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Int. J. Mol. Sci. 2011, 12(11), 7360-7400; doi:10.3390/ijms12117360

Review of Crystalline Structures of Some Selected Homologous Series of Rod-Like Molecules Capable of Forming Liquid Crystalline Phases

Institute of Physical Chemistry, TU Clausthal, Arnold-Sommerfeld-Str. 4,D-38678 Clausthal-Zellerfeld, Germany
Received: 7 July 2011 / Revised: 9 October 2011 / Accepted: 11 October 2011 / Published: 28 October 2011
(This article belongs to the Special Issue Liquid Crystals 2011)

Abstract

The crystal structures of four homologous series of rod-like molecules are reviewed, two of which form hydrogen bonds and two with a symmetric chemical constitution. Many of the compounds investigated turn into liquid crystalline phases upon temperature increase. It is of valuable interest to know possible conformations and possible packing arrangements as prerequisites to model liquid crystalline structures. The hydrogen bonds of homologous series of pure 4-(ω-hydroxyalkyloxy)-4′-hydroxybiphenyl (HnHBP, n the alkyloxy tail length) are realized through head to tail arrangements of the hydroxyl groups and crystallize except one compound in chiral space groups without the molecules containing any asymmetric carbon. The hydrogen bonds of the homologous series of 4-substituted benzoic acids with various lengths of the tail provide dimers through strong polar bonding of adjacent carboxyl groups and thus provide the stiff part of a mesogenic unit prerequisite for liquid crystalline phases. The homologous series of dialkanoyloxybiphenyls (BP-n, n = 1, 19), of which nine compounds could be crystallized, show liquid crystalline behavior for longer alkane chain lengths, despite the high mobility of the alkane chain ends already detectable in the crystal phase. A single molecule, half a molecule or two half molecules form the asymmetric unit in a centrosymmetric space group. The homologous series of 1,4-terephthalidene-bis-N-(4′-n-alkylaniline) (TBAA-n) exhibit a large variety of packing arrangements in the crystalline state, with or without relying on the symmetry center within the molecules. View Full-Text
Keywords: crystal structure of 4 homologous series; conformation and packing arrangement; unconventional packing arrangements crystal structure of 4 homologous series; conformation and packing arrangement; unconventional packing arrangements
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Zugenmaier, P. Review of Crystalline Structures of Some Selected Homologous Series of Rod-Like Molecules Capable of Forming Liquid Crystalline Phases. Int. J. Mol. Sci. 2011, 12, 7360-7400.

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