic anilinium trimolybdate dihydrate, respectively.

Reactions between Co(II), 1,2-bis(diphenylphosphino)ethane, and NaBH3CN in the presence and absence of CO. The crystal structure of bis(cyanotrihydroborato)tetrakis(N,N-dimethylformamide)cobalt(II)

1988 ◽  
Vol 66 (7) ◽  
pp. 1770-1775 ◽  
Author(s):  
David J. Elliot ◽  
Sanna Haukilahti ◽  
David G. Holah ◽  
Alan N. Hughes ◽  
Stanislaw Maciaszek ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
R Factor

Reactions between Co(II), Diphos, and NaBH3CN lead to Co(BH3CN)2(Diphos)2, 1, or [Co(BH3CN)(Diphos)2]X, 2 (X = ClO4 or BPh4), and, in certain solvents, 2 reacts to produce [Co(CN)(Diphos)2](ClO4). Compound 1 can be reversibly converted to Co(BH3CN)2(DMF)4, 4, via Co(BH3CN)2(Diphos)(DMF). In addition, 1 reacts with CO to form the Co(I) and Co(III) compounds [Co(Diphos)2](CO)]X and [Co(Diphos)2(CN)2]X (X = BH3CN or BPh4). Single crystal X-ray diffraction studies of 4 show that the compound crystallizes in the triclinic space group [Formula: see text], with unit cell parameters a = 7.572(6), b = 9.695(6), c = 9.395(6) Å, α = 81.06(4), β = 68.46(5), γ = 68.19(5)°, V = 595.5 Å3, Z = 1, and dcalcd = 1.202 g cm−3. The structure converged to a conventional R factor of 0.040 for 2841 observations and showed an octahedral arrangement of four O atoms from DMF molecules and two trans N-bound BH3CN groups around the Co(II) center.

Phase Transitions in Tris(3,5-dimethylpyrazol-1-yl)methane. The Structure of the High-Temperature Phase from X-ray Powder Diffraction

1997 ◽  
Vol 53 (6) ◽  
pp. 939-944 ◽  
Author(s):  
L. E. Ochando ◽  
J. Rius ◽  
D. Louër ◽  
R. M. Claramunt ◽  
C. Lopez ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
High Temperature Phase ◽  
Unit Cell ◽  
Temperature Phase ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Search Structure ◽  
Patterson Search

The crystal structure of the sublimated form (m.p. = 424 K) of tris(3,5-dimethylpyrazol-l-yl)methane has been solved by a Patterson search method from laboratory X-ray powder diffraction data. Crystal data: trigonal symmetry with the unit-cell parameters a = 16.152 (1) and c = 5.353 (1) Å, space group P3, C16H22N6, Z = 3, 293 K. After indexing the powder pattern by two methods, the unit-cell parameters found were refined by a least-squares technique. A whole pattern-fitting program was used to extract the integrated intensities. The structure was solved taking a related compound as a search model and the final Rietveld refinement converged to R wp = 0.077 and R p = 0.059. This study is one of the first examples of Patterson search structure determination from an hemihedral space group using powder data. The complexity of the structural determination is increased by the presence of three molecules in the asymmetric unit.

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).

Structures and phase transition of three isomers of 1-phenylindolin-2-one derivatives: 6-chloro-1-phenylindolin-2-one, 4-chloro-1-phenylindolin-2-one and 1-(3-chlorophenyl)indolin-2-one

2018 ◽  
Vol 74 (12) ◽  
pp. 1750-1758
Author(s):  
Bing Wang ◽  
Qi Fang
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Phenyl Ring ◽  
Density Functional ◽  
Room Temperature ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Functional Theory ◽  
Triclinic Space Group ◽  
Space Group

Three 1-phenylindolin-2-one derivatives, namely 6-chloro-1-phenylindolin-2-one (A), 4-chloro-1-phenylindolin-2-one (B) and 1-(3-chlorophenyl)indolin-2-one (C), all C14H10ClNO, have been synthesized and the structures of these compounds at room temperature (A RT, B RT and C RT) and low temperature (A LT, B LT and C LT) have been determined. Crystal A at 295 K (A RT) crystallized in the monoclinic space group P21/c and the phenyl ring of the unique molecule exhibits disorder over two positions. At low temperature, the disorder disappeared and crystal A at 90 K (A LT) crystallized in the triclinic space group P\overline{1} with a doubled unit-cell volume and four molecules in the asymmetric unit. Density functional theory (DFT) calculations revealed a low oscillation barrier (0.24 kcal mol−1) of the phenyl ring of molecule A and the phase transition from the P21/c structure to the P\overline{1} structure can be interpreted in terms of the freezing out of the two conformations at low temperature. Crystal B retains space group P21/c in the temperature range from 100 to 297 K. A kind of obtuse-cell to acute-cell change can be recognized; if the unit cell of B LT at 100 K is set to be a standard obtuse cell [β = 90.341 (2)°] and the cell is kept untransformed in the course of temperature changing, the cell of B RT at 297 K was found to be acute [β = 89.288 (2)°]. The molecules in structure C are packed in layers, with C—H...O hydrogen bonds between neighbouring layers.

Neutron diffraction study of [Pt(en)2][Pt(en)2I2](ClO4)4 at 20 K: structure and evidence of a new phase transition

1996 ◽  
Vol 52 (5) ◽  
pp. 854-864 ◽  
Author(s):  
J.-F. Bardeau ◽  
A. Bulou ◽  
W. T. Klooster ◽  
T. F. Koetzle ◽  
S. Johnson ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Neutron Diffraction Study ◽  
The Other ◽  
Space Group ◽  
Cell Parameters ◽  
Diffraction Peaks ◽  
Expected Values ◽  
New Phase

The structure at 20 K of fully deuterated [Pt(en)2][Pt(en)2I2](ClO4)4, where en = ethylenediamine, has been determined by neutron diffraction on a single-crystal. It is shown that the symmetry is monoclinic with cell parameters a = 16.650 (7), b = 5.760 (2), c = 14.751 (2) Å and β = 99.19 (1)°, that is, with respect to the previously reported room-temperature structures, a doubling of the c parameter is observed. The space group is C2/c and the refinements lead to an R value of 0.0374. All the bond lengths (C—C, C—N, C—D, N—D and Cl—O) and angles are consistent with the expected values and the main difference with respect to the previously reported room-temperature structures results in an ordering of the stacking of the ethylenediamines. The iodines are distributed over two sites, which gives two Pt—I distances, 2.712 (3) Å, attributed to the PtIV—I bond, and 3.048 (3) Å, attributed to PtII—I. Actually, very weak diffraction peaks that provide evidence for an additional doubling of the a and b parameters are also observed and a space group C2 is therefore proposed. This could result from a very slight ordering of the chains with respect to one another, but, due to the weakness of such signals and the large number of atoms to be considered, no reliable refinement has been obtained in C2. On the other hand, on heating the crystal the diffraction peaks with I odd greatly decrease in intensity between 150 and 160 K, which unambiguously argues for the existence of a phase transition presumably connected to an order—disorder of the ethylenediamines.

X-ray powder diffraction data for nicotine 3,5-dihydroxybenzoate dihydrate, C10H15N2⋅C7H5O4⋅2H2O

2021 ◽  
pp. 1-4
Author(s):  
Ji Yang ◽  
Zhi Hua Liu ◽  
Rui Zhi Zhu ◽  
Neng Jun Xiang ◽  
Shi Yun Tang ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

Nicotine 3,5-dihydroxybenzoate dihydrate is a nicotine salt and can be used as compositions in tobacco products. X-ray powder diffraction data, unit-cell parameters, and space group for nicotine 3,5-dihydroxybenzoate, C10H15N2⋅C7H5O4⋅2H2O, are reported [a = 8.424(1) Å, b = 13.179(8) Å, c = 8.591(1) Å, α = 90°, β = 102.073(8)°, γ = 90°, unit-cell volume V = 932.765(3) Å3, Z = 2, ρcal = 1.256 g⋅cm−3, and space group P21] at room temperature. All measured lines were indexed and are consistent with the P21 space group.

X-ray powder diffraction data for eluxadoline nitrate monohydrate, C32H35N5O5⋅2HNO3⋅H2O

2020 ◽  
Vol 35 (3) ◽  
pp. 213-215
Author(s):  
Xin Wei ◽  
Zi Li Suo ◽  
Man Zhang ◽  
Pei Xiao Tang ◽  
Hui Li
Keyword(s):  
Diffraction Data ◽  
Room Temperature ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Peaks

Single-crystal and powder X-ray diffraction data, collected at room temperature, unit-cell parameters and space group for eluxadoline nitrate monohydrate, C32H35N5O5⋅2HNO3⋅H2O, are reported [a = 11.066(5) Å, b = 13.452(6) Å, c = 24.373(9) Å, unit-cell volume V = 3628.15 Å3, Z = 4, ρcal = 1.344 g⋅cm−3, and space group P212121]. All the diffraction peaks in the experimental pattern have been indexed and are consistent with the P212121 space group.

Powder diffraction investigations of 2,2′-Thiobis(4-methyl-6-tert-butylphenol) and 2,2′-Methylenebis(4-methyl-6-tert-butylphenol)

2005 ◽  
Vol 20 (1) ◽  
pp. 67-70
Author(s):  
B. Lasocha ◽  
M. Grzywa ◽  
W. Lasocha
Keyword(s):  
Room Temperature ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Monoclinic System ◽  
Orthorhombic System ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Phenol Derivatives

X-ray diffraction investigations of two phenol derivatives - 2,2′-Thiobis(4-methyl-6-tert-butylphenol) and 2,2′-Methylenebis(4-methyl-6-tert-butylphenol) were carried out. Both compounds at room temperature have similar cell volume and the same number of molecules in an unit cell. However, 2,2′-Thiobis(4-methyl-6-tert-butylphenol) crystallizes in the monoclinic system with unit cell parameters refined to a=0.8278(2) nm, b=1.2968(4) nm, c=1.9493(7) nm, β=90.93(2)°, space group P21∕n(14), whereas 2,2′-Methylenebis(4-methyl-6-tert-butylphenol) crystallizes in the orthorhombic system with unit cell parameters refined to a=1.6203(5) nm, b=1.2827(5) nm, c=1.0197(3) nm, space group Pna21(33). The investigated C22H30O2S turned out to be a new polymorph of 2,2′-Thiobis(4-methyl-6-tert-butylphenol).

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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