Structural studies on Ph3MSMPh3 (M = Sn, Pb): Quest for a metal-metal bond

Article abstract of DOI:10.1016/j.poly.2008.11.033

The title compounds Ph₃PbSPbPh₃ (1) and Ph₃SnSSnPh₃ (2) were prepared in high yields by a reaction of Na₂S, respectively, with Ph₃Pb(SOCMe) and Ph₃Sn(SOCMe). X-ray crystallograph

Full text of DOI:10.1016/j.poly.2008.11.033

Polyhedron 28 (2009) 548–552
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structural studies on Ph MSMPh (M = Sn, Pb): Quest for a metal–metal bond
3
3
Neetu Singh, Rajendra Prasad, Subrato Bhattacharya *
Department of Chemistry, Banaras Hindu University, Varanasi 221 005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The title compounds Ph PbSPbPh (1) and Ph SnSSnPh3 (2) were prepared in high yields by a reaction of
3
3
3
Received 17 October 2008
Accepted 19 November 2008
Available online 2 January 2009
Na
2 3 3
S, respectively, with Ph Pb(SOCMe) and Ph Sn(SOCMe). X-ray crystallographic and density functional
studies were made to understand the structure and bonding in these molecules. Though the Pb–Pb dis-
tance in 1 is only marginally shorter than the sum of the corresponding van der Waals’ radii, a smaller
Pb–S–Pb angle suggests for a PbꢀꢀꢀPb interaction. DFT calculations were performed to analyse the nature
Keywords:
Organotin
Organolead
Metal sulfide
Weak interaction
Metal–metal bonding
of MꢀꢀꢀM interaction in 1 and 2. Strong intramolecular
p
–
p
interactions subsist between the different phe-
nyl rings of the molecules.
Ó 2008 Elsevier Ltd. All rights reserved.
1
. Introduction
drous sodium sulfide (E. Merck), triphenyltin chloride (Aldrich)
and triphenyllead chloride were used as received. Thioacetic acid
(96%, Aldrich) was distilled before its use.
The synthesis of compounds with bonds between heavier main
group elements have attracted attention of chemists over the last
decade due to their structures, bonding and in some cases, unusual
properties [1]. A large number of bi/polynuclear compounds of
group 14 metals have been prepared and many of them contain
M–M bonds. Though distannane [2] and diplumbane [3] with M–
M covalent bonds are known for a long time, a large number of com-
pounds containing various types of tin–tin [4] and lead–lead bonds
2.2. Instrumentation
Elemental analyses were performed using an Exter Model E-440
CHN analyser. NMR spectra were obtained using a JEOL AL 300
FTNMR spectrometer.
[
5] have been synthesized during past few years. On the other hand,
2.3. X-ray crystal structure determination
compounds with Sn–Sn or Pb–Pb weak interactions in bi/polynu-
clear M(II) or M(IV) complexes are rare. Recently, Magyar et al.
Single-crystal X-ray data on 1 and 2 were collected on a Bruker
[
6] have reexamined the structures of some Pb(II) compounds and
have found the existence of a weak intramolecular interaction in
tetraphenylarsonium Pb(II) iso-maleonitriledithiolate, [AsPh
Pb (i-mnt) ]. Importance of such interactions though unrevealed
SMART APEX CCD diffractometer using graphite monochromated
Mo Ka radiation (k = 0.71073 Å). The data integration and reduc-
4
]
4
tion were processed with SAINT+ [8] software. The structures were
2
[
2
4
solved by the direct method and then refined on F by the full-
yet, should be viewed in light of enzyme binding with the heavy
metal (poisoning). Here, we report a new route of synthesis of
Ph MSMPh [M = Pb(1), Sn(2)] and their X-ray structures along
3 3
with the results of quantum chemical studies to critically analyse
the possibility of a weak metal–metal interaction of significance.
matrix least-squares technique with the SHELXL-97 software [9]
using the WinGX (version 1.70.01) program package [10]. All
non-hydrogen atoms were refined anisotropically. All hydrogen
atoms were treated as riding atoms using SHELX default parameters.
Other crystallographic data are summarized in Table 1. Since the
data collections were done at room temperature the thermal ellip-
soids on the carbon atoms are large leading to large esds on the C–
C distances.
2
. Experimental
2.1. Starting materials
2.4. Theoretical calculations
All solvents were of reagent grade quality and purchased com-
mercially. These were purified by standard methods [7]. Anhy-
All theoretical calculations were performed with the GAUSSIAN
3W set of programs [11]. The effective core potential (ECP) stan-
dard basis set LanL2DZ [12] was utilized for all the atoms. Polariza-
0
*
Corresponding author. Tel.: +91 542 6702451/2307321x107; fax: +91 542
368127.
E-mail address: s_bhatt@bhu.ac.in (S. Bhattacharya).
2
tion functions (d,p) were included in the basis set for calculation of
0
277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.11.033

N. Singh et al. / Polyhedron 28 (2009) 548–552
549
Table 1
M¼Pb; Sn
Ph
3
MCl þ MeCOSH þ Et
3
N
!
Ph
3
MðSOCMeÞ þ Et
3
NHCl
Crystallographic data of compounds 1 and 2.
Compound
1
2
2
Ph
3
MðSOCMeÞ þ Na
2
S ! ðPh MÞS þ 2NaðOSCMeÞ
3
Empirical formula
Crystal color and habit
Crystal system
Space group
a (Å)
C
36
H
30 Pb
2
S
C
36 2
H30 Sn S
yellow needles
orthorhombic
P2(1)2(1)2(1)
9.9124(11)
17.741(2)
18.481(2)
90
90
90
3250.0(6)
4
1.858
colorless rods
orthorhombic
P2(1)2(1)2(1)
17.616(4)
9.835(2)
18.456(4)
90
90.099(4)
90
3197.6(11)
4
3.2. X-ray crystallography
Single crystals suitable for X-ray diffraction analyses were
b (Å)
c (Å)
grown from its benzene solution. 1 crystallizes in orthorhombic
crystal system (P2
scheme are given in Fig. 1 and important bond dimensions are gi-
ven in Table 2. The discrete molecular unit contains two Ph Pb
groups bonded to the sulfur asymmetrically. The two S–Pb dis-
tances are different and so are the alignments of the two Ph Pb
groups with respect to each other. As can be seen in Fig. 1 there
are two phenyl rings bonded to Pb1 atom which are sufficiently
close to other two phenyl rings bonded to Pb2 to allow p–p inter-
actions. Both the phenyl ring pairs are arranged in a displaced T-
shape with centroid–centroid distances of 4.86 and 5.24 Å.
An interesting feature in the molecular structure is the PbꢀꢀꢀPb
distance of 3.989 Å which is little shorter than the sum of their
van der Waals’ radii (4.04 Å) [16]. On the other hand the Pb–Pb dis-
tance in [AsPh
larly, in a binary intermetallic compound Ti
distance is 3.74 Å [17]. In these compounds the existence of a
PbꢀꢀꢀPb bond though weak is unquestionable. Structures of a few
b-diketonates of lead have been reported recently. The PbꢀꢀꢀPb dis-
tance in these dimeric compounds varies from 3.80 to 4.14 Å [18–
1 1 1
2 2 ). Molecular structure and numbering
a
(°)
b (°)
(°)
c
3
3
Volume (Å )
Z
3
Density (calculated)
1.521
ꢁ
3
(
Mg Å
)
F(000)
Index ranges
1704
1448
ꢁ13 6 h 6 8,
ꢁ23 6 h 6 22,
ꢁ13 6 k 6 12,
ꢁ24 6 l 6 20
293(2)
2.21–28.42
20981/7833
0.048
0.0400
0.0909
1.11
0.56 and ꢁ0.74
ꢁ
ꢁ
23 6 k 6 23,
24 6 l 6 24
Temperature (K)
h range (°) for data collection 2.30–28.36
Reflections collected/unique
293(2)
21497/7933
0.0724
0.0459
0.0963
R
R
int
a
1
[I > 2
r
(I)]
(I)]b
4
]
4
[Pb
2
(i-mnt)
4
] is much shorter being 3.70 Å. Simi-
Pb4.8 the Pb–Pb
wR
2
[I > 2r
S (all data)
Largest difference between
peak and hole (e Å
0.96
6
0.848 and ꢁ0.699
ꢁ
3
)
a
R
wR
1
=
R
(||F
0
| ꢁ |F
c
||)/
R
|F
0
|.
P
P
b
= f ½wðF0 ꢁ F Þꢂ= ½wðF Þ ꢂg1=2.
2
2
2
2
2
c
0
2
0] and existence of any PbꢀꢀꢀPb bonding is ambiguous in these
complexes.
It is sometimes vexing to interpret the nature of Pb–Pb bonding
*
*
bond order. Attempts to use LanL2DZ for Sn/Pb and 6–31V + G
[
[
13] for all other atoms were unsuccessful as convergence criteria
14] could not be met in single point energy calculations using X-
based on just bond distance measurements [21–22] The PbPb dou-
ble bond is known to be longer than the single bond [23]. Similar
inconsistencies are apparent in weak interactions too. Although
the sum of van der Waals’ radii is 4.04 Å [16], Pb–Pb distances in
ray atomic coordinates.
2
2
.5. Synthesis
4
+
Pb
6
O(OH)
6
ranges between 3.44 and 4.09 Å.[24]. The chains and
- and b-PbO are held together by real Pb–Pb bonds
.5.1. Improved preparation of complexes
layers in both
a
In a typical synthesis of 1, THF solutions of triethylamine
(not just van der Waals’ forces) but the Pb–Pb distances are quite
(
0
0.025 g, 0.25 mmol) (10 ml) and thioacetic acid (0.019 g,
.25 mmol) were mixed and added to a stirred solution of triphe-
nyllead chloride (0.120 g, 0.25 mmol) in the same solvent
25 ml). After stirring for 4 h the solvent was removed under re-
duced pressure and the residue was extracted in benzene
25 ml). The filtered solution was then added to a stirred suspen-
long (up to 3.97 Å) [25].
To gain further insight in the bonding we have reexamined the
molecular structure of the analogous tin compound 2. An ORTEP
drawing of the molecular structure of 2 is given in Fig. 2. Results
of our study are not much different from the earlier report [26].
However, we could refine the structure much better. The Sn–Sn
(
(
sion of anhydrous sodium sulfide (0.019 g, 0.25 mmol). After stir-
ring for 3 h the precipitate was filtered off and the solvent was
evaporated from the filtrate. The residue was recrystallized from
its benzene solution by slow evaporation of the solvent. Yield
(
2
0.183 g) 80%. Anal. Calc. for C36H30Pb S: C, 47.56; H, 3.33. Found:
C, 47.05; H, 3.30%. 2 was also prepared following a similar proce-
dure. Yield (85%), Anal. Calc. for C36H30S: C, 59.06; H, 4.13. Found:
C, 58.71; H, 4.19%.
3
. Results and discussion
3.1. Syntheses
Bahr and Boudjouk have reported the synthesis of 1 in 58%
yields by a reaction of Ph PbCl with Na S (generated in situ by a
3
2
reaction of elemental sulfur and sodium metal in presence of a cat-
alytic amount of naphthalene) [15]. In a similar reaction, when tri-
phenyllead chloride was treated with thioacetic acid in presence of
triethylamine followed by a reaction with anhydrous sodium sul-
fide 1 was isolated in more than 80% yields. In an analogous reac-
3
tion when Ph PbCl was replaced with its tin analogue 2 was
obtained:
Fig. 1. ORTEP drawing of 1.

5
50
N. Singh et al. / Polyhedron 28 (2009) 548–552
Table 2
Selected geometric parameters of 1 and 2.
Distances (Å)
M = Pb
M = Sn
M–M
S–M1
S–M2
C1–M1
C7–M1
C13–M1
C19–M2
C25–M2
C31–M3
3.989
2.491
2.484
2.214
2.200
2.202
2.179
2.196
2.199
3.879
2.402
2.397
2.120
2.148
2.142
2.126
2.138
2.145
Angles (°)
1
M –S–M
2
106.61
107.86
Dihedral angles (°)
M1–S–M2–C19
M1–S–M2–C25
M1–S–M2–C31
M2–S–M1–C13
M2–S–M1–C7
M2–S–M1–C1
ꢁ24.8
97.7
145.1
ꢁ166.9
76.4
ꢁ27.7
94.76
ꢁ147.0
ꢁ46.97
ꢁ163.92
78.8
ꢁ49.7
distance in this molecule being 3.879 Å (Table 2) is quite shorter
than the sum of their van der Waals’ radii (4.34 Å) which is indic-
ative of a weak SnꢀꢀꢀSn bonding.
Fig. 2. ORTEP drawing of 2.
The M–S–M angle in 1 is smaller than that in 2 which may
apparently be attributed to the higher electronegativity of 1
(
VSEPR theory). Glidewell and Liles have rationalized the geomet-
tional theory (DFT) method [27] to understand the electronic struc-
ture of the compound and nature of the PbꢀꢀꢀPb bond. The atomic
coordinates for the calculations were obtained from the X-ray data.
Single point energy calculation and bond order calculations were
performed using LanL2DZ (d,p) basis set at B3LYP level. PbꢀꢀꢀPb
bond order (Wiberg) is only 0.0085 which is too small to be of
any significance.
rical properties of (R M) S molecules on the basis of second order
3
2
Jahn–Teller effect. They have concluded that the angular geometry
of S will be anomalous in the context of the VSEPR [26]. Since the
electronegativity decreases from Ge to Sn (2.01 and 1.96, respec-
tively) the M–S–M angle also decrease in the same fashion (Ge–
S–Ge = 111.0°; Sn–S–Sn = 107.86°). Since electronegativity of Pb
is higher (2.33) than both Sn and Ge the Pb–S–Pb angle should
be still larger. Thus a smaller Pb–S–Pb angle in 1 indicates the exis-
tence of a Pb–Pb bond.
Recently, Inagaki and co-workers have reported the structures
0
of RCðOÞSMR (M = Ge, Sn, Pb) [28]. On the basis of NBO analyses
3
they have concluded intramolecular n
responsible for short M–O distances in these molecules. Results
of second order perturbation theory analysis of Fock matrix
O
! rMS interactions to be
3
.3. Theoretical studies
(
NBO) using LanL2DZ basis set reveal that similar bonding inter-
Since in the present case the Pb–Pb distance is almost at the
edge we performed theoretical calculations using density func-
actions are present both in 1 and 2 due to electron transfers from
r
*
SM to r M C orbitals. The contour diagram showing the overlap of
0
Fig. 3. Contour diagram showing natural bond orbital overlap.

N. Singh et al. / Polyhedron 28 (2009) 548–552
551
Fig. 4.
p–p interactions in 1.
orbitals is given in Fig. 3. It is clear from the figure that the extent
of overlap is small and the nature of bond is essentially very weak.
The stabilization energies associated with the delocalization are
Appendix A. Supplementary data
CCDC 691835 and 691836 contain the supplementary crystallo-
graphic data for (Ph Sn) S and (Ph Pb) S, respectively. These data
only 1.62 and 1.24 kcal/mol for 1 and 2, respectively. The stabiliza-
3
2
3
2
0
tion energies reported for RC(O)SMR
3
molecules are also of the
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.poly.2008.11.033.
same order (0.64–2.25 kcal/mol). Similar weak bonding by overlap
of molecular orbitals has also been reported in case of some thioa-
cylsulfanylarsines [29]. However, to our understanding it is not
logical to draw any conclusion on the basis of such small stabiliza-
tion energies. Moreover, the lowering in energy does not corrobo-
rate to the M–M distance shortening: SnꢀꢀꢀSn distance is shorter
than PbꢀꢀꢀPb distance but the stabilization energy is greater in the
later case. It should be kept in mind that the crystal packing and
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. Conclusion
3 3
Ph MSMPh (M = Sn, Pb) have been prepared using Ph M(SOC-
3
Me) in high yields. X-ray structures of the compounds showed
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van der Waals’ radii) which are indicative of weak MꢀꢀꢀM interac-
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[
[
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