scholarly journals Achirality in the low temperature structure and lattice modes of tris(acetylacetonate)iron(iii)

2016 ◽  
Vol 45 (19) ◽  
pp. 8278-8283
Author(s):  
Thomas K. Ellis ◽  
Gordon J. Kearley ◽  
Ross O. Piltz ◽  
Upali A. Jayasooriya ◽  
John A. Stride
Keyword(s):  
Molecular Dynamics ◽  
Low Temperature ◽  
Neutron Scattering ◽  
Coordination Complex ◽  
Temperature Structure ◽  
Space Group ◽  
Flexible Ligand ◽  
Ligand Shell ◽  
Lattice Modes

The relatively ubiquitous mononuclear inorganic coordination complex tris(acetylaceonate) iron(iii) has been studied using neutron scattering techniques. The molecular dynamics are shown to be dominated by motions of the highly flexible ligand shell in a non-chiral space group.

A Molecular Dynamics Study of SF6

1991 ◽  
Vol 02 (01) ◽  
pp. 413-417
Author(s):  
LU HUA ◽  
G.S. PAWLEY
Keyword(s):  
Molecular Dynamics ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Molecular Dynamics Method ◽  
Temperature Structure ◽  
Sulphur Hexafluoride ◽  
Space Group ◽  
Dynamics Method

The stress-free molecular dynamics method has been used to study the phases of sulphur hexafluoride (SF6). The low-temperature structure was found to be monoclinic of space group C2/m, and this is consistent with neutron diffraction experiments.

Towards a more reliable symmetry determination from powder diffraction: a redetermination of the low-temperature structure of 4-methylpyridine-N-oxide

2009 ◽  
Vol 65 (6) ◽  
pp. 784-786 ◽  
Author(s):  
Lukáš Palatinus ◽  
Françoise Damay
Keyword(s):  
Low Temperature ◽  
Powder Diffraction ◽  
Tunneling Spectroscopy ◽  
Temperature Structure ◽  
Determination Method ◽  
Neutron Data ◽  
Acta Cryst ◽  
Space Group ◽  
X Ray ◽  
New Space

The low-temperature structure of 4-methylpyridine-N-oxide was previously determined in symmetry P41 [Damay et al. (2006), Acta Cryst. B62, 627–633]. Using a recently published symmetry-determination method it was found that the true symmetry of the structure is P41212. The structure was refined in the new space group using X-ray and neutron data. The previously published structure is close to the newly refined structure, but the new structure is in agreement with the results of rotational tunneling spectroscopy, and, in contrast to the structure in symmetry P41, does not require a twofold degeneracy of the tunneling bands.

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.

The low-temperature crystal structure of the multiferroic melilite Ca2CoSi2O7

2016 ◽  
Vol 72 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Andrew Sazonov ◽  
Vladimir Hutanu ◽  
Martin Meven ◽  
Georg Roth ◽  
István Kézsmárki ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Low Temperature ◽  
Structural Parameters ◽  
Theoretical Description ◽  
Temperature Structure ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Precise Knowledge ◽  
Commensurate Phase

In the antiferromagnetic ground state, belowTN≃ 5.7 K, Ca2CoSi2O7exhibits strong magnetoelectric coupling. For a symmetry-consistent theoretical description of this multiferroic phase, precise knowledge of its crystal structure is a prerequisite. Here we report the results of single-crystal neutron diffraction on Ca2CoSi2O7at temperatures between 10 and 250 K. The low-temperature structure at 10 K was refined assuming twinning in the orthorhombic space groupP21212 with a 3 × 3 × 1 supercell [a= 23.52 (1),b= 23.52 (1),c= 5.030 (3) Å] compared with the high-temperature normal state [tetragonal space group P\overline {4}2_{1}m,a=b≃ 7.86,c≃ 5.03 Å]. The precise structural parameters of Ca2CoSi2O7at 10 K are presented and compared with the literature X-ray diffraction results at 130 and 170 K (low-temperature commensurate phase), as well as at ∼ 500 K (high-temperature normal phase).

Order and disorder in acenaphthylene

1973 ◽  
Vol 334 (1596) ◽  
pp. 19-48 ◽  
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Temperature Structure ◽  
Intermediate Form ◽  
X Ray Diffraction ◽  
Space Group ◽  
Order And Disorder ◽  
Temperature Form ◽  
Diffraction Effects

Acenaphthylene, C 12 H 8 , occurs in space group Pbam (or Pba2) at room temperatures (23 °C) with a = 7.705 (5), b = 7.865 (5), c = 14.071 (5) Å and Z = 4, and is disordered. At about 130 K it undergoes a reversible transition to space group P2 1 nm with a = 7.588 (13), b = 7.549 (10), c = 27.822 (2) Å and Z = 8 (85 K) with an ordered structure. A general study of the system has revealed that the structure of both forms consists of layers of closely packed molecules stacked in the c direction. The room temperature structure has a two-layer repeat and the low temperature form a four-layer repeat. Observation of diffuse X-ray diffraction effects at temperatures close to the transition indicates that an intermediate form having a six-layer repeat is formed. A preliminary structure determination of the low-temperature form reveals that the four layers though having a similar packing scheme differ in the orientation of the constituent molecules relative to c . It is proposed that the almost circular shape of the molecules allows each layer to change its identity under thermal agitation by a rotation of its constituent molecules in their own planes. The transition can be explained in terms of changes of the correlations between neighbouring layers. A simple model based on short-range order parameters is described, which explains the occurrence of the six-layer intermediate and the observed sequence of diffuse diffraction phenomena. The nature of the structure of the disordered room temperature form, which is predicted by this model, is confirmed as far as possible with the data available which are limited because of the dearth of high-angle diffraction maxima.

A study of the low-temperature structure of SF6

1992 ◽  
Vol 202 (3-4) ◽  
Author(s):  
Lu Hua ◽  
G. Stuart Pawley
Keyword(s):  
Molecular Dynamics ◽  
Low Temperature ◽  
Molecular Dynamics Method ◽  
Temperature Structure ◽  
Array Processor ◽  
Distributed Array ◽  
Dynamics Method

AbstractThe stress-free molecular dynamics method has been carried out on a Distributed Array Processor (DAP) to study the phases of SF

scholarly journals Evidence for differentiation in the iron-helicoidal chain in GdFe3(BO3)4

2005 ◽  
Vol 61 (5) ◽  
pp. 481-485 ◽  
Author(s):  
S. A. Klimin ◽  
D. Fausti ◽  
A. Meetsma ◽  
L. N. Bezmaternykh ◽  
P. H. M. van Loosdrecht ◽  
...  
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Structural Phase ◽  
Structure Study ◽  
Temperature Structure ◽  
Space Group ◽  
X Ray ◽  
First Order ◽  
New Perspective ◽  
Insight Into

A single-crystal X-ray structure study of gadolinium triiron tetraborate, GdFe_3(BO_3)_4, at room temperature and at 90 K is reported. At room temperature GdFe_3(BO_3)_4 crystallizes in a trigonal space group, R32 (No. 155), the same as found for other members of the iron borate family RFe_3(BO_3)_4. At 90 K the structure of GdFe_3(BO_3)_4 transforms to the space group P3_{1}21 (No. 152). The low-temperature structure determination gives new insight into the weakly first-order structural phase transition at 156 K and into the related Raman phonon anomalies. The presence of two inequivalent iron chains in the low-temperature structure provides a new perspective on the interpretation of the low-temperature magnetic properties.

The low-temperature structure and phase transition of hemimorphite, Zn4Si2O7(OH)2 · H2O

1998 ◽  
Vol 213 (12) ◽  
Author(s):  
E. Libowitzky ◽  
A. J. Schultz ◽  
D. M. Young
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Temperature Structure ◽  
Space Group

AbstractThe low-temperature structure of hemimorphite, ZnAccording to the general reflection conditions, the low-temperature superstructure of hemimorphite was refined in space group

Low-Temperature Structure and Magnetic Properties of Tetraphenylarsonium Tetrachloronitridotechnetate(VI)

1996 ◽  
Vol 49 (5) ◽  
pp. 633 ◽  
Author(s):  
BN Figgis ◽  
PA Reynolds ◽  
FK Larsen ◽  
GA Williams ◽  
CD Delfs
Keyword(s):  
Crystal Structure ◽  
Magnetic Properties ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Single Crystals ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
Magnetic Susceptibilities ◽  
Space Group ◽  
X Ray

The crystal structure of [As(C6H5)4] [TcNCl4] was determined at 120 K by X-ray diffraction and at 28 K by neutron diffraction. The crystals are tetragonal, space group P4/n, with a 1260.4(3) and c 773.2(2) pm at 120 K. The [TcNCl4]-anion possesses exact C4v symmetry, with Tc≡N distances of 160.3(2) and 162.5(4)pm at 120 and 28 K respectively. Magnetic susceptibilities were measured on single crystals from 300 to 4.5 K. The results indicate a well behaved S ½ system following the Curie-Weiss law with θ -0.13 K

Sign in / Sign up

Export Citation Format

Share Document