Dibromo-diphenyl-stannane: Isolated centrosymmetric dimers as a new structure motif for the inter-molecular association of diorganotin(IV) dihalides

Article abstract of DOI:10.1107/S0108270112012504

In the crystalline state, the low-melting title compound [common name: diphenyl-tin(IV) dibromide], [SnBr2(C6H5)2], consists of distorted tetra-hedral mol-ecules with compressed halide and enlarged carbon opening angles of 102.741 (9) and 123.53 (8)°, respectively, and Sn - C and Sn - Br bond lengths of 2.109 (2)/2.113 (2) and 2.4710 (3)/2.4947 (3) A, respectively. Inter-molecular Sn...Br inter-actions, typical for diorganotin(IV) dihalides, R 2SnHal2 (with Hal = Cl, Br, I), and sterically less demanding organic groups lead to the formation of a hitherto unknown association pattern consisting of centrosymmetric dimers with an anti-parallel orientation of the dipole moments and two weak inter-molecular Sn...Br distances of 3.8482 (3) A between one of the two Br atoms and its neighbouring Sn atom, and vice versa. The second Br atom is not involved in inter-molecular inter-actions and lies somewhat outside the association plane that, therefore, is not coplanar [inter-planar angle = 1.750 (2)°] with the tin-halide plane. The new structure motif of inter-molecular tin-halide inter-action can be classified as 2a i , which indicates the number of mol-ecules (i.e. 2) composing the oligomer, the anti-parallel orientation (i.e. a) of their dipole moments and the centre of symmetry (i.e. i) giving rise to the association pattern.

Full text of DOI:10.1107/S0108270112012504

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
Duthie, 2003; Haiduc, 2007) or metal–organic frameworks
(MOFs) (Shankar et al., 2011), but are also used in industry as
PVC stabilizers (Arkis, 2008) or catalysts (Evans & Karpel,
1985).
ISSN 0108-2701
Dibromodiphenylstannane: isolated
centrosymmetric dimers as a new
structure motif for the intermolecular
association of diorganotin(IV)
dihalides
In the gas phase, diorganotin(IV) dihalides consist of
monomeric molecules of point-group symmetry C2v with a
¨
considerable dipole moment (Lorberth & Noth, 1965) in the
Fei Ye and Hans Reuter*
direction of the twofold axis of symmetry. For dimethyltin(IV)
dichloride, Me2SnCl2 (Fujii & Kimura, 1971), and di-tert-
butyltin(IV) dichloride, tBu2SnCl2 (Belyakov et al., 1988), the
four main structural parameters (Sn—Hal, Sn—C, Hal—Sn—
Hal and C—Sn—C) were determined by electron diffraction
experiments. Deviations from a tetrahedral bond arrangement
at the Sn atom mainly result from bond-angle distortions,
which are small in the case of Me2SnCl2 (Cl—Sn—Cl =
Institut fur Chemie, Anorganische Chemie II, Universitat Osnabruck, Barbara-
¨
¨
¨
strasse 7, 49069, Osnabruck, Germany
¨
Correspondence e-mail: hreuter@uni-osnabrueck.de
Received 2 March 2012
Accepted 22 March 2012
Online 30 March 2012
t
107.5ꢂ3.9ꢀ) but considerable for Bu2SnCl2 (C—Sn—C =
In the crystalline state, the low-melting title compound
[common name: diphenyltin(IV) dibromide], [SnBr2(C6H5)2],
consists of distorted tetrahedral molecules with compressed
halide and enlarged carbon opening angles of 102.741 (9) and
123.53 (8)ꢀ, respectively, and Sn—C and Sn—Br bond lengths
118.6ꢂ4.2ꢀ and Cl—Sn—Cl = 103.1ꢂ4.5ꢀ).
In different noncoordinating organic solvents, such as
toluene or chloroform, they also represent monomeric mol-
ecules, whereas coordination compounds are formed in the
case of solvent molecules with donor atoms such as N [e.g.
N,N-dimethylformamide (DMF) or dimethyl sulfoxide
(DMSO)] as a result of Lewis base–Lewis acid adduct
formation between the solvent molecule and the diorgano-
tin(IV) dihalide unit.
˚
of 2.109 (2)/2.113 (2) and 2.4710 (3)/2.4947 (3) A, respectively.
Intermolecular Snꢁ ꢁ ꢁBr interactions, typical for diorgano-
tin(IV) dihalides, R2SnHal2 (with Hal = Cl, Br, I), and
sterically less demanding organic groups lead to the formation
of a hitherto unknown association pattern consisting of
centrosymmetric dimers with an antiparallel orientation of
the dipole moments and two weak intermolecular Snꢁ ꢁ ꢁBr
In the solid state, diorganotin(IV) dichlorides, dibromides
and diiodides with large organic residuals like tert-butyl
(tBu2SnCl2; Dakternieks et al., 1994), 2-methyl-2-phenylpropyl
[(MePhPr)PhSnBr2; Bomfim et al., 2003] or mesityl (Mes2-
SnBr2; Chandrasekhar & Thirumoorthi, 2010) are monomeric
also, with large respective carbon and small halide opening
˚
distances of 3.8482 (3) A between one of the two Br atoms and
its neighbouring Sn atom, and vice versa. The second Br atom
is not involved in intermolecular interactions and lies some-
what outside the association plane that, therefore, is not
coplanar [interplanar angle = 1.750 (2)ꢀ] with the tin–halide
plane. The new structure motif of intermolecular tin–halide
interaction can be classified as 2ai, which indicates the number
of molecules (i.e. ‘2’) composing the oligomer, the antiparallel
orientation (i.e. ‘a’) of their dipole moments and the centre of
symmetry (i.e. ‘i’) giving rise to the association pattern.
t
angles, viz. 133.1 (2) and 101.86 (5)ꢀ in Bu2SnCl2, 127.0 (1)
and 102.18 (1)ꢀ in (MePhPr)PhSnBr2, and 118.7 (2) and
100.51 (2)ꢀ in Mes2SnBr2.
The corresponding diorganotin(IV) dihalides with organic
ligands having small steric requirements, however, show a
strong tendency for intermolecular association as a result of
intermolecular tin (Lewis acid)–halide (Lewis base) inter-
actions for which such terms as ‘secondary bonding’ (Alcock
& Sawyer, 1977), ‘supramolecular architecture’ (Buntine et al.,
2003) or ‘soft–soft interactions’ (Haiduc, 2007) have been
used. Usually, these additional (sec) bonds are considerably
longer than normal (cov) ones, but shorter than van der
Comment
Diorganotin(IV) dihalides, denoted R2SnHal2 (Hal = Cl, Br, I;
R = nonfunctionalized organic groups), are easy to prepare
and versatile starting materials for the preparation of many
other diorganotin derivatives, such as alkoxides (Bradley et al.,
1978), hydrides (Ingham et al., 1960), tetraorganodistannox-
anes (Jurkschat, 2008), carboxylates (Mehrotra & Bohra,
1980) or different coordination monomers and polymers, that
are not only important in basic research for the formation of,
for example, supramolecular assemblies (Dakternieks &
Waals (vdW) contacts: d(Sn—Hal)cov < d(Snꢁ ꢁ ꢁHal)sec
<
d(Snꢁ ꢁ ꢁHal)vdW. Furthermore, they are accompanied by an
increase in the coordination number at tin from four to five or
six, resulting in a distorted trigonal bipyramid or a distorted
octahedron as the coordination polyhedron.
In the case of small organic ligands, predominantly infinite
polymeric chains are formed which we propose to term einer-
m104 # 2012 International Union of Crystallography
doi:10.1107/S0108270112012504
Acta Cryst. (2012). C68, m104–m108

metal-organic compounds
single chains following the terminology of silicates (Liebau,
1985) in order to delimit these structures from others. There
are two main structure-type families in this area: one with an
antiparallel (A) or nearly antiparallel ordering of the dipole
moments of neighbouring molecules and the other where they
are parallel (P) or nearly parallel to each other. The aristo-
types of these structure-type families (Fig. 1) are represented
by dimethyltin(IV) dichloride (Me2SnCl2; Reuter & Pawlak,
2001a) as type A and diethyltin(IV) diiodide (Et2SnI2; Alcock
& Sawyer, 1977) as type P. The less symmetrical members of
both structure-type families can be further classified according
to the symmetry elements responsible for the chain propaga-
tion. Other structure types based on an infinite polymeric
association pattern can be classified as einer-double chains or
bands (ꢀ-Cy2SnCl2; Ganis et al., 1986), zweier-single chains
(Ph2SnCl2; Greene & Bryan, 1971) or sheets (EtPhSnCl2;
Casas et al., 2003).
On the other hand, finite oligomeric association patterns are
rare. Applying the bond criteria defined above, there is only
one example of a noncentrosymmetric dimer, viz. trans-
Myr2SnCl2 (Myr = myrtanyl; Beckmann et al., 2008), with an
antiparallel orientation of the dipole moments, and one
example of a centrosymmetric tetramer (MePhSnCl2; Amini et
al., 1987), also with an antiparallel orientation of the dipole
moments.
(I) is a colourless low-melting solid (m.p. 309–311 K) that
can easily be prepared (Chambers & Scherer, 1926) from
commercially available tetraphenylstannane and bromine
using carbon tetrachloride as solvent. Yields are usually
moderate (’35%) because of the formation of the side
products bromotriphenylstannane and bromobenzene.
The asymmetric unit of (I) (Fig. 2) consists of one molecule
of local point-group symmetry C1. Both phenyl groups are
almost planar [maximum deviation from the least-squares
˚
˚
plane = ꢂ0.002 (2) A for the C11–C16 ring and ꢂ0.003 (2) A
for the C21–C26 ring] and bond lengths within the phenyl
˚
groups, covering the range 1.375 (4)–1.395 (3) A, with a mean
˚
value of 1.385 (7) A, are as expected (Allen et al., 1987).
Distortions of the bond angles within the organic groups are
small and in the range 119.1 (2)–120.9 (2)ꢀ; an ipso effect
(Domenicano et al., 1983) is not recognizable, but the Sn atom
˚
lies significantly outside [0.038 (3) and ꢃ0.044 (3) A] the least-
squares planes through both phenyl groups. Both Sn—C
˚
bonds (Table 1) are very similar [mean value = 2.111 (3) A]
and comparable with other tin–phenyl bond lengths with tin in
a predominantly tetrahedral environment, such as in
triphenyltin(IV) bromide (Ph3SnBr; Preut & Huber, 1979),
˚
where a mean value of 2.114 (8) A (T = 293 K) was found.
Both Sn—Br bond lengths are also very similar [Á =
˚
0.0237 A and mean value = 2.483 (17) A] but considerably
˚
˚
˚
With the crystal structure of dibromodiphenylstannane,
Ph2SnBr2, (I), we present the first example of a diorgano-
tin(IV) dihalide exhibiting a centrosymmetric dimeric asso-
ciation pattern in the solid state.
shorter (’0.1 A) than the sum (2.59 A) of the covalent radii
˚ ˚
(Cordero et al., 2008) of tin (1.39 A) and bromine (1.20 A).
˚
They fit very well into the range (2.44–2.54 A) of Sn—Br bond
lengths found in other diorganotin(IV) dibromides with
nonfunctionalized hydrocarbon groups [ten compounds with
14 individual values; Cambridge Structural Database (Allen,
2002)], even if the literature data cover all kinds of inter-
molecular association patterns and are derived from X-ray
diffraction measurements at different temperatures. They are,
however, longer than the corresponding bond lengths [mean
˚
value = 2.423 (4) A, T = 249 K] in tin(IV) bromide (Reuter &
Pawlak, 2001b). Because of the low symmetry of the molecule,
the tin–halide plane is not exactly perpendicular to the tin–
carbon plane, but the deviation of 0.14 (4)ꢀ is negligible.
The bromine and carbon opening angles (Table 1) of (I) are
compressed and significantly enlarged, respectively.
detailed comparison with the corresponding values of other
A
Figure 1
Schematic representation of the tin–halide interactions (broken bonds)
and the orientation of the dipole moments (red arrows of arbitrary units)
in the crystal structures Me2SnCl2 and Et2SnI2. In both cases, the halide
atoms of one molecule are individually labelled although they are
symmetry related in the real structures. Organic groups have been
omitted for clarity.
Figure 2
A view of the molecule of (I) in parallel projection, showing the atom-
labelling scheme. Displacement ellipsoids are drawn at the 50%
probability level.
ꢄ
Acta Cryst. (2012). C68, m104–m108
Ye and Reuter [SnBr2(C6H5)2] m105

metal-organic compounds
Figure 4
The crystal packing of (I), viewed down the b axis, showing the isolated
centrosymmetric dimers formed by intermolecular Snꢁ ꢁ ꢁBr interactions.
H atoms have been omitted for clarity.
almost planar in the present case, in contrast to the nonplanar
aggregation plane in trans-Myr2SnCl2. In relation to the
˚
aggregation plane, atom Br1 is 0.0742 (3) A below it. As a
consequence, the tin–halide plane is not coplanar with the
reference plane, resulting in an interplanar angle of 1.750 (2)ꢀ.
Furthermore, the dipole moments of both molecules, which
are exactly antiparallel to each other (inversion centre), will
be situated somewhat outside the association plane. Taking
the weak intermolecular interactions into account, the Sn
atoms adopt a fivefold trigonal–bipyramidal coordination with
the organic groups in equatorial and atoms Br1 and Br2i in
axial positions [symmetry code: (i) ꢃx + 1, ꢃy, ꢃz]. This may
be the reason why the Sn—Br distance to Br1 is somewhat
longer than to Br2, although this atom interacts with the
neighbouring Sn atom. The crystal packing (Fig. 4) reveals that
the phenyl groups completing the dimers inhibit further
intermolecular Snꢁ ꢁ ꢁBr interactions.
Figure 3
(a) Capped sticks model of the centrosymmetric dimers resulting from
˚
intermolecular Snꢁ ꢁ ꢁBr interactions [3.8482 (3) A, broken sticks] in the
crystal structure of (I). (b) A detailed view of the centrosymmetric dimers
projected (above) on the association plane [Sn1—Br2—Sn1i—Br2i, grey;
i = centre of inversion] and a view (below) showing the antiparallel
orientation of the dipole moments (arrows of arbitrary units) and the out-
of-plane positions of the exocyclic Br1 and Br1i atoms. The positions of
the phenyl groups are indicated by shortened sticks. Ellipsoids are drawn
at the 50% probability level. [Symmetry code: (i) ꢃx + 1, ꢃy, ꢃz.]
diorganotin(IV) dibromides, however, is difficult because
other association patterns will give clearly different values. In
addition, monomeric diorganotin(IV) dibromides show a
similar broad spectrum of carbon and bromine opening angles,
as can be seen from the examples Mes2SnBr2 and (MePhPr)-
PhSnBr2 above.
In order to classify the association pattern of diorgano-
tin(IV) dihalides more rationally, we propose to denote the
new association pattern as 2ai, where ‘2’ indicates the number
of molecules comprising the oligomer, ‘a’ represents the
antiparallel orientation of the dipole moments of both mol-
ecules and the subscript ‘i’ represents the symmetry element
leading to the association pattern. In doing this, the non-
centrosymmetric dimers of trans-Myr2SnCl2 (see above) can
be classified as 2a1.
In addition, the new structure motif for the intermolecular
Snꢁ ꢁ ꢁBr interaction in Ph2SnBr2 shows some important rela-
tionships to other structure types in the field of diorgano-
tin(IV) dihalides: for one thing, dimers with an antiparallel
orientation of dipole moments are the shortest possible
oligomeric sections within the structure family of Me2SnCl2,
and for another thing, the structure type of Ph2SnCl2, which is
characterized as a zweier-single chain, is built up of two
different centrosymmetric dimers of type 2ai with each Sn
atom undergoing an additional interaction to the exocyclic Cl
atom of a neighbouring dimer, and vice versa. Applying our
In looking for intermolecular Snꢁ ꢁ ꢁBr interactions, we have
taken into account all intermolecular Snꢁ ꢁ ꢁBr distances
˚
shorter than the sum (4.00 A) of the van der Waals radii
˚
˚
(Mantina et al., 2009) of tin (2.17 A) and bromine (1.83 A).
Indeed, there are only two intermolecular Snꢁ ꢁ ꢁBr contacts of
˚
3.8482 (3) A fulfilling this criterion. These contacts exist
between the Sn and Br atoms (Br2) of two molecules related
to each other by a crystallographic (12,0,0; Wyckoff letter b)
centre of symmetry (Fig. 3). The intermolecular bond angles
within the four-membered centrosymmetric tin–bromine ring
are Sn—Brꢁ ꢁ ꢁSn = 101.92 (1)ꢀ and Br—Snꢁ ꢁ ꢁBr = 78.08 (1)ꢀ.
For further discussion of the association pattern of oligo-
meric diorganotin(IV) dihalides, it seems helpful to treat the
four-membered tin–halide ring as an aggregation plane.
Because of the centre of symmetry, this reference plane is
ꢄ
m106 Ye and Reuter [SnBr2(C6H5)2]
Acta Cryst. (2012). C68, m104–m108

metal-organic compounds
Table 1
Selected geometric parameters (A, ).
classification scheme, this structure type can be expressed by
the term C2(2ai), with the letter C being an abbreviation for
the chain structure motif and 2(2ai) denoting the repeat unit.
ꢀ
˚
Sn1—C21
Sn1—C11
2.109 (2)
2.113 (2)
Sn1—Br2
Sn1—Br1
2.4710 (3)
2.4947 (3)
Experimental
C21—Sn1—C11
C21—Sn1—Br2
C11—Sn1—Br2
123.53 (8)
107.70 (5)
109.12 (6)
C21—Sn1—Br1
C11—Sn1—Br1
Br2—Sn1—Br1
105.46 (5)
106.33 (5)
102.741 (9)
A solution of tetraphenyltin (21.36 g, 50 mmol, Janssen Chimica) and
bromine (15.98 g, 100 mmol, Fluka) in carbon tetrachloride (150 ml,
Fluka) was heated for 3 h under reflux. After filtration, the solvent
was removed under reduced pressure. The residue was purified by
fractional distillation of PhBr (300 K, 37 kbar; 1 bar = 100 kPa),
PhSnBr3 (358–361 K, 17 kbar) and Ph2SnBr2 (396–402 K, 16 kbar).
After cooling, colourless crystals of the title compound were obtained
in a yield of 33.09%. Elemental data (Elementar vario MICRO Cube,
calculated/found, %): C 33.31/32.91, H 2.33/2.26.
DIAMOND (Brandenburg, 2006) and Mercury (Macrae et al., 2008);
software used to prepare material for publication: SHELXTL
(Sheldrick, 2008).
ATR–FT–IR (Bruker VERTEX 70, cmꢃ1): 3068.0 [w, ꢁ(CH)],
1576.2 [w, ꢁ(CC)], 1479.0 [w, ꢁ(CC)], 1430.6 [s, ꢁ(CC)], 1331.8 [m,
ꢁ(CC) and ꢂ(CH)ip], 1301.5 [w, ꢂ(CH)ip], 1189.3 [w, ꢂ(CH)ip], 1159.8
[w, ꢂ(CH)ip], 1070.5 [m, ꢂ(CH)ip], 1020.3 [w, ꢂ(CH)ip], 995.3 [m,
ꢂ(ring)], 913.2 [m, ꢂ(CH)oop], 724.5 [s s, ꢂ(CH)oop], 688.0 [s s,
ꢂ(CH)oop]; assignments according to Poller (1962).
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FG3245). Services for accessing these data are
described at the back of the journal.
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3
˚
[SnBr2(C6H5)2]
Mr = 432.71
Monoclinic, P21=c
V = 1317.71 (12) A
Z = 4
Mo Kꢃ radiation
ꢄ = 7.97 mmꢃ1
T = 100 K
˚
a = 8.9553 (5) A
˚
b = 8.7468 (5) A
˚
c = 17.0671 (8) A
0.23 ꢅ 0.17 ꢅ 0.13 mm
ꢀ = 99.713 (2)ꢀ
Data collection
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diffractometer
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
Tmin = 0.262, Tmax = 0.419
46736 measured reflections
3182 independent reflections
2856 reflections with I > 2ꢅ(I)
Rint = 0.031
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Refinement
R[F2 > 2ꢅ(F2)] = 0.017
wR(F2) = 0.039
S = 1.05
138 parameters
H-atom parameteꢃrs3 constrained
˚
Áꢆmax = 0.43 e A
ꢃ3
˚
3182 reflections
Áꢆmin = ꢃ0.48 e A
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˚
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ˇ
ˇ
´ˇ
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(Bruker, 2009); data reduction: SAINT; program(s) used to solve
structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine
structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
ꢄ
Acta Cryst. (2012). C68, m104–m108
Ye and Reuter [SnBr2(C6H5)2] m107

metal-organic compounds
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Acta Cryst. (2012). C68, m104–m108