Two modifications of a five-coordinate silicon complex

Article abstract of DOI:10.1107/S0108270107045465

TBPY-5-34-(Butane-1,4-di-yl)(2-{[1-(2-oxidophen-yl)ethyl-idene-O]amino-N} ethano-lato-O)silicon, C14H19NO2Si, crystallizes in two modifications. The monoclinic form, (IIm), was obtained by crystallization over a period of 2 d at room temperature; the ortho-rhom-bic form, (IIo), crystallized overnight at 248 K. The main difference between the two mol-ecular structures involves the angles in the equatorial plane of the trigonal bipyramid around silicon. Form (IIm) has an O - Si - O angle of ca 121° and O - Si - C angles of ca 121 and 116°. In form (IIo), the corresponding angles are 123, 124 and 111°. There are also significant differences in the packing: (IIm) shows π stacking, whereas (IIo) does not. International Union of Crystallography 2007.

Full text of DOI:10.1107/S0108270107045465

organic compounds
O,N,O0-coordination ability. The reaction of this ligand with
1,1-dichlorosilacyclopentane in the presence of triethylamine
yields the desired silicon complex (II), which was character-
ized by NMR spectroscopy. The 29Si NMR chemical shift at
53.15 p.p.m. indicates the formation of a ®ve-coordinate
silicon complex. A saturated solution of the reaction product
was left standing for two days at room temperature. During
this time, large clear colourless hexagonal prisms were formed
from the pale-yellow solution. Investigation of several crystals
from this crystallization batch showed the formation of
monoclinic crystals (space group P21/c), which are denoted
here as (IIm). Fig. 1 shows the molecular structure of (IIm)
and the atomic labelling scheme. Selected bond lengths and
angles are listed in Table 1.
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
Two modifications of a five-
coordinate silicon complex
Uwe Bohme* and Ines C. Foehn
È
Institut fur Anorganische Chemie, Technische Universitat Bergakademie Freiberg,
È
È
Leipziger Strasse 29, 09596 Freiberg, Germany
Correspondence e-mail: uwe.boehme@chemie.tu-freiberg.de
The remaining solution was separated from this ®rst batch
and left overnight at 248 K in a freezer. Another crystalline
fraction was formed consisting of small colourless prisms with
a rectangular shape. Investigation of the cell constants of
several crystals from this crystallization batch showed,
surprisingly, the exclusive formation of orthorhombic crystals,
denoted (IIo). The orthorhombic dimorph crystallizes in the
chiral space group P212121. Fig. 2 shows the molecular struc-
ture of (IIo) and the atomic labelling scheme. Selected bond
lengths and angles are listed in Table 3.
Because of the unusual crystallization behaviour, the crys-
tallization experiments were repeated and were shown to be
reproducible. Furthermore, mixtures of (IIm) and (IIo) are
obtained by crystallization at 278 K. One dimorph can be
transformed into the other by complete dissolution of the
crystals in n-hexane and 1,2-dimethoxyethane, followed by
selection of the crystallization conditions. Analysis of (IIo)
with differential thermal analysis and thermogravimetry
(DTA/TG) shows that there is a weakly endothermic effect at
349 K. Cooling of the sample to room temperature and
repeated heating shows that this endothermic effect no longer
occurs. This hints at a transformation point at 349 K from the
orthorhombic to the monoclinic form. The DTA sample melts
Received 14 August 2007
Accepted 17 September 2007
Online 13 October 2007
TBPY-5-34-(Butane-1,4-diyl)(2-{[1-(2-oxidophenyl)ethylidene-
ꢀO]amino-ꢀN}ethanolato-ꢀO)silicon, C14H19NO2Si, crystal-
lizes in two modi®cations. The monoclinic form, (IIm), was
obtained by crystallization over a period of 2 d at room
temperature; the orthorhombic form, (IIo), crystallized over-
night at 248 K. The main difference between the two
molecular structures involves the angles in the equatorial
plane of the trigonal bipyramid around silicon. Form (IIm) has
an OÐSiÐO angle of ca 121ꢀ and OÐSiÐC angles of ca 121
and 116ꢀ. In form (IIo), the corresponding angles are ꢁ123,
124 and 111ꢀ. There are also signi®cant differences in the
packing: (IIm) shows ꢁ stacking, whereas (IIo) does not.
Comment
Silicon complexes with tridentate Schiff base ligands and
O,N,O0-coordination modes are known, having been prepared
by various groups (Prasad & Tandon, 1973; Abe et al., 1986;
Singh & Singh, 1987; Koacher et al. 1980). A number of
applications of these complexes have been proposed and
described. Investigations have focused on photovoltaic appli-
cations (Nagao et al., 2004), colouring materials (Nagao et al.,
2002; Misono et al., 1985, 1987), antimicrobial activity (Nath &
Goyal, 2002) and use as electrophotographic toner (Yama-
naka & Sugawara, 1991). The existence of polymorphs is of
importance for many applications that depend on the solid-
state properties of a given compound (Bernstein, 2003;
Hil®ker, 2006). We report here the dimorphic solid-state
structures of the title compound, (II).
Figure 1
The molecular structure of form (IIm), drawn with 50% probability
displacement ellipsoids. (Atom coordinates were inverted to facilitate
comparison of the two forms.)
The reaction of 2-aminoethanol with o-hydroxyaceto-
phenone gives facile access to a Schiff base ligand, (I), with
Acta Cryst. (2007). C63, o613±o616
DOI: 10.1107/S0108270107045465
# 2007 International Union of Crystallography o613

organic compounds
after repeated heating at 387 K. Investigation of a sample of
(IIo) with powder diffraction shows the presence of ortho-
rhombic and monoclinic phases in the ®nely ground substance.
Therefore, we assume that the sample of (IIo) is contaminated
by small amounts of (IIm). Heating of this sample to 363 K
shows that a complete transformation into the monoclinic
phase takes place. It seems, therefore, that (IIm) is the ther-
modynamically stable modi®cation and (IIo) is a kinetically
formed modi®cation. Usually the thermodynamically more
stable product has the greater density (Bernstein, 2003).
Exceptions to this rule have been discussed in the literature
(Burger & Ramberger, 1979). In the present case, the less
stable orthorhombic form has the greater density.
differences are illustrated by a least-squares ®t of the two
molecules (Fig. 3). The ®t of atoms Si1, O1, O2, N1 and C1±
Ê
C11 has an r.m.s. deviation of 0.0921 A. The plot clearly shows
the differing orientations of the ®ve-membered ring.
Furthermore, the two structures are different with respect
to the conformation of the silacyclopentane ring. The plane of
the envelope is formed by atoms C11, Si1, C14 and C13 [the
Ê
Ê
r.m.s. deviation of ®tted atoms is 0.026 A for (IIo) and 0.053 A
Ê
for (IIm)]. Atom C12 lies out of this plane by 0.669 (2) A in
Ê
(IIo) and 0.609 (2) A in (IIm). This means that the envelope of
the silacyclopentane ring is more folded in (IIo).
The two molecular structures have common features. The Si
atom is bound to the cyclopentane ring and to atoms O1, N1
and O2 of the chelate ligand. The coordination geometry is
trigonal bipyramidal, as seen from the bond angles. Atoms N1
and C11 occupy the apical positions, with a C11ÐSi1ÐN1
angle of 177.51 (5)ꢀ for (IIm) and 178.35 (6)ꢀ for (IIo); atoms
O1, O2 and C14 are situated in the equatorial plane. The
chelate ligand coordinates in a capping fashion, with the two
terminal O atoms in equatorial positions and the central N
atom in an apical position. The SiÐO bonds are rather short,
Ê
at 1.676 (1)±1.712 (1) A. The coordinative bond Si1ÐN1 is
Ê
substantially longer [2.067 (1) and 2.055 (1) A]. The SiÐO
bond to phenolate atom O2 is somewhat longer than that to
aliphatic atom O1. This can be explained by postulating a
stronger CÐO bond from the phenoxy group and was also
È
observed in related silicon and titanium complexes (Bohme &
Gunther, 2006, 2007). The Si1ÐC11 bond is longer than Si1Ð
È
C14, consistent with the different positions of these two C
atoms in the coordination polyhedron. The main differences
between the molecular structures are found in the bond angles
in the equatorial plane. Form (IIm) has O1ÐSi1ÐO2 and
O1ÐSi1ÐC14 angles of ca 121ꢀ, and an O2ÐSi1ÐC14 angle
of 115.72 (5)ꢀ. In (IIo), the ®rst two angles are expanded to ca
123ꢀ, and the latter is compressed to only 111.44 (6)ꢀ. These
Figure 3
A least-squares ®t of the two structures. The solid line indicates form
(IIo) and the broken line form (IIm). Fitted atoms are labelled.
Figure 4
The packing of (IIm), showing the stacking of the molecules parallel to
the a axis and hydrogen bonds as dashed lines. Displacement ellipsoids
are drawn at the 50% probability level. H atoms that do not participate in
hydrogen bonding have been omitted for clarity.
Figure 2
The molecular structure of form (IIo), drawn with 50% probability
displacement ellipsoids.
ꢂ
o614 Bohme and Foehn C14H19NO2Si
Acta Cryst. (2007). C63, o613±o616
È

organic compounds
CH3), 3.79±3.89 (m, 4H, CH2ÐN, CH2ÐO), 6.97±7.03 (m, 2H, ar),
7.37±7.55 (m, 2H, ar). 13C NMR (CDCl3): ꢂ 14.02 (CH2ÐSi), 17.11
(CH3), 25.28 (CH2), 48.28 (CH2ÐN), 59.20 (CH2ÐO), 119.97, 121.91,
122.46, 127.98, 133.72 (ar), 158.57 (C N), 165.76 (ar, CÐO). 29Si
NMR (CDCl3): ꢂ 52.99.
Form (IIm)
Crystal data
3
Ê
C14H19NO2Si
Mr = 261.39
V = 1321.8 (5) A
Z = 4
Monoclinic, P21=c
Mo Kꢄ radiation
ꢅ = 0.17 mm
T = 93 (2) K
0.60 Â 0.40 Â 0.33 mm
1
Ê
a = 8.2780 (17) A
Ê
b = 10.694 (2) A
Ê
c = 15.155 (3) A
ꢃ = 99.86 (3)ꢀ
Figure 5
Data collection
The packing of (IIo), viewed parallel to the b axis, showing hydrogen
bonds as dashed lines. Displacement ellipsoids are drawn at the 50%
probability level. H atoms that do not participate in hydrogen bonding
have been omitted for clarity.
Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.90, Tmax = 0.95
25940 measured re¯ections
3522 independent re¯ections
3115 re¯ections with I > 2ꢆ(I)
Rint = 0.029
Re®nement
The polymorphs necessarily show major differences in
molecular packing; whereas form (IIm) is a racemate, only one
enantiomer is present in the packing structure of (IIo). The
main characteristic of the (IIm) packing is the stacking of the
substituted benzene rings (Fig. 4). These rings form pairs with
R[F2 > 2ꢆ(F2)] = 0.035
wR(F2) = 0.102
S = 1.07
164 parameters
H-atom parameters constrained
3
Ê
Áꢇmax = 0.83 e A
3
Ê
0.32 e A
3522 re¯ections
Áꢇmin
=
Ê
a distance of 3.430 A (normal between least-squares planes;
symmetry code: x + 1, y + 1, z + 1). The distance between
Table 1
Selected geometric parameters (A, ) for form (IIm).
ꢀ
Ê
Ê
successive pairs is 4.076 A (normal between least-squares
Si1ÐO1
Si1ÐO2
Si1ÐC14
1.687 (1)
1.706 (1)
1.907 (1)
Si1ÐC11
Si1ÐN1
1.929 (1)
2.067 (1)
planes; symmetry code: x + 2, y + 1, z + 1). Besides these
contacts there are also two weak intermolecular interactions
(see Table 2). The packing of form (IIo) (Fig. 5) shows two
weak intermolecular interactions, one of which, C7ÐH7Á Á Á
O1ÐSi1ÐO2
O1ÐSi1ÐC14
O2ÐSi1ÐC14
O1ÐSi1ÐC11
O2ÐSi1ÐC11
121.37 (5)
121.40 (5)
115.72 (5)
95.26 (5)
94.71 (5)
C14ÐSi1ÐC11
O1ÐSi1ÐN1
O2ÐSi1ÐN1
C14ÐSi1ÐN1
C11ÐSi1ÐN1
92.21 (6)
82.58 (4)
85.40 (5)
89.98 (5)
177.51 (5)
3
O1( x + , y + 1, z 12 ), is essentially linear (Table 4).
2
Experimental
2-[1-(2-Hydroxyethylimino)ethyl]phenol, (I), was prepared by the
reaction of o-hydroxyacetophenone (10.89 g, 0.08 mol) with 2-amino-
ethanol (4.76 g, 0.078 mol) in absolute ethanol (150 ml). The mixture
was re¯uxed for 2 h, cooled to room temperature and the volume of
the solvent reduced on a rotary evaporator to about 50 ml. The
remaining solid was ®ltered off, washed twice with small portions of
diethyl ether and dried in air overnight [yellow crystals, yield 14.44 g
(100%), m.p. 366 K]. The preparation of (II) was performed in
Schlenk tubes under argon with dry and air-free solvents. Compound
(II) was prepared by reaction of triethylamine (5.1 ml, 3.72 g,
36.8 mmol) and 1,1-dichlorosilacyclopentane (2.59 g, 16.7 mmol) with
(I) (3.0 g, 16.7 mmol) in dry tetrahydrofuran at 273 K. A white
precipitate of triethylamine hydrochloride formed immediately upon
addition of (I). The reaction mixture was warmed to room
temperature and stirred for one week. The triethylamine hydro-
chloride was ®ltered off and washed with tetrahydrofuran. The
solvent was removed in vacuo from the resulting clear yellow solu-
tion. The remaining solid was extracted with n-hexane and a small
amount of 1,2-dimethoxyethane. Filtration of this solution gave the
solid product for NMR investigations and a suitable solution for
growing single crystals. Analysis calculated for C14H19NO2Si: C 64.33,
H 7.33, N 5.36%; found: C 64.57, H 7.26, N 5.54%. 1H NMR (CDCl3):
ꢂ 0.26±0.33 (m, 4H, CH2ÐSi), 1.32±1.42 (m, 4H, CH2), 2.41 (s, 3H,
Table 2
Short intermolecular contacts (A, ) in form (IIm).
ꢀ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C4ÐH4BÁ Á ÁO1i
0.98
0.99
2.59
2.68
3.445 (2)
3.330 (2)
147
124
C1ÐH1BÁ Á ÁO2ii
Symmetry codes: (i) x; y ‡ 12; z ‡ 21; (ii) x ‡ 2; y
;
z ‡ 12.
1
2
Form (IIo)
Crystal data
3
Ê
C14H19NO2Si
Mr = 261.39
V = 1310.53 (10) A
Z = 4
Orthorhombic, P212121
Ê
Ê
b = 9.9284 (5) A
Ê
c = 13.7788 (6) A
Mo Kꢄ radiation
ꢅ = 0.17 mm
T = 93 (2) K
0.56 Â 0.50 Â 0.35 mm
1
a = 9.5798 (4) A
Data collection
Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.90, Tmax = 0.95
15312 measured re¯ections
3813 independent re¯ections
3525 re¯ections with I > 2ꢆ(I)
Rint = 0.034
ꢂ
Acta Cryst. (2007). C63, o613±o616
Bohme and Foehn C14H19NO2Si o615
È

organic compounds
Re®nement
Financial support for this work from the Deutsche
Forschungsgemeinschaft is gratefully acknowledged.
R[F2 > 2ꢆ(F2)] = 0.034
wR(F2) = 0.087
S = 1.04
3813 re¯ections
164 parameters
H-atom parameters constrained
Áꢇmax = 0.49 e A
3
Ê
3
Ê
0.23 e A
Áꢇmin
=
Absolute structure: Flack (1983),
1638 Friedel pairs
Flack parameter: 0.10 (9)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: JZ3090). Services for accessing these data are
described at the back of the journal.
Table 3
Selected geometric parameters (A, ) for form (IIo).
References
ꢀ
Ê
Abe, Y., Sawamura, K., Nagao, Y. & Misono, T. (1986). Kagaku Kaishi, 6, 830±
833.
Bernstein, J. (2003). In Polymorphism in Molecular Crystals. Oxford:
Clarendon Press.
Si1ÐO1
Si1ÐO2
Si1ÐC14
1.676 (1)
1.712 (1)
1.895 (2)
Si1ÐC11
Si1ÐN1
1.913 (1)
2.055 (1)
È
È
Bohme, U. & Gunther, B. (2006). Acta Cryst. E62, m1711±m1712.
È
È
Bohme, U. & Gunther, B. (2007). Inorg. Chem. Commun. 10, 482±484.
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O1ÐSi1ÐO2
O1ÐSi1ÐC14
O2ÐSi1ÐC14
O1ÐSi1ÐC11
O2ÐSi1ÐC11
123.32 (6)
123.55 (6)
111.44 (6)
96.29 (6)
94.23 (6)
C14ÐSi1ÐC11
O1ÐSi1ÐN1
O2ÐSi1ÐN1
C14ÐSi1ÐN1
C11ÐSi1ÐN1
92.14 (6)
82.55 (5)
85.44 (5)
89.49 (5)
178.35 (6)
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Table 4
Short intermolecular contacts (A, ) in form (IIo).
ꢀ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C7ÐH7Á Á ÁO1i
0.95
0.98
2.52
2.69
3.424 (2)
3.406 (2)
159
130
C4ÐH4CÁ Á ÁO2ii
Symmetry codes: (i) x ‡ 32; y ‡ 1; z 21; (ii) x
;
y ‡ 12; z.
1
2
Nagao, Y., Ooki, T. & Kozawa, K. (2004). Shikizai Kyokaishi, 77, 51±56.
Nath, M. & Goyal, S. (2002). Phosphorus Sulfur Silicon Relat. Elem. 177, 447±
463.
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È
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For both forms, data collection: SMART (Bruker, 2004); cell
re®nement: SAINT (Bruker, 2004); data reduction: SAINT;
program(s) used to solve structure: SHELXS97 (Sheldrick, 1997);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);
molecular graphics: ORTEP-3 (Farrugia, 1997); software used to
prepare material for publication: SHELXL97.
È
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Singh, S. V. & Singh, R. V. (1987). Synth. React. Inorg. Met. Org. Chem. 17,
947±960.
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JP03149568.
ꢂ
o616 Bohme and Foehn C14H19NO2Si
Acta Cryst. (2007). C63, o613±o616
È