A low temperature reversible phase transition for 1,1'-bis-(ferrocenyldimethylsilyl)ferrocenylene, (η5-FcSiMe2C5H4)2Fe, an oligomeric model for silyleneferrocenylene polymers

2000 ◽  
Vol 78 (11) ◽  
pp. 1511-1518 ◽  
Author(s):  
Mikhail Yu Antipin ◽  
Ivan I Vorontsov ◽  
Irene I Dubovik ◽  
Vladimir Papkov ◽  
Francisco Cervantes-Lee ◽  
...  
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Phase Space ◽  
Low Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Space Group ◽  
Reversible Phase Transition ◽  
Reversible Phase

We have reinvestigated the solid state structure of 1,1'-bis-(ferrocenyldimethylsilyl)ferrocenylene, (η5-FcSiMe2C5H4)2Fe, Fc = (η5-C5H5)Fe(η5-C5H4). Using a DSC technique we observed a reversible phase transition for this compound at 169(3)K with ΔH = 1.1 kJ/mol, and ΔS = 6.54 J/mol K. A single crystal X-ray diffraction study has demonstrated that this phase change involves a transformation from a high temperature phase, space group P21/c, Z = 2, to a triclinic low temperature phase, space group P[Formula: see text], Z = 4. The phase transition involves the loss of the molecular crystallographic center of symmetry and rotations about the terminal and central cyclopentadienyl ring pairs. The results are compared to those reported for ferrocene.Key words: solid state, phase transition, silyleneferrocenylene.

An X-Ray, Raman and IR Study of α-CsReO4, the High-Temperature Modification of Cesium Perrhenate

1992 ◽  
Vol 47 (11) ◽  
pp. 1513-1520 ◽  
Author(s):  
Klaus-Jürgen Range ◽  
Peter Rögner ◽  
Heyns Anton M. ◽  
Prinsloo Linda C.
Keyword(s):  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Data Set ◽  
Space Group ◽  
X Ray ◽  
Reversible Phase Transition ◽  
Ir Study ◽  
Reversible Phase

Cesium perrhenate undergoes a reversible phase transition from the orthorhombic room-temperature phase (β-CsReO4, space group Pnma) to a tetragonal high-temperature phase (α-CsReO4). The space group of α-CsReO4 was unambiguously confirmed by high-temperature X-ray diffraction to be I41/amd in contrast to the earlier literature, in which space group I41/a (and hence, a scheelite type structure) was assumed for α-CsReO4. From a data set obtained at 468 K the crystal structure of α-CsReO4 (a = 5.9607(4), c = 14.446(1)Å, Z = 4) was refined to R = 0.032, Rww = 0.029 using anisotropic displacement factors.In the vibrational spectra not all of the predicted com ponents for β-CsReO4 could be confirmed by the experiments, but for α-CsReO4 very good agreement was obtained between the predicted and observed bands. The fact that v2 at ~ 300 cm–1 is not observed in the IR spectra of α-CsReO4 confirms the space group I41/amd, since, under I41/a symmetry, this band is allowed.The structure of α-CsReO4 consists of isolated ReO4 tetrahedra which are linked together by cesium atoms. The relationships between the scheelite, α-CsReO4 and β-CsReO4 structural types are discussed.

Crystal Data for Two Molybdates MIV (MoO4)2 With MIV = Zr, Hf

1987 ◽  
Vol 2 (1) ◽  
pp. 36-38 ◽  
Author(s):  
M. Auray ◽  
M. Quarton ◽  
P. Tarte
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Crystal Data ◽  
Powder Diffraction Data ◽  
Automatic Indexing ◽  
Space Group ◽  
Reversible Phase Transition ◽  
Cell Dimensions ◽  
Zirconium Molybdate ◽  
Reversible Phase

AbstractTwo molybdates MIV (MoO4)2 (with MIV = Hf or Zr) were synthesized by solid state reaction between MIVO2 and MoO3. Zirconium molybdate undergoes a reversible phase transition at 952 K.Hf(MoO4)2 and H.T. Zr(MoQ4)2, obtained as single crystals, are trigonal, space group with Z = 6; the cell dimensions are respectively a = 10.1005(3), c = 11.7230(5)Å; V = 1035.76(11)Å3; Dm(298 K) = 4.78(4), Dx = 4.792 Mg m−3 and a = 10.1409(3), c = 11.7097(5)Å; V = 1042.88(11)Å3; Dm (298 K) = 3.91(4), Dx = 3.926 Mg m−3.L.T. Zr(MoO4)2, indexed by the Visser automatic indexing program (1969) was found to be monoclinic, possible space group P2, P21 or Pm with Z = 4; the cell dimensions are a = 9.7557(5), b = 7.9373(5), c = 7.4631(4)Å, β = 97.959°(5); V = 572.3(5)Å Dm(298 K) = 4.74(5), Dx = 4.770 Mg m−3. Powder diffraction data were obtained at 293 K on a counter diffractometer with Ni-filtered copper radiation ( = 1.5418 Å).

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

scholarly journals Inorganic Anion Regulates the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

2017 ◽  
Author(s):  
Yuan Chen ◽  
Yang Liu ◽  
Binzu Gao ◽  
Chuli Zhu ◽  
Zunqi Liu
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Variable Temperature ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Space Group ◽  
X Ray

Two novel inorganic–organic hybrid supramolecular assemblies, namely, (4-HNA)(18-crown-6)(HSO4) (1) and (4-HNA)2(18-crown-6)2(PF6)2(CH3OH) (2) (4-HNA = 4-nitroanilinium), were synthesized and characterized by infrared spectroscopy, single X-ray diffraction, differential scanning calorimetry (DSC), and temperature-dependent dielectric measurements. The two compounds underwent reversible phase transitions at about 255 K and 265 K, respectively. These phase transitions were revealed and confirmed by the thermal anomalies in DSC measurements and abrupt dielectric anomalies during heating. The phase transition may have originated from the [(4-HNA)(18-crown-6)]+ supramolecular cation. The inorganic anions tuned the crystal packings and thus influenced the phase-transition points and types. The variable-temperature X-ray diffraction data for crystal 1 revealed the occurrence of a phase transition in the high-temperature phase with the space group of P21/c and in the low-temperature phase with the space group of P21/n. Crystal 2 exhibited the same space group P21/c at different temperatures. The results indicated that crystals 1 and 2 both underwent an iso-structural phase transition.

Polymorphism of Li2Zn3

2012 ◽  
Vol 68 (1) ◽  
pp. 34-39 ◽  
Author(s):  
Volodymyr Pavlyuk ◽  
Ihor Chumak ◽  
Helmut Ehrenberg
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Tight Binding ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Space Group ◽  
Temperature Modification ◽  
Rhombic Dodecahedra ◽  
Low Temperature Phase

Crystal structures of low- and high-temperature modifications of the binary phase Li2Zn3 were determined by single-crystal X-ray diffraction techniques. The low-temperature modification is a disordered variant of Li5Sn2, space group R\bar 3m (No. 166). The high-temperature modification crystallizes as an anti-type to Li5Ga4, space group P\bar 3m1 (No. 164). Two polymorphs can be described as derivative structures to binary Li5Ga4, Li5Sn2, Li13Sn5, Li8Pb3, CeCd2 and CdI2 phases which belong to class 2 with the parent W-type in Krypyakevich's classification. All atoms in both polymorphs are coordinated by rhombic dodecahedra (coordination number CN = 14) like atoms in related structures. The Li2Zn2.76 (for the low-temperature phase) and Li2Zn2.82 (for the high-temperature phase) compositions were obtained after structure refinements. According to electronic structure calculations using the tight-binding–linear muffin-tin orbital–atomic spheres approximations (TB–LMTO–ASA) method, strong covalent Sn—Sn and Ga—Ga interactions were established in Li5Sn2 and Li5Ga4, but no similar Zn—Zn interactions were observed in Li2Zn3.

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.

A low-temperature modification of hexa-tert-butyldisilane and a new polymorph of 1,1,2,2-tetra-tert-butyl-1,2-diphenyldisilane

2014 ◽  
Vol 70 (7) ◽  
pp. 697-701 ◽  
Author(s):  
Stefan Scholz ◽  
Hans-Wolfram Lerner ◽  
Jan W. Bats
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Torsion Angles ◽  
Lattice Constants ◽  
Bond Lengths ◽  
Twofold Axis ◽  
Reversible Phase Transition

Crystals of hexa-tert-butyldisilane, C24H54Si2, undergo a reversible phase transition at 179 (2) K. The space group changes fromIbca(high temperature) toPbca(low temperature), but the lattice constantsa,bandcdo not change significantly during the phase transition. The crystallographic twofold axis of the molecule in the high-temperature phase is replaced by a noncrystallographic twofold axis in the low-temperature phase. The angle between the two axes is 2.36 (4)°. The centre of the molecule undergoes a translation of 0.123 (1) Å during the phase transition, but the conformation angles of the molecule remain unchanged. Between the two tri-tert-butylsilyl subunits there are six short repulsive intramolecular C—H...H—C contacts, with H...H distances between 2.02 and 2.04 Å, resulting in a significant lengthening of the Si—Si and Si—C bonds. The Si—Si bond length is 2.6863 (5) Å and the Si—C bond lengths are between 1.9860 (14) and 1.9933 (14) Å. Torsion angles about the Si—Si and Si—C bonds deviate by approximately 15° from the values expected for staggered conformations due to intramolecular steric H...H repulsions. A new polymorph is reported for the crystal structure of 1,1,2,2-tetra-tert-butyl-1,2-diphenyldisilane, C28H46Si2. It has two independent molecules with rather similar conformations. The Si—Si bond lengths are 2.4869 (8) and 2.4944 (8) Å. The C—Si—Si—C torsion angles deviate by between −3.4 (1) and −18.5 (1)° from the values expected for a staggered conformation. These deviations result from steric interactions. Four Si—C(t-Bu) bonds are almost staggered, while the other four Si—C(t-Bu) bonds are intermediate between a staggered and an eclipsed conformation. The latter Si—C(t-Bu) bonds are about 0.019 (2) Å longer than the staggered Si—C(t-Bu) bonds.

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.

Temperature-Dependent Solid-state Luminescence and Reversible Phase Transition of (n-Bu4N)[Au(SC6H3-3,5-Me2)2]

2003 ◽  
Vol 32 (11) ◽  
pp. 1002-1003 ◽  
Author(s):  
Seiji Watase ◽  
Takayuki Kitamura ◽  
Nobuko Kanehisa ◽  
Masami Nakamoto ◽  
Yasushi Kai ◽  
...  
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Temperature Dependent ◽  
Reversible Phase Transition ◽  
Reversible Phase ◽  
State Luminescence
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