Process for preparing metal halides by the sol-gel-method

The present invention concerns a process for obtaining metal halides, in particular rare earth and/or alkali earth halides. This process consists of forming a homogeneous solution by mixing one or more rare earth and/or alkali earth halogenoalkoxides in an anhydrous organic solvent, and hydrolyzing this solution. The novel materials are obtained at room temperature and are in powder, fibre, film or bulk material form.

FIELD OF THE INVENTION 
The present invention concerns a process for obtaining metal halides, in 
particular rare earth and/or alkaline earth halides, and novel materials 
in powder, film or bulk material form obtained from these metal halides. 
BACKGROUND OF THE INVENTION 
Metal halides are compounds which have been known for a long time. For 
example, alkaline earth fluorides (group IIA), 4th period transition metal 
fluorides or rare earth fluorides (group IIIB) are known. These metal 
fluorides have interesting electrical, magnetic and optical properties. 
Alkaline earth fluorides have low refractive indexes, which enables them to 
be used in an anti-reflective layer on supports with a high reflective 
index. 
The layers obtained from these fluorides in general have low dielectric 
constants, are transparent and have excellent mechanical properties. 
All these special properties mean that metal fluorides are compounds which 
are advantageous for piezoelectric, ferromagnetic or antiferromagnetic, 
electro-optical, pyroelectrical or non-linear optics applications. 
Mixed rare earth and alkaline earth metal halides are also known as 
luminescent substances used for example to convert X-rays or gamma 
radiation into visible light. 
Many publications describe the use of mixed alkaline earth halides as 
luminescent substances, in particular in radiographic products. 
For example, European patent EP 149148 describes radiographic image 
recording screens which contain, in the storage layer, a mixed alkaline 
earth halide of general formula BaF(XY):Eu:Sr in which X and Y are halide 
atoms. These luminescent substances are obtained by mixing BaF.sub.2, 
BaCl.sub.2, BaBr.sub.2, EuF.sub.3 and SrCl in a ball mill. The mixture is 
then baked red hot in a bromium vapour chamber for 1 to 5 hours at a 
temperature of between 800.degree. and 1000.degree. C. After cooling, the 
product is broken up, washed and then dried. In this way the luminescent 
substance described above is obtained. This technique, which is difficult 
to implement, does not make it possible to control the stoichiometry of 
the final product. 
It is known that thin layers of luminescent substances can be formed by 
chemical vapour phase deposition. Such layers are obtained with difficulty 
because of the differences in vapour tension and stability of each of the 
constituents. 
A process for obtaining layers of metal fluorides was described in U.S. 
Pat. No. 3,475,192. Such a process consists of coating, on a substrate, a 
magnesium fluoride solution in a polar solvent and heating the substrate 
thus covered at between 100.degree. and 1000.degree. C. In this process, 
it is necessary, in order to obtain a film, to use a substrate which is 
resistant to high temperatures. 
It is known that metal fluoride layers can be obtained by the decomposition 
of a metal fluoride precursor. 
For example, in U.S. Pat. No. 4,492,721, magnesium fluoride layers are 
obtained by the decomposition of fluorinated organic compounds of 
magnesium, such as magnesium trifluoroacetate. 
U.S. Pat. Nos. 5,051,278 and 5,271,956 describe a process for forming films 
of metal fluorides, in particular binary and ternary alkaline earth or 
lanthanide fluorides. This process consists of forming a coating solution 
containing a non-fluorinated organometallic compound, a solvent and a 
fluorination agent and coating this solution on a support. The film thus 
obtained is then heated at a temperature of approximately 500.degree. C. 
in order to decompose the products contained in the coating solution into 
pure metal fluoride. In order to obtain a uniform layer, a temperature 
increase is effected with a gradient of around 50.degree. C./min. 
U.S. Pat. Nos. 5,208,101 and 5,268,196 describe a process for forming 
layers comprising alkali metal or alkaline earth fluorides using sol-gel 
technology. This process consists of forming a layer on a glass substrate 
using a coating solution containing a light metal oxide precursor, a 
non-aqueous solvent and water, heating the layer in order to densify the 
layer of light metal oxides, and exposing this densified layer at a high 
temperature to a gaseous current containing fluorine. The densification of 
the oxide layer is effected at a temperature of around 500.degree. C. and 
the fluorination is effected at temperatures of around 300.degree. C. 
In all the known processes set out above, the metal halide layers are 
obtained using high temperatures, either to vaporise the metal halides or 
to decompose a precursor of the metal halides, or to densify the base 
metal oxide layer and to halogenate this same layer. 
All these processes enabling layers of metal halides to be obtained have 
many drawbacks related to the necessity to use high temperatures. In 
particular, the choice of the support for the metal halide layer is very 
limited. In addition, at high temperature, it is very difficult to obtain 
homogeneous metal halide layers having controlled stoichiometry. 
SUMMARY OF THE INVENTION 
The object of the present invention concerns a process for obtaining 
homogeneous metal halides at low temperature, in powder, layer, fibre or 
bulk material form. 
The present invention makes it possible to eliminate the problems relating 
to the use of high temperatures. For example, the process of the present 
invention makes it possible to obtain metal halide layers on a much wider 
variety of supports, in particular organic supports which have very little 
resistance to high temperatures. 
The above object is achieved in a process for preparing rare earth and/or 
alkaline earth metal halides which comprise: 
(1) forming a homogeneous solution by mixing one or more rare earth and/or 
alkaline earth halogenoalkoxides in an anhydrous organic solvent; and 
(2) adding to this solution a quantity of water which is at least 
stoichiometric for hydrolysing the halogenoalkoxides. 
Within the scope of the invention, the halogenoalkoxides and consequently 
the metal halides may contain one or more halogen atoms chosen from 
amongst fluorine, bromine, chlorine and iodine.

DETAILED DESCRIPTION OF THE INVENTION 
The metal halides which can be obtained by the process of the present 
invention are for example halides of elements in group IIA such as 
beryllium, magnesium, calcium, strontium, barium or radium halides or 
halides of elements in group IIIB, such as scandium, yttrium, lanthane and 
cerium, gadolinium, erbium or ytterbium halides. For example, the metal 
halides which can be obtained are barium bromide, barium fluoride, barium 
bromofluoride, magnesium fluoride, magnesium bromide, ytterbium fluoride, 
barium and thulium fluoride, cerium bromide, cerium (III) fluoride, 
europium fluoride, etc. 
According to the invention, mixed metal halides, for example rare earth and 
alkaline earth halides, can also be obtained. 
The alkaline earth and/or rare earth halides of the invention are obtained 
from one or more rare earth and/or alkaline earth halogenoalkoxides, which 
can be obtained by any one of the known methods of the art. These 
halogenoalkoxides are put in solution in an anhydrous solvent, which may 
be chosen from a large number of organic solvents. The preferred solvents 
of the invention are anhydrous organic solvents which are miscible in 
water, such as, for example, tetrahydrofurane, alcohols or ketones. 
The rare earth and/or alkaline earth halogenoalkoxides are in general 
obtained from the corresponding alkaline earth or rare earth alkoxide or 
alkoxides. 
The preparation of the alkaline earth alkoxides may be effected by various 
syntheses known in the art. 
The easiest synthesis to implement consists of reacting an alcohol directly 
on an alkaline earth. The yield of such a synthesis depends in particular 
on the steric hindrance of the alcohol used. The smaller the steric 
hindrance, the faster will be the synthesis of the alkaline earth 
alkoxides. The alcohol is preferably chosen from amongst methanol, ethanol 
or propanol. 
The rare earth alkoxides can be synthesised according to one of the 
following two methods. 
The first method consists of reacting a rare earth chloride, for example 
lanthane chloride, directly with an alkali metal alkoxide, for example a 
sodium or lithium alkoxide. This synthesis has drawbacks related to the 
presence of chloride in the reaction medium. In addition, lanthanide 
chlorides are particularly stable chemical species which are difficult to 
activate, which gives rise to low reaction yields. 
A second method of synthesising rare earth alkoxides consists of reacting 
the rare earth directly with an alcohol such as 2-propanol or a 
functionalised alcohol such as 2-methoxyethanol. 
Within the scope of the invention, it is also possible to use heterometal 
oxides obtained by mixing several homometal oxides. 
According to the present invention, the rare earth or alkaline earth 
halogenoalkoxides of the invention are obtained by alcoholisation of rare 
earth or alkaline earth alkoxides by a halogenated or perhalogenated 
alcohol hereinafter referred to as a "halogenoalcohol". 
For example, when it is desired to prepare metal fluorides according to the 
process of the present invention, it is possible to prepare the 
corresponding rare earth and/or alkaline earth fluoroalkoxide by reacting 
one or more rare earth and/or alkaline earth alkoxides with a 
fluoroalcohol chosen from amongst 1,1,1,3,3,3-hexafluro-2-propanol, 
perfluoro-tert-butanol, 2,2,2-trifluoroethanol, 2-fluoroethanol, 
1,1,1,2,2,3,3-heptafluoro-4-butanol or 2,2,3,4,4,4-hexafluoro-1 -butanol. 
When it is desired to prepare metal bromides according to the process of 
the present invention, it is possible to prepare the rare earth and/or 
alkaline earth bromoalkoxide by reacting one or more rare earth and/or 
alkaline earth alkoxides with a bromoalcohol chosen from amongst 
2-bromoethanol, 3-bromo-2-propanol, 3-bromo-2-methyl-1-propanol or 
3-bromo-2,2-dimethyl-1-propanol. 
These halogenoalkoxides can be defined by the formula M(ORx).sub.n 
(ORy).sub.m in which M is a rare earth or an alkaline earth, Rx and Ry are 
each separately alkyl groups containing one or more identical or different 
halogen atoms, and n and m are such that the sum of n and m is equal to 
the valency of M. 
When it is desired to obtain a metal halide containing several halides, a 
halogenoalkoxide as defined above in which the groups Rx and Ry are 
differently halogenated is preferably used. It is also possible to use as 
a starting halogenoalkoxide a halogenoalkoxide of formula M(ORx).sub.n 
X.sub.m in which M, Rx, n and m as defined previously and X is a halogen 
atom. 
The alkaline earth halogenoalkoxides can also be prepared by directly 
reacting the alkaline earth in solution in a polar solvent with a 
halogenoalcohol as defined previously. When fluoroalkoxides are prepared, 
the reaction is highly exothermic, which causes a degradation of the 
organic compounds present in the reaction medium. In this case, the 
reaction can be catalysed and must be carried out under very severe 
anhydrous conditions. When bromoalkoxides are prepared, the reaction is 
not exothermic and must be catalysed by forming in situ a highly reactive 
species such as an amidide by the addition of NH.sub.3, Et.sub.2 NH or 
(Me.sub.3 Si).sub.2 NH in the reaction medium. 
According to one embodiment of the invention, in order to prepare a mixed 
metal halide containing several metal elements, each of the metal 
halogenoalkoxides forming part of the final composition of the metal 
halide are prepared separately. 
According to the invention, the hydrolysis may be catalysed by means of an 
acid. Preferably, this acid is halogenated with the same halogen as the 
one constituting the final metal halide in order to avoid the presence of 
secondary products related to the counterion associated with the hydrogen. 
For example, hydrolysis of the fluoroalkoxides was effected at a pH of 
less than 7, and preferably between 1 and 3, in the presence of 
hydrofluoric acid. 
The quantity of water used to hydrolyse the halogenoalkoxides according to 
the invention varies in accordance with the type of material desired. When 
it is desired to obtain the metal halides of the invention in the form of 
layers or fibres, hydrolysis of the halogenoalkoxides is effected with a 
quantity of water which is at least stoichiometric and less than 5 times, 
and preferably less than twice, this stoichiometric quantity. 
When it is desired to obtain powders, this quantity of water may be up to 
50 times and preferably 10 to 30 times greater than the stoichiometric 
quantity of water for hydrolysing the halogenoalkoxides. 
The present invention surprisingly makes it possible to obtain pure rare 
earth or alkaline earth halides at low temperature. The process and the 
metal halides of the invention are particularly useful for manufacturing 
organic/inorganic devices in thin film, fibre or solid material form. 
Within the scope of the invention, thin layers of metal halides were 
obtained dip-coating a support in a solution of metal halogenoalkoxides 
and hydrolysing the halogenoalkoxides of this layer solely by means of 
atmospheric moisture. The thickness of the layer can be varied either by 
varying the initial concentration of metal halogenoalkoxides or by 
dip-coating several times the support covered with a first layer obtained 
according to the process of the present invention. 
The supports which can be used to obtain layers within the scope of the 
present invention can be conventional supports such as glass or ceramics 
or supports degradable at high temperature, such as supports made from 
organic polymer materials. The preferred organic supports are supports 
with reactive groups at the surface, for example hydroxyl groups as in 
cellulosic supports. 
The deposition of a metal halide layer of the invention on a cellulose 
support makes it possible for example to improve the resistance to pH of 
such a support. 
According to one embodiment, layers of metal fluorides on a cellulose 
support were thus obtained. 
The process of the invention also makes it possible to obtain a material 
having a controlled stoichiometry since it is very easy to control the 
metal halogenoalkoxide concentration of the starting solution. In 
addition, since the layers of metal halides of the invention are obtained 
using perfectly homogeneous solutions, homogeneous metal halide layers are 
obtained, which is not the case with the prior art. 
According to the prior art, it is known that, by hydrolysis of metal 
alkoxides, metal oxides are formed. Such a process is generally 
implemented at low temperature in order to form inorganic lattices of 
metal oxides, for example polysiloxane lattices. 
It is therefore particularly surprising that, by hydrolysis of 
halogenoalkoxides, alkaline earth or rare earth halides rather than 
alkaline earth or rare earth oxides are obtained. 
Without being bound by theoretical considerations, it appears that the 
hydrolysis conditions are particularly important for obtaining rare earth 
and/or alkaline earth halides. This is because it appears that rapid 
hydrolysis favours the formation of halides rather than the formation of 
oxides. Halogenoalkoxides, in particular fluoroalkoxides, have a 
hydrophobic character, which brings about the formation of micelles in the 
reaction medium. Each micelle fulfils the role of a microreactor in which 
the hydrolysis is accelerated, which favours the formation of metal 
halides rather than the formation of metal oxides. 
EXAMPLES 
All the following reactions were carried out in an inert gas, at room 
temperature. 
The materials obtained were analysed by the following techniques: 
FT-RAMAN spectroscopy, which consists of irradiating a sample with a 
monochromatic laser and measuring the frequency of the dispersed light. 
X-ray diffraction, which consists of irradiating the surface of a sample by 
means of a beam of parallel monochromatic X-rays and studying the 
variation in intensity as a function of the angle of incidence. X-ray 
diffraction affords qualitative identification of the crystalline material 
and notably. determination of the crystalline structure. 
Energy dispersive X-ray microanalysis spectroscopy (ED-XRMA), which enables 
the elements present in a sample to be identified. This identification is 
based on the exploitation of the X-rays emitted by a sample bombarded by 
an electron beam focused on the surface, each chemical element having a 
characteristic line. 
From the teaching of the examples described below, rare earth and/or 
alkaline earth halides containing one or more halide atoms can easily be 
obtained. 
EXAMPLE 1 
Synthesis of Ba[OCH(CF.sub.3).sub.2 ].sub.2 
38 g of 2-hexafluoropropanol is added to a mixture consisting of 15 g of 
barium (0.109 moles, Aldrich.RTM.) and 100 ml of anhydrous 
tetrahydrofurane. The mixture is left to react for 12 hours whilst being 
stirred (a highly exothermic reaction). The reaction medium is filtered 
and a colourless filtrate is recovered, which is then dried and 
crystallised in anhydrous hexane. In this way 48 g of 
Ba[OCH(CF.sub.3).sub.2 ] characterised by the Raman spectrum of FIG. 1 is 
obtained (yield 95%). 
EXAMPLE 2 
Synthesis of Y[OCH(CF.sub.3).sub.2 ].sub.2 
100 ml of freshly distilled 2-propanol is added to a mixture consisting of 
16.1 g of yttrium (0.181 moles; Aldrich.RTM.) and 100 ml of anhydrous 
toluene. 13 mg of HgCl.sub.2 is then added to the reaction medium. The 
reaction medium is then refluxed whilst stirring for 2 days. After 
filtration of the medium, the filtrate is concentrated and then purified 
by crystallisation in a dichloromethane/toluene mixture (50/50). In this 
way 32 g of Y.sub.5 O(OiPr).sub.13 is obtained (yield 72%). 
15 g of Y.sub.5 O(OiPr).sub.13 (0.0122 moles) in solution in 50 ml of 
anhydrous tetrahydrofurane and 27 g of 2-hexafluoropropanol are mixed 
(exothermic reaction). In this way Y[OCH(CF.sub.3).sub.2 ].sub.3 is 
obtained, which is then purified in anhydrous hexane (34 g, yield 95%). 
EXAMPLE 3 
Synthesis of Yb[OCH(CF.sub.3).sub.2 ].sub.3 
A mixture of 2-methoxyethanol and 2-propanol (30/70 ml) is added to a 
mixture consisting of 18.3 g of ytterbium (0.105 moles, Aldrich.RTM.) and 
100 ml of anhydrous toluene. The reaction medium is refluxed whilst 
stirring for 2 days. After filtration of the reaction medium and 
crystallisation of the raw product, 33 g (80%) of Yb(OCH.sub.2 CH.sub.2 
OCH.sub.3).sub.3 is obtained. 
25 g of 2-hexafluoropropanol is added to a solution of 20 g (0.05 moles) of 
Yb(OCH.sub.2 CH.sub.2 OCH.sub.3).sub.3 in tetrahydrofurane (exothermic 
reaction). After filtration of the reaction medium and crystallisation of 
the raw product in anhydrous hexane, 32 g of Yb[OCH(CF.sub.3).sub.2 
].sub.3 is obtained (yield 96%). 
EXAMPLE 4 
Synthesis of Tm[OCH(CF.sub.3).sub.2 ].sub.3 
A mixture of 2-methoxyethanol and 2-propanol (7.5/7.5 ml) is added to a 
solution of 1 g (5.9 mmol, Aldrich.RTM.) of thulium in 20 ml of toluene. 
The reaction medium is then refluxed whilst stirring for 2 days. After 
filtration of the reaction medium, a colourless filtrate is obtained which 
is concentrated and then purified by crystallisation. In this way 1.67 g 
of Tm(OCH.sub.2 CH.sub.2 OCH.sub.3).sub.3 is obtained (yield 72%). 
2.1 g of 2-hexafluoropropanol is added to a solution of 1.67 g of 
Tm(OCH.sub.2 CH.sub.2 OCH.sub.3).sub.3 in anhydrous tetrahydrofurane. The 
reaction is exothermic. In this way, after crystallisation in a mixture of 
anhydrous pentane and ethyl ether, 2.06 g of Tm[OCH(CF.sub.3).sub.2 
].sub.3 is obtained (yield 98%). 
EXAMPLE 5 
Synthesis of BaF.sub.2 
5 g of barium (36 mmol) is put in solution in 50 ml of anhydrous 
tetrahydrofurane, and then 12.2 g of 2-hexafluoropropanol is added to form 
the barium fluoroalkoxide of Example 1. The reaction is exothermic. The 
reaction medium, which has become clear, is hydrolysed at room temperature 
by the addition of 6.48 g of water. The hydrolysis is exothermic. In this 
way 6.3 g of BaF.sub.2 powder is obtained. 
FIG. 2 is an X-ray spectrum of the BaF.sub.2 powder thus obtained. 
The same experiment was carried out by hydrolysing the reaction medium with 
a solution of HF and a solution of HClO.sub.4. In this case, the 
hydrolysis is more rapid and BaF.sub.2 is obtained as before. 
EXAMPLE 6 
Synthesis of MgF.sub.2 
100 ml of absolute methanol is added to 5 g of magnesium in chip form. The 
reaction is exothermic. A white suspension is thus obtained. 70 g of 
2-hexafluoropropanol is then added to this suspension drop by drop in 
order to form the corresponding magnesium fluoroalkoxide. The reaction is 
exothermic and the reaction medium clears. After eliminating the colloidal 
residues by filtration, the clear filtrate is hydrolysed at room 
temperature by the rapid addition of 38 g of H.sub.2 O. 7.9 g of MgF.sub.2 
is then obtained. 
EXAMPLE 7 
Synthesis of EuF.sub.3 
In accordance with the method of the previous examples, fluorinated alcohol 
HOCH(CF.sub.3).sub.2 was reacted with a europium alkoxide Eu(OCH.sub.2 
CH.sub.2 OCH.sub.3).sub.3. In this way europium fluoroalkoxide 
Eu[OCH.sub.2 (CF.sub.3).sub.2 ] was formed, which by hydrolysis made it to 
obtain perfectly crystallised europium fluoride, at room temperature. The 
quantity of water used is equal to 30 times the stoichiometric hydrolysis 
quantity. 
FIG. 3 is an X-ray diffraction spectrum of the EuF.sub.3 powder obtained. 
EXAMPLE 8 
Synthesis of a mixed rare earth and alkaline earth fluoride 
4.03 g of Ba[OCH(CF.sub.3).sub.2 ].sub.2 is added to 5 g of 
Yb[OCH(CF.sub.3).sub.2 ].sub.3 in solution in 50 ml of anhydrous 
tetrahydrofurane. A second solution containing 5.71 g of 
Yb[OCH(CF.sub.3).sub.2 ].sub.3 in anhydrous tetrafurane and 0.11 g of 
Tm[OCH(CF.sub.3).sub.2 ].sub.3 is then added to this solution. 
The mixture thus obtained is stirred strongly for 1 hour and then 
transferred to a Teflon reactor and hydrolysed with 40 ml of water 
containing 0.5 ml of 40% HF. 
A very rapid increase in the viscosity of the mixture is observed, which is 
maintained under strong stirring for one night. The reaction medium is 
then filtered and in this way, after drying, a white powder is obtained, 
the structure of which was confirmed by ED-XRMA (FIG. 4). 
This powder, when it is excited by a laser with a wavelength of 650 nm, 
emits blue light, as shown by FIG. 5. 
EXAMPLE 9 
Synthesis of a thin layer of BaF.sub.2 fluoride 
A cellulose substrate (Nadir.RTM. sold by Roth) is immersed in a solution 
of Ba[OCH(CF.sub.3).sub.2 ] (0.1M) in absolute ethanol, the system being 
maintained under an inert gas. The substrate is then withdrawn and left in 
the open air for 5 min. Hydrolysis takes place with atmospheric moisture. 
After 5 min, the substrate is immersed into osmosed water in order to 
terminate the hydrolysis. 
A layer of BaF.sub.2 is thus obtained. Such layers are stable even when 
they are immersed in solutions having pH values varying between 8 and 12, 
for several days. 
In order to measure the hydrophobia of the layers of BaF.sub.2 of the 
invention, the wetting angle of the previously obtained layer and that of 
the cellulose substrate before deposition of the layer were measured: 
______________________________________ 
Wetting angle 
______________________________________ 
Nadir .RTM. cellulose 
36 .+-. 2 degrees 
BaF.sub.2 layer 74 .+-. 4 degrees 
______________________________________ 
The results show that the process of the present invention makes it 
possible to obtain hydrophobic layers resistant to any variation in pH. 
Tests showed that layers of variable thickness could be obtained by 
modifying the concentration of starting alkoxides and reimmersing the 
BaF.sub.2 layer in the starting alkoxide solution. 
EXAMPLE 10 
Synthesis of BaBr.sub.2 
5.7 g of barium (41 mmol) is mixed, under argon, with 50 ml of anhydrous 
tetrahydrofurane, and then 4 ml of 2-bromoethanol is added drop by drop in 
order to form barium bromoalkoxide. The reaction is not exothermic and it 
is catalysed by the controlled introduction of two equivalents of 
hexamethyldisilazane. The reaction is accelerated by introducing 30 ml of 
methanol into the reaction medium. The reaction medium, which is stirred, 
becomes clear. 
When the barium is completely used up, the solution is concentrated and a 
white solid is obtained, barium bromoalkoxide Ba(OCH.sub.2 CH.sub.2 Br). 
Ba(OCH.sub.2 CH.sub.2 Br) was also obtained by direct alcoholisation of 
Ba(OEt).sub.2. 
The white solid thus obtained is solubilised in ethanol. Hydrolysis of the 
medium is then effected by the addition of a quantity of water 10 to 30 
times the stoichiometric hydrolysis quantity. The reaction is exothermic. 
After stirring for 30 min, a white crystallised powder is obtained. This 
powder was analysed by FT-RAMAN spectrometry. The spectrum obtained has 
two very fine large bands at 416 and 442 cm.sup.-1. Comparison of this 
spectrum with the spectrum obtained with BaBr.sub.2,H.sub.2 O manufactured 
by Aldrich shows that barium bromide has indeed been obtained. 
The X-ray diffractometry spectrum of the powder obtained shows 
unambiguously the presence of a crystalline phase identical to that of the 
commercial product. 
Consequently the present process makes it possible to manufacture extremely 
pure hydrated barium bromide from the metal at room temperature. 
EXAMPLE 11 
Synthesis of SrBr.sub.2 
3.8 g of strontium (4.2 10.sup.-2 mol) is dissolved in 80 ml of methanol 
under argon atmosphere. The reaction is exothermic with the release of 
hydrogen. When the strontium is completely used up, a crystallised white 
powder corresponding to Sr(OCH.sub.3).sub.2 is recovered. 
8 g of Sr(OCH.sub.3).sub.2 (12.3 mmol) is dissolved under argon atmosphere 
in 60 ml of anhydrous tetrahydrofurane, and then 2 ml of 2-bromoethanol is 
added drop by drop. 
In this way a white solid is obtained which is dissolved in 30 ml of 
methanol. Hydrolysis of the medium is then effected by the addition of 15 
ml of water. Fine colloidal particles in suspension are thus formed. After 
30 min of stirring, the solution is concentrated: a white crystallised 
power is obtained. 
This powder, analysed by FT-RAMAN spectrometry and X-ray diffractometry, 
has a structure identical to that of the commercial product SrBr.sub.2 
manufactured by Strem.RTM.. 
EXAMPLE 12 
Synthesis Of BaBrF 
3.5 g of Ba[OCH(CF.sub.3).sub.2 ].sub.2 (7.5 mmol synthesised in accordance 
with the method of Example 1) in solution in 40 ml of anhydrous methanol 
is added to 2.9 g of Ba(OCH.sub.2 CH.sub.2 Br).sub.2 (7.5 mmol synthesised 
in accordance with the method of Example 10) in solution in 40 ml of 
anhydrous methanol. The reaction medium is stirred for 3 hours at room 
temperature and then concentrated. In this way a white powder Ba(OCH.sub.2 
CH.sub.2 Br) (OCH(CF.sub.3).sub.2 is isolated, characterised by FT-RAMAN. 
This barium bromofluoroalkoxide in solution in 20 ml of methanol is 
hydrolysed by the addition of a 0.2M solution of hydrofluoric acid. The 
solution becomes cloudy and, after concentration, a slightly coloured 
solid is obtained. 
This powder is analysed by FT-RAMAN, ED-XRMA and X-ray diffractometry. 
The FT-RAMAN spectrum has two bands at 212.3 and 238.9 cm.sup.-1, which 
correspond to the Ba-F bond. 
X-ray spectrometry microanalysis confirms the presence of the three 
elements Ba, Br and F. 
The diffraction spectrum is entirely comparable to the reference spectrum 
of BaBrF crystals. 
EXAMPLE 13 
Another method of synthesising BaBrF 
25.6 g of Me.sub.4 NOH,5H.sub.2 O is heated at 100.degree. C. in order to 
remove the water by azeotropic distillation. The anhydrous Me.sub.4 NOH 
solid is then dissolved in 60 ml of anhydrous ethanol, and then 30 g of 
anhydrous BaBr.sub.2 is added thereto. After stirring for half a day, a 
precipitate of NMe.sub.4 Br is recovered. This compound is then dissolved 
in 9.4 ml of hexafluoropropanol. After stirring, the solution is filtered 
and the solvent is removed under vacuum. 40 g of (CF.sub.3)CHOBaBr is thus 
recovered in the form of a whim solid. 
(CF.sub.3)CHOBaBr is solubilised in methanol and this solution is 
hydrolysed by the addition of water. The solid obtained is placed in an 
oven at 250.degree. C. in order to eliminate any organic species still 
present. 
The heat treatment is not obligatory. The same product was obtained after 
drying at a much lower temperature but for a longer time. 
X-ray diffraction analysis confirms that BaBrF has indeed been obtained. 
The invention has been described in detail with particular reference to 
certain preferred embodiments thereof, but it will be understood that 
variations and modifications can be effected within the spirit and scope 
of the invention.