Gallium alkoxides: Synthesis and properties

Article abstract of DOI:10.1134/S003602360805001X

Compounds Ga(OR)₃ (R = Me, Et, Prⁱ, Buⁿ, C₂H₄OMe) were synthesized by exchange reactions between gallium chloride and alkali metal alkoxides, the reetherefication of Ga(OPr ⁱ)₃ and Ga(OC₂H₄OMe)₃ by other ROH (R = Me, Et), and anodic dissolution of metallic gallium in the presence of a electroconductive additive (LiCl, Bu₄NBr). When solid GaCl₃ is introduced into an alcoholic solution of NaOEt, stable soluble gallium oxoalkoxyhalides are formed. The same reaction with a GaCl ₃ solution in toluene or electrochemical synthesis produces nonvolatile Ga(OEt)₃ samples, which have the polymer zigzag configuration [Ga(OR)_4/2(OR)]_∞. Mass spectrometry shows that only Ga(OPrⁱ)₃ and freshly prepared X-ray amorphous Ga(OEt)₃ samples (produced by reetherefication) are transferred to the gas phase. The spectra of the latter contain ions generated by penta-and hexanuclear oxoalkoxide molecules, along with fragments of orthospecies [Ga(OEt)₃]_2-4. IR spectra are described for all compounds synthesized.

Full text of DOI:10.1134/S003602360805001X

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2008, Vol. 53, No. 5, pp. 665–675. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © E.V. Suslova, N.Ya. Turova, A.S. Mityaev, A.V. Kepman, S. Gohil, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 5, pp. 725–735.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Gallium Alkoxides: Synthesis and Properties
E. V. Suslovaa, N. Ya. Turovaa, A. S. Mityaeva, A. V. Kepmana, and S. Gohilb
a Moscow State University, Vorob’evy gory, Moscow, 119992 Russia
b Swedish University of Agricultural Sciences, Uppsala, Sweden
Received June 25, 2007
Abstract—Compounds Ga(OR)3 (R = Me, Et, Pri, Bun, C2H4OMe) were synthesized by exchange reactions
between gallium chloride and alkali metal alkoxides, the reetherefication of Ga(OPri)3 and Ga(OC2H4OMe)3
by other ROH (R = Me, Et), and anodic dissolution of metallic gallium in the presence of a electroconductive
additive (LiCl, Bu4NBr). When solid GaCl3 is introduced into an alcoholic solution of NaOEt, stable soluble
gallium oxoalkoxyhalides are formed. The same reaction with a GaCl3 solution in toluene or electrochemical
synthesis produces nonvolatile Ga(OEt)3 samples, which have the polymer zigzag configuration
[Ga(OR)4/2(OR)]∞. Mass spectrometry shows that only Ga(OPri)3 and freshly prepared X-ray amorphous
Ga(OEt)3 samples (produced by reetherefication) are transferred to the gas phase. The spectra of the latter con-
tain ions generated by penta- and hexanuclear oxoalkoxide molecules, along with fragments of orthospecies
[Ga(OEt)3]2–4. IR spectra are described for all compounds synthesized.
DOI: 10.1134/S003602360805001X
Current interest to organogallium derivatives is due
to their utility as precursors for some oxide composites
in the manufacturing of gas sensors [1], luminophores
[2], solid electrolytes (above all, LaGaO doped with
some metals [3]), and zeolite catalytic systems [4].
Alkoxides have recently been used in CVD and sol–
gel processes for the manufacture of Ga2O3 films and
ZnGa2O4 ceramics [2, 11, 12].
As a rule, product yields were not indicated in the
description of Ga(OR)3 syntheses; accessible prepara-
The pioneering studies of gallium alkoxides date to tion methods remained to be developed. Property data
for alkoxides are quite controversy. Here, we attempted
to repeat the Ga(OR)3 syntheses described in the litera-
ture via exchange reactions between GaCl3 and alkali
alkoxides and transetherification reactions Ga(OR)3 +
R’OH; we also developed a new electrochemical syn-
thesis. Products were characterized by elemental anal-
ysis, IR spectroscopy, mass spectrometry, and X-ray
powder diffraction. The most accessible homologues
are proposed for use in sol–gel processes.
the middle 1960s [5–8]; at that time, Ga(OR)3 was syn-
thesized via exchange reactions between GaCl3 and
NaOR (R = Et, Pri). Another synthesis method is the
transetherification of Ga(OEt)3 with isopropanol [7],
Ga(OPh)3 with methanol or ethanol [9], and Ga(OPri)3 with
several ROH alcohols (R = Me, Et, nPr, nBu, sBu, tBu) [10].
The third described synthesis Ga(OR)3 is alcoholysis of
Ga[N(SiMe3)2]3 [2] or [Ga(NMe2)3]2 [11, 12]. 2-methoxy-
ethoxides Ga(OC2H4OMe)3 and Ga(OCåÂ2ëH2OMe)3,
aminoalkoxides, and volatile Ga(OR)3 (R = Pri, Bui, But,
ë5Ht11, C8Ht17 , C6H1t 3 ) were prepared in this way [11].
The configuration of a tetrameric gallium isopro-
EXPERIMENTAL
Methods
All manipulations associated with the synthesis,
analysis, and characterization of alkoxides were carried
out in a dry box under an N2 or Ar atmosphere. Abso-
lute organic solvents were used: MeOH was absolu-
tized by long boiling over Mg(OMe)2; EtOH, over
Ca(OEt)2; and iPrOH, over Al(OPri)3. Methylcellosolve
from Merck was distilled under atmospheric pressure
(124.6°ë). Toluene and hexane were stored over P2O5
for several days; then, they were boiled over metallic
sodium. GaCl3 was prepared by direct chlorination of
metallic gallium followed by vacuum distillation [15],
1
poxide molecule proposed on the basis of H NMR
data as an analogue of [Al(OPri)3]4 [13] was verified
by single-crystal X-ray diffraction data for Ga[(µ-
OPri)2Ga(OPri)2]3 [11]. Dimeric molecules [Ga(µ-
OR)(OR)2]2 are found in the structure of tert-amoxide;
monomers [Ga(OBut)3(HNMe2)] are found in the tert-
butoxide complex with amine [11]. 1H NMR was used
to study dimer
tetramer equilibrium for Ga(OPri)3
in hydrocarbon solutions [14], and the thermodynamic
parameters of the process were determined [11].
665

666
SUSLOVA et al.
Table 1. Parameters of the reaction GaCl3 + 3MOR and characteristics of the product
Precursors
For Ga(OR)3 found (calcd.), %
No.
1
Observations
GaCl3
MOR
Ga
–
C
–
H
–
Sln of GaCl3
LiOMe
No precipitate. After boiling
(0.84 g, 4.76 mmol) (0.54 g, 14.3 mmol) and evacuation of sln
pre-
in PhMe (10 mL)
in MeOH (10 mL)
cipitate insoluble in MeOH
and PhMe
2
3
NaOMe
(0.77 g, 14.3 mmol)
in MeOH (10 mL)
Precipitate NaCl + Ga(OMe)3
–
–
–
–
–
»
Sln of GaCl3
NaOEt
Precipitate NaCl + Ga(OEt)3;
after sln
35.86
(34.14)
(1.91 g, 10.8 mmol) (2.31 g, 34 mmol)
in PhMe (20 mL)
in EtOH (50 mL)
was evacuated
Ga(OEt)3
microcrystals (yield, ~20%)
4
5
Solid GaCl3
(2.85 g, 16.0 mmol) (3.60 g, 53 mmol)
in EtOH (80 mL)
NaOEt
Precipitate NaCl (2.39 g,
38.86
29.09
6.29
(7.30)
41 mmol); after sln was evacu- (34.14)
(35.12)
ated
product (2.65 g)
Solid GaCl3
NaOPr1
Precipitate NaCl;
31.68
(32.73)
40.20
(43.72)
6.31
(8.50)
(6.61 g, 37.5 mmol) (8.47 g, 124.6 mmol) from sln, Ga(OPri)3*
in ester (50 mL)
in iPrOH (150 mL)
and PhMe (50 mL)
(7.04 g, 28.5 mmol; yield, 76%)
i
* IR spectrum of Ga(OPr ) is described in Table 3. Mass spectrum: 925 (2), 866 (2), 764 (1), 725 (0.1), 679 (5), 620 (1), 577 (0.3), 433 (35),
3
418 (1), 374 (64), 331 (10), 316 (9), 272 (8), 214 (24), 200 (9), 170 (5) (Fig. 1).
or a GaCl3 sample purchased from Merck was used. mode. The temperature at which the dissociation pres-
Ga(OPri)3 from Aldrich was used in several syntheses.
sure reached 10 mm Hg (for a sample size of 0.5 g) was
believed equal to the decomposition onset.
Another precursor was liquid solvate GaCl3 · EtOH
prepared by a new method: metallic gallium was dis-
To determine solubilities, solid Ga(OEt)3 and EtOH
solved in a 6 M HCl solution in absolute ethanol. This were placed into an ampoule with a finger and thermo-
solvate with Tm = 10°C was earlier synthesized by the stated; then, the saturated solution was poured into the
finger.
direct reaction between stoichiometric amounts of the
components [16].
Gallium was determined by back complexometric
titration with a CuSO4 solution (PAN indicator) at pH 4.
Exchange Reactions of GaCl3 with Alkali Alkoxides:
GaCl3 + 3MOR
Ga(OR)3 + 3MCl↓
IR spectra were recorded as Nujol and hexachlorob-
utadiene mulls on a PE 1600 FTIR spectrometer. X-ray
diffraction patterns were recorded from powders sealed
between X-ray amorphous films on an Image Plate
Guinier Camera G670 instrument. Mass spectra were
recorded on a Jeol JMS-SX/SX-102A DSQ-2 or Trace
JC Ultra DSQ-2 instrument with direct injection and
dynamic heating from 2 to 180°ë at 10 K/min (based
on 69Ga).
GaCl3 entered the reaction as a solid product, a solu-
tion in alcohol, ether, or toluene, or GaCl3 · EtOH in etha-
i
nol. A solution of NaOR in EtOH or PrOH–toluene
was accurately added to a solution of CaCl3 with vigor-
ous stirring at 0°C. The reaction mass strongly heated,
and a white precipitate appeared. The reaction mixture
was rufluxed for 2–3 h; the solution was centrifuged
and decanted from the precipitate, which was twice
The onset decomposition temperature was deter- washed with hot toluene or alcohol and evacuated. The
mined in a tensimeter in vacuum in an isothermal results of the synthesis are compiled in Table 1.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

GALLIUM ALKOXIDES: SYNTHESIS AND PROPERTIES
667
Table 2. Parameters of reetherefication reactions and characteristics of the products*
No.
1
Precursors
Ga(OPri)3 (0.33 g, 1.34 mmol)
Product composition, % Ga found (calcd.),
MeOH (2 mL, 50 mmol) Ga(OMe)3
41.39
(42.94)
2
3
4
»
32.00
EtOH (2 mL, 35 mmol)
Ga(OEt)3
(34.14)
Ga(OC H OMe) (0.33 g, 1.12 mmol)
37.40
(37.83)
MeOH (2 mL, 50 mmol) Ga(OMe)2.5(OC H OMe)0.5
2
4
3
2
4
»
25.05
(26.41)
EtOH (2 mL, 35 mmol)
Ga(OEt)(OC H OMe)
2 4 2
* IR spectra for all products are described in Table 3.
Ga(OEt) mass spectrum: 1031 (6), 986 (4), 957 (1), 943 (1), 901 (7), 897 (20), 883 (40), 856 (1), 838 (30), 827 (100), 771 (8), 764 (4),
3
726 (6), 697 (50), 652 (2), 567 (11), 522 (6), 493 (21), 478 (16), 448 (15), 363 (28), 318 (55), 274 (89), 229 (90), 200 (10) (Fig. 2).
Transetherification Reactions:
and methylcellosolve were colorless liquids. Electroly-
sis lasted 4–15 h. Solid products were separated from
the electrolyte, washed with absolute alcohol two times
(to remove electroconducting additives), and dried in
vacuo. In the case of Ga(OC2H4OMe)3, the residue after
the solvent was evacuated was separated from LiCl by
extraction to toluene.
For Ga(OMe)3 anal. calcd., %: Ga, 42.94; C, 20.11;
H 4.37.
Found, %: Ga, 42.07; C, 22.09; H, 5.52.
For Ga(OEt)3 anal. calcd., %: Ga, 34.14; C, 35.12;
H, 7.30.
Ga(OR)3 +3R'OH
Ga(OR')3↓ + 3ROH↑
(R = Pri, ë2H4OMe; R'= Me, Et)
Synthesis was carried out as follows: to a solution of
Ga(OPri)3 or Ga(Oë2H4OMe)3 in toluene (8 mL) at
room temperature, a considerable excess of MeOH or
EtOH was added. A white jel precipitated instanta-
neously. Solid products remaining after evacuation had
the compositions specified in Table 2. Ga(OEt)3 sam-
ples prepared as described above (they contained trace
unreacted Ga(OPri)3) were volatile. The product of the
same composition after the reaction mixture was
refluxed for 1 h was, however, nonvolatile.
Found, %: Ga, 36.80; C, 33.95; H, 6.93.
For Ga(OBun)3 anal. calcd., %: Ga, 24.22; C, 49.83;
H, 6.23.
The treatment of 2-methoxyethanol with MeOH or
EtOH induced only partial replacement of MeOë2H4O
groups and the formation of Ga(OMe)2.5(OC2H4OMe)0.5
and Ga(OEt)(OC2H4OMe)2.
For GaO0.75(OBun)1.5 anal. calcd., %: Ga, 36.55;
C, 37.60; H, 7.05.
Found, %: Ga, 36.67; C, 35.73; H, 6.95.
For Ga(OC2H4OMe)3 anal. calcd., %: Ga, 22.73;
C, 36.61; H, 7.12.
Electrochemical Synthesis:
Ga + 3ROH
Ga(OR)3 + 3/2H2↑
Found, %: Ga, 22.33; C, 35.29; H, 6.31.
Synthesis was performed in a cell with unseparated
cathodic and anodic spaces equipped with a cooling
jacket and a refluxer. The anode was a metallic gallium
pool into which a platinum wire was dipped. The cath-
ode was a platinized platinum plate ~10 cm2 in surface
area. The electroconductive additive was Bu4NBr,
Et3BzNCl, or LiCl in appropriate alcohols (80–100 mL) in
the form of ~0.05 M solutions (in MeOH, 0.01 M solu-
tions). All electroconductive additive s were recrystal-
lized from MeOH and dried in vacuo. The process was
performed at a direct current (current, 0.0017–0.10 A;
voltage, 50–110 V; for MeOH, 20 V); vigorous hydro-
gen evolution on the cathode was observed, and white
The product obtained from butanol was likely an
oxo complex.
Electrolysis was accompanied by metal refining,
which generated metallic gallium microparticles in
Ga(OR)3 samples; the proportion of the particles
increased with time. To illustrate this phenomenon, we
list below the analyses of Ga(OEt)3 samples depending
on the electrolysis time.
For Ga(OEt)3 anal. calcd., %: Ga, 34.14; C, 35.12;
H, 7.30.
Found, %: Ga, 36.80 (4 h); C, 30.60; H, 5.61.
Found, %: Ga, 44.81 (10 h); C, 19.95; H, 4.93.
Found, %: Ga, 50.29 (15 h); C, 13.78; H, 3.43.
IR spectra are described in Table 3.
t
solids precipitated from MeOH, EtOH, and BuOH.
The products of electrochemical synthesis from iPrOH
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

668
SUSLOVA et al.
Table 3. IR spectra for gallium alkoxides. The synthesis method is indicated in parentheses: I, exchange reaction; II,
transetherification ; III, anodic dissolution of metal
Ga(OMe)3
(II, III)
Ga(OEt)3
(II, III)
Ga(OPri)3
(I)
“Ga(OBun)3”
(III)
Ga(OMe)2.5(OR)0.5
Ga(OEt)(OR)
2
Ga(OC H OMe)3
2
4
(III)
R = C H OMe (II) R = C H OMe (II)
2
4
2 4
2992–2846 2964 vs
2960 s
2956 vs
2930 vs
2872 vs
1204 w
1096 m sh
1066 m
1026 m
888 vw
842 w
716 w
652 w
590 w
564–414 m br
2920 vs
2922 vs
2848 s
2922 vs
2850 m sh
–s br
2902 vs
2844 vs
2720 m
2710 m
2604 w
1288 w
1156 s
1108 vs
1068 vs
1038 vs
912 m
2920 m
2848 m
2650 vw
1558 vw
1460 vs
1376 vs
1366 s sh
1342 m
1258 m
1144 m
1128 vs
986 vs
2878 vs
2632 vw
2724 sh
1942 w
1696 vw
1618 vs
1452 vs
1382 w sh
1366 s
2826 s
1460 vs
1376 s
1308 w
1260 m
1178 m
1078 vs
1044 vs
978 w
1626 vs
1612 s
1306 vw
1260 w
1240 s
938 w
1240 w
1194 m
1086 vs
1044 vs
966 msh
894 msh
834 m
852 m
888 vs
782 m
844 vs
834 vs
792 m
1196 s
1098 m sh
1050 vs
792 w
720 m
1106 vs
1058 vs
1018 vs
976 m sh
898 s
836 s
710 m sh
624 m
964 w
880 w
824 w
714 s
600 s
480 vs br
682 w sh
660 w sh
654 m
524 m sh
490 m br
622 s sh
570 vs
646 w sh
628 vs
536 w br
488 w br
414 m
600–500 vs br
456 m
Crystallography
nates, interatomic distances, and bond angles in the
Ga(OEt)3 structure are compiled in Tables 6 and 7.
X-ray diffraction patterns for Ga(OEt)3 powders
prepared electrochemically and by the exchange reac-
tion are displayed in Fig. 1. The sample prepared by the
second method (Table 1; sample 3) contains trace NaCl.
The details of the structure experiment are listed in
Table 4.
RESULTS AND DISCUSSION
In attempted to repeat Ga(OR)3 two syntheses
described in the literature: (1) an exchange reaction
between GaCl3 and alkali alkoxides and (2) reetherefi-
cation of gallium isopropoxide by other alcohols. In
addition, we pioneered the use of anodic oxidation of
metals in absolute alcohol to prepare Ga(OR)3. LiOR
was used to prepare methoxide and ethoxide (because
LiCl is soluble in the relevant alcohols). As a result of
the reaction, however, Ga(OR)3 did not precipitate,
likely because of the formation of stable lithium
alkoxochlorogallates.
TREOR90 software [17] was used to determine unit
cell parameters; the STOE WinXPow program package
was used in the final indexing (Table 5). The crystal
structure was solved ab initio proceeding from powder
data. Suggested space group P421Ò was chosen pro-
ceeding from systematic extinctions. The primary
model was found using FOX software [18]. Isolated Ga
atoms and Et groups as rigid fragments are randomly
distributed over the unit cell. Jana2000 software was
Repeating many times the exchange reaction of
used for the Rietveld refinement of the calculated alcoholic solutions of GaCl3 with sodium ethoxide in
model [19]. Thermal parameters were fixed at Uiso
=
the proportion 1 : 3 or using solid gallium chloride
0.05 for all atoms. Mild constraints were imposed on (which was described as a method for Ga(OEt)3 synthe-
the geometry of ethoxy groups during the refinement:
sis [6–8]), we obtained soluble oxoethoxochlorides of
variable composition, which did not degrade during
dC–C = 1.40(6) Å, dC–O = 1.40(6) Å, and ∠OCC =
113(2)°. Figure 2 displays the measured, simulated, and long boiling (the yield of an NaCl precipitate was ~80%
difference X-ray diffraction patterns. Atom coordi- of the theory). The products formed after the solutions
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

GALLIUM ALKOXIDES: SYNTHESIS AND PROPERTIES
669
I, arb. un
100
90
80
70
60
50
40
30
20
10
0
were evacuated ranged in color from white yellow;
their solubility in alcohol or toluene also varied widely.
Complexes [Ga5(µ5-O)(µ-OEt)8Cl5] and [Ga12(µ4-
O)2(µ3-O)5(µ-OEt)10Cl12Py4]Py crystallized in insignif-
icant yields from reaction solution upon addition of
solid MeCN and Py, respectively [20]. The appearance
of oxo groups in the above-described compounds was
likely due to alcoholysis of solid GaCl3 (a strong Lewis
acid) and partial HCl evolution. HCl reacts with alcohol,
yielding water (this reaction is catalyzed by MCln) [13].
*
*
1
2
When the reaction was carried out with GaCl3 dis-
solved in toluene or with GaCl3 · EtOH in alcohol (i.e.,
under the conditions maximally excluding alcoholysis
[21]), the product was microcrystalline Ga(OEt)3,
which is sparingly soluble in alcohol or toluene. Elec-
trochemical synthesis gave the same result.
*
10
15
20
25
30
35
40
45
2θ, deg
Fig. 1. Powder X-ray diffraction pattern for Ga(OEt) sam-
ples prepared by (1) exchange reaction or (2) anodic disso-
lution of metal (*NaCl lines).
3
The exchange reaction of GaCl3 with NaOPri is the
only method for preparing Ga(OPri)3; the product yield
is high (anodic dissolution of gallium is inefficient in
this case because of the impossibility of separating the
desired product from the electroconductive additive .
All Ga(OR)3 samples were studied by IR spectros-
copy. The spectra measured in the range of the vibra-
tions of OR groups were close to the spectra of individ-
Ga(OEt)3, Ga(OPh)3, and Ga(OPri)3 were earlier
proposed as precursors for reetherefication [7, 9, 10]. In
view of their solubility in toluene, it is pertinent to use
Ga(OPri)3 or Ga(OC2H4OMe)3 in this reaction. Elemen-
tal analysis showed that methoxide and ethoxide were
prepared in this way. However, mass spectrometry
showed residual isopropoxide groups in Ga(OEt)3 pre-
Table 4. Details of the X-ray diffraction experiment and
structure parameters for Ga(OEt)3
T, K
293
Formula weight
Crystal system
189.78
Tetragonal
pared from Ga(OPri)3 (Fig. 3).
Space group
P4 21c (114)
18.0047(3)
5.5957(2)
1813.96(5)
8
Anodic gallium dissolution yielded Ga(OR)3 with
a, Å
R= Me, Et, C2H4OMe, or GaO(OBun). Metal micropar-
ticles were piled up in solid samples during long elec-
trolysis (which was verified by X-ray powder diffrac-
tion); as a result, the metal prevalence decreased and
that of carbon and hydrogen decreased. However, liq-
uid Ga(OC2H4OMe)3 was readily separated from impu-
rity metallic gallium.
c, Å
V, Å3
Z
dcalc, g/cm3
1.3894
Radiation, λ, Å
CuKα1, 1.54051,
Ge-monochromator,
Image Plate Detector
All Ga(OR)3—derivatives of aliphatic alcohols—
are white solids. A freshly prepared Ga(OPri)3 sample is
a yellow waxy substance, which cures in 3–5 weeks, in
accordance with [6, 7]. Ga(OC2H4OMe)3 is a colorless
vitrifying liquid.
µ, cm–1
Diffractometer
2θ range, deg
h, k, l range
3.770
G670 Huber
3–85
Gallium ethoxide and gallium oxobutoxide decom-
pose without melting at 195 and 174°ë, respectively.
Ga(OEt)3 decomposes under solution at 135°ë. The melt-
ing temperature of Ga(OPri)3 is 75–80°C/10–3 mmHg.
Ga(OMe)3 and Ga(OBun)3 are insoluble in alcohols
and aromatic hydrocarbons. Ga(OEt)3 is sparingly sol-
uble in alcohol and hot toluene. Ga(OPri)3 and
Ga(OC2H4OMe)3 are well soluble in alcohols and
hydrocarbons. The solubility of Ga(OEt)3 samples pre-
pared electrochemically or by exchange reaction
increases from 3 to 6 wt % in the range 20−100°ë
(Table 8).
0
–10
0
h
15
10
k
l
4
Refinement technique
Software
Full profile
Jana2000
1.41/1.86
0.97/0.95
73
RP/RwP
GOOF/χ2
Number of refined parameters
Weighting scheme (∆/σ)max
Single
Orientation parameter
(direction)
March-Dollase
0.860(4), (001)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

670
SUSLOVA et al.
Table 5. Indexing of powder X-ray diffraction patterns for Ga(OEt)3
I, %
2θobs, deg
2θcalc, deg
∆2θ, deg
dobs, Å
dcalc, Å
hkl
5.2
62.9
100
7.6
6.5
3
6.937
9.821
6.933
9.811
0.0039
0.0095
0.0200
0.0087
0.0252
0.0284
0.0029
0.0068
0.0148
–0.0084
0.0066
0.0027
0.0009
–0.0045
0.0038
0.0303
0.0142
0.0229
0.0298
0.0295
0.0220
0.0257
–0.0367
–0.0023
–0.0067
0.0278
0.0019
0.0486
0.0110
0.0107
0.0168
0.0222
0.0442
0.0108
0.0087
0.0494
0.0241
–0.0150
0.0396
0.0169
0.0251
–0.0018
0.0383
–0.0082
0.0253
0.0332
0.0329
12.7321
8.9993
8.0425
6.3657
5.6880
4.9888
4.7513
4.5933
4.3664
4.2481
4.0919
3.9909
3.7263
3.5087
3.4430
3.3418
3.2673
3.1823
3.0866
2.9998
2.9597
2.8689
2.8519
2.7970
2.7323
2.7024
2.6709
2.6419
2.6167
2.5601
2.5372
2.5121
2.4954
2.4398
2.3551
2.3352
2.3173
2.2983
2.1909
2.1779
2.1313
2.1016
2.0734
2.0469
1.9947
1.9822
1.9600
12.7393
9.0081
8.0571
6.3697
5.6972
4.9968
4.7520
4.5949
4.3696
4.2464
4.0931
3.9914
3.7265
3.5081
3.4435
3.3455
3.2690
3.1848
3.0897
3.0027
2.9618
2.8712
2.8486
2.7968
2.7318
2.7046
2.6710
2.6456
2.6175
2.5608
2.5384
2.5136
2.4984
2.4405
2.3556
2.3381
2.3187
2.2974
2.1929
2.1788
2.1325
2.1015
2.0752
2.0466
1.9957
1.9836
1.9614
110
200
210
220
310
320
201
211
410
330
301
311
321
401
411
520
421
440
530
600
610
521
620
002
112
531
202
601*
611
222
621*
541*
640
322
412
701*
711
422
512
731
651
442
811*
602
622
542
751
10.992
13.901
15.566
17.764
18.660
19.309
20.322
20.894
21.701
22.257
23.860
25.364
25.857
26.654
27.273
28.016
28.903
29.759
30.171
31.150
31.341
31.972
32.750
33.123
33.525
33.904
34.240
35.022
35.348
35.714
35.960
36.808
38.183
38.521
38.831
39.165
41.169
41.425
42.375
43.003
43.618
44.212
45.434
45.736
46.283
10.972
13.892
15.541
17.736
18.658
19.302
20.307
20.902
21.695
22.255
23.859
25.368
25.853
26.623
27.259
27.993
28.873
29.729
30.149
31.125
31.378
31.974
32.757
33.095
33.523
33.855
34.229
35.011
35.331
35.692
35.916
36.797
38.174
38.471
38.807
39.180
41.129
41.408
42.350
43.005
43.579
44.220
45.409
45.702
46.250
9
12.2
8.9
5.2
8.7
9.5
2.6
5.8
3.7
2.1
5.9
2.1
3.3
1.8
2.5
8.5
1.3
2.1
1.1
1.9
2.2
11.9
6.2
1.4
1.7
4.9
1
3.8
2.3
3.1
0.9
1.4
0.7
2.5
0.7
1
5.1
0.3
1.4
1.2
1.5
* Reflections to which more than one set of indices can be assigned (within an error of 0.05 in ꢀ ).
2θ
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GALLIUM ALKOXIDES: SYNTHESIS AND PROPERTIES
671
I, arb. un.
1.0
18517 COUNTS (o)
17904 COUNTS (c)
Ga(OEt)
3
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
IÓÚÌ
0.2
0.1
31 32 33 34 35 36 37 38 39
2θ, deg
0.1
0
2θ, deg
10
20
30
40
50
60
70
Fig. 2. Measured, simulated, and difference X-ray diffraction powder patterns for an electrochemically prepared Ga(OEt) sample.
2
ual homologues of other metals, which verifies the indi- Al(OEt)3 spectra in [22], we can infer that these polynu-
viduality of our Ga(OR)3 samples (Table 3). Mass
clear ions refer to oxo species Ga6O2(OEt)+13 and
spectra showed that Ga(OR)3 with R = Me or Bun and
crystalline Ga(OEt)3 samples prepared by anodic Ga5O(OEt)+ . The adequacy of this interpretation is
12
stripping, exchange reaction, or transetherification
during boiling are not volatile, as opposed to [8].
However, amorphous gallium ethoxide samples pre-
pared by transetherification at room temperature (they
are loose, unlike microcrystalline powders) are volatile.
In the mass spectrum of this product (Table 2, Fig. 4),
validated by the nature of the fragmentation species
(OR, R2O, R), which are typical of mass spectra of
metal alkoxides [13, 22–24].
Table 7. Bond lengths (α) and bond angles (ω) in the struc-
there are ions whose compositions indicate an incom- ture of Ga(OEt)3
plete substitution of ethoxy for isopropoxy groups
Bond
d, Å
Bond
d, Å
(Ga (OEt) (OPri)1+2 – n, n = 2, 3); the other mass num-
4
n
Ga(1)1–O(1)4
Ga(1)1–O(2)1
Ga(1)1–O(3)5
1.74(1) Ga(1)1–O(2)2
1.89(2) Ga(1)1–O(3)6
1.98(2)
2.00(2)
2.01(2)
bers correspond to Ga(OEt)3 and are similar to those
reported in [8]. High-mass ions were interpreted in [8]
as resulting from the fragmentation of ortho species
[Ga(OEt)3]5–6. Comparing Ga(OEt)3 spectra and the
Angle
ω, deg
Angle
ω, deg
O(3)6Ga(1)1O(2)2
O(3)6Ga(1)1O(3)5
O(3)6Ga(1)1O(2)1
O(3)6Ga(1)1O(1)4
O(2)2Ga(1)1O(3)5
O(2)1Ga(1)1O(2)2
O(2)2Ga(1)1O(1)3
O(3)5Ga(1)1O(2)1
O(3)5Ga(1)1O(1)4
O(2)1Ga(1)1O(1)4
176.8(9) Ga(1)7O(1)1C(2)1 134.8(15)
101.4(8) Ga(1)1O(2)1C(4)1 126.6(15)
79.7(9) Ga(1)8O(3)1C(6)1 123.8(14)
94.5(8) Ga(1)3O(2)1C(4)1 120.3(15)
77.7(8) Ga(1)9O(3)1C(6)1 136.0(14)
97.6(9) Ga(1)9O(3)1Ga(1)8 99.3(8)
88.4(9) Ga(1)1O(2)1Ga(1)3 102.7(9)
108.7(9) C(1)1C(2)1O(1)1 114.4(16)
125.7(9) C(3)1C(4)1O(2)1 111.1(17)
125.2(9) C(5)1C(6)1O(3)1 111.2(17)
3
Table 6. Atomic coordinates in the structure of Ga(OEt)3
Atom
x
y
z
Ga(1)
O(1)
O(2)
O(3)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
0.7055(2)
0.724(1)
0.709(1)
0.166(1)
0.614(1)
0.673(1)
0.755(1)
0.702(1)
0.118(1)
0.156(1)
0.1593(2)
0.594(1)
0.243(1)
0.385(1)
0.527(1)
0.555(2)
0.373(1)
0.322(2)
0.497(1)
0.454(2)
0.760(1)
0.772(4)
0.964(4)
0.437(3)
0.707(4)
0.606(3)
1.045(3)
0.893(3)
0.508(3)
0.351(3)
1
2
x, y, z; 1/2 + y, –1/2 + x, m –1/2 + z; 1/2 + y, –1/2 + x, 1/2 + z;
4
7
5
6
3/2 – x, –1/2 + y, 3/2 – z; 1 – y, x, 1 – z; 1/2 + x,1/2 – y, 3/2 – z;
8
9
3/2 – x, 1/2 + y, 3/2 – z; y , 1 – x, 1 – z; –1/2 + x, 1/2 – y, 3/2 – z.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

672
SUSLOVA et al.
Ga4(OPri)012 (984; 0)
–OR
Ga4(OPri)+11 (925; 2)
–OR
–R2O
Ga4(OPri)+1+0 (866; 2)
Ga4O(OPri)+8+ (764; 1)
–C3H6
Ga4O(OPri)7(OH)++ (725; 0.1)
Ga3(OPri)09 (738; 0)
–OR
Ga3(OPri)+8 (679; 5)
–OR
–R2O
Ga3O(OPri)6+ (577; 0.3) Ga3(OPri)+7+ (620; 1)
–Me
Ga2(OPri)06 (492; 0)
–OR
Ga2(OPri)5(OC2H4)+ (477; 2)
–OR
Ga2(OPri)4(OC2H4)+ (418; 1)
–R2O
Ga2(OPri)+5 (433; 35)
–R2O
–OR
Ga2O(OPri)+3 (331; 10)
Ga2(OPri)+4+ (374; 64) Ga2O(OPri)2(OC2H4)+ (316; 9)
–R2O
–R2O
–OC2H4
–OR
Ga2O(OPri)+2+ (272; 8)
Ga2O2(OC2H4)+ (214; 24)
–CH2
–R2O
–OR
Ga2O2++ (170; 5)
Ga2O2(OCH2)+ (200; 9)
Ga2O(OPri)(OC2H4)+ (257; 20)
i
Fig. 3. Fragmentation in the mass spectrum of Ga(OPr ) .
3
Freshly prepared Ga(OPri)3 enters the gas phase in
Ga(OMe)3, Ga(OEt)3 (a freshly prepared transether-
the dimer form. Tetramer fragments appear in the spec- ification product), Ga(OPri)3, and Ga(OBun)3 samples
trum of an aged sample (Fig. 3); this spectrum resem-
bles that reported in [8]. The fragmentation character
does not differ from that observed in the [Al(OPri)3]4
spectrum [25].
were X-ray amorphous. The X-ray diffraction patterns
for nonvolatile Ga(OEt)3 powders (produced by either
the exchange reaction of electrochemical synthesis)
contain well-resolved peaks. The solution of this struc-
ture showed that it is built of polymer zigzag chains of
trigonal bipyramids [Ga(µ-OEt)4/2(OEt)]∞. Axial atoms
Table 8. Ga(OEt)3 solubility in EtOH
are é(3)6 and é(2)2; equatorial atoms are O(1)4, O(2)1,
and O(3)5 (Figs. 5, 6). Pentacoordinate gallium atoms
are linked to one another via two pairs of (µ-OEt)2
bridges, each being formed by one axial group and one
equatorial group; the fifth equatorial group O(1)4 is ter-
minal. The latter forms the shortest bond with the metal
atom (1.74(1) Å). The bridges lying in the equatorial
plane (1.89(2) and 1.98(2) Å) are slightly shorter than
the axial ones (2.00(2) and 2.01(2) Å). On the whole,
the lengths of the terminal and bridging bonds in the
Ga(OEt)3 structure do not differ from those found in
[Ga5O(OEt)8Cl5] and [Ga12O7(µ-OEt)10Cl12Py4]Py,
Ga(OEt)3 concentration
Point no.
t, °C
in solution, wt %
1
2
3
4
5
6
22
40
3.51
4.90
70
5.79
100
130
135
6.02
7.05
Decomposes
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GALLIUM ALKOXIDES: SYNTHESIS AND PROPERTIES
673
Ga4(OEt)2(OPri)9+ (897; 20)
–OPri
Ga4(OEt)3(OPri)+8 (883; 40)
–OEt
Ga4(OEt)2(OPri)+8+ (838; 30)
–Et2O
Ga4O(OPri)8++ (764; 4)
Ga6O2(OEt)1+3 (1031; 6)
–R2O
–OR
++
12
Ga6O3(OEt)1+1 (957; 1) Ga6O2(OEt)
(986; 4)
–CH2
–GaO(OEt)
Ga6O3(OEt)10(OMe)+ (943; 1)
Ga5O(OEt)++ (901; 7)
12
–OR
++
11
Ga5O(OEt)
(856; 1)
–R2O
–Et
Ga5O2(OEt)1+0 (827; 100)
Ga4(OEt)102 (816; 0)
–OR
Ga4(OEt)1+1 (771; 8)
–R2O
–OR
++
10
Ga4O(OEt)+9 (697; 37) Ga4(OEt)
(726; 6)
–OR
Ga4O(OEt)+8+ (652; 2)
–GaO(OR)
Ga3(OEt)+8 (567; 11)
–OR
Ga3(OEt)7++ (522; 6)
–R2O
Ga3O(OEt)+6 (493; 21)
–Me
Ga2(OEt)06 (408; 0)
–OR
–OR
Ga3O(OEt)5(OCH2)+ (478; 16) Ga3O(OEt)+5+ (448; 15) Ga2(OEt)+5 (363; 28)
–Ga(OR)3
–OR
Ga2(OEt)+4+ (318; 55)
Ga2O(OEt)2(OCH2)+ (274; 89)
–OR
–R2O
Ga2O(OEt)(OCH2)++ (229; 90)
Ga2O2(OCH2)+ (200; 10)
i
Fig. 4. Fragmentation in the mass spectra of Ga(OEt) and the product of incomplete substitution of EtOH for Ga(OPr ) .
3
3
which also contain trigonal bipyramids [GaO5] [20]. A [Ti(OEt)4]4 [28], cluster [W(OEt)4]4 [29], and poorly
similar structure motif is known in the structure of structured polymers [M(OEt)n]∞ with M = Ca, Sr, Ba,
2-methoxyethanol, a zigzag polymer: [Bi2(µ,η1- Pb, or Ni [30–32]. Ethoxy groups are mainly encoun-
OC2H4OMe)4(η1-OC2H4OMe)2]∞ [26, 27]; however,
metal coordination in this case is tetragonal-pyramidal.
tered in oxoalkoxides, in which they reside on the sur-
face of [MnOm] aggregates [33].
Methoxides are virtually the only studied alkoxide
Most of the structures studied are derivatives with
structures with n-radicals described. The exceptions are branched and sterically crowded radicals, whose con-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

674
SUSLOVA et al.
C1
C1
C2
C2
O1
O1
C4
C3
C5
C6
O3
C4
C3
C5
C6
O3
C5
C6
Gal
Gal
O2
O2
O2
O3
O2
O3
O2
O3
Gal
O1
Gal
C3
C4
C6
C3
C4
C5
C6
C3
C4
C5
O1
C2
C2
C1
C1
Fig. 5. Configuration of a fragment of a polymeric [Ga(OEt) (OEt)] structure.
4/2
∞
figuration makes it possible to overcome the effect of tion polymerism [13]. This phenomenon, in particular
known for aluminum alkoxides and manifested as wide
variations in the physical state, melting point, gas-tran-
sition temperature, solubility, and other physicochemi-
cal parameters, is associated with the history of the
sample: synthesis temperature, the solvent from which
it was separated, aging time, and other parameters.
hydrocarbon chain entangling. Most metal ethoxides
are amorphous polymers. The presence of ortho- and
oxoalkoxides species of various nuclearity in Ga(OEt)3
samples is another example of what we call coordina-
O(3)6
ACKNOWLEDGMENTS
The authors are grateful to the Russian Foundation
for Basic Research for financial support (project no. 07-
03-00128), V.V. Chernyshov and A.I. Belokon’ for dis-
cussion, and students E.A. Sinditskaya and D.I. Neskre-
bin for help in work.
O(1)4
Ga(1)1
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