Neutron Scattering by a Liquid Crystal Substance with a “Cubic” Phase

The applicability of the rotational diffusion model around the long molecular axes in liquid crystalline phases is being questioned.     

Orientational Distribution Function and Order Parameters of Two 4′-Alkoxy-4-Cyanobiphenyls in Mesomorphic Phase

X-ray diffraction studies on samples of 4′-Pentyloxy-4-Cyanobiphenyl and 4′-Octyloxy-4-Cyanobiphenyl over the entire mesomorphic range are reported in this paper. A magnetic field was used to align samples. The orientational distribution functions f(β) have been calculated from the angular distribution of X-ray intensities. Orientational order parameters ( P ₂) and ( P ₄) have been calculated and compared with Maier-Saupe theoretical values. Expressions for the angular part of the pseudopotentials have been obtained from the temperature variation of f(β). The intermolecular distances D have been calculated from the experimental data and it is found that D is significantly smaller for well aligned samples. The apparent molecular length in the nematic phase and the layer thickness in the smectic phase have also been determined and are found to be about 1.4 times larger than the true molecular length in the fully extended form. This is in accordance with the findings from other cyano compounds.     

A Natural Progression from Smectic C to Tilted Smectic B Properties in the n-Alkyl 4′-n-Alkoxybiphenyl-4-carboxylates

Recently^1,2 the n-alkyl esters of the 4′-n-heptyloxy- to 4′-n-decyloxy-biphenyl-4-carboxylic acids (inclusive) were prepared. These homologous series all showed a sudden injection of smectic C properties at the n-butyl ester. In the current work, a number of esters of the 4′-n-dodecyloxy-4′-n-tetradecyloxy-, 4′-n-hexadecyloxy-, and 4′-n-octadecyloxy-biphenyl-4-carboxylic acids have been prepared in order to establish the smectic phase sequences at longer, terminal alkoxy chain lengths. It was found that, as the terminal alkoxy chain length was increased there was a natural, smooth progression to esters which exhibit tilted smectic B phases rather than tilted smectic C phases.     

4,4′-Di(N)Hexoxybenzalazine: Crystal and Molecular Structure and Phase Characterization of the Liquid Crystalline Compound

Abstract

The crystal and molecular structure of the mesogenic title compound (HBA) is described. Lattice parameters are: space group P1, a = 9.003(2) Å, b = 8.850(2) Å, c = 8.510(2) Å, α = 79.63(1)°, β = 65.04(1)°, γ = 87.41(1)° (at T = 299 K). The molecules contain a centre of symmetry and the phenyl rings are coplanar. In order to obtain better structural data for a comparison with its methoxy derivative (MBA) a redetermination of this structure was carried out using a new data set. The melting enthalpy of HBA is 45(2) kJmol^?1 (127.8(5)°C) its clearing enthalpy is 1.5(4) kJmol^?1 (153.2(5) °C). The fluctuation wave-length 2π/q_‖ of 27(2) Å in the nematic state can be compared with the molecular length of 31.63 Å.     

Crystal and Molecular Structure of the Nematogenic Compound 4′-Cyanophenyl-4-n-Pentoxybenzoate

The title compound with the formula C₅H₁₁O-C₆H₄-COO-C₆H₄-CN (CPPOB) crystallizes in the orthorhombic space group Pnam with a = 16.465 Å, b = 13.577 Å, c = 7. 621 Å and four molecules per unit cell. The structure has been solved by direct methods and refined to a final R value of 0.050. The CPPOB molecules have exact C_s symmetry as a consequence of their location on crystallographic mirror symmetry planes, the benzene ring to which the cyano group is attatched has a perpendicular orientation to the other ring in the plane. The molecules adopt a nearly optimal stretched form, neighbouring molecules make an angle of 35.2°. The results are discussed in relation to the mesomorphic behaviour of CPPOB.     

Study of the Phase Situation in 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate (7S5)

Results of measurements of the specific heat of 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate in the temperature range from about 90 K to about 370 K are presented. They were carried out with an adiabatic calorimeter, a differential scanning calorimeter and a polarizing microscope. Adiabatic calorimetry revealed four anomalies in the specific heat vs. temperature curve viz., two associated with transitions in the solid phase, one with melting and one with the liquid-crystalline nematic-to-isotropic phase transition. Also, two modifications of the solid, stable and metastable, were found to exist. In addition, the DSC method applied in the 285 K to 370 K range revealed a smectic C phase, but only when the sample is being cooled. The polarizing microscope showed the structural polymorphism of the solid phase in the 297 K to 327 K range to be more complex than would stem from adiabatic calorimetry and DSC measurements alone. It also confirmed the occurence of the S_c phase on cooling as ascertained by the DSC method.     

Synthesis and Evaluation of Liquid Crystal Behavior of a Novel Homologous Series: 4-(4′-n-Alkoxy benzoyloxy) Phenylazo-2″, 6″-dimethylbenzenes

A novel homologous series entitled 4-(4′-n-alkoxy benzoyloxy) phenyl azo 2^″, 6^″-dimethyl benzenes consisting of 12 members is reported. Liquid crystal behavior as a nematogenic mesophase commences from the pentyloxy homologue monotropically and then continues enantiotropically until the last hexadecyloxy homologue without exhibition of any smectogenic behavior. An odd-even effect is observed for nematic-isotropic transition curve of the phase diagram. The textures of the nematic mesophase are of the threaded or Schlieren type. Analytical and spectral data support the molecular structure of the homologues. Transition temperatures of the novel homologues were determined by an optical polarizing microscopy. Liquid crystal properties of a novel homologous series are compared with other known homologous series. The average thermal stability for the nematic phase is 77.1°C.     

Dielectric Study on the Alignment or Orientation of N(4-n-heptyloxy benzylidene)4´-n-butylaniline and the Anomalous Dielectric Behavior in the Smectic G Phase

The present article reports on the alignment or orientation of a particular compound N(4-n-heptyloxy benzylidene)4´-n-butylaniline through dielectric study. The effect of using two different alignment layers (for homogenous alignment) and doping silver nanoparticles (0.25% by weight) on the behavior in dielectric property with varying temperature and biasing electric field was studied in terms of liquid crystal alignment or orientation using the mechanism proposed by earlier workers. The study includes the anomalous dielectric behavior in SmG phase by presenting a technique for the analysis of the absorption process, which exists only in SmG phase at fixed frequency while varying temperature, is also presented.     

Crystal and Molecular Structure Studies of 1′-Benzyl-8-(4-fluorobenzyl)-8-azaspiro[bicyclo-[3.2.1]octane-3,4′-imidazolodine]-2′,5′-dione

Abstract  

The title compound, C₂₃H₂₃FN₃O₂ has been synthesized and the structure was investigated by X-ray diffraction studies. The compound crystallizes in the triclinic crystal class in the space group P[`1]P\overline{1} with cell parameters a = 9.345(2) ?, b = 10.940(3) ?, c = 11.986(4) ?, α = 72.349(6)°, β = 68.106(18)°, γ = 66.867(5)°, Z = 2 and V = 1027.8(5) ?³. The hydantoin ring adopts a planar conformation and is affected by the π conjugation. The pyrrolidine and piperidine rings in the bicyclo octane moiety adopt envelope and chair conformations respectively. The structure exhibits both inter and intramolecular hydrogen bonds of the type N–H···O, C–H···O and C–H···N. One of the oxygen atoms attached to the hydantoin ring simultaneously accepts two hydrogen bonds to form a three centered hydrogen bonding pattern.     

The Existence of SA 1, SA d,SA 2 and S∼C Smectic Phases in the New Series 4-Alkoxyphenyl-4′- [4″-Cyanobenzyloxv] Benzoates

A homologous series of 4 - alkoxyphenyl-4′-[4″-cyano-benzyloxy] benzoates have been synthesized. Within this series three smectic A phases : S_{A 1}, S_{A d} and S_{A 2} were identified by mean of small angle X-Ray scattering. Furthermore three derivatives exhibit the novel smectic phase made of ribbons S～_C.     

Liquid Phase Epitaxy of SiC in the System Si?Tb?SiC by Temperature Gradient Zone Melting (I). Investigation of Solubilities in the System Si?Tb?SiC

In the paper which is divided into three parts the liquid phase epitaxy of SiC by temperature gradient zone melting with the solvent Si Tb is discussed. In the first part the solubility of SiC at different initial compositions of the Si Tb solvent is studied in the temperature range 2000–2500 K.     

Crystal and molecular structures of 1,1′-di-tert-butylnickelocene (η5-C5H4C4H 9 t )2Ni in the temperature range 143–243 K: Thermal motion in the crystal

The crystal structure of 1,1′-di-tert-butylnickelocene is studied by the X-ray diffraction technique in the temperature range 143–243 K. The crystals are monoclinic, space group P2₁/n, Z = 2. The molecule is centrosymmetric. The cyclic ligands are parallel and adopt a staggered conformation. At 143 K, the mean bond lengths are as follows: Ni-C, 2.194(6); C-C (in the ring), 1.421(6); and C-C (Me), 1.538(2) Å. Analysis of the thermal motion of the molecule is performed within the single-parameter model, which allows for the independent motion of the cyclopentadienyl ring with the tert-butyl group as a whole and the motion of the tert-butyl group. It is shown that the molecule is structurally nonrigid and the tert-butyl group executes librational motion. The B ₅ heights of the rotation barriers are estimated from the rms libration amplitudes: 〈?²〉 are equal to 40(5) and 34(4) kJ/mol at 143 and 243 K, respectively.     

Crystal and Molecular Structures of 2-Amino-4-Nitrobenzoic Acid and Its Cocrystals with 2,2′-Bipyridine (2/1) and Bis(pyridin-2-yl)ketone (1/1)

Abstract  

The eight-membered {···HOC=O}₂ synthon featured in the crystal structure of 2-amino-4-nitrobenzoic acid (1) is replaced by carboxylic acid···N-pyridine hydrogen bonds in its cocrystals with 2,2′-bipyridine (2/1; 2) and bis(pyridin-2-yl)ketone (1/1; 3) indicating the robust nature of the latter synthon. Disruption of the three-dimensional architecture based on O–H···O and N–H···O(nitro) hydrogen bonds in (1) is evident in the cocrystals which form supramolecular tubes (2) and chains (3) based on O–H···N and N–H···O hydrogen bonding. Compound (1) crystallizes in the monoclinic space group P2₁/n with a = 3.6291(1) ?, b = 7.7339(3) ?, c = 26.561(1) ?, β = 91.385(2)°, and Z = 4. Compound (2) crystallizes in the monoclinic space group C2/c with a = 27.562(3) ?, b = 6.8300(6) ?, c = 12.923(1) ?, β = 110.593(5)°, and Z = 4. Compound (3) crystallizes in the monoclinic space group P2₁/c with a = 3.795(3) ?, b = 12.024(8) ?, c = 35.65(2) ?, β = 92.131(6)°, and Z = 4 (determined from synchrotron data).     

Observation of Strong Antiferromagnetic Exchange Interactions in [1-(4′-methobenzyl)isoquinolinium][Ni(mnt)<Subscript>2</Subscript>]: Crystal Structures,Magnetic Properties

Abstract  

An new ion-pair compound, [CH₃BzQl][Ni(mnt)₂] (1), (CH₃BzQl = 1-(4′-methobenzyl)isoquinolinium and mnt²⁻ = maleonitriledithiolate), has been synthesized, structurally and magnetically characterized. The [Ni(mnt)₂]⁻ anions (A) and [CH₃BzIQl]⁺ cations (C) of 1 alternate to form a mixed columnar stack in the manner of ···ACAC··· along the a-axis, and the neighboring columns connect together to generate a three-dimensional (3D) network structure via intermolecular H-bonding interactions and van der Waals forces. Variable-temperature magnetic susceptibility measurements in the temperature range 2–300 K show that 1 is a spin gap system with strong antiferromagnetic interaction.     

New Data on the Isomorphism in Eudialyte-Group Minerals. ХI: Crystal Structure of a Potentially New Mineral—A Case of Complete Substitution of Fe2+ with $${\text{Na}}_{{{\text{2/3}}}}^{{\text{ + }}}{\text{Zr}}_{{{\text{1/3}}}}^{{{\text{4 + }}}}$$ in the Eudialyte-Type Structure

Crystallography Reports - The crystal structure and crystallochemical features of a Fe-deficient zirconium-rich analog of eudialyte from the Lovozero alkaline massif (Kola peninsula) have been...