Structures, semi-empirical calculations and thermolyses of some five- and six-membered chelate organotin mercaptide complexes

Article abstract of DOI:10.1016/S0022-328X(00)00259-X

Characterization of Ph₂Sn(Cl)(MBT) (1) (HMBT=2-mercaptobenzothiazole) has been carried out by IR, M?ssbauer, ¹H, ¹³C and ¹¹⁹Sn spectroscopies and by X-ray crystallography for 1 together with that of Ph₂

Full text of DOI:10.1016/S0022-328X(00)00259-X

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Journal of Organometallic Chemistry 605 (2000) 82–88
Structures, semi-empirical calculations and thermolyses of some
five- and six-membered chelate organotin mercaptide complexes
Ana Paula G. de Sousa a, Rosalice M. Silva a,*, Amary Cesar a, James L. Wardell b,
John C. Huffman c, Anuar Abras d
a Departamento de Qu´ımica, Uni6ersidade Federal de Minas Gerais, 31270-901, Belo Horizonte, MG, Brazil
b Department of Chemistry, Uni6ersity of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, UK
c Department of Chemistry and Molecular Structure Center, Indiana Uni6ersity, Bloomington, IN 47405, USA
d Departamento de F´ısica, Uni6ersidade Federal de Minas Gerais, 31270-901, Belo Horizonte, MG, Brazil
Received 28 July 1999; received in revised form 12 March 2000
Abstract
1
Characterization of Ph2Sn(Cl)(MBT) (1) (HMBT=2-mercaptobenzothiazole) has been carried out by IR, Mo¨ssbauer, H, 13C
and 119Sn spectroscopies and by X-ray crystallography for 1 together with that of Ph2Sn(SCH2CH2S) (2). Compound 1,
unexpectedly obtained from the reaction between Ph2SnCl2 and KMBT in a 1:2 mole ratio, has a trigonal-bipyramidal geometry,
due to intramolecular SnꢀN interactions, both in the solid state and in solution; the axial sites are occupied by N and Cl,
N(24)ꢀSnꢀCl(4)=155.27(17)°, the chelate bite angle, N(24)ꢀSNꢀS(15), is 64.65(17)°. Compound 2 is essentially monomeric in the
solid state and has a distorted tetrahedral structure; the bond angles at tin vary from 92.50(16)° [S(2)ꢀSnꢀS(5)] to 116.4(6)°
,
[C(6)ꢀSnꢀC(12)]. The shortest intermolecular Sn···S contact in 2 is 3.885 A, just within the sum of the van der Waals’ radii for
,
Sn and S (4.0 A). PM3 semi-empirical calculations for 2 indicated that the geometry at the tin center can be accounted for by a
high degree of p-character in the tin bonding orbitals to sulfur; PM3 semi-empirical calculations on Ph2Sn(SCH2CH2CH2S) (3)
indicated the geometry at tin to be less distorted from tetrahedral, with a SꢀSnꢀS angle of 99°; the calculations further indicated
that the only stable conformation of the six-membered ring in 3 is the chair form. © 2000 Published by Elsevier Science S.A. All
rights reserved.
Keywords: Organotin mercaptides; Dithiolates; X-ray structure; Semi-empirical calculations
pyrolysis of phenyltin chalcogenides produced SnS
[4,5]. We have initiated a study of diorganotin dimer-
1. Introduction
captides as SnS and/or SnS2 precursors. This report is
concerned with diphenyltin derivatives of the thiolato
Interest in complexes, which incorporate thiolate lig-
ands, has been generated for various reasons. Among
compounds shown in Fig. 1. The ligand HMBT was
these are their relevance to biological systems [1], the
chosen in order to determine the effect of using a
potential in CꢀS bond cleavages and in de-sulfuriza-
tions [2], and their use as precursors of ceramic materi-
thiolate, containing an additional N-donor site.
als [3]: Boudjouk et al. have shown, for example, that
2. Experimental
2.1. General comments
All operations were carried out under pure dinitro-
gen, using Schlenk and vacuum techniques. Nitrogen
was predried by passing in a column consisting of
molecular sieves, calcium chloride and calcium sulfate.
Hexane and tetrahydrofuran were distilled from
Fig. 1. Ligands used in the present work.
* Corresponding author. Tel.: +55-31-4995734; fax: +55-31-
4995700.
E-mail address: rosalice@apolo.qui.ufmg.br (R.M. Silva).
0022-328X/00/$ - see front matter © 2000 Published by Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00259-X

A.P.G. de Sousa et al. / Journal of Organometallic Chemistry 605 (2000) 82–88
83
sodium–benzophenone. All solvents were used immedi-
2.2.2. Diphenyltin thiolates
ately following distillation or stored under nitrogen
over the appropriate molecular sieves. Ph2SnCl2,
2.2.2.1. Ph2SnCl(MBT) (1). A reaction mixture of
Ph2SnCl2 (0.30 g, 0.87 mmol) and KMBT (0.35 g, 1.71
mmol) in THF (20 ml) was refluxed in a Schlenk flask
under nitrogen for 5 h, cooled and hexane added. The
white precipitate of Ph2SnCl(MBT) was collected as an
air stable compound and was recrystallized from THF–
hexane; yield 61%, m.p. \300°C. Anal. Found: C,
48.35; H, 2.93; N, 3.41; Sn, 22.48. Calc. for
C19H14SnClNS2: C, 48.07; H, 2.95; N, 2.95; Sn, 25.09%.
ethane-1,2-dithiol
(H2EDT),
propane-1,3-dithiol
(H2PDT) and 2-mercaptobenzothiazole (HMBT), from
119
Aldrich, were used as supplied.
Sn Mo¨ssbauer spec-
troscopy was performed in a constant acceleration
equipment moving a CaSnO3 source kept at room
temperature. The samples were cooled at liquid nitro-
gen temperature. All spectra were computer-fitted as-
suming Lorentzian lineshape. Infrared spectra were
recorded on a Perkin–Elmer 283 spectrophotometer in
the 4000–200 cm−1 range in Nujol mulls, on CsI
1
IR (cm−1, Nujol): w(CꢁN) 1620,w(SnꢀS) 275. H-NMR
(l, CDCl3): 7.46–7.79 (m, C6H5). 13C-NMR (l,
CDCl3): 112.27, 121.37, 124.70, 127.22, 129.57 (C6H5),
140.2 (CꢁN).119Sn-NMR (l, CDCl3): −177.1. Mo¨ss-
bauer (mm s−1): l=0.9090.01, Z=1.9690.01.
1
plates. H (200 MHz) and 13C (50 MHz) NMR spectra
were recorded on a Brucker AC-200 and referenced to
internal SiMe4 and 119Sn( 149.21 MHz) NMR spectra
were recorded on a Brucker AC-400 and referenced to
internal SnMe4. C and H analyses were performed
using a Perkin–Elmer PE-2400 CHN microanalyser.
Atomic absorption for tin was performed on a Hitachi
Z-8200 Polarized Zeeman Atomic Absorption Spec-
trophotometer. TG analysis was performed on a Mett-
ler Thermobalance TG 50 of TA 4000 System at a flow
2.2.2.2. Ph2Sn(EDT) (2). This was prepared by a mod-
ification of published procedures [7]. A reaction mixture
of Ph2SnCl2 (0.50 g, 1.45 mmol) and Na2EDT (0.20 g,
1.45 mmol) in THF (20 ml) was refluxed in a Schlenk
flask under nitrogen for 24 h, cooled and hexane added.
The white precipitate of Ph2Sn(EDT) was collected and
recrystallized from THF–hexane; yield 57%. Anal.
Found: Sn, 31.9. Calc. Sn, 32.6%. IR (cm−1, Nu-
rate of 10°C min−1
.
1
jol):,w(SnꢀS) 290 and 275. H-NMR (l, CDCl3): 7.76–
2.2. Synthesis
7.32 (m, 2 C6H5), 3.68–3.52 (m, 2CH2). 13C-NMR (l,
CDCl3): 104.89, 112.85, 121.75, 124.99, 127.55 (C6H5),
18.78 (s, CH2). Mo¨ssbauer (mm s−1): l=1.3890.01,
Z=1.5690.01; [lit. values [8] l=1.37, Z=1.67].
2.2.1. Alkali metal thiolates
2.2.1.1. NaMBT. A reaction mixture of HMBT (0.400
g, 2.50 mmol) and Na (0.058 g, 2.50 mmol) in THF (20
ml) was stirred for 2 h in a Schlenk flask. To the yellow
solution was added hexane; the white KMBT precipi-
tate was collected and dried under vacuo. Yield: 90%.
The product was shown to be free of the SH group by
the absence of a w(SꢀH) stretch at 2500 cm−1 [6].
M.p.\300°C. Anal. Calc. for C7H4S2NNa: C, 44.44;
H, 2.11; N, 7.40. Found: C, 43.67; H, 2.11; N, 6.98%.
2.2.2.3. Ph2Sn(PDT) (3). This was similarly prepared to
2 from Ph2SnCl2 (0.450 g, 1.32 mmol) and Na2PDT
(0.200 g, 1.32 mmol) in THF (20 ml) on refluxing in a
Schlenk flask under nitrogen for 24 h; yield 53%. Anal.
Found: Sn, 30.4. Calc. Sn, 31.4%. IR (cm−1, Nu-
jol):w(SnꢀS) 240. 1H-NMR (l, CDCl3): 0.84 (m, 2H,
CH2), 1.26 (s, 4H, CH2), 7.45 (m, 10H, C6H5). 13C-
NMR (l, CDCl3): 24.7 (CH2), 39.3 (CH2), 129.10,
130.41, 134.74, 135.35 (C6H5). 119Sn-NMR (l, CDCl3):
25.7. Mo¨ssbauer (mm
s
−1): l=1.3890.01, Z=
2.2.1.2. Na2EDT. A reaction mixture of H2EDT (0.600
g, 6.38 mmol) and NaOMe (0.700 g, 12.96 mmol) in
THF (20 ml) was stirred for 1 h in a Schlenk flask. The
solvent was carefully removed from the white Na2EDT
precipitate using a cannula and the solid was collected
and dried under vacuo. The product was shown to be
free of the SH group by the absence of w(SꢀH) stretch
at 2500 cm−1 [6]. M.p. 230°C (dec). Anal. Calc. for
C2H4S2Na2: C, 17.39; H, 2.89. Found: C, 17.27; H,
2.68%.
1.8090.01; [lit. values [8]: l=1.39, Z=1.72.].
2.3. X-ray crystal structure elucidation
General operating procedures and listings of pro-
grams have been given previously [9]. Data were col-
lected using a standard moving crystal, moving detector
technique with fixed background counts at each ex-
treme of the scan. All data were corrected for Lorentz
and polarization effects, and equivalent data were then
averaged to yield a unique set of intensities. An absorp-
tion correction was made, based on the measured di-
mensions of the crystal. The structures were solved by
direct methods and Fourier techniques and refined by
full-matrix least-squares. Details of crystallographic
2.2.1.3. Na2PDT. This was prepared in a similar man-
ner to that described for Na2EDT. M.p. 250°C (dec).
Anal. Calc. for C3H6S2Na2: C, 23.68; H, 3.94. Found:
C, 23.08; H, 3.92%.

84
A.P.G. de Sousa et al. / Journal of Organometallic Chemistry 605 (2000) 82–88
Table 1
3. Results and discussion
Summary of crystallographic data collection for complexes 1 and 2
The thiolate ligands used and the complexes, 1–3,
obtained are shown in Figs. 1 and 2, respectively. The
salts of the ligands could be handled in air but should
be kept under an inert atmosphere because they can
suffer hydrolysis in the presence of moisture, after some
days. All complexes were soluble in common organic
solvents like THF, toluene and CH2Cl2. Despite using a
1:2 mole ratio of Ph2SnCl2: KMBT, only one chloride
was replaced in Ph2SnCl2, see Eq. (1):
Empirical formula
Formula weight
C19H14ClNS2Sn
474.59
C14H14S2Sn
365.07
6.191(1)
13.000(1)
17.612(2)
,
a (A)
9.146(1)
9.259(1)
12.347(1)
74.62(1)
78.89(1)
67.87(1)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
Z
4
−3
,
V (A
)
928.77
1417.46
P212121
Mo–Ka
(0.71073)
1.711
20.680
45
0.0491, 0.0453
1.838
(
Space group
Radiation
P1
Ph2SnCl2+2MBT−
Mo–Ka
(0.71073)
1.697
Dcalc (g cm−3
)
“Ph2Sn(Cl)(MBT)+MBT− +Cl−
(1)
v (cm−1
)
17.411
50
0.0505, 0.0502
2.220
−165
212
2qmax (°)
R, Rw
GOF
Temperature (°C)
No. of parameters refined
No. reflections
The retention of a chloride group at tin maintains
sufficient Lewis acidity at tin to allow its strong coordi-
nation with the hard internal nitrogen center in the
thiolato ligand and hence formation of a relatively
strong chelate complex [10]. As shown later, the pres-
ence of a chelated structure for 1, with five-coordinate
tin, in the solid state is clear from the X-ray study (and
also from the Mo¨ssbauer data). The l119Sn-NMR value
for 1 −177.1 ppm in solution suggests that the SnꢀN
interaction probably survives in solution and that a
five-coordinate species is maintained. Five-coordinate
ClPh2SnXY compounds (X and Y=eletronegative
groups) in solution have l 119Sn-NMR values in the
region −140 to −180 ppm, depending on the groups
present, e.g. l119Sn-NMR values of −14393 and
−17393 ppm for five-coordinate anions in
[cation][ClPh2Sn(dmit)] [10] and [cation][ClPh2Sn-
(dmio)] [11] complexes, respectively, in solution [H2–
dmit=4,5-dimercapto-1,3-dithiole-2-thione and H2–
dmio=4,5-dimercapto-1,3-dithiole-2-one]. Complexes
2 and 3 have been previously described in the literature
[7]. Their syntheses appear deceptively straight forward;
however serious problems were encountered in isolating
pure materials from the reaction mixtures. Compound 2
was also particularly sensitive to hydrolysis, as reported
by other workers [12]. As described below, the tin
center in 2 is essentially four-coordinate in the solid
state, from the X-ray study and from the Mo¨ssbauer
spectrum [13]. The Mo¨ssbauer and 119Sn-NMR spectra
point to 3 being a four-coordinate species too.
−165
154
1146/1109
3560/3258
(collected/independent)
Fig. 2. Compounds studied in the present work.
data collection, structure refinement and crystal data
are given in Table 1. Complex 1 crystallizes in the space
(
group P1. Cell constants were obtained from the refine-
ment of 115 reflections. A total of 3560 reflections were
collected of which 3258 were independent and 2717
were flagged as observed (F\2.33|(F)). Their reflec-
tions were collected at −165° in 2q–q scan mode with
a scan rate of 8.0° min−1. Most hydrogen atoms were
visible in a difference Fourier phased on the non-hydro-
gen atoms and were included in their idealized positions
as fixed isotropic contributors in the final cycles of
refinement. Compound 2 crystallizes in the space group
P212121. Cell constants were obtained from the refine-
ment of 156 reflections. A total of 1146 reflections were
collected of which 1109 were independent and 999 were
flagged as observed (F\2.33|(F)). Hydrogen atoms
were readily located in a difference Fourier phased on
the non-hydrogen atoms, and were included as fixed
contributions in the final cycles of refinement.
3.1. X-ray crystal structures
Crystals of complex Ph2Sn(Cl)(MBT) (1), suitable for
X-ray crystallographic analysis was obtained from a
hexane solution that was allowed to evaporate at room
temperature. Crystals of Ph2SnEDT, 2, were obtained
in the same way. Crystallographic data for the com-
plexes are shown in Table 1. Selected bond lengths and
bond angle parameters are presented in Tables 2 and 3
for complexes 1 and 2, respectively. The molecular

A.P.G. de Sousa et al. / Journal of Organometallic Chemistry 605 (2000) 82–88
85
structures and labeling schemes are shown in Figs. 3
and 4, respectively.
3.1.1. Compound 1
The geometry about tin in 1 is distorted trigonal-
bipyramidal. Tin forms four primary bonds: two to the
phenyl groups one to the chloride and sulfur atoms.
Table 2
,
X-ray selected bond distances (A) and angles (°) for complex 1
Bond distances
SnꢀCl
SnꢀN
SnꢀC(8)
S(17)ꢀC(16)
NꢀC(16)
2.443(22)
2.405(7)
2.119(8)
1.738(8)
1.306(11)
SnꢀS(15)
SnꢀC(2)
S(15)ꢀC(16)
S(17)ꢀC(18)
NꢀC(23)
2.485(22)
2.128(8)
1.703(9)
1.767(9)
1.397(11)
Fig. 4. Atom arrangements and numbering system for compound 2.
Probability ellipsoids drawn at 30%.
There is also an intramolecular SnꢀN interaction which
produces a four-membered chelate ring and a five-coor-
dinate tin atom. The axial–Sn–axial angle,
[N(24)ꢀSnꢀCl(4)=155.27(17)°], is well removed from
the ideal trigonal-bipyramidal angle, but is strongly
affected by the small bite angle. The SnꢀN(24) distance,
Bond angles
ClꢀSnꢀS(15)
ClꢀSnꢀC(2)
S(15)ꢀSnꢀN
S(15)ꢀSnꢀC(8)
NꢀSnꢀC(8)
SnꢀSꢀC(16)
90.90(8)
96.72(23)
64.65(17)
114.08(23)
94.0(3)
ClꢀSnꢀN
ClꢀSnꢀC(8)
S(15)ꢀSnꢀC(2)
NꢀSnꢀC(2)
C(2)ꢀSnꢀC(8)
C(16)ꢀS(17)ꢀC18)
155.27(17)
99.71(24)
118.57(22)
92.32(28)
124.20(3)
89.20(4)
,
2.4057 A is greater than the sum of the covalent radii of
82.3(3)
,
Sn and N (2.15 A), but is considerably less than the
,
sum of the van der Waal’s radii (3.75 A) [14] and less
than values reported in various five-coordinate
triphenyltin heteroarenethiolates [12]: this is as expected
from the differences in the Lewis acidities of tin centers
in a ClPh2Sn–thiolate and in Ph3Sn–thiolates. The
SnꢀS bond length in 1 is generally also slightly longer
than the SnꢀS bond lengths in the five-coordinate
triphenyltin heteroarenethiolates [12].
Table 3
,
X-ray selected bond distances (A) and angles (°) for complex 2
Bond distances
SnꢀS(2)
SnꢀC(6)
S(2)ꢀC(4)
2.424(5)
2.147(14)
1.821(21)
SnꢀS(1)
SnꢀC(12)
S(1)ꢀC(3)
2.408(5)
2.155(15)
1.831(18)
Bond angles
S(2)ꢀSnꢀS(1)
S(2)ꢀSnꢀC(6)
S(2)ꢀSnꢀC(12)
SnꢀS(1)ꢀC(3)
S(2)ꢀC(4)ꢀC(3)
92.50(16)
107.20(4)
111.20(5)
95.70(5)
S(1)ꢀSnꢀC(12)
C(6)ꢀSnꢀC(12)
SnꢀS(2)ꢀC(4)
S(1)ꢀSnꢀC(6)
C(4)ꢀC(3)ꢀS(1)
111.90(4)
116.40(6)
95.30(6)
114.00(94)
113.40(12)
3.1.2. Compound 2
The two SnꢀS bond lengths in 2 (Table 3) are shorter
than the SnꢀS bond length in 1: the SnꢀC bonds lengths
in the expected region. The geometry about tin is
distorted tetrahedral. The distortion away from ideal
tetrahedral geometry is apparent from the range of
bond angles at tin: −92.50(16)° [S(2)ꢀSnꢀS(1)] to
116.4(6)° [C(6)ꢀSnꢀC(12)]. Both the bond lengths and
range of bond angles in 2 are similar to those in other
diorganotin ethanedithiolates, R2Sn(EDT); R=Me
{89.55(3)° [SꢀSnꢀS] to 121.73(18)° [CꢀSnꢀC] [16], Bu
{[90.5° [SꢀSnꢀS] to 122.6° [CꢀSnꢀC] [15] and tBu
{92.2(1)° [SꢀSnꢀS] to 118.5(3)° [C(6)ꢀSnꢀC(12)] [18].
However, diorganotin dithiolates are coordinatively un-
saturated species and will tend to extend their coordina-
tion numbers, at least in the solid state, beyond four, if
steric effects allow. This is frequently achieved by inter-
molecular SnꢀS associations [17], as for examples in
Bu2Sn(EDT) and Bu2Sn(EDT) [17] and Me2Sn(EDT)
[16]. The closest intermolecular Sn···S distance in 2 is
117.00(15)
,
3.885 A and is just within the sum of the van der
,
Waals’ radii of Sn and S (4.0 A) [15]. It is apparent,
Fig. 3. Atom arrangements and numbering system for compound 1.
Probability ellipsoids drawn at 30%.
that the presence or absence of the additional inter-

86
A.P.G. de Sousa et al. / Journal of Organometallic Chemistry 605 (2000) 82–88
Table 4
Semi-empirical PM3 geometrical parameters for complexes 2 and 3
,
Bond distances (A)
Bond angles (°)
Complex 2
Complex 3
Complex 2
Complex 3
SnꢀS(2)
SnꢀS(1)
SnꢀC(4)
SnꢀC(5)
S(2)ꢀC(26)
S(1)ꢀC(27)
C(26)ꢀC(27)
C(26)ꢀC(32)
2.52(7)
2.52(8)
2.08(6)
2.08(3)
1.82(4)
1.82(4)
1.51(5)
2.52(9)
2.52(7)
2.09(2)
2.08(3)
1.82(5)
1.82(4)
S(2)ꢀSnꢀS(1)
S(2)ꢀSnꢀC(4)
S(2)ꢀSnꢀC(5)
S(1)ꢀSnꢀC(4)
S(1)ꢀSnꢀC(5)
C(4)ꢀSnꢀC(5)
SnꢀS(2)ꢀC(26)
SnꢀS(1)ꢀC(27)
89
99
112
114
114
112
112
97
110
111
111
110
111
104
104
1.52(0)
97
Torsion angles (°)
SnS(2)C(26)ꢀC(27)
SnS(2)C(26)ꢀC(32)
SnS(2)C(26)ꢀH(28)
SnS(2)C(26)ꢀH(29)
SnS(1)C(27)ꢀC(26)
SnS(1)C(27)ꢀC(32)
SnS(1)C(27)ꢀH(31)
SnS(1)C(27)ꢀH(30)
S(2)C(26)C(27)ꢀS(3)
S(1)C(27)C(32)ꢀC(26)
−41
55
175
−71
85
198
−41
−56
184
71
85
198
61
87
S(2)SnC(4)ꢀC(11)
S(2)SnC(4)ꢀC(12)
S(1)SnC(4)ꢀC(11)
S(1)SnC(4)ꢀC(12)
−94
85
5.6
−175
2.7
−177
112
−68
S(2)SnC(5)ꢀC(6)
S(2)SnC(5)ꢀC(7)
S(1)SnC(5)ꢀC(6)
S(1)SnC(5)ꢀC(7)
S(2)SnC(5)ꢀC(6)
−135
45
123
−56
−136
−131
48
119
−62
−131
molecular Sn···S interactions have only a small effect on
the molecular geometry of the R2Sn(EDT) compounds.
If any trend is detected it is that the greater the strength
of the intermolecular Sn···S interaction, i.e. the smaller
the Sn···S separation, the smaller is the SꢀSnꢀS in-
tramolecular angle. In all cases this intramolecular an-
gle is very close to 90° and suggests the importance of
p-orbitals in the bonding in these 1,2-dithiolates. As a
comparison, the SꢀSnꢀS bond angle in Ph2Sn(SPh)2 is
110.8(1)° [19].
computed SnꢀS bond distances were, on average, about
,
0.1 A longer than the values obtained in the X-ray
determination and the calculated S(2)ꢀSnꢀS(1) bond
angle for complex 2 was 89.2°, a figure close to the
value determined by X-ray, Table 3.
A Mulliken populational analysis showed that the
electron density left on the s, px, py and pz tin atomic
3.2. Semi-empirical calculations
We could not obtain crystals of good quality of
complex 3 to solve the structure by X-ray, therefore,
PM3 semi-empirical calculations [20] were performed in
order to determine a equilibrium molecular geometry
for this complex. To allow a comparison with experi-
mental data obtained from the X-ray investigation,
PM3 semi-empirical calculations were also carried out
on 2. The data obtained for these complexes are shown
in Table 4 and Fig. 5. As can be observed, Table 4, the
Fig. 5. Proposed molecular structure for compound 3 according to
PM3 calculations.

A.P.G. de Sousa et al. / Journal of Organometallic Chemistry 605 (2000) 82–88
87
tion of SnS. The experimental yield, 31.23%, agreed
very well with the calculated yield, 31.82%. The identity
and phase purity of the residue was determined by
comparison of the X-ray diffractogram with that found
in the ICDD Powder Diffraction File (21-1250). Com-
plex 2, in the first stage of decomposition, formed
(C6H5)2SnS; yields: 84.29 (exp.) and 83.56 (calc.) and
complex 3, (C6H5)2SnS2; yields: 91.24 (exp.) and 89.89
(calc.)
4. Conclusions
Fig. 6. TGA curve, in nitrogen, for compound 1.
PM3 semi-empirical calculations on 2 were in basic
agreement with parameters obtained in an X-ray crys-
tallographic study. In particular, the calculations pre-
dicted the near 90° SꢀSnꢀS bond angle. The
calculations indicated different orbital contributions to
the SnꢀS bonding in 2 and 3.
The N,S-chelate 1 was found to be a better source of
SnS on thermolysis than either of the S,S-chelates 2
and 3.
orbitals makes an excess of 41% of s orbital character
and a reduction of 15% of p orbital character, as
compared with pure sp3 hybrids orbitals. This 15%
atomic p orbital reduction leads to an increase of 5%
per p atomic tin orbital to the molecular bond orbitals,
what corresponds to a total of 90% p character, instead
of the 75% pure sp3 hybrid orbitals. On the other hand,
the SnꢀS and SnꢀC bound Mulliken populations analy-
sis showed tin using more p orbitals to form bonds with
the S atoms, whereas the density population over the
SnꢀC bonds are more uniformly distributed among the
s and p orbitals. Therefore, according to these results,
one should expect a deviation of the SꢀSnꢀS bond angle
to be less than the sp3 109° bond angle; found 89.2°,
Table 4, while the remaining two SꢀSnꢀC and CꢀSnꢀC
bond angles were expected to be less sensitive, staying
slightly larger than 109°.
In complex 3, tin forms a six-membered ring with the
[PDT]−2 ligand, and, among others, boat and chair
minimum energy conformations, could be expected for
the chelate ring. The PM3 results however, showed that
only the chair conformation is stable, Fig. 5; an initial
boat conformation always leads to a chair form. In 3
the geometry around tin is found to be less distorted
from an ideal tetrahedral arrangement, with bonding
angles close to those expected from the ‘pure’ sp3
hybrid orbitals. The larger SꢀSnꢀS bond angle in 3, as
compared with that of 2, is accounted for by the
decrease in the tension energy of the six-membered ring.
The Mulliken population analysis for this complex
parallels the results found for 2. The analysis confirms
that the formation of the chelate ring is very favorable
and it predicts the orbitals used to form the bonds in
order to diminish the ring tension.
5. Supplementary material
A table of complete crystallographic data, tables of
fractional atomic coordinates for all atoms, complete
list of bond distances and angles and tables of an-
isotropic displacement parameters are available, free of
charge, from The Director, Cambridge Crystallographic
Data Center, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: +44-1223-336033; e-mail: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk) quot-
ing codes 132683 and 132684 for compounds 1 and 2,
respectively.
Acknowledgements
The agencies Fapemig, CNPq and CENAPAD/MG-
CO are thanked for their support.
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