Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3]- and Pt(R2SO)2Cl2

Article abstract of DOI:10.1016/j.ica.2007.06.004

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (

Full text of DOI:10.1016/j.ica.2007.06.004

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 16–28
www.elsevier.com/locate/ica
Multinuclear magnetic resonance study of Pt(II) compounds
with sulfoxide ligands and crystal structures of complexes
of the types [Pt(R2SO)X3]ꢀ and Pt(R2SO)2Cl2
*
Fernande D. Rochon , Corinne Bensimon, Christian Tessier
`
´ ´
De´partement de chimie, Universite´ du Que´bec a Montreal, C.P. 8888, Succ. Centre-ville, Montreal, Canada H3C 3P8
Received 17 May 2007; accepted 3 June 2007
Available online 12 June 2007
Abstract
Pt(II) complexes of the types K[Pt(R2SO)X3], NR4[Pt(R2SO)X3] and Pt(R2SO)2Cl2 (where X = Cl or Br) were characterized by mul-
tinuclear magnetic resonance spectroscopy (195Pt, 1H and 13C). In 195Pt NMR, the chloro ionic compounds have shown signals between
ꢀ2979 and ꢀ3106 ppm, while the cis disubstituted complexes were observed at higher fields, between ꢀ3450 and ꢀ3546 ppm. The signal
of the compound trans-Pt(DPrSO)2Cl2 was found at higher field (ꢀ3666 ppm) than its cis analogue (ꢀ3517 ppm), since p-back-donation
is considerably less effective in the trans geometry. In 1H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl3]ꢀ, but for
the other more sterically hindered ligands, two series of resonances were observed for the protons in a and b positions. The coupling
constant 3J(195Pt–1H) are between 15 and 33 Hz. The 13C NMR results were interpreted in relation to the concept of inversed polariza-
2
3
tion of the p sulfoxide bond. The J(195Pt–13C) values vary between 35 and 66 Hz, while a few J(195Pt–13C) couplings were observed
(13–26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)4[Pt(TMSO)Cl3], N(Me)4[Pt(DPrSO)Cl3], K[Pt(EM-
SO)Cl3], K[Pt(TMSO)Br3] Æ H2O and N(Et)4[Pt(DPrSO)Br3] and one disubstituted complex cis-Pt(DBuSO)2Cl2 were determined. The
trans influence of the different ligands is discussed.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Platinum; Sulfoxide; X-ray crystal structure; NMR
1. Introduction
Structural parameters of free and metal coordinated sulfox-
ides have been reviewed by Calligaris [2,3].
Our research group has been involved in Pt–sulfoxide
complexes for several years. These ligands have interesting
behaviors, especially because of their p-back electron accept-
ing properties. Sulfoxides are bonded to Pt(II) (soft metal)
through their S atom, except for very sterically demanding
ligands like di-isoamylsulfoxide or in the cis-[Pt(DMSO)4]2+
ion, which contains two S-bonded and two O-bonded
DMSO ligands [1]. Most of the studies on Pt–sulfoxide com-
plexes were done with the most common ligand, DMSO,
while published results on other sulfoxides are less common.
Because of the large trans effect of sulfoxides, the aque-
ous reaction of K2[PtCl4] with an excess of sulfoxide pro-
duces the trans disubstituted isomer, which rapidly
isomerizes to cis-Pt(R2SO)2Cl2, unless the ligand is very
sterically demanding. The greater stability of the cis-disulf-
oxide complexes has been explained by the enhanced (d–d)p
bonding, which is more effective in the cis configuration
[4,5]. The crystal structures of several cis-Pt(R2SO)2Cl2
have been published but only one trans dichloro structure
was reported, namely trans-Pt(DPrSO)2Cl2 [6] and one dii-
odo compound, trans-Pt(DMSO)2I2 [7]. Monosubstituted
complexes are more difficult to prepare, especially those
containing the longer chain sulfoxides, which are not very
soluble in water.
*
Corresponding author. Tel.: +1 514 987 3000x4896; fax: +1 514 987
4054.
E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.06.004

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
17
Multinuclear magnetic resonance spectroscopy is a good
method to study the nature of the metal–ligand bonds in
Pt–sulfoxides complexes. The r bond (L!Pt) increases
the electron density on the Pt atom and reduces it on the
sulfoxide ligand. Back-donation from the Pt atom (Pt!L)
reduces the electron density on the Pt atom, while it is
increased on the sulfoxide. The overall electron density
cell dimensions were determined at room temperature,
from a least-squares refinement of the angles 2h, x and v
obtained for well-centered reflections. The data collections
were made by the 2h/x scan technique using the XSCANS
program [8] and the P3/P4 program for crystal 3 [9]. Inten-
sities of three standard reflections were monitored every 97
reflections to check the stability of the crystals. The coordi-
nates of the Pt atoms were determined by direct methods
using the Siemens SHELXTL system [10]. All the other non-
hydrogen atoms were found by the usual Fourier methods.
The refinement of the structures was done on F2 by full
matrix least-squares analysis using all reflections. Hydro-
gen atom positions were fixed in their calculated position
with Ueq = 1.2 Ueq (or 1.5 for methyl group) of the carbon
to which they are bonded. Corrections were made for
absorption (psi-scan for crystals 2 and 4 and Gaussian
integration for the others), Lorentz and polarization effects
using the XPREP program [11]. The residual peaks were
located in the close environment of the platinum atom.
Disorder was observed in the two terminal C atoms of
one butyl chain in crystal 1. The experimental details and
crystallographic data of the six crystals are shown in
Table 1.
The K[Pt(R2SO)Cl3] complexes were synthesized by
slight variations of the method described by Kukushkin
et al. [12] for the preparation of the DMSO compound.
Purified K2[PtCl4] was dissolved in a minimum quantity
of water. The sulfoxide is added in a 1:1 proportion. The
ligands DPrSO and DBuSO were dissolved in a small
quantity of methanol and DPhSO in ethanol before their
addition to the Pt salt. The mixture is stirred at room tem-
perature for 24 h (48 h for DPhSO), filtered and the filtrate
evaporated to dryness. The residue is shaken with acetone
to remove KCl and unreacted K2[PtCl4], which are filtered
out. The yellow solution is evaporated to dryness, washed
with diethylether and dried in a dessicator under vacuum.
K[Pt(DMSO)Cl3]: Yield 88%, dec. 180–185°C; K[Pt(EM-
SO)Cl3]: Yield 75%, dec. 170–173°C; K[Pt(DPrSO)Cl3]:
Yield 68%, dec. 145–152°C; K[Pt(TMSO)Cl3]: Yield 71%,
dec. 185–195°C; K[Pt(DBuSO)Cl3]: Yield 67%, dec. 159–
161°C; K[Pt(DPhSO)Cl3]: Yield 51%, dec. 192–195°C;
K[Pt(MeBzSO)Cl3]: Yield 49%, dec. 180–183°C.
1
on the Pt atom can be studied in 195Pt NMR, while H
and 13C NMR will give information on the electron density
on the ligand.
Complexes of the types K[Pt(R2SO)Cl3], and
Pt(R2SO)2Cl2 have been synthesized and their multinuclear
magnetic resonance spectra measured. Most of the ionic
compounds are soluble in water and insoluble in chloro-
form or other organic solvents except for the ligands
containing a long organic radical chain, while the disubsti-
tuted compounds are completely insoluble in water. In
order to compare the NMR data, compounds of the type
N(n-C4H9)4 [Pt(R2SO)Cl3] were also prepared, since these
are usually soluble in organic solvents like CDCl3.
Sulfoxides with different steric hindrance were chosen:
dimethylsulfoxide (DMSO), cyclic tetramethylenesulfoxide
(TMSO), ethylmethylsulfoxide (EMSO) di-n-propylsulfox-
ide (DPrSO), di-n-butylsulfoxide (DBuSO), dibenzylsulfox-
ide (DBzSO), methylbenzylsulfoxide (MeBzSO) and
diphenylsulfoxide (DPhSO). These complexes were charac-
1
terized mainly by H, 13C and 195Pt NMR spectroscopy.
The crystal structure of five ionic monosulfoxide and
one disubstituted complexes were studied by X-ray diffrac-
tion methods and the results are also reported in this paper.
2. Experimental
K2[PtCl4] was obtained from Johnson Matthey Inc. and
it was recrystallized in water before use. The sulfoxide
ligands were purchased from Aldrich except dipropylsulf-
oxide, which was bought from Phillips Petroleum Com-
pany. The solvents CD2Cl2, CDCl3 and D2O were
bought from MSD Isotopes.
A Fisher-Johns instrument was used to determine melt-
ing and decomposition points which were not corrected.
The IR spectra were measured in KBr pellets on a Perkin
Elmer 783 spectrometer between 4000 and 280 cmꢀ1. Most
of the NMR spectra were measured on a Varian Gemini
300BB spectrometer operating at 300.075 MHz,
75.462 MHz and 64.270 MHz for 1H, 13C and 195Pt respec-
tively. A few 13C NMR spectra (mostly the potassium ionic
compounds) were measured with a Bruker WH-80 instru-
ment operating at 20.15 Hz. The residual solvent peaks
The compounds K[Pt(R2SO)Br3] were prepared from
the reaction of the trichloro analogue with an excess of
KBr in water.
The complexes N(n-Bu)4[Pt(R2SO)Cl3] were prepared as
follows. K[Pt(R2SO)Cl3] (ꢁ100 mg) is dissolved in a mini-
mum quantity of water. N(n-Bu)4Cl is added in a 1:1 pro-
portion and a yellow precipitate appears immediately,
except for the DPrSO compound which forms an oil. The
precipitate is filtered, washed with water, dried and finally
washed with diethylether. The oily compound N(n-
Bu)4[Pt(DPrSO)Cl3] is washed only with diethylether and
dried. The yields are quantitative.
1
were used as references for the H and 13C NMR spectra.
The external reference for 195Pt was K[Pt(DMSO)Cl3] in
D2O adjusted at ꢀ2998 ppm from Na2[PtCl6] (d(195Pt) =
0 ppm).
The crystallographic studies were done on a Siemens P4
diffractometer using graphite-monochromatized Mo Ka
The Pt(R2SO)2Cl2 compounds were prepared as already
published [4,13] for most of the ligands. The yields vary
between 71% and 86%. Pt(DPhSO)2Cl2 was synthesized
˚
(k = 0.71073 A). The crystals were selected after examina-
tion under a polarizing microscope for homogeneity. The

18
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
Table 1
Crystallographic data for the six crystals
Crystal
1
2
3
4
5
6
Name
N(Bu)4[Pt(TMSO)Cl3] N(Me)4[Pt(DPrSO)Cl3] K[Pt(EMSO)Cl3] K[Pt(TMSO)Br3] Æ H2O N(Et)4[Pt(DPrSO)Br3] Pt(DBuSO)2Cl2
Chemical
formula
Mw
C20H44Cl3NOPtS
C10H26Cl3NOPtS
C3H8Cl3OPtSK C4H10Br3KO2PtS
C14H34Br3NOPtS
C16H36Cl2O2PtS2
648.06
509.82
P212121
7.755(2)
13.696(5)
16.794(5)
90
423.69
P21/n
596.10
P21/n
699.30
Cc
590.56
ꢀ
ꢀ
Space group
P1
P1
˚
a (A)
11.361(3)
11.622(2)
12.287(2)
67.578(12)
66.454(14)
89.158(16)
9.092(8)
6.951(4)
16.828(11)
90
8.218(2)
20.959(5)
14.368(4)
90
10.852(2)
15.810(3)
13.727(2)
90
103.112(15)
90
2293.7(7)
4
2.025
8.222(3)
12.431(5)
13.132(6)
64.69(3)
81.71(5)
72.97(4)
1159.9(8)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
90
90
103.18(6)
90
94.16(2)
90
3
˚
Volume (A ) 1356.6(5)
1783.7(10)
4
1.898
8.421
1035.5(13)
4
2468.2(11)
8
Z
2
qcalc (g cmꢀ3
l(Mo Ka)
)
1.587
5.554
2.776
3.208
1.691
6.465
14.868
21.554
11.434
(cmꢀ1
)
F(000)
Measured
reflections
Independent
reflections
(Rint
R1 (observed) 0.0384
648
5582
984
2008
792
3745
2144
19073
1328
10358
584
3164
5296 (0.019)
2008 (0.0)
1836 (0.018)
4844 (0.084)
5274 (0.055)
2917 (0.031)
)
0.0400
0.0963
1.064
0.0207
0.0488
0.967
0.0574
0.1429
0.829
0.0426
0.0832
1.008
0.0502
0.1348
1.056
wR2 (all)
0.0997
S
1.139
P
P
P
P
2
2
1=2
R1 = (jFo ꢀ Fcj)/ jFoj, wR2 ¼ ½ ðwðF 2o ꢀ F c2Þ Þ= ðwðF o2Þ Þꢂ
.
using a large excess of ligand (Pt:DPhSO = 1:3) and using
slight heating (ꢁ40°) during 24 h. The mixture was then fil-
tered and the precipitate washed several times with ethanol
and then with diethylether. The yield is only 17%. For the
DPrSO compound, the method of Rochon et al. [13] was
used. K2[PtCl4] was dissolved in a minimum volume of
water with the ligand in a proportion Pt:DPrSO = 1:2.5.
A bright yellow compound can be filtered after 15 min.
The product is trans-Pt(DPrSO)2Cl2. The filtrate is stirred
overnight. The white precipitate can then be filtered,
washed with water, dried and washed with diethylether.
The yield for cis-Pt(DPrSO)2Cl2 is 35%.
A few other complexes were prepared by simply reacting
K2[PtCl4] with R2SO in a 1:2 proportion in order to obtain
a mixture of K[Pt(R2SO)Cl3] and Pt(R2SO)2Cl2, which can
be easily separated by dissolving the monosubstituted ionic
compound in water.
sterically hindered ligands. When the ratio is reduced to
1:<2, both the disubstituted compound and the soluble
K[Pt(R2SO)Cl3] will be formed. The two complexes can
be easily separated by filtering the insoluble Pt(R2SO)2Cl2.
For the longer chain sulfoxides which are insoluble in
water, a mixture of water and methanol or ethanol was
used as solvent.
For ligands which cannot accept p back-donation like
amines, the trans isomers are thermodynamically more sta-
ble than the cis isomers because of steric effects. Sulfoxides
can form strong p-bonding with Pt(II). The trans effect of
sulfoxide ligands is much larger than the one of chlorides.
Therefore its aqueous reaction with K2[PtCl4] produces
trans-Pt(R2SO)2Cl2, which then normally isomerizes to
the cis isomer. Disubstituted Pt(R2SO)2Cl2 compounds
have been shown to be cis isomers except for very bulky
ligands like trans-Pt(diisoamylsulfoxide)2Cl2 (4). For
DMSO, the trans dichloro compound cannot be isolated,
but trans-Pt(DPrSO)2Cl2 has been isolated after a few min-
utes of reaction and its crystal structure was published [6].
The trans–cis isomerization in water has been explained by
the enhanced (d–d)p bonding which is much more effective
in the cis configuration than in the trans geometry, because
of the geometry of the d orbitals [4,5].
3. Results and discussion
3.1. Preparation of the complexes
The aqueous reaction of K2[PtCl4] with R2SO in a 1:>2
proportion produces Pt(R2SO)2Cl2 which is very insoluble
in water. The time of reaction depends on the steric hin-
drance of the sulfoxide ligand. A yellow precipitate forms
in the first few minutes of the reaction indicating the pres-
ence of the trans compound. The colour of the precipitate
changes gradually to the almost white cis isomer. The
change is very rapid for DMSO and much slower for more
The ionic compounds N(n-Bu)4[Pt(R2SO)Cl3] were pre-
pared from the aqueous reaction of K[Pt(R2SO)Cl3] with
[N(n-Bu)4]Cl. The tetrabutylammonium complexed salt
precipitates almost instantaneously.
The m(S–O) absorption band of free sulfoxides are in the
region 1020–1060 cmꢀ1. In Pt(II) complexes, sulfoxides are

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
19
bonded to the metal by the S atom and the vibration is
expected to absorb at higher energy than in the free sulfox-
ide molecule [14]. An increase in frequency of 50–120 cmꢀ1
is usually observed.
The nature of the Pt–S bond is not well known yet,
although sulfoxides are known to accept p back-donation
because of the presence of vacant p* orbitals on the ligand.
The greater stability of the cis isomer has been attributed to
the more effective (d–d)p bonding in the cis geometry and
can overcome the interligand repulsions, which are larger
in the cis configuration. Therefore it is generally accepted
that the Pt–sulfoxide bond is of multiple character. Thus
back-donation is quite important in these complexes and
its extent could be studied by multinuclear magnetic reso-
nance spectroscopy.
For the disubstituted compounds, the spectra of the cis
isomers show two m(Pt–Cl) bands but only one vibration
mode is observed for the trans complexes (as expected
for C2v and D2h symmetries). For example, one band
was reported for trans-Pt(DPrSO)2Cl2 and trans-Pt(MeBz-
SO)2Cl2 at 340 and 349 cmꢀ1 respectively, whereas two
m(Pt–Cl) modes were observed for the cis analogues at
349, 324 and 331, 311 cmꢀ1 respectively [13]. In crystal
6, two bands were observed at 335 and 320 cmꢀ1 as
expected.
The 13C NMR spectra of the complexes K[Pt(R2SO)Cl3]
were measured in D2O and the chemical shifts are shown in
Table 2. The Dd values ðdcomplex ꢀ dfree R SOÞ were also cal-
2
Several synthesized compounds were characterized in
culated from the spectra of the free sulfoxides measured
in D2O. The experimental results will be discussed for a
few representative complexes. Most of the complexes in
this section were measured on a lower field instrument in
order to determine more accurately the coupling constants
J(195Pt–13C).
1
solution by multinuclear (195Pt, 13C and H) magnetic res-
onance spectroscopy. A few complexes gave adequate crys-
tals which were studied by X-ray diffraction methods. The
discussion will start with the 13C NMR results of the
K[Pt(R2SO)Cl3] complexes measured in D2O, in order to
present the concept of inversed polarization of the p sulfox-
ide bond to interpret the results.
Coordinated DMSO shows a single resonance at lower
field than free DMSO (Dd = 4.45 ppm). This deshielding
is caused by removal or donation of electron density
through the Pt–S r-bond. The extent of the deshielding
can be interpreted by inversed polarization of electron den-
sity in the sulfoxide p bond. Cooper and Powell [15] sug-
gested polarization of electron density from oxygen
towards carbon (CO ligand) for a series of para-substituted
pyridine complexes of the type trans-Pt(CO)(NC5-
H4-4X)Cl2. Small changes in the dC of the CO ligand
3.2. 13C NMR spectroscopy of K[Pt(R2SO)Cl3]
The sulfoxide multiple bond can be pictured as a reso-
nance hybrid of three contributing structures [14].
S+
O
S
O+
S
O
l
and J(195Pt–13C) data have been interpreted by these
I
II
one (p-d) π bond
III
two (p-d) π bonds
authors in terms of slight fluctuations in the r-donor com-
ponent of the platinum–carbon bond, resulting from polar-
ization of the soft carbon–oxygen bond. As the group X on
the trans pyridine ligand became more electron withdraw-
ing, there was an increase of shielding on the C atom of
the CO ligand. The analogy between carbonyl (Pt–C„O)
and sulfoxide (Pt–S„O) compounds lead us to believe that
this effect could also be present in sulfoxide complexes. The
ꢀS„O+ bond can also be considered as a soft group and
polarization can shift the electron density from oxygen
towards the S atom when bonded to Pt(II) as in the
C„O group. An increase of electron density should be
present on the S atom, which will be reflected in a stronger
r S!Pt bond. Yonemoto [16] also explained his 13C and
14N NMR data for a series of nitriles by polarization of
the carbon–nitrogen triple bond. The concept has also been
used to interpret the 13C NMR results on Pt–acetylides [15]
and Pt–carboxylato complexes [17].
no (p-d) π-bond
The r bond (S+!Oꢀ) is formed from the overlap of a
sp3 orbital of S with the 2px orbital of the O atom. The
2py orbital of O overlaps with the 3dxy of S to form a p
bond. A second p bond can be formed from the overlap
of the 2pz orbital of O with the 3dxz orbital of the S atom.
The two back-donating p bonds feed electron density into
the vacant 3d orbitals of S. The overlap between the 3p
orbitals of S with the 2p orbitals of the C atoms is not very
effective because of the shape the orbitals and the distance
between the two centers.
Sulfoxide molecules have two potential donor sites.
When the oxygen atom is the binding site, structure I
is favored and there is a decrease in the bond order of
the S–O bond and in the vibration frequency of the
bond. When the donor site is S, the pp–dp bond charac-
ter is increased (structure III is favored) and the fre-
quency of the S–O vibration is increased. The
preference of Pt(II) (soft metal) for the sulphur donor site
is now well known and almost all Pt–sulfoxide complexes
are S-bonded, except when steric hindrance is important
as in cis-[Pt(DMSO)4]2+ (2 S-bonded and 2 O-bonded
DMSO) [1].
Cl
O
1
H3C
S
Pt
Cl
CH3
1'
Cl

20
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
When the binding site of the sulfoxide ligand is the S
enhanced in the DPrSO complex than in the DMSO
complex.
atom, resonance structure III is favored. The charge distri-
bution is then similar to the one obtained by polarization in
the carbonyl complexes (15) as discussed above. When
polarization of the S–O bond increases, the electron density
will shift from the O to the S atom and the S!Pt r bond
should also increase. The increased electron density on the
S atom will also slightly affect the C atoms, where the elec-
tron density should also slightly increase. This polarization
will result in a shielding effect on the two carbon atoms in a
position of the sulfoxide bond. The overall polarization
effect will reduce the loss of electron density on the ligand
caused by r bonding to Pt. Therefore a decrease in
The chemical shifts of the carbon atoms in free diphe-
nylsulfoxide are found at much lower field than those in
the other sulfoxides, since the atoms are influenced by the
inductive effect of both the phenyl and sulfoxide groups.
C1 is the most affected and appear at lowest field. The
13C NMR spectrum of the complex suggests that the
inversed polarization of the S–O p-bond is much more
important in this complex, since the chemical shift of C1
shows a very large shielding effect upon coordination
(Dd = ꢀ4.65 ppm). Since the electron density has increased
on the C atom of the ligand, it must also increase on the Pt
atom. Therefore the Pt–S r bond is very favored because of
the great electron attracting effect of the phenyl groups,
which pulls the p electrons from the O atom towards the
S atom in the S–O bond. The coupling constant
2J(195Pt–13C1) should be smaller than the others. But the
hybridization of C1 in the other sulfoxides is sp3, while it
is sp2 in DPhSO. The increase in s character of C1 in
DPhSO results in an increase of the coupling constant.
Therefore a high value of 56 Hz is observed. The S–O bond
in K[Pt(DPhSO)Cl3] absorbs at 94 cmꢀ1 higher than in the
free ligand.
Ddðdcomplex ꢀ dfree R SOÞ should be an indication that the
2
S–Pt r bond is also increased.
We can compare our results on K[Pt(DMSO)Cl3] with
those on K[Pt(DPrSO)Cl3] (Table 2). First, we can look
at the spectra of the two free sulfoxides. C1 in DMSO
(d = 39.91 ppm) is more shielded than C1 in dipropylsulf-
oxide (d = 53.83 ppm). Therefore, the –CH3 group in
DMSO will cause a smaller polarization of the S–O bond.
Since the two p bonds in the ionic structure III are of the
type O+!Sꢀ it seems that structure III will be more
favored in the DPrSO Pt compound than in the DMSO
complex. Therefore DMSO should form a weaker r bond
with platinum than DPrSO. The inductive effect of the
alkyl groups is a small factor, much less than the inverse
polarization of the p electrons of the S–O bond, because
of the larger freedom of mobility of the p electrons com-
pared to the r electrons. The differences of electron density
caused by the movement of the p electrons will affect not
only the Pt–S r bond, but it will also increase the electron
density on the C atoms. Since the polarization of the sulf-
oxide p bond is smaller in K[Pt(DMSO)Cl3], a larger
It seems that the Dd values are influenced by the electron
density on C1 of the free ligands. A linear relationship was
observed when Dd was plotted versus the position (d13C) of
0
C1 and C1 in the free sulfoxides (Fig. 1). For the unsym-
metrical sulfoxides, both C in a position are included in
the plot. Therefore, it seems that the C atoms (in a posi-
tions) observed at lowest fields will increase more the polar-
ization of the S–O group. Even DPhSO, which is very
different from the other sulfoxides, fits well on the plot.
Ddðdcomplex ꢀ dfree R SOÞ of C1 (4.45 ppm) is observed in
3.3. 195Pt NMR spectroscopy of all Pt(II) complexes
2
K[Pt(DMSO)Cl3] when compared with Dd of C1 in
K[Pt(DPrSO)Cl3] (3.21 ppm). For the same reasons, the
The complexes Pt(R2SO)2Cl2 and N(n-Bu)4[Pt(R2SO)-
Cl3] were studied by 195Pt NMR spectroscopy in CDCl3.
Several disubstituted compounds were also measured in
CD2Cl2. Most of the ionic salts K[Pt(R2SO)Cl3] were mea-
sured in D2O, although K[Pt(DBzSO)Cl3] was measured in
acetone since its solubility in water is too low. The chemical
shifts of the complexes are shown in Table 3 along with a
few published results.
2
coupling constant J(195Pt–13C) is larger for the DMSO
complex (56 Hz) than for the DPrSO compound (46 Hz).
These results are in agreement with the IR spectroscopic
results. The change of frequency of the S–O bond upon
co-ordination is smaller for the DMSO complex
(48 cmꢀ1) than for the DPrSO complex (120 cmꢀ1). We
can therefore conclude that the ionic structure III is more
Table 2
13C chemical shifts (d) of the complexes K[Pt(R SO)Cl ] in D O, Ddðdcomplex ꢀ dfree SOÞ in ppm and J(195Pt–13C) in Hz
R2
2
3
2
R2SO
d and (Dd)
C1
2J
C2
3J
C3
C4
C5
C11
2J
DMSO
EMSO
DBuSO
DPrSO
TMSO
MeBzSO
DPhSO
44.36 (4.45)
51.65 (4.45)
54.86 (3.50)
57.04 (3.21)
57.55 (3.20)
61.20 (2.79)
141.85 (ꢀ4.65)
56
50
47
46
44
35
56
7.46 (0.59)
25.32 (0.36)
17.30 (ꢀ0.44)
25.10 (ꢀ0.81)
128.14 (ꢀ1.94)
127.70 (1.97)
15
41.58 (4.74)
56
21.75 (0.44)
13.00 (ꢀ0.58)
13.87 (0.00)
13
26
132.59 (1.31)
129.60 (ꢀ1.02)
129.74 (ꢀ0.03)
130.26 (0.76)
41.07 (4.61)
56
133.76 (0.95)

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
21
6
5
complexes. Table 3 shows that the signals of the complexes
Pt(R2SO)2Cl2 were found between ꢀ3451 and ꢀ3546 ppm
in CDCl3, while most of the tetrabutylammonium
monosulfoxide salts were observed between ꢀ2992 and
ꢀ3025 ppm (ave. ꢀ3002 ppm) in the same solvent.
NBu4[Pt(DPhSO)Cl3] was observed at higher fields
(ꢀ3106 ppm) than the others because of the presence of
the phenyl group on the S atom. However, in the disubsti-
tuted series, the DPhSO complex was not observed at much
higher field (ꢀ3546 ppm) than the other analogues (ave.
ꢀ3503 ppm). For comparison, the spectra of some potas-
sium monosubstituted salts were measured in D2O (acetone
for the DBzSO compound). These values are also shown in
Table 3 along with a few results from the literature in dif-
ferent solvents. For a few disubstituted complexes, the
spectra were measured in CDCl3 and CD2Cl2, two very
similar solvents. Therefore the differences should be small.
For 5 compounds, the differences vary between 0 and
17 ppm (ave. 8 ppm). The signals seems slightly shifted to
lower field in CD2Cl2.
4
y= -0,0858x + 7,9541
R2 = 0,9943
3
2
1
0
30 40
50
60
70
80
90 100 110 120 130 140 150
-1
-2
-3
-4
-5
-6
δ(C1) in free ligand (ppm)
Fig. 1. Relation between Dd (ppm) of the complexes K[Pt(R2SO)Cl3] vs.
The two unsymmetrical sulfoxides EMSO and MeBzSO
form chiral Pt complexes. Only one signal was detected for
cis-Pt(EMSO)2Cl2 but two signals were observed for cis-
Pt(MeBzSO)2Cl2 at ꢀ3504 and ꢀ3511 ppm. There should
be three isomers of the latter compound, the (S,S), the
(R,R) and the meso (R,S) forms. The crystal structures of
the (S,S) form as a methanol solvate [19] and the one of
the meso form [20] were reported.
0
d (ppm) of C1 or C1 in free R2SO.
Table 3
195Pt chemical shifts (ppm) of the complexes (in CDCl3, except those
mentioned in other solvents) and DdðdNBu
ꢂ ꢀ dPtðR
Þ
½PtðR2SOÞCl3
2SOÞ2Cl2
4
R2SO
cis-
NBu4[Pt(R2SO)Cl3] Dd K[Pt(R2SO)Cl3]
Pt(R2SO)2Cl2
in D2O
TMSO
DMSO
ꢀ3451
ꢀ2993
ꢀ3009
458 ꢀ2983
The 195Pt NMR spectrum of trans-Pt(DPrSO)2Cl2 was
also rapidly measured in CDCl3. A signal readily appeared
at ꢀ3666 ppm, which disappeared also quite rapidly, while
a new signal at ꢀ3517 ppm was observed. The first signal
was assigned to the trans isomer, which isomerized rapidly
in CDCl3 solution to the more stable cis compound. To our
knowledge, this is the first report of the 195Pt NMR spec-
trum of a trans-Pt(R2SO)2Cl2 complex. The trans isomer
is observed at much higher field (Dd = 149 ppm) than its
cis analogue. This difference is in our opinion quite large.
For ligands which cannot form p-bonds like amines, the
trans isomers are more stable and they are observed at
slightly lower fields than their cis analogues. The difference
is 50 ppm for Pt(pyridine)2Cl2 [21], but close to zero for
Pt(NH3)2Cl2 [22,23] and about 15 ppm for cyclic amines
[24]. The fact that in the sulfoxides series, the cis complexes
are observed at much lower fields than the trans analogues
indicate that p-bonding is present and is much more impor-
tant in the cis complex than in the trans compound. The r
bond (L!M) causes a reduction of electron density on the
ligand and an increase on the metal atom. The p bond
(M!L) causes the reverse effect, since it increases the elec-
tron density on the ligand and reduces it on the metal
atom. If p-bonding is more important in the cis compound
than in the trans isomer, the overall electron density on the
Pt atom will be smaller in the cis geometry. Therefore the
cis isomers should be observed at lower fields than the cor-
responding trans compounds as found in the two isomers
of Pt(DPrSO)2Cl2. Since the Dd (149 ppm) is quite large,
ꢀ3450a
ꢀ3471
462 ꢀ2998 [36]
ꢀ2951 [37]b
ꢀ3459a
ꢀ3513
EMSO
DPrSO
ꢀ3517
ꢀ2987
530 ꢀ2990
ꢀ3500a
ꢀ3666 (trans)
ꢀ3519
DBuSO
ꢀ2992
ꢀ3025
527 ꢀ2991
ꢀ3509a
MeBzSO ꢀ3504
ꢀ3511
486
DBzSO
DPhSO
ꢀ3538
ꢀ3546
ꢀ3546a
ꢀ3003
ꢀ3106
535 ꢀ2979d
440 ꢀ3075
ꢀ3054c
ꢀ3075 [26]
ꢀ3064 [37]b
a
In CD2Cl2.
b
c
In acetone–water.
In CDCl3.
d
In acetone.
The shielding of a heavy atom like the 195Pt nucleus has
been expressed in the Ramsey equation [18]. Sulfoxides
form strong bonds with Pt and the metallic coefficients
terms of the platinum d orbitals in the Ramsey equation
will decrease and hence a shielding of the 195Pt NMR sig-
nals will be observed. Therefore bonded sulfoxides will
shift the 195Pt signals to higher fields compared to amines
or chloro ligands.
The resonance of the disubstituted complexes should be
observed at higher fields than the one of the monosulfoxide

22
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
the difference in p-bonding seems a very important factor.
This difference should vary with the bulkiness of the sulfox-
ide ligand, since steric hindrance is also a factor in the sta-
bility of the cis compounds. It should be larger for the less
hindered ligands. But it is not possible to isolate the trans
dichloro complexes with smaller ligands like DMSO or
TMSO.
Similar results were observed for cis- and trans-
Pt(R2SO)(pyrimidine)Cl2 where the trans complexes were
observed at higher fields than the cis isomers. The Dd
values were slightly greater for the less hindered sulfoxides
(153 ppm for DMSO and 106 ppm for DBuSO) [25]
showing the influence of steric hindrance in the stability
of the cis compounds. The results on cis- and trans-
Pt(DPhSO)(R–C„N)Cl2 are very similar. The trans
compounds were observed at higher fields and the Dd val-
ues are about 136 ppm [26]. The Dd values are smaller when
the second ligand cannot form p bonds, as in cis- and trans-
Pt(DMSO)(NH3)Cl2 (22 ppm) [27,28].
enhanced effect will increase the electron density not only
on the phenyl groups but also on the Pt atom. The effect
is not so evident in cis-Pt(DPhSO)2Cl2, probably because
of the presence of two Pt–S p bonds in cis positions com-
pared to the monosubstituted complex, where only one p
bond is formed. As already mentioned, p-bonding reduces
the electron density on the Pt atom. The benzylsulfoxide
complexes are different from the DPhSO compounds, since
the phenyl groups are not located on the binding S atom.
The presence of the methylene group is important and
the complexes behave more like alkyl sulfoxides.
The difference between the 195Pt chemical shifts of the
monosubstituted and disubstituted complexes measured
in the same solvent seems to vary with the sulfoxides.
For the ligands which do not contain any aromatic ring,
the difference seems to vary with the bulkiness around
the binding atom. It is lowest in TMSO (458 ppm) where
the C–S–C angle is the smallest (94.0(16)° [29]) and the
DMSO (462 ppm) with C–S–C angles of 98.4(6)° [30].
For the DPrSO and DBuSO compounds, the difference is
the largest (530 ppm). For the other ligands containing aro-
matic rings, the difference is 440 ppm for the DPhSO com-
plexes, 535 ppm for the DBzSO compounds and at an
intermediate value (486 ppm) between the DMSO and
DBzSO for the unsymmetric MeBzSO compounds.
In the complexes cis-Pt(R2SO)2Cl2, the d(195Pt) seems to
depend slightly on the bulkiness of the sulfoxide ligand.
The least hindered is the cyclic TMSO ligand since the
C–S–C angle is only about 94.0(16)° [29] (because of its
more rigid five-membered ring) and the next one is DMSO,
where the C–S–C angle is 98.4(6)° [30]. The angle in the
sulfoxides of the other complexes are more constant
(100–103°) [25,31,32]. Table 3 shows that the signal of
the TMSO complex was found at ꢀ3451 ppm, the DMSO
compound at ꢀ3471 ppm, while the others were observed
at slightly higher fields (ꢁꢀ3515 ppm). This is also the
opposite of the observations reported for amine ligands
where there are no p bonds. For the latter complexes, the
presence of bulkiness around the binding atom causes a
deshielding effect in 195Pt NMR, which was attributed to
the solvent effect. In a less crowded complex, the molecules
of solvent can normally approach the Pt atom on both
sides of the coordination plane and increase the electron
density in the Pt environment (shielding in 195Pt NMR).
When the ligands are sterically hindered close to its binding
site, the molecules of solvent cannot approach the Pt atom
as easily, which reduces the electron density on the Pt atom
(deshielding effect in 195Pt NMR). When two sulfoxides are
bonded to Pt, the p bonds which are located on each side of
the coordination plane will reduce the influence of the sol-
vent, since it cannot approach the Pt atom as easily as in
complexes without p-bonding.
For comparison, the 195Pt spectra of the K[Pt(R2SO)Cl3]
complexes were measured in D2O. A few results have
already been published in the literature and they are also
shown in Table 3. For most of the ligands, the d(Pt) are
close to the values measured in CDCl3 for the NBu4 com-
plexed salts. The experimental values are usually more
shielded in water compared to chloroform because of the
solvent effect. Water is a better ligand for Pt(II) than chlo-
roform and will approach more effectively the Pt atom on
both sides of the coordination plane. The presence on these
molecules of water will increase the electron density on the
Pt atom, resulting in a shielding in 195Pt NMR compared to
a more neutral solvent like chloroform. Our results do not
show this behavior, but a second factor is probably as
important as the solvent effect. The replacement of a K+
þ
cation by a much larger Nðn-BuÞ4 cation has probably a
shielding effect, which counterbalances the solvent effect.
For the DPhSO complexes, the difference between the K+þ
salt measured in water (ꢀ3075 ppm) and the Nðn-BuÞ4
salt measured in CDCl3 (ꢀ3106 ppm) seems significant
(31 ppm). This ligand has always shown a different behav-
ior, because of the presence of aromatic groups directly on
the binding atom and also because it is the most sterically
demanding ligand.
The monosubstituted compounds containing DPhSO
were observed at higher fields than the others (75–
120 ppm). This ligand is the most bulky and contains two
aromatic rings on the binding S atom. The phenyl groups
might account for a stronger r-bond and/or a weaker p-
bond. We suggest that inversed polarization of the p-elec-
trons of the ꢀS„O+ bond is responsible for the increased
electronic density on the sulfoxide ligand when bonded to
Pt as discussed in the previous section. This inverse polar-
ization would be more important in sulfoxides containing
aromatic groups attached directly on the S atom. This
1
3.4. H NMR spectroscopy
The 1H chemical shifts of the complexes cis-
Pt(R2SO)2Cl2 and NBu4[Pt(R2SO)Cl3] are listed in Tables
S1–S2 (Supplementary material). The Ddðdcomplex
ꢀ
dfree R SOÞ where the free sulfoxides were measured in the
2
same solvent are also included in the tables. The binding

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
23
of a ligand to platinum normally leads to a deshielding of
the signals in H spectroscopy, since the r bond (L!Pt)
for the –CH3 (H0) protons (difference 0.16 ppm). For the
–CH2 group, there are four different doublets of equal
intensity (Fig. 2, lower spectrum). We can compare with
the results observed in N(n-Bu)4[Pt(MeBzSO)Cl3], where
two doublets are observed for the –CH2 groups (Fig. 2,
upper). The rotation around the S–C is limited and the
geminal protons are in different environment, one close
to the O atom and one farther away. Therefore the gem-
inal protons will couple with each other to form two dou-
blets. In the chiral complex cis-Pt(MeBzSO)2Cl2, each
isomer will produce two doublets. We assume that one
series of signals (two doublets) is caused by the meso
(R,S and S,R) isomer, while the (R,R) and (S,S) forms
are responsible for the second series of resonances (also
two doublets).
1
reduces the electron density on the ligand. For sulfoxides
which are capable of accepting back-donation from the
metal, the p bond (Pt!L) will increase the electron density
on the ligand. The experimental results in Tables S1–S2
have shown that the ligands are deshielded upon coordina-
tion as indicated by the positive Dd values. The protons
close to the binding site are more affected by coordination
to the metal as expected. All the complexes containing no
aromatic groups have similar chemical shifts. The Dd val-
ues for the disubstituted compounds are slightly larger than
those of the monosubstituted complexes as expected.
The ligand TMSO is a cyclic sulfoxide and the geminal
protons on each C atom have different environment. The
protons closer to the O atom are more deshielded than
the second H on the same C atom. Therefore there should
be two different signals for the H in a positions and 2 for
those in b positions as observed. In the DMSO complexes,
only one signal is observed, but for all the other ligands the
rotation around the S–C bonds is limited and two signals
are observed for the H atoms located in a position to the
S atom. Steric factors are quite important around the S
atom. The H atoms located close to the O atom are more
deshielded that the others. In the two DBuSO complexes,
two signals are also observed for the H atoms located in
b positions.
3
Several couplings J(195Pt–1H) were observed. The val-
ues vary between 15 and 33 Hz (Tables S1–S2 (Supplemen-
tary material)). They do not seem to differ in the
disubstituted and the monosubstituted complexes.
3.5. 13C NMR spectroscopy
The 13C chemical shifts of the complexes cis-
Pt(R2SO)2Cl2 and NBu4[Pt(R2SO)Cl3] are listed in Tables
S3–S4 (Supplementary material). The Ddðdcomplex
ꢀ
dfree R SOÞ are also included in the two tables. The results
2
on the NBu4[Pt(R2SO)Cl3] species measured in CDCl3
are not very different from the results shown in Table 2
on the K+ salts measured in D2O, although the Dd values
seem slightly larger for the K+ salts in D2O. For most sulf-
oxides, the Dd values observed for the monosubstituted
complexes are smaller than those observed in the disubsti-
tuted complexes.
EMSO and MeBzSO are particularly interesting
ligands since they form chiral Pt(II) compounds. For
cis-Pt(EMSO)2Cl2, two signals (difference 0.02 ppm) were
observed for the –CH3 protons (H0) located in a position.
The different isomers are more obvious with the MeBzSO
ligand in cis-Pt(MeBzSO)2Cl2. Two signals were observed
NBu4[Pt(MeBzSO)Cl3]
–CH3
+
NBu4
CDCl3
O
H
H
H
H
S
H
C
H
H
H
C
ArH
H
–CH2–
H
–CH3
ArH
CDCl3
cis-Pt(MeBzSO)2Cl2
–CH2–
5.0
7.0
7.5
6.5
6.0
4.5
3.5
5.5
4.0
3.0
chemical shift (ppm)
Fig. 2. 1H NMR spectra of NBu4[Pt(MeBzSO)Cl3 (upper) and cis-Pt(MeBzSO)2Cl2 (lower) in the 2.8–7.7 ppm region.

24
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
The Dd values are not as large as observed on other
ligands like amines. These smaller changes upon coordina-
tion have been attributed to the inversed polarization of
the S–O p bond as discussed in Section 3.2. Again, the effect
is striking in the DPhSO compounds, where the signal of C1
(in the aromatic ring) is strongly shielded by coordination to
Pt(II). In NBu4[Pt(DPhSO)Cl3], the Dd value is ꢀ2.60 ppm
and it is ꢀ5.00 ppm in cis-Pt(DPhSO)2Cl2. As already
mentioned, the aromatic groups withdraw electron density
from the S–O p bond more effectively than in the other ana-
logues, resulting in a large increase of electron density on C1
and on the Pt atom, as observed in 195Pt NMR.
Fig. 3. Labeled diagram of the anion [Pt(TMSO)Cl3]ꢀ in crystal 1. The
A linear relationship was observed when Dd was plotted
ellipsoids correspond to 40% probability.
0
versus the position of C1 and C1 in the free sulfoxide.
These plots are shown in Fig. S1 (Supplementary material)
for cis-Pt(R2SO)2Cl2 and in Fig. S2 (Supplementary mate-
rial) for NBu4[Pt(R2SO)Cl3]. For the unsymmetrical sulf-
oxides, both C in a position are included in the plot.
Therefore, it seems that the C atoms (in a positions)
observed at lowest fields will increase more the polarization
of the S–O group, not only in the ionic monosubstituted
compounds, but also in the disubstituted complexes.
The two chiral isomers in cis-Pt(EMSO)2Cl2 and cis-
Pt(MeBzSO)2Cl2 have shown two signals for C1. The differ-
ence between the two resonances is small in the EMSO
compound (0.09 ppm) and larger in the MeBzSO species
(0.32 ppm).
It is interesting to note that several couplings
2J(195Pt–1H) and 3J(195Pt–1H) were observed. The 2J values
vary between 43 and 66 Hz and they do not seem to differ
in the disubstituted and the monosubstituted complexes.
Only one J(195Pt–1H) was observed and it was evaluated
as 25 Hz in cis-Pt(TMSO)2Cl2.
3
Fig. 4. Labeled diagram of the anion [Pt(DPrSO)Cl3]ꢀ in crystal 2. The
ellipsoids correspond to 40% probability.
3.6. Crystal structures
The crystal structures of five ionic monosubstituted
complexes and one cis disubstituted compound were
determined by X-ray diffraction methods. These crystal
are N(n-Bu)4[Pt(TMSO)Cl3] (1), NMe4[Pt(DPrSO)Cl3]
(2), K[Pt(EMSO)Cl3] (3), K[Pt(TMSO)Br3] Æ H2O (4),
NEt4[Pt(DPrSO)Br3] (5) and cis-Pt(DBuSO)2Cl2 (6).
Labeled diagrams of the six complexes are shown in Figs.
3–8. Selected bond distances and angles are listed in Tables
4 and 5. There are two independent molecules in the unit
cell of the crystal K[Pt(TMSO)Br3] Æ H2O (4).
The coordination around the Pt atom is square planar in
each crystal structure as shown by the calculation of the
best planes. The mean deviations are 0.015, 0.009, 0.095,
˚
0.033 (ave.), 0.028 and 0.006 A for crystals 1–6 respectively.
Fig. 5. Labeled diagram of the anion [Pt(EMSO)Cl3]ꢀ in crystal 3. The
ellipsoids correspond to 40% probability.
The angles around the platinum atom are close to the
expected 90° and 180° in the monosubstituted complexes.
In cis-Pt(DBuSO)2Cl2 (6), where steric hindrance is an
important factor, the deviations are larger, especially for
the S–Pt–S angle which is 96.10(11)°. These deformations
were also observed in cis-Pt(DPrSO)2Cl2 (95.9(1)°) and
cis-Pt(EMSO)2Cl2 (95.0(2)°) [31].
In the cis disubstituted compounds, the oxygen atoms of
the sulfoxide ligands are often close to the Pt(II) coordina-
tion plane, especially for more bulky ligands. In this con-
formation, the alkyl groups of the two sulfoxide ligands

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
25
are farther from the Pt plane, where steric hindrance is
most important. This was observed in cis-Pt(DBuSO)2Cl2
(6) where the deviations of the O atoms from the Pt plane
˚
are 0.028(10) and ꢀ0.070(10) A. In trans-Pt(DMSO)2I2 [7]
and trans-Pt(DPrSO)2Cl2 [6] the O atoms are not in the
˚
Pt coordination plane (deviations of ꢀ1.08 and ꢀ0.57 A
respectively), since steric hindrance is not a factor in the
trans geometry. For crystal 6, the butyl chains adopt also
the all trans conformation and the C–C–C angles are
slightly flattened (ave. 112.7(13)°) in order to reduce steric
hindrance to a minimum.
For monosubstituted complexes, steric hindrance is less
important and the deviations of the O atom from the calcu-
lated best plane are ꢀ1.335(6) (1), ꢀ0.536(13) (2),
˚
ꢀ0.469(5) (3), ꢀ1.281(13), 1.282(10) (4) and ꢀ0.011(9) A
Fig. 6. Labeled diagram of K[Pt(TMSO)Br3] Æ H2O showing the asym-
metric unit in crystal 4. The ellipsoids correspond to 40% probability.
(5). For the latter crystal which contains DPrSO, the O
atom is in the Pt plane. The results of a Cambridge search
[33,34] on published crystals containing the ion
[Pt(RR’SO)X3]ꢀ (15 structures) have shown deviations of
˚
the O atom from the Pt(II) plane between 0 and 1.36 A.
Most of the structures where the deviations from the plane
are large contain an ammonium ion or hydrogen bonds.
For the K salts, the torsion angles O–S–Pt–X are usually
small. In the reported structure of K[Pt(DMSO)Cl3] [35],
the O atom is in the Pt coordination plane by symmetry.
In N(Bu)4[Pt(DPhSO)Cl3] and N(Et)4[Pt(DPhSO)Br3] [26]
one C atom is located in the Pt plane.
The Pt–S bonds lengths are similar in the five ionic com-
˚
˚
plexes (ave. 2.202(3) A). For the TMSO complexes, the Pt–
S bond is 2.187(2) A for the trichloro compound and
˚
2.193(5) A (ave.) for the tribromo analogue. For the
DPrSO compounds, the values are 2.205(3) and 2.217(3)
respectively for the chloro and bromo salts. It seems that
the trans influence of the bromo ligand is slightly larger
than the one of the chloro ligand. Our results are similar
to those found in the compounds described in the litera-
ture. For example, in NBu4[Pt(DPhSO)Cl3] the Pt–S bond
˚
˚
Fig. 7. Labeled diagram of the anion [Pt(DPrSO)Br3]ꢀ in crystal 5. The
ellipsoids correspond to 40% probability.
is 2.201(2) A (26), while it is 2.222(4) A in NEt4[Pt(DPh-
SO)Br3] [26].
Fig. 8. Labeled diagram of cis-Pt(DBuSO)2Cl2 (6). The H atoms have been omitted for clarity. The ellipsoids correspond to 40% probability.

26
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
Table 4
Bond distances and angles in the ionic complexes [Pt(R2SO)Cl3]ꢀ
N(Bu)4[Pt(TMSO)Cl3] (1)
N(Me)4[Pt(DPrSO)Cl3] (2)
K[Pt(EMSO)Cl3] (3)
Pt–Cl trans
Pt–Cl cis
Pt–Cl cis
Pt–S
S–O
S–C (ave.)
2.319(2)
2.289(2)
2.290(3)
2.187(2)
1.462(5)
1.784(9)
2.317(3)
2.290(4)
2.293(4)
2.205(3)
1.456(10)
1.795(14)
2.332(3)
2.319(2)
2.298(2)
2.209(2)
1.471(4)
1.782(7)
Cl–Pt–Cl trans
Cl–Pt–Cl cis
Cl–Pt–Cl cis
S–Pt–Cl trans
S–Pt–Cl cis
178.52(10)
89.16(9)
91.05(10)
177.91(7)
90.94(8)
88.80(9)
116.1(3)
115.8(3)
107.8(5)
90.5(5)
177.66(13)
89.86(13)
88.11(15)
178.94(14)
90.10(12)
91.91(13)
117.3(4)
111.9(5)
106.8(7)
100.8(6)
174.67(5)
88.80(7)
89.11(7)
174.15(5)
91.44(7)
91.14(7)
117.67(19)
109.9(3)
107.8(3)
102.8(3)
112.1(5)
S–Pt–Cl cis
Pt–S–O
Pt–S–C (ave.)
O–S–C (ave.)
C–S–C
S–C–C (ave.)
C–C–C (R2SO ave.)
C–N–C (cation ave.)
104.8(7)
109.8(8)
109.5(7)
112.5(10)
110.8(13)
109.5(12)
Table 5
Bond distances and angles in the ionic complexes [Pt(R2SO)Br3]ꢀ (4, 5) and cis-Pt(DBuSO)2Cl2 (6)
K[Pt(TMSO)Br3] Æ H2O (4)
N(Et)4[Pt(DPrSO)Br3] (5)
Pt1
2.424(3)
2.403(2)
2.417(2)
2.202(5)
1.463(13)
1.80(2)
Pt2
2.406(3)
2.434(3)
2.427(2)
2.183(4)
1.471(11)
1.774(18)
Pt–Br trans
Pt–Br cis
Pt–Br cis
Pt–S
S–O
S–C (ave.)
2.4387(13)
2.4285(16)
2.4247(16)
2.217(3)
1.4726(7)
1.783(11)
Br–Pt–Br trans
Br–Pt–Br cis
Br–Pt–Br cis
S–Pt–Br trans
S–Pt–Br cis
177.73(9)
176.22(8)
177.23(7)
88.24(5)
89.29(5)
177.83(9)
90.64(8)
91.87(8)
117.4(3)
111.0(4)
107.5(6)
102.6(5)
109.0(9)
111.5(13)
109.5(9)
88.99(10)
90.84(9)
179.59(15)
91.35(15)
88.83(14)
115.3(6)
115.3(8)
107.9(9)
92.9(11)
103.4(18)
113(2)
89.57(9)
89.94(10)
178.72(14)
91.29(13)
89.23(13)
115.0(5)
115.6(7)
107.7(8)
93.1(10)
104.3(15)
110.8(18)
S–Pt–Br cis
Pt–S–O
Pt–S–C (ave.)
O–S–C (ave.)
C–S–C
S–C–C (ave.)
C–C–C (R2SO ave.)
C–N–C (cation ave.)
cis-Pt(DBuSO)2Cl2 (6)
Pt–Cl
Pt–S
S–O
S1–C
S2–C
2.283(4)
2.262(3)
1.467(9)
1.786(13)
1.794(12)
2.299(3)
2.238(3)
1.477(9)
1.791(13)
1.792(13)
S–Pt–Cl trans
S–Pt–Cl cis
S–Pt–S
Cl–Pt–Cl
Pt–S–O
Pt–S–C (ave.)
O–S–C (ave.)
C–S–C
S–C–C (ave.)
C–C–C (ave.)
175.11(12)
88.70(12)
96.10(11)
87.78(14)
117.7(4)
110.7(4)
107.0(6)
102.8(6)
110.8(9)
112.8(13)
176.42(11)
87.40(12)
116.4(3)
111.2(5)
107.7(6)
101.6(6)
112.6(9)
112.6(13)

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
27
In the cis disubstituted complexes where steric hindrance
is an important factor, the Pt–S bond lengths will also
depend on the bulkiness of the sulfoxide. In our crystal
cis-Pt(DBuSO)2Cl2 (6), the Pt–S bonds (trans position to
The conformation of the TMSO ligand in crystals 1 and
4 is of the envelope type. In N(Bu)4[Pt(TMSO)Cl3], the
four C atoms of TMSO are in a plane with a mean devia-
˚
˚
tion of 0.032 A and the S atom is ꢀ0.824(13) A out of the
plane. Similar results were found in the two molecules in
K[Pt(TMSO)Br3] Æ H2O (4), where the mean deviations
˚
chloro ligands) are longer (2.262(3) and 2.238(3) A) than
in the monosubstituted complexes, although the structure
of [Pt(DBuSO)Cl3]ꢀ was not reported. For published cis-
Pt(R2SO)2Cl2 compounds the average Pt–S bond is
˚
from the perfect plane are 0.003 and 0.049 A. The S atoms
˚
are out of the plane by ꢀ0.72(3) A in the first complexed
˚
˚
˚
2.231(2) A for DMSO [30] and 2.255(3) A for DPrSO
[31]. In cis-Pt(TMSO)2Cl2 where the bulkiness is the small-
est (the angle C–S–C is only 94°), the average Pt–S bond is
ion and 0.74(3) A in the second. This conformation is
different from the ones observed in cis-Pt(TMSO)2Cl2,
where the conformation of both TMSO ligands was also
of the envelope type, but the S atoms were in the plane,
along with the two C atoms in a positions and one of the
C in b positions. Therefore, for each TMSO ligand, the
atom outside the plane was a C atom located in b position
[29].
˚
2.238(3) A [29]. All these values are smaller than those
reported in the trans-Pt(R2SO)2Cl2 compounds, since the
trans influence of the sulfoxide ligand is much larger than
the one of the chloro ligand. In trans-Pt(DMSO)2I2, the
˚
˚
Pt–S bonds are 2.289(2) A [7] and 2.292(2) A in trans-
Pt(DPrSO)2Cl2 [6].
Crystal
4 crystallized with two independent [Pt-
The Pt–Cl bonds located in trans position to a sulfoxide
ligand are longer than those in trans position to a chloro
ligand. In the trichloro complexes, the average trans bond
(TMSO)Br3]ꢀ anions and a molecule of water for each Pt
atom. Fig. 6 shows the asymmetric unit in the unit cell.
The two water molecules are H-bonded to a cis bromo
ligand (Br11) of one Pt(II) complexed anion and the O
atom (O2) of the second anion as shown in Fig. 6. The
˚
˚
is 2.323(3) A, while the average cis bond is 2.299(3) A.
For the tribromo ionic complexes, the Pt–Br bonds are
˚
˚
more uniform. The average trans bond is 2.427(2) A, while
O2ꢃ ꢃ ꢃOw distances are 2.881(5) and 2.858(12) A with
˚
the average cis bond is 2.423(2) A. Similar results were
angles O2ꢃ ꢃ ꢃH–Ow = 171 and 179°. The Br11ꢃ ꢃ ꢃOw dis-
˚
published for the structures of two ammonium salts of
tances are 3.369(4) and 3.416(8) A with Br11ꢃ ꢃ ꢃH–
the anion [Pt(DPhSO)X3]ꢀ. The Pt–Cl in trans position
Ow = 175° and 171°.
to DPhSO is longer (2.312(2) A) than the others (ave.
Each K+ ion in crystal 4 is surrounded by the three non
H-bonded O atoms at distances between 2.750(12) and
˚
˚
˚
2.291(2) A), while the trans Pt–Br bond (2.416(2) A) is
ꢀ
˚
˚
almost the same as the cis bonds (ave. 2.409(3) A) [26].
2.963(16) A and by five non H-bonded Br ligands at dis-
˚
These results seem to indicate that the order of the trans
influence of the three ligands is in the order R2SO >
Br > Cl.
tances from 3.259(6) to 3.712(6) A. A view of the packing
around each K+ ion is shown in Fig. S3 (Supplementary
material). Therefore electrostatic forces around the K+
ion are important in this crystal. The environment around
the K+ ion in crystal 3 is similar. There are one O atom
The bond distances and angles of the sulfoxide ligands
are normal and similar in all the compounds. Reviews on
the subject were reported [2,3]. The S–O bond lengths in
crystal 1–6 vary between 1.456(10) and 1.471(4) (ave.
ꢀ
˚
(Kꢃ ꢃ ꢃO = 2.756(4) A) and seven Cl ligands at distances
˚
between 3.231(3) and 3.615(3) A.
˚
1.467 A). For free sulfoxides, the average S–O bond dis-
No H-bonds are expected in the crystals other than com-
pound 4. The molecules are held together by electrostatic
forces for the ionic compounds and by van der Waals
attractions.
˚
tance has been shown to be 1.4918(9) A [2]. This value
is lengthened to 1.528(1) upon metal O-coordination,
˚
while it is reduced to 1.4731(6) A upon S-coordination
[2]. For Pt(II) complexes, the average S–O bond was
˚
reported to be 1.467(1) A for a bonded sulfoxide ligand
4. Conclusion
whose trans ligand was not another sulfoxide [2], exactly
the average value found for our six crystals. The S–C
bonds are quite uniform for all the six crystals (ave.
The results of the 13C NMR study of the platinum com-
plexes were rationalized by considering inversed polariza-
tion of the sulfoxide p-bond. When the ligand contains
alkyl or aryl substituents, the extent of polarization
˚
1.786 A for the monosubstituted compounds and
˚
1.791(1) A for crystal 6). The S atom in the sulfoxide
ligands is in an approximate tetrahedral environment.
The Pt–S–O angles (116.4(3)–117.7(4)°) are larger than
the Pt–S–C angles (109.9(3)–111.9(5)°) for the linear suf-
oxides as expected and about the same for the TMSO
compounds (ꢁ115.6°) due to the smaller C–S–C angle
in the cyclic sulfoxide. The O–S–C bond angles are also
larger (ave. 107.5(6)°) than the C–S–C angles (ave.
91.8(8)° for TMSO, 102.1(7)° for the others). The C–S–
C angles do not seem to vary with the lengths of the alkyl
chains.
S
dꢀ„Od+ increases, which results in a stronger S!Pt r-
bonding. Back-donation (p-bond, Pt!L) is also present,
but it is probably more uniform than the r-bonding com-
ponent. Theoretically, an increase in the p-bonding charac-
ter of the Pt!L bond should result in a shielding of the
carbon atoms (smaller Dd upon co-ordination) similarly
to the effect of increased p-polarization of the S–O bond.
But this last explanation was chosen because of the similar-
ity between sulfoxide and carbonyl complexes. Cooper and
Powell [15] chose to explain their 13C NMR results by the

28
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 16–28
effect of p-polarization of the carbonyl bond, since it con-
firmed also their results obtained in infrared spectroscopy.
The inverse polarization of the p-electrons has also been
suggested in understanding the 13C NMR results on Pt–
acetylides [15] and by our group in the 13C NMR spectro-
scopic interpretation of the complexes Pt(amine)2(RCOO)2
[17].
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2007.06.004.
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Appendix A. Supplementary material
CCDC 647526, 647527, 647528, 647529, 647530 and
647531 contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
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