Molecular Structure of a Cyclic Dimeric Model of Poly(6-hexanelactam)

1993 ◽  
Vol 58 (10) ◽  
pp. 2403-2414 ◽  
Author(s):  
Bohdan Schneider ◽  
Jan Kvarda ◽  
Jiří Dybal ◽  
Pavel Schmidt ◽  
Miloš Suchopárek ◽  
...  
Keyword(s):  
Molecular Structure ◽  
High Temperature ◽  
Low Temperature ◽  
Hydrogen Bonds ◽  
Computational Methods ◽  
Conformational Structure ◽  
Temperature Modification ◽  
Crystalline Forms ◽  
Dimeric Model ◽  
High Temperature Modification

Two crystalline forms of the cylindric dimer of 6-hexanelactam were studied by DSC, Raman, IR, NMR and computational methods. It was found that the high-temperature modification contains the energetically most favoured conformational structure, the low temperature modification contains the energetically less favoured conformation stabilized by stronger hydrogen bonds.

Eine neue Modifikation von Lanthanmonogermanid – lT-LaGe /A New Modification of Lanthanummonogermanide – lT-LaGe

2004 ◽  
Vol 59 (5) ◽  
pp. 559-561 ◽  
Author(s):  
Hansjürgen Mattausch ◽  
Arndt Simon
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Single Crystals ◽  
Structure Type ◽  
Space Group ◽  
Temperature Modification ◽  
Moisture Sensitive ◽  
High Temperature Modification ◽  
Trigonal Prisms

Abstract Single crystals of the low temperature modification of LaGe are obtained as a byproduct in the reaction of La metal, LaBr3 and Ge powder at 1000 °C as silver colored, moisture sensitive needles. lT-LaGe crystallizes in space group Cmcm with a = 4.5590(10), b = 13.766(2), c = 6.745(2)Å . The Ge atoms form cis-trans-cis-trans-chains with dGe−Ge = 2.621(1) and 2.799(1) Å in contrast to Ge zigzag chains found in the high temperature modification of LaGe crystallizing in the FeB structure type. In both structures the Ge atoms are surrounded by trigonal prisms of lanthanum atoms with CN = 6+1 but different connection of the prisms.

Compounds with perovskite-type slabs. V. A high-temperature modification of La2Ti2O7

1982 ◽  
Vol 38 (2) ◽  
pp. 368-372 ◽  
Author(s):  
N. Ishizawa ◽  
F. Marumo ◽  
S. Iwai ◽  
M. Kimura ◽  
T. Kawamura
Keyword(s):  
High Temperature ◽  
Temperature Modification ◽  
Perovskite Type ◽  
High Temperature Modification

Structural characterization of the high-temperature modification of the Cu2ZnGeTe4quaternary semiconductor compound

2016 ◽  
Vol 253 (6) ◽  
pp. 1195-1201 ◽  
Author(s):  
L. Nieves ◽  
G. E. Delgado ◽  
G. Marcano ◽  
Ch. Power ◽  
S. A. López-Rivera ◽  
...  
Keyword(s):  
High Temperature ◽  
Structural Characterization ◽  
Semiconductor Compound ◽  
Temperature Modification ◽  
High Temperature Modification

High- and low-temperature phases in isostructural 4-chloro-3-nitroaniline and 4-iodo-3-nitroaniline

2014 ◽  
Vol 70 (12) ◽  
pp. 1153-1160 ◽  
Author(s):  
Jan Fábry ◽  
Michal Dušek ◽  
Přemysl Vaněk ◽  
Iegor Rafalovskyi ◽  
Jiří Hlinka ◽  
...  
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Low Temperature ◽  
Hydrogen Bonds ◽  
Primary Amine ◽  
Zigzag Chain ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Acta Cryst ◽  
Graph Set

The structures of 4-chloro-3-nitroaniline, C6H5ClN2O2, (I), and 4-iodo-3-nitroaniline, C6H5IN2O2, (II), are isomorphs and both undergo continuous (second order) phase transitions at 237 and 200 K, respectively. The structures, as well as their phase transitions, have been studied by single-crystal X-ray diffraction, Raman spectroscopy and difference scanning calorimetry experiments. Both high-temperature phases (293 K) show disorder of the nitro substituents, which are inclined towards the benzene-ring planes at two different orientations. In the low-temperature phases (120 K), both inclination angles are well maintained, while the disorder is removed. Concomitantly, thebaxis doubles with respect to the room-temperature cell. Each of the low-temperature phases of (I) and (II) contains two pairs of independent molecules, where the molecules in each pair are related by noncrystallographic inversion centres. The molecules within each pair have the same absolute value of the inclination angle. The Flack parameter of the low-temperature phases is very close to 0.5, indicating inversion twinning. This can be envisaged as stacking faults in the low-temperature phases. It seems that competition between the primary amine–nitro N—H...O hydrogen bonds which form three-centred hydrogen bonds is the reason for the disorder of the nitro groups, as well as for the phase transition in both (I) and (II). The backbones of the structures are formed by N—H...N hydrogen bonding of moderate strength which results in the graph-set motifC(3). This graph-set motif forms a zigzag chain parallel to the monoclinicbaxis and is maintained in both the high- and the low-temperature structures. The primary amine groups are pyramidal, with similar geometric values in all four determinations. The high-temperature phase of (II) has been described previously [Gardenet al.(2004).Acta Cryst.C60, o328–o330].

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