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Document Type and Number:
WIPO Patent Application WO/1999/023865
Kind Code:
Methods of forming metal alkoxides and methods of forming precursor solutions of metal alkoxides suitable for the coating of glass in the manufacture of electrochromic devices are disclosed. The method of forming metal alkoxides involves dissolving the a metal halide in an anhydrous solvent and reacting it with an alcohol and (together with the addition of the alcohol or subsequently) adding an epoxide, and then evaporating-off the volatile components of the reaction product to leave a solid metal alkoxide that is substantially free of halide. The alkoxide may then be dissolved in a solvent including an alcohol (preferably ethanol) containing a small proportion of water to produce a precursor solution suitable for coating glass, the coating then being hydrolysed to form a sol-gel and then baked to remove volatile components and to yield a thin layer of metal oxide.

Application Number:
Publication Date:
May 20, 1999
Filing Date:
November 06, 1998
Export Citation:
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International Classes:
B05D5/12; C07F11/00; C07F19/00; C09K3/00
Attorney, Agent or Firm:
Grant, Paul A. (ACT 2611, AU)
Sustainable Technologies Australia Limited (11 Aurora Avenue Queanbeyan NSW 2620, AU)
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1. A method of preparing metal alkoxides characterised in that a metal halide is reacted with an alcohol and an epoxide under anhydrous conditions to form a reaction product that includes metal alkoxides and haloalkyl moieties.
2. A method according to claim 1 wherein: said metal halide and said alcohol are first reacted in an anhydrous solvent to form a first reaction product, and said epoxide is then added to said first reaction product to generate said haloalkyl moieties.
3. A method according to claim 1 wherein: said metal halide and said epoxide are reacted prior to the addition of said alcool.
4. A method according to claim 1 wherein : said metal halide is dissolved in an anhydrous solvent to produce a metal halide solution prior to the addition of said alcool, and said alcohol and said epoxide are then added together or in sequence to said metal halide solution.
5. A method according to any preceding claim including the step of removing said haloalkyl moieties by evaporation to leave a metal alkoxide residue substantially free of halogens.
6. A method according to any preceding claim wherein: said metal halide is a metal chloride, said anhydrous solvent is npentane or hexane, said haloalkyl moieties are chloroalkyl moieties, said epoxide is a member of the group comprising ethylene oxide, propylene oxide and butylene oxide, and/or said alcohol is selected from the group comprising branched or straightchain alcools with 18 carbon atoms.
7. A method according to any preceding claim wherein said metal halide is a halide of a metal selected from the group comprising Fe, In, Nb, Mo, Ce, Ir, Co, Cu, Zr, Ta, Al, Cd, Sb, Zn, W and Y.
8. A method of preparing a precursor solution for use in forming a transparent metal oxide coating on glass, said method including the step of dissolving the metal alkoxide reaction product of any one of the preceding claims in an alcool.
9. A method of forming a precursor solution for use in forming a transparent metal oxide coating on glass, said method comprising the following steps: adding nbutanol and/or ethanol to the metal alkoxide product of the method of any preceding claim to form a mixture, and heating said mixture to dissolve said product to produce the precursor solution.
10. A method of preparing a precursor solution for use in forming a transparent metal oxide film on glass in the manufacture of an electrochromic device, said method comprising the following steps: dissolving a metal chloride in a solvent comprising a pentane or hexane to form a metal chloride solution under anhydrous conditions, adding a straight or branched chain alcohol having 18 carbon atoms to the metal chloride solution to generate a reaction product including chloroalkyl moieties, under anhydrous conditions, removing said chloroakyl moieties by evaporation to leave an alkoxide residue, and dissolving said alkoxide residue in a nonaqueous solvent to form the precursor solution.
11. A method according to claim 10 wherein the metal chloride is tungsten chloride and said alkoxide residue is a tungsten alkoxide residue.
12. A method of forming a metal oxide film on glass comprising the steps: dissolving at least one metal chloride, selected from the chlorides of the metals Fe, In, Nb, Mo, Ce, Ir, Co, Cu, Zr, Ta, Al, Cd, Sb, Zn, W and Y, in an anhydrous organic solvent, selected from the group npentanes and hexanes, to form a metal chloride solution, adding an anhydrous branched or straight chain alcohol of 18 carbon atoms to said solution to form a metal alkoxide solution, adding to said metal alkoxide solution an anhydrous epoxide selected from the group ethylene oxide, propylene oxide and butylene oxide to form a reaction product that includes metal alkoxide and haloalkyl moieties, separating said haloalkyl moieties from the reaction product by evaporation to produce a metal alkoxide residue, dissolving said residue in a nonaqueous solvent and a minor proportion of water to form a precursor solution, applying said precursor solution to a glass substrate and allowing it to dry to form a thin alkoxide layer thereon, exposing the layer to moisture to hydrolyse said layer and to form a sol gel layer on said substrate, and heating said solgel layer to drive off volatile components thereof and to form a layer of metal oxide on the substrate.
13. A method according to any preceding claim wherein a mixture of two or more metal halides is employed and the precursor solutions comprises a mixture of the corresponding alkoxides.
TITLE: PREPARATION OF METAL ALKOXIDES TECHNICAL FIELD This invention primarily relates to metal alkoxides and metal alkoxide solutions suitable for use as precursors in the production of metal oxide coatings on glass and similar substrates, to methods for the preparation of such metal alkoxide precursors and to the coatings and devices employing such coatings. The glass substrates of particular interest are those employed in large-are electrochromic 'smart windows'that require a variety of nanocrystalline metal oxide coatings.

Unless otherwise made clear by the context : 'Metai'refers to any of the conventional metals and also those'metals'or 'metalloids'of Groups III-A, IV-A and V-A of the Periodic Table of the elements, such as silicon, boron, aluminium, tin, antimony and the like.

* Metal alkoxide'refers to any metal compound derived from an alcohol or alcohol-containing organic moiety wherein the hydroxylic hydrogen of at least one hydroxyl group has been replace by a metal, and thus includes alkali and alkali earth metal alkoxides.

'Metal haiides'includes oxymetal halides.

The metal alkoxides and alkoxide precursor solutions of this invention have particular use in the production of nanocrystalline metal oxide films on large- area glass panels. The films are of high quality, transparent and suitable for use in electrochromic devices. They have valuable application in other areas of industry and technology, such as in catalysts and electronic devices.

BACKGROUND TO THE INVENTION Metal alkoxides are important in the formation of thin nanocrystalline transparent layers of metal oxides on glass substrates by sol-gel techniques. Typically, the metal alkoxide is applied in a liquid solvent (precursor solution) to a substrate such as a glass by dip-coating or spin-coating. The solvent is removed by evaporation and the metal alkoxide is exposed to water vapour to enable hydrolysis and condensation to produce a metal oxide and/or hydroxide sol-gel

and alcool. The coated substrate is then baked at moderate temperatures to remove residual alcohol and form the desired nanocrystalline metal oxide thin layer.

The production of alkoxides from metal halides-especially metal chlorides-for use in electrochromic devices is well known, but the methods are generally tedious and can result in low yields because of the problem posed by the removal of the hydrogen halide by-product. Whereas the reaction of metal chlorides with any of the common alcools is mildly exothermic and proceeds without difficulty, the standard method of removing by-product HCI (Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P.; Metal Alkoxides, Academic Press, London, 1978) is laborious and involves the use of anhydrous agents in non-aqueous solvents. The HCI by-product is reacted with a base such as ammonia, alkyl amines, pyridine or sodium alkoxide to produce chloride salts that are insoluble and precipitate from the solvent used. The above textbook reports the use of ammonia for the preparation of alkoxides from the metal halides of Si, Ge, Ti, Zr, Hf, Nb, Ta, Fe, Sb, V, Ce, U and Th. It also reports the use of sodium alkoxide for the preparation of the corresponding metal alkoxides from the metal halides of Ga, In, Si, Ge, Sn, Fe, As, Sb, Bi, Ti, Th, U, Se, Te, W, lanthanides, Ni and Cr.

These methods, however, are cumbersome and suffer from several disadvantages. The fine precipitates (eg. NH4CI, NaCI) are impractical to filter and the products are obtained only after several prolonge steps of settling, decantation and washing with excess solvent to obtain the maximum yield.

Further, in some cases (eg. Sn, W) the products are often contaminated by the presence of varying amounts of chloride and sodium ions and also NH3 or its derivatives. Washing the non-aqueous solution with water to remove chlorides is unacceptable because the metal alkoxides would be rapidly transformed to metal hydroxides and alcool.

In particular, we have found that, during the preparation of tungsten (VI) oxo- tetra-alkoxide, WO (OR) 4, from WOC14, alcohol and ammonia, an insoluble tungsten-containing compound often coprecipitates with ammonium chloride, making the extraction of the product extremely difficult. Reasons for this behaviour are unclear, but insoluble tungsten material could be due to dimer formation or some other incompletely understood interaction of NH3 and/or NH4CI with tungsten alkoxide in hydrocarbon solvent. Excess ammonia can be added to dissolve the precipitated tungsten compound, but we have found that the final tungsten oxide obtained from such precursors is unsuitable as a film for electrochromic applications since the reversibility of the colouration-bleaching cycle is inadequate. This is still the case even when no significant amounts of chloride ions and ammonia-derived impurities were detectable in the alkoxide.

We believe that the behaviour of W03 in the film prepared by this route is heavily dependent upon the structure of the precursor tungsten alkoxide, which in turn is influence by the NH3 concentration during its preparation.

Furthermore, we have found that alcoholic solutions of metal alkoxides prepared by the NH3 route are often unstable, resulting in the precipitation of insoluble metal-containing material over time. This means that a single batch of alkoxide produces variable quality coatings.

Similar difficulties with the removal of chloride are encountered in the production of tin alkoxides for use in glass coatings and are addressed in US Patent No.

4,731,461 (1988). This patent teaches the use of ammonia as described by Bradley et a/. as the first step of a two step process in which the product of the first step is treated with a metal amide or a metal alkoxide and additional alcool. This results in the precipitation of a metal halide salt that can then be removed by filtration. With other metals of interest, particularly tungsten, the two step process taught by patent 4,731,461 is not satisfactory. As explained above, the first step is cumbersome, has a poor yield and generates little understood side products that render the resultant alkoxide material unsuitable for electrochromic purposes.

A number of prior art patents disclose the production and use of metal alkoxide for use in electrochromic coatings but do not address the problem of chloride removal. For example, in U. S. Patent No. 4,347,265 (1982) tungsten (VI) chloride (WCI6) is dissolved in an organic solvent such as methanol, isobutanol, ethanol, or acetic anhydride and it is implied that the resultant solution is applied to the substrate without further treatment and then baked to form the desired electrochromic layer. Similarly, U. S. Patent Nos. 4,996,083 (1991) and 4,855,161 (1989) disclose the preparation of electrochromic coating solutions by reacting anhydrous transition metal halides, preferably chlorides, such as tungsten chloride, with lower carbon, anhydrous alcools, but no manner of removing contaminating chloride is disclosed. While U. S. Patent No. 5,659,417 (1997) discloses the use of tungsten and molybdenum alkoxides in alcohol solutions, the method of preparing the alkoxides from metal chlorides, is that of U. S. Patent No. 4,996,083 outlined above.

Our experience has been that, while satisfactory coatings can be made in rare instances by the methods of the just-mentioned patents without removing the chloride impurities, the precursor solutions are not stable, the coatings are prone to discolouration and crazing and, if electrochromic, have poor reversibility and bleaching qualities. We have found that, in contrast with the above prior-art methods, the addition of an epoxide to the initial reagents results in the formation of volatile chloro-organic compounds which can be readily removed by evaporation from the alkoxide product to leave a residue that can be readily re-dissolved in a suitable solvent. This allows effective removal of the hydrogen halides from the solution without causing complicated side reactions like those associated with the use of NH3. The use of such alkoxide precursors results in superior nanocrystalline coatings of metal oxides on glass substrates.

We have also found that the epoxide can be reacted directly with some metal halides (such as WCI6 and VoCts) and that the an alkoxide precursor solution prepared without removing the chloro-organic compounds performs surprisingly well in forming oxide coatings on glass. It appears that the chloro compounds

vaporise off the wet film during drying and/or baking, leaving the properties of the metal oxide coating unaffected.

U. S. Patent No. 3,458,306 (1969) discloses the addition of epoxy compounds to hydrated metal chlorides of nickel and aluminium dissolved in an alcohol to produce a metal hydroxide gel. The gel is first heated in an oxidising atmosphere to remove the remaining organics and is then heated in a reducing hydrogen atmosphere to reduce the hydroxide to the metal powder. However, the method cannot produce intermediate alkoxides because of the presence of the water of crystallisation in the hydrated metal chloride. Similarly, U. S. Patent No. 4,551,358 (1985) discloses a method for the preparation of nickel oxide electrodes by dissolving hydrated cobalt and/or nickel chloride (eg. NiC12. 6H20) in an alcool, optionally with addition water. After applying this solution to a porous nickel substrate and allowing the epoxy compound to contact the impregnated substrate, the volatile by-products are removed by baking. As in the last mentioned patent, the formation of alkoxides is prevented by the presence of water in the solution derived from the water of crystallisation.

U. S. Patent No. 3,931,260 (1976) discloses the formation of organometallic compounds for coating glass fibres to impart abrasion resistance. The compounds were prepared by the reaction of metal halides and one or more epoxides and characterised by the presence of beta-haloalkoxy groups that were said to improve resistance to hydrolysis. Often, more complex epoxides containing from 2 to 20 carbon atoms with one or more functional groups were employed. The preferred metal halides were TiCI4 and TiBr4. The organometallic compounds and treatments disclosed by patent 3,931,260 are not suited for producing metal oxide coatings on glass and such use was not disclosed.

European Patent No. 369,979 (1989) discloses a way of making fine spherical powders of Zr02 by dissolving anhydrous zirconyl chloride in n-propanol, to which 1,2-epoxypropane and triethylamine are added. The intermediate zirconyl compound was then treated with a mixture of water, oleic acid and propanol to

effect the hydrolysis and to produce spherical particles of zirconium oxide.

Again, alkoxides and their solutions suitable for the production of metal oxide films are not disclosed.

OBJECTIVES OF THE INVENTION The general objective of the present invention is to provide methods for the preparation of metal alkoxides that will avoid one or more of the disadvantages associated with the prior art. More particularly, but not essentially, a further objective of the invention is to provide alkoxide coating precursor solutions suitable for use in forming coatings of metal oxides on large-area substrates, such as glass, by the sol-gel technique.

OUTLINE OF THE INVENTION From one aspect, the present invention involves the reaction of epoxides with metal halides so that the presence-or the addition-of an alcohol will result in the formation of volatile haloalkyl compounds that are readily removed by evaporation or distillation. The removal may be done at the time of the alkoxide reaction or, for example, after the reaction product has been applied as a film on a substrate. The latter procedure has been found to be satisfactory in the preparation of tungsten oxide and tin oxide coatings, but the former procedure is more widely applicable and is generally preferred.

A typical procedure for forming a transparent metal oxide coating on glass will therefore be: (i) suspend or dissolve the halide (s) of the selected metal (s) in an anhydrous organic solvent, (ii) add a mixture of an alcohol and an epoxide at a rate to control the reaction which forms the alkoxide (s), (iii) remove the volatile components of the new reaction product by evaporation or distillation to thereby remove the halogen (s), (iv) dissolve the residue in an alcohol to form a precursor solution, (v) apply the precursor solution to the glass as thin film, (vi) dry the film releasing any alcohol and residual volatile components, solidifying the coating, (vii) allow the film to adsorb moisture and hydrolyse to form a sol- gel, and (viii) bake the glass and the film to form the desired transparent metal

oxide coating.

If the haloalkyls are removed by evaporation when they are formed, the resulting residue is readily re-dissolved in alcohol to give stable precursor solutions from which thin, transparent and substantially defect-free nanocrystalline metal oxide films can be formed on glass substrates by the simple dip-coating, hydrolysis and firing steps known in the art. Preferably, a minor proportion of water is included in the precursor solutions (for example, by inclusion in ethanol) to improve its physical properties. Electrochromic films (eg, W03) formed from such precursors have been found to have good reversibility and long working lives.

Epoxides such as ethylene oxide, propylene oxide and butylene oxide react with hydrogen halides such as HCI to form halogenated alcools which in turn can also displace halide anions from the initial metal halide, oxymetal halide or its intermediates to form metal haloalkoxy derivatives and the hydrogen halide.

For example, in the case of a chloride: <BR> <BR> <BR> <BR> <BR> <BR> <BR> MCI, + ROH- M (OR) Clin 1 + HCI<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> Epoxide + HUI OH<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> M (OR) Cln., + R'OH- M (OR) (OR') On. 2 + HCI<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> M (OR) (OR') Clin 2 + xROH + yR'OH n M (OR) : +X where:'epoxide'denotes preferably ethylene oxide, propylene oxide or butylene oxide; 0<n<6, 0<x<4 0 # y # 4; x + y = 4; M is a metal or metal oxide; R is an alkyl group preferably with 1 to 10 carbon atoms and R'is a chloroalkyl group resulting from the addition of HCI to the corresponding epoxide.

The method of the invention can be adapted to form alkoxides from a variety of halides, alcools and epoxy compounds and metal elements in various oxidation states, though halides other than chlorides (eg, fluorides, bromides and iodides) are generally less satisfactory. Metal chlorides which can be used to produce alkoxides by the method of this invention include: WCI61 WOCI4, WCI4, MoOCI4, VC15, VOC13, VC13, NbCl5, TaCl5, TiCl4, ZrCl4, ZrOCl2, IrCIs, FeCl2, FeCl3, CoCl2, NiCl2, CuCl2, ZnCl2, CdCl2, AIC13, GaCl3, InCl3, TiCI, GeCl4, SnCl2, SnCl4, SbCls, YC13, and lanthanide chlorides.

The alcools can be straight-, branched-or cyclic-alcohols, preferably, containing 1 to 10 carbon atoms, most preferably 1 to 8 carbon atoms. Similarly, a wide variety of epoxides may be used with the lower carbon epoxides such as ethylene oxide, propylene oxide or butylene oxide being preferred. Even polymers or other high molecular weight materials containing epoxide groups, which are insoluble in the reaction medium eg. bisphenol-A-diglycidylether, triglycidylisocyanurate, glycidyl 3-(pentadecadienyl) phenylether, poly [(phenyl glycidylether)-co-formaldehyde] may be used for ease of separation from the other volatile reaction products in certain cases. The preferred organic solvent for the metal chloride is pentane or hexane.

As already noted, it is envisaged that the epoxides could react with the metal halide directly to displace and capture halide ions in a concerted process forming metal haloalkoxide derivatives which can then be dissolved in alcohol to form a dip-coat solution. However, it must be noted that the chloroalcohol fumes given off by films formed from such dip-coat precursor solutions are toxic and require suitable safety measures during the drying and baking stages. Prior art methods that have employed sodium alkoxide or ammonia to remove by-product HCI were often contaminated by NaCI or NH3-derived residues, but this problem is avoided by the methods of the present invention

DESCRIPTION OF EXAMPLES Having broadly portrayed the nature of the present invention, a number of particular examples will now be described by way of illustration only.

Example 1 illustrates the prior art method of producing tungsten alkoxide by the conventional NH3 route.

Examples 2,3 and 4 illustrate methods of producing tungsten alkoxides that conform to the present invention.

Examples 5 and 6 illustrate the preparation of dip-coat tungsten alkoxide precursor solutions from the alkoxide product of Example 1.

Examples 7 to 11 illustrate the preparation of dip-coat tungsten alkoxide precursor solutions from the alkoxide products of Examples 2,3 and 4.

Examples 12 to 28 illustrate the preparation of metal alkoxides other than tungsten by the methods of the invention.

Examples 29 and 30 illustrate the preparation of metal alkoxides wherein the metal halide is treated initially with epoxide only and the resultant product is then dissolved in solvent alcool.

PREPARATION OF ALKOXIDES Example 1 [Prior Art] To a 1-litre 3-necked flask, with a gas inlet closed with a Teflon tap and also a variable length gas inlet tube secured in position by the rubber seal of an adaptor, is added sublimed WOCI4 (35.6g, 0.104mol) in a nitrogen-filled dry box.

The flask is then connected to a source of dry nitrogen and LiAIH4-dried n- pentane (ca. 800cm3) is added by cannula from a storage vessel. The reaction flask is cooled in water/ice bath and dry n-butanol (46.3g, 58cm3,0.625mol) is added to the mixture by syringe. The solid partially dissolves giving a two-phase liquid system. A reflux condenser is then fitted to the flask with two paraffin oil bubbler vessels at the exit to prevent ingress of moist air and allow the exit of gases.

Dry NH3 gas is distille from sodium metal and allowed to pass into the reaction mixture. The addition of NH3 is stopped once the gas emerging from the second bubbler reacts alkaline (blue colour) with a piece of damp Universal Indicator paper.

The NH4CI precipitate usually begins to settle at this stage, leaving a colourless supernatant liquid containing the alkoxide. After leaving the mixture to settle overnight, the supernatant n-pentane is removed by cannula and filtered into a 1-litre receiver flask. The alkoxide (28.5g, 58% yield based on WOC14) is recovered as a white powder after distilling the solvent and excess n-butanol.

Two further extractions of the NH4CI remaining in the reaction flask with 500cm3 portions of n-pentane can increase the yield to 80-85%.

A typical elemental analysis of the product is C, 39.0; H, 8.01; N, 0.16; Cl, 0. 1%; C16H36OW requires: C, 39.0; H, 7.39%. The detection of small amounts of N in the products of such syntheses has generally been observed. Some samples of alkoxide have been obtained in which the amount of N is over 1 % and where the carbon percentages are lower than expected, eg. C, 37.7 ; H, 7.34; N, 1.38, Cl, 0.12%. Dip-coat solutions prepared from tungsten alkoxide isolated in this manner generally have adequate but variable stability and the electrochromic properties are reasonable but inconsistent.

Very often, however, it has been observed that a tungsten-containing material coprecipitates with the NH4CI and causes the whole reaction mixture to thicken.

The insoluble mixture can easily be dispersed by the further addition of excess dry NH3 gas, but dip-coat solutions of tungsten alkoxides from such reaction mixtures produce thin films with very poor and inconsistent electrochromic properties.

Example 2 A 1-litre 3-necked flask was rigorously dried and flushed with dry nitrogen before being charged with WOC14 (21.0g, 0.062mol). After adding n-pentane (500- 600cm3) under a flow of nitrogen, a reflux condenser was fitted. As n-butanol (9.2g, 124mol) was allowed to react with WOC14, acidic fumes of HCI were evolved. The addition of n-butanol was gradual to avoid a violent reaction.

To the reaction mixture, 1,2-epoxybutane (22.4g, 31 mol) was slowly added by dropping funnel to give a clear pale yellow pentane solution containing a mixture of tungsten alkoxide species. The n-pentane and n-butanol were dried by molecular sieves (4A) at least 24h before use. After distillation of the solvent and volatile products at atmospheric pressure, a solid tungsten alkoxide was isolated and used directly without further purification in the preparation of a dip- coat solution suitable for forming amorphous tungsten oxide layers on glass.

Example 3 A 10-litre flanged flask with an appropriate head, fitted with an inlet for dry nitrogen, reflux condenser, mechanical stirrer and dropping funnel, was purged of moisture and air. The outlet of the condenser was attached by tube to a paraffin oil bubbler to prevent ingress of moist air and to allow the exit of gases.

The whole reactor was immersed in a water bath held at about 5-10°C. The reactor was charged with WOC14 (697.89g, 2.043mol) under a flow of nitrogen and then with 5 litres of n-pentane pre-dried by molecular sieves (4A). In a separate flask some n-pentane (about 200mut), 1,2-epoxypropane (711 g, 857ml, 12.26mol) and n-butanol (187m1, 151g, 2.043mol) were mixed and this mixture was added by dropping funnel to the WOCI4/pentane reaction medium over a period of about 1 hour. The rate of addition was adjusted so that the mixture was kept under gentle reflux. When the addition was complete, further n- butanol (757g, 935moi, 10.215mol) was added and the solvent and volatiles were distilled at atmospheric pressure. Excess n-butanol and displaced chloropropanols were removed under reduced pressure to give a white tungsten alkoxide, which was used without purification to prepare a dip-coat solution.

Example 4 To tungsten (VI) chloride (5.79g, 14.6mmol) in n-pentane (100cm3) was added a mixture of n-butanol 94g, 0.146mol) and 1,2-epoxypropane (12. 2cm3,10.13g, 0.175mol) through a dropping funnel over a period of 15 minutes. The reaction was slow, but eventually a clear, slightly blue-green solution formed.

PREPARATION OF PRECUSOR SOLUTIONS Example 5 To tungsten n-butoxide (41.6g, 0.085mol), from Example 1, was added dry n- butanol (117g, 144cm3 1.579mol) and then dry ethanol (600cm3) to form a slurry.

After stirring for about 30 minutes, a solution of water (1.53g, 0.085cm3) in dry ethanol (95cm3) was added to the alkoxide slurry upon which the residual tungsten alkoxide dissolved completely. An aliquot of a solution of titanium (IV) isopropoxide in ethanol or isopropanol was added by syringe so that the ratio of W: Ti was 4: 1. The solution was slight yellow in colour and after standing overnight was filtered through celite to remove any insoluble particles (see Table 1).

Example 6 Tungsten n-butoxide (20.6g, 0.042mol), from Example 1, isolated from an n- pentane solution to which an excess of NH3 had been added was used to make a slurry with dry n-butanol (72cm3) and ethanol (300cm3). On stirring for about 30-60 minutes, a solution of water (0.75g, 0.042mol) in dry ethanol (45cm3) was added to the alkoxide solution. An aliquot of a solution of titanium (IV) isopropoxide in ethanol (5cm3) was added by syringe so that the ratio of W: Ti was 4: 1. The solution was slight yellow in colour and after standing overnight was filtered through celite to remove trace amounts of insoluble material (see Table 1).

Example 7 To the mixed tungsten alkoxide (0.062mol), from Example 2, was added n- butanol (105cm3) to form a slurry and then a mixture of water (1.1g, 0.061mol) and dry ethanol (408cm3). After gently heating the solution, the solid tungsten alkoxide quickly dissolved and then Ti (O'Pr) 4 was added as a solution in ethanol so that the ratio of W: Ti was 4: 1. The solution has remained stable for over 6 months without any precipitation and the electrochromic properties of amorphous W03 thin films produced from this solution showed excellent colouration-bleaching capabilities (see Table 1).

Example 8 To tungsten alkoxide (23.2g, 0.068mol), prepared as in Example 3, was added n-butanol (58cm3) and then a mixture of water (1.2g, 0.068mol) and ethanol (282cm3). The alcoholic solution of tungsten alkoxide was heated under reflux for about 40 minutes and after standing overnight, was filtered to remove trace amounts of insoluble material. The solution remained stable for several months (see Table 1).

Example 9 To tungsten alkoxide (0.063mol), prepared as in Example 3, was added a mixture of water (1.13g, 0.063mol) and ethanol (313cm3) and the solution was heated under reflux for 40-60 minutes. Titanium (IV) isopropoxide was added as a solution in ethanol so that the ratio of W: Ti was 4: 1 and heating was continued for a further 60 minutes. After heating, the solution appeared slightly opaque and a small amount of insoluble material settled out. After filtering through celite the solution remained stable, free of any insoluble material.

Example 10 To tungsten alkoxide (0.059mol), prepared as in Example 3, was added n- butanol (50cm3) and then a mixture of water (1.07g, 0.059mol) and ethanol (246cm3). The solution was heated under reflux for about 40 minutes and then Ti (O'Pr) 4 was added as a solution in ethanol so that the ratio of W: Ti was 10:

1. Heating was continued for a further 60 minutes. The slight yellow solution was filtered through celite to remove trace amounts of insoluble material.

Example 11 To tungsten alkoxide (0.066mol), prepared as in Example 3, was added, n- butanol (56cm3) and then a mixture of water (1.18g, 0.066mol) and ethanol (272cm3). The solution was heated under reflux until the solid alkoxide dissolved and then Ti (O'Pr) 4 was added as a solution in ethanol so that the ratio of W: Ti was 10: 1. This was followed by the cautious addition of a solution of BuLi in hexane so that the ratio of W: Li was 10: 1. The mixture was heated a further 30 minutes and filtered through celite to give a faint yellow solution.

PREPARATION OF METAL ALKOXIDES OTHER THAN TUNGSTEN In examples 12 to 28 the utility of the method is illustrated. Metal alkoxides of Fe, In, Nb, V, Mo, Ce, Ir, Co, Cu, Zr, Ta, Al, Cd, Sb, Zn, W, and Y have been prepared. Combinations eg. W/Ti, V/Ti, Ce/Ti, In/Sn, Cd/Sn, W/lr, Sb/Sn, of metal alkoxides can be readily prepared in solutions of ethanol.

Example 12 To anhydrous iron (III) chloride (3.24g, 0.02mol) was added dry n-pentane (50cm3). Then a mixture of n-butanol (11cm3,8.9g, 0.12mol) and 1,2- epoxypropane 0g, 0.12mol) was slowly added to the iron chloride.

The dark red solution was heated under vacuum to remove all volatiles to give a viscous dark red liquid (ca. 9.7g) which readily dissolved in ethanol.

Example 13 To anhydrous indium chloride (4.2g, 0.019mol) in n-pentane (ca, 50cm3) was added a mixture of n-butanol (87cm3,7.0g, 0.095mol) and 1,2-epoxypropane (10cm3,8.3g, 0.143mol). The resulting mixture was heated under reflux until the indium trichloride dissolved. The volatiles were removed under vacuum to give a colourless viscous liquid (ca. 7.7g) which could be easily dissolved in ethanol.

Example 14 To anhydrous niobium pentachloride (10.2g, 0. 038mol) in n-pentane (ca, 1 OOcm3) was added a portion of n-butanol (4.4cm3). A vigorous reaction occurred and then a mixture of 1,2-epoxypropane 8g, 0.376mol) and n-butanol (30cm3) were cautiously added whilst the reaction flask was externally cooled in an ice-water bath. After the addition was complete, the volatile material was distilled to give a yellow-brown viscous liquid (17.0g), which could be easily dissolved in ethanol.

Example 15 To VOC13 (33.66g, 0.194 mol) was added n-pentane (200cm3) and the reaction flask was cooled in a water bath. A mixture of isopropanol (15cm3) and 1,2- epoxypropane (81 cm3,67.2g, 1.164mol) was added through a dropping funnel.

As the reaction progressed, the colour changed from brown to light yellow. A further 60cm3 of isopropanol was added so that the total amount of isopropanol was (75cm3,58.5g, 0.973mol). After distilling the n-pentane, the mixed vanadium alkoxide was dissolved in a solution of isopropanol to which had been added titanium (IV) isopropoxide so that the ratio of V: Ti was 100: 1. The solution was pale yellow in colour and remained stable.

Example 16 To dark green crystals of MoOCl4 (16.24g, 0.064mol) was added n-pentane. A mixture of n-butanol (35cm3,28.5g, 0.384mol) and 1,2-epoxypropane (27cm3, 22.3g, 0.384mol) was slowly added through a dropping funnel. The dark red pentane solution slowly changed to a yellow-brown colour as the molybdenum oxychloride reacted. After distilling the n-pentane and other volatile material, the molybdenum (VI) oxoalkoxide easily dissolved in ethanol to form a stable brown solution. On exposure to air the colour changed to dark blue.

Example 17 To anhydrous cerium (11I) chloride (2.03g, 8.24mmol) was added dry ethanol (25cm3) and the mixture was heated to form a creamy suspension. On addition

of 1,2-epoxypropane 87g, 49.42mmol) a greyish-coloured suspension developed. After about 15 minutes of heating, titanium (IV) <BR> <BR> <BR> <BR> isopropoxide dissolved in ethanol was added so that the ratio of Ce: Ti was 1 : 1. The colour of the suspension changed to khaki.

Example 18 To anhydrous grey-coloured iridium (III) chloride (1.04g, 3.48mmol) was added n-butanol 03g, 13.90mmol) and the mixture was heated under reflux until the chloride dissolved to give a brown solution. On cooling, 1,2- epoxypropane (ca. 6-8cm3) was added and the mixture was heated a further 15 minutes. After distilling all volatile material at room temperature and under vacuum, the brown material was redissolved in ethanol.

Example 19 To anhydrous blue-purple cobalt (II) chloride (2.88g, 22.2 mmol) was added excess n-butanol (ca. 10cm3) and the mixture was heated under reflux until the metal chloride dissolved. On cooling, excess 1,2-epoxypropane (ca. 10cm3) was added to afford a blue-coloured solution, presumably of cobalt alkoxide.

Example 20 To anhydrous brown-yellow copper (II) chloride (1.61 g, 11.97mmol) was added n-butant (20cm3) to give a brown-green solution after gentle heating. On addition of excess 1,2-epoxypropane (ca. 5-6cm3) the solution remained brown and stable.

Example 21 To anhydrous zirconium (IV) chloride (4.21 g, 1.81 mol) was added excess n- butanol (ca. 12cm3) to give a pink-coloured solution. The reaction was exothermic. On addition of excess 1,2-epoxypropane (ca. 8cm3) a colourless solution developed and remained stable.

Example 22 To anhydrous tantalum (V) bromide (1.87g, 3.22mmol) was added excess ethanol (ca. 20cm3) to give an immediate orange solution. On the addition of excess 1,2-epoxypropane (ca. 2-3cm3) the solution turned colourless.

Example 23 To anhydrous aluminium (III) chloride (3.44g, 2.58mmol) was added 25cm3 of ethanol to form a solution. On adding excess 1,2-epoxypropane (ca. 1 Ocm3) an immediate precipitation occurred presumably of a mixed alkoxide.

Example 24 To anhydrous cadmium chloride (1.83g, 0.01 mol) was added excess dry ethanol (ca. 50cm3) and the mixture was heated under reflux. To the partially dissolved CdCI2 was added excess 1,2-epoxypropane (ca. 10cm3) yielding a solution of milky appearance. After the cautious addition of anhydrous SnCI4 6g, 0.01 mol) dissolved in ethanol (1 Ocm3) a clear, pale yellow solution resulted. The same procedure may be used with combined cadmium and tin chlorides to produce combined cadmium and tin alkoxides.

Example 25 To anhydrous SbC ! s (22.5g, 0.075mol) in n-pentane (ca. 100cm3) was added a mixture of n-butanol 5g, 0.451mol) and 1,2-epoxypropane 2g, 0.451 mol) through a dropping funnel over a period of about 30 minutes. The reaction was exothermic. An oily immiscible product formed initially and then towards the end of the addition a light-brown-coloured solution resulted as the mixed antimony (V) alkoxide was completely soluble in n- pentane. After distilling the solvent and other volatile material, a light brown viscous material remained.

Example 26 To zinc chloride (6.8g, 0.05mol) was added dry ethanol (50cm3) and the mixture was heated under reflux until the zinc chloride partially dissolved to give an

opaque solution. An excess of 1,2-epoxypropane (ca. 1 Ocm3) was added and the reaction mixture was heated for a further 20 minutes under reflux. After distilling the volatile material, a clear viscous liquid (ca. 12g) remained which was extremely moisture sensitive.

Example 27 To yttrium chloride (0.715g, 3.66mmol) was added ethanol (20cm3) and a clear solution formed. After the addition of excess 1,2-epoxypropane (ca. 3cm3) the clear solution gelled on standing after about 1.0h.

Example 28 To vanadium oxychloride (6.09g, 35.14mmol) in n-pentane (200cm3) was added 2,3-epoxypropyl isocyanurate (20.25g, 70.29mmol) as a scavenger of HCI. After the cautious addition of isopropanol 75g, 35.14mmol) the colour of the reaction mixture changed from orange-red to a light yellow. The mixture was filtered to remove the solid isocyanurate and after distillation afforded, presumably, vanadium (v) oxoisopropoxide (4.3g) in 50% yield.

Example 29 To WOC14 (6.1 g, 0.018mol) suspended in about 100cm3 of hexane was added by dropping funnel excess 1,2-epoxypropane (7cm3) in hexane (1 Ocm3). A reaction took place immediately and after heating under reflux, a clear yellow solution resulted in 30 minutes. On cooling a white crystalline material formed which filtered easily and dissolved in n-butanol.

Example 30 A mixture of WCte (3.3g, 0.01mol) in 100cm3 of dry n-hexane was cooled to about 5-10°C in an ice/water bath. Excess 1,2-epoxypropane (5cm3) in 20cm3 of hexane was added by dropping funnel to the mixture. Initially, a red colour developed and finally a light yellow hexane solution of tungsten alkoxide formed.

On evaporation of the n-hexane, a yellow viscous liquid remained which dissolved freely in n-butanol. The same procedures were conducted with VOCI3, FeCts and ZrOCtz.


Results showing the Contrast Ratio of Nanocrvstalline Electrochromic Tungsten Oxide Films Formed from Alkoxides Prepared bv Different Methods Example Method Reproducibility Contrast Reversibility (a) Ratio (c) (b) 5 adequate NH3 very poor 3.20 good d 6 excess NH3 good 2.05 extremely (d) poor 7 1,2-epoxypropane excellent 4.05 excellent 8 1,2-epoxypropane excellent 7.00 excellent (e) Notes a) Reproducibility of the method of forming the tungsten alkoxide. b) The contrast ratio is the ratio of the light transmittance of the W03 layer between its bleached and charged state. The thickness and applied charge of 15 mC of the layer was the same in all cases. The wavelength of light employed was 670 A. <BR> <BR> c) Reversibility refers to the ability of the W03 films to be cycled between their bleached and coloured states without significant loss of contrast ratio. d) See Example 1 for details of experimental procedure. e) In contrast to Examples 5 to 7, Example 8 employs a solution of tungsten alkoxide in ethanol with no added titanium (IV) isopropoxide.