Common features in the crystal structures of the compounds bis(dimethylstibanyl)oxane and -sulfane, and the minerals valentinite and stibnite (grauspiessglanz)

Article abstract of DOI:10.1002/1521-3749(200007)626:7<1595::AID-ZAAC1595>3.0.CO;2-Q

Bis(dimethylstibanyl)oxane (1) and -sulfane (2), the two simplest organoelement species with an Sb-E-Sb fragment (E = O, S), were prepared by alkaline hydrolysis of bromodimethylstibane and by oxidation of tetramethyldistibane with sulfur [18], respectively. As shown by an x-ray structure analysis of compound 1 (m.p. <-20°C; P2₁,2₁2₁, a = 675.9(2), b = 803.1(2), c = 1666.8(4) pm at -70 ± 2°C; Z = 4; R1 = 0.042), the molecules (O-Sb 198.8 and 209.9 pm, Sb-O-Sb 123.0°) adopt a syn-anti conformation in the solid state and are arranged in zigzag chains along [010] via weak intermolecular O··Sb interactions (258.5 pm, Sb-O··Sb 117.8°, O··Sb-O 173.5°) making use, however, of only one Me₂Sb moiety. Primary and secondary bond lengths and angles agree very well with corresponding values published for valentinite, the orthorhombic modification of antimony(III) oxide [3]. Bis(dimethylstibanyl)sulfane (2) (m.p. 29 to 31 °C) crystallizes in the uncommon space group P6₅22 (a = 927.8(3), c= 1940.9(7) pm at -100 ± 2°C; Z = 6; R1 =0.021). Owing to coordination numbers of (1 + 1) and (2 + 2) for both Me₂Sb groups and the sulfur atom, respectively, molecules with an approximate syn-syn conformation (S-Sb 249.8 pm, Sb-S-Sb 92.35°) build up a three-dimensional net of double helices which are linked together by Sb · · S contacts (316.4 pm). These parameters shed more light onto the rather complicated structure and bonding situation in stibnite (antimony(III) sulfide [4]). The molecular packing of compound 2 is compared with the structures of relevant inorganic solids, especially with that of ss-quartz [37].

Full text of DOI:10.1002/1521-3749(200007)626:7<1595::AID-ZAAC1595>3.0.CO;2-Q

Common Features in the Crystal Structures of the Compounds
Bis(dimethylstibanyl)oxane and -sulfane, and the Minerals Valentinite
and Stibnite (Grauspieûglanz)
H. J. Breunig*, E. Lork, R. RoÈsler
Bremen, Institut fuÈr Anorganische und Physikalische Chemie der UniversitaÈt Bremen
G. Becker*, O. Mundt, W. Schwarz
Stuttgart, Institut fuÈr Anorganische Chemie der UniversitaÈt Stuttgart
Received March 20th, 2000.
Dedicated to Professor Ulrich MuÈller on the Occasion of his 60th Birthday
Abstract. Bis(dimethylstibanyl)oxane (1) and -sulfane (2),
the two simplest organoelement species with an Sb±E±Sb
fragment (E = O, S), were prepared by alkaline hydrolysis of
bromodimethylstibane and by oxidation of tetramethyldistib-
ane with sulfur [18], respectively. As shown by an x-ray
structure analysis of compound 1 (m. p. < ±20 °C; P212121,
a = 675.9(2), b = 803.1(2), c = 1666.8(4) pm at ±70 ± 2 °C;
Z = 4; R1 = 0.042), the molecules (O±Sb 198.8 and 209.9 pm,
Sb±O±Sb 123.0°) adopt a syn-anti conformation in the solid
state and are arranged in zigzag chains along [010] via weak
intermolecular O ´ ´ Sb interactions (258.5 pm, Sb±O ´ ´ Sb
117.8°, O ´ ´ Sb±O 173.5°) making use, however, of only one
Me2Sb moiety. Primary and secondary bond lengths and an-
gles agree very well with corresponding values published for
valentinite, the orthorhombic modification of antimony(III)
oxide [3]. Bis(dimethylstibanyl)sulfane (2) (m. p. 29 to 31 °C)
crystallizes in the uncommon space group P6522 (a = 927.8(3),
c = 1940.9(7) pm at ±100 ± 2 °C; Z = 6; R1 = 0.021). Owing to
coordination numbers of (1 + 1) and (2 + 2) for both Me2Sb
groups and the sulfur atom, respectively, molecules with an ap-
proximate syn-syn conformation (S±Sb 249.8 pm, Sb±S±Sb
92.35°) build up a three-dimensional net of double helices
which are linked together by Sb ´ ´ S contacts (316.4 pm). These
parameters shed more light onto the rather complicated struc-
ture and bonding situation in stibnite (antimony(III) sulfide
[4]). The molecular packing of compound 2 is compared with
the structures of relevant inorganic solids, especially with that
of b-quartz [37].
Keywords: Antimony compounds; Bis(dimethylstibanyl)ox-
ane; Bis(dimethylstibanyl)sulfane; Crystal structure; Valen-
tinite; Stibnite; Bond-valence analyses
Gemeinsamkeiten in den Kristallstrukturen der Verbindungen
Bis(dimethylstibanyl)oxan und -sulfan und den Mineralien Valentinit und Stibnit
(Grauspieûglanz)
InhaltsuÈbersicht. Bis(dimethylstibanyl)oxan (1) und -sulfan (2),
die beiden einfachsten elementorganischen Vertreter mit einer
Sb±E±Sb-Einheit (E = O, S) wurden durch alkalische Hydro-
lyse von Bromdimethylstiban bzw. durch Oxidation von
Tetramethyldistiban mit Schwefel [18] dargestellt. Nach den
Ergebnissen einer RoÈntgenstrukturanalyse an Verbindung 1
(Schmp. < ±20 °C; P212121, a = 675,9(2), b = 803,1(2),
c = 1666,8(4) pm bei ±70 ± 2 °C; Z = 4; R1 = 0,042) nehmen die
MolekuÈle (O±Sb 198,8 und 209,9 pm; Sb±O±Sb 123.0°) im
FestkoÈrper die syn-anti Konformation ein und ordnen sich un-
ter Beteiligung nur einer der beiden Me2Sb-Gruppen uÈber
kurze intermolekulare O ´ ´ Sb Kontakte (258,5 pm; Sb±O ´ ´ Sb
117,8°; O ´ ´ Sb±O 173,5°) zu Zickzack-Ketten laÈngs [010] an.
Øhnliche BindungslaÈngen, -winkel und Kontakte treten in der
bekannten Kristallstruktur des Minerals Valentinit, der ortho-
rhombischen Modifikation des Antimon(III)-oxids [3], auf.
Bis(dimethylstibanyl)sulfan (2) (Schmp. 29 bis 31 °C) kristalli-
siert in der verhaÈltnismaÈûig seltenen Raumgruppe P6522
(a = 927,8(3), c = 1940,9(7) pm bei ±100 ± 2 °C; Z = 6;
R1 = 0,021). Mit Koordinationszahlen von (1 + 1) fuÈr nun alle
Me2Sb-Gruppen bzw. (2 + 2) fuÈr die Schwefelatome bauen die
annaÈhernd syn-syn konformierten MolekuÈle (S±Sb 249,8 pm;
Sb±S±Sb 92,35°) uÈber Sb ´ ´ S Kontakte (316,4 pm) eine dreidi-
mensional verknuÈpfte Anordnung von Doppelhelices auf. Mit
den an Verbindung 2 bestimmten Werten lassen sich entspre-
chende Parameter aus der verhaÈltnismaÈûig komplizierten und
bindungstheoretisch schwer verstaÈndlichen Struktur des Mine-
rals Stibnit (Grauspieûglanz, Sb2S3 [4]) gut einordnen. Die
Packung der Bis(dimethylstibanyl)sulfan-MolekuÈle wird mit
einigen im Aufbau aÈhnlichen anorganischen FestkoÈrpern, ins-
besondere aber mit b-Quarz [37] verglichen.
* Prof. Dr. H. J. Breunig,
Institut fuÈr Anorganische und,
Physikalische Chemie,
der UniversitaÈt Bremen,
Fachbereich 2,
D-28334 Bremen
Prof. Dr. G. Becker,
Institut fuÈr Anorganische Chemie,
der UniversitaÈt Stuttgart,
Pfaffenwaldring 55 (Stgt.-Vaihingen),
D-70569 Stuttgart
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607 Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0044±2313/00/6261595±1607 $ 17.50+.50/0 1595

H. J. Breunig, E. Lork, R. RoÈsler, G. Becker, O. Mundt, W. Schwarz
Introduction
at antimony and E for oxygen or sulfur, were used;
these parameters are easily calculated from the corre-
sponding pairs of torsional angles C±Sb±E±Sb (Ta-
ble 3). With an assignment of the expressions syn and
anti to angles of 0° and 180°, the extreme molecular
conformations of compounds 1 and 2 are syn-syn and
syn-anti, i. e. C2v and Cs symmetry, respectively
(Scheme 1).
As a continuation of our studies on distibanes and re-
lated compounds [1], which to a considerable extent
display intermolecular associations in the solid state,
we were interested to learn more about the structures
of distibanyl chalcogenanes in different states of ag-
gregation. It would be of particular interest if structur-
al features, which are typical for the different modifi-
cations of antimony(III) oxide [2, 3] and sulfide [4±
10], can also be recognized in the solid state of simple
species like the methyl derivatives (Me2Sb)2O (1) and
(Me2Sb)2S (2). With respect to bis(dimethylstibanyl)-
sulfane (2) especially, these studies are expected to
bring forth a deeper insight into the rather compli-
cated structure of stibnite (Grauspieûglanz); for this
black (or grey) modification of antimony(III) sulfide
the results of several crystal structure determinations
in space group Pnma, carried out at ambient tempera-
ture, were reported [4].
Scheme 1
DFT calculations on compounds 1 and 2 revealed that
molecules with a conformation strictly or near syn-syn
(Ep±Sb±E±Sb < 45°) are in an extremely flat minimum of
energy; the syn-anti conformer was found to be higher in en-
ergy by only 4.6 and 3.9 kJ mol±1, respectively. In agreement
with these results, the presence of both conformers in the
gas phase had to be assumed in structure determinations
from electron diffraction data; the mole fractions of the syn-
syn conformers were refined to values of 0.49(7) and 0.52(4)
for bis(dimethylstibanyl)oxane (1) and -sulfane (2), respec-
tively [11, 12].
In this context one should emphasize that research on the
modifications of antimony(III) sulfide is still being contin-
ued. To begin with, the structure of synthetic stibnite was re-
determined by èukaszewicz et al. [5] at 320 K on the basis of
the acentric space group Pmn21, since physical properties
such as the dielectric permittivity and the pyroelectric effect
had been interpreted to indicate diffuse phase transitions at
about 420 and 300 K as well as the absence of a center of
symmetry at lower temperatures in both natural and melt-
grown crystals of antimony(III) sulfide, respectively. How-
ever, with regard to space group Pnma only an insignificant
improvement of the R-index from 0.0311 to 0.0301 could be
achieved. One year before, a completely different, previously
unknown structure had been published [6] for a mineral
from Andra Pradesh, India, which, remarkably, crystallizes
in dark grey needles as well. Heating a coprecipitate of anti-
mony(III) oxide and sulfide with a saturated solution of so-
dium carbonate in a sealed tube for three days at 250 °C re-
sulted in the formation of a few bronze-colored crystals; the
x-ray structure analysis revealed that the compound Sb10S15,
a lead-free analogue of the mineral fuÈloÈppite (Pb3Sb8S15),
had been isolated [7]. Without doubt, from a structural as
well as a preparative point of view both results do need a de-
tailed substantiation. Furthermore, it has been reported [8]
that the diffraction patterns of commercially available or-
ange antimony(III) sulfide do not match that obtained from
the black modification. Finally, elucidating the structure of
the orange form, which is precipitated by hydrogen sulfide
from aqueous solutions, turned out to be extremely difficult
[9, 10].
Now we report the results of crystal structure analyses
of compounds 1 and 2 and discuss structural features
that are in common with the organoelement species
and the inorganic solids valentinite and stibnite. Since
knowledge of the atomic arrangements in these two
minerals is not believed to be widespread, for a better
comparison elaborate representations of the crystal
structures and detailed descriptions are given in order
to substitute abstract projections and simplified fig-
ures which are found in previous publications ([3, 4];
[10], p. 239) and monographs [14±16].
Experimental Section
Preparation. Bis(dimethylstibanyl)oxane (1) was first iso-
lated in 1925 by Morgan and Davies [17] as a colorless oil
from an alkaline hydrolysis of bromodimethylstibane, but
unfortunately preparative details were reported only very
briefly by the authors. It is also formed as an intermediate,
which undergoes further oxidation, when tetramethyldisti-
bane is exposed to air [18]. We synthesized compound 1 at
ambient temperature by adding freshly prepared bromodi-
methylstibane to an aqueous solution of sodium hydroxide
(eq. (1)) and extracting the crude product with petroleum
ether. After repeated distillation it was obtained in 60%
yield as a colorless liquid that ignites in air. The maximum
purity of only 98.5% is attributed mainly to traces of tri-
methylstibane, which was already the major by-product in
the starting material Me2SbBr. Compound 1 solidifies at a
temperature just below ±20 °C; it shows a medium solubility
in water, is miscible with many organic solvents and forms
In preceding publications [11±13] the structures and
conformational preferences of the gaseous molecules
(Me2Sb)2O (1) and (Me2Sb)2S (2) and of the congener-
ous selenium and tellurium compounds as determined
by gas electron diffraction (GED) and density func-
tional theory (DFT) calculations were reported. In or-
der to describe the different conformations of these
molecules, the torsional angles Ep±Sb±E±Sb, where
Ep stands for the assumed direction of the lone pair
1596
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607

Bis(dimethylstibanyl)oxane and -sulfane
azeotropes with tetrahydrofuran and diethyl ether. However,
we cannot confirm the description of bis(dimethylstibanyl)-
oxane (1) as a white, microcrystalline solid that is stable to-
wards oxidation [19].
F2 with full-matrix least-squares methods, utilizing the pro-
gram system SHELX-97 [21 d] and complex scattering fac-
tors of the neutral atoms [21 e, f] as included therein. Finally,
when individual anisotropic displacement parameters to all
<H2O>
2 Me2Sb±Br + 2 OH±
! (Me2Sb)2O + 2 Br± + H2O (1)
Table 1 Summary of crystal data, details of data collections
and results of structure refinements for compounds 1 and 2
1
The congenerous compound 2 was obtained from the pre-
viously reported oxidation of tetramethyldistibane with sul-
fur in benzene at 25 °C (eq. (2)) [18]; the colorless liquid iso-
lated in 96% yield solidifies to give yellow crystals with a
melting point of 29 to 31 °C. Exposure to light results in the
formation of trimethylstibane and yellow resinous products;
this decomposition is particularly rapid in organic solvents.
1
2
empirical formula
CAS registry number
formula mass (g mol±1
melting point (°C)
space group
C4H12OSb2
[73513-49-2]
319.64
C4H12SSb2
[84372-76-9]
335.70
)
< ±20
P212121
29 to 31
P6522
(No 19 [21 a])
a = 675.9(2)
b = 803.1(2)
c = 1666.8(4)
904.8
(No 179 [21 a])
a = 927.8(3)
c = 1940.9(7)
unit cell dimensions (pm)
<C6H6>
Me2Sb±SbMe2 + 1/8 S8
! (Me2Sb)2S
(2)
2
cell volume (10±30 m3)
1446.9
6
2.312
924
5.733
0.8 ´ 0.7 ´ 0.4
Z (molecules)
4
Bis(dimethylstibanyl)oxane (1) and -sulfane (2) are both ex-
tremely malodorous compounds; hence the trivial names
antimony-cacodyl oxide and sulfide are fully justified. Until
now the knowledge of their chemical reactivity was rather
poor; however, recent investigations by some of us [20] on
the behavior of these molecules versus tetracarbonyl(norbor-
nadiene)chromium resulted in the isolation of the cyclic
complexes [l2-(Me2Sb±E±SbMe2)(OC)4Cr]2 (E = O, S) and
their characterization by x-ray structure analyses. Addition-
ally, bis(dimethylstibanylsulfanyl)(methyl)stibane, one of the
decomposition products of compound 2, could be trapped as
the chelate complex [MeSb(±S±SbMe2)2](OC)4Cr.
calc. dens. q (103 kg m±3
F(000)
)
2.346
584
5.891
abs.coeff. l (102 m±1) [21 b]
crystal size (mm)
column of 0.3 mm
diameter
Siemens P3
MoKa (71.073)
±70 ± 2
Wyckoff
2.44° to 30.05°
0 £ h £ 9;
0 £ k £ 11;
±1 £ l £ 23
DIFABS [21 c]
±
diffractometer
radiation (pm)
temperature (°C)
scan type
h range
index ranges
Siemens P4
MoKa (71.073)
±100 ± 2
x/2h
2.53° to 27.52°
±1 £ h £ 11;
±12 £ k £ 10;
±25 £ l £ 25
empirical by w-scans
0.178/0.663
7261
absorption correction
min./max. transmission
reflections collected
Crystal Growth. Colorless single crystals of compound 1
were obtained in a quartz capillary of 0.3 mm diameter uti-
lizing the commercially available crystal growing device CR-
LK93 of COMRAY Analytics GmbH, D-42553 Velbert. The
sample was sealed, mounted on the diffractometer and
cooled to a temperature of ±70 ± 2 °C which is sufficiently
far below the melting point. Subsequent zone melting was
accomplished by moving the beam of a CO2 laser gradually
up and down the sample; its intensity had to be adjusted
such as to liquify a small cylindrical section only. By this pro-
cedure a single crystal of appropriate length and quality
could be grown fairly easily. Owing to a higher melting
point, suitable crystals of compound 2 were already formed
on cooling the melt slowly.
2992
independent reflections (z)
restraints/parameters (p)
2641; Rint = 0.0453 1111; Rint = 0.0873
0/69
2/37
goodness-of-fit at F2 (GoF)a) 1.099
1.197
extinction coefficient
±
0.0161(5)
0.01(7)
0.67/±0.42
abs. structure parameter
largest diff. peak and hole
±0.03(13)
1.49/±0.74
(1030 e m±3
)
R-indicesb) (I > 2r(I))
R-indicesb) (all data)
R1 = 0.042;
wR2 = 0.099
R1 = 0.052;
wR2 = 0.105
R1 = 0.021;
wR2 = 0.052
R1 = 0.022;
wR2 = 0.052
a)
b)
GoF = {Rw(F2o ± F2c)2/(z ± p)}1/2
;
R1 = R||Fo| ± |Fc||/R|Fo|;
wR2 = {R[w(F2o ± Fc2)2]/R[w(F2o)2]}1/2 with w±1 = r2(F2o) + (aP)2 + bP
(1, a = 0.0555; b = 2.850; 2, a = 0.0054; b = 1.190) and P = (F2o + 2 Fc2).
Table 2 Atomic coordinates and equivalent isotropic dis-
placement parameters (pm2)
The position (x; 1 ± x; 1/12) of the sulfur atom S located
on a twofold rotation axis is designated by the Wyckoff let-
ter b [21 a]. The Ueq value is defined as one third of the trace
of the orthogonalized Uij tensor.
Data Collections and Structure Refinements. Automated
centering of 25/27 selected reflections in
a range of
15° < h < 18°/8° < h < 13° and least-squares routines were em-
ployed to obtain the cell parameters of compounds 1 and 2.
The results as well as details of data collections and structure
refinements are summarized in Table 1. From the dimensions
of the unit cell, additional E-value statistics and systematic
absences the correct space group P212121 was derived for
bis(dimethylstibanyl)oxane (1). In the case of the sulfur
compound 2 the choice of the pair P6122/P6522 over P61/P65
was decided during the course of the structure refinement.
Furthermore, for the crystal under inspection the assumption
of space group P6522 could be justified by an absolute struc-
ture parameter of 0.01(7) and an R1-index of 0.0211 ± in
contrast to corresponding results of 1.00(8) and 0.0223 ob-
tained with space group P6122.
(Me2Sb)2O (1)
x ´ 104
y ´ 104
z ´ 104
Ueq ´ 10±1
Sb1
Sb2
O
C1
C2
C3
C4
3644(1)
5079(1)
4650(10)
5248(16)
966(14)
6795(14)
2203(15)
8676(1)
6550(1)
8714(7)
10822(14)
10020(16)
5398(13)
5629(15)
9325(1)
7521(1)
8205(3)
9750(6)
9088(6)
8448(6)
7840(8)
43(1)
41(1)
47(1)
60(2)
61(3)
54(2)
62(3)
(Me2Sb)2S (2)
x ´ 104
y ´ 104
z ´ 104
Ueq ´ 10±1
Sb
S
C1
C2
7352(1)
5147(1)
7247(8)
9341(7)
4906(1)
4853(1)
6573(8)
6801(8)
78(1)
833
±660(2)
681(2)
20(1)
21(1)
45(1)
46(1)
After the usual Lp-corrections, phases were determined
with statistical methods and the structures were refined on
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607
1597

H. J. Breunig, E. Lork, R. RoÈsler, G. Becker, O. Mundt, W. Schwarz
heavier atoms and absorption corrections, which were cho-
sen differently for both data sets (Table 1), had been applied,
the positions of the hydrogen atoms could be refined by
means of a riding model and with a common isotropic dis-
placement factor for each (1) or all (2) methyl groups.
Thereafter, the final difference Fourier maps showed largest
difference peaks and holes of 1.49/±0.74 ´ 1030 and 0.67/
±0.42 ´ 1030 e m±3, respectively. Atomic coordinates and
equivalent isotropic displacement parameters of the heavier
atoms are given in Table 2; bond lengths, bond angles and
torsional angles are compiled in Table 3. With the exception
of Fig. 6 b [21 g] all structural illustrations were prepared by
means of the XP program incorporated into the SHELXTL
package [21 h].
The crystallographic data ± excluding structure factors ±
have been deposited with the Cambridge Crystallographic
Data Centre, receiving the CCDC numbers 124951 (1) and
124952 (2). Copies of the data can be obtained free of
charge on application to The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk).
groups of neighbouring molecules. As expected from
the different coordination numbers of the two di-
methylstibanyl fragments, the Sb±O distances within a
single molecule are not uniform. Whereas the bond
not involved in the chain is found to be nearly as short
as in the gaseous state (198.8(5) vs. 197.6(14) pm [11]),
the other is elongated to a value of 209.9(6) pm (see
below).
Unlike species 1 the molecules of bis(diphenylstib-
anyl)oxane [22] adopt the syn-syn conformation in the
solid state so that quite obviously an analogous zigzag
arrangement cannot be formed. Furthermore, when in
cyclic complexes such as ([l2-(H5C6)2Sb±O±Sb-
(C6H5)2]LnM)2 (LnM = (OC)4Cr [23], (OC)2Ni [24])
the antimony atoms of this compound are coordinated
to transition metal carbonyl fragments, a slight but sig-
nificant shortening of the mean Sb±O distance from
197.1 to 195.5 and 194.3 pm, respectively, is ascer-
tained. Since the same observation has been reported
recently for the analogous bis(dimethylstibanyl)oxane
complex ([l2-(Me2Sb±O±SbMe2)](OC)4Cr)2 (198.8 to
195.3 pm [20]), we assume that the shift of electron
density from antimony to the metal atom enhances
the positive charge at the pnicogen atom so that in
spite of its now higher coordination number the length
of the a priori polar Sb±O bond decreases. A similar
mean Sb±O bond length of 196.4 pm [25 a] was deter-
mined for the adduct (F2Sb)2O ´ 2 (H2N)2C=O [25];
but in our opinion this compound is not appropriate
as a comparison.
Results and Discussion
Bis(dimethylstibanyl)oxane (1). The x-ray structure
determination of compound 1 shows the solid to be
built up of bent bis(dimethylstibanyl)oxane molecules;
they are arranged in zigzag chains along [010] via
short intermolecular Sb ´ ´ O contacts between the cen-
tral oxygen atom and only one of the two dimethylstib-
anyl moieties (Fig. 1). This type of association gives
rise to a molecular conformation that is close to syn-
anti with torsional angles Ep1±Sb1±O±Sb2 and
Ep2±Sb2±O±Sb1 of 15.7° and 177.9° (Table 3), respec-
tively, and avoids steric hindrance between the methyl
The intermolecular contact O ´ ´ Sb2', the length of
which remains far below the sum of the corresponding
van der Waals radii (258.5 vs. 370 pm [26 a]), and the
longer bond O±Sb2 form the backbone of the infinite
zigzag chain; its conformation is best characterized by
a torsional angle Ep2±Sb2±O ´ ´ Sb2' of 7.9° (Table 3).
1
In the sequence 1[±O(Sb) ´ ´ Sb±O(Sb) ´ ´ Sb] two struc-
tural features deserve special attention, namely, with
an angle of 173.5° an almost complete linearity of the
fragment O ´ ´ Sb2'±O' and, with an angular sum of
359.3°, the trigonal planar environment of the oxygen
atom. Regarding the linearity, the atom Sb2 is located
in the center of an octahedron in which two cis-re-
lated vertices have been removed; usually such an ar-
rangement is referred to as w-trigonal bipyramidal1)
with the methyl groups and the non-bonding electron
pair in equatorial and both oxygen atoms in axial
positions (Fig. 2 a). The bonding situation in the
O±Sb ´ ´ O fragment may best be explained in terms of
1)
As the s-character of the lone electron pair at antimony is
Fig. 1 Molecular model of bis(dimethylstibanyl)oxane (1)
and the association of molecules to form zigzag chains along
[010]
Weak intermolecular Sb ´ ´ O interactions are indicated by
thin dashed lines; primed and unprimed atoms are symmetry
related by a twofold screw axis along (0.5; y; 0.75).
considered to be high, we make use of both possibilities to de-
scribe its coordination sphere. During the last three decades
several reviews on this subject have been published [27 a, b]
and detailed physical studies in this field, including antimo-
ny(III) sulfide, selenide and telluride, have been reported, for
example, by Olivier-Fourcade and others [27 c].
1598
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607

Bis(dimethylstibanyl)oxane and -sulfane
Table 3 Individual bond lengths (pm), bond angles and torsional angles (deg) of bis(dimethylstibanyl)oxane (1) and -sulfane
(2) from crystal structure analyses (a) and a comparison of selected x-ray diffraction (XRD) parameters with data from gas
electron diffraction (GED) and density functional theory (DFT) calculations (b)
In addition to structural data the table contains symmetry operations for primed and starred atoms. Individual and mean val-
ues used for the comparison of part b) are given in italics. The symbol Ep stands for the assumed direction of the lone electron
pair at antimony (see text).
a) Individual values of compounds 1 and 2
1
O±Sb1
O±Sb2
198.8(5)
209.9(6)
215.5(10)
214.4(10)
214.3(10)
214.7(11)
258.5
Sb1±O±Sb2
O±Sb1±C11
O±Sb1±C12
C11±Sb1±C12
O±Sb2±C21
O±Sb2±C22
C21±Sb2±C22
123.0(3)
97.1(3)
96.2(3)
94.8(5)
92.3(3)
91.5(3)
99.4(5)
Sb1±O ´ ´ Sb2'
Sb2±O ´ ´ Sb2'
O ´ ´ Sb2'±O'
O ´ ´ Sb2'±C21'
O ´ ´ Sb2'±C22'
Sb2±O±Sb1±C11
Sb1±O±Sb2±C21
Sb2±O±Sb1±C12
Sb1±O±Sb2±C22
118.5
117.8
173.5
85.3
C21±Sb2±O ´ ´ Sb2'
C22±Sb2±O ´ ´ Sb2'
138.3
±122.5
Sb1±C11
Sb1±C12
Sb2±C21
Sb2±C22
O ´ ´ Sb2'
symmetry operation:
(') = (±x + 1; y + 0.5; ±z + 1,5)
82.9
148.0
±51.7
±116.7
47.5
characteristic mean values:
Sb±C
O±Sb1±C
214.7
96.7
O±Sb2±C
O ´ ´ Sb2'±C 84.1
91.9
2
S±Sb
249.8(1)
214.5(5)
215.1(5)
316.4
Sb±S±Sb'
S±Sb±C1
S±Sb±C2
C1±Sb±C2
92.35(5)
94.2(2)
93.2(1)
95.9(3)
S* ´ ´ Sb±C1
S* ´ ´ Sb±C2
S±Sb ´ ´ S*
Sb±S ´ ´ Sb''
Sb±S ´ ´ Sb'''
Sb'' ´ ´ S ´ ´ Sb'''
Sb'±S±Sb±C1
85.6
83.7
176.8
109.9
134.0
83.4
symmetry operations:
Sb±C1
Sb±C2
Sb ´ ´ S*
(*) = (x ± y + 1; x; z ± 0.166);
(') = (±y + 1; ±x + 1; ±z + 0.166);
('') = (x ± y; ±y + 1; ±z);
(''') = (y; ±x + y + 1; z + 0.166)
characteristic mean values:
Sb±C 214.8
S±Sb±C
93.7
173.5
Sb'±S±Sb±C2
±90.5
b) Selected x-ray diffraction parameters in comparison with data from GED and DFT
1 (E = O)
2 (E = S)
XRD
GED [11]
DFT [11]
XRD
GED [12]
DFT [11]
E±Sb
198.8(5)
214.7
96.7
94.8(5)
123.0(3)
197.6(14)
214.4(9)
92.3(6)
97.8(18)
122.3(16) (syn-syn)
131.1(18) (syn-anti)
±28(4) (syn-syn)
[0; 180] (syn-anti)
±
204.3
219.4
95.2
93.5
119.0 (syn-syn)
127.7 (syn-anti)
±18.6 (syn-syn)
0; 180 (syn-anti)
±
249.8(1)
214.8
93.7
95.9(3)
92.35(5)
241.4(4)
213.2(3)
92.6(6)
95(3)
98.7(5) (syn-syn)
104.5(5) (syn-anti)
±
248.9
220.0
94.6
94.0
101.4 (syn-syn)
107.4 (syn-anti)
±
Sb±C (mean)
E±Sb±C (mean)
C±Sb±C
Sb±E±Sb
Ep1±Sb1±O±Sb2
Ep2±Sb2±O±Sb1
Ep±Sb±S±Sb'
15.7
177.9
±
±
±
±
±
41.5
±33(4) (syn-syn)
[0; 180] (syn-anti)
0.0 (syn-syn)
0; 180 (syn-anti)
a strongly asymmetric four-electron three-center bond
utilizing the rSb±O and r* orbitals. As for the envi-
Sb±O
ronment at oxygen the bond angle Sb1±O±Sb2 is
found to be slightly smaller than the corresponding
parameter determined or calculated for the gaseous
molecule in its syn-anti conformation (123.0(3)° vs.
131.1(18)° or 127.7°; Table 3). Furthermore, the solid
state structure of compound 1, though characterized
by three different Sb±O distances, anticipates the
completely symmetric situation realized in the star-
shaped cation of tris(dimethylstibanyl) oxonium bro-
mide (Sb±O 211.6(1) pm), which has been isolated
and characterized by some of us a few years ago [28].
Comparison with Valentinite. The intermolecular
interactions in solid bis(dimethylstibanyl)oxane (1)
have to be ascribed to the field of secondary bonding
([29, 30]; see also [31]) ± a phenomenon which is ob-
served frequently with antimony compounds. In order
to allow a reasonable interpretation of the special fea-
tures discussed above, we inspected the known struc-
ture of valentinite (AntimonbluÈte, Weiûspieûglanz)
[3], the orthorhombic modification of antimony(III)
oxide, for similarities. As can be seen in Fig. 3, the
mineral is built up of infinite Sb±O double chains
Fig. 2 Different coordination spheres of the antimony
atoms in the solid-state structures of bis(dimethylstib-
anyl)oxane (1) and valentinite
The figure shows (a) an octahedron with two cis-related
vertices removed (w-trigonal bipyramid) and (b) a square
pyramid (w-octahedron). Dashed open lines indicate weak
Sb ´ ´ O interactions. Except for the symmetry-related atom
O1''' (x; 0.5 ± y; 0.5 + z) the labeling of atoms has been
adopted from Table 3 and publication [3b], respectively.
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607
1599

H. J. Breunig, E. Lork, R. RoÈsler, G. Becker, O. Mundt, W. Schwarz
Fig. 3 Stereoscopic view of oxygen-
bridged Sb±O double chains aligned
along [001] in the structure of valen-
tinite, the orthorhombic modification
of antimony(III) oxide
The figure is based on atomic coor-
dinates given in the literature [3 b].
Antimony and oxygen atoms are rep-
resented by large and small circles,
respectively; solid lines stand for
Sb±O bonds, thin dashed ones for
weak Sb ´ ´ O interactions (see Fig. 2 b).
To illustrate the linkage between dif-
ferent layers, four translationally iden-
tical Sb±O units, two of an upper- (*)
/
and two of a lower-lying double chain
(*), are additionally shown.
\
along [001], the opposing antimony atoms of which
are bridged by oxygen in such a way that strongly
puckered eight-membered rings are formed. Consider-
ing the three different bond lengths between antimony
(Sb) and the two crystallographically independent
oxygen atoms O1 and O2 in the bridge (O1±Sb
202.3(4) pm) and in the single chain (O2±Sb 201.9(6),
O2'''±Sb 197.7(7) pm [3b]; Fig. 2 b), respectively, one
finds only two to deviate significantly, by about 8 and
3 pm, from the distances O±Sb2 of 209.9(6) and
O±Sb1 of 198.8(5) pm in compound 1 (Table 3); the
third one matches almost exactly the length of the
shorter bond O±Sb1 and coincides with the value of
197.7(1) [2 c] reported for senarmontite [2], the cubic
modification of antimony(III) oxide.
In the crystal structure of valentinite two types of
secondary Sb ´ ´ O contacts are observed. Within the
aforementioned double chains the bridging oxygen
atom O1 is involved in two contacts of equal length
increasing its coordination number to (2 + 2). A sec-
ond type of Sb ´ ´ O contact is incorporated in centro-
symmetric four-membered Sb ´ ´ O±Sb ´ ´ O rings be-
tween the double chains (Fig. 3); it connects the five-
coordinate antimony atom in a strongly distorted
Fig. 4 Molecular model of bis(dimethylstibanyl)sulfane (2)
and its relationship to antimony and sulfur atoms of adjacent
species
square
pyramidal
(w-octahedral)
environment
The weak Sb ´ ´ S interactions are indicated by dashed
open lines; the positions of symmetry related atoms may be
obtained from the values of Table 2 by operations given in
Table 3.
(Fig. 2 b; angles between 67.0° and 149.1°) with the trig-
onal-planar coordinate oxygen atom O2. In a manner
similar to compound 1, its angles sum up to 357.3°;
here, however, with values of only 149.1° and 139.2°
at antimony the sequences O1±Sb ´ ´ O2@ and
O2±Sb ´ ´ O1'@ deviate considerably from linearity.
Nevertheless, the different Sb ´ ´ O contact distances
within (261.9 pm) and between the double chains
(251.8 pm) both approach closely the related value
(258.5 pm) of bis(dimethylstibanyl)oxane (1).
Bis(dimethylstibanyl)sulfane (2). As can be taken
from Fig. 4, the molecules of compound 2 differ from
those of bis(dimethylstibanyl)oxane (1) not only by an
almost syn-syn conformation exhibiting symmetry-re-
1600
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607

Bis(dimethylstibanyl)oxane and -sulfane
lated torsional angles Ep±Sb±S±Sb' and Ep'±Sb'±S±Sb
of 41.5° (Table 3), but also by a totally different pack-
ing and an increase in coordination numbers. They
change from (2 + 1) for oxygen to (2 + 2) for sulfur;
furthermore, the antimony atom of every dimethylstib-
anyl group is now linked to two chalcogen atoms. As
a consequence, instead of a one-dimensional chain in
the oxygen derivative 1 a three-dimensional network
is formed (see below).
As for the intermolecular Sb ´ ´ S contacts, which are
responsible for the unique molecular arrangement of
compound 2, the pertinent angles Sb ´ ´ S ´ ´ Sb and
Sb±S ´ ´ Sb range from 83.4° to 134.0°; together with
the angle Sb±S±Sb' already discussed above they de-
fine a strongly distorted tetrahedron at sulfur. Quite
obviously the extreme variation of these values is to a
great extent brought about by the molecular packing
(see below). At 316.4 pm the two symmetry-related
secondary Sb ´ ´ S bonds [29, 30] are found again to be
by far shorter than the corresponding sum of van der
Waals radii (400 pm [26 a]). Since in our opinion the
high affinity of antimony for sulfur is evidently dem-
onstrated by the formation of an 1 : 1 adduct2) be-
tween cyclo-octasulfur and antimony(III) chloride
[33], its Sb ´ ´ S distances were supposed to be appro-
priate for a comparison; however, at 333 and 349 pm
they are rather long with respect to bis(dimethylstib-
anyl)sulfane (2). Furthermore, for the following com-
plexes of cyclic thioethers which were selected from a
larger number of compounds the values given in
parentheses have been reported:
With the two sulfur atoms S and S* in axial and the
carbon atoms C1 and C2 of two methyl groups as well
as the non-bonding electron pair in equatorial sites,
the coordination sphere at antimony is again de-
scribed as an octahedron with two cis-related vertices
removed or as a w-trigonal bipyramid. At 249.8(1) pm
the length of the two symmetry-related S±Sb bonds
slightly exceeds the Schomaker-Stevenson corrected
sum of covalent radii (244 pm [26 c]) and to a
greater extent the value of 241.4(4) pm already deter-
mined by electron diffraction for the gaseous molecule
[12]. In our opinion this elongation has to be corre-
lated with the higher coordination number of sulfur in
the solid (see below). For comparison, in the com-
pounds (H5C6)2Sb±S±Sb(C6H5)2 ® Cr(CO)5 [23] and
[MeSb(±S±SbMe2)2](OC)4Cr [20] the uncomplexed
parts of the two stibanylsulfane ligands show S±Sb dis-
tances of 244.6(1) and 243.3(1) pm, whereas coordina-
tion of the antimony atoms is accompanied by a short-
ening of the adjacent S±Sb bonds to values of 240.2(1)
and 241.2(1) pm, respectively. Since similar bond
lengths of 242.1(2) and 242.4(2) pm have been re-
ported recently by some of us [20] for the cyclic com-
plex [l2-(Me2Sb±S±SbMe2)(OC)4Cr]2, we are convinced
that the interpretation of this shortening already given
above for the related oxygen compounds holds for the
stibanylsulfane complexes as well. In contrast, poly-
meric dimethylstibanyl(dimethylthiophosphoranyl)sul-
1,3,5-trithia-cyclo-hexane ´ SbCl3 (326 pm) [35 a],
1,4-dithia-cyclo-heptane ´ SbCl3 (313 to 340 pm) [35b],
1,4,7-trithia-cyclo-nonane ´ SbCl3 (316 to 341 pm) and
1,4,7,10,13,16-hexathia-cyclo-octadecane ´ 2 SbCl3 (297 to
346 pm) [36].
The Sb±C bond lengths of compounds (1) and (2), although
associated with relatively high standard deviations, vary only
slightly from 214.3(10) to 215.5(10) pm and 214.5(5) to
215.1(5) pm, respectively (Table 3); the mean corresponds
fairly well to the sum of covalent radii (218 pm [26 a]). As
far as the bond angles at antimony are concerned, only in
the oxygen derivative 1, which is characterized by two differ-
ent dimethylstibanyl groups, a small but significant effect of
intermolecular association can be recognized. Whereas at
the antimony atom Sb1, which is not involved in secondary
bonding (Fig. 1), the angles C±Sb±C and O±Sb±C are found
to be quite uniform (94.8(5)° to 97.1(3)°), the corresponding
values of the second group vary from 91.5(3)° or 92.3(3)°
to 99.4(5)°; in our opinion the increase of the angle
C21±Sb2±C22 is caused by the relatively short O' ´ ´ Sb2 con-
tact of 258.5 pm. As a result of the by far longer Sb ´ ´ S con-
tacts (316.4 pm), in compound 2 all bond angles at antimony
lie in a narrow range of 93.2(1)° to 95.9(3)°.
fane [32] exhibits
255.5(2) pm.
a much longer distance of
The formal replacement of oxygen for sulfur is ac-
companied by a drastic change of the corresponding
bond angle from 123.0(3)° in compound 1 to 92.35(5)°
in compound 2 (Table 3). Similarly, for the gaseous
molecules with syn-syn conformation Sb±O±Sb and
Sb±S±Sb angles of 122.3(16)° and 98.7(5)°, respec-
tively, were determined by electron diffraction. This
decrease of the central angle is a phenomenon gener-
ally observed when in congenerous compounds a pni-
cogen or chalcogen atom of either the second or the
third period is bound to two less electronegative ele-
ments. In the compounds discussed here, the differ-
ences in bond angles of 30.7° and mean bond lengths
of 45.5 pm balance each other to such an extent that
both the intramolecular Sb ´ ´ Sb contacts adopt equal
lengths of 359.2 and 359.3 pm; these values are consid-
erably below twice the van der Waals radius of anti-
mony (440 pm [26 a]).
Salient features in the crystal structure of compound 2
(Fig. 5) are double helices generated by 65 screw axes
along [001] and built up of alternating short S±Sb
bonds (249.8(1) pm) and longer Sb ´ ´ S* contacts
(316.4 pm); remarkably, there is no direct connection
between the individual chains. As they are symmetry-
related by twofold rotation axes in, for example,
(2x ± 1; x; 5/12), both helices are left-handed but display
a phase shift of c/2 and, with respect to the 65 screw
2)
As the structure of the adduct SbI3 ´ 3 S8 [34] is governed
by intermolecular S ´ ´ I and Sb ´ ´ I interactions, this compound
should not be chosen for a comparison.
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607
1601

H. J. Breunig, E. Lork, R. RoÈsler, G. Becker, O. Mundt, W. Schwarz
Fig. 5 Crystal
structure
of
bis(dimethylstibanyl)sulfane (2)
in stereoscopic view
To illustrate the topological
relationships as clearly as possi-
ble, a simple wire model has
been applied, but for three single
helices, which are discussed at
some length in the text, the sul-
fur and antimony atoms, the
S±Sb bonds and the Sb ´ ´ S con-
tacts are highlighted as small and
large circles, thick solid lines
(sticks) and solid dashed lines,
respectively. Carbon atoms are
not shown, with the exception of
the molecule referring to the
asymmetric unit (Table 2).
Fig. 6 Crystal structure of bis(dimethylstibanyl)sulfane (2) viewed along [001]
a) Parallel projection based on Fig. 5. One should note that only hexagons formed by the antimony atoms (large circles)
give rise to a honeycomb-like pattern.
b) Simplified representation generated with the program DIAMOND [21 g]. The illustration shows only vertex-sharing SSb4
tetrahedra; the hexagonal channels contain the methyl groups (see text).
axes, a reverse sequence of S±Sb bond and Sb ´ ´ S con-
tact. Since, with an angle of 176.8° at the antimony
atom of the (1 + 1)-coordinate dimethylstibanyl group,
the array S±Sb ´ ´ S* does not deviate significantly from
linearity, the rather large Sb±S ´ ´ Sb''' value of 134.0° at
the (2 + 2)-coordinate sulfur atom is almost exclusively
responsible for the kink within a helix. Therefore, its
pitch can be described by a torsional angle of ±36,4° be-
tween four successive sulfur atoms and the cross-section
of the double helices approximates a regular hexagon.
Indeed, hexagonal tubes as spanned, for example, by
the antimony atoms (Fig. 6 a) and their honeycomb-like
pattern (Fig. 6 b) become particularly obvious when the
crystal structure is viewed along the 65 screw axes. In
the latter representation the heavy-atom framework is
depicted as an arrangement of distorted vertex-sharing
SSb4 tetrahedra with the sulfur atoms hidden at the cen-
ters. The methyl groups are located inside these hexago-
nal tubes (Fig. 6 a), but owing to the twofold rotation
axes the two sets of a molecule are found in different
interiors. In this context one should point out that such
a structural separation of the more inorganic and the
more organic parts of a molecule has frequently been
observed with organoelement compounds.
1602
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607

Bis(dimethylstibanyl)oxane and -sulfane
or 1,12-dibromododecane derivative [40], optically active di-
lactylamide, the molecules of which are arranged in infinite
chains by hydrogen bonds [41], or even bis(g5-cyclo-penta-
dienyl)bis(g1-cyclo-pentadienyl)titanium, the structure of
which does not show any discernible intermolecular interac-
tions [42]. With respect to the much smaller number of inor-
ganic representatives, the oft studied complex Cs[CuCl3] [43]
and the isostructural fluorides AuF3 [44] and AgF3 [45] have
to be mentioned first; their helical chains are built up by
strongly distorted face-sharing octahedra of chloride anions
surrounding the Cu2+ cations [43 b] and of planar, only
slightly distorted squares joined by a symmetrical sharing of
two cis-related fluoride ligands, respectively. Furthermore,
the inclusion compound Sn[Ta2Cl9]2 ´ C6H6 isolated from the
reduction of tantalum(V) chloride with tri-n-butylstannane
also belongs to this group; in the rather complicated struc-
ture the [Ta2Cl9]± anions are arranged in chains coiling
around the 65-screw axis [46].
In an individual 65 helix, each bis(dimethylstib-
anyl)sulfane molecule contributes only one antimony
atom to its backbone, whereas the remaining di-
methylstibanyl groups point outwards (Fig. 5). Since,
however, the two halves of a single molecule are sym-
metry-related by a twofold rotation axis, each double
helix is connected with a total of six adjacent ones by
sharing the sulfur atoms that are arranged at the axial
edges of the hexagonal prisms (Fig. 6 a). As a conse-
quence, the cross-linking of double helices gives rise
to different helices with a trigonal projection (Fig. 6 a);
they are right-handed though coiling around 32 screw
axes (Fig. 5). This apparent contradiction is readily re-
solved when the inherent symmetry of such a helix is
carefully inspected. Indeed, owing to the sequence
1
1[Sb±S±Sb ´ ´ S ´ ´ ], in which a pair of S±Sb bonds is
followed by a pair of Sb ´ ´ S contacts each, the 32
screw axis by itself correlates only every second sulfur
atom so that the resulting conjunction line ± though
chemically meaningless ± describes a left-handed he-
lix. Finally, the two subsets of sulfur atoms are symme-
try-related by 21 screw axes perpendicular to [001].
Within the three-dimensional net thus formed,
strongly puckered twelve-membered macrocycles with
the sequence [Sb±S±Sb ´ ´ S ´ ´ Sb±S ´ ´ ]2 can be identi-
fied as shortest circuits.
However, to our knowledge the borophosphates
MI(H2O)2MII[BP2O8] ´ H2O are the only class of inorganic
compounds with vertex-sharing EO4 tetrahedra (E = B, P),
for which space group P6122 has been reported so far [47].
Their framework {(MI[BP2O8])2±} features double helices
1
1
which are built up of MI cations on the one hand and of al-
ternating BO4 and PO4 moieties on the other. Since the
channels formed are filled with water molecules, the struc-
tures of the borophosphates show a relatively high degree of
similarity to that of bis(dimethylstibanyl)sulfane (2), the
channels of which contain the methyl groups.
From a topological point of view the arrangement
of sulfur and antimony atoms in compound 2 is identi-
cal to that of silicon and oxygen in the high tempera-
ture modification of quartz (b-quartz) [37]. Since,
however, the silicon atoms in this structure occupy po-
sitions of site symmetry 222 and all Si±O bonds are of
equal length, translational identity is already achieved
after one turn (360°) of the trigonal single helices and
after half a turn (180°) of the hexagonal double he-
lices (cf. Fig. 5). In terms of symmetry, P6422, the
space group of b-quartz, constitutes a minimal klassen-
gleiche supergroup of index 2 in relation to P6522, the
space group of bis(dimethylstibanyl)sulfane (2), the
group-supergroup transition being associated with a
bisection of the lattice parameter c and a transforma-
tion of the left-handed 32 screw axes in space group
P6522 into its right-handed counterpart 31 in P6422.
As already derived from the symbol of the achiral
space group P63/mmc, the structural relationships be-
tween b-tridymite [38] and compound 2 are by far less,
and we have therefore not attempted a detailed analy-
sis.
Comparison with Stibnite. As reflected by the German
mineral name ªGrauspieûglanzº (Spieû means spear),
1
the structure of stibnite [4] features [Sb4S6] ribbons
1
aligned along [010] (Fig. 7). If, as a first approxima-
tion, all direct Sb±S bonds and contacts within these
entities (Fig. 8 a) are taken as topologically equivalent,
the ribbons may be described as zigzag chains of face-
sharing Sb4S4-cubes, the outer antimony atoms of
which are bridged in pairs by additional sulfur atoms.
In other words, the ribbons are regarded as sections of
the rock salt (halite) structure (Fig. 8 b). This view is
Some Remarks on the Space-Group of Compound 2. Follow-
ing an inspection of crystallographic databases [39], the en-
antiomorphous space groups P6122 and P6522 appear more
frequently than originally supposed. In the field of organic
and organoelement compounds, including metal complexes
mostly with large organic ligands, approximately fifty struc-
tures were reported. The compilation includes references to
the well-known high-temperature modifications of alkane/
urea inclusion compounds such as the 1,10-dibromodecane
1
Fig. 7 Almost hexagonal close packing of [Sb4S6] ribbons
1
in the crystal structure of stibnite (space group Pnma)
In contrast to the following more detailed representation
of Figure 8 c no distinction between primary and short sec-
ondary (coordinative) Sb±S bonds is made and in addition
distances exceeding 285.4 pm are not shown.
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607
1603

H. J. Breunig, E. Lork, R. RoÈsler, G. Becker, O. Mundt, W. Schwarz
for example justified by the observation that sodium
dithioantimonate(III) (NaSbS2) [48] adopts an or-
dered variant of that structural type.
If in contrast to this generalized approach the weak Sb ´ ´ S
contacts within the ribbons are totally ignored, the rather
complicated framework may be described alternatively by
two sequences of Sb2S2 quadrangles, the common vertices of
which are occupied by the antimony atoms Sb2 (Fig. 8 a).
Owing to a center of inversion in (0.5; 0.5; 0.5) the sequences
are found to be shifted relative to each other so that short
bonds of 245.6 pm between the antimony atoms Sb2 of one
layer and the so-called inner sulfur atoms S2 of the second
layer become possible. The arrangement depicted so far is
completed by two Sb1±S1 zigzag chains which are connected
to the outer sulfur atoms of each sequence by nearly perpen-
dicular Sb1±S3 bonds. Remarkably, the structural feature of
vertex-sharing quadrangles with square pyramidally (w-octa-
hedrally) coordinate antimony atoms is observed for exam-
ple in the polymeric [Sb2S54±] anions of the thioantimona-
1
1
te(III) Sr3Sb4S9 ([49]; see also [50], p. 267).
When the structures of stibnite and rock salt (Fig. 8)
are compared to each other in detail with respect to
the individual S±Sb distances as listed in Table 4, con-
siderable deviations from an idealized arrangement
become obvious. Indeed, significant distortions are ex-
pected since the Allred-Rochow electronegativities
[26 b] of antimony (1.82) and sulfur (2.44) differ by
only 0.62 units and the bonding situation has therefore
to be considered as mostly covalent3). As a conse-
quence, the antimony and sulfur atoms are a priori ex-
pected to be found three- and two-coordinate in a trig-
onal pyramidal and bent arrangement, respectively,
but only in case of the outer antimony (Sb1) and the
bridging sulfur atom S1 (Fig. 8 a) an unambiguous as-
signment of three or two primary bonds is possible
(Table 4). However, any attempt to assign localized
two-center two-electron bonds in the tetragonal pyra-
midal (w-octahedral)4) coordination sphere of Sb2
(c. n. = 1 + 2 + 2) and the approximately trigonal pyra-
midal environments of S2 and S3 (c. n. = 1 + 2) would
require an arbitrary discrimination between primary
and short secondary (coordinative) bonds. Despite
these restrictions, however, for didactic reasons such
a representation of the stibnite structure has been in-
corporated in Fig. 8.
Fig. 8 Relationships between the stibnite and the rock salt
structure
1
1
a) Centrosymmetric section of a [Sb4S6] ribbon aligned
along [010] as shown in Fig. 7 at the center of the unit cell.
S±Sb bonds up to a length of 285.4 pm and contacts in a
range from 311.0 to 418.9 pm are depicted as solid and thin
dashed lines, respectively. For the coordinates of labeled
atoms see Table 4.
In order to classify the different distances, we car-
ried out a bond-valence analysis (Table 4) making
use of I. D. Brown's relationship [52]. Surprisingly,
the original standard value R0 for S±SbIII and
S±SbV bonds of 245 pm afforded valence sums dif-
b) Corresponding section of an undistorted rock salt
structure. The representation of interatomic distances within
a ribbon follows part a).
c) Structure of stibnite from a covalent but more tradi-
tional point of view. In order to distinguish arbitrarily be-
tween primary and short secondary (coordinative) S±Sb
bonds, solid and dashed solid lines have been employed.
Thin dashed lines indicate longer Sb ´ ´ S contacts between
atoms of the same ribbon.
3)
One has to point out that in this approach structural rela-
tionships to metal sulfides of the same stoichiometry such as
U2S3 ([51]; see also [15]) and electronic interactions, which
can be classified as mostly ionic, are deliberately neglected.
4)
At this level of discussion weak Sb ´ ´ S contacts between
different ribbons are not taken into consideration.
1604
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607

Bis(dimethylstibanyl)oxane and -sulfane
Table 4 Bond-valence analysis of the stibnite structure
Individual bond-valences si (valence units, v. u.) were calculated for all heteronuclear ligands Li at distances Ri up to 450 pm
making use of I. D. Brown's formula si = (Ri/R0)±N [52] and the parameters (R0 = 241.6 pm; N = 6); in addition, the sum of
bond-valences is specified for each central atom Z. To obtain a coherent set of atoms, we transformed the published coordi-
nates [4 c] and changed the numbering scheme accordingly; for clarity, ligands of adjacent ribbons were placed in parentheses.
One should note that Wang and Liebau [27 b] have reported a brief bond- valence analysis of stibnite applying, however, a
modified approach.
Z
Li
Coordinates and
Ri
si (v. u.)
Z
Li
Coordinates and
Ri
si (v. u.)
symmetry operations
symmetry operations
i
i
X
X
Sb1
0.5293; 0.75; 0.1739
si = 3.0
Sb2
0.6495; 0.25; 0.4640
si = 3.0
S3
S1
S1
S2
S2
(S1)
(S3)
x; y; z
x; y; z
252.2
254.0
254.0
311.0
311.0
316.7
364.1
0.77
0.74
0.74
0.22
0.22
0.20
0.09
S2
S3
S3
S2
x; y; z
x; y; z
x; y ± 1; z
±x + 1; ±y; ±z + 1
±x + 1; ±y + 1; ±z + 1
±x + 1.5; ±y; z + 0.5
±x + 1.5; ±y + 1; z + 0.5
±x + 1.5; ±y + 1; z + 0.5
245.6
267.8
267.8
285.4
285.4
337.3
337.3
418.9
0.91
0.54
0.54
0.37
0.37
0.14
0.14
0.04
x; y + 1; z
x; y; z
x; y + 1; z
±x + 1; ±y + 1; ±z
x ± 0.5; y; ±z + 0.5
S2a)
(S1)
(S1)
(S3)
i
i
X
X
S1
0.6251; 0.25; 0.0614
si = 1.9
S2
0.4503; 0.25; 0.3769
si = 2.1
Sb1
Sb1
(Sb1)
(Sb2)
(Sb2)
x; y; z
x; y ± 1; z
±x + 1; ±y + 1; ±z
±x + 1.5; ±y; z ± 0.5
±x + 1.5; ±y + 1; z ± 0.5
254.0
254.0
316.7
337.3
337.3
0.74
0.74
0.20
0.14
0.14
Sb2
Sb2
Sb2
Sb1
Sb1
x; y; z
245.6
285.4
285.4
311.0
311.0
0.91
0.37
0.37
0.22
0.22
±x + 1; ±y; ±z + 1
±x + 1; ±y + 1; ±z + 1
x; y; z
x; y ± 1; z
i
X
S3
0.7079; 0.75; 0.3083
si = 2.0
Sb1
Sb2
Sb2
(Sb1)
(Sb2)
x; y; z
x; y; z
x; y + 1; z
x + 0.5; y; ±z + 0.5
±x + 1.5; ±y + 1; z ± 0.5
252.2
267.8
267.8
364.1
418.9
0.77
0.54
0.54
0.09
0.04
a)
This atom is marked with an asterisk in Figure 8.
fering considerably from the expected results of 3.0
and 2.0 valence units (v. u.) for antimony and sulfur.
Therefore a slightly shorter distance R0, which at
241.6 pm is very close to the length of the S±SbIII
single bond (241.4(4) pm) in gaseous bis(dimethylsti-
banyl)sulfane (2) [12], was applied; remarkably, a sim-
ilar approach has been reported by Skowron and
Brown [53] for a series of lead thioantimonates(III).
With S ´ ´ Sb distances up to a limit of 420 pm taken
into account, our calculations resulted in coinciding
sums of 3.0 v. u. for both antimony atoms, indicating
the valences of these atoms to be completely bal-
anced ± despite of quite different coordination num-
bers of (3 + 3 + 1) and (1 + 2 + 2 + 2 + 1) for Sb1 and
Sb2, respectively.
As with numerous chalcogenoantimonates(III) [50],
an adequate explanation of the bonding situation in
stibnite is based on the finding that the valences of
trans-related bonds in the distorted octahedral and
tetragonal pyramidal (w-octahedral)4) coordination
spheres of the antimony atoms Sb1 and Sb2 (Fig. 8 a)
add to 1.0 and 0.9 v. u., respectively. According to that,
in these almost linear fragments the bonding may be
qualitatively described in terms of three-center four-
electron bonds with a differing degree of asymmetry
(Sb1, 252.2 vs. 316.7 pm, 254.0 vs. 311.0 pm; Sb2,
267.8 vs. 285.4 pm). In this context, one has to point
out that more than thirty years ago H. Krebs used sim-
ilar but not the same arguments of mesomeric pr
bonds in his famous textbook on the fundamentals of
inorganic crystal chemistry [15]. At present, the dis-
cussion of related Cl±Sb ´ ´ Cl systems should also be
taken into account [30].
With distances of 245.6, 252.2 and 254.0 pm for
Sb2±S2, Sb1±S3 and Sb1±S1, respectively, the three
shortest bond lengths of the mineral stibnite are found
in the same range as the corresponding value of
249.8(1) pm (Table 3 a) determined for solid bis(di-
methylstibanyl)sulfane (2). Since in trans position to
these bonds only weak Sb ´ ´ S interactions can be ob-
served, these four values are only slightly influenced
by a participation in three-center four-electron bonds.
However, from the corresponding valences in stibnite
(0.91, 0.77 and 0.74 v. u.; Table 4) and bis(dimethylstib-
anyl)sulfane (2, 0.82 v. u.) as well as from a compari-
son with the S±Sb bond length of only 241.4(4) pm for
compound 2 in the gaseous state (Table 3 b; [12]), a rel-
atively small but nevertheless significant influence of
weak Sb ´ ´ S interactions and hence of higher coordi-
nation numbers in the solids becomes evident. In con-
formity with these findings the contact of 311.0 pm
(0.22 v. u.), which occurs between the atoms Sb1 and
Z. Anorg. Allg. Chem. 2000, 626, 1595±1607
1605

H. J. Breunig, E. Lork, R. RoÈsler, G. Becker, O. Mundt, W. Schwarz
S2 of the same ribbon5), and higher values of 316.7
and 337.3 pm (0.20 and 0.14 v. u.) between adjacent
ribbons of stibnite correspond very well with a length
of 316.4 pm (0.20 v. u.) determined for the two second-
ary Sb ´ ´ S bonds of compound 2 by x-ray analysis. As
a consequence a sum of 1.02 v. u. is achieved even for
the organoelement species.
[2] a) R. M. Bozorth, J. Am. Chem. Soc. 1923, 45, 1621; b)
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98, 1; b) C. Svensson, Acta Crystallogr. 1974, B 30, 458.
Ï
Â
[4] a) W. Hofmann, Z. Kristallogr. 1933, 86, 225; b) S. Scav-
Ï
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W. Nowacki, Z. Kristallogr. 1972, 135, 308; d) N. V.
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Preparative Section
All operations were carried out under an argon atmosphere
with strict exclusion of air.
Â
[5] K. èukaszewicz, A. Pietraszko, J. Stepien-Damm, J. Gri-
Bis(dimethylstibanyl)oxane (1). 21.62 g (93.30 mmol) of
bromodimethylstibane were added dropwise to a stirred so-
lution of sodium hydroxide (3.92 g, 98.01 mmol) in 15 ml of
water. After two hours of further stirring at ambient tem-
perature the product was separated and the aqueous phase
was extracted with three portions of 40 ml of petroleum
ether. Product and organic solution were combined and
dried with anhydrous sodium sulfate; after removal of the
solvent at a pressure of 80 mbar, distillation of the remaining
liquid at 57.5 to 58.5 °C/7 mbar furnished compound 1 with
98.5% purity. 59.7% yield (8.9 g, 27.8 mmol).
gas, A. Kajokas, Pol. J. Chem. 1997, 71, 390 and refer-
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[9] E. Diemann, Z. Anorg. Allg. Chem. 1977, 433, 242.
Ï
Â
[10] L. Cervinka, A. Hruby, J. Non-Crystalline Solids 1982,
48, 231.
Characterization: colorless, malodorous liquid.
[11] A. Haaland, V. I. Sokolov, H. V. Volden, H. J. Breunig,
M. Denker, R. RoÈsler, Z. Naturforsch. 1997, B 52, 296.
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NMR (benzene-d6 solution). 1H (200 MHz): 0.84 ppm (s,
1JCH = 131.2 Hz, CH3); 13C{1H} (50 MHz): 13.31 ppm (s,
CH3).
Bis(dimethylstibanyl)sulfane (2). Compound 2 was pre-
pared as already described in the literature [18]. The yellow
solid melts at 29 to 31 °C to give a colorless, mobile liquid
(b. p. 65 °C/0.2 mbar).
NMR (benzene-d6 solution). 1H (200 MHz): 0.99 ppm (s,
1JCH = 133.5 Hz, CH3); 13C{1H} (50 MHz): 5.70 ppm (s,
CH3).
[14] J. Zemann,
Kristallchemie,
Sammlung
GoÈschen,
Vol. 1220/1220 a, de Gruyter, Berlin 1966, p. 133.
[15] H. Krebs, GrundzuÈge der anorganischen Kristallchemie,
Enke Verlag, Stuttgart 1968, p. 241 f.
We thank the Fonds der Chemischen Industrie, D-60329
Frankfurt, for financial support as well as Prof. Dr.
Th. Schleid, Institut fuÈr Anorganische Chemie der Universi-
taÈt Stuttgart, Prof. Dr. W. S. Sheldrick, Lehrstuhl fuÈr Analy-
tische Chemie der Ruhr-UniversitaÈt Bochum, and Prof. Dr.
B. Engelen, Fachbereich Chemie±Biologie der UniversitaÈt±
GH Siegen, for helpful discussions.
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