Cyclic and polycyclic gallium-antimony compounds: Synthesis and crystal structures of [GaCl(PnPr2Ph)(SbSiiPr3)]2 and [(GaCl)4(SbSiiPr3)4 (PnPr2Ph)2]

Article abstract of DOI:10.1002/1099-0682(200212)2002:12<3268::AID-EJIC3268>3.0.CO;2-N

The reaction of [(DME)LiE(SiMe₃)₂] (E = As, Sb) with iPr₃SiCl in DME yields the mixed silylated compounds iPr₃SiE-(SiMe₃)₂ (1: E = As, 2: E = Sb). Compounds 1 and 2 were characterised by multinuclear NMR spectroscopy and mass spectrometry. The antimony compound 2 reacts with [GaCl₃PnPr₂Ph to give the cyclic compound [GaCl(PnPr₂Ph)(SbSiiPr₃)]₂ (3). The polycyclic Ga-Sb compound [(GaCl)₄(SbSiiPr₃)₄ (PnPr₂Ph)₂] (4) can be obtained from a solution of 3 in benzene. The central structural motif of 3 is a folded Ga₂Sb₂ four-membered ring. Compound 4 consists of a ladder-like Ga₄Sb₄ unit and is the first polycyclic Ga-Sb compound described. Compounds 3 and 4 were characterised by single crystal X-ray diffraction. The thermal decomposition of both compounds results in the formation of the binary phase GaSb.

Full text of DOI:10.1002/1099-0682(200212)2002:12<3268::AID-EJIC3268>3.0.CO;2-N

FULL PAPER
Cyclic and Polycyclic Gallium-Antimony Compounds: Synthesis and Crystal
Structures of [GaCl(PnPr2Ph)(SbSiiPr3)]2 and [(GaCl)4(SbSiiPr3)4(PnPr2Ph)2]
Carsten von Hänisch,*[a] Petra Scheer,[a] and Birgit Rolli[a]
Keywords: Gallium / Antimony / Polycycles / Heterocycles / Semiconductors
The reaction of [(DME)LiE(SiMe3)2] (E = As, Sb) with iPr3SiCl
in DME yields the mixed silylated compounds iPr3SiE-
(SiMe3)2 (1: E = As, 2: E = Sb). Compounds 1 and 2 were
characterised by multinuclear NMR spectroscopy and mass
from a solution of 3 in benzene. The central structural motif
of 3 is a folded Ga2Sb2 four-membered ring. Compound 4
consists of a ladder-like Ga4Sb4 unit and is the first polycyclic
Ga-Sb compound described. Compounds 3 and 4 were char-
acterised by single crystal X-ray diffraction. The thermal de-
spectrometry. The antimony compound
2 reacts with
[GaCl3PnPr2Ph] to give the cyclic
compound composition of both compounds results in the formation of
[GaCl(PnPr2Ph)(SbSiiPr3)]2 (3). The polycyclic Ga-Sb com-
pound [(GaCl)4(SbSiiPr3)4(PnPr2Ph)2] (4) can be obtained
the binary phase GaSb.
Introduction
antimony compound 2 reacts with the phosphane complex
[GaCl3PnPr2Ph] in diisopropyl ether to give the cyclic com-
In the last few years different groups have reported the pound 3 as illustrated in Equation (1). Compound 3 can be
synthesis of four- and six-membered Ga-Sb ring com- obtained in crystalline form by cooling the reaction mixture
to 6 °C.
pounds of the general formula [R2GaSbRЈ2]n (R ϭ alkyl,
chloride; RЈ ϭ alkyl, silyl; n ϭ 2, 3).[1] In these compounds
the Ga and Sb atoms have the coordination number four.
Cyclic compounds with lower coordinated Ga and/or Sb
atoms or polycyclic molecules are unknown so far. In con-
trast, several cyclic or polycyclic gallium phosphorus or gal-
lium arsenic compounds with low-coordinate Ga and P/As
atoms have been described.[2,3] We obtained the cyclic and
polycyclic Ga-Sb compounds [GaCl(PnPr2Ph)(SbSiiPr3)]2
(3) and [(GaCl)4(SbSiiPr3)4(PnPr2Ph)2] (4) from the reac-
tion of the mixed silylated antimony compound
iPr3SiSb(SiMe3)2 (2) with the gallium chloride phosphane
complex [GaCl3PnPr2Ph]. The structure of compounds 3
and 4 was determined by X-ray crystal structure analysis.[4]
2 [GaCl3·PnPr2Ph] ϩ 2 iPr3SiSb(SiMe3)2 Ǟ
(1)
[GaCl(PnPr2Ph)(SbSiiPr3)]2 (3) ϩ 4 Me3SiCl
Compound 3 crystallises with an orthorhombic unit cell
containing four molecules in the space group Pna21, and
has been refined as an inversion twin (Figure 1). The central
structural motif is a folded Ga2Sb2 four-membered ring in
which the Sb atoms are trigonal pyramidally coordinated
by two Ga atoms and one SiiPr3 group. The gallium centres
have a distorted tetrahedral geometry consisting of a chlor-
ide atom, a PnPr2Ph ligand and the two Sb atoms. Due to
the mutual repulsion of the sterically demanding PnPr2Ph
and SiiPr3 groups they are orientated on different sides of
the ring. The shape of 3 is therefore similar to the recently
described gallium phosphorus and gallium arsenic com-
pounds [GaCl(PtBu2Me)(ESiMe3)]2 (E ϭ P, As).[2b] The
clear folding of the ring — the SbϪGaϪSb planes have an
angle of 139.0° to each other — is caused by the lower
coordination number at the Sb atoms and by the cis ori-
entation of the sterically demanding SiiPr3 and PnPr2Ph
groups. The GaϪSb bonds in 3 are 264.1 pm on average
and therefore shorter than in the GaϪSb ring compounds
with coordination number four at the gallium and the anti-
mony atoms (267Ϫ277 pm) mentioned above. This
shortening can be explained by the lower coordination
number of the Sb atoms and the purely covalent character
of the GaϪSb bonds in 3. A GaϪSb bond length of
264.8(1) pm, however, can be observed in the acyclic com-
pound [LGaEt2ϪSb(SiMe3)2] [L ϭ 4-(dimethylamino)pyri-
dine], also featuring coordination number three at the anti-
Results and Discussion
The reaction of [(DME)LiE(SiMe3)2]2 (E ϭ As, Sb) with
iPr3SiCl in DME at 0 °C yields the mixed silylated com-
pounds iPr3SiE(SiMe3)2 (1: E ϭ As, 2: E ϭ Sb). These com-
pounds are highly viscous liquids which solidify to a glass-
like solid when cooled to Ϫ78 °C. Both compounds were
characterised by multinuclear NMR spectroscopy and mass
spectrometry. Whereas the arsenic compound 1 shows no
reaction towards gallium chloride phosphane complexes the
[a]
Institut für Nanotechnologie, Forschungszentrum Karlsruhe
Postfach 3640, 76021 Karlsruhe, Germany
Fax: (internat.) ϩ49-(0)7247/826-368
E-Mail: carsten.vonhaenisch@int.fzk.de
3268  2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/02/1212Ϫ3268 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 3268Ϫ3271

Cyclic and Polycyclic Gallium-Antimony Compounds
FULL PAPER
mony and four at the gallium atom.[5] The endocyclic angles
in 3 are 98.7° at the gallium and 75.2° at the antimony
atoms. The GaϪCl bonds are, on average, 225.2 pm long,
and the exocyclic dative PϪGa bond is 244.2 pm long.
Compound 3 is stable in the mother liquor but decomposes
over a period of two weeks time with release of the phos-
phane ligands and the formation of a brown residue when
isolated.
Figure 2. Molecular structure of 4; selected bond lengths (pm) and
bond angles (°): Ga(1)ϪSb(1) 271.7(1), Ga(1)ϪSb(1Ј) 269.1(1),
Ga(1)ϪSb(2) 264.4(1), Ga(2)ϪSb(1) 266.2(1) Ga(2)ϪSb(2)
261.8(1), Ga(1)ϪCl(1) 222.5(2), Ga(2)ϪCl(2) 222.9(2), Ga(2)ϪP:
242.9(2),
Sb(1)ϪSi(1)
258.9(2),
Sb(2)ϪSi(2)
259.1(2);
Ga(1)ϪSb(1)ϪGa(2) 80.4(1), Ga(1)ϪSb(1)ϪGa(1Ј) 86.3(1),
Ga(1Ј)ϪSb(1)ϪGa(2) 117.7(1), Ga(1)ϪSb(2)ϪGa(2) 82.6(1),
Sb(1)ϪGa(1)ϪSb(2) 97. 0(1), Sb(1)ϪGa(1)ϪSb(1Ј) 93.7(1),
Sb(1Ј)ϪGa(1)ϪSb(2) 110.9(1), Sb(1)ϪGa(2)ϪSb(2) 99.0(1),
Cl(2)ϪGa(2)ϪP 93.3(1)
Figure 1. Molecular structure of 3; selected bond lengths (pm) and
bond angles (°): Ga(1)ϪSb(1) 264.1(1), Ga(1)ϪSb(2) 265.1 (1),
Ga(2)ϪSb(1) 263.5 (1), Ga(2)ϪSb(2) 263.6(1), Ga(1)ϪCl(1)
224.8(2), Ga(1)ϪP(1) 244.8(2), Ga(2)ϪCl(2) 225.6(2), Ga(2)ϪP(2)
The coordination sphere of the outer Ga atoms [Ga(2)
and Ga(2Ј)] in 4 is completed by the phosphane ligands, so
that all Ga atoms have coordination number four. The Sb
atoms in 4 have two different coordination numbers: the Sb
atoms of the central ring [Sb(1) and Sb(1Ј)] have a coor-
dination number of four, whereas the outer Sb atoms are
trigonal pyramidal coordinated. The GaϪSb bond lengths
in 4 vary greatly. In the central ring they are 269.1(1) to
271.7(1) pm long, whereas the Ga(1)ϪSb(2) and the
Ga(2)ϪSb(1) bond lengths are 264.4(1) and 266.2(1) pm,
respectively. The shortest GaϪSb bond known so far can
be observed between Ga(2) and Sb(2) [261.8(1) pm].
The UV/Vis spectrum of the yellow compound 3 shows
a first absorption maxima at 425 nm. The red compound 4
reveals the first absorption maxima at 450 nm. In the IR
spectra of both compounds the typical peaks of the
PnPr2Ph ligands and the SiiPr3 groups are observed.
243.6(2),
Sb(1)ϪSi(1)
258.1(2),
Sb(2)ϪSi(2)
258.2(2);
Ga(1)ϪSb(1)ϪGa(2) 75.3(1), Ga(1)ϪSb(2)ϪGa(2) 75.1(1),
Sb(1)ϪGa(1)ϪSb(2)
Cl(1)ϪGa(1)ϪP(1)
98.4(1),
93.7(1),
Sb(1)ϪGa(2)ϪSb(2)
Cl(2)ϪGa(2)ϪP(2)
99.0(1),
92.3(1),
Si(1)ϪSb(1)ϪGa(1) 107.5(1), Si(1)ϪSb(1)ϪGa(2) 116.0(1),
Si(2)ϪSb(2)ϪGa(1) 117.1(1), Si(2)ϪSb(2)ϪGa(2) 105.9(1)
Red crystals with the composition [(GaCl)4(SbSi-
iPr3)4(PnPr2Ph)2] (4) · 2 C6H6 were obtained from a solu-
tion of 3 in benzene over a period of three days. Obviously
compound 3 undergoes a condensation reaction to give 4
and two free phosphane molecules [Equation (2)].
2 [GaCl(PnPr2Ph)(SbSiiPr3)]2 Ǟ
(2)
[(GaCl)4(SbSiiPr3)4(PnPr2Ph)2] (4) ϩ 2 PnPr2Ph
The molecular structure of 4 (Figure 2), which contains
Thermogravimetric analysis of compound 3 under va-
an inversion centre, consists of a central planar Ga2Sb2 cuum shows a one-step decomposition in the temperature
four-membered ring in which the silyl groups and the Cl range of 110 to 160 °C. The on-line mass spectra of the
atoms are trans orientated. Two slightly folded Ga2Sb2 rings cleavage products shows the phosphane ligands and the silyl
with an all cis orientation of the silyl groups and the Cl groups. The overall mass loss is 70.0% (calculated for the
atoms are connected to the central ring on opposite sides. formation of GaSb: 66.9%). Powder X-ray diffraction meas-
These three Ga2Sb2 rings are not coplanar, instead the three urements of the grey residue obtained display only the
moieties form a chair-like structure. A similar structure has reflections of cubic GaSb. From element analyses the car-
been observed for the aluminium-phosphorus compound bon content of the residue was determined to be 1.5(5)%.
[(AlCl)4(PR)4(OEt2)2] (R ϭ SiiPr3, SiiPr2Me) which was re- Analogous thermogravimetric experiments on 4 show a
cently obtained by reaction of AlCl3 with Li2PR in diethyl two-step decomposition. In a first step, between 75 and 120
ether.[6]
°C, the cleavage of the crystal solvent can be observed (mass
Eur. J. Inorg. Chem. 2002, 3268Ϫ3271
3269

C. von Hänisch, P. Scheer, B. Rolli
FULL PAPER
4: Compound 3 (0.2 g) was dissolved in 2 mL benzene and stirred
for two hours at room temperature. Subsequently the solution was
cooled to 6 °C. After three days red crystals of 4 formed from
this solution. Yield: 0.1 g (54%). C60H122Cl4Ga4P2Sb4Si4 · 2 C6H6
(2081.77): calcd. C 41.54, H 6.49; found C 41.38, H 6.96. 31P{1H}
NMR (C6D6): δ ϭ Ϫ20.2 (s) ppm. IR (KBr): ν˜ ϭ 3087(vw),
3059(w), 3033(vw), 2960(s), 2939(vs), 2862(vs), 1959(vw), 1859(w),
1816(vw), 1459(vs), 1437(s), 1413(w), 1384(m), 1365(w), 1292(w),
1224(m), 1105(w), 1083(m), 1069(m), 1020(s), 993(s), 918(m),
878(vs), 846(w), 802(w), 740(m), 690(m), 693(s), 658(m), 639(s),
564(s), 520(w), 494(vs), 458(m) cmϪ1. UV/Vis (suspension in min-
eral oil): λmax ϭ 450 nm, 380 (sh), 300.
loss: calcd. 7.5%, observed 7.1%). At 180 °C all volatile
constituents have been eliminated and the formation of cu-
bic GaSb occurs.
Experimental Section
All manipulations were performed with rigorous exclusion of oxy-
gen and moisture using a Schlenk line and nitrogen atmosphere.
Solvents were dried and freshly distilled before use. [(DME)LiE-
(SiMe3)2]2 was prepared according to a literature procedure.[7]
GaCl3 (99.99%) and iPr3SiCl (97%) were obtained from Aldrich
and used as received.
Acknowledgments
This research was supported by a grant from the G.I.F., the Ger-
man-Israeli Foundation for Scientific Research and Development.
We thank Dr. P. Kramkowski for his valuable help with the manu-
script.
iPr3SiAs(SiMe3)2 (1): A mixture of iPr3SiCl (12.1 g) in DME
(20 mL) was added to a solution of [(DME)LiAs(SiMe3)2]2 (20 g,
63 mmol) in DME (200 mL) over a period of two hours at 0 °C.
Subsequently the reaction mixture was stirred for an additional 16
hours at room temperature and then filtered. All volatile compon-
ents were then removed under vacuum and the resulting residue
was fractionally distilled to give 1 as a highly viscous liquid at
[1] [1a]
[1b]
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[1c]
E. E. Foos, R. J. Louet, R. L.
1
90Ϫ100 °C and 10Ϫ3 mbar. Yield: 15.5 g (65%). H NMR (C6D6):
δ ϭ 0.52 (s, 18 H, SiMe3), 1.29 (m, 21 H, SiiPr3) ppm. 13C{1H}
NMR (C6D6): δ ϭ 5.7 (s, SiMe3), 15.8 [s, CH(CH3)2], 20.3 [s,
CH(CH3)2] ppm. 29Si{1H} NMR (C6D6): δ ϭ 2.4 (s, SiMe3), 25.0
(s, SiiPr3) ppm. MS (EI, 70 eV): m/z (%) ϭ 378 (30) [Mϩ], 363 (0.5)
[Mϩ Ϫ Me], 335 (1) [Mϩ Ϫ iPr], 293 (0.7) [Mϩ Ϫ iPr, Ϫ
CH2CHCH3], 251 (0.7) [Mϩ Ϫ 2iPr Ϫ CH2CHCH3], 206 (22) [Mϩ
Ϫ Me Ϫ SiiPr3], 157 (18) [SiiPr3], 73 (100) [SiMe3].
[1d]
S. Schulz, M. Nieger, J. Or-
[1e]
R. L. Wells, E. E.
[1f]
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[1g]
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C1ϪC5.
[2] [2a]
C. von Hänisch, O. Hampe, Angew. Chem. 2002, 114,
iPr3SiSb(SiMe3)2 (2): A mixture of iPr3SiCl (10.5 g) in DME
(20 mL) was added to a solution of [(DME)LiSb(SiMe3)2]2 (20 g,
55 mmol) in DME (200 mL) over a period of two hours at 0 °C.
Subsequently the reaction mixture was stirred for an additional 16
hours at room temperature and then filtered. All volatile compon-
ents were removed under vacuum and the resulting residue was
fractionally distilled to give 2 as a highly viscous liquid at 110Ϫ120
°C and 10Ϫ3 mbar. Yield: 13.5 g (58%). 1H NMR (C6D6): δ ϭ 0.58
(s, 18 H, SiMe3), 1.27 (m, 21 H, SiiPr3) ppm. 13C{1H} NMR
(C6D6): δ ϭ 6.0 (s, SiMe3), 15.4 [s, CH(CH3)2], 20.6 [s, CH(CH3)2]
ppm. 29Si{1H} NMR (C6D6): δ ϭ Ϫ10.2 (s, SiMe3), 27.1 (s, SiiPr3)
[2b]
2198Ϫ2200; Angew. Chem. Int. Ed. 2002, 41, 2095Ϫ2097.
[2c]
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Pestana, P. P. Power, Angew. Chem. 1991, 103, 726Ϫ727; An-
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[3a] A. Dashti-Mommertz, B. Neumüller, Z. Anorg. Allg. Chem.
[3b]
1999, 625, 954Ϫ960.
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ppm. MS (EI, 70 eV): m/z (%) ϭ 424 (4) [Mϩ], 409 (0.4) [Mϩ
Ϫ
[3d]
K. Niedick, B. Ne-
Me], 252 (5) [Mϩ Ϫ Me Ϫ SiiPr3], 157 (30) [SiiPr3], 73 (100)
[3e]
R. L. Wells, A. P.
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[SiMe3].
[4]
STOE-IPDS2, graphite monochromator, Mo-Kα radiation, λ ϭ
3: PnPr2Ph (0.94 g, 4.88 mmol) was added to a solution of GaCl3
(0.43 g, 2.44 mmol) in 30 mL of iPr2O. After stirring for one hour
iPr3SiSb(SiMe3)2 (1.04 g, 2.44 mmol) was added. The reaction mix-
ture was then stirred for an additional 24 hours. Subsequently the
resulting red solution was filtered to remove small amounts of in-
soluble residues and the volume was reduced to 10 mL under va-
cuum. After addition of 5 mL heptane and cooling to 6 °C yellow
crystals of 3 formed over a period of two days. Yield: 0.59 g (42%).
C42H80Cl2Ga2P2Sb2Si2 (1157.02): calcd. C 43.60, H 6.97; found C
43.16, H 6.98. 31P{1H} NMR (C6D6/PnPr2Ph): δ ϭ Ϫ30.5 (s) ppm.
IR (KBr): ν˜ ϭ 3077(w), 3049(w), 2960(s), 2937(vs), 2860(vs),
1983(vw), 1959(vw), 1906(vw), 1806(vw), 1758(vw), 1484(m),
1463(vs), 1437(vs), 1407(m), 1380(m), 1364(w), 1358(w), 1226(m),
1105(w), 1068(s), 1027(m), 995(vs), 918(m), 882(s), 842(w), 828(m),
770(w), 746(vs), 693(s), 658(vs), 634(s), 557(vs), 503(m), 489(w),
˚
0.71073 A. 3: a ϭ 2070.9(4), b ϭ 1201.7(2), c ϭ 2125.6(4) pm,
α ϭ β ϭ γ ϭ 90°, V ϭ 5290.0(2) ϫ 106 pm3; orthorhombic,
Pna21, Flack parameter. 0.609, Z ϭ 4, ρber ϭ 1.453 g/cm3,
µ(Mo-Kα) ϭ 2.251 mmϪ1, T ϭ 200 K, 2Θmax ϭ 52°; 12172
reflections measured, 7798 independent reflections, (Rint
ϭ
0.0287), 7035 independent reflections with Fo Ͼ 4σ(Fo). The
structure was solved by direct methods and refined by full-
matrix least-squares techniques against F2, 470 parameters
(Ga, Sb, Si, P, Cl, C refined anisotropically, H atoms calculated
at ideal positions), R1 ϭ 0.0312, wR2 ϭ 0.0856 (all data), resid-
3
˚
ual electron density: 0.618 e/A . 4·2C6H6: a ϭ 1386.4(3), b ϭ
2006.5(4), c ϭ 1679.2(3) pm, α ϭ 90°, β ϭ 97.12(3)°, γ ϭ 90°,
V ϭ 4634.9(16) ϫ 106 pm3; monoclinic, P21/n, Z ϭ 2, ρber
1.492 g/cm3, µ(Mo-Kα) ϭ 2.527 mmϪ1, T ϭ 200 K, 2Θmax
ϭ
ϭ
52°; 16486 reflections measured, 8252 independent reflections,
(Rint ϭ 0.0754), 5909 independent reflections with Fo Ͼ 4σ(Fo).
The structure was solved by direct methods and refined by full-
matrix least-squares techniques against F2, 406 parameters
459(s), 393(w) cmϪ1. UV/Vis (suspension in mineral oil): λmax
425 nm (sh), 370 (sh), 260, 220.
ϭ
3270
Eur. J. Inorg. Chem. 2002, 3268Ϫ3271

Cyclic and Polycyclic Gallium-Antimony Compounds
FULL PAPER
F. Thomas, S. Schulz, M. Nieger, Eur. J. Inorg. Chem. 2001,
[5]
[6]
(Ga, Sb, Si, P, Cl, C refined anisotropically, H atoms calculated
at ideal positions), R1 ϭ 0.0475, wR2 ϭ 0.1126 (all data), resid-
161Ϫ166.
3
˚
ual electron density: 1.365 e/A . CCDC-187743 (3) and CCDC-
187744 (4) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
C. von Hänisch, F. Weigend, Z. Anorg. Allg. Chem. 2002,
628, 389Ϫ393.
[7] [7a]
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[7b]
1982, 492, 15Ϫ27.
Chem. 1982, 492, 29Ϫ36.
G. Becker, C. Witthauer, Z. Anorg. Allg.
Received June 25, 2002
[I02343]
Eur. J. Inorg. Chem. 2002, 3268Ϫ3271
3271