Nickel liquid crystal complex

Cobalt(II) nitrate induces a columnar nematic phase in the 1 2 complex with 98 (Table 7) as deduced from X-ray scattering which is stable for 30 K. Also, nickel(II) nitrate turned 98 into a liquid crystal with an unknown phase. The complex between 99 and copper(II) nitrate showed the same unknown mesophase. The phase range was 140 K but the samples decompose before clearing. A possible reason for the induction of a mesophase by complexation is the stiffening of the crown and the adjacent flexibly linked groups [112]. 

KEYWORDS liquid crystal, thermochromism, nickel complex, structure analysis... 

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... 

Among the three-chained complexes investigated ((78) M = Cu, Ni R = R = R" = OC H2 +i, n = 14, 16), only the nickel derivatives exhibited a Colh phase above about 65-70 °C, existing for about 5 °C only, while again the copper complexes were not liquid crystals. Here, the reduction in the mesophase stability most probably resulted from steric factors. These results somehow contradicted those obtained for the iminoketone compounds (X = Me), for which the presence of the methyl groups was expected to destabilize the mesomorphism and reduce the transition temperatures instead of enhancing the mesomorphic properties. 

Previous work has shown the nickel dithiolene dye as a desirable candidate for the LCPDl. The nickel dithiolene has a unique aromatic ring structure, which imparts a relatively high infrared absorption and a high thermal and photochemical stability. With 2 alkoxyphenyl substitutions onto the nickel dithiolene core, these complexes possess optical absorbance bands at the desirable wavelength of the laser. However, these alkoxyphenyl substituted compounds have demonstrated limited solubility in the host liquid crystal medium. The potential of an alkyl-phenyl substituents to increase the solubility of the dithiolene dye in the host liquid crystal medium was the primary topic of this investigation. 

The substituted nickel dithiolene dyes are discotic liquid crystals dissolved in the E7 nematic host. There are two molecular components to the nickel dithiolene dye the nickel bis (dithiolene) core and the substituted R groups. The nickel bis (ditholene) core is a unique conjugated transition metal aromatic complex which absorbs near infra-red radiation. 

Ohta, K. Discotic Liquid Crystals of Transition Metal Complexes. 4 1 Novel Disco tic Liquid Crystals Obtained from Substituted Bis(dithiolene)nickel Complexes by a New Method. Mol. Cryst. Liq. Cryst.,1987 Gordon and Breach Science Publishers S.A., Vol 147, pp 15-24. 

Both Bruce (1485) and Hoshino-Miyajima (1486) and co-workers prepared bis(dithiocarbamate) complexes with long-chain substituents as potential liquid crystals. Most are derived from four-substituted piperazines with flexible alkoxy tails (345), and are mesomorphic, showing smectic phases Sc and crystal B mesophases (1485). Palladium, copper, and zinc bis(dithiocarbamate) complexes of the same ligands showed similar behavior, but nickel piperazine complexes with 4-phenyl, alkyl, and 3-alkoxy tails are non-mesomorphic (1485). 

It was decided to study the system tetrakis (trifluorophosphine) nickel- (0) -ammonia (23) in some detail a smooth reaction was observed when the complex, condensed on excess ammonia at liquid air temperature, was allowed to warm up gradually. Precipitation of colorless crystals, identified as ammonium fluoride in almost stoichiometric amount, based on complete ammonolysis of the phosphorus-fluorine bonds, was observed at temperatures as low as —90° to —80°. Removal of the ammonium fluoride by filtration at temperatures not higher than —50°, and subsequent slow evaporation of the ammonia from the filtrate invariably led to a brown-yellow solid, although a colorless, crystalline material was formed initially. The product was decomposed almost instantaneously by water with precipitation of elemental nickel. Analysis of the hydrolyzate obtained in aqueous hydrochloric acid revealed a nickel-phosphorus-nitrogen atom ratio close to 1 4 4, corresponding to an apparently polymeric condensation product. 

K4[Ni(CN)4] also belongs to this group it is produced from potassium in liquid ammonia from normal K2[Ni(GN)4]. The former can perhaps be regarded as a complex, built up from a nickel atom and four CN ions, thus with 10 + 4 X 2 electrons around the central atom in a krypton configuration, in place of 8 + 4 X 2 as in the ordinary complex of Ni2+. One would have to expect tetrahedral sp3 bonding as opposed to the normal dsp2 bonding in K2[Ni(CN)4] the crystal structure is, however, not known. 

Hydrocyanic acid is most easily prepared from its potassium salt, K(CN), which is obtained principally by the decomposition of the complex double cyanides of iron as we shall soon consider. The acid is also obtained by the hydrolysis of certain glucosides, e.g., amygdalin, in bitter almonds. It is prepared synthetically by reactions to be discussed presently in connection with the constitution of it and its salts. It is a colorless liquid with a characteristic odor and burns with a violet flame. It boils at 26.1 and solidifies to crystals which melt at —14°. It is an extremely strong poison the best antidotes being chlorine and hydrogen dioxide. It is readily absorbed by metallic nickel which is thus used in gas masks for this purpose. It is stable in dry air but in presence of water is readily hydrolyzed yielding ammonia and formic acid as the chief products. 

The nickel complex, Ni ( 5115)2, has been made by the action of the Grignard reagent on nickel (II) acetylacetonate (217) or from potassium cyclopentadienyl and the ammine [Ni(NHs)el (S N)2 in liquid ammonia (58). It forms dark emerald-green crystals which sublime at 80-90° and which, when heated in nitrogen, melt, with decomposition and the formation of a nickel mirror, at 173-174°. It is only slowly oxidized in air, and cold water neither attacks nor dissolves it it is, however, readily soluble in organic liquids. Oxidation of the compound yields an orange-yellow solution containing the ion [Ni( 5H5)2]+, which is stable for a short period in weakly acidic media, and which may be precipitated as the reineckate or tetraphenylborate. 

After dissolving the metal oxides, the iron is precipitated and removed as jarosite (for problems, see Section 9.6.2), followed successively by copper and zinc (liquid extraction with various complexing agents, stripping with sulfuric acid and subsequent precipitation crystallization), chromium (oxidation and precipitation as lead chromate) and nickel (crystallization as sulfate). The estimated costs are around 200 ton which is only slightly above the costs for disposal. 

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