ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 12, pp. 1846–1854. © Pleiades Publishing, Inc., 2006.
Original Russian Text © E.V. Suslova, N.Ya. Turova, 2006, published in Zhurnal Neorganicheskoi Khimii, 2006, Vol. 51, No. 12, pp. 1963–1971.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
On the Interaction of Tetraethoxosilane with Metal Alkoxides:
Sol–Gel Synthesis of Alkaline-Earth Metal Silicates
E. V. Suslova and N. Ya. Turova
Moscow State University, Leninskie gory, Moscow, 119992 Russia
Received May 10, 2006
Abstract—Physicochemical analyses (solubility method, conductometry, and IR spectroscopy) revealed no
complex formation in M(OR)n–Si(OR)4–ROH systems (M = Na, Ba, Al; R = Et, Pri), unlike in the systems con-
taining alkoxides of two metals. IR and NMR spectroscopy showed that Si(OR)4 became reactive only due to
microhydrolysis, which is accompanied most likely by the formation of intermediates (asymmetric molecules
[Si(OH)n(OR)4 – n]). The hydrolysis was studied for model systems M(OEt)2–Si(OEt)4 (M = Ba, Ca), and con-
ditions for the synthesis of silicates were optimized.
DOI: 10.1134/S0036023606120023
Methods for the synthesis of various oxide materials reactions that occur in the initial steps of alkoxide
using the hydrolysis of alkoxide E(OR)n (a variant of hydrolysis [14]. The most important factors are the
molecular structure of the alkoxide, the composition of
the complexes in solution, the nature of the solvent
[15], and the affinity of alkoxides to the formation of
oxoalkoxo derivatives. The oxo bridges in their mole-
cules are, most likely, centers of formation of the crys-
tal structure of future oxides. In the case of heteroele-
ment precursors, the formation of M–O–E groups pro-
vides the chemical homogeneity of the target product at
the atomic level.
the sol–gel method) have been intensely developed in
recent decades. Most publications on the use and devel-
opment of sol–gel technology concern SiO2-based
composites. The number of these composites is contin-
uously increasing. Complex oxides used as highly dis-
persed powders [1], refractory ceramics [2], bio-ceram-
ics [3–5], films and coatings [6], membrane materials
[7], and glasses [8] occupy a special position. The advan-
tages of sol–gel technology over solid-phase synthesis
are the possibility to prepare crystalline or amorphous
powders with specified composition, particle size, and
morphology and the substantially lower duration and
temperature of the synthesis. The initial substances in the
synthesis of silicates are Si(OEt)4 (tetraethoxosilane,
which is the only large-tonnage synthesis product among
Si(OR)4) and metal alkoxides or salts.
It is accepted to distinguish two types of Si(OR)4
hydrolysis depending on the ratio h = [H2O] : [Si(OR)4].
The first type involves small water amounts at h ≤ 4
(microhydrolysis resulting in the formation of particles
of the [Si(OH)n(OR)4 – n] type), and the second type
involves a large excess of water at h ꢀ 4 (macrohydrol-
ysis yielding silicic acids [SiO2 · xH2O]n). The models
of combined hydrolysis (cohydrolysis) of Si(OR)4 and
M(OR)n, intermediates and the role of true precursors of
silicates are rather contradictory. Some procedures for
the reactions are related to further applications of prod-
ucts and have been developed for the solution of spe-
cific technological problems [9].
'
Unlike bimetallic alkoxides MxMy (OR)z or
'
oxoalkoxides MxMy ét(OR)z (which are widely and
successfully used in the syntheses of complex metal
oxides), ethoxosilanoxides (M(OEt)n · mSi(OEt)4 or
M[OSi(OEt)3]n)—hypothetical precursors of silicates
[9]—are virtually unstudied. Of the compounds of this
class, only tris-tert-butoxosilanoxides M[OSi(OBut)3]n
are described [10–12]. It should be mentioned that the
closest analogs of alkoxosilanoxides M(OSiR3)n are
studied in some detail, and their properties, structure,
and methods of synthesis resemble those of
M[E(ORt)n]m [13].
In the present work, we studied the interaction in
systems consisting of Si(OEt)4 and metal alkoxides and
their cohydrolysis under different conditions. Particular
stages of the process were studied for the formation of
alkaline-earth metal silicates, namely, the interaction of
components in solutions, influence of hydrolysis condi-
tions, behavior of products during thermal treatment,
It is known that the basic characteristics of oxide
materials are determined to a considerable extent by and other stages until silicate crystallization.
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