Cyanobiphenyl 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. 

The linear dichroism of nickel(II), palladium(II) and zinc(II) complexes of mesomorphic 4-alkoxydithiobenzoic acids has been investigated in the commercial eutectic mixture of cyanobiphenyls and cyanoterphenyls, E7 (from Merck) for the palladium(II) complexes and in the commercial mixture of cyanobicyclohexanes, ZLI2830 (from Merck) for the nickel(II) and zinc(II) complexes (Figure 2.12).For the nickel(II) and palladium(II) complexes both a ligand-based transition and a charge-transfer band (MLCT) were observed, whereas only a ligand-based transition was present for the zinc(II) complexes. These complexes had a much lower solubility in the liquid crystal host matrix than the dithiolene... 

Finally, 4-pentyl-4 -cyanobiphenyl (CB), a compound with mesogenic properties, has been co-condensed with europium and samarium atoms. On the basis of matrix IR spectra and DFT calculations at the B3LYP level, it has been proposed that at low temperatures (below 30 K) mononuclear sandwich complexes [(CB)2Eu] and [(CB)2Sm] were obtained while with higher concentration of metal and at higher temperatures bimetallic sandwich complexes [(CB)2Eu2] and [(CB)2Sm2] were present, in which both phenyl rings of CB are coordinated to Eu or Sm (Vlasov et al., 2005). 

The question as to whether hydrogen-bonded complexes are miscible with normal covalently bonded liquid-crystalline compounds arises for their application. Binary phase diagrams of a hydrogen-bonded mesogenic complex with normal liquid crystals have been prepared to examine the miscibility of two different classes of liquid crystals [67], Compound 16 or 4 -heptyl-4-cyanobi-phenyl was mixed with complex 14, These are miscible over the whole range of composition, A smectic C phase is induced for a mixture of 16 and the cyanobiphenyl. 

Figure 26. (Bio)mesogenic order-disorder patterns rather than geometric anisotropies as general preconditions for the appearance of mesophases a) classical thermotropic cyanobiphenyl nematic [25 a, 51e] and thermotropically designed steroid hormone cholesteric [17 a, c, d, 26 f, 51 a, s, u] b) protein-j3-sheet simulative diacylhydrazine smectic [17 a, c, d, 26f, 511] c) hexaalkanoyloxybenzene discoid [28 a, 51c] ending the century of rod-like dominance d) lyotropic poly(L-glutamic acid) [51 d, 52 k, 1] changing with an alkyl-disorder shell from lyotropic to thermotropic [58e] e) ds A-RNA lyotropic [52n-w, 75] f) am-photropic(L-Lys) /RNA recognition complex [17,18, 75],...

The butyl derivative of these nickel complexes was investigated as a dye in a guest-host system using 4-pentyl-4 -cyanobiphenyl (5CB) as the host. The complex was found to have a large extinction coefficient of absorption (e = 28,000 moC dm cm at 860 nm) and dissolved in 5CB at concentrations up to 10% (w/w). At 20 °C, such solutions showed a dichroic ratio (Rd. defined as + /+x = absorbance) of 4.97 and a dye order parameter of 0.57. 

N03)3], neither for the complexes with ligands similar to L27 and L28, but with methyl groups on the terminal cyanobiphenyl groups. An overview of the transition temperatures and mesophase behavior of the 2,6-bis(l-ethyl-benzimidazol-2-yl)pyridine complexes is given in Table 14. 

Co-condensates between metallic samarium and 4-pentyl-4 -cyanobiphenyl (5CB) in the solid phase have been obtained via joint atomic/molecular beam deposition on a cooled calcium fluoride surface at liquid nitrogen temperature (Shabatina et al., 2000, 2001, 2005). The film samples have been studied by IR and UVA IS spectroscopy in the temperature range from 80 to 300 K. Two types of complexes were detected, one complex with a metal to ligand... 

TABLE 22 Transition Temperatures and Mesophases of the Lanthanide tris 2-Thenoyltrifluoroacetylacetonate Complexes of Substituted lmidazo[4,5-f]-1,10-Phenanthroline Ligands with Appending Cyanobiphenyl Groups ... 

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