Synthesis and characterization of single-source precursors to nanocrystalline GaP, GaPxAs1-x, and GaPxSb1-x. X-ray crystal structures of [Et2GaP(SiMe3)2]2, (Me3Si)2P[μ-GaEt2]2As(SiMe 3)2

Article abstract of DOI:10.1016/S0022-328X(00)00055-3

The 1:1 mole ratio reaction of Et₂GaCl with P(SiMe₃)₃ resulted in the formation of [Et₂GaP(SiMe₃)₂]₂ (1). The mixed-pnicogen compounds (Me₃Si)₂P[μ-GaEt₂]₂As(SiMe ₃)₂ (2) and (Me₃Si)₂P[μ-GaEt₂]₂Sb(SiMe ₃)₂ (3) were prepared from the 2:1:1 mole ratio reactions of Et₂GaCl with P(SiMe₃)₃ and As(SiMe₃)₃ and P(SiMe₃)₃ and Sb(SiMe₃)₃, respectively. Compounds 2 and 3 were also synthesized by comproportionation reactions of 1 and [Et₂GaAs(SiMe₃)₂]₂, and 1 and [Et₂GaSb(SiMe₃)₂]₂, respectively. Characterization of 1, 2, and 3 was accomplished using multinuclear NMR, elemental analysis, mass spectrometry, and single-crystal X-ray crystallographic analysis. The X-ray crystal structures of compounds 1, 2 and 3 are reported. Thermolysis of 1, 2, and 3 results in the formation of nanocrystalline GaP, GaP_xAs_1-x, or GaP_xSb_1-x, respectively. Compound 3 represents the first example of a compound containing a P(μ-Ga)₂Sb core.

Full text of DOI:10.1016/S0022-328X(00)00055-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 601 (2000) 191–198
Note
Synthesis and characterization of single-source precursors to
nanocrystalline GaP, GaP As , and GaP Sb . X-ray crystal
x
1−x
x
1−x
structures of [Et GaP(SiMe ) ] , (Me Si) P[m-GaEt ] As(SiMe ) ,
2
3 2 2
3
2
2 2
3 2
and (Me Si) P[m-GaEt ] Sb(SiMe )
3
2
2 2
3 2
a
a,
b
Richard J. Jouet , Richard L. Wells *, Arnold L. Rheingold ,
b
Christopher D. Incarvito
a
Department of Chemistry, Paul M. Gross Chemical Laboratory, Duke Uni6ersity, Durham, NC 27708-0346, USA
b
Department of Chemistry, Drake Hall, Uni6ersity of Delaware, Newark, DE 19716, USA
Received 11 November 1999; accepted 21 January 2000
Abstract
The 1:1 mole ratio reaction of Et GaCl with P(SiMe ) resulted in the formation of [Et GaP(SiMe ) ] (1). The mixed-pnicogen
2
3 3
2
3 2 2
compounds (Me Si) P[m-GaEt ] As(SiMe ) (2) and (Me Si) P[m-GaEt ] Sb(SiMe ) (3) were prepared from the 2:1:1 mole ratio
3
2
2 2
3 2
3
2
2 2
3 2
reactions of Et GaCl with P(SiMe ) and As(SiMe ) and P(SiMe ) and Sb(SiMe ) , respectively. Compounds 2 and 3 were also
2
3 3
3 3
3 3
3 3
synthesized by comproportionation reactions of 1 and [Et GaAs(SiMe ) ] , and 1 and [Et GaSb(SiMe ) ] , respectively. Character-
2
3 2 2
2
3 2 2
ization of 1, 2, and 3 was accomplished using multinuclear NMR, elemental analysis, mass spectrometry, and single-crystal X-ray
crystallographic analysis and the X-ray crystal structure of 3 is reported. Thermolysis of 1, 2, and 3 results in the formation of
nanocrystalline GaP, GaP As
, or GaP Sb1−x, respectively. Compound 3 represents the first example of a compound
x
1−x
x
containing a P(m-Ga) Sb core. © 2000 Elsevier Science S.A. All rights reserved.
2
Keywords: Nanocrystalline; Gallium phosphide; Gallium phosphorus clusters
1. Introduction
GaX
and Sb(SiMe ) [6]. The elimination products
3 3 3
t
from the thermolysis of [ Bu GaSb(SiMe ) ] were iso-
2
3 2 2
Recently the research in our laboratories has been
lated and characterized as isobutylene and trimethylsi-
lane — consistent with the hypothesis of b-hydride
elimination and dehydrosilylation as proposed elimina-
aimed at the synthesis of precursors containing ligands
that have the potential for b-hydride elimination to
form nanocrystalline 13–15 materials [1–4]. Addition-
ally, it has been observed by Cowley and coworkers
that b-hydride elimination can be a lower-energy de-
composition pathway relative to Ga–C bond homolysis
tion pathways.
Our success with [ Bu
t
GaSb(SiMe
)
3
]
led us to ex-
2
2
2
pand our research in the area of precursors with the
capacity for b-hydride elimination with the syntheses of
[
5]. Our interest in this aspect of precursor design was
the ethyl-containing precursors [Et
2
GaAs(SiMe
As[m-GaEt Sb(Si-
) [2]. These compounds were shown to undergo
3 2
3 2 2
) ] ,
sparked by the superior quality of GaSb produced by
[Et
Me
2
GaSb(SiMe
)
3
2
]
2
and (Me
Si)
3
2
]
2 2
t
the thermolysis of [ Bu GaSb(SiMe ) ] [1] when com-
2
3 2 2
pared with that produced by the thermolysis of the
material formed from the 1:1 mole ratio reaction of
complete elimination of their alkyl and silyl substituents
upon thermolysis to produce nanocrystalline GaAs,
GaSb and GaAs Sb1−x, respectively.
x
As we noted in our previous report [2], compounds
that could serve as precursors to gallium-containing
*
Corresponding author. Fax: +1-919-660 1605.
E-mail address: wells@chem.duke.edu (R.L. Wells)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 0 ) 0 0 0 5 5 - 3

192
R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
ternary materials have only cursorily been investigated.
The only reported examples of compounds with such a
potential are (Me Si) P[m-GaI ] As(SiMe ) [7], Ga (As/
eV; the assignment of the ion fragments was supported
by comparisons with theoretical ion distributions. Pow-
der X-ray diffraction (XRD) data were collected on a
3
2
2 2
3 2
2
P)Cl3 [8], and the aforementioned (Me Si) As[m-
Phillips XRG-3000 diffractometer using Cu–K radia-
3
2
a
GaEt ] Sb(SiMe ) [2]. Preliminary studies of the
tion. Single-crystal X-ray diffraction studies were per-
formed at the University of Delaware on a Siemens
P4/CCD diffractometer.
2
2
3 2
decomposition of these compounds showed that they
did form nanocrystalline GaP As1−x, and GaAsx-
x
Sb1−x, respectively. Inspection of the literature regard-
ing precursors to gallium-containing ternary materials
shows that there are no gallium-containing mixed
pnicogen compounds containing P and Sb.
In an attempt to further explore the potential of
gallium-containing single-source precursors for the
formation of ternary nanocrystalline 13–15 materials,
2.2. Preparation of [Et GaP(SiMe ) ] (1)
2 3 2 2
A 100 ml round-bottom flask equipped with a stirbar
and a Teflon valve was charged with Et GaCl (0.490 g;
3.0 mmol) and 10 ml of hexane. A solution of
P(SiMe (0.752 g; 3.0 mmol) in 10 ml of hexane was
2
)
3 3
we
have
prepared
the
dimeric
compound
then added via pipette at room temperature (r.t.) in a
dry box. The flask was sealed and removed from the
dry box and the clear, colorless solution stirred for 12
h. The volume of the solution was then reduced in
vacuo, and storage at −30°C for 7 days afforded
colorless crystals of 1 (0.884 g, 97% yield). M.p.: 265–
272°C. Anal. Found: C, 39.64; H, 10.33. Calc. for
[Et GaP(SiMe ) ] (1) and the mixed-pnicogen com-
2
3 2 2
pounds
(Me Si) P[m-GaEt ] As(SiMe )
(2)
and
3
2
2 2
3 2
(
Me Si) P[m-GaEt ] Sb(SiMe ) (3). The X-ray crystal
3
2
2 2
3 2
structure of 3 is presented. In addition, preliminary
thermolysis experiments of 1, 2, and 3 have been con-
ducted for the purpose of determining their utility as
1
precursors to nanocrystalline GaP, GaP As1−x, and
GaP Sb1−x. Compound 3 is the first example of a
Ga P Si C H : C, 39.35; H, 9.25%. H-NMR: l
x
2
2
4
20 56
3
0.38 [t, 36H, –SiMe3 ( JP–H=3 Hz)], l 0.90 [q,
x
mixed-pnicogen compound containing phosphorus and
antimony.
8H, –CH CH3 (JH–H=8.0 Hz)], l 1.32 [t, 12H, –
2
13
1
CH CH – (JH–H=8.0 Hz)]. C{ H}-NMR: l 4.41 (t,
2
3
2
2
JP–C=4.4 Hz; –SiMe ) l 7.93 (t, JP–C=9.8 Hz;
3
3
2 3 2 3
–
CH CH ) l 10.76 (t, JP–C=3.2 Hz –CH CH ).
31
1
2. Experimental
P{ H}-NMR: l −227.8 [s, P(SiMe
ion): 581 (M–C H )*.
) ]. MS (m/e,
3 2
2
5
2.1. General considerations
2
.3. Preparation of (Me Si ) P[v-GaEt ] As(SiMe ) (2)
3
2
2 2
3 2
All manipulations of air- and moisture-sensitive ma-
terials were performed in a Vacuum Atmospheres HE-
93 Dri-Lab containing an argon atmosphere or by
standard Schlenk techniques. Solvents were distilled
from sodium–potassium alloy under dry dinitrogen.
P(SiMe3)3 [9], As(SiMe3)3 [9], Sb(SiMe3)3 [10],
A 100 ml round-bottom flask equipped with a stirbar
and a Teflon valve was charged with Et GaCl (0.653 g;
4.0 mmol) and 10 ml of hexane. A solution of
P(SiMe (0.501 g; 2.0 mmol) and As(SiMe (0.589 g;
2.0 mmol) in 10 ml of hexane was added via pipette at
r.t. in a dry box. The flask was sealed and removed
from the dry box and the clear, light yellow solution
was stirred for 12 h. The volume of the solution was
then reduced in vacuo, and storage at −30°C for 3
days afforded colorless blocks of 2 (1.220 g, 93.2%
yield). M.p.: 175–182°C. Anal. Found: C, 36.07; H,
4
2
)
3
)
3 3
3
[
Et GaAs(SiMe ) ] [2] and [Et GaSb(SiMe ) ] [2] were
2 3 2 2 2 3 2 2
prepared from methods described in the literature.
P(SiMe ) was also purchased from Strem Chemicals as
3
3
were Et Ga and GaCl . All were used as received.
3
3
Et GaCl was obtained from the 2:1 comproportiona-
2
1
13
1
tion reaction of Et Ga with GaCl . All H-, C{ H}-,
and P{ H}-NMR spectra were recorded on a Varian
Inova 400 NMR spectrometer operating at 399.937,
3
3
3
1
1
9.15. Calc. for Ga PAsSi C H56: C, 36.71; H, 8.63%.
2 4 20
1
3
H-NMR: l 0.37 [d, 18H, –P(SiMe3)2 ( JP–H=4.8
Hz)], l 0.42 [s, 18H, –As(SiMe ) ], l 0.94 [q, 8H,
1
00.577, and 161.901 MHz, respectively, in 5 mm tubes
3
2
septum-sealed under argon and referenced using gener-
ally accepted methods. Melting points (uncorrected)
were obtained with a Thomas–Hoover Uni-melt ap-
paratus, using capillaries that were flame-sealed under
argon. Elemental analyses were performed by E+R
Microanalytical Laboratory, Inc., Parsippany, NJ.
Mass spectra were collected using a JEOL JMS-SX
−CH CH (J
=8.0 Hz)], l 1.31 [t, 12H, –CH CH
2
3
H–H 2
1
3
13
(JH–H=8.0 Hz)]. C{ H}-NMR: l 4.34 [d, –PSiMe
3
2
( J
=8.4 Hz)], l 4.64 [s, –AsSiMe ], l 8.59 [s,
P–C
3
1
31
–CH CH ], l 10.93 [s, –CH CH ]. P{ H}-NMR: l
2
3
2
3
−227.7 [s, P(SiMe ) ]. MS (m/e, ion): 654, M*; 625,
3
2
[M–C H ]*; 349, [Et GaAs(SiMe ) ]*; 319, [Et Ga-
2
5
2
3 2
2
As(SiMe) –Et–H]*; 305, [Et GaP(SiMe ) ]*; 275,
2
2
3 2
102A spectrometer operating in the EI+ mode at 20
[Et GaP(SiMe) –Et–H]*.
2
2

R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
193
2
.4. In situ preparation of 2 by comproportionation
2.6. In situ preparation of 3 by comproportionation of
1 and [Et GaSb(SiMe
of 1 and [Et GaAs(SiMe ) ]
2
) ]
3 2 2
2
3 2 2
A solution of equivalent molar amounts of 1 (0.0123
g, 0.020 mmol) and [Et GaSb(SiMe ) ] (0.0159 g, 0.020
A solution of equivalent molar amounts of 1 (0.0063
g, 0.010 mmol) and [Et GaAs(SiMe ) ] (0.0072 g, 0.010
2
3 2 2
2
3 2 2
mmol) was prepared with ca. 0.75 ml of toluene-d8.
mmol) was prepared in 0.75 ml of toluene-d . This
8
This solution was then placed in a 5 mm NMR tube
solution was then placed in a 5 mm NMR tube and
flame-sealed under partial vacuum. Spectra, taken at
and flame-sealed under partial vacuum. Spectra, taken
at 25°C, were obtained immediately after preparation,
after 15 h of agitation, and after 24 h of agitation. To
avoid the complexity of the peaks associated with the
ethyl moieties comparisons were made using the peaks
associated with the trimethylsilyl moieties on P and Sb.
2
5°C, were obtained immediately after preparation and
1
after 24
following solution preparation: l 0.38 [t, JP–H
Hz; 36H, –SiMe , 1], l 0.42 [s, 36H, –SiMe ,
h of agitation. H-NMR: immediately
3
=
3
[
8
[
3
3
Et GaAs(SiMe ) ] ], l 0.90 [q, 8H, –CH CH (JH–H=
2 3 2 2 2 3
1
H-NMR: immediately following solution preparation:
.0 Hz) 1], l 0.95 [q, 8H, –CH CH (JH–H=8.0 Hz)
2
3
3
l 0.38 [t, J
=3 Hz; 36H, –SiMe , 1], l 0.50 [s, –Sb-
P–H
3
Et GaAs(SiMe ) ] ], l 1.32 [t, 12H, –CH CH – (J
2 3 2 2 2 3 H–
(
SiMe ) , [Et GaSb(SiMe ) ] ], l 0.51 [s, –Sb(SiMe ) ,
3 2 2 3 2 2 3 2
H=8.0 Hz) 1], l 1.34 [t, 12H, –CH CH – (JH–H=8.0
2
3
3
1
], l 0.57 [s, –Sb(SiMe ) , [Et GaSb(SiMe ) ] ]. After
3 2 2 3 2 3
Hz) [Et GaAs(SiMe ) ] ]. After 24 h: l 0.37 [d, 18H,
3
2
3 2 2
5 h: l 0.35 [d, –P(SiMe ) , 3, ( JP–H=4.8 Hz)], l 0.38
3
2
3
–
P(SiMe3)2 ( JP–H=4.8 Hz) 2], l 0.42 [s, 18H, –
3
[t, –P(SiMe ) , 1, ( JP–H=2.4 Hz)], l 0.50 [s, –Sb-
3 2
As(SiMe ) , 2], l 0.94 [q, 8H, –CH CH (JH–H=8.0
3
2
2
3
(SiMe ) , [Et GaSb(SiMe ) ] ], l 0.51 [s, –Sb(SiMe ) ,
3 2 2 3 2 2 3 2
Hz) 2], l 1.31 [t, 12H, –CH CH (JH–H=8.0 Hz) 2].
2
3
3], l 0.57 [s, –Sb(SiMe ) , [Et GaSb(SiMe ) ] ].
3
2
2
3 2 3
2
.5. Preparation of (Me Si ) P[v-GaEt ] Sb(SiMe ) (3)
3
2
2 2
3 2
2.7. Thermolysis of 1
A 100 ml round-bottom flask equipped with a stirbar
and a Teflon valve was charged with Et GaCl (0.653 g;
Compound 1 (0.884 g, 2.90 mmol based on the
monomeric unit) was loaded into a sublimator and
evacuated for 1 h. The sublimator was then heated to
425°C for 4 h under static vacuum. During this time,
2
4.0 mmol) and 20 ml of hexane. A solution of
P(SiMe ) (0.501 g; 2.0 mmol) and Sb(SiMe ) (0.682 g;
3
3
3 3
1
2.0 mmol) in 25 ml of hexane was added via pipette at
significant sublimation of 1 (later identified by H- and
13
1
r.t. in a dry box. The solution became cloudy and dark
gray upon addition. The flask was sealed and removed
from the dry box and the solution was stirred for 12 h
in the dark after which time it was light yellow and
completely clear. The volume of the solution was re-
duced in vacuo, and storage at −30°C for 8 days
afforded thick, colorless blocks of 3 (0.468 g, 63%
yield). M.p.: 165–171°C. Anal. Found: C, 35.64; H,
C{ H}-NMR spectroscopy) was observed as white
crystals that formed on the walls of the sublimator
above the heat source. A dull gray metallic mirror,
GaP, formed on the sides of the sublimator as well as
the cold finger during thermolysis. This material was
scraped from the sides and collected (0.023 g, 22.8%)
and its identity verified by comparison of the d-spacings
and line intensities obtained by XRD analysis with
those of GaP (JCPDS file 32-397). The approximate
average particle size of 6.4 nm was calculated using the
Scherrer equation. Anal. Found: C, 5.84; H, 0.46; Ga,
9
.44. Calc. for Ga PSbSi C H : C, 34.26; H, 8.05%.
2 4 20 56
1
3
H-NMR: l 0.35 [d, –P(SiMe ) , 3, ( JP–H=4.8 Hz)], l
3
2
3
0.37 [t, –P(SiMe ) , 1, ( JP–H=2.4 Hz)], l 0.50 [s,
3
2
6
6
2.60; P, 31.50. Calc. for GaP: C, 0.00; H, 0.00; Ga,
9.24; P, 30.76%.
–
Sb(SiMe ) , [Et GaSb(SiMe ) ] ],
l
0.51 [s,
–
3
2
2
3 2 2
Sb(SiMe ) , 3], l 0.57 [s, –Sb(SiMe ) , [Et GaSb-
3
2
3 2
2
(
SiMe ) ] ], l 0.87–0.97 [m, –CH CH ], l 1.37–1.29
3 2 3 2 3
2
.8. Thermolysis of 2
1
2 3 3
3
1
[m, –CH CH ]. C{ H}-NMR: l 4.20 [d, –PSiMe ,
2
2
3
4
, ( J
=7.6 Hz)], l 4.13 [t, –PSiMe , 1, ( JP–C=
P–C
3
Thermolysis of 2 (0.448 g, 0.68 mmol) was identical
.6 Hz)], l 5.38 [s, –SbSiMe , [Et GaSb(SiMe ) ] ],
3
2
3 2 2
to the procedure described for compound 1. Significant
sublimation of 2 (later identified by H-NMR spec-
troscopy) was observed as white crystals, which formed
on the walls of the sublimator above the heat source.
l 5.52 [s, –SbSiMe , 3], l 5.74 [s, –SbSiMe3,
1
3
2
[Et GaSb(SiMe ) ] ], l 7.93 [t, JP–C=10 Hz; –
2 3 2 3
2
CH CH , 1], l 8.67 [d, J
7
(
1
–
=9.6 Hz; –CH CH , 3], l
2
3
P–C
2
3
.93 [s, –CH CH , [Et GaSb(SiMe ) ] /[Et GaSb-
2 3 2 3 2 2 2
3
The material, GaP As1−x, formed as a dark gray mir-
x
SiMe ) ] ], l 10.75 [t, J
=3.2 Hz; –CH CH , 1], l
3
2 3
P–C
2
3
ror on the sides of the sublimator during thermolysis.
This material was scraped from the sides and collected
(0.048 g, 28.6%) and its identity verified by comparison
of the d-spacings and line intensities obtained by XRD
analysis with those of both GaP (JCPDS file 32-397)
3
1.53 [d, JP–C=4.2 Hz; -CH CH , 3], l 12.19 [s,
2
3
CH CH ,
[Et GaSb(SiMe ) ] /[Et GaSb(SiMe ) ] ].
2
3
2 3 2 2 2 3 2 3
MS (m/e, ion): 700 M*; 653 [M–Et–Me–2H]*; 623
M–2Et–Me–3H]*.
[

194
R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
and GaAs (JCPDS file 14-450). The approximate aver-
age particle size of 6.7 nm was calculated using the
Scherrer equation. Anal. Found: C, 1.73; H, 0.00; As,
be found in Fig. 1. Suitable crystals for data collection
were selected and mounted in nitrogen-flushed thin-
walled capillaries. All data were collected with a
Siemens P4 diffractometer equipped with a SMART/
CCD detector. The systematic absences in the diffrac-
tion data of 1, 2, and 3, are consistent for the
C-centered monoclinic space groups, Cc and C2/c. The
E-statistic suggested the centrosymmetric space group,
which yielded chemically reasonable and computation-
ally stable results of refinement. These isomorphous
structures were solved using direct methods or initiated
from analog coordinates, completed by subsequent dif-
ference Fourier syntheses and refined by full-matrix
least-squares procedures. The molecules for all three
structures lie on twofold rotation axes. There is ar-
senic–phosphorus compositional disorder in 2 (70/30).
There is a crystallographically imposed disorder be-
tween the phosphorus and antimony atoms of 3; the
unique atom was refined as an undersized antimony
atom and labeled SbP(1). All non-hydrogen atoms were
refined with anisotropic displacement coefficients and
hydrogen atoms were treated as idealized contributions.
All software and sources of the scattering factors are
contained in the SHELXTL (5.1) program library (G.
Sheldrick, Siemens XRD, Madison, WI).
3
3.43; Ga, 52.30; P, 12.72. Calc. for GaP As1–x: C,
x
0.00; H, 0.00; As, 30.54; Ga, 56.84; P, 12.62%.
2.9. Thermolysis of 3
Thermolysis of 3 was conducted in two parts. A
solution of Et GaCl (0.327 g; 2.0 mmol) and 50 ml of
2
decane was prepared and to it was added a solution of
P(SiMe ) (0.251 g; 1.0 mmol) and Sb(SiMe ) (0.341 g;
3
3
3 3
1
.0 mmol) at r.t. The resulting light yellow solution was
stirred at r.t. overnight. It was then heated to reflux at
74°C for 10 h. The solution turned rust-brown and
1
finally black at 100°C. The solvent was then removed in
vacuo and the sticky black material was transferred to
a sublimator. It was then evacuated for 2 h and heated
under dynamic vacuum to 425°C for 4 h. The material
GaP Sb
was collected as black chunks on the bot-
x
1−x
tom of the sublimator (0.172 g, 58.9%) and its identity
verified by comparison of the d-spacings and line inten-
sities obtained by XRD analysis with those of both
GaP (JCPDS file 32-397) and GaSb (JCPDS file 7-215).
The approximate average particle size of 9.3 nm was
calculated using the Scherrer equation. Anal. Found: C,
2
.10; H, 0.00; Ga, 44.82; P, 10.54; Sb, 42.52. Calc. for
3
. Results and discussion
GaP Sb(1−x): C, 0.00; H, 0.00; Ga, 47.73; P, 10.60; Sb,
x
41.67%.
The 1:1 mole ratio reaction of Et GaCl with
2
2.10. X-ray structural solution and refinement
P(SiMe ) leads to the isolation of the dimeric com-
3 3
pound [Et GaP(SiMe ) ] (1). Compounds 2 and 3 were
2
3 2 2
Crystal, data collection, and refinement parameters
prepared from the direct reaction of two equivalents of
for 1–3 are given in Table 1, while selected bond
lengths and angles are presented in Table 2. An ORTEP
diagram showing the solid-state conformation of 3 can
Et GaCl with one equivalent each of P(SiMe ) and
2
3 3
As(SiMe ) for 2 and one equivalent each of P(SiMe )
3
3
3 3
and Sb(SiMe ) for 3. This method was employed for
3
3
Table 1
Crystallographic data for [Et GaP(SiMe ) ] (1) (Me Si) P[m-GaEt ] As(SiMe ) (2) and (Me Si) P[m-GaEt ] Sb(SiMe ) (3)
2
3 2 2
3
2
2 2
3 2
3
2
2 2
3 2
Formula
C20H56Ga P Si
C20H56As1.44Ga2P0.56Si4
C20H56Ga PSbSi
2 4
2
2
4
Formula weight
Space group
610.39
C2/c
673.68
C2/c
701.17
C2/c
a (A
,
)
)
)
17.9864(3)
9.3513(2)
20.1239(3)
100.66(2)
3326.18(7)
4
18.1212(2)
9.3971(2)
20.3337(4)
100.4686(4)
3404.92(15)
4
18.1221(3)
9.5418(2)
20.6748(2)
99.7066(5)
3523.85(8)
4
b (A
,
c (A
b (°)
V (A
,
3)
,
Z
Crystal color, habit
Colorless, rod
1.219
18.67
Colorless, block
1.314
31.45
Dark brown, block
1.322
24.67
−
3
Dcalc (g cm
)
v(Mo–K ) (cm−1)
a
Temperature (K)
Diffractometer
Radiation
203(2)
Siemens P4/CCD
Mo–Ka (u=0.71073 A
5.00
173(2)
Siemens P4/CCD
Mo–Ka (u=0.71073 A
2.92
7.80
203(2)
Siemens P4/CCD
,
Mo–Ka (u=0.71073 A)
5.17
,
)
,
)
a
R(F) (%)
2
a
R(wF ) (%)
15.86
19.70
a
2
2
o
2 2
c
2 2 1/2
o
Quantity minimized=R(wF )=ꢀ[w(F −F ) ]/ꢀ[(wF ) ] ; R=ꢀZ/S(F ), Z=ꢁ(F −F )ꢁ.
o
o
c

R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
195
Table 2
Selected bond lengths (A
,
) and angles (°)
[
Et GaP(SiMe ) ] (1)
2 3 2 2
Ga(1)–P(1)
Ga(1)–C(7)
Ga(1)–C(9)
2.4558(7)
2.017(3)
1.996(3)
P(1)–Si(1)
P(1)–Si(2)
2.2602(11)
2.2634(10)
Ga(1)–P(1)–Ga(1A)
P(1)–Ga(1)–P(1A)
C(7)–Ga(1)–P(1)
C(7)–Ga(1)–P(1A)
C(9)–Ga(1)–P(1)
C(9)–Ga(1)–P(1A)
91.37(3)
88.63(3)
110.99(10)
112.08(9)
114.35(10)
113.42(10)
Si(1)–P(1)–Ga(1)
Si(1)–P(1)–Ga(1A)
Si(2)–P(1)–Ga(1)
Si(2)–P(1)–Ga(1A)
C(7)–Ga(1)–C(9)
Si(1)–P(1)–Si(2)
111.44(3)
114.73(4)
117.51(4)
113.60(3)
114.67(13)
107.77(4)
(
Me Si ) P[v-GaEt ] As(SiMe ) (2)
3 2 2 2 3 2
Ga(1)–As/P(1)
Ga(1A)–As/P(1)
Ga(1)–As/P(1A)
Ga(1)–C(7)
2.5273(4)
2.5200(4)
2.5200(4)
2.006(3)
Ga(1)–C(9)
As/P(1)–Si(1)
As/P(1)–Si(2)
1.999(3)
2.3334(8)
2.3347(8)
Ga(1)–As/P(1)–Ga(1A)
As/P(1)–Ga(1)–As/P(1A)
C(9)–Ga(1)–As/P(1)
C(9)–Ga(1)–As/P(1A)
C(7)–Ga(1)–As/P(1)
C(7)–Ga(1)–As/P(1A)
92.152(13)
87.845(13)
114.06(9)
113.41(9)
110.83(8)
111.89(9)
Si(1)–As/P(1)–Ga(1)
Si(1)–AS/P(1)–Ga(1A)
Si(2)–As/P(1)–Ga(1)
Si(2)–As/P(1)–Ga(1A)
C(9)–Ga(1)–C(7)
111.18(2)
114.50(2)
117.09(2)
114.28(2)
115.65(12)
107.33(3)
Si(1)–As/P(1)–Si(2)
(
Me Si ) P[v-GaEt ] Sb(SiMe ) (3)
3 2 2 2 3 2
Ga(1)–Sb/P(1)
Ga(1A)–Sb/P(1)
Ga(1)–Sb/P(1A)
Ga(1)–C(7)
2.5683(13)
2.5761(11)
2.5761(11)
1.995(8)
Ga(1)–C(9)
Sb/P(1)–Si(1)
Sb/P(1)–Si(2)
1.994(8)
2.445(2)
2.428(2)
Ga(1)–Sb/P(1)–Ga(1A)
Sb/P(1)–Ga(1)–Sb/P(1A)
C(9)–Ga(1)–Sb/P(1)
C(9)–Ga(1)–Sb/P(1A)
C(7)–Ga(1)–Sb/P(1)
C(7)–Ga(1)–Sb/P(1A)
92.77(3)
87.23(3)
114.0(3)
112.8(3)
110.4(3)
112.6(3)
Si(1)–Sb/P(1)–Ga(1)
Si(1)–Sb/P(1)–Ga(1A)
Si(2)–Sb/P(1)–Ga(1)
Si(2)–Sb/P(1)–Ga(1A)
C(9)–Ga(1)–C(7)
111.12(6)
114.37(6)
117.02(7)
115.31(6)
116.3(4)
Si(1)–Sb/P(1)–Si(2)
106.19(9)
the synthesis of the previously reported (Me Si) As[m-
Compound 2 is structurally distinct from all similar
previously reported mixed-pnicogen compounds
[2,7,14,15] in that the compositional disorder associated
with the pnicogen sites in the molecule is best solved
3
2
GaEt ] Sb(SiMe ) [2], however 3 represents the first
2
2
3 2
example of a compound with a core ring containing
phosphorus and antimony.
It was also shown, using H-NMR, that the synthesis
1
of compounds 2 and 3 was possible by equilibration of
1
2
with either of the two dimers, [Et GaAs(SiMe ) ] for
2 3 2 2
or [Et GaSb(SiMe ) ] for 3. Equilibration of 1 and
2
3 2 2
[
Et GaAs(SiMe ) ] in toluene-d afforded 2 in 100%
2
3 2 2
8
1
yield by H-NMR. Comparison of the peaks for the
trimethylsilyl moieties bound to P showed complete
conversion of the triplet associated with 1 to the dou-
blet associated with 2 after 24 h.
Compounds 1, 2, and 3 are isomorphous and crystal-
lize in the monoclinic space group C2/c. The ORTEP
diagram for 3 is depicted in Fig. 1. For 1 the average
Ga–P bond length of 2.4558 (7) A
and P–Ga–P endocyclic ring angles of 91.37(3)° and
8.63(3)°, respectively, fall well within the range of
,
and the Ga–P–Ga
8
values associated with the numerous dimeric gallium–
phosphorus compounds reported in the literature [11–
Fig. 1. ORTEP diagram of (SiMe ) P[m-GaEt ] Sb(SiMe ) (3). The
3
2
2 2
3 2
Sb/P disordered atom is labeled as Sb/P(1). Thermal ellipsoids at 30%
13].
probability and hydrogen atoms are omitted for clarity.

196
R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
Scheme 1.
Scheme 2.
with 70% As/30% P occupancy. This is in contrast with
the solution phase H-NMR of the material, which
The X-ray crystal structure for compound 3 (Fig. 1)
exhibits the more typical 50/50 occupancy of the ring
pnicogen atoms, namely P and Sb. The mixed pnicogen
structure of this species is again supported by EI MS
evidence in which a molecular ion peak at 700 mass
units corresponding to 3* was observed. Again the
same limitations of X-ray crystallography (vide supra)
exist for 3 in that differentiation between the highly
unlikely possibility of exact cocrystallization of the
dimers 1 and [Et GaSb(SiMe ) ] and crystallization of
1
shows an approximately equal integrated area for the
trimethylsilyl peaks, associated with the P and As
atoms. As with all previously reported ‘mixed pnicogen’
compounds, X-ray crystallography is unable to distin-
guish between two different structural possibilities in
the solid phase: (a) crystallization of discreet mixed-
pnicogen molecules or (b) a cocrystallization of the
corresponding dimers, namely
1
and [Et GaAs-
2
2
3 2 2
(
SiMe ) ] . Indeed the nonequivalent occupancy of the
3
2 2
discreet mixed-pnicogen molecules is not possible.
Again however, we can rely on multinuclear NMR for
P/As sites implies at least some sort of cocrystallization
of compounds. The structure of 2 is also supported by
EI MS evidence in which molecular ions of 654 and 625
mass units corresponding to 2* and (2–Et)*, respec-
tively, were observed. The use of multinuclear NMR
allows determination of the solution phase structure of
1
13
1
structural verification of 3. The H- and C{ H}-NMR
data for 3, however, are rather complex in that peaks
for 3, 1, [Et GaSb(SiMe ) ] , and [Et GaSb(SiMe ) ]
2
3 2 2
2
3 2 3
are observed. As with 2, we are able to establish that 3
is, in fact, a discreet mixed-pnicogen molecule as
evinced by the doublet peak observed for the
trimethylsilyl moieties bound to P in 3. The dimer/
trimer equilibrium of [Et GaSb(SiMe ) ] was described
2
, because of the characteristic splitting caused by P. In
the case of 1, a triplet is observed for exocyclic protons
and carbons) as is the case with all similar four-mem-
(
2
3 2 3
bered ring compounds containing P at opposing posi-
tions because of virtual coupling [16]. In the case of 2,
however, the protons (and carbons) of the trimethylsilyl
moiety bound to P are split into a doublet indicating
the presence of only one P in the ring and therefore
discreet mixed pnicogen molecules. Doublet resonances
are also observed for the ethyl moieties bound to Ga
further establishing the presence of only one P atom in
the molecule. The approximately equal integrated area
of the doublet associated with the trimethylsilyl moi-
eties bound to P and the singlet associated with the
trimethylsilyl moieties bound to As in 2 is in conflict
with the preponderance of As in the solid phase indi-
cated by the crystal structure. This behavior seems to
indicate the existence of an equilibrium in the solution
phase according to Scheme 1.
previously [2] and it seems that 3 is in equilibrium with
all three compounds according to Scheme 2. Compari-
son of the relative integrated area of the trimethylsilyl
peaks showed the concentration of 3 to be approxi-
mately four times that of 1 and [Et GaSb(SiMe ) ] /
2
3 2 2
[
Et GaSb(SiMe ) ] .
The C{ H}-NMR for 3 in the trimethylsilyl region
2 3 2 3
1
1
3
consists of a triplet at l 4.13 corresponding to 1, a
doublet at l 4.20 corresponding to the P-bound
trimethylsilyl moieties in 3, a singlet at l 5.52 corre-
sponding to the Sb-bound trimethylsilyl moieties in 3, a
singlet at l 5.38 corresponding to [Et GaSb(SiMe ) ]
2
3 2 2
and
a
singlet at
l
5.74 corresponding to
[
Et GaSb(SiMe ) ] . Additionally, the peaks associated
2
3 2 3
with the methylene and methyl carbons of the ethyl
groups of the previous compounds are also observed.
The P atom(s) split not only the carbons of the
trimethylsilyl moieties directly bound to them, but also
the carbons of the ethyl moieties attached to Ga in an
identical fashion and we are, therefore, able to unequiv-
ocally assign the peaks of the ethyl moieties to 1, 3, or
[Et GaSb(SiMe ) ] /[Et GaSb(SiMe ) ] . Thus, multinu-
This hypothesis is also supported by the fact that
synthesis of 2 is possible via comproportionation of 1
and [Et GaAs(SiMe ) ] . It has been observed that
2
3 2 2
[
Et GaAs(SiMe ) ] has a lower solubility in hexane
2 3 2 2
when compared to 1. This could explain the plurality of
As in the crystal structure of 2 in that crystals falling
out of solution early may have a higher As content
while later crystals may have a higher P content.
2
3 2 2
2
3 2 3
clear NMR, EI MS, and the fact that an exact cocrys-

R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
197
Fig. 2. XRD spectra of (a) GaP obtained from the thermolysis of 1 at 425°C. (b) GaP As
obtained from the thermolysis of 2 at 425°C. (c)
1−x
x
GaP Sb
obtained from the thermolysis of 3 at 425°C.
x
1−x
tallization of dimers is improbable support the existence
of the mixed-pnicogen compound.
spectively, lie closer in value to the analogous bond
angles in [Et GaAs(SiMe . This is no doubt the
result of the preponderance of [Et GaAs(SiMe in
the crystal but it is interesting to note that very similar
characteristics were observed in the case of the previ-
) ]
3 2 2
2
An equilibration study of 1 and [Et GaSb(SiMe ) ]
2
) ]
3 2 2
2
3 2 2
conducted in toluene-d resulted in the formation of 3
8
after 15 h of agitation at r.t. Comparison of the relative
integrated area of the trimethylsilyl peaks showed the
concentration of 3 to be approximately twice that of 1
and [Et GaSb(SiMe ) ] /[Et GaSb(SiMe ) ] . Com-
ously reported (Me Si) As[m-GaEt ] Sb(SiMe ) [2].
3
2
2 2
3 2
Conversely the average Ga–Sb/P bond length in 3 of
.5683(13) A is essentially equal to the average bond
lengths of the analogous bonds in 1 and [Et GaSb-
2
,
2
3 2 2
2
3 2 3
2
pound 3 exists in a dynamic equilibrium with 1 and
Et GaSb(SiMe ) ] /[Et GaSb(SiMe ) ] in toluene-d8
(
SiMe ) ] . In addition, the Ga–Sb/P–Ga angle of
3 2 2
[
2
3 2 2
2
3 2 3
9
2.77(3) and the Sb/P–Ga–Sb/P angle of 87.23(3) are
and so therefore complete conversion from the two
dimers to the mixed pnicogen does not occur. After 24
h however, the relative integration values for the peaks
associated with the trimethylsilyl moieties on 1, 3, and
very similar to the analogous bond angles in
Et GaSb(SiMe ) ] . In the previously reported Al, Ga,
[
2
3 2 2
and in mixed-pnicogen compounds, which were struc-
turally characterized [2,7,14,15], the metal–pnicogen
bond length was essentially the average of the lengths
of the starting dimers.
[
Et GaSb(SiMe ) ] /[Et GaSb(SiMe ) ] compared well
2 3 2 2 2 3 2 3
1
with those obtained from the H-NMR spectrum of 3.
The average Ga–As/P bond length in 2 is 2.5273(4)
In order to determine the suitability of 1, 2, and 3 as
A
,
and significantly larger than the average of the
precursors to GaP, GaP As
, and GaP Sb1−x, re-
x
1−x
x
gallium–pnicogen bond lengths in 1 and [Et GaAs-
2
spectively, preliminary thermolysis studies were con-
ducted. The maximum temperature used for the pyroly-
ses was 425°C in all cases. In the case of 1, the bulk
(
SiMe ) ] . Similarly, the Ga–As/P–Ga and As/P–Ga–
3 2 2
As/P bond angles of 92.152(13)° and 87.845(13)°, re-

198
R.J. Jouet et al. / Journal of Organometallic Chemistry 601 (2000) 191–198
powder produced from the pyrolysis was identified as
GaP by XRD, produced in a 22.8% yield. The approx-
imate average particle size of 6.4 nm was calculated
using the Scherrer equation. Elemental analysis of this
sample indicates that it is 94.10% GaP, with a total
residual carbon and hydrogen contamination of 6.30%.
The Ga:P ratio for this material was 1.00:1.13.
fractional coordinates) for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 136999 for 1, CCDC no.
137000 for 2, CCDC no. 137001 for 3. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2
1
EZ, UK (fax: +44-1223-336 033; email: de-
The material that was obtained from the pyrolysis of
posit@ccdc.cam.ac.uk
ccdc.cam.ac.uk).
or
www:
http://www.
2
amounted to a 28.6% yield and had an average
particle size of 6.7 nm. The powder XRD spectrum for
this material indicates the presence of GaP As1−x. This
x
observation is based on the fact that the XRD spectrum
contains three major peaks whose positions lie between
the values associated with GaP and GaAs, thus follow-
ing Vegard’s Law [17]. Such average values are also
associated with other compounds believed to be ternary
materials [2,7,8]. Elemental analysis of this sample indi-
Acknowledgements
We thank the Office of Naval Research and the Lord
Foundation of North Carolina for their financial sup-
port of this work.
cates that it is 98.45% GaP As1−x, with a small
x
amount (1.53% total) of residual carbon with no de-
References
tectable hydrogen, and
.83:1.00:1.09.
Compound 3 is unstable at r.t. and decompo
a
Ga:P:As ratio of
1
[
1] R.L. Wells, E.E. Foos, P.S. White, A.L. Rheingold, L.M. Liable-
Sands, Organometallics 16 (1997) 4771.
.
sition
was observed during its isolation and characterization.
In an attempt to minimize the decomposition prior to
pyrolysis, 3 was prepared and pyrolyzed in decane and
then under vacuum at 425°C. This method produced
material in a 58.9% yield. The XRD spectrum for the
[2] E.E. Foos, R.J. Jouet, R.L. Wells, A.L. Rheingold, L.M. Liable-
Sands, J. Organomet. Chem. 582 (1999) 45.
[
3] E.E. Foos, R.L. Wells, A.L. Rheingold, L.M. Liable-Sands, J.
Cluster Sci. 10 (1999) 121.
[
4] E.E. Foos, R.J. Jouet, R.L. Wells, P.S. White, J. Organomet.
Chem., in press.
powder indicates that it contains GaP Sb
again by
[5] See the following and the Refs. contained therein. (a) A.H.
Cowley, R.A. Jones, Polyhedron 13 (1994) 1149. (b) K.C. Wong,
B.G. McBurnett, R.D. Culp, A.H. Cowley, J.G. Ekerdt, Surf.
Sci. 416 (1998) 480.
x
1−x
the same analogy as for the material produced from the
decomposition of 2. In this case the peak positions
lie between the values for GaP and GaSb. Elemental
analysis of this sample indicates that it is 97.88%
[
6] R.A. Baldwin, E.E. Foos, R.L. Wells, Mat. Res. Bull. 32 (1997)
59.
1
GaP Sb1−x, with a small amount (2.10% total) of
x
[7] R.L. Wells, S.R. Aubuchon, M.S. Lube, P.S. White, Main
Group Chem. 1 (1995) 81.
[8] S.R. Aubuchon, M.S. Lube, R.L. Wells, Chem. Vap. Deposit. 1
residual carbon and no detectable hydrogen. The
Ga:P:Sb ratio for this material was 1.89:1.00:1.02.
XRD plots for the materials obtained from 1, 2, and 3
can be found in Fig. 2.
(
1995) 28.
[
9] (a) G. Becker, G. Gutekunst, H.J. Wessely, Z. Anorg. Allg.
Chem. 462 (1980) 113. (b) R.L. Wells, M.F. Self, J.D. Johansen,
J.A. Laske, S.R. Aubuchon, L.J. Jones, Inorganic Synth. 31
For 1 and 2, it is clear that while relatively clean
nanocrystalline material is produced, the overall yields
are low, ca. 20%. One contributing factor to these low
yields is the high volatility of the compounds, both of
which sublimed readily under the conditions of the
experiment. This behavior may be attributable in part
to the incorporation of the small alkyl group on the
gallium. While this volatility is detrimental to the de-
scribed studies, it does suggest that these compounds
may be excellent candidates for OMCVD experiments.
(
1997) 150.
[10] E. Amberger, G. Salazar, J. Organomet. Chem.
111.
8 (1967)
[
11] S.T. Barry, S. Belhumeur, D.S. Richeson, Organometallics 16
1997) 3588.
(
[
12] M.D.B. Dillingham, J.A. Burns, J. Byers-Hill, K.D. Gripper,
W.T. Pennington, G.H. Robinson, Inorg. Chim. Acta 216 (1994)
2
67.
[13] R.L. Wells, R.A. Baldwin, P.S. White, W.T. Pennington, A.L.
Rheingold, G.P.A. Yap, Organometallics 15 (1996) 91.
[
14] J.A. Laske-Cooke, R.L. Wells, P.S. White, Organometallics 14
1995) 3562.
15] L.J. Jones, A.T. McPhail, R.L. Wells, Organometallics 13 (1994)
504.
(
[
4. Supplementary material
2
[
[
16] R.K. Harris, Can. J. Chem. 42 (1964) 2275.
17] B.D. Cullity, Elements of X-Ray Diffraction, 2nd ed., Addison-
Wesley, Reading, MA, 1978, pp. 375–377.
Crystallographic data (tables of bond distances, bond
angles, anisotropic temperature factor parameters, and