Ambidentate coordination in hydrogen bonded dimethyl sulfoxide, (CH 3)2SO...H3O+, and in dichlorobis(dimethyl sulfoxide) palladium(ii) and platinum(ii) solid solvates, by vibrational and sulfur K-edge X-ray abso

Article abstract of DOI:10.1039/b814252a

The strongly hydrogen bonded species (CH₃)₂SO... H₃O⁺ formed in concentrated hydrochloric acid displays a new low energy feature in its sulfur K-edge X-ray absorption near edge structure (XANES) spectrum. Densit

Full text of DOI:10.1039/b814252a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Ambidentate coordination in hydrogen bonded dimethyl sulfoxide,
+
(
CH ) SO ◊ ◊ ◊ H O , and in dichlorobis(dimethyl sulfoxide) palladium(II)
3
2
3
and platinum(II) solid solvates, by vibrational and sulfur K-edge X-ray
absorption spectroscopy†
Emiliana Damian Risberg, J a´ nos Mink, Alireza Abbasi,a,d Ma ikhail Yu. Skripkin, Laszl o´ Hajba,b,c
a
b,c
a, f
e ´
b,c
Patric Lindqvist-Reis, Eva Bencze and Magnus Sandstr o¨ m*
Received 18th August 2008, Accepted 23rd October 2008
First published as an Advance Article on the web 13th January 2009
DOI: 10.1039/b814252a
+
The strongly hydrogen bonded species (CH
3
)
2
SO ◊ ◊ ◊ H
3
O formed in concentrated hydrochloric acid
displays a new low energy feature in its sulfur K-edge X-ray absorption near edge structure (XANES)
spectrum. Density Functional Theory-Transition Potential (DFT-TP) calculations reveal that the
strong hydrogen bonding decreases the energy of the transition S(1s) → LUMO, which has antibonding
s*(S–O) character, with about 0.8 eV. Normal coordinate force field analyses of the vibrational spectra
-
1
show that the SO stretching force constant decreases from 4.72 N cm in neat liquid dimethyl sulfoxide
to 3.73 N cm- for the hydrogen bonded (CH
on the ambidentate dimethyl sulfoxide molecule were investigated for the trans-Pd((CH
trans-Pd((CD SO) Cl and cis-Pt((CH SO) Cl complexes with square planar coordination of the
1
)
SO ◊ ◊ ◊ H
O species. The effects of sulfur coordination
SO) Cl
+
3
2
3
3
)
2
2
2
,
3
)
2
2
2
3
)
2
2
2
chlorine and sulfur atoms. The XANES spectra again showed shifts toward low energy for the
transition S(1 s) → LUMO, now with antibonding s*(M–Cl, M–S) character, with a larger shift
for M = Pt than Pd. DFT-TP calculations indicated that the differences between the XANES spectra of
the geometrical cis and trans isomers of the M((CH
3
)
2
SO)
2
2
Cl complexes are expected to be too small to
allow experimental distinction. The vibrational spectra of the palladium(II) and platinum(II)
complexes were recorded and complete assignments of the fundamentals were achieved. Even though
the M–S bond distances are quite similar the high covalency especially of the Pt–S bonds induces
-
1
significant increases in the S–O stretching force constants, 6.79 and 7.18 N cm , respectively.
Introduction
formation of reaction intermediates via non-occupied axial posi-
tions. Platinum and palladium are relatively rare noble metals and
their separation and recovery from used catalysts are important
issues, where solvents with different affinity to the metal ions can
be important.
Platinum metals are widely used as catalysts in numerous chemical
and technological processes such as selective oxidation of exhaust
gases from car engines, stereo-selective hydrogenation of non-
saturated organic compounds, etc. The square planar coordination
geometry of palladium(II) and platinum(II) complexes allows easy
Dimethyl sulfoxide, (CH ) SO, is of special interest because
3
2
of its unusual properties. The ambidentate solvent molecule is
able to coordinate to metal ions via either the oxygen or the
sulfur atom. Oxygen coordination is the more common and the
structural and spectroscopic features of such metal complexes
a
Department of Physical, Inorganic and Structural Chemistry, Stockholm
University, SE-106 91, Stockholm, Sweden. E-mail: magnuss@struc.su.se
b
Department of Molecular Spectroscopy, Chemical Research Center of the
1–4
have been widely studied. Less is known about the sulfur-
coordinated complexes that are formed with some soft metal
ions. Crystallographic studies indicate that in complexes with
platinum(II) ions at most two M–S bonds to dimethyl sulfoxide
ligands are formed for steric reasons depending on the other
Hungarian Academy of Sciences, P. O. Box 77, H-1525 Budapest, Hungary
c
Faculty of Information Technology, Research Institute of Chemical and
Process Engineering, University of Pannonia, P. O. Box 158, H-8201
Veszpr e´ m, Hungary
d
School of Chemistry, University College of Science, University of Tehran,
Tehran, Iran
e
ligands, and additional (CH ) SO molecules will coordinate via
Institut f u¨ r Nukleare Entsorgung, Forschungszentrum Karlsruhe, P.O. Box
3 2
1
,5–8
3
640, D-76021, Karlsruhe, Germany
oxygen.
In vibrational IR absorption spectra the character-
f
-1
Department of General and Inorganic Chemistry, Saint-Petersburg State
University, Universitetsky pr. 26, 198504, Saint-Petersburg, Russia
istic upshift to 1100–1160 cm of the band assigned to S–O
stretching, at 1070 cm for neat dimethyl sulfoxide, signifies sulfur
-1
†
Electronic supplementary information (ESI) available: Table S1 lists the
(Me SO) (Me SO)
coordination. However, in covalent complexes vibrational skeletal
modes are often extensively coupled, which makes comparisons
of the bond character based only on frequency shifts ambiguous.
In the low frequency region, the assignment of vibrational fun-
damentals often becomes tentative without isotopic substitution
studies.
refined force constants for trans-PdCl
complexes. Fig. S1 shows the shapes of the receiving MOs for the
2
2
2
and cis-PtCl
2
2
2
protonated dimethyl sulfoxide molecule corresponding to transitions 1,
2
, 3 and 4 in Fig. 6. Figs S2 and S3 display the MOs corresponding to the
marked transitions in the theoretical spectra of the cis- and trans-isomers
of the M(CH SO) Cl
complexes for M = Pt and Pd in Fig. 7 and 8,
respectively. See DOI: 10.1039/b814252a
3
)
2
2
2
1
328 | Dalton Trans., 2009, 1328–1338
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For the sulfur-coordinated trans-PdX
2
((CH
3
)
2
SO)
2
(X = Cl,
from that obtained in the experiment with dimethyl sulfoxide.
The experimental spectra are presented in Fig. 1–4 and the
vibrational frequencies are listed together with the potential energy
distribution (PED) in Table 1–3.
Br) complexes the only comprehensive study so far is that of
9,10
Tranquille and Forel. However, not all vibrational bands were
resolved and some revision seems desirable. In the present work
normal coordinate force field analyses of the solid state vibra-
tional spectra were performed for the trans-PdCl
2
((CH
3
)
2
SO)
2
and cis-PtCl ((CH SO) complexes to enable comparisons of
2
3
)
2
2
the character of the metal–sulfur and metal–chloride bonding
in square planar coordination. The results are combined with
sulfur K-edge XANES measurements, which when evaluated by
DFT-TP calculations provide information about the electronic
state of the investigated compounds. This method was previously
11
applied to study oxygen-coordinated dimethyl sulfoxide solvates,
and is in the current work complemented with a study of
the hydrogen bonded dimethyl sulfoxide molecule in concen-
trated hydrochloric acid, combining experimental XANES and
vibrational spectra with theoretical computations. The electronic
transitions were investigated for several possible models for
+
+
protonated (CH
3
)
2
SO species ((CH
3
)
2
SOH : H
2
O ◊ ◊ ◊ HOS(CH
3 2
)
+
and H
2
OH ◊ ◊ ◊ OS(CH
3
)
2
), and also for the other geometrical
SO) Cl and trans-Pt((CH SO) Cl
isomer of the cis-Pd((CH
3
)
2
2
2
3
)
2
2
2
solvates.
Experimental
Sample preparation
-
3
Two solutions, of ca. 0.05 mol dm dimethyl sulfoxide dissolved in
acetonitrile and concentrated hydrochloric acid, respectively, were
prepared. Complexes of cis-Pt((CH
3
)
2
SO)
2
2
Cl (yellow crystals)
and trans-Pd((CH SO) Cl (orange powder) were synthesized
3
)
2
2
2
by dissolving anhydrous platinum(II) and palladium(II) chloride,
◦
respectively, in dimethyl sulfoxide (heated to about 100 C for
12,13
PdCl
2
) followed by slow cooling to room temperature.
The
compounds were identified by single crystal X-ray diffraction
12,13
measurements of their cell parameters.
Vibrational spectra
Raman spectra of the solid compounds were obtained using
a Renishaw System 1000 spectrometer, equipped with a Leica
DMLM microscope, a 25 mW diode laser (780 nm), and a Peltier-
-
1
cooled CCD detector. Mid-infrared (200–4000 cm , resolution
-
1
4
cm , 128 scans) absorption spectra were recorded in a purged
atmosphere from nujol mulls on CsI windows using a Bio-Rad
Varian) FTS 175 dynamically aligned spectrometer equipped with
(
-
1
a CsI beamsplitter. Far-infrared spectra (50–700 cm ) were ob-
tained with polyethylene pellets in a Bio-Rad (Varian) FTS-40 air
bearing interferometer equipped with a wire-mesh beamsplitter,
high pressure mercury source and DTGS detector. All spectra were
measured at ambient temperature. To study the effects of hydration
and hydrogen bonding on the dimethyl sulfoxide molecule, IR and
Fig. 1 (Upper, middle) FT-IR difference spectrum of (CH
solution, after subtraction of the spectrum of HCl(aq); (lower) Raman
3 2
) SO in HCl
3 2
difference spectrum of (CH ) SO in HCl solution, after subtraction of
HCl(aq).
-
3
Raman spectra were recorded of 0.5 mol dm dimethyl sulfoxide
solutions in water and in concentrated hydrochloric acid (37%).
For Raman measurements a dedicated Bio-Rad (Varian) FT
Raman spectrometer was used, equipped with a Spectra Physics
Nd:YAG laser source (1064 nm wavelength) and a liquid nitrogen-
cooled Ge detector. Careful subtraction of corresponding aqueous
HCl solution spectra was performed to remove the background
Force field analysis
The M((CH
3
)
2
SO)
2
Cl
2
(M = Pd, Pt) complexes contain 23 atoms
generating 63 fundamental vibrational modes when including the
methyl hydrogens. Detailed analysis of methyl C–H stretching,
deformation, rocking and torsional modes are less important in
coordination studies than the ligand ‘skeletal’ modes and the
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-
1
Table 1 Vibrational transitions (cm ) in the spectra of dimethyl sulfoxide in liquid and gas phase compared with Me
2
SO(aq) and Me
2
SO(HCl) after
a
subtraction of the solvent contribution
3,9
3
b
b
Me
IR
2
SO (gas)
Me
IR
2
SO (liquid)
Me
IR
2
SO(aq)
(Me
2
SO in HCl) - HCl(aq)
Raman
2996 m
2913 m
Raman
3000 w
2915 w
IR
Raman
Assignment
3
2
010
933
2991 w
983 w
2905 w
2999 w
2969 sh
2915 w
3013 w
2923 w
3014 w
2970 vw
2925 m
n
a
n
a
n
s
(CH
(CH
3
)
)
)
2
3
(CH
3
2
2
810 vvw
740 vvw
1
725 vvw
1
1
662 w
638 sh
1660 vvw
1638 vw, sh
1429 w
1417 vw
1405 w
d(H
d(H
2
2
1
437 w
1438 sh
1420 sh
1406 w
d
d
d
d
d
d
a
a
a
s
1
1
1
1
419
406
319
304
1419 w
1406 w
1418 w
1419 m
1311 w
1415 vw
1327 w
(CH
(CH
(CH
1311 w
1
1070 s
1308 w
1067 w
1312 w
s
294 sh
s
1
1
102
056
1024 vs
1060 sh
1
1028 sh
1058 sh
1045 m
987 m
n(SO), r(CH
3
)
r(CH
r(CH
r(CH
r(CH
046 sh
1038 w
1032 vw, sh
1
1
021
016
1032 m
1012 m
957 w
1029 w
1010 w
957 w
9
53
954 sh
953 w
930 sh
944 sh
919 sh
897 w
n(SO), r(CH
n(SO), r(CH
n(SO), r(CH
3
3
3
)
)
)
9
8
32 m
98 w
8
75 vw
6
95
700 w
698 m
701 m
669 m
701 m
717 vw
727 m
683 s
n
n
n
a
s
s
2
)
)
)
6
86 vvw
6
3
3
3
72
82
33
08
670 w
383 w
335 w
307 w
668 s
671 s
668 vvw
382 m
322 m
306 m
384 w
335 m
307 w
d(SC
t(SC
w(SC
327 w
301 w
)
a
Notations: n = stretching, d = bending, t = twisting, w = wagging, r = rocking, s = symmetric, a = asymmetric modes unassigned band belong to
b
overtones and combination modes; intensities: s = strong, m = medium, w = weak, sh = shoulder. This work.
3 2 2 2
Fig. 3 Mid-IR spectra of the solid trans-Pd((CH ) SO) Cl (1) and
cis-Pt((CH SO) Cl (2) compounds.
3
)
2
2
2
3 2 2 2
Fig. 2 Raman spectra of the solid trans-Pd((CH ) SO) Cl (1) and
cis-Pt((CH SO) Cl (2) compounds.
3
)
2
2
2
in the assignment. The cis-Pt(Me
2
SO)
2
Cl
2
complex has in the C
s
metal–ligand vibrations. Therefore, point masses (16 and 19 a.m.u.
for CH and CD , respectively) were introduced for the methyl
groups to simplify the calculations, which leaves 27 fundamental
modes for the M(Me SO) Cl complexes.
The molecular structure of the complexes was adopted from the
point group 14 A¢ and 13 A¢¢ vibrational modes, all active both
in the Raman and IR spectra. However, their intensity difference
facilitates the assignment.
3
3
2
2
2
For the force field calculations the same set of symmetry
coordinates as previously was used for the dimethyl sulfoxide
molecule with an initial set of force constants derived from our
12,13
literature,
and the trans-Pd(Me
2
SO)
2
Cl
2
complex was treated
vibrations. All
modes
should not coincide in the vibrational spectra; a significant help
2,3
+
in the C point group that results in 12 A
i
g
and 15 A
u
previous work, and for the H
3
O ion C3v point group symmetry
A
g
vibrations are Raman active whereas the IR active A
u
was adopted. Wilson’s GF matrix method was used to calculate
vibrational frequencies using a symmetrized valence force field.
1
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-1
Table 2 Experimental and calculated (in point groups C
i
and C
s
2 2 2
), fundamental vibrational frequencies (cm ) for trans-Pd(Me SO) Cl and cis-
a
Pt(Me SO) Cl , respectively, and their potential energy distribution (PED in %) in symmetry coordinates
2
2
2
trans-Pd(Me
2
SO-h
6
)
2
Cl
2
trans-Pd(Me
2
SO-d
6
)
2
Cl
2
cis-Pt(Me
2
SO)
2
Cl
2
Raman
Raman
b
IR (A
u
)
(A
g
)
Calc. IR (A
u
)
(A
g
)
Calc. IR
Raman
Calc. PED
Assignment
1
110 m 1110
1117 1119 s
1117 m 1115 1128 s
1119 1151 s
1132 m A¢ 1130 96 n
1151 m A¢¢ 1150 96 n
s
(SO)
n
n
n
n
n
n
s
(SO)
(SO)
1
117 s
a
a
a
s
(SO)
a
a
a
s
7
31 m
731
729
688
685
645 m
643
646
630
630
735 s
A¢¢
735 92 n
737 92 n
696 89 n
(CS), 5 t
(CS), 5 t
(CS), 5 d
a
s
(SC
2
)
)
)
(SC
(SC
2
) – oop
) – ip
) – ip
7
6
29 m
88 s
644 m
631 m
737 m A¢
(SC
(SC
2
2
631 s
697 w
689
696 s
A¢
s
2
(SC
(SC
2
6
85 m
A¢¢
689 Pd: 91 n
s
(CS)
(CS), 5 n
(SC ), 17 n
(SC ), 21 n
(SC ), 41 n
(SC
), 7 n
s
2
) – oop
Pt: 88 n
452 Pd: 71 d
Pt: 72 d
431 Pd: 53 d
s
s
(PtS), 5 d
(PdS), 8 n
(PtS)
(PdS), 5 n
(PtS), 5 n (CS)
s
(SC
2
)
4
31 m
430
416
389 m
386
375
449 sh
430 s
452 m A¢
433 w A¢¢
s
2
s
s
(CS)
d
s
(SC
2
)
)
s
2
s
4
3
16 s
377 s
a
2
a
s
(CS)
d
a
(SC
2
Pt: 58 d
a
2
), 34 n
(CS)
(CS)
a
s
3
3
81 w
63 w
383
382
363
331
356
365 w
302 sh
363
364
304
285
335
381 m A¢
378 w A¢¢
381 84 t
376 85 t
s
(SC
(SC
2
a
t
t
s
(SC
(SC
2
)
)
2
)
82 m
367 m
376 s
a
2
), 6 n
a
a
2
319 s
A¢
A¢¢
319 95 w
319 94 w
s
(SC
(SC
2
)
)
w
w
s
(SC
3
3
30 m
54 s
288 m
337 s
320 s
309 s
a
2
a
(SC
2
)
309 m A¢¢
335 vs A¢
251 m A¢¢
308 Pd: 92 n
a
(PdCl), 6 r^a(SC
(PtCl), 11 d (SC
334 Pd: 100 n (PdCl)
Pt: 91 n (PtCl), 5 d
249 Pd: 47 n (PdS), 29 d
j(PdS
Pt: 59 n
2
)
2
)
n
n
n
a
(MCl)
(MCl)
(MS)
Pt: 82 n
a
a
3
09 vs
309
246
307 vs
306
243
335 s
s
s
s
s
(SC
2
)
(SC
2
46 m
245 m
251 w
a
a
2
), 14 rꢀa(SC
2
), 5
a
2
)
a
(PtS), 23 d
a
(SC
2
), 10 n (PtCl), 6
a
r
2
ꢀa(SC )
1
2
60 m
13 m
157
214
210
152 m
201 m
148
197
198
273 w
218 sh
234 sh
275 s
A¢
270 Pd: 63 n
Pt: 70 n
213 Pd: 82 rꢀs(SC
Pt: 46 rꢀs(SC
233 Pd: 51 rꢀa(SC
1 j(PdCl
Pt: 77 rꢀa(SC
208 88 r^a(SC ), 7 n
173 Pd: 48 r^s(SC ), 45 d
Pt: 88 r^s(SC
53 d (SPdCl), 39 r^s(SC
96 j(PdCl ) – linear bending
95 j(PdS ) – linear bending
(SPtCl) – linear bending, 15 rꢀa(SC
(SPtCl) – linear bending, 38 rꢀs(SC
s
(PdS), 28 d
(PtS), 14 rꢀs(SC
), 9 n (PdS), 8 d
), 27 j (SPtCl), 24 n
), 20 j(PdS ), 12 d (SC
s
(SC
2
), 9 rꢀs(SC
), 5 j (SPtCl)
(SC
2
)
n
s
(MS)
s
2
s
221 m A¢
234 sh A¢¢
2
s
s
2
)
r
r
ꢀs(SC
2
)
)
2
s
s
(PtS)
),
2
2
12 sh
25 m
202 sh
205 m
2
2
a
2
ꢀa(SC
2
1
2
)
2
), 14 j
a
a
(SPtCl), 5 n
a
(PtS)
226
138
209
132
208 m
175 m
208 w A¢¢
173 s
2
(MCl)
(SPdCl)
r
r
^a(SC
^s(SC
2
2
)
)
1
1
42 w
86 m
136 w
181 m
A¢
2
s
2
)
185
173
116
183
176
114
s
2
), 6 t
s
(SC
2
)
d
s
(SPdCl)
1
1
72 m
20 s
173 m
118 s
2
2
j(PdCl )
2
j(PdS
2
)
1
1
47 m
30 w
147 w A¢¢
134 m A¢
143 72 j
140 53 j
a
2
)
)
j
j
a
(SPtCl)
(SPtCl)
s
2
s
7
5
9 s
83
80 s
81
92 d
a
(SPdCl)
(PtL ), 33 d
d
a
(SPdCl)
c
7
7 s
A¢
A¢
79 67 d
s
4
s
¢(PtL
4
)
s 4
d (PtL )
6
5
61
57
43
52 89 sym MS tors, 9 w
s
(SC
2
)
Sym MS torsion
4 m
56
56 m
80 d
a
¢(SPdCl)
d
a
¢(SPdCl)
4
4
66 sh
5 m
A¢¢
A¢¢
A¢
62 75 asym MS tors, 9 w
a
(SC
2
)
asym MS torsion
5
59 95 d
48 58 d
a
(PtL
¢(PtL
4
)
d
d
a
(PtL
¢(PtL
4
)
4
)
s
4
), 33 d
s
(PtL
4
)
s
a
Notations: n = stretching, d = bending, t = twisting, w = wagging, r = rocking, j = linear bending, s = symmetric, a = asymmetric modes,
ip = in-phase, oop = out-of-phase; ꢀ and ^ denote direction of dipole moment change vs. movement; intensities: vs = very strong, s = strong,
b
c
m = medium, w = weak, sh = shoulder. PED values refer to non-deuterated complexes. PtL
4
refers to the four equatorial ligand atoms.
-1
+
Table 3 Experimental vibrational frequencies (cm ) and refined force constants of the H
3
O ion in different systems
+
-
27
+
-
+
H
3
O ◊ ◊ ◊ ClO
4
(soln.)
H
3
O ◊ ◊ ◊ Cl (soln.)
H
3
2
O ◊ ◊ ◊ Me SO (HCl soln.)
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
A
E
E
A
1
1
n
1
n
3
n
4
n
2
3288
3100
1577
1175
5.797
-0.105
0.594
0.049
3285
3100
1577
1175
3320
2980
1705
1093
5.739
-0.288
0.625
-0.013
3320
2981
1705
1093
3220
3070
3220
3070
1643
1032
(1644)
1032
5.607
-0.063
0.573
-0.020
a
K(OH)
a
k(OH, OH)
b
H(HOH)
b
h(HOH, HOH)
a
N cm-1. b 10-18 Nm rad-2.
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a [5s,4p,1d] basis set contracted as (311/211/1) to eliminate the
15
S(1s,2s,2p) levels, using a procedure described elsewhere.
Results and discussion
Assignments of vibrational spectra
The SO bond stretching contributes strongly to two fundamental
vibrational modes in the dimethyl sulfoxide molecule, at 1102 and
-
1
9
53 cm in the gas phase, which usually are assigned as SO stretch-
ing and CH rocking after their major components in the potential
energy distribution. In neat liquid dimethyl sulfoxide the former
3
1,3,9
-
1
band downshifts to 1070 cm due to intermolecular interactions
-
1
whereas the latter remains nearly unchanged (957 cm ). Hydra-
tion, with formation of a relatively strong (CH SO ◊ ◊ ◊ HOH
hydrogen bond, decreases the SO bond strength and leads to
)
3 2
-
1
-1
downshifts to 1024/1028 cm (IR/Raman) and 932/930 cm
+
Fig. 4 Far-IR spectra of the solid trans-Pd((CH
cis-Pt((CH SO) Cl (2) compounds.
3
)
2
SO)
2
Cl
2
(1) and
(IR/Raman), respectively. The H O interaction with the dimethyl
3
3
)
2
2
2
sulfoxide molecule in aqueous HCl solution downshifts the two
-
1
bands further to 987 and 919 cm , respectively (Table 1). The
relatively small shifts of the OH stretching frequencies (Table 3)
indicate that the type of hydrogen bonding is similar in the three
All normal coordinate and force field calculations were performed
by means of the PC-based program package developed by Mink
14
systems studied. The observation of the fundamental frequencies
and Mink. The results are summarized in Table 3, Table 4 and
Table S1.†
+
for H
3
O in the Me
2
SO(HCl) system, especially the umbrella mode
-
1
+
at 1032 cm , indicates that the H
3
O proton is not transferred
close to the dimethyl sulfoxide oxygen atom, and the interaction
X-Ray absorption measurements
+
in aqueous HCl solution can be described as H
3
O ◊ ◊ ◊ OSMe
2
1
-
Sulfur K-edge X-ray absorption near edge structure (XANES)
spectra were recorded at Stanford Synchrotron Radiation Light-
source at beamline 6-2. Details of the measurements are described
hydrogen bond. The O–H stretching force constant, 5.607 N cm ,
-
3
-1
is smaller than that for 10 mol dm HCl, 5.739 N cm for
+
-
H
3
O ◊ ◊ ◊ Cl , Table 3. Thestronghydrogen bondingis alsoreflected
15
-1
elsewhere. The energy scale was obtained by setting the lowest
energy peak maximum of sodium thiosulfate (Na O) to
·5H
469.2 eV, which is the calibration scheme that seems to agree most
by the very low S=O stretching frequency (987 cm ) and S–O force
-
1
2
S
2
O
3
2
constant (3.73 N cm ) for the Me
lower than for Me SO(aq), Table 4.
The SC asymmetric and symmetric stretching modes are also
2
SO(HCl) system, significantly
2
2
1
6
closely to the calculated values. The liquid samples were held in
a 1 mm Teflon spacer between 5 mm sulfur-free polypropylene film
windows. The solids were finely ground and dusted on as a thin
layer on sulfur-free Mylar adhesive tape.
2
affected by the interaction of dimethyl sulfoxide with other species.
The gas–liquid transition and hydration do not lead to pronounced
-
1
shifts in the positions of those bands, from 695, 672 cm in the
-
1
gas phase to 700, 670 cm for liquid (CH
the interaction with a H
3
)
2
SO, respectively, but
+
O ion causes a significant increase in
Computational details
3
-
1
the corresponding frequencies, to 727 and 683 cm , respectively.
Similar tendencies were observed for oxygen-coordinated metal
ion complexes, and can be explained by an increase in the
The experimental spectra were evaluated by computing theoretical
XANES spectra by means of the Density Functional Theory-
Transition Potential (DFT-TP) method, using the same procedure
1–4
positive charge on the sulfur atom, while the deformation modes
seem less affected.
For the sulfur-coordinated dimethyl sulfoxide solvates the op-
posite trends would be expected. The assignment of the vibrational
15
as described elsewhere. No symmetry constraints were imposed
on the starting model. The description of the orbital and auxiliary
16
basis sets was for sulfur, carbon, oxygen, hydrogen and chlorine
15
as in our previous studies. For platinum the pseudo potential
bands for trans-Pd(Me
experimental spectra of normal and deuterated samples. For
cis-Pt(Me SO) Cl both the band positions and the intensities
2
SO)
2
Cl
2
was supported by comparing the
17
developed by K u¨ chle et al. was used in the representation
18
proposed by Pelissier et al., while for palladium the DZVP
633321/53211/531) orbital description with auxiliary (5,5;5,5)
2
2
2
(
were compared with those of the palladium complex. In the
bases was employed. Sulfur atoms other than the core-excited
one were described by means of an effective core potential with
-1
region around 1100 cm where the main SO stretching mode
appears, deuteration of trans-Pd(Me
the medium intensity Raman band to 1110/1117 (H/D) cm
and the strong IR-band to 1117/1119 cm . Deuteration should
2
SO)
2
Cl only slightly shifted
2
-
1
-
1
Table 4 Variation of S=O stretching frequencies and force constants
affect methyl group deformational vibrations, e.g., bendings that
-
1
Me
2
SO(g) Me
2
SO(l)
Me
2
SO(aq) Me
2
SO(HCl)
usually are observed at higher wavenumbers (1300–1420 cm )
-
1
and rockings at lower (950–1050 cm ). Hence, the above bands
were assigned to the symmetric (Raman) and asymmetric (IR)
1
n
7
/cm-
1102
5.06
1070
4.72
1026
3.98
987
3.73
-1
K(SO)/N cm
SO stretching modes of trans-Pd(Me
2
SO)
2
2
Cl , respectively. For
1
332 | Dalton Trans., 2009, 1328–1338
This journal is © The Royal Society of Chemistry 2009

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the platinum complex, the corresponding strong IR and medium
intensity Raman bands were found at higher wavenumbers,
by far. In this region the dimethyl sulfoxide wagging modes were
-
1
observed as well, at 320/319 cm (IR/Raman). All these skeletal
vibrations are shifted to higher wavenumbers in a comparison with
neat dimethyl sulfoxide, in contrast to the downshift in oxygen-
coordinated complexes.
The metal–sulfur bonding for the palladium(II) and especially
the platinum(II) complexes is not very polar, which results in
lower intensity of the corresponding IR bands. Also, the coupling
-
1
1
128/1132 cm , respectively.
The doublets at 685, 731/688, 729 cm (IR/Raman) for the pal-
ladium(II) complex shifted significantly upon deuteration to form
-
1
-
1
single bands at lower wavenumbers (644/631 cm ; IR/Raman)
and were attributed to SC stretching vibrations, as also the
2
-
1
similar doublets at 696, 737/689, 735 cm (IR/Raman) for the
platinum(II) complex. The higher frequency bands originate from
asymmetric modes and the lower from symmetric modes. The
comparison of band intensities in Raman and IR allowed the in-
phase (ip) and out-of-phase (oop) modes to be distinguished, see
Table 2.
of these modes with ligand vibrations (mostly with SC bending
2
and rocking modes) may to some extent decrease their intensity.
Based on such considerations, the palladium–sulfur asymmetric
stretching mode was assigned as the medium intensity IR band
-
1
at 246 (245) cm , and the symmetric mode as the Raman feature
-
1
For complexes with sulfur-coordinated dimethyl sulfoxide,
at 160 (152) cm that only shifts slightly at deuteration. For the
platinum complex the corresponding asymmetric and symmetric
-
1
characteristic bands at 410–450 and 370–390 cm are reported
19
-1
in the literature. We have assigned these features as bending and
twisting modes of the coordinated dimethyl sulfoxide molecule,
respectively. In the currently studied complexes the corresponding
modes were observed at 251 cm (weak in IR, medium intensity
-
1
in Raman) and 273 (weak in IR)/275 cm (strong in Raman).
The lower frequency of the symmetric palladium–sulfur stretching
vibration results from the trans-influence of the sulfur-coordinated
ligands. Similar trends of the frequencies for M–S symmetric and
asymmetric stretching modes are observed as for the M–Cl modes:
-
1
bands were obtained at 416/431 cm (IR/Raman) and 449,
-
1
4
3
30/452, 433 cm (IR/Raman) for bending modes and at
82/381 cm- (IR/Raman) and 376/381, 378 (IR/Raman) cm
1
-1
for twisting modes of the palladium and platinum complexes,
respectively. Higher frequency bands were assigned as symmet-
ric modes and lower frequency bands as asymmetric. Normal
coordinate analysis revealed significant coupling of the bending
vibrations with other modes, especially with metal–sulfur stretch-
ings. Deuteration induced well defined low-frequency shifts for
these bands as expected from the contribution of the methyl group
vibrations in these modes.
n
s
> n for cis-complexes, whereas for trans-configuration this
a
order is reversed. The larger separation between the symmetric
and asymmetric stretching frequencies for the trans complex is a
result of the stronger vibrational interaction between the ligands
in trans-positions. The stretch–stretch interaction force constants
for both the MCl and MS vibrations are about 3 times larger for
trans- than for cis-complexes (Table S1†). The significantly higher
M–S stretching frequency for the platinum complex compared to
palladium corresponds to a higher force constant, which reflects
the increase in bond covalence. The stronger coordination of
sulfur-donor ligands by the platinum atom is consistent with
The assignment of the bands between 300 and 365 cm-1 was
less straight-forward because both metal–chloride stretchings
and dimethyl sulfoxide wagging modes appear in this region.
20
21
According to literature data, Pd–Cl stretching vibrations in trans-
Pearson’s hard–soft acid–base principles.
-
1
PdCl
for cis-PtCl
2
L
2
complexes occur at 262–353 cm , and Pt–Cl stretchings
The SC
2
rocking modes were observed as weak to medium spec-
-
1
-1
2
L
2
complexes at 281–374 cm , depending on the
tral features at 225, 212/142, 213 cm (IR/Raman) and the linear
bendings at 120, 172 cm (IR) for trans-Pd(Me
corresponding bands at 175, 208, 218, 234/173, 208, 221, 234 cm
(IR/Raman) and 130, 147 cm (IR) for cis-Pt(Me
Assignments of all observed fundamentals, supported by normal
coordinate calculations, together with potential energy distribu-
tions, are given in Table 2.
-
1
nature of other ligands (L) and the geometry of the molecule.
Our assignment (Table 2) was based on the shifts observed upon
deuteration and on the relative intensities of the bands in the
Raman and IR spectra.
High polarity of the bond allows significant changes of the
molecular dipole moment along the normal mode and promotes
high intensity of the corresponding IR absorption band. There-
2
SO)
2
Cl
2
, with
-
1
-
1
2
SO)
2
Cl
2
.
fore, for trans-Pd(Me
2
SO)
2
Cl
2
we assigned the strong IR band
Force field calculations. To follow the trends in the metal–
ligand bonding, force constants were calculated (summarized in
Table 3, Table 4 and Table S1†) using literature data for the
at 354 cm- (337 cm for the deuterated sample) as the Pd–
1
-1
Cl asymmetric stretching, despite its relatively large shift upon
12,13
deuteration, see below. The medium intensity IR band at 330
molecular structure,
studied compounds. For dimethyl sulfoxide (Me
the SO stretching force constant was of particular interest for cor-
relations to the shifts in the SO stretching frequencies: Me SO(g) >
Me SO(l) > Me SO(aq) > Me SO(HCl). A qualitative explanation
of this trend was indicated above. Noteworthy is that the hydrogen
and the vibrational spectra of the presently
1
(
288) cm- was attributed to the wagging mode of the ligand.
2
SO) the trend in
-
1
The strongest Raman band at 309 (307) cm was assigned as
symmetric Pd–Cl stretching and the weak band at 363 (302) cm
as in-phase wagging. The pronounced shift of the asymmetric Pd–
Cl stretching upon deuteration could be explained by its coupling
with the dimethyl sulfoxide rocking modes.
-
1
2
2
2
2
+
bond to the H
3
O ion influences the SO bond much more than
The most intense bands in the IR spectra of cis-Pt(Me
2
SO)
2
Cl
2
coordination to metal ions: the SO force constant decreases to
-
1
-1
-1
3
were observed at 335 and 309 cm ; the high Raman intensity of the
former supports the assignment of the high frequency band to the
symmetric Pt–Cl stretching mode and the lower frequency band to
3.73 N cm from 4.72 N cm in liquid Me
2
SO, whereas for
some trivalent metal ion solvates the force constants range from
-
1
-1
2–4
4.17 N cm for Ga(Me
2
SO)
6
I
3
to 4.69 N cm for Lu(Me
2
SO)
8
I
3
.
the asymmetric. This order of the bands (n
s
> n ) is characteristic
a
Normal coordinate force field calculations were performed to
2
-
for the cis-MX complexes containing ligands with sulfur donor
2
L
2
compare the force constants of square planar MCl
4
complexes
20
sites, while for trans-complexes the reverse order is more common
with those of the M(Me SO) Cl
2
2
2
, M = Pd and Pt, solvates.
This journal is © The Royal Society of Chemistry 2009
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Literature data were used for molecular geometry and vibrational
molecules in dilute acetonitrile solution an asymmetric peak is
observed at 2473.5 eV with a shoulder at 2475.0 eV. Protonation
of the dimethyl sulfoxide molecule could occur either at the sulfur
22–25
spectra.
The results show higher force constants for the
2
-
platinum–ligand bonds: for the MCl
constant increases from 1.48 N cm (Pd) to 1.80 N cm (Pt)
without change in the metal–ligand bond distances (2.306 and
4
species the stretching force
-
1
-1
2-
15
or oxygen atom as for the sulfite (SO ) ion, but since the sulfur
3
atom has a softer character in dimethyl sulfoxide the proton forms
a hydrogen bond to the oxygen atom.
2
-
2-
22,23
˚
2
.308 A for PdCl
4
and PtCl
4
, respectively).
For the presently
studied M(Me SO)
2
2
Cl complexes the separation between the Pd–
2
The dimethyl sulfoxide ligands, coordinated via the sulfur atom
to the divalent metal ions palladium(II) and platinum(II), as in
the dichlorobis(dimethyl sulfoxide) solvates, splits the asymmetric
peak observed for the free dimethyl sulfoxide molecule. The spec-
Cl and Pt–Cl force constants is smaller due to the lack of trans-
influence for M = Pt. The relatively high Pd–Cl force constant for
trans-Pd(Me
2
SO)
2
Cl is accompanied by a slightly shorter Pd–Cl
2
2
-
˚
bond distance than for PdCl
platinum(II) complexes the bond distance remains similar (Pt–Cl,
4
(2.288 vs. 2.306 A), whereas for the
trum of the trans-Pd(Me
shows larger splitting than for cis-Pt(Me
2
SO)
2
Cl
2
complex with high symmetry
SO) Cl . The X-ray
2
2
2
˚
2
.309 vs. 2.308 A). The higher force constants of the platinum(II)
absorption spectrum of the former complex exhibits four peaks
resolved at 2472.7, 2474.4, 2474.8 and 2476.0 eV, while the latter
solvate displays three features at 2473.8, 2474.8 and 2476.4 eV.
compounds reflect the higher covalency of the Pt–Cl than the Pd–
Cl bonds.
The even higher preference for sulfur-donor ligands in the
+
M(Me
2
SO)
2
Cl
2
complexes for M = Pt(II) than for Pd(II) is
Protonated dimethyl sulfoxide, (CH
3
)
2
SOH . For the calcu-
-
1
reflected in the higher M–S force constant, 2.21 and 1.52 N cm ,
lations of theoretical spectra the crystal structure geometry of
the protonated dimethyl sulfoxide molecule was used. Different
models were constructed by adding one hydrogen bonded water
26
respectively. The much lower Pd–S force constant for trans-
Pd(Me
2
SO)
2
2
Cl corresponds to a longer Pd–S bond distance: 2.299
˚
˚
vs. 2.236 A for the platinum(II) complex. The coordination to the
molecule (assuming the H–O bond distance 1.0 A with tetrahedral
sulfur atom of dimethyl sulfoxide increases the S–O stretching
HOH angles) in addition to the hydrogen bonding proton placed
-
1
˚
force constant, from 4.72 N cm for neat Me
7
2
SO to 6.79 and
at 1.12 and 1.3 A from the dimethyl sulfoxide oxygen atom,
.18 N cm- for the palladium and platinum solvates, respectively.
1
i.e. forming H
OH ◊ ◊ ◊ OS(CH
+
)
or H
O ◊ ◊ ◊ H OS(CH
+
)
entities,
˚
2
3
2
2
3
2
2–4
Oxygen coordination leads to lower SO force constants, and
is a striking difference between O and S coordination. Sulfur
coordination also increases the C–S stretching force constants
respectively, while keeping the O–H ◊ ◊ ◊ O distance at 2.414 A
as in the crystal structure (Fig. 6). The theoretical spectra were
15,16
calculated as described elsewhere,
applying corrections due to
-
1
somewhat, from 2.06 N cm for neat Me
2
SO to 2.22 and
relativistic and relaxation effects as well as an additional empirical
shift (-0.5 eV for model A and -0.6 eV for models B and C) of
the energy scales to obtain coincidence of the main features in
the experimental and theoretical spectra. The overall corrections
consisted, for most states, except for the first 9, 6 and 9 states for
models A, B and C, respectively (see below), of a shift of these
theoretical states to higher energies by 3.23, 3.21, and 3.22 eV for
2
.27 N cm- for trans-Pd(Me
1
2
SO)
2
Cl
2
and cis-Pt(Me SO) Cl
2
2
2
,
respectively.
Sulfur K-edge X-ray absorption
The experimental sulfur K-edge XANES spectra of the dimethyl
sulfoxide solutions in CH CN and concentrated HCl are com-
pared with those of the solid samples M(Me SO) Cl
, M = Pd and
Pt, in Fig. 5. The hydrogen bonded H O–H ◊ ◊ ◊ OSMe species,
3
+
+
the species: (CH
3
+
)
2
SOH (model A), H
2
O ◊ ◊ ◊ HOS(CH
3
) (model
2
2
2
2
B), and H
2
O–H ◊ ◊ ◊ OS(CH
3
)
2
(model C), respectively. For each of
+
2
2
the first 9, 6 and 9 states corresponding to the models A, B and C,
the relaxation energies were calculated and applied individually,
while the remaining states were corrected with the mean value for
each model of these calculated relaxation energies.
which dominates in the highly acidic HCl solution, shows two
resolved peaks with similar intensity and a shoulder on the high
energy side. The features are centered at about 2472.9, 2474.1 and
2
475.3 eV, respectively, while for uncoordinated dimethyl sulfoxide
The two experimental spectral features at about 2472.9 and
2
474.1 eV are reproduced by transitions 1 and 2 for all three
models. The splitting between these states decreases gradually,
from 1.6 (A), to 1.2 (B), to 1.1 eV (C), mostly because the 2nd state
shifts toward lower energy (Table 5). The experimental shoulder
corresponds to transition 3 for models B and C, and to 3 and 4
for model A. In the theoretical spectra for all three models, state
1
is attributed to the transition from S(1 s) to an antibonding
s*(S–O) molecular orbital (MO), and transition 2 to an MO with
p*(S–O) bond character. The main discrepancies in the calculated
transition energies and intensities are found for the unhydrated
model A, where states 3 and 4 are attributed to MOs with s*(O–
H) character and s*(S–O, S–C) contribution from the two methyl
groups. State 3 for model B, mainly with s*(S–O, S–C) character,
resembles state 4 for model A (cf. Fig. S1†). The shapes of the
MOs for the main transitions for models B and C are also similar
to those for the uncoordinated dimethyl sulfoxide molecule.
The character of the MOs of states 1, 2 and 3 and the
corresponding transitions are similar for models B and C. The
Fig. 5 Normalized sulfur K-edge XANES experimental spectra of
.05 mol dm-3 dimethyl sulfoxide solutions in acetonitrile (—), concen-
0
trated hydrochloric acid (-·-), and the solid solvates Pd((CH SO) Cl
3
)
2
2
2
(
◊ ◊ ◊ ) and Pt((CH SO) Cl (---), respectively.
3
)
2
2
2
1
334 | Dalton Trans., 2009, 1328–1338
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satisfactorily. Thus, increasing the distance of the proton from
the dimethyl sulfoxide oxygen atom only induces small changes
in the energy and intensity of the transitions, and the computed
spectrum is not very sensitive to the position of the proton in the
hydrogen bond.
cis- and trans-Isomers of the dichlorobis(dimethyl sulfoxide) plat-
inum(II) complex. The theoretical XANES spectra were calcu-
lated for both isomers of the sulfur-coordinated Pt((CH
solvate based on the previously determined geometry.
3
)
2
1
SO)
2
Cl
The
2
2,13
theoretical spectra generated for these species were obtained
by applying corrections for relativistic (+7.4 eV) and relaxation
effects. The relaxation energy contributions were calculated and
applied individually for each of the first nine excited states,
while their mean values (-3.32/-3.36 eV for the cis- and trans-
configurations, respectively) were used for the remaining states.
A minor additional empirical shift, -0.3 and -0.05 eV, was
applied to the convoluted calculated spectra of the cis- and trans-
PtCl
2
(Me
2
SO) complexes, respectively, to match the position of
2
16
the main peak in the experimental spectra, cf. Fig. 7A,B.
The intensity and the corresponding absolute energy values
obtained for the first six transitions for both isomers of the
PtCl
theoretical XANES spectra for the geometric isomers of the
PtCl (Me SO) complex reproduce reasonably well the experimen-
2
(Me
2
SO)
2
complex are given in Table 6. The resulting
2
2
2
tal features, except for the first low energy peak. The calculated
transitions are distributed over a region of 2.3/2.1 eV for the cis-
and trans-species, respectively, and do not properly represent the
experimental splitting of about 3.3 eV observed between the near
edge features. For both isomers the two most intense peaks, at
2
474.8 and 2476.4 eV, were generated by three transitions, 1, 2, 3
and 4, 5, 6, respectively. The pseudo potential description of the
heavy platinum atom in the calculation seems to be the most likely
reason for the relatively poor agreement with the experimental
peak for the LUMO transition 1 observed at 2473.8 eV.
The similarity of the calculated spectra for the geometric
isomers is also evident when inspecting the shape of the MOs
that correspond to the states 1–6. The probability of the LUMO
transition 1 is almost unaffected by the change in configuration
(
Fig. 7A,B and Table 6), but the intensity ratios and energy
differences between the remaining transitions are slightly more
sensitive. The shape of the LUMO for both isomers is virtually
identical, showing delocalization over the platinum and its nearest
neighbour atoms and has antibonding s*(Pt–Cl, Pt–S) character
(
cf. Fig. S2†). The MOs corresponding to transitions 2 and 3
of the cis-isomer display mixed antibonding s*–p* character
delocalized over the platinum atom and one of the dimethyl
sulfoxide molecules. LUMO + 1 has mainly s*(S–O) and some
p*(Pt–S) character, while LUMO + 2 is dominated by antibonding
s*(S–C) together with some p*(S–O, Pt–S) character. LUMO + 1
and LUMO + 2 for the trans-isomer are almost identical
displaying mostly s*(S–C, S–O) with some p*(Pt–S) character.
The transition 3, which has its highest cross-section for the
cis-isomer, can mainly be attributed to an S(1s) → s*(S–C)
transition, but with the electron charge distributed over several
atoms (cf. Fig. S2†). The MOs for this isomer corresponding to
Fig. 6 Theoretical S K-edge XANES spectra ( ◊ ◊ ◊ ) calculated for: model
A, the unsolvated protonated dimethyl sulfoxide molecule; model B,
+
solvated with one hydrogen bonded water molecule H
2
O ◊ ◊ ◊ HOS(CH
3
)
2
;
+
and model C, H
2
O–H ◊ ◊ ◊ OS(CH
3
)
2
, and the experimental spectrum of
0
.05 M dimethyl sulfoxide in concentrated hydrochloric acid (—). The
vertical bars represent the calculated transition energies and cross-sections,
convoluted with 0.9 eV (model A) and 1.1 eV (models B and C) FWHM
Gaussians below 2476.2 eV, linearly increasing to 8 eV FWHM above
2
496.2 eV. The LUMO contour (transition 1) for models B and C is shown
above, the MOs corresponding to 1, 2, 3 and 4 are shown in Fig. S1.†
the states 5 and 6 involve only one of the Me SO ligands and
2
best match to the experimental spectrum is achieved for model
B, even though models A and C also represent the main features
are almost identical, exhibiting mainly antibonding s*(S–C, S–O)
character.
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+
+
Table 5 Energy and intensity of the calculated S(1s) electronic transitions for the following species: (CH
3
)
2
SOH (model A), H
2
3 2
O ◊ ◊ ◊ HOS(CH ) (model
+
B) and H
2
3 2
O–H ◊ ◊ ◊ OS(CH ) (model C) (Fig. 6A,B,C)
Energy/eV
Model A
Oscillator strength/Mbarn
Transition no.
Model B
Model C
Model A
Model B
Model C
1
2
3
4
2472.8
2474.4
2475.1
2475.9
2472.9
2474.1
2475.2
—
2472.9
2474.0
2475.0
—
0.1415
0.1234
0.0454
0.0227
0.1399
0.1226
0.0533
—
0.1292
0.1175
0.0459
—
Table 6 Energy and intensity of the calculated transitions for the cis- and
trans-isomers of the Pt(Me SO) Cl complex (Fig. 7A,B)
2
2
2
Oscillator
strength/Mbarn
Energy/eV
Transition no.
cis
trans
cis
trans
1
2
3
4
5
6
2474.2
2474.5
2475.0
2475.7
2476.1
2476.5
2474.5
2474.8
2475.0
2476.0
2476.5
2476.6
0.0226
0.0792
0.1221
0.0301
0.0494
0.0175
0.0209
0.0904
0.0797
0.0463
0.0403
0.0343
and has mostly s*(S–O) and p*(S–O) character. The state 5 is
attributed on the other hand to a MO which is mostly dominated
by antibonding p*(Pt–S) character.
cis- and trans-Isomers of the dichlorobis(dimethyl sulfoxide)
palladium(II) complex. The molecular geometries used for the
calculation of the spectra were derived from the crystal structure
12
of trans-isomer. Similar corrections as for the platinum complex
were applied for the geometric isomers of the Pd((CH SO) Cl
3
)
2
2
2
solvate. For both isomers, separate relaxation effects were eval-
uated and applied to the first nine states and their mean values
-
2.97/-2.82 eV to the remaining transitions, in addition to the rel-
ativistic (+7.4 eV) and additional empirical shifts of -0.5/-0.9 eV
for the cis- and trans-Pd((CH SO) Cl complexes, respectively.
3
)
2
2
2
The convoluted corrected theoretical spectra obtained for both
isomers are displayed in Fig. 8A,B, while the absolute energy and
intensity for the transitions marked in these figures are given in
Table 7.
The experimental peak observed at 2472.7 eV seems to be
best matched by transition 1 computed for the trans-isomer (cf.
Table 7). State 1 is for both isomers attributed to the excitation
of the S(1s) electron into the LUMO, which has antibonding
s*(Pd–Cl, Pd–S) character (cf. Fig. S3†), involving as for the
Fig. 7 Calculated S K-edge XANES spectra ( ◊ ◊ ◊ ) of the cis- (A) and
trans- (B) isomers of the Pt((CH SO) Cl complex compared with
the experimental XANES spectrum of the solid Pt((CH SO) Cl com-
Table 7 Energy and intensity of the calculated transitions for the cis and
trans isomers of the Pd(Me SO) Cl complex (Fig. 8A,B)
2 2 2
3
)
2
2
2
3
)
2
2
2
pound (—). The vertical bars represent the calculated transition energies
and cross-sections, convoluted with FWHM Gaussians of 0.8/0.8 eV
below 2479.1/2479.2 eV, linearly increasing to 8 eV FWHM above
Oscillator
strength/Mbarn
Energy/eV
Transition no.
cis
trans
cis
trans
2
499.1/2499.2 eV, respectively. The LUMO contours (receiving transition
1
) for the cis- and trans-isomers are shown in C; all MOs for marked
1
2
3
4
5
6
2473.3
2474.2
2474.9
2475.4
2475.9
2476.4
2472.8
2473.8
2474.8
2475.6
2475.7
—
0.0188
0.0771
0.1190
0.0412
0.0155
0.0238
0.0208
0.0790
0.1298
0.0558
0.0251
—
transitions in Fig. S2.†
The MO for the trans-isomer corresponding to state 4 has
antibonding s*(S–C, S–O) character, while the distribution of the
charge for the orbital associated with transition 6 is very diffuse
1
336 | Dalton Trans., 2009, 1328–1338
This journal is © The Royal Society of Chemistry 2009

View Article Online
different mixed antibonding s*–p* character of the receiving MOs.
For the cis-isomer the MO is dominated by antibonding s*(S–C)
character with some p*(Pt–S, S–O) contribution involving only
one of the Me SO ligands, while for the trans-isomer the receiving
2
MO is dominated by p*(S–O) as well as some antibonding s*(S–C)
character. LUMO + 4 corresponds for both isomers to transition
4
and has s*(S–C, S–O) antibonding character. The state 5
transition calculated for the cis-isomer occurs into LUMO + 5 that
shows mixed contributions of antibonding s* character between
the sulfur, oxygen and one of the carbon atoms belonging the
same Me
2
SO ligand (cf. Fig. S3†). The last transitions marked in
SO) Cl
Fig. 8A,B, namely 6 and 5 for the cis- and trans-Pd((CH
3
)
2
2
2
are attributed to LUMO + 6 and LUMO + 8, respectively. These
MOs are quite similar with the charge delocalized over almost the
entire molecule with major contributions of s*(S–O) and some
s*(S–C) antibonding character. Transitions to LUMO + 2 for
both isomers, and to LUMO + 5, LUMO + 6 and LUMO + 7 for
the trans-isomer, have too low intensity to show up in the spectra.
Conclusions
A force field study of the vibrational spectra of strongly hydro-
gen bonded dimethyl sulfoxide, combined with sulfur K-edge
X-ray absorption measurements has been performed to evaluate
the effect of the changed charge distribution in the dimethyl
sulfoxide molecule. The experimental spectra of dimethyl sulfoxide
in concentrated HCl solution are in satisfactory agreement with
those calculated for a molecular model of dimethyl sulfoxide with a
+
hydrogen bond to an H
3
O ion, Fig. 6c. The effect of the hydrogen
bonded proton on the SO bond is much stronger than oxygen-
coordination of dimethyl sulfoxide ligands to metal ions. The
-
1
decrease of the SO force constant is from 4.72 N cm in neat
-
1
liquid dimethyl sulfoxide to 3.73 N cm in the protonated species,
-
1
whereas the values range from 4.17 N cm for Ga(Me
2
SO)
6
3
I to
-
1
2–4
4
.69 N cm for Lu(Me
Complete assignments of the fundamental vibrational
modes have been achieved for the sulfur-coordinated
trans-PdCl ((CH SO) Cl trans-Pd((CD SO) Cl and cis-
PtCl ((CH SO) Cl complexes. Normal coordinate analyses of
2
SO)
8
I
3
.
2
3
)
2
2
2
,
3
)
2
2
2
Fig. 8 Calculated S K-edge XANES spectra ( ◊ ◊ ◊ ) of the cis- (A) and
trans- (B) isomers of the Pd((CH SO) Cl complex compared with the
experimental XANES spectrum of the solid Pd((CH SO) Cl compound
—). The vertical bars represent the calculated transition energies and
cross-sections, convoluted with FWHM Gaussians of 0.75/0.75 eV
below 2479.2/2478.8 eV, linearly increasing to 8 eV FWHM above
2
3
)
2
2
2
3
)
2
2
2
the vibrational spectra showed substantial changes from those
in neat dimethyl sulfoxide. The sulfur coordination induced
upshifts of some intramolecular modes, in contrast to oxygen-
3
)
2
2
2
(
coordination for which the SO stretching and all Me SO bending
2
modes shift to lower wavenumbers. A significant strengthening
of the SO bonds was indicated by the high force constants of
2
1
499.2/2498.8 eV, respectively. The LUMO contours (receiving transition
) for the cis- and trans-isomers are shown in C; all MOs for marked
-
1
transitions in Fig. S3.†
the SO stretching mode (6.79 and 7.18 N cm for the palladium
-
1
and platinum complexes, respectively, vs. 4.72 N cm for neat
dimethyl sulfoxide). The higher covalency of the platinum–ligand
bonds results in higher frequencies and higher force constants of
ML stretching modes, both for M–Cl and M–S bonds, than for
the corresponding palladium compounds, even though the bond
distances remain similar.
The effects on the electronic state of the dimethyl sulfoxide
molecules in these compounds was investigated by means of
sulfur K-edge XANES spectroscopy combined with theoretical
DFT-TP calculations. The first transition in the spectra occurred
at lower energy than for uncoordinated dimethyl sulfoxide but
with different character of the receiving LUMOs for oxygen- and
sulfur-coordinated species. The high covalency of the Pt–S bonds,
Pt((CH SO) Cl complex all the sulfur and chlorine atoms. The
transitions 2, 3, 4 and 2, 3, evaluated for the isomeric cis- and
trans-structures, reproduce the experimental peaks appearing at
3
)
2
2
2
2
474.4 and 2474.8 eV, respectively. The splitting obtained between
the states 2 and 3 as well as their absolute energy positions are quite
well reproduced for the cis-isomer. The states 5 and 6 for the cis-
isomer and 4 and 5 for the trans-isomer correspond to the shoulder
observed at 2476.0 eV. For both of the isomers the LUMO + 1
(
state 2) has mainly s*(S–O) character, but with some minor
contribution from antibonding p*(Pt–S) for the cis-conformer.
The most intense computed transition, 3, was attributed to
S(1 s) → LUMO + 3 for both conformers, but with slightly
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1328–1338 | 1337

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which also is indicated by the highly delocalized receiving LUMOs,
resulted in larger energy shifts than for the palladium(II) complex.
The differences in the XANES spectra between the geometrical
isomers of the dichlorobis(dimethyl sulfoxide) palladium(II) and
platinum(II) complexes were found be too small to allow distinc-
tion experimentally.
6 B. F. G. Johnson, J. Puga and P. R. Raithby, Acta Crystallogr., Ser. B,
1
981, 37, 953.
7
E. Alessio, E. Iengo, S. Geremia and M. Calligaris, Inorg. Chim. Acta,
2
003, 344, 183.
8 E. Alessio, B. Serli, E. Zangrando, M. Calligaris and N. S. Panina,
Eur. J. Inorg. Chem., 2003, 17, 3160.
9
M. Tranquille and M. T. Forel, Spectrochim. Acta, Ser. A, 1972, 28,
1
305.
1
1
0 M. Tranquille and M. T. Forel, Canadian J. Spectrosc., 1976, 21, 11.
1 E. Damian, F. Jalilehvand, A. Abbasi, L. G. M. Pettersson and M.
Sandstr o¨ m, Phys. Scrip., 2005, T115, 1077.
2 M. J. Bennett, F. A. Cotton, D. L. Weaver, R. J. Williams and W. H.
Watson, Acta Crystallogr., 1967, 23, 788.
3 R. P. Shibaeva, Koord. Khim., 1985, 11, 129.
Acknowledgements
1
We gratefully acknowledge the Swedish Research Council, the
Hungarian National Research Foundation (OTKA #K61611)
for financial support, the Swedish Institute for the support
through the Visby programme, and SSRL for allocation of beam-
time. SSRL is operated by the Department of Energy, Office
of Basic Energy Sciences. The SSRL Biotechnology program is
supported by the National Institute of Health, National Center
for Research Resources, Biomedical Technology Program, and by
the Department of Energy, Office of Biological and Environmental
Research. We thank Professor Lars G. M. Petterson, Stockholm
University, for advice in performing the DFT-TP calculations.
1
14 J. Mink and L. M. Mink, Computer Program System for Vibrational
Analyses of Polyatomic Molecules (in Lahey-Fujitsu Fortran Win32),
Stockholm, 2004.
1
5 E. Damian Risberg, L. Eriksson, J. Mink, L. G. M. Pettersson, M. Yu.
Skripkin and M. Sandstr o¨ m, Inorg. Chem., 2007, 46, 8332.
16 E. Damian Risberg, F. Jalilehvand, B. O. Leung, L. G. M. Pettersson
and M. Sandstr o¨ m, Dalton Trans., submitted.
1
7 W. K u¨ chle, M. Dolg, H. Stoll and H. Preuss, Mol. Phys., 1991, 74,
1
245.
18 M. Pelissier, N. Komiha and J. P. Daudey, J. Comput. Chem., 1988, 9,
98.
9 L. V. Konovalov and Yu. N. Kukushkin, Russ. J. Coord. Chem., 1997,
3, 885.
20 J. Mink and P. L. Goggin, Kemiai K o¨ zlem e´ nyek., 1984, 61, 275.
2
1
2
References
2
1 R. G. Pearson, Chemical Hardness – Applications from Molecules to
Solids, Wiley-VCH, Weinheim, 1997.
1
2
M. Calligaris, Coord. Chem. Rev., 2004, 248, 351, and refs cited therein.
A. Molla-Abbassi, M. Skripkin, M. Kritikos, I. Persson, J. Mink and
M. Sandstr o¨ m, Dalton Trans., 2003, 1746.
22 H. Takazawa, S. Ohba and Y. Saito, Acta Crystallogr., Ser. B, 1988, 44,
580.
3
4
M. Skripkin, P. Lindqvist-Reis, A. Abbasi, J. Mink, I. Persson and M.
Sandstr o¨ m, Dalton Trans., 2004, 4038.
A. Abbasi, E. Damian Risberg, L. Eriksson, J. Mink, I. Persson, M.
Sandst o¨ m, Y. V. Sidorov, M. Yu. Skripkin and A.-S. Ullstr o¨ m, Inorg.
Chem., 2007, 46, 7731.
A. R. Davies, F. W. B. Einstein, N. P. Farrell, B. R. James and R. S.
McMillan, Inorg. Chem., 1978, 17, 1965.
23 S. Ohba, S. Sato and Y. Saito, Acta Crystallogr., Ser. B, 1983, 39,
49.
24 L. A. Degen and A. J. Rowlands, Spectrochim. Acta, Ser. A, 1991, 47,
1263.
25 P. L. Goggin and J. Mink, J. Chem. Soc., Dalton Trans., 1975, 381.
26 J. S. Jaswal, S. J. Rettig and B. R. James, Can. J. Chem., 1990, 68, 1808.
27 R. C. Taylor and G. L. Vidale, J. Am. Chem. Soc., 1956, 78, 5999.
5
1
338 | Dalton Trans., 2009, 1328–1338
This journal is © The Royal Society of Chemistry 2009