High-Resolution X-ray Study of the Smectic A-Smectic B Phase Transition and the Smectic B Phase in Butyloxybenzylidene Octylaniline

We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q ²⊥ + γ² q ² _z). Unless the elastic constant C₄₄ is more than an order of magnitude smaller than previously reported values of ～ 10⁸ ergs/cm³ the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.     

X-ray Diffraction Study of a New Germanate Phase Ca3Cr2(GeO4)3

Crystallography Reports - A new germanate phase, grown in the Li2O · MoO3–CaO–GeO2 pseudoternary system with addition of Cr2O3, has been studied by X-ray diffraction. The...     

A Convenient Synthesis of 4-(trans-4'- n-alkylcyclohexyl) Benzoic Acids

A convenient method of obtaining 4-(trans-4'- n-alkylcyclohexyl) benzoic acids from alkanoyl chlorides, cyclohexene and benzene is described. Homologous series of above mentioned acids and their nitriles with alkyl tail 2 to 10 carbon atoms were prepared and temperatures of their phase transitions were determined.     

Molecular structure and reactivity of the 1,2-dihydrocarbazol-4(3H)-one: X-ray crystal structure of N-methyl and N-(p-methylbenzenesulfonyl) derivatives

Synthesis and reactivity analysis of the 1,2-dihydrocarbazol-4(3H)-one, and the N-methyl, N-tosyl and 2,2-dimethyl derivatives have been carried out. Molecular structures of the N-methyl and N-tosyl derivatives have been analyzed by X-ray diffraction. Crystals of the N-methyl derivative are monoclinic, space group P2₁/c,a=8.868(1),b=16.652(1),c=7.5440(4) Å, =113.657(3). Crystals of the N-tosyl derivative are monoclinic, P2₁/c,a=12.0016(3),b=8.9178(2),c=16.0485(4) Å, =104.372(2). An extended conjugation from the carbonyl group to the nitrogen atom and an envelope conformation for the common cyclohexenone fragment are evident in both cases. Oximation and Beckmann rearrangement, and etherification of the carbonyl group is reported.     

The Dielectric Anomaly Near the Transition from the Smectic A* to Smectic C* Phase and Visco-Elastic Properties of Ferroelectric Liquid Crystals

A pyro-electric technique is developed which allows the measurement of the dielectric response near the A*-C* phase transition in ferroelectric liquid crystals. The temperature dependence of the elastic modulus K _θ(T) corresponding to the molecular tilt in smectic layers is calculated from the experimental data. Direct pyro-electric measurements of the relaxation time for the spontaneous polarization P _s and the data on K _θ(T) allow us to calculate the temperature behaviour of the twist-viscosity γ₁(T) for the smectic C* phase. The curves γ₁(T) are compared for the smectic C* and the nematic phase of the same compound and the dependence of the twist viscosity on the molecular tilt angle in the C* phase is investigated. The results of the dielectic measurements are discussed in terms of the mean-field approximation.     

Structural Defects and Phase Transition in a Lyotropic System: Optical Birefringence and Order Parameter Measurements

We show that the birefringence of the lamellar phase of the C₁₂E₆-H₂O system decreases abruptly as the temperature increases towards the lamellar-isotropic transition. As the order parameter does not show such behaviour, but decreases regularly, we attribute this phenomenon to disorienting defects whose concentration increases with temperature and diverges when approaching the phase transition, as observed previously by electron microscopy.     

X-Ray Diffraction Studies of 4-n-Decyl(oxy)phenyl-4'-n'-butyl(oxy)benzoate and 4-n-Decyl(oxy)phenyl-4'-n'-hexyl(oxy)benzoate

Liquid crystal aromatic esters of compositions C₁₀H₂₁OC₆H₄C(O)OC₆H₄OC₄H₉ (1) and C₁₀H₂₁OC₆H₄C(O)OC₆H₄OC₆H₁₃ (2) have been investigated by X-ray structural analysis. On temperature rise, these compounds undergo phase transitions crystal-smectic (S_A)-nematic-isotropic (1) and crystal-smectic (S_C)-smectic(S_A)-nematic-isotropic (2) at temperatures 64.5, 80.7, 89.1°C and 62.0, 77.0, 82.5, 88.5°C, respectively. Crystal packing of the compounds consists of alternating loosely packed aliphatic and closely packed aromatic regions. The number of types of weak directional interactions in aromatic regions in both crystal packings was found to be equal to a number of phase transitions in crystal-mesophase-isotropic systems.     

Conformational polymorphism of N-(4-butoxyphenyl)-4-(4′-nitrophenyl)-2-thiazolamine

Crystallography Reports - The molecular and crystal structures of three concomitant polymorphic modifications of N-(4-butoxyphenyl)-4-(4′-nitrophenyl)-2-thiazolamine are investigated by X-ray...     

Synthesis and X-ray Crystal Structures of Two Luminescent Imidazopyridinium Derivatives from the Corresponding N-(aryl)-Pyridine-2-aldimines

Syntheses and X-ray structural characterizations of two new luminescent imidazopyridinium derivatives, 2-(phenyl)-N(3)-(4(methyl)phenyl)-imidazo[1,5a] pyridinium perchlorate (1) and 2-(pyridyl)-N(3)-(4-(chloro)phenyl)-imidazo[1,5a] pyridinium perchlorate (2) are reported. The compounds are prepared in one step from N-(4-(methyl)phenyl) pyridine-2-aldimine and N-(4-(chloro)phenyl) pyridine-2-aldimine respectively in a transformation mediated by Mn(OAc)₂-KMnO₄ mixture. It is found that the molecular structures of the two compounds are similar. In the solid state, 1 forms a three-dimensional network through a series of hydrogen bonds between the cations and anions in the lattice while 2 forms a similar but less extensively linked network. The substitution of hydrogen at the 2-position of the imidazopyridinium ring by phenyl or 2-(pyridyl) affects the nature of their first excited states as detected by changes in their emission and absorption spectra.     

Etude par Calorimetrie,Diffraction des Rayons X et Diffusion Raman d'une Transition de Phase dans (C4 H4P) Mn (CO)3

Abstract

Heat capacity measurements (95-300K), X-ray diffraction (78-300K) and low frequency Raman spectroscopy (10-350K) have evidenced an order-disorder phase transition in phosphacymantrene, (C₄ H₄P) Mn (CO)₃. This transition has been characterized by a monoclinic ←→ triclinic structural change at about 110 K and by a pretransitional phenomenon. The measured transition enthalpy and entropy are 480 ± 10J.mil^?1 and 4.17 ± 0.08J.K^?1 mol^?1, at 115 K, respectively.

A complete assignment of the observed Raman bands in h₄ and d₄ derivatives is proposed. From the temperature dependence of frequencies, intensities and half-widths of some Raman bands we have discussed the order, the nature and the mechanism of the phase transition: intermolecular interactions appear to be mainly involved in the mechanism and an activation energy roughly equal to 2100 ± 840 J. mol^?1 has been determined.     

The Smectic A-Smectic A Transition in a Homologous Series of 4-(4-Alkoxyphenoxycarbonyl)phenyl 5-Cyano-2-furancarboxylates

The thermal properties for a homologous series of 4-(4-alkoxyphenoxycarbonyl)phenyl 5-cyano-2-furancarboxylates have been examined. The smectic A phase commences from the hexyloxy homolog, and the octyloxy, nonyloxy and decyloxy homologs show two kinds of smectic A phases and experience the S_A-S_A transition. The lower phase which shows a typical fan shaped texture is assigned to a smectic A with a bilayer arrangement of the molecules (S_A2). The higher phase which shows a typical fan shaped texture on the cooling stage and a broken fan one on the heating stage, is assigned to a smectic A with a partially bilayer arrangement of the molecules (S_Ad). The S_A-S_A transitions could be easily detected by both differential scanning calorimeter and optical microscopic method.     

Effect of the Terminal Substituents on the Smectic Layer Spacings in 4-(trans-4′-n-Alkyleyelohexyl) Benzoates

The spacings of the smectic layers are compared with the lengths of molecules of p-substituted phenyl 4-(trans-4′-n-decylcyclohexyl) benzoates. It has been found that if the NO₂, CN or CHO groups are substituted in the p-position of the phenyl, then the smectic layers consist of dimers, whereas in the presence of the NCS, COCH₃, I, Cl, Br, F substituents the smectic layers reveal a monomolecular spacing.     

Phase Transition Studies in Some 4-n-Alkyl-N-(4-n-Alkyloxy-Benzylidene)-Anilines

The results of phase transition investigations in two homologous series of 4-n-alkyl-N-(4-n-alkyloxy-benzylidene)-anilines, viz., 60. m and 70. m compounds using thermal microscopy, differential scanning calorimetry, density and refractive index measurements are reported. The nature of the order of various phase transitions and the pre-transitional effects in the fluctuation dominated non-linear regions in the vicinity of IN, IA and NA transitions are discussed in the light of the available data on other nO. m compounds.     

Discontinuous Dielectric Reorientation in the Smectic C Phase of 3-n-Heptyl-6-[4-n-hexyloxyphenyl]-1,2,4,5-tetrazine

In the nematic phase and smectic C phase of 3-n-Heptyl-6-[4-n-hexyloxyphenyl]- 1,2,4,5-tetrazine the Freedericksz transition was studied. In both phases the threshold voltage and the switching times were measured. In the smectic C phase two thresholds were observed which can be explained by an asymmetric chevron structure.     

Hydrogen-bis[2-(4-dimethylaminostyryl)-quinoline-1-oxide]dichlorocuprate (I) from X-ray study

X-ray diffraction data on powder and single-crystal samples were used to determine the crystal structure of hydrogen-bis[2-(4-dimethylaminostyryl)-quinoline-1-oxide]dichlorocuprate (I): monoclinic system, sp. gr. P2₁/n, and Z = 2. Two molecules of N oxide of 2-(4-dimethylaminostyryl)quinoline are bound through a hydrogen atom located at the center of symmetry, thus forming a complex cation.     

Phase transitions in Cs5(HSO4)2(H2PO4)3 crystal

The symmetry (sp. gr.I $\bar 4$ 3d) and lattice parameters have been determined for the first time for Cs₅(H₂SO₄)₂(H₂PO₄)₃ crystals in the temperature range from 172 to 390 K. The thermal and optical properties of crystals, as well as their conductivity, have been investigated at elevated temperatures. It is shown that a crystal heated to T = 365 K undergoes a phase transition with symmetry lowering to the tetragonal phase (with the parameters a = 4.965(1) Å and c = 5.016(1) Å), while at T ≈ 390 K a phase transition to the cubic phase is presumably observed. With a decrease in temperature, a phase transition without a change in symmetry occurs at T = 240 K.     

Phase Characterization,Enthalpies and Entropies of Transition,of Five Substituted N-(1-Biphenylethylidene) Benzylamines

Five N-(1-biphenylethylidene) benzylamines expressed by the general formula C₆H₅C₆H₄C(CH₃) = N-CH₂-C₆4HX (X = H, m-F, m-Cl, M-Br and p-OCH₃) were synthesized and their thermal behavior studied within the temperature range of -75 to 250°C.

The solid-liquid, liquid-solid transition temperatures were recorded with a DSC analyzer and the thermodynamic parameters ΔH_m and ΔS_m were estimated. A relationship between these parameters and the molecular weigth was found. The compound m-fluoro N- (1-biphenylethylidene) benzylamine showed an l_i → l_n transition at 341.5°K, which was better observed by cooling the sample at 10°C/min. The liquid crystal behavior was confirmed by cross polarized microscopy.