Magnetic Phase Transition between Ferromagnetic High-Temperature Phase and Antiferromagnetic Low-Temperature Phase in 5-Carboxy-2-thienyl Nitronyl Nitroxide

2001 ◽  
Vol 30 (1) ◽  
pp. 32-33 ◽  
Author(s):  
Tadashi Sugano
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Magnetic Phase Transition ◽  
Magnetic Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Nitronyl Nitroxide ◽  
Low Temperature Phase

Topological polymorphism and temperature-driven topotactic transitions of metal–organic coordination polymers

CrystEngComm ◽  
2020 ◽  
Vol 22 (38) ◽  
pp. 6295-6301
Author(s):  
Vadim A. Dubskikh ◽  
Anna A. Lysova ◽  
Denis G. Samsonenko ◽  
Danil N. Dybtsev ◽  
Vladimir P. Fedin
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Solid State ◽  
Low Temperature ◽  
High Temperature Phase ◽  
Phase Changes ◽  
Organic Ligands ◽  
Temperature Phase ◽  
Metal Organic ◽  
Low Temperature Phase

A facile crystal-to-crystal solid-state phase transition between a low-temperature phase and a high temperature phase changes the MOF topology and involves a significant rearrangement of bulky organic ligands.

Monoclinic-to-orthorhombic phase transition of the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal with temperature-dependent dynamic molecular disorder

2016 ◽  
Vol 72 (12) ◽  
pp. 971-980 ◽  
Author(s):  
Tze Shyang Chia ◽  
Ching Kheng Quah
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Structural Phase ◽  
Point Group ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Temperature Dependent ◽  
Space Group ◽  
Low Temperature Phase

As a function of temperature, the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal, C6H12N4·2C8H8O2, undergoes a reversible structural phase transition. The orthorhombic high-temperature phase in the space groupPccnhas been studied in the temperature range between 165 and 300 K. At 164 K, at2phase transition to the monoclinic subgroupP21/cspace group occurs; the resulting twinned low-temperature phase was investigated in the temperature range between 164 and 100 K. The domains in the pseudomerohedral twin are related by a twofold rotation corresponding to the matrix (100/0-10/00-1. Systematic absence violations represent a sensitive criterium for the decision about the correct space-group assignment at each temperature. The fractional volume contributions of the minor twin domain in the low-temperature phase increases in the order 0.259 (2) → 0.318 (2) → 0.336 (2) → 0.341 (3) as the temperature increases in the order 150 → 160 → 163 → 164 K. The transformation occurs between the nonpolar point groupmmmand the nonpolar point group 2/m, and corresponds to a ferroelastic transition or to at2structural phase transition. The asymmetric unit of the low-temperature phase consists of two hexamethylenetetramine molecules and four molecules of 2-methylbenzoic acid; it is smaller by a factor of 2 in the high-temperature phase and contains two half molecules of hexamethylenetetramine, which sit across twofold axes, and two molecules of the organic acid. In both phases, the hexamethylenetetramine residue and two benzoic acid molecules form a three-molecule aggregate; the low-temperature phase contains two of these aggregates in general positions, whereas they are situated on a crystallographic twofold axis in the high-temperature phase. In both phases, one of these three-molecule aggregates is disordered. For this disordered unit, the ratio between the major and minor conformer increases upon cooling from 0.567 (7):0.433 (7) at 170 Kvia0.674 (6):0.326 (6) and 0.808 (5):0.192 (5) at 160 K to 0.803 (6):0.197 (6) and 0.900 (4):0.100 (4) at 150 K, indicating temperature-dependent dynamic molecular disorder. Even upon further cooling to 100 K, the disorder is retained in principle, albeit with very low site occupancies for the minor conformer.

scholarly journals Synthesis of by the Flux Method

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Yuki Maruyama ◽  
Chihiro Izawa ◽  
Tomoaki Watanabe
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Low Temperature ◽  
Diffuse Reflectance ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Flux Method ◽  
Phase Crystal ◽  
Euhedral Crystal ◽  
Low Temperature Phase

has been successfully synthesized using Bi2O3–B2O3 eutectic flux. In particular, we succeeded in synthesizing a low-temperature-phase crystal (α-) at 1073 K as well as high-temperature-phase crystal (β-). The morphology of α- and β- particles prepared by the flux method is a euhedral crystal. In contrast, the morphology of particles prepared by solid state reaction differs: α- is aggregated and β- is necked. Ultraviolet-visible diffuse reflectance spectra indicate that the absorption edge is at a longer wavelength for β- than for α- with β- absorbing light of wavelengths up to nearly 400 nm.

35Cl NQR Studies of Hexachlorometallates(IV) with Organic Cations, A2 [MCl6] and A'[MCl6], M=Sn, Te, Pb and A+, A'2+ = Organic Cation

1990 ◽  
Vol 45 (3-4) ◽  
pp. 293-302 ◽  
Author(s):  
Dirk Borchers ◽  
Alarich Weiss
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Resonance Line ◽  
Organic Cation ◽  
Phase Changes ◽  
Organic Cations ◽  
Temperature Phase ◽  
35Cl Nqr ◽  
Low Temperature Phase

Abstract35Cl NQR spectra of eleven hexachlorometallates (IV) A1 [MCl6] and A'[MCl6], M = Sn, Te, Pb, and A+ =ethylammonium, 4-picolinium, anilinium, triethylammonium, chinoxalinium, and piperi-dinium ions, and A'2+ = 1.3-propylenediammonium ion, have been observed as a function of tem-perature. The ethylammonium hexachlorometallates(IV) (C2H5 NH3)2 [MCl6], M = Sn, Te, show a phase transition at 128.8 K and 204 K, respectively. Both compounds yield a single resonance line in their high temperature phases. In case of the stannate this single 35Cl resonance line splits up into two lines at Tc = 128.8 K, whereas for the tellurate no 35Cl NQR signals could be found in the low temperature phase. A phase transition was also found for the 1.3-propylenediammonium hexa-chlorostannate(IV) at 287 K where the six line NQR spectrum of the low temperature phase changes into a four line spectrum. In contrast, the corresponding plumbate shows no transition. All other compounds studied contain distorted [MCl6]2- octahedra, and therefore they yield more than one 35Cl resonance line. The complexes have been investigated in the temperature range temperature where the lines fade out. In case of the hexachlorostannates(IV) with the ethylammonium, the 1.3-propylenediammonium and the triethylammonium ions, the crystal structures of the compounds are known and compared with the results of the 35Cl NQR spectroscopy.

Phase transitions in solid cycloheptene

1990 ◽  
Vol 68 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Julian Haines ◽  
D. F. R. Gilson
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Low Temperature Phase

The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.

Irreversible single-crystal to polycrystal and reversible single-crystal to single-crystal phase transformations in cyanurates

2001 ◽  
Vol 57 (6) ◽  
pp. 791-799 ◽  
Author(s):  
Menahem Kaftory ◽  
Mark Botoshansky ◽  
Moshe Kapon ◽  
Vitaly Shteiman
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Low Temperature ◽  
Single Crystal ◽  
High Temperature Phase ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Space Group ◽  
Reversible Phase ◽  
Low Temperature Phase

4,6-Dimethoxy-3-methyldihydrotriazine-2-one (1) undergoes a single-crystal to single-crystal reversible phase transformation at 319 K. The low-temperature phase crystallizes in monoclinic space group P21/n with two crystallographically independent molecules in the asymmetric unit. The high-temperature phase is obtained by heating a single crystal of the low-temperature phase. This phase is orthorhombic, space group Pnma, with the molecules occupying a crystallographic mirror plane. The enthalpy of the transformation is 1.34 kJ mol−1. The small energy difference between the two phases and the minimal atomic movement facilitate the single-crystal to single-crystal reversible phase transformation with no destruction of the crystal lattice. On further heating, the high-temperature phase undergoes methyl rearrangement in the solid state. 2,4,6-Trimethoxy-1,3,5-triazine (3), on the other hand, undergoes an irreversible phase transformation from single-crystal to polycrystalline material at 340 K with an enthalpy of 3.9 kJ mol−1; upon further heating it melts and methyl rearrangement takes place.

35Cl NQR and Structural Studies of Chloroacetanilides C6H3Cl2NHCOCH3-xClx, 1 ≤ x ≤ 3

1992 ◽  
Vol 47 (1-2) ◽  
pp. 160-170
Author(s):  
Dirk Groke ◽  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Phenyl Group ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Chlorine Atoms ◽  
Space Group ◽  
Low Temperature Phase

AbstractThe temperature dependence of 35Cl NQR frequencies and the phase transition behaviour of chloroacetanilides (N-[2,6-dichlorophenyl]-2-chloroacetamide, -2,2-dichloroacetamide, -2,2,2-trichloroacetamide) were investigated. The crystal structure determination of N-[2,6-dichlorophenyl]- 2-chloroacetamide leads to the following: a = 1893.8 pm, b = 1110.7 pm, c = 472.1 pm, space group P212121 = D24 with Z = 4 molecules per unit cell. The arrangement of the molecules and their geometry is comparable to the high temperature phase of the acetyl compound N-[2,6-dichlorophenyl]- acetamide. For N-[2,6-diclorophenyl]-2,2,2-trichloroacetamide it was found: a = 1016.6 pm, b = 1194.3 pm, c = 1006.7 pm, ß= 101.79°, space group P21/c = C52h, Z = 4. The structure is similar to the low temperature phase of N-[2,6-dichlorophenyl]-acetamide. Parallelism between the temperature dependence of the 35C1 NQR lines of the CCl3 group and the X-ray diffraction results concerning the different behaviour of the chlorine atoms was observed. The structures of the compounds show intermolecular hydrogen bonding of the N - H • • • O - C type. The phenyl group and the HNCO function are nearly planar. A bleaching out of several 35Cl NQR lines at a temperature far below the melting point of the substances was observed. The different types of chlorine atoms (aromatic, chloromethyl) can be distinguished by their temperature coefficients of the 35Cl NQR frequencies. All the resonances found show normal "Bayer" temperature behaviour. N-[2,6-dichlorophenyl]-2,2-diehloroacetamide shows several solid phases. One stable low temperature phase and an instable high temperature phase (at room temperature) were observed. The different phases were detected by means of 35Cl NQR spectroscopy and thermal analysis

V CYCLE DYNAMICAL EXPONENT OF THE MULTI-SCALE-UPDATE ALGORITHM FOR THE 2-d XY MODEL

1993 ◽  
Vol 04 (05) ◽  
pp. 947-954
Author(s):  
S. L. ADLER ◽  
G. V. BHANOT
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
High Temperature Phase ◽  
Xy Model ◽  
Temperature Phase ◽  
Dynamical Correlation ◽  
Dynamical Exponent ◽  
Multi Scale ◽  
Correlation Exponent ◽  
Low Temperature Phase

We have computed the dynamical correlation exponent for the Multi Scale Algorithm recently proposed by us for the 2-d XY model. We find that z = 1.70 (2) in the high temperature phase and z = 1.60 (2) in the low temperature phase.

scholarly journals Crystal structures of di-tin-hexa(seleno)hypodiphosphate, Sn2P2Se6, in the ferroelectric and paraelectric phase

1998 ◽  
Vol 213 (1) ◽  
Author(s):  
R. Israël ◽  
R. de Gelder ◽  
J. M. M. Smits ◽  
P. T. Beurskens ◽  
S. W. H. Eijt ◽  
...  
Keyword(s):  
Molecular Structure ◽  
High Temperature ◽  
Low Temperature ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Crystal And Molecular Structure ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Monoclinic System ◽  
Low Temperature Phase

AbstractThe crystal and molecular structure of SnIn both phases, the structure crystallizes in the monoclinic system. The ferroelectric phase withComparison of the two structures showed that the tin ions shift to positions of about 0.13 Å from an individual disorder-site in the high temperature phase (paraelectric) to the corresponding tin position in the low temperature phase (ferroelectric). The shift from the average Sn-position in the paraelectric phase to the Sn-positions in the ferroelectric phase is about 0.30 Å (on average 10° off the vector

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