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The structural impact of hydrogen-donating moieties on the liquid crystalline behavior of hydrogen-bonded assemblies (HBAs) is comprehensively investigated. Therefore, a series of phenol derivatives such as phenol, catechol (CA), resorcinol (RE), hydroquinone (HQ), pyrogallol, hydroxyhydroquinone, and phloroglucinol (PHG) were combined with alkoxyazopyridines (Ap-N) yielding 49 new HBAs, which were studied with respect to their mesomorphic properties. The present study revealed significant differences in the liquid crystalline behavior of the structurally diverse assemblies, ranging from the absence of a mesophase to smectic or nematic phases. In contrast to previous studies a comprehensive crystallographic analysis provides insight into the structure–property relationships of the assemblies and proves a correlation between the supramolecular architecture and the macroscopic properties (=liquid crystallinity). More specifically, comparison of the single crystal data with the 2D X-ray diffraction patterns indicates that linear assemblies tend to form crystalline or smectic phases (for the HQ and RE, respectively), while a bent-shaped assembly yields nematic phases (for CA and PHG). Furthermore, our results suggest that segregation of aliphatic and aromatic segments, as observed in the solid state structures, supports the formation of stable mesophases.
The structural impact of hydrogen-donating moieties on the liquid crystalline behavior of hydrogen-bonded assemblies (HBAs) is comprehensively investigated. Therefore, a series of phenol derivatives such as phenol, catechol (CA), resorcinol (RE), hydroquinone (HQ), pyrogallol, hydroxyhydroquinone, and phloroglucinol (PHG) were combined with alkoxyazopyridines (Ap-N) yielding 49 new HBAs, which were studied with respect to their mesomorphic properties. The present study revealed significant differences in the liquid crystalline behavior of the structurally diverse assemblies, ranging from the absence of a mesophase to smectic or nematic phases. In contrast to previous studies a comprehensive crystallographic analysis provides insight into the structure–property relationships of the assemblies and proves a correlation between the supramolecular architecture and the macroscopic properties (=liquid crystallinity). More specifically, comparison of the single crystal data with the 2D X-ray diffraction patterns indicates that linear assemblies tend to form crystalline or smectic phases (for the HQ and RE, respectively), while a bent-shaped assembly yields nematic phases (for CA and PHG). Furthermore, our results suggest that segregation of aliphatic and aromatic segments, as observed in the solid state structures, supports the formation of stable mesophases.
The polymorphism of 2-bromo-2-methyl-propane ((CH 3) 3 CBr) has been investigated by both thermal and X-ray powder diffraction experiments. The long time unknown structure of the low-temperature phase III has been determined by X-ray powder diffraction as orthorhombic Pmn2 1 , with lattice parameters a = 19.1350(4) Å , b = 5.7378(1) Å , and c = 10.9626(2) Å at 180 K, Z = 8 and with an asymmetric unit containing one molecule in a general position and two additional molecules placed in a mirror (Z 0 = 1 þ 1/2 þ 1/2). The phase transitions between the different phases have been characterized at normal pressure as well as at high pressures (up to 300 MPa). From the p T slopes of the two-phase coexistence lines and density measurements as a function of pressure, the volume variations at the transition points have been obtained and compared with those obtained by means of X-ray powder diffraction at normal pressure. The packing as well as the anisotropy of the intermolecular interactions have been analyzed by means of the thermal-expansion tensor and compared with tert-butyl ((CH 3) 3 CX, X = Cl, CN) related compounds.
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