Further study of tris(cyclohexyl)stannane compounds, Cy3SnX. Syntheses of the compounds with X = Br, I, N3 and NCS and redetermination of the crystal structures of Cy3SnX (X = Br and I)

Article abstract of DOI:10.1016/j.poly.2004.08.001

Compound sythesis and far IR data are presented for various Cy ₃SnX compounds. Redeterminations of the crystal structures of tris(cyclohexyl)tin bromide and iodide, Cy₃SnBr and Cy ₃SnI, confirm their molecular nature providing, in particular, a revised estimate of the Sn-I bond length, now 2.7463(6) ?. The nature of the solid state structure of Cy₃SnCl is also discussed.

Full text of DOI:10.1016/j.poly.2004.08.001

Polyhedron 23 (2004) 2331–2336
www.elsevier.com/locate/poly
Further study of tris(cyclohexyl)stannane compounds,
Cy3SnX. Syntheses of the compounds with X = Br, I, N3 and
NCS and redetermination of the crystal structures of
Cy3SnX (X = Br and I)
a,
b
b
c
R. Alan Howie *, Marcelo V.H. Moura , James L. Wardell , Solange M.S.V. Wardell
a
Department of Chemistry, University of Aberdeen, Old Aberdeen, AB24 3UE, Scotland, UK
´
b
´
^
Departamento de Quımica Inorganica, Instituto de Quımica, Universidade Federal do Rio de Janeiro, CP 68563, 21945-970 Rio de Janeiro, RJ, Brazil
Far-Manguinhos, Fiocruz, Rua Sizenando Nabuco 100, Manguinhos, CEP 21041-250, Rio de Janeiro, RJ, Brazil
c
Received 21 July 2004; accepted 3 August 2004
Available online 28 August 2004
Abstract
Methods of preparation and far IR data are presented for various Cy3SnX compounds. The synthesis of tris(cyclohexyl)tin
hydroxide, Cy3SnOH, is also described. Redeterminations of the crystal structures of tris(cyclohexyl)tin bromide and iodide,
Cy3SnBr and Cy3SnI, confirm their molecular nature and improve considerably upon the results reported earlier [S. Calogero,
P. Ganis, V. Peruzzo, G. Tagliavini, G. Valle, J. Organomet. Chem. 220 (1981) 11] providing, in both cases, lower R-factors
˚
and, in particular, a revised estimate of the Sn–I bond length, now 2.7463(6) A.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Tris(cyclohexyl)tin; Halostannanes; Crystal structure
1. Introduction
of the temperature dependent order–disorder transition
in tris(cyclohexyl)tin chloride, 1 (X = Cl), [1, and refer-
ences therein], and reports on the structures of 1
(X = F, Br and I) [2] and of various tris(2-methyl-2-phe-
nyl-propyl)stannane derivatives (Neo)3SnX, 2 (X = Cl,
Br, I, N3 and NCS) [3]. We now report the synthesis
of 1 (X = Br, I, N3 and NCS) and of tris(cyclohexyl)tin
hydroxide, along with redeterminations of the structures
of 1 (X = Br) and 1 (X = I). Far IR data are also pre-
sented for various Cy3SnX compounds.
Halo- and pseudo-halostannanes of the general form
R4ꢀnSnXn, (R = an organic group, X = halide or pseudo
halide and n =1–13), have received much attention. Of
interest in compounds of this type, particularly for those
with n = 2 and more especially those with n = 1, has
been the investigation of the occurrence and nature of
secondary Sn–X contacts to establish whether they con-
tribute to the coordination of tin and change its nominal
tetrahedral nature to one with a higher coordination
number. Typical examples of this are the detailed report
2. Experimental
*
Corresponding author. Tel.: +44 1224 272907; fax: +44 1224
Melting points were measured on Melt-Temp-II
equipment. Far IR spectra were obtained using a Nicolet
272921.
E-mail address: r.a.howie@abdn.ac.uk (R.A. Howie).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.08.001

2332
R.A. Howie et al. / Polyhedron 23 (2004) 2331–2336
Magna 760 FTIR instrument with samples suspended in
Nujol between polythene plates. Cy3SnCl was a recrys-
tallised commercial sample, m.p. 127–129 ꢁC.
2.5. Preparation of tris(cyclohexyl)tin isothiocyanate, 1
(X = NCS)
Far IR: m 492, 439, 420, 327, 271, 252, 199 cmꢀ1
.
A solution of Cy3SnCl (2 mmol) in Me2CO (15 ml)
and a suspension of NaNCS (5 mmol) in Me2CO (15
ml) were mixed. After stirring at RT overnight, the reac-
tion mixture was filtered and the filtrate collected. The
filtrate was shaken with a further suspension of NaNCS
(5 mmol) in Me2CO (15 ml) for 4 h, all volatiles removed
by rotary evaporation and the residue extracted into
CHCl3. The chloroform extract was dried and rotary
evaporated to leave a solid residue which was recrystal-
lised from CH2Cl2/hexane, m.p. 120–122 ꢁC.
2.1. Preparation of tris(cyclohexyl)tin iodide, I (X = I)
Solutions of Cy3SnCl (2 mmol) in Me2CO (15 ml)
and NaI (5 mmol) in Me2CO (15 ml) were mixed. After
stirring at RT for 4 h the reaction mixture was filtered
and the filtrate evaporated to leave a residue which
was extracted into CHCl3. The chloroform extract was
evaporated and the solid residue was recrystallised from
EtOH, m.p. 64–66 ꢁC.
IR: m: 2071 cmꢀ1. Far IR: m: 570(br), 491, 439, 420,
326, 252, 220, 200 cmꢀ1
Far IR: m: 492, 439, 420, 324, 250(sh), 239, 212, 161
cmꢀ1
.
2.6. X-ray crystallography
2.2. Preparation of tris(cyclohexyl)tin hydroxide, 1
(X = OH)
2.6.1. Data collection
Intensity data for 1 (X = Br and I) were obtained with
˚
A solution of Cy3SnCl (2 mmol) in Et2O (15 ml) was
added to a solution of NaOH (5%) in H2O (15 ml) and
the mixture was stirred for 1 h, and then filtered. The
ether layer in the filtrate was collected, dried and evap-
orated. The residue from the ether layer was added to
the original solid collected by filtration and the com-
bined solids were recrystallised from aqueous EtOH,
m.p.174–179 ꢁC. The wide m.p. range is attributed to
the presence in trace amounts, and in situ formation,
of bis[tris(cyclohexyl)tin] oxide, (Cy3Sn)2O, in accord
with the previous report [4] that only with great diffi-
culty can pure samples of either the oxide or the hydrox-
Mo Ka radiation, k = 0.71073 A, by means of the Enraf
Nonius KappaCCD area diffractometer of the EPSRCÕs
crystallography service at Southampton. For 1 (X = Br),
for which the crystal shattered on cooling, the data were
obtained at 298 K and at 120 K for 1 (X = I). The entire
process of data collection, cell refinement and data
reduction was accomplished by means of the programs
DENZO [5] and COLLECT [6]. Correction for absorption
by a semi-empirical method based upon the variation
in intensity of equivalent reflections was achieved with
the program SORTAV [7,8]. The transmission factors
for each compound (Table 1) are not then on an abso-
lute scale. Unfortunately both data sets have proved to
be less than fully complete (see Table 1). This is espe-
cially true in the case of 1 (X = Br), where the available
crystals were of particularly dubious quality, but is per-
ceived to have no more deleterious effect than to limit
the precision with which derived quantities such as bond
lengths and bond angles are estimated.
ide be obtained, m(OH) 3623 cmꢀ1
.
2.3. Preparation of tris(cyclohexyl)tin bromide,
(X = Br)
1
Concentrated HBr (2 ml) was added to a solution of
Cy3SnOH (0.5 mmol) in EtOH (20 ml). The mixture was
stirred at room temperature for 2 h, the volatiles re-
moved under vacuum and the solid product recrystal-
lised from CHCl3; m.p. 77–79 ꢁC.
2.6.2. Structure solution and refinement
In both cases initial solution of the structure was ob-
tained by the heavy atom technique with the program
SHELXS-86 [9] and completed and refined by full matrix
least squares on F2 with SHELXL-97 [10]. In the case of 1
(X = Br) the structure was finally re-refined with the
atomic coordinates from the refinement of 1 (X = I) as
starting parameters but with bromine substituted for io-
dine thus ensuring total equivalence between the label-
ling schemes of these two refinements. One reflection
showing particularly poor agreement due to extinction
was omitted from the refinement of 1 (X = Br). Despite
a degree of disorder affecting the atoms of the cyclohexyl
groups of 1 (X = Br), which was not modelled in detail,
anisotropic thermal vibration parameters were refined
for all non-H atoms. In all cases the residual electron
Far IR: m: 491, 438, 419, 322, 250(sh), 228(br), 203(sh)
cmꢀ1
.
2.4. Preparation of tris(cyclohexyl)tin azide, 1 (X = N3)
A solution of Cy3SnCl (2 mmol) in Me2CO (15 ml)
and a suspension of NaN3 (5 mmol) in Me2CO (15
ml) were mixed. After stirring at RT overnight, the reac-
tion mixture was filtered. The filtrate was shaken with a
further suspension of NaN3 (5 mmol) in Me2CO (15 ml)
for 4 h, all volatiles removed by rotary evaporation and
the residue extracted into CHCl3. The chloroform ex-
tract was dried and rotary evaporated to leave a solid
residue. m(N3) 2071 cmꢀ1: no m(OH)

R.A. Howie et al. / Polyhedron 23 (2004) 2331–2336
2333
Table 1
Crystal data and structure refinement
Compound
1 (X = Br)
C18H33BrSn
448.04
1 (X = I)
C18H33ISn
495.03
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
298(2)
orthorhombic
Pnma
120(2)
orthorhombic
Pnma
Unit cell dimensions
˚
a (A)
˚
11.2576(10)
16.6583(17)
12.2446(8)
17.1651(14)
9.0044(6)
1892.5(2)
4
b (A)
˚
c (A)
10.2199(9)
1916.6(3)
3
˚
Volume (A )
Z
4
1.553
Calculated density (Mg/m3)
1.737
2.973
Absorption coefficient (mmꢀ1
F(000)
)
3.410
904
976
0.30 · 0.20 · 0.20
3.05–27.50
Crystala size (mm)
0.22 · 0.16 · 0.07
2.69–20.97
h range for data collection (ꢁ)
Index ranges
Reflections collected/unique
ꢀ10 6 h 6 10, ꢀ15 6 k 6 12, ꢀ7 6 l 6 10
1346/741
[Rint = 0.0955]
ꢀ15 6 h 6 13, ꢀ19 6 k 6 22, ꢀ11 6 l 6 10
10576/2179
[Rint = 0.0737]
97.1
Completeness to max. h (%)
Absorption correction Tmin/max
Data/restraints/parameters
Goodness-of-fit on F2
69.4
0.2059/0.3222
0.7415/0.8258
2179/0/97
1.018
741/0/97
1.026
Final R indices [I > 2r(I)]
R indices (all data)
Largest peak and hole (e/A )
R1 = 0.0690, wR2 = 0.1826
R1 = 0.0930, wR2 = 0.2085
0.405 and ꢀ0.460
R1 = 0.0402, wR2 = 0.0763
R1 = 0.0674, wR2 = 0.0855
1.218 and ꢀ1.307
3
˚
a
Colourless crystals in every case.
density features noted in Table 1 are in the vicinity
˚
(within 0.90 A) of heavy atoms. In the final stages of
3.2. Crystal structures of 1 (X = Br and I)
refinement H atoms were introduced in calculated posi-
tions and refined with a riding model. The program OR-
TEP-3 for Windows [11] was used in the preparation of
the Figures and SHELXL-97 and PLATON [12] for bond
length and angle and other molecular geometry calcula-
tions. PLATON was used, in particular, for calculations
based upon crystallographic data extracted from the
Cambridge Structural Database [13]. It is noted here
that in Table 4 for those compounds with more than
one molecule in the asymmetric unit, e.g. all 2, the bond
distances and bond angles and the associated estimated
errors are average values. Further details of the data col-
lection and structure refinement processes are available
in Table 1.
The compounds 1 (X = Br) and 1 (X = I) are isomor-
phous and it is for this reason that both the drawing of
the molecule (Fig. 1) and the layer of molecules shown
in Fig. 2, although based on data for 1 (X = I), are appli-
cable to both compounds. In these structures the tin and
halogen atoms lie on a crystallographic mirror plane
which also bisects one of the cyclohexyl groups and re-
C10
C9i
C8i
C9
C8
C7
3. Results and discussion
C6i
C6
3.1. General features of the structures
C5i
C5
C4i
Sn1
C1i
C4
All of the cyclohexyl rings are found to be in the chair
conformation with C–C distances and internal C–C–C
angles more or less as expected provided that due allow-
ance is made for the disorder in 1 (X = Br) noted above.
Apart from this the real significance of the structures
presented here lies in the nature of the tin coordination
which they reveal which is discussed below.
C1
C2i
C3
C3i
C2
I1
Fig. 1. The molecule of 1 (X = I) showing the labelling scheme. Non-H
atoms are shown as 50% probability displacement ellipsoids and H
atoms as small circles of arbitrary radius. Symmetry code (i) x, 3/2 ꢀ y, z.

2334
C5iv
R.A. Howie et al. / Polyhedron 23 (2004) 2331–2336
accommodate the steric requirements of the cyclohexyl
groups. Particularly notable in this table is the Sn(1)–
I1iv
I1iii
C10v
˚
I(1) bond length of 2.7463(6) A which is much more rea-
sonable than the previous published value [2] of 2.54(1)
c
˚
A. The molecules are found in layers on the crystallo-
graphic mirror planes as shown in Fig. 2 within which
the next nearest neighbour Sn–X distances are 5.375(5)
˚
and 4.8013(7) A for X = Br and X = I, respectively.
C10iii
C10iv
I1v
The surprisingly shorter next nearest neighbour distance
for X = I is attributed primarily to the different temper-
atures at which the intensity data were collected (see
Table 1).
C2v
C3v
C5ii
I1
b
I1ii
C7
o
a
3.3. Structural trends in R3SnX compounds with X = F,
Cl, Br and I
C10ii
C10
C9
Fig. 2. A layer of molecules of 1 (X = I). Non-H atoms are shown as
50% probability displacement ellipsoids and H atoms have been
omitted for clarity. Only selected atoms are labelled. Symmetry codes
(ii) x ꢀ 1, y, z; (iii) x, y, 1 + z; (iv) x ꢀ 1, y, 1 + z; (v) x ꢀ 1/2, y, 1/2 ꢀ z.
The nature, polymeric or molecular, of the solid state
structure of 1 (X = Cl) has been a matter of conjecture
for many years. Initial X-ray structural results [14] were
taken to be indicative of a molecular structure with four
coordinate tin in contrast to earlier results from
Mo¨ssbauer spectoscopy suggestive of a polymeric struc-
ture with five coordinate tin. Means were then found [2]
to resolve this disparity in favour of the molecular struc-
tural model. Further support for this model was ob-
tained, by comparison of 119Sn chemical shifts in the
solid state (CP/MAS) with those found for the com-
pounds in solution, by Harris et al. [15]. The results of
this study were considered to be compatible with 1
(X = Cl) existing as a molecular species in the solid state
in the same manner as 1 (X = Br) and 3 (X = Cl). Most
recently Asadi et al. [1] have investigated the X-ray crys-
tal structure of 1 (X = Cl) over the temperature range
120–298 K. This study reveals, in addition to an or-
der–disorder transition at about 248 K, an inverse and
temperature dependent relationship between the nearest,
Sn–Cl, and next nearest, Snꢁ ꢁ ꢁCl0, distances. These dis-
tances tend to equality with reducing temperature. Also
present are essentially linear Cl–Snꢁ ꢁ ꢁCl0 and Sn–
Clꢁ ꢁ ꢁSn0 groups (see Table 3). The findings of Asadi et
al. support the earlier suggestion [4], based on NMR
lates the two remaining cyclohexyl groups by symmetry.
Thus the asymmetric unit consists of one complete
cyclohexyl group [C(1–6)], four atoms of another cyclo-
hexyl group [C(7–10)] and the tin and halogen atoms
(see Fig. 1). In both cases the bond length and bond an-
gle data in Table 2 are consistent with tin in a tetrahe-
dral environment distorted primarily in order to
Table 2
˚
Selected bond lengths and angles (A, ꢁ) for isomorphous 1 (X = Br and I)
X = Br
X = I
Bond lengths
Sn(1)–C(1)
Sn(1)–C(7)
Sn(1)–X(1)
2.09(2) · 2
2.09(2)
2.501(4)
2.167(4) · 2
2.166(6)
2.7463(6)
Bond angles
C(1)–Sn(1)–C(1i)
C(1)–Sn(1)–C(7)
C(1)–Sn(1)–X(1)
C(7)–Sn(1)–X(1)
119.6(16)
115.9(2)
112.6(7) · 2
102.5(9) · 2
104.5(6)
114.45(12) · 2
104.90(10) · 2
99.71(14)
(solution) and Mo¨ssbauer spectroscopy, that
(X = Cl) is weakly polymeric in the solid state but
1
Symmetry code: (i) x, 3/2 ꢀ y, z.
Table 3
˚
Comparison table of selected geometric parameters (A, ꢁ) in 1 (X = F, Cl, Br and I)
X
Temperaturea (K)
Sn–Xb
Snꢁ ꢁ ꢁX0
Sn–Xꢁ ꢁ ꢁSn0
180
X–Snꢁ ꢁ ꢁX0
180
Reference
F
2.052(10)
2.415(3)
2.4657(7)
2.501(4)
2.7463(6)
2.302(10)
3.298(3)
3.0077(7)
5.375(5)
4.8013(7)
[16]
[1]
Cl
Cl
Br
I
298
108
298
120
178.95(17)
171.95(3)
135.39(15)
140.03(2)
178.95(12)
178.58(3)
116.67(9)
129.70(2)
[1]
c
c
a
b
c
Room temperature unless otherwise stated.
Primed and unprimed labels indicate next nearest and nearest neighbour atoms, respectively.
Isomorphs, this work.

R.A. Howie et al. / Polyhedron 23 (2004) 2331–2336
2335
Table 4
Comparison of selected interatomic distances (A) in (Neo)3 SnX, 2, and Ph3 SnX, 3
˚
Ph3Sn–X
Sn–Xa
(Neo)3Sn–X
X
Snꢁ ꢁ ꢁX0
Temperatureb (K)
110
Reference
Sn–X
Snꢁ ꢁ ꢁX0
>7.31
Temperature (K)
150
Reference
[21]
Clc
Clc
Brc
I
2.3548(17)
2.3605(12)
2.495(2)
2.6988(9)e
2.7080(7)f
>5.84
>5.63
>5.79
>6.30
>6.30
[17]
[17]
[18]
[19]
[20]
2.382(3)
2.5444(14)
2.7424(6)
>5.64
>5.67
150
150
[3]d
[3]d
I
a
Primed and unprimed labels indicate next nearest and nearest neighbour atoms, respectively.
Room temperature unless otherwise stated.
Isomorphous pairs of compounds.
b
c
d
e
f
Isomorphous pairs of compounds.
Triclinic polymorph with Z = 4.
Triclinic polymorph with Z = 2.
monomeric in solution. Thus in the context of com-
the corresponding, but molecular, 2 and 3 in which last
two this distance is very similar. Third, for all molecular
1, 2 and 3 (X = Br and I) the Sn–X distances are much
the same for any particular X. The implication of the
above is that, at least for X = halogen, a polymeric com-
pound of the form R3Sn–X will display temperature
dependency of the type noted above for 1 (X = Cl), more
or less linear X–Snꢁ ꢁ ꢁX0 groups and an Sn–X distance
longer than that found in a molecular compound with
the same X but, obviously, a different R. In general
terms it appears that the formation of polymeric species
with bridging X in R3SnX (X = halogen) in the solid
state is favoured for more electronegative and smaller
X and disfavoured by large R. On the other hand, as
in the case of 3 (X = Cl, Br and I), polymerisation with
bridging X may be supplanted by other intermolecular
interactions.
The structures for 1 (X = Br and I) presented here im-
prove upon those previously reported [2] not only be-
cause they are better determined but also, in the case
of 1 (X = I), because the data derived from the original
structure determination are very similar to those ob-
tained both here and previously for 1 (X = Br). Likewise
the previously reported [2] structure of 1 (X = F) has
been ignored in favour of that of Tudela et al. [16] be-
cause the data derived from the original determination
closely resembled that of 1 (X = Cl). There is, therefore,
doubt as to the authenticity of the samples used in the
original structure determinations [2] of 1 (X = F and I).
pounds of the form R3 SnCl (R = alkyl or aryl) 1
(X = Cl) is perceived as being polymeric but intermedi-
ate in this respect between, on the one hand, such as pol-
ymeric Me3 SnCl and on the other, for example,
molecular Ph3 SnCl, 3 (X = Cl).
With the information now available the status of var-
ious 1 can be considered further in terms of the nature of
X as well as R. Thus from the data in Table 3 1 (X = F
and Cl), with Snꢁ ꢁ ꢁX0 distances much shorter than the
sums of the contact radii of the relevant atoms (PLATON
˚
contact radii 2.26, 1.47, 1.75, 1.85 and 1.98 A for Sn, F,
Cl, Br and I, respectively) and essentially linear X–
Snꢁ ꢁ ꢁX0 groups, are clearly polymeric. The remainder,
1 (X = Br and I) with Snꢁ ꢁ ꢁX0 distances greater than
the relevant contact radii sums and non-linear X–
Snꢁ ꢁ ꢁX0 groups, are equally clearly molecular species.
Table 4 shows Sn–X and Snꢁ ꢁ ꢁX0 distances for com-
pounds of the form R3 SnX, R = Neo, 2, and R = Ph,
3, with, in both cases, X = Cl, Br and I. All of these com-
pounds are molecular species as shown by the Snꢁ ꢁ ꢁX0
distances, all much greater than the sums of the contact
radii. For 2 this is largely because of the bulk of the non-
halogen substituents. For 3 it comes about because the
molecules occur in stacks in such a way as to permit
large numbers of C–H–p intermolecular contacts. The
Sn–X bonds of successive molecules in the stack are then
directed in opposite directions away from the mid-line of
the stack. In other words, in the case of 3 (X = Cl, Br
and I), the stacking of the molecules favours interactions
between the phenyl groups rather than Snꢁ ꢁ ꢁX0 intermo-
lecular contacts.
4. Supplementary material
Three notable features arise from comparison of Ta-
bles 3 and 4. First, whereas in 3 (X = Cl), the only case
for which the necessary data are available in Table 4, re-
duced temperature has virtually no effect on the Sn–Cl
distance but shortens the Snꢁ ꢁ ꢁCl0 contact dramatically,
in 1 (X = Cl) both types of distance are temperature
dependent but in opposite senses. Second, the Sn–Cl dis-
tance is longer in polymeric 1 (X = Cl) than in either of
Supplementary data, including atomic coordinates,
anisotropic thermal parameters and bond lengths and
angles are available from the Cambridge Crystallo-
graphic Data Centre with reference codes CCDC
231208 and 231209 for 1 (X = I) and 1 (X = Br), respec-
tively. Copies of this information may be obtained, free
of charge, from the Director, CCDC, 12 Union Road,

2336
R.A. Howie et al. / Polyhedron 23 (2004) 2331–2336
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Cambridge CB2 1EZ, UK (fax: +44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk) or via http://www.
ccdc.cam.ac.uk/conts/retrieving.html.
[6] R. Hooft, COLLECT, Nonius BV, Delft, The Netherlands, 1998.
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Acknowledgements
We are indebted to the EPSRC for the use of both the
Chemical Database Service at Daresbury, primarily for
access to the Cambridge Structural Database, and the
X-ray service at the University of Southampton for data
collection. We thank CNPq and FUJB, Brazil, for finan-
cial support.
[15] R.K. Harris, A. Sebald, D. Furlani, G. Tagliavini, Organometal-
lics 7 (1988) 388.
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