A three-dimensional mesophase with rhombohedral structure formed by double-swallow-tailed compounds

In five double-swallow-tailed compounds a weakly birefringent high temperature phase occurs which exhibits a characteristic optical texture. On the basis of X-ray diffraction measurements on well oriented monodomains, the structure of this phase could be described by a rhombohedral lattice of space group R3c or R32/c; the lattice parameters are not far from a cubic lattice. In spite of the three dimensional superstructure with long range character, the lateral packing of the molecules is liquid-like - similar to the well known cubic mesophases.     

A new high temperature mesophase of a double-swallow-tailed compound with weak optical anisotropy

A new six-ring double-swallow-tailed compound is presented which shows four liquid crystalline phases. In addition to a smectic C phase and two columnar phases (oblique and hexagonal), a high temperature mesophase was observed which exhibits a very weak birefringence and which shows unusual optical textures.     

Structure of gyroid mesophase formed by monodendrons with fluorinated alkyl tails

The structure of a three-dimensional mesophase has been studied by the methods of small-angle X-ray diffraction and reconstruction of electron-density maps of the cubic lattice. In the oriented samples based on monodendrons with partially fluorinated alkyl tails, this mesophase has been shown to coexist with a two-dimensional columnar phase through a wide temperature interval. Epitaxial relationships between (10) planes of the hexagonal lattice and (211) planes of the cubic lattices lead to the ten-point pattern of azimuthal intensity distribution for the first X-ray 211 reflection and to the six-point intensity distribution for the second 220 reflection. The observed 12-point pattern of the 220 reflection is due to the presence of twin “crystallites” of the three-dimensional phase, and their [110] axis is parallel to the axis of cylinders in the columnar phase. The reconstructed electron-density maps show that the regions with increased electron density, which are composed of fluorinated aliphatic tails, form a bicontinuous gyroid structure.     

Multi-arm ionic liquid crystals formed by cholesteric mesophase and pyridinium groups

ABSTRACT

A series of novel star-shaped ionic liquid crystals (ILCs) compounds with various counterions (derived from HBF₄, HPF₆, CF₃COOH, d-MH-SO₃H, H₃PO₄, p-Toluenesulfonic acid) were designed and synthesised starting from precursors of pyridines and liquid crystalline monomer cholesteryl 4-bromobutanoate. Inducing various counterions by use of ionic self-assembly due to electrostatic attraction of various ion clusters was one of the most essential factors for intermolecular separation. The chemical structures, liquid crystalline properties, self-assembly behaviour and ionic conductivity of these compounds were researched during multiple experimental techniques. The star-shaped ILCs showed a smectic A (SmA) mesophase. The d-spacing of star-shaped ILCs increased slightly due to the increase volume of anion. The clearing temperatures of the pyridinium salts suggested that the effect of the stabilisation on the SmA structures was in the order H₂PO₄^?>BF₄^?>T_S^?>D-MH-SO₃^?>CF₃COO^?>PF₆^?. All these star-shaped ILCs displayed ionic conductivity in mesophase. It was noted that the conductivity (σ) increased with the increase of the anion size and temperature.     

Lamellar and three-dimensional hybrid compounds formed by cyclohexene- and cyclohexanedicarboxylates of Pb, La, and Cd

To establish factors that determine the formation of three-dimensional hybrid structures of metal dicarboxylates involving metal-oxygen-metal linkages, we have investigated metal dicarboxylates derived from 1,2-cyclohexene as well as 1,2-, 1,3-, and 1,4-cyclohexane dicarboxylic acids. Thus, we have synthesized a 1,2-cyclohexenedicarboxylate of Cd, [Cd(1,2-CHeDC)(H2O)] (I), a 1,2-cyclohexanedicarboxylate of Pb, [Pb(1,2-CHDC)] (II), and three 1,4-cyclohexanedicarboxylates of La [La2(1,4-CHDC)3(H2O)4] (III), [La3(1,4-HCHDC)2(1,4-CHDC)5(H2O)2].H2O (IV) and [La2(1,4-CHDC)3(H2O)].2.5 H2O (V) under hydrothermal conditions and determined their structures. A mixed dicarboxylate involving both 1,3- and 1,4-cyclohexenedicarboxylates of Pb, [Pb3O(1,3-CHDC)(1,4-CHDC)].0.5 H2O (VI) and a 1,4-cyclohexanedicarboxylate of Pb, [Pb(6)O(2)(1,4-CHDC)3(1,4-HCHDC)2], have also been synthesized and characterized. While the 1,2-dicarboxylates have layered structures, the 1,4-dicarboxylates and the mixed dicarboxylates possess three-dimensional structures. Interestingly, both the 1,2 and 1,4-dicarboxylates are true hybrid compounds composed of infinite M-O-M linkages. The equatorial-equatorial (e,e) conformation is adopted commonly in all these compounds, although less stable conformations are encountered occasionally. The formation of the layered and the three-dimensional structures can be understood based on the relative disposition of the two carboxylic groups, the 1,4-isomer favoring the three-dimensional structure. Based on the results of the present study along with the available literature, we conclude that in order to obtain three-dimensional hybrid structures with metal-oxygen-metal networks, it appears necessary to make use of the 1,4-cyclohexanedicarboxylic acid.     

Modifications of the mesophase formation of discotic triphenylene compounds by substituents

Columnar discotic carboxylic esters of 2-hydroxy-3,6,7,10,11-penta(1-pentyloxy)triphenylene, characterized by a variety of functional groups, were prepared with the purpose of studying the effects of the substituents on the mesophase behaviour. Bulky substituents and polar substituents were found to destabilize the columnar mesophase. The clearing temperature is lowered and the melting point of the crystalline phase, as well as the tendency to crystallize from the mesophase, is increased. Specific substituents cause the formation of novel discotic mesophases characterized by a superstructure.     

Preliminary communication Helical superstructures in a novel smectic mesophase formed by achiral banana-shaped molecules

A new smectic type mesophase without in-plane order is presented which is formed by nitro substituted banana-shaped compounds. The structure of this phase is not yet known in detail. The growth of germs and also the textures point to a helicoidal structure. The helical structure is obviously the result of the chirality of the smectic layers which is caused by the tilt of the molecules together with the polar arrangement of the angled molecules.     

A lanthanum pyromellitate coordination polymer with three-dimensional structure

A new three-dimensional metal-organic coordination polymer, [La₂(H₂O)₂(H₂BTEC)(BTEC)], 1, was hydrothermally synthesized and characterized by single crystal X-ray diffraction. The three-dimensional framework is built up from La₂O₁₆ dimers connected by carboxylate anions. The polymer exhibits strong photoluminescence at room temperature with the main emission band at 390 nm (λ_ex = 338 nm). Crystal data: triclinic, space group P(−1),a = 6.4486(3),b = 9.4525(5),c = 9.6238(5) ?, α= 88.24(1), β = 74.67(2), γ= 76.76(1)°,V = 550.45(5)     

A self-organized 2-dimensional bifunctional structure formed by supramolecular design

The production of a novel two-dimensional bimolecular surface structure using weak noncovalent interactions is demonstrated and observed by scanning tunneling microscopy. This work follows the three-dimensional (3D) ideas of crystal engineering and applies the concepts of supramolecular synthons to molecular systems constrained to 2D by physisorption on a conducting surface. We demonstrate a well-ordered planar structure that self-assembles through the influence of fluorine-phenyl interactions. This study provides a concrete example of the "bottom up" construction of nanostructures and of the systematic design of self-organized layers. To our knowledge, this is the first in a new class of fully 2D materials based both upon weak intermolecular interactions and upon image charges and weak interactions associated with adsorption on metal surfaces.     

A novel mesophase formed by top-shaped molecules in the bulk and unsupported thin films: a molecular dynamics study

We have used molecular dynamics simulations to investigate the ordering of top-shaped molecules in bulk phases and in unsupported thin films. Each rigid anisotropic molecule was composed of 11 Lennard-Jones interaction centers (beads). In an attempt to enhance the nematic stability in preference to smectic, the three central beads were assigned a larger Lennard-Jones diameter than the tail beads, giving the molecule a shape resembling a top. The molecular model was found to exhibit an unusual bulk mesophase with long-range orientational order and with molecular center-of-mass positions arranged in parallel interdigitated layers, with layer spacing smaller than half the length of the long axis of a molecule. However, despite the toplike molecular shape, no nematic phase was observed in the pressure range studied. Unsupported films of the isotropic liquid were cooled in order to locate a triple point between the novel mesophase, vapor, and isotropic liquid. At temperatures slightly above the triple point, enhanced surface ordering of molecules was found to occur in the unsupported film. At temperatures slightly below the triple point, the preferred molecular alignment in the unsupported film was parallel to the interface, in violation of arguments that have been proposed based on the relative enthalpies of various cleavage planes for close-packed structures.     

A bicontinuous mesophase geometry with hexagonal symmetry

We report that a specific realization of Schwarz's triply periodic hexagonal minimal surface is isotropic with respect to the Doi-Ohta interface tensor and simultaneously has minimal packing and stretching frustration similar to those of the commonly found cubic bicontinuous mesophases. This hexagonal surface, of symmetry P6(3)/mmc with a lattice ratio of c/a = 0.832, is therefore a likely candidate geometry for self-assembled lipid/surfactant or copolymer mesophases. Furthermore, both the peak position ratios in its powder diffraction pattern and the elastic moduli closely resemble those of the cubic bicontinuous phases. We therefore argue that a genuine possibility of experimental misidentification exists.     

Molecular structures of compounds formed by benzo-15-crown-5 with calcium salts

X-ray structural and spectroscopic results are given on the compound formed by benzo-15-crown-5 with calcium perchlorate, Ca(ClO₄)₂·C₁₄H₂₀O₅·2H₂O; the combination does not involve any substantial change in the dihedral angles in the macrocycle, as the coordination sphere is constructed as a result of supplementing the positions occupied by the macrocycle oxygen atoms with three other atoms (oxygen atoms from the perchlorate group and two water molecules). The results are compared with published data on the structures of the compounds formed by benzo-15-crown-5 with NaClO₄, Mg(NCS)₂, CuCl₂, Ca(NCS)₂ and Ca(3,5-dinitrobenzoate)₂.Translated from Teoreticheskaya i Éksperimental' naya Khimiya, Vol. 24, No. 2, pp. 242–247, March–April 1988.