Preparation of [Et2InSb(SiMe3)2]3; A trimeric single-source precursor to indium antimonide

Article abstract of DOI:10.1016/S0022-328X(99)00674-9

The 1:1 mole ratio reaction of Et₂InCl with Sb(SiMe₃)₃ results in the formation of [Et₂InSb(SiMe₃)₂]₃ (1), a trimeric compound containing a six-membered indium-antimony ring. An X-ray crystal structure has been obtained for the compound substantiating the trimeric nature of 1 in the solid state, however variable-temperature ¹H-NMR studies show a dimer/trimer equilibrium for this species in solution. Preliminary thermolysis studies demonstrate its utility in the formation of nanocrystalline InSb.

Full text of DOI:10.1016/S0022-328X(99)00674-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 598 (2000) 182–186
Note
Preparation of [Et2InSb(SiMe3)2]3; a trimeric single-source
precursor to indium antimonide
Edward E. Foos a, Richard J. Jouet a, Richard L. Wells a,*, Peter S. White b
a Department of Chemistry, Paul M. Gross Chemical Laboratory, Duke Uni6ersity, Durham, NC 27708, USA
b Department of Chemistry, Venable Hall, Uni6ersity of North Carolina at Chapel Hill, Chapel Hill, NC 27514, USA
Received 2 September 1999; received in revised form 29 October 1999
Abstract
The 1:1 mole ratio reaction of Et2InCl with Sb(SiMe3)3 results in the formation of [Et2InSb(SiMe3)2]3 (1), a trimeric compound
containing a six-membered indium–antimony ring. An X-ray crystal structure has been obtained for the compound substantiating
the trimeric nature of 1 in the solid state, however variable-temperature 1H-NMR studies show a dimer/trimer equilibrium for this
species in solution. Preliminary thermolysis studies demonstrate its utility in the formation of nanocrystalline InSb. © 2000
Elsevier Science S.A. All rights reserved.
Keywords: Indium antimonide; Precursor; Nanocrystalline; Trimer
dium atom. Our recent studies of gallium–antimony
compounds incorporating ethyl groups on the Group
13 center [2a] have resulted in the isolation of several
interesting compounds, and prompted us to examine
similar reactions in the indium system. We report
herein, as a result of these studies, the isolation, charac-
terization and preliminary thermolysis of the trimeric
compound [Et2InSb(SiMe3)2]3 (1).
1. Introduction
Recently, there has been a surge of interest in the
preparation of organometallic compounds containing a
direct Group 13 antimony bond. This interest stems
from the fact that these compounds have traditionally
been neglected during studies of other Group 13–
Group 15 precursor systems, which are now prevalent
in the literature [1]. As a result, a number of fully
characterized compounds have been reported by
ourselves [2] and others [3] which contain a direct bond
between aluminum, gallium or indium and antimony,
with the majority of the work thus far concentrated on
gallium. Reports of indium–antimony compounds re-
main scarce, with [t-Bu2InSb(SiMe3)2]2 [2b], (Me3-
2. Experimental
2.1. General considerations
’
All manipulations of air- and moisture-sensitive ma-
terials were performed in a Vacuum Atmospheres HE-
493 Dri-Lab containing an argon atmosphere, or by
standard Schlenk techniques. Hexane and toluene were
distilled over sodium/potassium alloy under dry dinitro-
gen. Et3In [4] and Sb(SiMe3)3 [5] were prepared from
literature procedures. Et2InCl was prepared from the
2:1 comproportionation reaction of Et3In with InCl3.
InCl3 was purchased from Strem Chemicals and used as
SiCH2)3In Sb(SiMe3)3 [2d], [(Me3SiCH2)2InSb(SiMe3)2]2
[2d], [Me2InSb(t-Bu)2]3 [3d], [(t-Bu2Sb)(Cl)InSb(t-Bu)2]2
[3e], and [(Me3SiCH2)2InSbMe2]3 [3f] as the only exam-
ples of such compounds to be characterized in the solid
state through X-ray crystallography. With the excep-
tion of [Me2InSb(t-Bu)2]3 [3d], all of these compounds
contain sterically demanding ligands bound to the in-
* Corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00674-9

E.E. Foos et al. / Journal of Organometallic Chemistry 598 (2000) 182–186
183
received. The integrity of starting materials, when appli-
lected. The onset of thermal decomposition of 1,
characterized by the formation of several peaks from l
0.28 to 0.03, was observed at 50°C. Upon cooling back
to 25°C, it was apparent that the sample had undergone
extensive decomposition during the experiment.
1
1
cable, was confirmed using H-NMR spectroscopy. H-
and 13C{1H}-NMR spectra were recorded on a Varian
Unity XL-400 spectrometer operating at 400 and 100.6
1
MHz, respectively. H- and 13C{1H}-spectra were refer-
enced to TMS using the residual protons or carbons of
benzene-d6 at l 7.15 or l 128.0, respectively. All NMR
samples were prepared in 5-mm tubes, which were
septum-sealed under argon. Powder X-ray diffraction
(XRD) data were collected on a Phillips XRG-3000
diffractometer utilizing Cu–Ka radiation. Mass spectra
were collected using a Jeol JMS-SX 102A spectrometer
operating the EI+ mode at 20 eV. The melting point
(uncorrected) was obtained with a Thomas-Hoover Uni-
melt apparatus, using capillaries that were flame-sealed
under argon. IR spectra of volatile gases were acquired
using a gas cell on a Bomem Michelson MB-100 FTIR
spectrometer. Elemental analyses were performed by
E+R Microanalytical Laboratory, Inc., Parsippany,
NJ.
2.4. Thermolysis of [Et2InSb(SiMe3)2]3 (1)
Compound 1 (0.450 g, 1.02 mmol) was loaded into a
sublimator which was attached to a liquid N2 cold trap.
The sample was heated under static vacuum to 400°C,
where the temperature was maintained for 10 h. Signifi-
cant sublimation of [Et2InSbSiMe3)2]3 was observed on
the walls of the sublimator above the heat source. InSb
was formed as a gray coating on the sides of the
sublimator during thermolysis. This material was recov-
ered (0.032 g, 13% yield) and its identity verified by
comparison of the d-spacings and line intensities ob-
tained by XRD analysis with those of InSb (JCPDS file
6-0208). Elemental In was also present in the sample
and observed in the pattern (JCPDS file 5-0642). The
approximate average particle size of 10 nm was calcu-
lated using the Scherrer equation. Condensable gases
(0.72 mmol) were trapped during the decomposition,
and identified as ethylene and HSiMe3 through IR
spectroscopy.
2.2. Preparation of [Et2InSb(SiMe3)2]3 (1)
Et2InCl (0.208 g; 1.0 mmol) in 20 ml of hexane was
added to a 250 ml round-bottomed flask equipped with
a stir-bar and Teflon valve. A solution of Sb(SiMe3)3
(0.341 g; 1.0 mmol) dissolved in 20 ml hexane was then
added via pipette at room temperature (r.t.), and an
immediate color change to an orange–red mixture oc-
curred. The red mixture was stirred for 12 h. The
volatiles were removed in vacuo, and the dark solid was
extracted with toluene. A small amount of hexane was
added to the yellow solution, and storage at −30°C
afforded thick, colorless needles of 1 (0.387 g, 88%
yield). m.p. 132–140°C (dec. to a black liquid). Anal.
Calc. for C30H84In3Sb3Si6: C, 27.23; H, 6.4. Found: C,
2.5. X-ray structural solution and refinement
A single crystal of 1 was mounted on a glass fiber with
viscous oil under a stream of cold dinitrogen. X-ray
intensity data were recorded at −135°C on a Bruker
SMART CCD diffractometer utilizing graphite-
,
monochromated Mo–Ka radiation (u=0.71073 A) and
the structure was solved by direct methods. Intensity
data were collected to 2q=50° resulting in 9789 unique
reflections of which 5356 were considered observed and
included in the subsequent computations. Full-matrix
least-squares refinement with weights based upon count-
ing statistics was performed. Hydrogen atoms were
incorporated at their calculated positions using a riding
model in the later iterations of refinement which con-
verged at R=0.059 (Rw=0.065). The parameter to data
ratio in the final cycle was 379 to 5356. A final difference
Fourier synthesis revealed no unusual features. Crystal-
lographic calculations were performed using the NRC-
VAX [6] suite of structure determination programs. For
all structure-factor calculations, neutral atom scattering
factors and their anomalous dispersion corrections were
taken from Ref. [7].
1
27.36; H, 6.56%. H-NMR: l 0.52 (s, dimer, ꢀSiMe3), l
0.56 (s, trimer, ꢀSiMe3), l 0.82 (q, dimer, ꢀCH2CH3), l
1.19 (q, trimer, ꢀCH2CH3), l 1.44 (t, dimer, ꢀCH2CH3),
l 1.62 (t, trimer, ꢀCH2CH3). 13C{1H}-NMR: l 5.79 (s,
dimer, ꢀSiMe3), l 5.94 (s, trimer, ꢀSiMe3), l 10.16
(s, dimer/trimer, ꢀCH2CH3), l 14.21 (s, dimer, ꢀCH2-
CH3), l 14.75 (s, trimer, ꢀCH2CH3). MS (m/e, ion):
853 ([Et2InSb(SiMe3)2]2−C2H5)*; 795, ([Et2InSb(Si-
Me3)2]2−3C2H5)*; 651 ([Et2InSb(SiMe3)2]2−3C2H5−
2SiMe3+2H)*.
1
2.3. Variable-temperature H-NMR study of 1
Approximately 0.017 g (0.013 mmol) of 1 was dis-
solved in 0.6 ml of benzene-d6 and loaded into a 5 mm
NMR tube, which was then flame sealed under reduced
pressure. Spectra were taken at 25, 35, 40, 45, 50, 55, 60,
and again at 25°C. Peaks corresponding to trimer and
dimer were present in varying intensity ratios through-
out the temperature range in which spectra were col-
3. Results and discussion
The 1:1 mole ratio reaction of Et2InCl with
Sb(SiMe3)3 results in the formation of 1 with concomi-

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E.E. Foos et al. / Journal of Organometallic Chemistry 598 (2000) 182–186
diagram of 1, Table 1 lists crystallographic data for 1,
while Table 2 lists selected bond lengths and angles.
The average indium–antimony bond length of
tant elimination of Me3SiCl. Compound 1 is the third
reported example of a solid state structurally character-
ized indium–antimony trimer, the others being the
aforementioned [Me2InSb(t-Bu)2]3 [3d] and [(Me3Si-
CH2)2InSbMe2]3 [3f]. Each of these compounds con-
tains a relatively undemanding alkyl group (methyl or
ethyl), thus it seems reasonable that they all adopt
similar trimeric conformations. Fig. 1 shows an ORTEP
,
2.8732(15) A found in 1 is the longest of the three
reported trimeric compounds, with average indium–an-
,
timony bond lengths of 2.855(2) A for [Me2InSb(t-
,
Bu)2]3 [3d] and 2.8615(6) A for [(Me3SiCH2)2InSbMe2]3
[3f]. The average endocyclic ring angles about indium
and antimony in 1 of 104.38(5) and 125.13(5)°, respec-
tively, compare favorably with the analogous average
angles of 106.94(5) and 121.64(5)° in [Me2InSb(t-Bu)2]3.
The endocyclic ring angles in [(Me3SiCH2)2InSbMe2]3
are significantly different when compared with these
two compounds, with values of 95.94(2) and 132.83(2)°.
This is attributable to the greater steric bulk of the
Me3SiCH2 moieties bound to indium as well as the
reduced steric bulk of the methyl groups on antimony.
Significant variation can also be seen in the angles
about the antimony atoms in 1, which range from
119.09(5)° for In(1)ꢀSb(2)ꢀIn(2) to 129.69(5)° for
In(2)ꢀSb(3)ꢀIn(3). Atoms In(1), Sb(1), In(2), and Sb(3)
are very close to planar, with Sb(2) and In(3) located
,
1.1747(15) and 0.4908(17) A, respectively, above the
least squares plane. This indicates, in conjunction with
the torsion angles (Table 2), that the core indium–anti-
mony ring adopts a severely distorted twist-boat con-
formation (Fig. 2). Similar observations were made for
[Me2InSb(t-Bu)2]3.
Like its gallium analogue [2a], 1 appears to exhibit a
1
dynamic process in solution in that the r.t. H-NMR
Fig. 1. ORTEP diagram (30% probability ellipsoids) showing the
solid-state structure and atom numbering scheme for [Et2InSb-
(SiMe3)2]3 (1). Hydrogen atoms are omitted for clarity.
spectrum contains two sets of the expected singlet–
quartet–triplet peak pattern. This is indicative of an
equilibrium exchange phenomenon and a variable-tem-
perature 1H-NMR study of 1 was conducted in an
attempt to clarify this process. Due to the complexity of
the ethyl region, analysis of the ratio of trimer to dimer
was based on the integrated peak intensities of the
antimony bound SiMe3 moieties. Initially, at 25°C,
there were two singlets present in this region at l 0.52
and l 0.57 in a ratio of 6.7:1. As the temperature was
increased to 50°C this ratio fell to 1.9:1, however, at
this temperature, the formation and growth of several
peaks from l 0.28–0.03 was observed indicating sec-
ondary elimination/decomposition events. As the tem-
perature reached 60°C, the ratio of peak intensities fell
to 1.5:1. Upon cooling of the sample back to 25°C, the
ratio rose to 2.1:1. It is assumed that the sample then
contained significantly less of the starting material 1
due to the aforementioned thermal decomposition pro-
cesses. We are able to account for the smaller final ratio
of trimer to dimer after cooling to 25°C because of the
significant loss of starting material due to thermal
decomposition, i.e. as the concentration of 1 decreases,
the equilibrium favors the less-associated form. Because
these peaks favor higher temperatures and lower con-
Table 1
Crystallographic data for [Et2InSb(SiMe3)2]3 (1)
Empirical formula
Formula weight
Space group
C30H84In3Sb3Si6
1323.21
P21/c
Unit cell dimensions
,
a (A)
10.1899(4)
24.9740(10)
21.7632(9)
93.605(1)
5527.4(4)
4
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Crystal color, habit
Colorless block
1.590
2.82
Dcalc. (g cm3)
v (Mo–Ka) (mm−1
)
Temperature (K)
173
No. of reflections measured
No. of unique reflections
No. of observed reflections with I\3.0|(I)
Radiation
79 536
9789
5356
Mo–Ka
,
(u=0.71073 A)
5.9
6.5
R(F) (%) a
R(wF2) (%) a
a
Quantity minimized=S[w(Fo−Fc)2]/S[(wFo)2]1/2; R=SZ/S(Fo),
Z=ꢀ(Fo−Fc)ꢀ.

E.E. Foos et al. / Journal of Organometallic Chemistry 598 (2000) 182–186
185
Table 2
the solution and solid phases. The sold state structure
of the gallium analogue, [Et2GaSb(SiMe3)2]2, indicates
it is dimeric in nature, yet it exhibits a well-behaved
dimer/trimer equilibrium in solution with the predomi-
nant species in solution being the dimer [2a]. The solid
state structure of 1 has been characterized as a trimer.
Like the gallium analogue, 1 also exhibits a well-be-
haved dimer/trimer equilibrium in solution, however, in
this case the species that predominates is the trimer.
Preliminary investigations indicate that 1 can also
serve as a single-source precursor to InSb. Thermolysis
of this compound results in the formation of nanocrys-
talline InSb powder in low yield, which is contaminated
with elemental indium. The low yield observed for this
process is attributable to the significant sublimation of
the precursor out of the hot zone of the apparatus
during the course of the experiment. This sublimation is
the result of the fact that 1 is extremely volatile. While
detrimental to these studies, this volatility is a necessary
requirement for any precursor that is to be used in a
chemical vapor deposition process. Similar observations
have been made for other ethyl-containing Group 13-
antimony species [2a] and more detailed thermolysis
studies on these compounds are currently being
conducted.
,
Selected bond lengths (A) and angles (°) for [Et2InSb(SiMe3)2]3 (1) with
estimated standard deviations in parentheses
Bond lengths
In(1)ꢀSb(1)
In(1)ꢀC(71)
In(2)ꢀSb(2)
In(2)ꢀC(81)
In(3)ꢀSb(1)
In(3)ꢀC(91)
Sb(1)ꢀSi(1)
Sb(2)ꢀSi(3)
Sb(3)ꢀSi(5)
2.8741(15) In(1)ꢀSb(2)
2.187(21) In(1)ꢀC(73)
2.8707(15) In(2)ꢀSb(3)
2.235(17) In(2)ꢀC(83)
2.8241(15) In(3)ꢀSb(3)
2.8583(15)
2.231(17)
2.9113(15)
2.179(16)
2.9010(16)
2.237(18)
2.624(5)
2.210(15)
2.575(5)
2.580(4)
2.630(5)
In(3)ꢀC(93)
Sb(1)ꢀSi(2)
Sb(2)ꢀSi(4)
Sb(3)ꢀSi(6)
2.597(5)
2.538(5)
Bond angles
Sb(1)ꢀIn(1)ꢀSb(2)
Sb(1)ꢀIn(1)ꢀC(73)
Sb(2)ꢀIn(1)ꢀC(73)
Sb(2)ꢀIn(2)ꢀSb(3)
Sb(2)ꢀIn(2)ꢀC(83)
Sb(3)ꢀIn(2)ꢀC(83)
Sb(1)ꢀIn(3)ꢀSb(3)
Sb(1)ꢀIn(3)ꢀC(93)
Sb(3)ꢀIn(3)ꢀC(93)
In(1)ꢀSb(1)ꢀIn(3)
In(1)ꢀSb(1)ꢀSi(2)
In(3)ꢀSb(1)ꢀSi(2)
In(1)ꢀSb(2)ꢀIn(2)
In(1)ꢀSb(2)ꢀSi(4)
In(2)ꢀSb(2)ꢀSi(4)
In(2)ꢀSb(3)ꢀIn(3)
In(2)ꢀSb(3)ꢀSi(6)
In(3)ꢀSb(3)ꢀSi(6)
104.59(5) Sb(1)ꢀIn(1)ꢀC(71)
111.4(5)
111.4(5)
121.4(8)
113.8(4)
107.3(5)
114.9(6)
106.3(4)
106.9(4)
103.2(4)
103.2(5)
Sb(2)ꢀIn(1)ꢀC(71)
C(71)ꢀIn(1)ꢀC(73)
102.39(4) Sb(2)ꢀIn(2)ꢀC(81)
109.9(4)
107.5(4)
Sb(3)ꢀIn(2)ꢀC(81)
C(81)ꢀIn(2)ꢀC(83)
106.16(5) Sb(1)ꢀIn(3)ꢀC(91)
107.2(5)
111.0(6)
Sb(3)ꢀIn(3)ꢀC(91)
C(91)ꢀIn(3)ꢀC(93)
118.5(7)
126.60(5) In(1)ꢀSb(1)ꢀSi(1)
110.67(12) In(3)ꢀSb(1)ꢀSi(1)
104.77(12) Si(1)ꢀSb(1)ꢀSi(2)
119.09(5) In(1)ꢀSb(2)ꢀSi(3)
119.68(11) In(2)ꢀSb(2)ꢀSi(3)
102.85(11) Si(3)ꢀSb(2)ꢀSi(4)
129.69(5) In(2)ꢀSb(3)ꢀSi(5)
109.67(12) In(3)ꢀSb(3)ꢀSi(5)
99.57(12) Si(5)ꢀSb(3)ꢀSi(6)
102.34(11)
107.81(11)
102.11(16)
101.39(11)
111.28(12)
101.16(14)
103.64(13)
110.34(12)
100.39(16)
4. Supplementary material
Torsion angles
Sb(2)ꢀIn(1)ꢀSb(1)ꢀIn(3) −24.90(6) Sb(3)ꢀIn(2)ꢀSb(2)ꢀIn(1) −50.62(7)
Sb(3)ꢀIn(3)ꢀSb(1)ꢀIn(1) −13.86(5) Sb(1)ꢀIn(1)ꢀSb(2)ꢀIn(2) +63.10(7)
Sb(2)ꢀIn(2)ꢀSb(3)ꢀIn(3) +0.12(5) Sb(1)ꢀIn(3)ꢀSb(3)ꢀIn(2) +28.87(6)
The structural data have been deposited with the
Cambridge Crystallographic Data Centre: CCDC no.
136568. Copies of this information can be obtained
from: The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
centrations, the singlet occurring at l 0.52, quartet at l
0.82 and triplet at l 1.44 can be assigned to the dimeric
form of 1. These peaks also lie upfield from those
attributed to the trimeric form of 1, consistent with
observations made for [Et2GaSb(SiMe3)2]2 [2a].
Acknowledgements
It is interesting to note that three analogous anti-
mony compounds with ethyl groups bound to the
Group 13 metal have been prepared and examined
utilizing X-ray crystallography: [Et2AlSb(SiMe3)2]2 [3c],
[Et2GaSb(SiMe3)2]2 [2a], and 1. Since these three com-
pounds differ only by the Group 13 atom present in the
monomeric unit, the effect of the metal in each is
clearly demonstrated. For example, the aluminum com-
pound has been fully characterized as a dimer in both
The authors thank the Office of Naval Research and
the Lord Foundation of North Carolina for their finan-
cial support of this work.
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