Enantiotropic phase transition in a binuclear tin complex with anO,N,O′-tridentate ligand

2013 ◽  
Vol 69 (11) ◽  
pp. 1336-1339 ◽  
Author(s):  
Anke Schwarzer ◽  
Lydia E. H. Paul ◽  
Uwe Böhme
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Tridentate Ligand ◽  
Asymmetric Unit ◽  
Disorder Transition ◽  
Vinyl Group

The crystal structure of chlorido{μ-2-[(2-oxidobenzylidene)amino]ethanolato-κ4O,N,O′:O′}{2-[(2-oxidobenzylidene)amino]ethanolato-κ3O,N,O′}trivinylditin(IV), [Sn2(C2H3)3(C9H9NO2)2Cl], is disordered above 178 K. A doubling of the unit-cell volume is observed on cooling. The asymmetric unit at 93 K contains two ordered molecules. The phase transition corresponds to an order–disorder transition of one vinyl group bound to the SnIVatom.

2,3,5′,6,6′,7-Hexamethoxy-3′H,10H-spiro[anthracene-9,1′-isobenzofuran]-3′,10-dione

2007 ◽  
Vol 63 (11) ◽  
pp. o4390-o4391 ◽  
Author(s):  
Marlon R. Lutz ◽  
Matthias Zeller ◽  
Daniel P. Becker
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Spiro Compound ◽  
Π Interactions ◽  
Rigid Molecule ◽  
Title Molecule ◽  
Solvent Molecules

The title molecule, C27H24O9, was formed via a transannular electrophilic addition of a putative cyclotriveratrylene triketone and is made up of an anthrone and an isobenzofuranone ring that are connected via one C atom to form a spiro compound. The anthracene and isobenzofuranone ring systems of the spiro compound are both essentially planar and perpendicular to each other, with an angle of 89.90 (2)° between them. The rigid molecule crystallizes with large voids of 598.7 Å3, or 21.5% of the unit-cell volume, that are partially filled with unmodelled disordered solvent molecules. The voids stretch as infinite channels along the [101] direction. The packing of the structure is partially stabilized by a range of weak C—H...O hydrogen bonds and also by C—H...π interactions. No significant π–π interactions are present in the crystal structure.

Atomic displacements at and order of all phase transitions in multiferroic YMnO3 and BaTiO3

2009 ◽  
Vol 65 (4) ◽  
pp. 450-457 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Landau Theory ◽  
Unit Cell ◽  
Paramagnetic Phase ◽  
First Order ◽  
Atomic Displacements ◽  
Magnetic Symmetry

Coordinate analysis of the multiple phase transitions in hexagonal YMnO3 leads to the prediction of a previously unknown aristotype phase, with the resulting phase-transition sequence: P63′cm′(e.g.) ↔ P63 cm ↔ P63/mcm ↔ P63/mmc ↔ P6/mmm. Below the Néel temperature T N ≃ 75 K, the structure is antiferromagnetic with the magnetic symmetry not yet determined. Above T N the P63 cm phase is ferroelectric with Curie temperature T C ≃ 1105 K. The nonpolar paramagnetic phase stable between T C and ∼ 1360 K transforms to a second nonpolar paramagnetic phase stable to ∼ 1600 K, with unit-cell volume one-third that below 1360 K. The predicted aristotype phase at the highest temperature is nonpolar and paramagnetic, with unit-cell volume reduced by a further factor of 2. Coordinate analysis of the three well known phase transitions undergone by tetragonal BaTiO3, with space-group sequence R3m ↔ Amm2 ↔ P4mm ↔ Pm\overline 3m, provides a basis for deriving the aristotype phase in YMnO3. Landau theory allows the I ↔ II, III ↔ IV and IV ↔ V phase transitions in YMnO3, and also the I ↔ II phase transition in BaTiO3, to be continuous; all four, however, unambiguously exhibit first-order characteristics. The origin of phase transitions, permitted by theory to be second order, that are first order instead have not yet been thoroughly investigated; several possibilities are briefly considered.

scholarly journals Polder maps: improving OMIT maps by excluding bulk solvent

2017 ◽  
Vol 73 (2) ◽  
pp. 148-157 ◽  
Author(s):  
Dorothee Liebschner ◽  
Pavel V. Afonine ◽  
Nigel W. Moriarty ◽  
Billy K. Poon ◽  
Oleg V. Sobolev ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Cell Volume ◽  
Electron Density ◽  
Unit Cell Volume ◽  
Model Building ◽  
Unit Cell ◽  
Structure Factors ◽  
Structure Solution ◽  
Solvent Model ◽  
Solvent Molecules

The crystallographic maps that are routinely used during the structure-solution workflow are almost always model-biased because model information is used for their calculation. As these maps are also used to validate the atomic models that result from model building and refinement, this constitutes an immediate problem: anything added to the model will manifest itself in the map and thus hinder the validation. OMIT maps are a common tool to verify the presence of atoms in the model. The simplest way to compute an OMIT map is to exclude the atoms in question from the structure, update the corresponding structure factors and compute a residual map. It is then expected that if these atoms are present in the crystal structure, the electron density for the omitted atoms will be seen as positive features in this map. This, however, is complicated by the flat bulk-solvent model which is almost universally used in modern crystallographic refinement programs. This model postulates constant electron density at any voxel of the unit-cell volume that is not occupied by the atomic model. Consequently, if the density arising from the omitted atoms is weak then the bulk-solvent model may obscure it further. A possible solution to this problem is to prevent bulk solvent from entering the selected OMIT regions, which may improve the interpretative power of residual maps. This approach is called a polder (OMIT) map. Polder OMIT maps can be particularly useful for displaying weak densities of ligands, solvent molecules, side chains, alternative conformations and residues both in terminal regions and in loops. The tools described in this manuscript have been implemented and are available inPHENIX.

scholarly journals Crystal structure of lutetium aluminate (LUAM), Lu4Al2O9

2020 ◽  
Vol 76 (5) ◽  
pp. 752-755
Author(s):  
Rayko Simura ◽  
Hisanori Yamane
Keyword(s):  
Crystal Structure ◽  
Rare Earth ◽  
Single Crystal ◽  
Cell Volume ◽  
Title Compound ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Molar Ratio ◽  
Lanthanide Series ◽  
Two Component

The crystal structure of the title compound containing lutetium, the last element in the lanthanide series, was determined using a single crystal prepared by heating a pressed pellet of a 2:1 molar ratio mixture of Lu2O3 and Al2O3 powders in an Ar atmosphere at 2173 K for 4 h. Lu4Al2O9 is isostructural with Eu4Al2O9 and composed of Al2O7 ditetrahedra and Lu-centered six- and sevenfold oxygen polyhedra. The unit-cell volume, 787.3 (3) Å3, is the smallest among the volumes of the rare-earth (RE) aluminates, RE 4Al2O9. The crystal studied was refined as a two-component pseudo-merohedric twin.

scholarly journals Low-temperature phase transition and highpressure phase stability of 1H-pyrazole-1carboxamidine nitrate

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Piotr Rejnhardt ◽  
Marek Drozd ◽  
Marek Daszkiewicz
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase I ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Negative Thermal Expansion ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Scanning Calorimetry

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.

Dehydration leads to a phase transition in monoclinic factor XIII crystals

1999 ◽  
Vol 55 (11) ◽  
pp. 1858-1862 ◽  
Author(s):  
Manfred S. Weiss ◽  
Rolf Hilgenfeld
Keyword(s):  
Phase Transition ◽  
Rigid Body ◽  
Cell Volume ◽  
Factor Xiii ◽  
Unit Cell Volume ◽  
Crystal Form ◽  
Molecular Replacement ◽  
Asymmetric Unit ◽  
Body Rotation ◽  
Peg 6000

Monoclinic factor XIII crystals have been transferred to a solution containing increasing amounts of the precipitant PEG 6000. At a concentration of about 36%(w/v) PEG 6000, a phase transition was observed. The space group of the crystals was preserved on the transition, but half of the 21 screw axes were lost, which meant that the unit-cell volume and the content of the asymmetric unit were doubled. The structure of factor XIII in the new crystal form was solved by molecular replacement. About 80% of the changes accompanying the transition can be explained by a rigid-body rotation of half of the factor XIII dimers in the lattice by about 5°. The remaining changes are mostly small interdomain movements of the four domains which constitute one factor XIII monomer.

A low-temperature polymorph ofm-quinquephenyl

2012 ◽  
Vol 68 (12) ◽  
pp. o492-o497 ◽  
Author(s):  
Ligia R. Gomes ◽  
R. Alan Howie ◽  
John Nicolson Low ◽  
Ana S. M. C. Rodrigues ◽  
Luís M. N. B. F. Santos
Keyword(s):  
Low Temperature ◽  
Cell Volume ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Geometric Parameters ◽  
Asymmetric Unit ◽  
Cell Axis ◽  
Space Group ◽  
Π Interactions

A low-temperature polymorph of 1,1′:3′,1′′:3′′,1′′′:3′′′,1′′′′-quinquephenyl (m-quinquephenyl), C30H22, crystallizes in the space groupP21/cwith two molecules in the asymmetric unit. The crystal is a three-component nonmerohedral twin. A previously reported room-temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993).Chem. Commun.pp. 1795–1797] also crystallizes with two molecules in the asymmetric unit in the space groupP\overline{1}. The unit-cell volume for the low-temperature polymorph is 4120.5 (4) Å3, almost twice that of the room-temperature polymorph which is 2102.3 (6) Å3. The molecules in both structures adopt a U-shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit-cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C—H...π interactions.

The Effect of Substituting Ga for Alon Crystal Structure of Phosphors MAl 2Si2O8: Eu2+ (M= Ca, Sr, Ba)

2022 ◽  
Vol 905 ◽  
pp. 91-95
Author(s):  
Fei Wang ◽  
Hui Hui Chen ◽  
Shi Wei Zhang
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Cell Volume ◽  
Solid Solutions ◽  
Solid State Reaction ◽  
Unit Cell Volume ◽  
Lattice Parameter ◽  
Unit Cell ◽  
Lattice Parameters ◽  
Reductive Atmosphere

A series of luminescence phosphors M0.955Al2 –xGaxSi2O8∶Eu2+ (M=Ca, Sr, Ba, x = 0~1.0) were prepared via solid-state reaction in weak reductive atmosphere. The lattice positions were discussed. It was found that when Ga3+ entered MAl2Si2O8 lattice and substituted Al3+, complete solid solutions formed. The lattice parameters (a, b, c) and unit cell volume of phosphors M 0.955Al2 –xGaxSi2O8: Eu2+ (M=Ca, Sr, Ba, x = 0~1.0) increased linearly, the lattice parameters (α, β,γ) of Ca0.955Al2–xGaxSi2O8∶Eu2+(CAS) decreased linearly and the lattice parameter β of Sr0.955Al2–xGaxSi2O8∶Eu2+(SAS) and Ba0.955Al2–xGaxSi2O8∶Eu2+(BAS) increased linearly as Ga3+ content increased.

scholarly journals Geometric considerations of the monoclinic–rutile structural transition in VO2

2019 ◽  
Vol 48 (25) ◽  
pp. 9260-9265
Author(s):  
Shian Guan ◽  
Aline Rougier ◽  
Matthew R. Suchomel ◽  
Nicolas Penin ◽  
Kadiali Bodiang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Structural Transition ◽  
Unit Cell

Geometrical and experimental examinations of VO2 show how hysteretic phase transition phenomena across the MIT can be driven by positive crystal energy effects of increasing unit cell volume.

Variable-temperature X-ray crystal structure determinations of {Fe[tren(6-Mepy)3]}(ClO4)2and {Zn[tren(6-Mepy)3]}(ClO4)2compounds: correlation of the structural data with magnetic and Mössbauer spectroscopy data

2007 ◽  
Vol 40 (6) ◽  
pp. 1135-1145 ◽  
Author(s):  
Maksym Seredyuk ◽  
Ana B. Gaspar ◽  
Joachim Kusz ◽  
Gabriela Bednarek ◽  
Philipp Gütlich
Keyword(s):  
Crystal Structure ◽  
Cell Volume ◽  
High Spin ◽  
Unit Cell Volume ◽  
Variable Temperature ◽  
Unit Cell ◽  
X Ray ◽  
Cell Parameters ◽  
Bond Lengths ◽  
Structure Determinations

Variable-temperature X-ray crystal structure determinations (80–330 K) on compounds {Fe[tren(6-Mepy)3]}(ClO4)2(1-Fe) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} and {Zn[tren(6-Mepy)3]}(ClO4)2(1-Zn) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} were carried out together with a detailed analysis of the unit-cell volume and parameters in the spin transition region for (1-Fe). Both compounds crystallize in the monoclinic system and retained the space groupP21/cat all measured temperatures. The Fe and Zn atoms are surrounded by six N atoms belonging to imine groups and pyridine groups of the trifurcated ligand, adopting a pseudo-octahedral symmetry. The average Fe—N bond lengths of 2.013 (1) Å (80 K) and 2.216 (2) Å (330 K) are consistent with a low-spin (LS) and a high-spin (HS) state for the iron(II) ions. In contrast to (1-Fe), the structures of (1-Zn) at low and high temperatures are similar and repeat the structural features of the high-spin structure of (1-Fe). The volume of the unit cell increases on heating from 80 to 330 K for (1-Fe) and (1-Zn). On the other hand, while thea,bandccell parameters increase for (1-Fe), they show less variation for (1-Zn). For (1-Fe), variation of the unit-cell volume with temperature recalculated per Fe atom shows a change ΔV= 27.16 Å3during the spin crossover process. Magnetic susceptibility and Mössbauer spectroscopy studies performed on (1-Fe) reveal an inversion temperature,T1/2of 233 K, where the molar fractions of LS and HS sites are both equal to 0.5. The variation in metal–ligand bond lengths, the distortion parameters and the cell parameters are very close to the character of the magnetic curve and the curve of γHS(the molar fraction of HS molecules) derived from the Mössbauer data; this result shows the correlation between structure and physical properties in (1-Fe).

Sign in / Sign up

Export Citation Format

Share Document