μ-Oxobridged heterotrinuclear compounds containing antimony(V) and arsenic(III). Crystal structures of Ar3Sb(μ-OAsPh2)2 (Ar=Ph or p-tol)

Article abstract of DOI:10.1016/S0022-328X(98)00908-5

Novel compounds containing open chain Sb(OAs)₂ units have been synthesised by reacting Ar₃SbBr₂ (Ar=Ph or p-tol) with Ph₂AsLi in dry THF/benzene under a N₂ atmosphere, followed by a work up of the reaction mixture under ambient conditions. Their single crystal structures revealed that the geometry of antimony is trigonal bipyramidal and that of arsenic somewhat distorted pyramidal. The SbAs distance is shorter than the sum of their van der Waals radii, but this does not severely distort the regular trigonal bipyramidal geometry of antimony. The ¹H- and ¹³C-NMR spectra of these compounds are generally as expected. In the mass spectrum of Ph₃Sb(μ-OAsPh₂)₂, the molecular ion peak was observed, but for the other compound, peaks of only its fragments were observed. The ν(Sb-O-As) appears at 744 cm^-1 in IR spectra of these compounds.

Full text of DOI:10.1016/S0022-328X(98)00908-5

Journal of Organometallic Chemistry 572 (1999) 87–91
v-Oxobridged heterotrinuclear compounds containing antimony(V) and
arsenic(III). Crystal structures of Ar3Sb(v-OAsPh2)2 (Ar=Ph or p-tol)
C. Valan Amburose a, Ajai K. Singh a,*, N.K. Jha a, Pankaj Sharma b, A. Cabrera b,
G. Espinosa-Perez b
a Department of Chemistry, Indian Institute of Technology, New Delhi 110 016, India
b Instituto de Quimica, UNAM, Circuito Exterior, Coyoacan, D.F. 04510, Mexico
Received 16 June 1998
Abstract
Novel compounds containing open chain Sb(OAs)2 units have been synthesised by reacting Ar3SbBr2 (Ar=Ph or p-tol) with
Ph2AsLi in dry THF/benzene under a N2 atmosphere, followed by a work up of the reaction mixture under ambient conditions.
Their single crystal structures revealed that the geometry of antimony is trigonal bipyramidal and that of arsenic somewhat
distorted pyramidal. The Sb···As distance is shorter than the sum of their van der Waals radii, but this does not severely distort
the regular trigonal bipyramidal geometry of antimony. The 1H- and 13C-NMR spectra of these compounds are generally as
expected. In the mass spectrum of Ph3Sb(v-OAsPh2)2, the molecular ion peak was observed, but for the other compound, peaks
of only its fragments were observed. The w(SbꢀOꢀAs) appears at 744 cm−1 in IR spectra of these compounds. © 1999 Elsevier
Science S.A. All rights reserved.
Keywords: Antimony; Arsenic; Crystal structure; Oxobridged compound
1. Introduction
unit in which antimony is in oxidation state V and
arsenic in III. In the literature, only a few reports on
cage compounds [1] having SbꢀOꢀSb and SbꢀOꢀP as
units exist. Recently, compounds having oxobridged
Sb(V) and As(V) have also been described [2]. An
adduct of 10-chlorophenoxarsine oxide with SbCl5 re-
ported by Holliday et al. ([10]a) also has AsꢀOꢀSb
units. In the structure of dimeric triphenylstibine oxide
([10]b) the presence of SbꢀOꢀSb units has also been
established. The distance between antimony and arsenic
in the present AsOSbOAs unit is shorter than the sum
of the van der Waals radii of both Sb and As.
There is current interest [1–8] in small clusters, cages
and rings formed by antimony alone or with phospho-
rus and arsenic. The attractive features of these systems
include the novel co-ordination geometry of antimony
[5], the unusual ligation mode of groups [4] used as
building blocks in these systems and the possible appli-
cations as CVD precursors [9] for III–V semiconduc-
tors. In two recent publications, a trinuclear antimony
moiety has been synthesised, in one case as a cation [5]
[Me2SbꢀSb(Me)2ꢀSbMe2]+ and in another as a neutral
entity R%R4Sb3 [7] (R=Ph or p-tol; R%=Ph, p-tol or
3
Me). It was therefore thought worthwhile to design an
oxobridged triheteronuclear cluster Ar3Sb(v-OAsPh2)2.
These are the first examples containing a AsOSbOAs
2. Experimental
All solvents were dried, made oxygen free and redis-
tilled before use. Triphenylarsine (Merck), lithium
metal (Merck) and 2-chloro-2-methylpropane (Fluka)
* Corresponding author. Fax: +91-11-686-2037; e-mail: aks-
ingh@chemistry.ernet.in.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00908-5

88
C.V. Amburose et al. / Journal of Organometallic Chemistry 572 (1999) 87–91
that of 1, except that p-tol3SbBr2 (2.77 g, 5 mmol) was
used in place of Ph3SbBr2 and 2 was finally recrystal-
lized from a chloroform:hexane mixture (1:1), as
colourless crystals. Yield: 2.88 g, 65%, m.p. 176°C.
Anal. Calc. for C45H41As2O2Sb: C, 61.05; H, 4.67.
were used as-received. The published method ([11]a)
was used to prepare a deep red solution (in dry THF)
of Ph2AsLi. To synthesise Ph3SbBr2 ([11]b) and p-
tol3SbBr2 [12], published methods were used. These
compounds were stored under oxygen-free nitrogen.
C and H analyses were performed on a 240C Perkin-
Elmer Analyser. The IR spectra were recorded on a
Nicolet 5DX FT-IR spectrometer as KBr pellets. NMR
spectra, 1H (99.55 MHz) and 13C (25.0 MHz), were
recorded on a JEOL JNM FX-100 FT-NMR spectrom-
eter using SiMe4 as an internal standard. The FAB MS
spectra were recorded on a JEOL JMS-SX 102A mass
spectrometer using 3-NOBA as matrix.
1
Found: C, 61.32; H, 4.64. H-NMR (C6D6): l 1.99 (s,
9H, CH3), 7.10 (m, 18H, ArH, m to Sb plus m and p to
As), 7.64 (m, 8H, ArH, o to As), 8.26 (m, 6H, ArH, o
to Sb). 13C-NMR (CDCl3): l 152.0 (C p to Sb), 143.6
Table 1
Crystallographic data, measurements and refinements of
Ph3Sb(OAsPh2)2, 1, and p-tol3Sb(OAsPh2)2, 2
2.1. Triphenylantimony(V)bis{(v-oxo)-
diphenylarsenic(III)}, Ph3Sb(OAsPh2)2, 1
Compound
1
2
Empirical formula
Formula weight
Colour, habit
C42H30As2O2Sb
838.3
Colourless, irregu- Colourless, prism
lar
298
Triclinic
C45H41As2O2Sb
885.4
Ph3SbBr2 (2.56 g, 5 mmol) dissolved in dry benzene
(20 ml) was added dropwise to a solution of Ph2AsLi
(10 mmol) generated in situ in dry THF (freshly dis-
tilled) under an oxygen-free nitrogen atmosphere (15
ml). The deep red colour of mixture due to Ph2AsLi
faded to light yellow. Thereafter, the mixture was
stirred for 30 min, the solvent was removed in vacuo
and the pasty mass left was extracted with 50 ml of
benzene. The undissolved LiBr and LiCl were filtered
off from the benzene extract and it was concentrated to
10 ml. Ph3Sb(OAsPh2)2 was obtained as a colourless
crystalline solid by adding hexane (5 ml) to this concen-
trate. It was recrystallised from benzene:hexane (mois-
ture-free) mixture (1:1) and dried in vacuo. Yield: 2.53
g, 60%, m.p. 144°C. Anal. Calc. for C42H35As2O2Sb: C,
59.82; H, 4.18. Found: C, 59.30; H, 4.03. 1H-NMR
(C6D6): l 7.10 (m, 21H, ArH, m and p to As plus m and
p to Sb), 7.60 (m, 8H, ArH, o to As), 8.30 (m, 6H, ArH,
o to Sb). 13C-NMR (CDCl3): l 150.9 (C ipso to Sb),
140.6 (C ipso to As), 137.2(C o to Sb and As), 132.9(C
p to Sb), 131.0(C m to Sb), 130.1 (C p and C m to As).
IR (KBr): 744 cm−1 (w(SbꢀOꢀAs)). FAB MS: m/z 842,
844 (M), 840 (M-2H), 765, 767 (M-Ph), 686 (M-(Ph2+
2H)), 613, 615 (M-Ph2As), 597, 599 (M-Ph2AsO), 551
(Ph2SbSbPh2+H), 520, 522 (M-(Ph2AsO+Ph)), 504,
506 (Ph2SbAsPh2), 490 (M–Ph3Sb), 474 (M-Ph3SbO),
458 (Ph2AsAsPh2), 369, 371 (Ph3SbO+H), 352, 354
(Ph3Sb), 322 (Ph2AsOPh), 306 (Ph3As), 275, 277
(Ph2Sb), 273, 275 (C12H8Sb), 245 (Ph2AsO), 229
(Ph2As), 227 (PhAs2), 198, 200 (PhSb), 168 (PhAsO),
154 (Ph2), 152 (PhAs), 137, 139 (SbO), 75 (As). The
isotopic pattern of antimony was observed for strong
peaks only.
Temperature (K)
Crystal system
Space group
293
Triclinic
(
(
P1
P1
Unit cell dimensions:
˚
a (A)
10.136(2)
14.002(2)
14.287(2)
113.71(2)
96.45(2)
93.33(2)
1832.8(3)
2
10.210(2)
13.933(2)
15.323(2)
107.18(2)
102.36(2)
97.29(2)
1991.8(4)
2
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
V (A )
Z
Dcalc. (Mg m−3
)
1.519
2.578
1.476
2.377
Absorption coefficient
(mm−1
F(000)
Crystal size (mm3)
)
830
888
0.56×0.4×0.3
0.42×0.24×0.10
Variable; 4.00–
100.00
Scan speed (° min−1 in Variable; 8.00–
ꢀ)
100.00
1.24
Scan range, ꢀ (°)
Index ranges
1.06
05h513, −165 05h513, −175
k516, −185l5
18
8587
k516, −195l5
19
10 354
9755 (Rint=
Reflections collected
Independent reflections
8128 (Rint
=
3.41%)
11.81%)
Min/max transmission
Quantity minimized
Extinction correctiona
Number of parameters
refined
0.2973/0.3566
ꢀ w(Fo−Fc)2
=−0.00014(7)
415
0.3162/0.4444
ꢀ w(Fo−Fc)2
=−0.00021(7)
452
Final R indicesb (obs.
data)
R indices (all data)
R=5.56%, wR= R=6.07%, wR=
5.92% 6.17%
R=12.42%, wR= R=15.69%, wR=
9.14%
1.13
8.61%
1.16
3.116, 0.009
9.0:1
0.80, −0.64
Goodness-of-fit
Largest, mean D/|
Data-to-parameter ratio 9.7:1
2.043, 0.016
Largest difference peak
0.74, −0.79
−3
˚
and hole (eA
)
2.2. Tri-p-tolylanitmony(V)bis{(v-oxo)-
a F*=F[1+0.002F2/sin(2q)]−1/4
.
diphenylarsenic(III)}, p-tol3Sb(OAsPh2)2, 2
Compound 2 was prepared by a method similar to
b Weighing scheme, w−1=|2(F)+0.0008F2.

C.V. Amburose et al. / Journal of Organometallic Chemistry 572 (1999) 87–91
89
tion data were collected on a Siemens P4/PC system
using graphite monochromated Mo–Kh radiation
˚
(u=0.71073 A). The ꢀ scan mode was used. The 2q
values were in the range 3.0°–55.0°. The background
measurements were made for 25% of total scan time
keeping the crystal and counter stationary at the be-
ginning and end of the scan. Three standard reflec-
tions were measured after every 97 reflections. The
semi-empirical absorption corrections were made. The
SHELXTL PLUS (PC version) [13] program was used
to refine the structures. The structure was solved by
direct methods and for final refinement cycle the full-
matrix least-squares method was used. The hydrogen
atoms were included by the riding model (fixed
isotropic U). The crystal data and other details of
data collection, solution and refinement are given in
Table 1.
3. Results and discussion
The Ph2AsLi generated according to Eq. (1) on re-
action with Ar3SbBr2, results in 1 or 2 (Eq. (2)),
which are the first examples of compounds containing
the Sb(OAs)2 unit.
Fig. 1. Molecular structure (ORTEP diagram) of Ph3Sb(OAsPh2)2, 1.
(i) 2Li/THF/N
2
Ph3As ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁ Ph2AsLi+C6H6+LiCl+(CH3)2CꢂCH2
(1)
(2)
(ii) t−BuCl/THF/N
2
benzene/N
2Ph2AsLi+Ar3SbBr2 ꢀꢀꢀꢀꢀꢁ2Ar3Sb(AsPh2)2“air Ar3Sb(OAsPh2)2
2LiBr
Ar=Ph or p−tol
It appears that the open chain triheteronuclear
compound containing the SbAs2 unit was the most
probable intermediate formed by the method sum-
marised in Eqs. (1) and (2) with the oxygen inserted
into the SbꢀAs bond from air during the work up
under ambient conditions. The insertion of oxygen
(using molecular O2) into a SbꢂSb bond has been
used recently [14] to prepare a SbꢀOꢀSb unit. How-
ever, we failed to isolate the intermediate containing
the AsꢀSbꢀAs unit even after using very stringent
conditions and Schlenk techniques. The compounds 1
and 2 are soluble in common organic solvents and
authenticated by elemental analyses. They can be
stored under ambient conditions for several months
without any sign of decomposition.
(C ipso to As), 138.0 (C ipso to Sb), 133.6 (C o to Sb
and As), 132.4 (C m to Sb), 131.0 (C p and C m to
As) 23.0 (CH3). IR (KBr): 744 cm−1 (w(SbꢀOꢀAs)).
FAB MS: m/z 716 (M-(p-tol+Ph)), 702 (M-(p-tol)2),
655, 657 (M-Ph2As), 639, 641 (M-Ph2AsO), 548, 550
(M-(p-tol+Ph2AsO)), 534 (M-((p-tol)2+PhAsO)),
487 (p-tol)3SbOPh), 474 (Ph2AsOAsPh2), 411, 413 (p-
tol3SbO+H), 303, 305 (p-tol2Sb), 245 (Ph2AsO), 229
(Ph2As), 154 (Ph2), 137, 139 (SbO), 91 (p-tol). Only in
strong peaks was the isotopic pattern of antimony
noticed.
2.3. X-ray diffraction analysis
The colourless single crystals of 1 and 2 were
grown from benzene:hexane (1:1) and chloro-
form:hexane(1:1) mixtures, respectively. The diffrac-
3.1. Spectral data
1
The H- and 13C-NMR spectra of 1 and 2 are gen-

90
C.V. Amburose et al. / Journal of Organometallic Chemistry 572 (1999) 87–91
Fig. 2. Molecular structure (ORTEP diagram) of p-tol3Sb(OAsPh2)2, 2.
erally as expected. The 13C-NMR assignments are
based on the literature reports [12]. In the FAB MS
spectrum of 1, the molecular ion peak was observed,
but was not observed in that of 2. However, there are
peaks in the mass spectrum of 2 that may be assigned
to its fragments, e.g. (M-(p-tol)2), (M-(p-tol+Ph2AsO))
and (M-Ph2As), supporting indirectly the molecular
stoichiometry of 2. In the IR spectra of 1 and 2, a band
appearing at 744 cm−1 was not noticed in the spectra
of Ph3Sb, Ph3SbBr2, p-tol3Sb, p-tol3SbBr2, Ph3As.
Moreover, was(AsꢀOꢀAs) is reported in [15] at 920
cm−1 in the IR spectrum of Me2As(S)OAs(S)Me2 and
was(SbꢀOꢀSb) is assigned to a band ([10]b) appearing at
658/664 cm−1 in the IR spectrum of triphenylstibine
oxide dimer. Consequently, it is reasonable to conclude
that the band appearing at 744 cm−1 most probably
originates from the asymmetric vibrations of the
SbꢀOꢀAs unit.
Table 2. The crystal of 1 was not of good quality,
which resulted in disorder in one of the phenyl rings.
The arrangement of donor atoms of various ligands
around antimony is nearly a regular trigonal bipyrami-
dal. The geometry of arsenic is somewhat distorted
pyramidal. The distances between arsenic and antimony
˚
in 1 and 2 are within the range 3.330–3.418 A, which is
significantly less than the sum of their van der Waals
˚
radii (4.210 A) [16]. This may be interpreted in terms of
intramolecular secondary interaction between arsenic
and antimony. Some role of this secondary intramolec-
ular linkage in stabilising the v-oxobridged Sb(OAs)2
unit of 1 and 2 may be possible but in the structure of
either of these two compounds, the proposed secondary
linkage does not severely distort the geometry of Sb as
expected for a hepta-co-ordination. So far only one
authentic report on the VII co-ordination of Sb is
available [17] in the literature. The CꢀC distances and
CꢀCꢀC bond angles of phenyl rings (1.250(38)–
˚
3.1.1. Crystal structures
1.442(26) A and 110.1(22)–129.8(20)°, respectively) are
The atomic co-ordinates for 1 and 2 along with
equivalent isotropic displacement coefficients are avail-
able as supplementary material. The ORTEP diagrams
(molecular structures) are shown in Figs. 1 and 2. The
selected bond lengths and bond angles are given in
normal. The SbꢀO and AsꢀO bond lengths are in the
˚
ranges 2.041(7)–2.054(7) and 1.758(6)–1.781(5) A, re-
spectively, and comparable with the earlier reported
As/SbꢀO single bond length [18]. However, the present
AsꢀO bond lengths are longer than those reported [2]

C.V. Amburose et al. / Journal of Organometallic Chemistry 572 (1999) 87–91
91
˚
˚
Table 2
(2.090(13)–2.175(6) A/1.820(3)–1.911(4) A). The
SbꢀOꢀAs bond angles (120.7(4)–128.1(4)°) are larger
than the values (119.0(1)–119.5(1)°) reported recently
[2] for [(SbAr2)2(v-O)2(v-O2AsMe2)2]. This may be due
to strong steric effects of bulky aryl groups attached to
antimony and arsenic both.
˚
Selected bond lengths (A) and angles(°) with estimated S.D.s in
parentheses
Compound
1
2
˚
Bond length (A)
Sb(1)ꢀO(1)
Sb(1)ꢀO(2)
Sb(1)ꢀC(1)
Sb(1)ꢀC(7)
2.041(7)
2.051(7)
2.112(9)
2.112(10)
2.108(9)
1.758(6)
1.969(9)
1.777(23)
2.326(31)
1.781(5)
1.961(13)
1.952(11)
–
2.051(8)
2.054(7)
2.123(12)
2.101(10)
2.117(9)
1.768(7)
–
References
Sb(1)ꢀC(13)
As(1)ꢀO(1)
As(1)ꢀC(37)
As(1)ꢀC(31)
As(1)ꢀC(31A)
As(2)ꢀO(2)
As(2)ꢀC(19)
As(2)ꢀC(25)
As(1)ꢀC(19)
As(1)ꢀC(25)
As(2)ꢀC(31)
As(2)ꢀC(37)
Sb(1)···As(1)
Sb(1)···As(2)
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Clearfield, M. Veith, V. Huch, Inorg. Chem. 35 (1996) 3235 and
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35 (1996) 1005.
–
–
1.762(5)
–
–
1.969(9)
1.967(14)
1.972(14)
1.964(13)
3.389
–
–
–
3.418
3.330
3.373
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Commun. (1994) 875.
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123.
Bond angles (°)
O(1)ꢀSb(1)ꢀO(2)
O(1)ꢀSb(1)ꢀC(1)
O(2)ꢀSb(1)ꢀC(1)
O(1)ꢀSb(1)ꢀC(7)
O(2)ꢀSb(1)ꢀC(7)
C(1)ꢀSb(1)ꢀC(7)
O(1)ꢀSb(1)ꢀC(13)
O(2)ꢀSb(1)ꢀC(13)
C(1)ꢀSb(1)ꢀC(13)
C(7)ꢀSb(1)ꢀC(13)
O(1)ꢀAs(1)ꢀC(37)
O(1)ꢀAs(1)ꢀC(31)
C(37)ꢀAs(1)ꢀC(31)
O(1)ꢀAs(1)ꢀC(31A)
C(37)ꢀAs(1)ꢀC(31A)
C(31)ꢀAs(1)ꢀC(31A)
O(2)ꢀAs(2)ꢀC(19)
O(2)ꢀAs(2)ꢀC(25)
C(19)ꢀAs(2)ꢀC(25)
Sb(1)ꢀO(1)ꢀAs(1)
Sb(1)ꢀO(2)ꢀAs(2)
O(1)ꢀAs(1)ꢀC(19)
O(1)ꢀAs(1)ꢀC(25)
C(19)ꢀAs(1)ꢀC(25)
O(2)ꢀAs(2)ꢀC(31)
O(2)ꢀAs(2)ꢀC(37)
C(31)ꢀAs(2)ꢀC(37)
177.5(3)
92.7(3)
89.7(3)
87.0(3)
91.3(3)
122.6(3)
92.6(3)
86.7(3)
117.1(3)
120.3(3)
99.2(4)
108.5(7)
94.0(7)
83.6(8)
97.2(7)
24.9(10)
96.6(4)
99.7(3)
96.0(5)
128.1(4)
120.7(4)
–
176.5(3)
93.3(4)
89.2(4)
86.1(3)
90.5(4)
120.3(4)
94.4(4)
86.6(3)
118.3(4)
121.3(4)
–
–
–
–
–
–
–
–
–
124.9(4)
124.1(4)
100.3(4)
98.0(5)
95.2(5)
95.9(4)
101.0(4)
97.6(6)
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Uekusa, Y. Ohashi, J. Am. Chem. Soc. 120 (1998) 433.
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Chem. Commun. (1984) 896.
–
–
–
–
–
[18] (a) R.R. Holmes, R.O. Day, V. Chandrasekhar, J.M. Holmes,
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Crystallogr. C49 (1993) 1044.
˚
(1.701(3)–1.711(3)
A),
for
[(SbPh2)2(v-O)2(v-
O2AsMe2)2]·2CHCl3 and [{Sb(p-MeC6H4)2}2(v-O)2(v-
O2AsMe2)2]. The bond lengths of
(2.101(10)–2.117(9) A) and AsꢀC (1.777(23)–1.972(14)
A) observed in the structures of 1 and 2 are similar to
SbꢀC
˚
˚
those reported for Sb/AsꢀC single bond [18,19]
.