Liquid crystalline complexes

Liquid-crystalline complexes (metallomesogens) containing platinum(II) are new types of materials that have been the subject of several studies. These have largely included complexes of the type trans-[PtX2L2] (X = C1, L = cyanobiphenyls 229 X = C1, carboxylate, L = 4-alkoxy-4 stilbazoles 230 X = C1, L = 2,4-, 3,4-, or 3,5-dialkoxystilbazoles, 2,3,4-, 2,4,5-, or 3,4,5-trialkoxystilbazoles).231,232 Their liquid-crystalline properties have also been reported. 

Sallenave X, Bazuin CG. Interplay of ionic, hydrogen-bonding, and polar interactions in liquid crystalline complexes of a pyridylpyridinium polyamphiphile with (azo)phenol-functionalized molecules. Macromolecules 2007 40 5326-5336. 

Complexation of 100 with carbonyl complexes of chromium, molybdenum, and tungsten yielded liquid crystalline complexes lOla-c [114] (Scheme 50). All derivatives 101 melted at similar temperatures into the columnar rectangular mesophase (deduced from WAXS and SAXS measurements). However, the clearing points were strongly dependent on the metal center and increased with increasing atom number. Upon complexation, the aza crown macrocycle loses its flexibility, with the metal carbonyl fragment located above the crown leading to a cone-shaped... 

Liquid-crystalline complexes of silver(I) were among the first complexes we studied and even now, some sixteen years later, we continue to find aspects that fascinate us. The silver complexes are different fi om the other complexes we have considered in that they are formally ionic, and the anion is an additional variable to take into accoimt. As will be seen, this proves to be a most subtle structural parameter. 

Marcos M, Alcala R, Barbera J et al (2008) Photosensitive ionic nematic liquid crystalline complexes based on dendrimers and hyperbranched polymers and a cyanoazobenzene carboxylic acid. Chem Mater 20 5209-5217... 

Figure 2.56 Effective magnetic moment / eff (in Bohr magneton units) of the liquid-crystalline complex [Tb(LH)3(DOS)3]3 as a function of the temperature. Reprinted with permission from Galyametdinov etal., 2007 [179]. Copyright (2007) American Chemical Society...

Cyclopalladation of 4 -(functionalized)-6 -phenyl-2)2,-bipyridine ligands (HL) afforded several new [PdLCl] complexes liquid crystalline complex 50 exhibits thermotropic nematic mesomorphism, which represents the first example of an organometallic mesogen with a terdentate o-C deprotonated ligand. Complex 50 is photoluminescent at 77 K [48]. Other researchers have reported the applications of orf/m-platinated or -palladated complexes bearing azobenzene or imine ligands as liquid crystalline materials [49]. 

Liquid crystals are unique molecular materials because of their anisotropic nature and molecular dynamics [1-4]. Over the last three decades, these materials have been developed as advanced materials for electrooptical applications such as display devices. Liquid crystals also have close relationships to biomolecular systems [5]. Cell membranes form dynamic and anisotropic molecular states, which possess liquid-crystalline behavior. Recently, liquid-crystalline complexes of DNAs and liposomes have been considered as potential systems for gene therapy [6]. The design of liquid crystals by using a variety of structures and interactions may lead to wider applicability of mesomorphic materials. 

Fig. 3. Supramolecular liquid-crystalline complex 1 obtained by the formation of hydrogen bonding between benzoic acid and pyridine moieties...

Fig. 5. Plot of transition temperatures for supramolecular liquid-crystalline complex 10 as a function of chain length (n) of the stilhazole moiety...

Table 2. Comparison of transition temperatures of hydrogen-bonded liquid-crystalline complexes and normal liquid crystals ...

Double hydrogen bonding has been used for molecular recognition and organization [60]. Doubly H-bonded supramolecular liquid-crystalline complexes based on 2,6-bis(acylamino)pyridines show unique mesomorphic behavior. Complexes 21 exhibit monotropic crystal B phases [61, 62]. 

Triply hydrogen-bonded 1 1 liquid-crystalline complexes 23 are formed by molecular-recognition processes of uracyl and 2,6-diaminopyridine derivatives [27], The complex with R - CH3, k = 1 = 10, m = 11, and n = 16 exhibits a metastable columnar hexagonal phase below 72 °C, In this case, the complex contains four long aUcyl chains. An X-ray study has shown that two complex molecules form one column side-by-side. 

The resulting optical pattern is shown in Fig. 2.12e. However, no formation of SRGs was observed for the investigated liquid crystalline complexes. 

Wang Jiu-fen, Zhu Long-Xin., Huo Hong-Xing. (2003). The Method for Producing Thermotropic Liquid-Crystalline Complex Copolyester of Polyethyleneterephthalate. J. Funct. Polym, 16(2), 233-237. 

TBBA with temperature of phase transition crystalline 113.0 C, smectic G 144.5 C, smectic A 199.0 C, nematic 235.0°C, isotropic (Scheme 5). Liquid-crystalline complex with transition metal ion [e.g., Cu(ll)] (Scheme 6). 

It is possible to achieve good separation of drugs, environmental pollutants, and components of biological liquids having electron donor properties on liquid-crystalline complexes with ions of transition metals. In recent years, remarkable progress in research on the use of liquid-crystalline compounds as stationary phases, in both gas... 

More than 200 compounds are provided by salts of aliphatic or aromatic acids and alkali or alkaline earth metals. Liquid crystalline complexes of transition metals have also been synthesized, e.g., where M is Pt or Ni. 

II. Supramolecular Low-Molecular Weight Complexes A. Liquid-Crystalline Complexes... 

Figure 11 Disklike liquid-crystalline complexes 14 and 15 consisting of identical molecules.

Figure 6 Typical examples of low-molecular weight, hydrogen-bonded, liquid-crystalline complexes [43-47],...

Isocyanides have also found their way into mesogenic (liquid crystalline) complexes of platinum(ii). Rod-like isocyanides 112 that are themselves liquid crystalline continue to exhibit mesophases when coordinated in a trans-fashion to platinum, with the additional bonus of an increase in thermal stability. Thus, whereas the uncomplexed isocyanides show smectic A and nematic phases in the range 60-90 °C (with decomposition evident even at these temperatures), the platinum complexes 113 show smectic G and nematic phases in the temperature range 125-275 °G with no decomposition. Both cis- and trans-geometr ics were investigated, but the m-complexes exhibited no mesogenic behavior at all. 

Ambrozic, G., Mavri, J., Zigon, M. (2002), Liquid-crystalline complexes of polyurethane containing an isonicotinamide moiety with 4-dodecyloxy benzoic acid, Macromolecular Chemistry and Pl sics, 203,439—47. 

The same group [30 b] prepared platinum and palladium complexes. The coordination of the isonitrile to a metal increases the thermal stability of the ligand. Both Pt and Pd complexes show mesomorphic properties. The liquid crystalline complex [Ptl2(CNC6H4C6H40C7H,5)2] has been crystallographically characterized. 

Copper(I) complexes show a lamellar structure not conclusively assigned [175]. Liquid crystalline complexes with chromium, molybdenum and tungsten as metallic centers have also been reported. The 1,4,7-trisubstituted 1,4,7-triazacyclononane and three carbonyl groups, 80, are coordinated in an octahedral geometry. 

Table 3. Transition temperatures of liquid-crystalline complexes 10 and 11 based on 4-hex-yloxybenzoic acid and 4-octylpyridine, and of 4-octylphenyl 4-hexyloxybenzoates (OPHOB and OPHOFB).

Variable temperature infrared spectra for hydrogen-bonded liquid-crystalline complexes have shown that the structure of the hydrogen-bonded mesogen is stabilized by molecular ordering and packing in the liquid-crystalline state [16,18,27]. The stability of the hydrogen bond suddenly decreases once the complex becomes isotropic disordered [16, 18, 27]. 

Fig. 11.20 Liquid crystalline complexes composed of rod-shaped mesogenic molecule containing hydroxyl groups and ionic liquid...

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