Alkali-metal-directed hydrolytic condensation of trifunctional phenylalkoxysilanes

Article abstract of DOI:10.1002/ejic.200300583

The alkali-metal-directed hydrolysis of phenyltrialkoxysilanes, PhSi(OR)₃ (R = Me, Et, nBu), was performed under various reaction conditions. The alkali metal ions were used both as templating entities and as structural elements. The crystalline sodium and potassium phenylsiloxanolates (Na-PhS and K-PhS) were obtained in two different molecular compositions based on a cis-tetraphenylcyclotetrasiloxanolate, cis-[PhSi(O)O^-] ₄, or on a cis-triphenylcyclotrisiloxanolate, cis-[PhSi(O)O ^-]₃, anions assembled into a chain or double-layer supramolecular structure through coordination with alkali cations and hydrogen-bonding contacts. Conditions for selective preparation of crystalline Na-PhS or K-PhS of both structural types were identified. The molecular and crystal structures of [(Na⁺)₃{PhSi(O)O^-} ₃]·8H₂O (2), [(Na⁺)₃{PhSi(O) O^-}₃]·4H₂O·1EtOH (3) and [(K ⁺)₃{PhSi(O)O^-}₃]₂· 7H₂O·3MeOH (4) were determined by single-crystal X-ray analysis. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300583

FULL PAPER
Alkali-Metal-Directed Hydrolytic Condensation of Trifunctional
Phenylalkoxysilanes
Yulia A. Pozdniakova,[a] Konstantin A. Lyssenko,[a] Alexandr A. Korlyukov,[a]
Inessa V. Blagodatskikh,[a] Norbert Auner,[b] Dimitris Katsoulis,[c] and
Olga I. Shchegolikhina*[a]
Keywords: Hydrolytic condensation / Potassium / Self-assembly / Silanes / Sodium / Template synthesis
The alkali-metal-directed hydrolysis of phenyltrialkoxysil-
cations and hydrogen-bonding contacts. Conditions for
anes, PhSi(OR)3 (R = Me, Et, nBu), was performed under vari- selective preparation of crystalline Na-PhS or K-PhS of both
ous reaction conditions. The alkali metal ions were used both
as templating entities and as structural elements. The crystal-
line sodium and potassium phenylsiloxanolates (Na-PhS and
K-PhS) were obtained in two different molecular composi-
tions based on a cis-tetraphenylcyclotetrasiloxanolate, cis-
[PhSi(O)O−]4, or on a cis-triphenylcyclotrisiloxanolate, cis-
[PhSi(O)O−]3, anions assembled into a chain or double-layer
supramolecular structure through coordination with alkali
structural types were identified. The molecular and
crystal structures of [(Na+)3{PhSi(O)O−}3]·8H2O (2),
[(Na+)3{PhSi(O)O−}3]·4H2O·1EtOH (3) and [(K+)3{PhSi-
(O)O−}3]2·7H2O·3MeOH (4) were determined by single-crys-
tal X-ray analysis.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
At present the template and self-assembly approach to
the design of metal-based molecules and supramolecules
from oligodentate ligands and appropriate metal ions is one
of the most popular and fastest growing areas of exper-
imental chemistry that offers an alternative to the classical
organic route. The effectiveness of metal-mediated self-as-
sembly for the construction of one-, two- and three-dimen-
sional structures has been demonstrated in an enormous
number of examples published in various articles, reviews
and books.[2] As an alternative to the traditional approaches
used in siloxane chemistry we have taken advantage of a
metal-directed self-assembly strategy to selectively create
metallasiloxane molecules with well-defined architectures
by hydrolysis of various trifunctional alkoxysilanes in the
presence of alkaline and/or transition and lanthanide me-
tal ions.[3]
The focus of our present work is a study of the alkali-
metal-directed hydrolytic condensation of phenyltrialkoxy-
silanes under a wide variety of different experimental con-
ditions. The alkali metal ions were used both as templating
entities and as structural elements.
Literature data on the synthesis and structure of alkali
metal organosiloxanolates are presented in details in our
previous publication[4] and references cited therein.
The hydrolytic condensation of trifunctional organosil-
anes [e.g. RSiCl3 or RSi(OR)3], generally used for the prep-
aration of silsesquioxane materials, is a multistep and rather
complicated process. Due to a statistical distribution of in-
termediate components the process is very sensitive to a
combination of experimental factors and usually produces
a wide range of products, from small oligomers and poly-
hedral silsesquioxanes to mixtures of resin materials and
gels.[1] The purpose of our investigations is to direct a hy-
drolytic condensation process to the formation of only one
desired compound, with a well-defined structure, using a
template. The proposed method includes the assembling of
silicon-containing species on the template through non-co-
valent bonding, thus bringing the functional groups at-
tached at the silicon atom into close contact. Such a mutual
arrangement will favor the cyclocondensation and, finally,
the formation of well-organized architecture. Subsequent
removal of the template will give an individual siloxane
molecule with a well-defined structure.
[a]
A. N. Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences,
Vavilova 28, 119991 Moscow, Russian Federation
E-mail: olga@ineos.ac.ru
Results
[b]
Chemistry Department, Goethe University of Frankfurt,
Marie Curie Strasse 11, 60439 Frankfurt, Germany
Reactions of phenyltrialkoxysilanes PhSi(OR)3 (R ϭ
nBu, Et, Me) with NaOH or KOH [Si/Na(K) ϭ 1:1] were
[c]
Dow Corning Corporation,
Midland, MI 48686, USA
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DOI: 10.1002/ejic.200300583
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O. I. Shchegolikhina et al.
FULL PAPER
performed in the presence of water according to Scheme 1 presence of an equimolecular amount of water (molar ratio
and the description given in the Exp. Sect. The H2O/Si ratio H2O/Si ϭ 1:1). Crystalline Na-PhS-4 was isolated in about
was varied within the range 1Ϫ12:1. Alcohols (nBuOH, 80% yield under similar conditions from the reaction of
EtOH, MeOH) or their mixtures with either aromatic sol- PhSi(OEt)3 in ethanol.
A
single crystal of cis-
vents (xylene, toluene, benzene) or with hexane, were used [(Naϩ)4{PhSi(O)OϪ}4]·8nBuOH (1; Figure 1), obtained
as solvents.
from PhSi(OnBu)3, was characterized by X-ray crystal-
lography.[4] Treatment of both crystalline bulks with
Me3SiCl yielded cis-[PhSi(O)OSiMe3]4 exclusively.
Scheme 1
From some reaction solutions suitable single crystals
were isolated and their molecular and crystal structures
were determined by X-ray analysis. Trapping reactions of
the bulk samples with Me3SiCl were used in order to estab-
lish a correspondence between one element in the crystal
structure (namely the size of the siloxanolate cycle) and the
overall crystalline mass composition (Scheme 2). The corre-
sponding trimethylsiloxy-substituted derivatives of alkali
metal phenylsiloxanolates were analyzed by NMR spec-
troscopy and GPC.
Scheme 2
Figure 1. General view of the molecular structure of sodium phe-
nylsiloxanolate 1[4]
The analytical data obtained from the above combination
of physical methods proved unambiguously that crystalline
sodium phenylsiloxanolates (Na-PhS) as well as potassium
Crystalline sodium phenylsiloxanolate based on a cis-tri-
phenylsiloxanolates (K-PhS) are compounds that contain phenylcyclotrisiloxanolate fragment (Na-Ph-3) was synthe-
cyclic phenylsiloxanolate fragments, cis-[PhSi(O)OϪ]n, sur- sized from PhSi(OEt)3 under different reaction conditions.
rounded by sodium or potassium ions. Two different molec- A summary of reactions performed with PhSi(OEt)3 under
ular structures can be generated based on either a cis-tetra- different conditions is given in Table 1. The formation of
phenylcyclotetrasiloxanolate (Figure 1) or on a cis-tri- the six-membered cycle was promoted by an increase of the
phenylcyclotrisiloxanolate fragment (Figures 2Ϫ4); their H2O/Si ratio and/or by the addition of a strongly hydro-
specific formation depends on the reaction conditions (see phobic solvent (hexane) to the reaction medium. Reactions
below).
performed in pure ethanol solution with a high excess of
Sodium phenylsiloxanolates of both types crystallize in water (H2O/Si ϭ 4Ϫ12:1; Table 1, Entries 2 and 3) led to
good yields over a wide range of different reaction con- the selective formation of Na-PhS-3 as the only crystalline
ditions (Table 1). Crystalline sodium phenylsiloxanolate, product in yields up to 63%. A single crystal (Table 1, Entry
based on a cis-tetraphenylcyclotetrasiloxanolate fragment 3; H2O/Si
ϭ
12:1) was characterized as cis-
(Na-PhS-4), was selectively produced from the reaction of [(Naϩ)3{PhSi(O)OϪ}3]·8H2O (2) by X-ray analysis (Fig-
[4]
PhSi(OnBu)3
with sodium hydroxide in nBuOH, in the ure 2). The use of an ethanol/hexane mixture as reaction
Table 1. Formation of Na-PhS-3 and/or Na-PhS-4 from PhSi(OEt)3 under different experimental conditions
Entry
H2O/Si
ratio
Solvent
Yield of crystalline
Na-PhS[a] (%)
Na-PhS-3/Na-PhS-4
ratio
1
2
3
4
5
1:1
4:1
12:1
1:1
2:1
ethanol
ethanol
ethanol
ethanol/hexane
ethanol/hexane
83
42
63
95
95
؊:1
1:؊
1:؊
1:1
1:؊
[a]
Amorphous, powder-like by-products add to 100%; their trimethylsiloxy derivatives are the set of oligomers.
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Alkali-Metal-Directed Hydrolytic Condensation
FULL PAPER
medium resulted in the selective formation of Na-PhS-3 in ratio of 1:1. Thus, the formation of both structural types
yields up to 95% even at molar H2O/Si ratios of about 2:1 occurs under these reaction conditions.
(Table 1, Entry 5). Derivatization of the crystalline bulk ma-
terials (Table 1, Entries 2, 3 and 5) with Me3SiCl afforded
the quantitative formation of cis-[PhSi(O)OSiMe3]3 in all
cases.
Figure 3. General view of 3 with thermal ellipsoids at 50% prob-
ability level
Figure 2. General view of 2 with thermal ellipsoids at 50% prob-
ability level
No crystalline products could be isolated from reactions
X-ray structure analysis of a single crystal isolated from of PhSi(OMe)3 with NaOH in the presence of different
the hydrolysis of PhSi(OEt)3 in EtOH/hexane solution (mo- amounts of water (H2O/Si ϭ 1Ϫ10:1) and in different sol-
lar ratio H2O/Si ϭ 1:1; Table 1, Entry 4) documents the vents (MeOH, MeOH/benzene, MeOH/toluene, MeOH/
formation of [(Naϩ)3{PhSi(O)OϪ}3]·4H2O·1EtOH (3; Fig- hexane). The derivatization of the products obtained with
ure 3). The molecular structure of 3 differs from that of Me3SiCl gave a mixture of oligomers, as proven by GPC
compound 2 with respect to the coordination sphere of the analytical methods.
sodium cations. In 3 one solvate molecule of ethanol re-
Crystallization of potassium phenylsiloxanolate, unlike
places four water molecules in the molecular unit. Although the corresponding sodium salt, occurs only under a narrow
the molecular structure of Na-PhS-3 is based on a trisilox- range of conditions, probably due to a higher solubility of
anolate cycle as the main fragment, the trapping reaction the potassium siloxanolate intermediate compared to its so-
of the whole crystalline bulk with Me3SiCl yielded a mix- dium analogue. Thus, the use of a high dielectric constant
ture of [PhSi(O)OSiMe3]3 and [PhSi(O)OSiMe3]4 in a molar medium (neat alcohol, excess of water) results in a low yield
Figure 4. General view of 4 with thermal ellipsoids at 50% probability level
Eur. J. Inorg. Chem. 2004, 1253Ϫ1261
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O. I. Shchegolikhina et al.
FULL PAPER
of crystalline material or even prevents crystallization. A Molecular Structures of 2, 3, and 4
defined molar ratio of H2O/Si from 1:1 to 1.5:1 is required
for a successful crystallization.
The single-crystal X-ray investigations revealed that the
independent unit cells of compounds 2 and 3 contain one
triphenylcyclotrisiloxanolate anion, three sodium cations
and water (2) or water and alcohol molecules (3) (Figures 2
and 3, respectively). The peculiarity of the crystal structure
of the potassium salt 4 is the presence of two independent
siloxanolate anions and, consequently, of six potassium cat-
ions (see Table 2, Figure 4) in the unit cell. In all molecular
structures the geometry of the siloxanolate anions is charac-
terized by typical bond lengths and angles usually observed
for this class of compounds (Tables 3 and 4).[5,6] Thus, the
The reaction of PhSi(OMe)3 with KOH, even in an equi-
molar ratio of H2O/Si in neat MeOH, did not yield any
crystalline material. In contrast, reactions of PhSi(OnBu)3
and of PhSi(OEt)3 with KOH using an equimolar ratio of
H2O/Si in pure nBuOH or EtOH, respectively, gave crystal-
line potassium phenylsiloxanolate with a tetraphenylcyclo-
tetrasiloxanolate fragment (K-PhS-4), but only in low yields
ranging from 10 to 28%. Although we failed to grow suit-
able single crystals for X-ray analysis, reactions of the crys-
talline bulk with Me3SiCl yielded [PhSi(O)OSiMe3]4 selec-
tively, proving the formation of a potassium salt based on
a tetrasiloxanolate cyclic fragment.
˚
SiϪC bonds of the SiϪPh groups are equal to 1.862(2) A
(average value), the cyclic SiϪO bonds are significantly
˚
elongated [1.639(2)Ϫ1.661(1) A] compared to terminal ana-
˚
Decreasing the dielectric constant of the reaction me-
dium by addition of non-polar solvent supports the bulk
crystallization of potassium triphenylcyclotrisiloxanolate
(K-PhS-3). Crystalline materials in high yields (up to 95%)
were isolated from phenyltrialkoxysilanes PhSi(OR)3 (R ϭ
Me, Et, nBu) used for KOH treatment in mixtures of
MeOH/benzene, EtOH/toluene, and of nBuOH/xylene. In
all cases the derivatization of the crystalline bulk with Me3-
SiCl gave exclusively [PhSi(O)OSiMe3]3. A single crystal
suitable for X-ray analysis was obtained from the reaction
of PhSi(OMe)3. The molecular structure is shown
logues [1.577(2)Ϫ1.596(1) A]. The six-membered SiϪO
cycles exhibit an all-cis arrangement of the phenyl substitu-
ents. Their conformations vary from an approximately
planar one in 2 and in 4 (in one of the two independent
molecules) to an envelope conformation in 3 [deviation of
Si(3) atom], and a distorted boat conformation [deviation
of Si(3Ј) and O(1Ј) atoms] for the second independent mol-
ecule in 4. This variation of the siloxanolate ring confor-
mations is in line with the high flexibility of the siloxanol-
ate rings.
The coordination sphere of the alkali cations is predomi-
nantly determined and formed by the negatively charged
siloxanolates oxygen atoms and water (in 2), and the sur-
in
Figure 4
and
proves
the
formation
of
[(Kϩ)3{PhSi(O)OϪ}3]2·7H2O·3MeOH (4).
Table 2. Crystallographic data and parameters of refinement for 2Ϫ4
2
3
4
Empirical formula
Formula mass
Crystal system
T [K]
Space group
Radiation
C18H31Na3O14Si3
624.67
triclinic
C20H29Na3O11Si3
598.67
monoclinic
110
C19.5H28K3O11Si3
1279.98
triclinic
110
110
¯
¯
P1
Mo-Kα (λ ϭ 0.71072 A)
P21/c
P1
˚
Scan type
ω-scan with 0.3 step and 10 s exposure per frame
Diffractometer
Smart 1000 K CCD
˚
a [A]
9.2873(5)
9.3329(5)
17.7565(9)
79.822(1)
83.524(1)
63.844(1)
1358.7(1)
2
16.803(4)
9.761(2)
17.177(4)
90
103.979(5)
90
2734(1)
4
10.569(3)
16.387(5)
16.658(4)
101.352(6)
97.692(6)
92.636(6)
2795(1)
4
6.70
1.521
60
23178
15938 (0.0315)
0.0591 (for 10645 refl.)
0.1482 (for 15938 refl.)
1.065
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
3
˚
V [A ]
Z
µ [cmϪ1
]
2.88
1.527
2.76
1.454
Dcalcd. [g·cmϪ3
2θmax [°]
]
60
10451
54
11641
Total number of reflections
Independent reflections [R(int)]
R1 for refl.with I Ͼ 2σ(I)
wR2 for all reflections
GOF
74550 (0.0152)
0.0351 (for 6564 refl.)
0.0978 (for 7455 refl.)
1.052
5582 (0.0519)
0.0464 (for 3136 refl.)
0.0929 (for 5582 refl.)
0.96
1256
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Eur. J. Inorg. Chem. 2004, 1253Ϫ1261

Alkali-Metal-Directed Hydrolytic Condensation
FULL PAPER
˚
˚
Table 3. Selected bond lengths [A] and angles [°] in 2 and 3
Table 4. Selected bond lengths [A] and angles [°] for two indepen-
dent molecules in 4
2
3
4A
4B
Bond lengths:
Si(1)ϪO(1)
Si(1)ϪO(3)
Si(1)ϪO(4)
Si(1)ϪC(11)
Si(2)ϪO(1)
Si(2)ϪO(2)
Si(2)ϪO(5)
Si(2)ϪC(21)
Si(3)ϪO(2)
Si(3)ϪO(3)
Si(3)ϪO(6)
1.652(1)
1.652(1)
1.584(1)
1.861(1)
1.6533(9)
1.643(1)
1.594(1)
1.864(1)
1.638(1)
1.6529(9)
1.596(1)
1.857(1)
1.645(2)
1.659(2)
1.576(2)
1.864(3)
1.648(2)
1.669(2)
1.576(2)
1.864(3)
1.660(2)
1.650(2)
1.580(2)
1.864(3)
Bond lengths:
Si(1)ϪO(1)
Si(1)ϪO(3)
Si(1)ϪO(4)
Si(1)ϪC(11)
Si(2)ϪO(1)
Si(2)ϪO(2)
Si(2)ϪO(5)
Si(2)ϪC(21)
Si(3)ϪO(2)
Si(3)ϪO(3)
Si(3)ϪO(6)
1.638(2)
1.641(2)
1.590(2)
1.857(3)
1.652(2)
1.649(2)
1.579(2)
1.858(3)
1.653(2)
1.648(2)
1.591(2)
1.863(3)
1.645(2)
1.648(2)
1.591(2)
1.859(3)
1.660(2)
1.642(2)
1.576(2)
1.861(3)
1.654(2)
1.649(2)
1.579(2)
1.860(3)
Si(3)ϪC(31)
Bond angles:
Si(3)ϪC(31)
Bond angles:
O(1)ϪSi(1)ϪO(3)
O(1)ϪSi(1)ϪO(4)
O(3)ϪSi(1)ϪO(4)
O(1)ϪSi(1)ϪC(11)
O(3)ϪSi(1)ϪC(11)
O(4)ϪSi(1)ϪC(11)
O(1)ϪSi(2)ϪO(2)
O(1)ϪSi(2)ϪO(5)
O(2)ϪSi(2)ϪO(5)
O(1)ϪSi(2)ϪC(21)
O(2)ϪSi(2)ϪC(21)
O(5)ϪSi(2)ϪC(21)
O(2)ϪSi(3)ϪO(3)
O(2)ϪSi(3)ϪO(6)
O(3)ϪSi(3)ϪO(6)
O(2)ϪSi(3)ϪC(31)
O(3)ϪSi(3)ϪC(31)
O(6)ϪSi(3)ϪC(31)
Si(1)ϪO(1)ϪSi(2)
Si(3)ϪO(2)ϪSi(2)
Si(3)ϪO(3)ϪSi(1)
107.38(5)
105.5(1)
110.01(5)
107.38(5)
107.67(6)
106.70(5)
113.81(5)
105.23(5)
110.87(5)
112.10(5)
107.26(5)
108.20(5)
112.78(6)
106.74(5)
112.21(5)
108.99(5)
109.31(6)
108.02(5)
111.37(6)
133.31(6)
135.02(6)
131.67(6)
111.2(1)
109.2(1)
107.1(1)
109.3(1)
114.0(1)
105.2(1)
111.3(1)
112.2(1)
107.3(1)
107.1(1)
113.1(1)
106.7(1)
112.6(1)
109.2(1)
108.1(1)
108.0(1)
112.0(1)
135.6(1)
131.9(1)
132.1(1)
O(1)ϪSi(1)ϪO(3)
O(1)ϪSi(1)ϪO(4)
O(3)ϪSi(1)ϪO(4)
O(1)ϪSi(1)ϪC(11)
O(3)ϪSi(1)ϪC(11)
O(4)ϪSi(1)ϪC(11)
O(1)ϪSi(2)ϪO(2)
O(1)ϪSi(2)ϪO(5)
O(2)ϪSi(2)ϪO(5)
O(1)ϪSi(2)ϪC(21)
O(2)ϪSi(2)ϪC(21)
O(5)ϪSi(2)ϪC(21)
O(2)ϪSi(3)ϪO(3)
O(2)ϪSi(3)ϪO(6)
O(3)ϪSi(3)ϪO(6)
O(2)ϪSi(3)ϪC(31)
O(3)ϪSi(3)ϪC(31)
O(6)ϪSi(3)ϪC(31)
Si(1)ϪO(1)ϪSi(2)
Si(2)ϪO(2)ϪSi(3)
Si(1)ϪO(3)ϪSi(3)
106.6(1)
106.2(1)
111.4(1)
110.1(1)
108.7(1)
109.1(1)
110.8(1)
105.5(1)
109.2(1)
112.9(1)
108.5(1)
108.7(1)
111.7(1)
106.9(1)
112.4(1)
110.4(1)
108.0(1)
105.5(1)
113.3(1)
134.4(1)
133.3(1)
132.5(1)
111.2(1)
110.0(1)
109.8(1)
108.7(1)
110.9(1)
111.4(1)
112.5(1)
105.5(1)
107.3(1)
109.7(1)
110.3(1)
106.5(1)
111.3(1)
112.0(1)
106.4(1)
106.4(1)
113.8(1)
132.3(1)
132.4(1)
131.9(1)
rounding siloxanolate oxygen atoms, water and alcohol
molecules (ethanol in 3, and methanol in 4, respectively).
The presence of a significant amount of solvate molecules
In spite of the differences in the number of solvate mol- (water and alcohol) leads to the formation of a complicated
ecules in sodium salts 2 and 3, both are characterized by hydrogen-bonding network, with O···O distances varying
˚
some common features: only two of the cations are directly from 2.568(1) to 3.037(2) A. Analysis of the crystal struc-
connected to the siloxanolate ring’s oxygen atoms, while the tures of 2Ϫ4 revealed that, depending on the solvate con-
coordination sphere of the third cation contains only the tents and the nature of the cations, the hydrogen bonds are
solvate molecules, and thus can consequently be described formed solely between the solvate and SiϪOϪ (3) and/or
as a ‘‘bridging cation’’. An equivalent ‘‘bridging sodium’’ only between the solvate molecules (2, 4). In general, the
was previously detected in the corresponding salt 1[4] and hydrogen bonds between solvate and ϪOϪSi are charac-
therefore is probably a general feature of such sodium salts. terized by slightly shorter O···O distances than those be-
In contrast to compounds 1Ϫ3, in salt 4 all potassium tween solvate molecules. The maximum number of hydro-
atoms are linked to the siloxanolate ring’s oxygen atoms; gen bonds formed by the siloxanolate oxygen atoms is three,
this is probably due to the larger van der Waals radius of with a pseudo-tetrahedral arrangement around the oxygen
potassium cations. The number of oxygen atoms coordi- atom. The number and strength of these hydrogen bonds is
nated to the potassium or to the sodium cations in 2Ϫ4 mainly dominated by the coordination of the corresponding
varies between five and six and is dependent mainly on the SiϪOϪ bond to the alkali metal atom, resulting in a system-
type of coordinated oxygen atoms (in water or in alcohol atic shortening of the hydrogen bond lengths of the centers
molecules). The NaϪO and KϪO distances are weakly coordinated or uncoordinated by alkali.
˚
˚
2.287(3)Ϫ2.599(2) A, and 2.625(3)Ϫ3.053(3) A, respec-
In 2Ϫ4 the hydrogen-bonding pattern leads to an overall
tively, with the shortest contacts to the water molecules. The supramolecular architecture: the molecules are assembled
coordination polyhedra of the alkali metal atoms are dis- into double layers (Figure 5), which have a hydrophilic ‘‘fill-
torted trigonal-bipyramidal or octahedral, depending on ing’’ (alkali, water and alcohol molecules) and a hydro-
the coordination number.
phobic ‘‘coating’’ (Ph groups).
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O. I. Shchegolikhina et al.
FULL PAPER
cle:[4] the molecules of the latter are assembled into a chain-
like structure by coordination bonds. Each chain is sur-
rounded by phenyl substituents and solvated alcohol mol-
ecules without bridging ions connecting neighboring
chains (Figure 6).
Discussion
Several coupled equilibrium reactions must take place
when the hydrolysis of trialkoxysilane is performed in an
alcoholic medium in the presence of an equimolar amount
of the base (e.g. NaOH; Scheme 3. As a result of these reac-
tions, and a rapid proton-cation exchange,[7] the generation
Figure 5. Double-layer structure in 2Ϫ4
of
a
labile alkaline intermediate, suggested[4] to be
[PhSi(OH)(OR)(OϪNaϩ)] (A) (Scheme 3), is quite possible.
Presumably, these alkaline intermediates, containing sol-
vent-separated ion pairs,[8] tend to associate (equilibrium
I),[9] forming complex aggregates (B) in which an ionic part
(alkali metal ion, alcohol and water molecules) is sur-
rounded by silicon species containing functional OH and
OR groups. These groups can undergo a condensation pro-
cess with both water and alcohol elimination resulting in
the formation of either a mixture of oligomers or cyclic
products, depending on the reaction parameters
(Scheme 4). The equilibrium I is a function[10] of the charge
density of Mϩ, the solvating ability of the solvent, the nu-
cleophilicity of the anion, and the solvent/salt ratio. Such a
complicated and multi-argument process leads to results
that are relatively difficult to predict. In the course of our
Figure 6. Cyclotetrasiloxanolate tetraanion/tetracation arrange-
ment to form chains in 1;[4] phenyl groups are omitted for clarity
The packing of the sodium phenylsiloxanolates 2 and 3, study we found an appropriate set of conditions whereby
based on trisiloxanolate cycles, is different from that of the the condensation process can be selectively directed to the
sodium phenylsiloxanolate based on a tetrasiloxanolate cy- generation of cyclotri- or cyclotetrasiloxanolate anions as-
Scheme 3
1258
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 1253Ϫ1261

Alkali-Metal-Directed Hydrolytic Condensation
FULL PAPER
Scheme 4
sembled into supramolecular architectures (double layers or metal ions from Na-PhS-4 by reaction with dilute HCl solu-
chains) through coordination with metal cations and hydro- tion gives cis-[PhSi(O)OH]4 in high yield.[3b]
gen bonding.
The high-yield crystallization of sodium phenylsiloxanol-
ate of different structural types in a wide range of con-
ditions can be explained by the possible shift of equilibrium
I to the formation of the complex aggregates (B).
Experimental Section
General: 1H and 29Si NMR spectra were recorded with a Bruker
DRX-500 spectrometer (500 MHz for H and 99 MHz for 29Si) at
1
In contrast, crystallization of potassium phenylsiloxanol-
ate from an alcohol solution is quite rare. Moreover, an
excess of water (H2O/Si Ͼ 1.5:1) prevents crystallization.
This could be caused by the tendency of potassium phenyl-
siloxanolate to exist as a solvent-separated ion pair (A). A
decrease in the dielectric constant of the reaction medium
should shift the equilibrium I to the opposite side and force
the crystallization. This is in line with the experimental
data — a high-yield crystallization of potassium phenylsi-
loxanolate was achieved only upon addition of non-polar
aromatic solvents.
20 °C in C6D6 or CDCl3 as solvents and with TMS as internal
reference standard. GPC was performed with a Waters instrument
with an M-600 pump and an M-484 UV detector (wavelength
˚
254 nm) on U-Styragel 500, 1000 A columns, using a Maxima in-
formation processing computer system. Structure-determined[12]
crystals of [PhSi(OSiMe3)O]12 (retention time
[PhSi(OSiMe3)O]6 (retention time ϭ 16.95 min), [PhSi(OSiMe3)O]4
(retention time ϭ 17.43 min) and [PhSi(O)OSiMe3]3
time ϭ 17.79 min) were used as the standards. THF was used as
an eluent. Calculations on KOH were made based on the content
of KOH (85%, Aldrich). The H2O/Si ratio in the synthesis with
KOH was calculated taking into account the water content in KOH
(15% according to Aldrich).
ϭ 16.12 min),
[13]
(retention
The cis configuration of sodium and potassium phenylsi-
loxanolates of both structural forms should be governed by
the existence of aggregates B as micelles in the reaction
solutions. The presence of these micelles was detected in
our preliminary investigations of the reaction solutions by
a light-scattering method. These results are now under
further investigation and will be published elsewhere.
The removal of metal ions by treatment of the crystals
obtained with Me3SiCl gave the corresponding cyclosilox-
anes without a change of their size or configuration. It has
to be noted that the cis-tetraphenyl(trimethylsiloxy)cyclote-
trasiloxane obtained exhibits properties of a plastically
General Synthesis of Na-PhS: A mixture of phenyltrialkoxysilane,
sodium hydroxide, water and solvents was stirred vigorously either
at room temperature or under reflux conditions until the solution
became completely transparent; for completion, the solution was
stirred for an additional hour. Within a few hours or days (de-
pending on the alkoxysilane and amount of water) crystals formed
and precipitated from the solution. The crystalline bulk was sepa-
rated by filtration through a Schott filter, washed with hexane and
dried in vacuo (10 Torr/40 °C/1 h).
General Synthesis of K-PhS: A mixture of phenyltrialkoxysilane,
crystalline (3D) mesophase.[11] The analogous removal of potassium hydroxide, water and solvents was vigorously stirred at
Eur. J. Inorg. Chem. 2004, 1253Ϫ1261
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O. I. Shchegolikhina et al.
FULL PAPER
room temperature until a clear solution had formed. For com-
pletion, stirring was continued for an additional hour. Most of the
solvents (ca. 75%) were removed in a rotary evaporator, and an
equal amount of an aromatic solvent was added to the residue.
White, tiny needle-like crystals precipitated within 20 h (usually
after cooling of the reaction mixture to ca. 10 °C). The crystalline
solid was filtered, washed with hexane and dried in vacuo (10 Torr/
40 °C/1 h).
one peak corresponding to [PhSi(OSiMe3)O]3 (retention time.
17.79 min).
Na-PhS Obtained from PhSi(OEt)3 in Ethanol/Hexane and Trimeth-
ylsilylation: H2O/Si ϭ 1:1 (Table 1, Entry 4). PhSi(OEt)3 (4.98 g,
20.7 mmol), NaOH (0.83 g, 20.7 mmol), and H2O (0.38 g,
20.7 mmol) were allowed to react in a mixture of ethanol (7 mL)
and hexane (10 mL) to give two fractions of crystals. Yield of the
first fraction: 1.64 g (45%). [C6H5Si(O)ONa]4·EtOH
ϭ
General Procedure for the Trimethylsilylation of Alkali Metal Phe-
nylsiloxanolates: Na-PhS or K-PhS was added as a solid to a vigor-
ously stirred mixture of dry hexane, Me3SiCl and pyridine at room
temperature. The mixture was refluxed for 1 h, then cooled to room
temperature, filtered and washed with water until it was chloride-
free. After drying with Na2SO4, the solvent was removed and the
residue was dried under vacuum (10 Torr/40 °C/1.5 h). The remain-
ing product was characterized by NMR spectroscopy and GPC.
C26H26Na4O9Si4 (687): calcd. C 45.47, H 3.82, Na 13.39, Si 16.36;
found C 45.52, H 3.63, Na 12.98, Si 16.19. Yield of the second
fraction: 1.82 g (50%). [C6H5Si(O)ONa]3·2H2O ϭ C18H19Na3O8Si3
(517): calcd. C 41.85, H 3.71, Na 13.36, Si 16.31; found C 41.70,
H 4.05, Na 13.17, Si 17.08. A suitable single crystal from the second
fraction was analyzed by single-crystal X-ray crystallography, giv-
ing the molecular composition [(Naϩ)3{PhSi(O)OϪ}3]·4H2O·EtOH
(2). The first fraction of the Na-PhS crystalline compound (1.64 g,
2.4 mmol), Me3SiCl (2.78 g, 25.6 mmol), and pyridine (1.21 g,
15.3 mmol) were allowed to react in hexane (30 mL) to give 1.28 g
(76%) of a white solid product. GPC (THF): one peak correspond-
ing to [PhSi(OSiMe3)O]4 (retention time: 17.43 min). The second
fraction of the Na-PhS crystalline product (1.82 g, 3.5 mmol), Me3-
SiCl (2.66 g, 24.5 mmol), and pyridine (1.11 g, 14.0 mmol) were al-
lowed to react in hexane (20 mL). A colorless liquid product was
formed: 1.72 g (78%). GPC (THF): one peak corresponding to
[PhSi(OSiMe3)O]3 (retention time: 17.79 min).
Na-PhS Obtained from PhSi(OnBu)3 and Trimethylsilylation:[4]
PhSi(OnBu)3 (5 g, 15.4 mmol), NaOH (0.62 g, 15.4 mmol), and
H2O (0.28 g, 15.4 mmol) in n-butanol (15 mL). Yield of Na-PhS-4:
2.35 g (78%). [C6H5Si(O)ONa]4·3nBuOH
ϭ C36H50Na4O11Si4
(863): calcd. C 50.10, H 5.84, Na 10.66, Si 13.02; found C 50.43,
H 6.14, Na 10.95, Si 12.98. The Na-PhS-4 obtained above (2.35 g,
2.7 mmol), Me3SiCl (1.17 g, 10.8 mmol) and pyridine (0.64 g,
8.1 mmol) in benzene (40 mL) were allowed to react to give 2.3 g
(96%) of a white solid product. GPC (THF): one peak correspond-
ing to [PhSi(OSiMe3)O]4 (retention time: 17.43 min).
Na-PhS Obtained from PhSi(OEt)3 in Ethanol/Hexane and Trimeth-
ylsilylation: H2O/Si ϭ 2:1 (Table 1, Entry 5). PhSi(OEt)3 (4.98 g,
20.7 mmol), NaOH (0.83 g, 20.7 mmol), and H2O (0.75 g,
41.4 mmol) were allowed to react in a mixture of ethanol (21 mL)
and hexane (21 mL). Yield: 3.56 g (95%) of a crystalline solid.
[C6H5Si(O)ONa]3·3H2O ϭ C18H21Na3O9Si3 (535): calcd. C 40.44,
H 3.96, Na 12.91, Si 15.76; found C 40.71, H 4.28, Na 13.32, Si
16.01. Na-PhS (3.56 g, 6.6 mmol), Me3SiCl (6.45 g, 59.3 mmol),
and pyridine (3.13 g, 39.6 mmol) were allowed to react in hexane
(35 mL). A colorless liquid product was formed: 2.92 g (70%). GPC
(THF): one peak corresponding to [PhSi(OSiMe3)O]3 (retention
time: 17.79 min).
Na-PhS Obtained from PhSi(OEt)3 in Ethanol and Trimethyl-
silylation: H2O/Si ϭ 1:1 (Table 1, Entry 1). PhSi(OEt)3 (4.98 g,
20.7 mmol), NaOH (0.83 g, 20.7 mmol), and H2O (0.37 g,
20.7 mmol) were allowed to react in ethanol (10.5 mL). Yield of
Na-PhS-4:
3.18 g
(83%).
[C6H5Si(O)ONa]4·2EtOH
ϭ
C28H32Na4O10Si4 (733): calcd. C 45.89, H 4.40, Na 12.55, Si 15.33;
found C 45.51, H 4.27, Na 12.62, Si 15.13. Na-PhS-4 (3.18 g,
4.3 mmol), Me3SiCl (5.65 g, 52.0 mmol), and pyridine (3.48 g,
44.0 mmol) were allowed to react in hexane (50 mL) according to
the General Procedure. Yield of the white solid product: 2.49 g
(74%). GPC (THF): one peak corresponding to [PhSi(OSiMe3)O]4
(retention time: 17.43 min).
K-PhS Obtained from PhSi(OnBu)3 in nBuOH (H2O/Si ؍ 1:1) and
Trimethylsilylation: PhSi(OnBu)3 (4.73 g, 14.6 mmol), KOH
(0.96 g, 14.6 mmol), and H2O (0.12 g, 6.6 mmol) in nBuOH (5 mL)
were allowed to react. Yield: 0.85 g (28.6%) of needle-like crystals.
[C6H5Si(O)OK]4·nBuOH·2H2O ϭ C28H34K4O11Si4 (815): calcd. C
41.25, H 4.20, K 19.18, Si 13.78; found C 41.19, H 4.03, K 19.28,
Si 13.53. K-PhS-4 (0.85 g, 1 mmol), Me3SiCl (1.57 g, 14.4 mmol),
and pyridine (0.76 g, 9.6 mmol) in hexane (10 mL) were allowed to
react to give a white crystalline product: 0.69 g (82%). GPC (THF):
one peak corresponding to [PhSi(O)OSiMe3]4 (retention time:
17.43 min).
Na-PhS Obtained from PhSi(OEt)3 in Ethanol and Trimethyl-
silylation: H2O/Si ϭ 4:1 (Table 1, Entry 2). PhSi(OEt)3 (4.98 g,
20.7 mmol), NaOH (0.83 g, 20.7 mmol), and H2O (1.49 g,
82.8 mmol) were allowed to react in ethanol (35 mL). Yield of crys-
talline Na-PhS-3: 1.59 g (42%). [C6H5Si(O)ONa]3·3H2O
ϭ
C18H21Na3O9Si3 (535): calcd. C 40.44, H 3.96, Na 12.91, Si 15.76;
found C 40.50, H 3.73, Na 12.80, Si 15.63. Na-PhS-3 (1.59 g,
3.0 mmol), Me3SiCl (3.83 g, 35.2 mmol), and pyridine (1.85 g,
23.4 mmol) were allowed to react in benzene (40 mL). A colorless,
transparent liquid was formed: 1.6 g (85%). GPC (THF): one peak
corresponding to [PhSi(OSiMe3)O]3 (retention time 17.79 min).
K-PhS Obtained from PhSi(OEt)3 in EtOH (H2O/Si ؍ 1:1) and
Trimethylsilylation: PhSi(OEt)3 (4.98 g, 20.7 mmol), KOH (1.37 g,
20.7 mmol), and H2O (0.17 g, 9.3 mmol) in EtOH (5 mL) were al-
lowed to react to give 0.4 g (10%) of small needle-like crystalline
material. [C6H5Si(O)OK]4·EtOH ϭ C26H26K4O9Si4 (751): calcd. C
41.57, H 3.49, K 20.82, Si 14.95; found C 41.75, H 3.38, K 20.95,
Si 15.07. K-PhS-4 (0.4 g, 0.5 mmol), Me3SiCl (0.62 g, 5.7 mmol),
and pyridine (0.27 g, 3.4 mmol) in hexane (10 mL) were allowed to
react to yield a white crystalline product: 0.3 g (67%). GPC (THF):
one peak corresponding to [PhSi(O)OSiMe3]4 (retention time:
17.43 min).
Na-PhS Obtained from PhSi(OEt)3 in Ethanol and Trimethyl-
silylation: H2O/Si ϭ 12:1 (Table 1, Entry 3). PhSi(OEt)3 (4.98 g,
20.7 mmol), NaOH (0.83 g, 20.7 mmol) and H2O (4.48 g,
248.4 mmol) were allowed to react in ethanol (15 mL). Yield of
crystalline Na-PhS-3: 2.33 g (60%). A suitable single crystal was
analyzed by X-ray crystallography to give the molecular compo-
sition [(Naϩ)3{PhSi(O)OϪ}3]·8H2O (3). [C6H5Si(O)ONa]3·4H2O ϭ
C18H23Na3O10Si3 (553): calcd. C 40.54, H 5.04, Na 11.66, Si 16.17;
found C 40.12, H 5.20, Na 11.49, Si 16.25. Na-PhS-3 (2.33 g,
4.2 mmol), Me3SiCl (5.00 g, 46.0 mmol), and pyridine (2.64 g,
33.4 mmol) were allowed to react in benzene (80 mL). A colorless,
K-PhS Obtained from PhSi(OnBu)3 in nBuOH/o-Xylene (H2O/Si ؍
transparent liquid product was formed: 1.58 g (63%). GPC (THF): 1.5:1) and Trimethylsilylation: PhSi(OnBu)3 (4.73 g, 14.6 mmol),
1260  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1253Ϫ1261

Alkali-Metal-Directed Hydrolytic Condensation
FULL PAPER
KOH (0.96 g, 14.6 mmol), and H2O (0.26 g, 14.6 mmol) were al-
lowed to react in a mixture of butanol (7 mL) and o-xylene
(28 mL). A crystalline solid product was formed: 2.43 g (72%).
PLUS 5[15] on an IBM PC AT. CCDC-217730 to -217732 for crystal
structures 2Ϫ4 contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge at
[C6H5Si(O)OK]3·3H2O·nBuOH ϭ C22H31K3O10Si3 (657): calcd. C www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
39.14, H 4.93, K 17.38, Si 12.48; found C 38.77, H 4.62, K 17.21, Crystallographic Data Centre, 12 Union Road, Cambridge
Si 12.83. K-PhS-3 (2.43 g, 3.7 mmol), Me3SiCl (3.04 g, 28.0 mmol), CB2 1EZ, UK; Fax: (internat.) ϩ 44-1223-336-033; E-mail:
and pyridine (1.33 g, 16.8 mmol) were allowed to react in hexane
(30 mL). A colorless liquid product was formed. Yield 1.53 g (67%).
GPC (THF): one peak corresponding to [PhSi(OSiMe3)O]3 (reten-
tion time: 17.79 min).
deposit@ccdc.cam.ac.uk].
Acknowledgments
Financial support of this work by Dow Corning Corporation and
Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowl-
edged.
K-PhS Obtained from PhSi(OEt)3 in EtOH/Toluene (H2O/Si ؍
1.5:1) and Trimethylsilylation: PhSi(OEt)3 (4.98 g, 20.7 mmol),
KOH (1.37 g, 20.7 mmol), and H2O (0.37 g, 20.7 mmol) were al-
lowed to react in a mixture of ethanol (7 mL) and toluene (28 mL).
Yield of solid K-PhS-3: 3.97 g (92%). [C6H5Si(O)OK]3·5H2O ϭ
C18H25K3O11Si3 (619): calcd. C 35.68, H 4.46, K 17.64, Si 14.02;
found C 35.93, H 4.07, K 17.52, Si 13.61. K-PhS-3 (3.97 g,
6.4 mmol), Me3SiCl (6.12 g, 56.3 mmol), and pyridine (2.67 g,
33.8 mmol) were allowed to react in hexane (100 mL). A colorless
liquid product was formed. Yield 3.29 g (81%). GPC (THF): one
peak corresponding to [PhSi(OSiMe3)O]3 (retention time:
17.79 min).
[1] [1a]
M. G. Voronkov, V. I. Lavrentyev, Top. Curr. Chem. 1982,
[1b]
102, 199Ϫ236.
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Suzuki, Chem. Rev. 1995, 95, 1409Ϫ1430.
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10454Ϫ10459.
K-PhS Obtained from PhSi(OMe)3 in MeOH/Benzene (H2O/Si ؍
1.5:1) and Trimethylsilylation: PhSi(OMe)3 (5.31 g, 26.8 mmol),
KOH (1.77 g, 26.8 mmol), and H2O (0.48 g, 26.8 mmol) were al-
lowed to react in a mixture of methanol (7 mL) and benzene
[3] [3a]
Yu. A. Molodtsova, Yu. A. Pozdniakova, K. A. Lyssenko,
I. V. Blagodatskikh, D. E. Katsoulis, O. I. Shchegolikhina, J.
Organomet. Chem. 1998, 571, 31Ϫ36. [3b] O. I. Shchegolikhina,
Yu. A. Pozdnyakova, Yu. A. Molodtsova, S. D. Korkin, S. S.
Bukalov, L. A. Leites, K. A. Lyssenko, A. S. Peregudov, N.
Auner, D. E. Katsoulis, Inorg. Chem. 2002, 41, 6892Ϫ6904.
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E. Katsoulis, N. Auner, B. Herrschaft, Organometallics 2000,
19, 1077Ϫ1082.
(28 mL).
Crystalline
K-PhS-3
formed:
5.09 g
(95%).
[C6H5Si(O)OK]3·MeOH·2H2O ϭ C19H23K3O9Si3 (597): calcd. C
38.23, H 3.88, K 19.65, Si 14.12; found C 38.01, H 3.69, K 19.61,
Si 13.86. A single crystal was analyzed by X-ray crystallography.
[4]
[5]
The
molecular
composition
is
[(Kϩ)3{PhSi-
(O)OϪ}3]2·7H2O·3MeOH (4). K-PhS-3 (5.06 g, 8.5 mmol), Me3SiCl
(7.85 g, 72.2 mmol), and pyridine (3.43 g, 43.4 mmol) were allowed
to react in hexane (80 mL). A liquid, colorless product formed.
Yield 4.47 g (83%). GPC (THF): one a peak corresponding to
[PhSi(OSiMe3)O]3 (retention time: 17.79 min).
Yu. T. Struchkov, S. V. Lindeman, J. Organomet. Chem. 1995,
488, 9Ϫ14.
[6]
[7]
P. D. Lickiss, Adv. Inorg. Chem. 1995, 42, 147Ϫ262.
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od’ko, S. E. Esipov, Zh. Obshch. Khim. 1979, 50, 1044Ϫ1048.
[8] [8a]
L. H. Sommer, Stereochemistry, McGraw-Hill, New York,
1
NMR Data for [PhSi(OSiMe3)O]4: H NMR (500 MHz, C6D6, 20
[8b]
1965.
L. H. Sommer, Stereochemistry and Reaction Mecha-
°C): δ ϭ 0.21 (s, 9 H, SiMe3), 7.11 (t, 3J ϭ 7.4 Hz, 2 H, m-C6H5Si),
nisms of Organosilicon Compounds, Mir, Moscow, 1966.
3
3
[9] [9a]
7.28 (t, J ϭ 7.4 Hz, 1 H, p-C6H5Si), 7.33 (d, J ϭ 7.4 Hz, 2 H, o-
C6H5Si) ppm. 29Si{1H} NMR (99 MHz, C6D6, 20 °C): δ ϭ 10.99
(OSiMe3), Ϫ78.49 (O3SiPh) ppm.
M. Szwarc, Carbanions, Living Polymers and Electron-
Transfer Processes, John Wiley & Sons, New York, London,
[9b]
Sydney, Toronto, 1968.
Mir, Moscow, 1971.
M. Szwarc, Anion Polymerisation,
NMR Data for [PhSi(OSiMe3)O]3: 1H NMR (500 MHz, CDCl3,
20 °C): δ ϭ 0.24 (s, 9 H, SiMe3), 7.25 (t, 3J ϭ 7.4 Hz, 2 H, m-
C6H5Si), 7.36 (t, 3J ϭ 7.4 Hz, 1 H, p-C6H5Si), 7.50 (d, 3J ϭ 7.4 Hz,
2 H, o-C6H5Si) ppm. 29Si{1H} NMR (99 MHz, C6D6, 20 °C): δ ϭ
11.58 (OSiMe3), Ϫ69.56 (O3SiPh) ppm.
[10]
[11]
N. R. Poonia, A. V. Bajaj, Chem. Rev. 1979, 79, 389Ϫ445.
E. Matukhina, O. Shchegolikhina, N. Makarova, Yu.
Pozdniakova, D. Katsoulis, Yu. Godovsky, Liq. Cryst. 2001,
28, 869Ϫ879.
[12]
I. V. Blagodaskikh, O. I. Shchegolikhina, Yu. A. Pozdniakova,
Yu. A. Molodtsova, A. A. Zhdanov, Izv. Akad. Nauk SSSR
1994, 6, 1057Ϫ1062.
X-ray Crystal Structure Determination: Colorless single crystals of
compounds 2, 3, and 4 were grown from solutions (see above).
Details of crystal data, data collection and structure refinement
parameters for siloxanolate salts 2Ϫ4 are given in Table 2. The
structures were solved by direct methods and refined by a full-ma-
trix least-squares technique against F2, with anisotropic tempera-
ture factors for all non-hydrogen atoms. All hydrogen atoms in 2Ϫ4
were located from the Fourier synthesis of electron density and
refined in the isotropic approximation. Data reduction and further
calculations were performed using SAINT[14] and SHELXTL
[13]
[14]
Unpublished data.
SMART V5.051 and SAINT V5.00, Area detector control and
integration software, Bruker AXS, Inc., Madison, WI 53719,
USA, 1998.
[15]
G. M. Sheldrick, SHELXTL Version 5, Software Reference
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USA, 1994.
Received August 20, 2003
Early View Article
Published Online February 10, 2004
Eur. J. Inorg. Chem. 2004, 1253Ϫ1261
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1261