This invention relates to liquid crystals and more particularly to liquid crystals containing a transition

-*• _n metal and to ionic liquid crystals.

5 Known liquid crystals containing a transition metal are complexes of the type [ (L-H)PdCl] _, [ (L-H) _Cu_ , or [ (L-H) _M] where M represents Cu, Ni, Pd or Pt and L represents a ligand precursor. In order to form these complexes hydrogen must be lost from the compound L, i.e. 10 the ligand precursor (which can be a mesogen) to form the chelating ligand (L-H) . In addition an anionic ligand for example a halide must be lost from the metal. These two requirements limit the ligands and metals from which the liquid crystals can be formed.

15 According to the present invention there is provided a liquid crystal compound formed by coordination of a mesogenic organo nitrogen ligand, via a nitrogen donor atom, or of a lyotropic organic carboxylate with a metal or the metal centre of a transition metal complex. Many

20 of these liquid crystals are coloured.

The invention also provides a method for preparing a liquid crystal compound by combining a mesogenic organo nitroge ligand via a nitrcgen donor atom, or a lyotropic organic carboxylate with a metal or the metal centre of a transition metal 25 complex .

The invention also provides liquid crystal compounds formed, by ionic interaction of mesogenic cations with mesogenic anions. The anion and/or the cation may contain a metal. Alternatively the anion and cation may both be purely organic materials.

The invention provides, therefore,-a general method for. obtaining a wide variety of liquid crystals having useful properties. Organo-nitrogen compounds which can be used in the present invention include nitriles, heterocyclic compounds such as pyridines and amines. The transition metals most usefully employed in the present invention include d-block transition metals.

The liquid crystal compound of the invention may be of different types. The first type can be represented by the general formula

L-MX- (I)

where L represents organo-nitrogen mesogen

M represents a metal X represents halide

Preferred embodiments of type I compounds are obtained when the metal is palladium (type la) or platinum (type lb) .

A further type of compound obtainable in accordance with the present invention is represented by the general formula

LRh(CO)-X (II)

LAuX (III)

where L and X are as defined above.

Yet another type comprises the ionic materials represented by the formula

+ -

[L ₂ Ag] BF ₄ (IV) [L ₂ Ag] ⁺ Y ^" (V)

X ⁺ Y~ (VI)

where L is as defined above, Y is a mesogenic anion and X is a mesogenic cation.

A further type of compound is represented by the formula

t(RCOO) ₄ M ₂ 3 (VII)

where R represents an alkyl or aryl group, for example C, .H-- and M is as defined above.

The compounds of the present invention are readily synthesised from easily obtainable materials. The compounds are air stable.

The liquid crystal compounds of the present invention display a variety of separate phases. In particular the preferred materials of types I, II, III, IV, V and VI showed nematic phases and in some cases smectic phases. The transitions between the phases were in some instances enantiotropic and in other cases monotropic. Mixtures of; compounds for example of type la but derived from di ferent organo-nitrogen mesogens having monotropic phase transitions can be obtained with enantiotropic phase transitions.

The following Examples further illustrate the invention.

In the Examples the composition and structure of the compounds was established by elemental analysis (C, H, Cl and N) by ¹ H and ¹³ C NMR spectroscopy and by IR spectroscopy. Phase transition temperatures were measured by hot stage optical microscopy and the esophases were identified by their optical textures.

EXAMPLE 1

4-Carbonitrile-4'-nonyloxybiphenyl (0.34 cm , 1.0 mmol) was added to [PdCl- (PhCN) (0.2 g, 0.52 mmol) dissolved

3 in acetone (30 cm ). The solution was stirred (20°C, 2h) , the acetone was removed in vacuo, and the residual solid was triturated with ethanol (20 cm ) to give the product, bis (4-carbonitrile-4'-nonyloxybiphenyl)dichloropalladium (la, L = C ₉ H ₁₉ OCgH.CgH ₄ C ; 0.35 g 84%) as orange crystals.

EXAMPLE 2

4-Carbonitrile-4-octylbiphenyl (0.25 ml, 0.9 mmol) and [PtCl_ (PhCN) (0.2 g, 0.42 mmol) were refluxed in

3 toluene (50 cm , 20 h) . The toluene was then removed in vacuo, the residue triturated with ethanol, and crystallised from dichloromethane-ethanol to give bis (4-carbonitrile-4'-octylbiphenyl)dichloroplatinum

(lb, L = CgH ₁₇ CgH.C ₆ H ₄ C ; 0.15 g, 43%) as yellow crystals.

EXAMPLE 3

Addition of 4-carbonitrile-4'-nonyloxybiphenyl

(0.17 g, 0.54 mmol) to a solution of [ ₂ (CO) ₄ C1-,] (0.1 g, 0.26 mmol) dissolved in hexane (10 cm 3) gave a yellow precipitate. This was filtered off and washed with hexane to give orange cis-dicarbonyl(4-carbonitrile-4'- nonyloxybiphenyl)chlororhodium (0.2 g, 77%)

(II, L = C.H ₁₉ OC ₆ H ₄ C ₆ H ₄ CN).

EXAMPLE 4

4-Butoxy-4'-stilbazole (0.078 g) was added to a solution of silver tetrafluoroborate (0.03 g) dissolved in dry acetone (5 cm 3) . A solid slowly precipitated

(over 1 h/20°C). The solvent was then removed in vacuo, to leave a yellow residue which was washed with hexane and air dried to give yellow bis(4-butoxy-4'-stilbazole) silver tetrafluoroborate [IV, L = C ₄ H ₅ OC-H ₄ CH=CHC_H ₄ N

0.07 g, 67%) .

EXAMPLE 5

Molybdenum hexacarbonyl (1 g) was refluxed (4 h)

3 in dry diglyme (38 cm ) with lauric acid (2.25 g) under

N_. A yellow precipitate formed on cooling which was filtered off and washed with diethyl ether under nitrogen to leave yellow crystals. These crystals were dried

(under vacuum at 70°C/24 h) to give the compound VII, [Mo ₂ (C ₁₂ H ₂₁ 0 ₂ ) ₄ 3 (1.73 g, 92%).

EXAMPLE 6

Rhodium trichloride hydrate (0.18 g) , sodium laurate 5. (0.5 g) , lauric acid (1.5 g) and ethanol (absolute, 20 cm 3) were, refluxed together (1 h) under nitrogen. After cooling the solution was filtered; the ethanolic filtrate was allowed to stand overnight and the green-blue precipitate which formed was collected by filtration and 0 dried under vacuum (20°C/18 h; 65°C/20 h) to give the

• green-blue complex (VII) [ ₂ (C. ₂ H ₂₁ 0 ₂ ) (0.12 g;. 36%).

EXAMPLE 7

Cetyltrimethylammonium laurylsulphate, compound VI, X ⁺ = [ e- C ₁₆ H ₃₃ ] ⁺ , Y~ = [SO^ ₂ ^H 25 ^3" ' ^was obtained by

15 extracting with dichloromethane an aqueous solution

3 (200 cm ) of cetyltrimethylammonium bromide (2 g) and sodium laurylsulphate (1.6 g) .

The properties of specific materials of the invention were investigated and thesresults are set out below.

Bis (4-carbonitrile- '-pentylbiphenyl)dichloropalladium (la, L = C _j -H- .C-H.C-H.CN) melted to give an isotropic fluid at 125°C. On cooling, a monotropic nematic phase was observed at 92°C.

Bis (4-carbonitrile-4'-nonyloxybiphenyl) dichloropalladium (la, L = C-H ₁₉ OCgH ₄ CgH ₄ C ) melted to give a mesophase at 119°C which persisted until an isotropic liquid was present at 147°C. On cooling from the isotropic liquid, a nematic phase was formed and the material was totally nematic at 130°C.

Bis(4-carb onitrile-4'-octylbip enyl) dichloroplatinum melted to give a nematic phase at 170°C which turned into an isotropic fluid at 190°C.

The complex cis-dicarbonyl-(4-carbonitrile-4'- nonyloxybiphenyl)chlororhodium melted to give a nematic phase at 52°C which turned into an isotropic liquid at 80°C.

The complex bis (4-butoxy-4'-stilbazole)silver tetrafluoroborate (iv, L = C^-OCgE CI^CHC-EL ) melted at 180°C to a smectic phase which on heating to 305°C became an isotropic liquid.

Mixtures of (la, L = C-^CgH^ _Q CgH^CN; X = Cl) and

(la, L = C ₅ H _1l CgH ₁₀ CgH ₁₀ CN; X = Cl) showed enantiotropic nematic phases whereas the second component only showed a monotropic nematic phase.