scholarly journals Low-temperature redetermination of benzofurazan 1-oxide

2009 ◽  
Vol 65 (6) ◽  
pp. o1275-o1275 ◽  
Author(s):  
Seik Weng Ng
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Room Temperature ◽  
Membered Ring ◽  
Temperature Structure ◽  
Double Bonds ◽  
Acta Cryst ◽  
Low Temperature Crystal Structure

In the six-membered ring of the low-temperature crystal structure of benzofurazan 1-oxide, C6H4N2O2, the two C atoms adjacent to the N atoms are linked by a delocalized aromatic bond [1.402 (2) Å]; each is connected to its neighbour by a longer, more localized, bond [1.420 (2), 1.430 (2) Å]. However, the next two bonds in the ring approximate double bonds [1.357 (2), 1.366 (2) Å]. As such, the six-membered ring is better described as a cyclohexadiene system, in contrast to the description in the room-temperature structure reported by Britton & Olson (1979) [Acta Cryst.B35, 3076–3078].

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

scholarly journals TheZ′ = 12 superstructure of Λ-cobalt(III) sepulchrate trinitrate governed by C—H...O hydrogen bonds

2016 ◽  
Vol 72 (3) ◽  
pp. 372-380 ◽  
Author(s):  
Somnath Dey ◽  
Andreas Schönleber ◽  
Swastik Mondal ◽  
Siriyara Jagannatha Prathapa ◽  
Sander van Smaalen ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Structural Parameters ◽  
Molecular Packing ◽  
Nitrate Group ◽  
Structural Variations ◽  
Monoclinic Symmetry ◽  
Low Temperature Crystal Structure

Λ-Cobalt(III) sepulchrate trinitrate crystallizes inP6322 withZ= 2 (Z′ = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groupsAandB. Coordinated by six sepulchrate molecules, highly disordered nitrate groupsCare accommodated between the slabs. Here we report the fully ordered, low-temperature crystal structure of Co(sep)(NO3)3. It is found to be a high-Z′ structure withZ′ = 12 of the 12-fold 6a_{h}\times\sqrt{3}b_{h}\times c_{h} superstructure with monoclinic symmetryP21(cunique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate groupC, the latter assuming different orientations for each of theZ′ = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groupsAandBvary less than the orientations of the nitrate groupCdo. Molecular packing in the superstructure is found to be determined by short C—H...H—C contacts, with H...H distances of 2.2–2.3 Å, and by short C—H...O contacts, with H...O distances down to 2.2 Å. These contacts presumably represent weak C—H...O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N—H...O hydrogen bonds with observed H...O distances of 2.4–2.6 Å.

Synthese und Kristallstrukturen von N-[ω-(Dimethylammonio)alkyl]- N´,N´,N´´,N´´-tetramethylguanidinium-chlorid-tetraphenylboraten / Synthesis and Crystal Structures of N-[ω-(Dimethylammonio)alkyl]-N´,N´,N´´,N´´- tetramethylguanidinium Chloride Tetraphenylborates

2010 ◽  
Vol 65 (7) ◽  
pp. 907-916 ◽  
Author(s):  
Ioannis Tiritiris ◽  
Falk Lissner ◽  
Thomas Schleid ◽  
Willi Kantlehner
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Hydrogen Bonds ◽  
Crystal Structures ◽  
Room Temperature ◽  
Chloride Ions ◽  
Monoclinic Space Group ◽  
Temperature Structure ◽  
Space Group ◽  
Temperature Modification

Dicationic N,N´,N´,N´´,N´´-pentasubstituted guanidinium dichlorides 4a, b are obtained from the chloroformamidinium salt 2 and diamines 3a, b. N-[2-(Dimethylammonio)ethyl]-N´,N´,N´´,N´´-tetramethylguanidinium chloride tetraphenylborate (5a) and N-[3-(dimethylammonio)propyl]-N´,N´,N´´,N´´-tetramethylguanidinium chloride tetraphenylborate (5b) were synthesized from 4a, b by anion metathesis with one equivalent of sodium tetraphenylborate. The thermal properties of the salts 5a, b were studied by means of DSC methods, and their crystal structures were determined by single-crystal X-ray diffraction analysis. For 5a a solid-solid phase transition is observed at −156 ◦C to a low-temperature structure. The room-temperature modification (α-5a) crystallizes in the centrosymmetric orthorhombic space group Pbca (a = 13.1844(4), b = 13.8007(4), c = 34.7537(11) A° ).The guanidinium ions are interconnected via chloride ions through bridging N-H· · ·Cl hydrogen bonds, providing isolated units. The tetraphenylborate ions show some dynamic disordering in the crystal structure. The low-temperature modification (β -5a) also crystallizes orthorhombically, but in the non-centrosymmetric space group Pna21 (a = 13.1099(4), b = 69.1810(11), c = 13.5847(5) A° ) and consists of four crystallographically independent cations and anions in the unit cell. Compared with the room-temperature structure, a similar N-H· · ·Cl hydrogen bond pattern is observed in the β -phase, but the tetraphenylborate ions are now completely ordered. 5b crystallizes in the monoclinic space group P21/c (a = 10.8010(3), b = 14.1502(5), c = 20.9867(9) A° , β = 94.322(1)◦). In the crystal structure the guanidinium ions are linked via chloride ions through N-H· · ·Cl hydrogen bonds, but in contrast to 5a two infinite strands are formed along the a axis with the tetraphenylborate ions interspersed between them for charge compensation.

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.

Thermally Induced Symmetry and Disorder: The Low-Temperature Crystal Structure of Diaquadichlorodimethyltin · 15-crown-5

1996 ◽  
Vol 1 (3) ◽  
pp. 359-363 ◽  
Author(s):  
Glenn P. A. Yap ◽  
Mostafa M. Amini ◽  
Seik W. Ng ◽  
Anne E. Counterman ◽  
Arnold L. Rheingold
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Thermally Induced ◽  
Low Temperature Crystal Structure

Single-Crystal X-Ray Scattering Study of Superstructures and Phase Transitions in Graphite-Hno3 and Graphite-Br2 Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
R. Moret ◽  
R. Comes ◽  
G. Furdin ◽  
H. Fuzellier ◽  
F. Rousseaux
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Room Temperature ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray ◽  
X Ray Scattering ◽  
Scattering Study ◽  
Temperature Liquid ◽  
Low Temperature Phase

ABSTRACTIn α-C5n-HNO3 the condensation of the room-temperature liquid-like diffuse ring associated with the disorder-order transition around 250 K is studied and the low-temperature. superstructure is examined.It is found that β-C8n-HNO3 exhibits an in-plane incommensurate order at room temperature.Two types of graphite-Br2 are found. Low-temperature phase transitions in C8Br are observed at T1 ≍ 277 K and T2 ≍ 297 K. The room-temperature structure of C14Br is reexamined. Special attention is given to diffuse scattering and incommensurability.

The role of hydrogen bonds in order-disorder transition of a new incommensurate low temperature phase β-[Zn-(C7H4NO4)2]·3H2O

2018 ◽  
Vol 233 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Masoumeh Tabatabaee ◽  
Morgane Poupon ◽  
Václav Eigner ◽  
Přemysl Vaněk ◽  
Michal Dušek
Keyword(s):  
Low Temperature ◽  
Hydrogen Bonds ◽  
Dicarboxylic Acid ◽  
Room Temperature ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Modulated Structure ◽  
Q Vector ◽  
Low Temperature Phase

AbstractThe room temperature structure withP21/csymmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid.Acta Crystallogr. C.2000,56, 305). Here we report crystal structure of the low temperature phaseβ-[Zn(pydcH)2]·3H2O, pydc=C7H3NO4, resulting from the phase transition around 200K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3+1)Dincommensurately modulated structure. The modulated structure was solved in the superspace groupX21/c(0b0)s0, whereXstands for a non-standard centring vector (½, 0, 0, ½), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.

scholarly journals Two polymorphs of 1,8-dichloroanthracene

2013 ◽  
Vol 69 (2) ◽  
pp. 199-203 ◽  
Author(s):  
Peter Müller ◽  
Frank R. Fronczek ◽  
Stacey J. Smith ◽  
Teresa Mako ◽  
Mindy Levine
Keyword(s):  
Low Temperature ◽  
Crystal Packing ◽  
Three Dimensional ◽  
Crystal Form ◽  
Temperature Structure ◽  
Orthorhombic Crystal ◽  
Acta Cryst ◽  
Monoclinic Form ◽  
Compound C ◽  
Dimensional Network

A second, monoclinic, polymorph of the title compound, C14H8Cl2, has been found. In addition to the structure of this monoclinic form, the structure of the previously described orthorhombic form [Desvergne, Chekpo & Bouas-Laurent (1978).J. Chem. Soc. Perkin Trans. 2, pp. 84–87; Benites, Maverick & Fronczek (1996).Acta Cryst.C52, 647–648] has been redetermined at low temperature and using modern methods. The low-temperature structure of the orthorhombic form is of significantly higher quality than the previously published structure and additional details can be derived. A comparison of the crystal packing of the two forms with a focus on weak intermolecular C—H...Cl interactions shows the monoclinic structure to have one such interaction linking the molecules into infinite ribbons, while two crystallographically independent C—H...Cl interactions give rise to an interesting infinite three-dimensional network in the orthorhombic crystal form.

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