Dynamic study of homoleptic bimetallic platinum(II) complexes bridged by fluorinated benzenethiolates

Article abstract of DOI:10.1021/ic010437n

A variable-temperature ¹⁹F NMR study of the homoleptic bimetallic anionic complexes X₂[Pt₂(μ-SC₆F₅)₂ (SC₆F₅)₄] (X = K⁺, 1a; Bu₄N⁺, 1b), X₂[Pt₂ (μ-p-SC₆HF₄)₂ (p-SC₆HF₄)₄] (X = K⁺, 2a; Bu₄N⁺, 2b), and X₂[Pt₂(μ-p-SC₆F₄ (CF₃))₂(p-SC₆F₄ (CF₃))₄] (X = K⁺, 3a; Bu₄N⁺, 3b) demonstrates the occurrence of dynamic processes that give rise to several stereoisomeric species in solution. Experimental evidence suggests that both inversion of configuration at the sulfur bridging atoms and hindered rotation about the carbon-sulfur bond are involved in generating the observed isomers. The solid-state X-ray diffraction structures of compounds 1b, 2b, and 3b show that all three complexes contain planar [Pt₂(μ-S)₂] rings with an anti configuration.

Full text of DOI:10.1021/ic010437n

Inorg. Chem. 2001, 40, 5575-5580
5575
Dynamic Study of Homoleptic Bimetallic Platinum(II) Complexes Bridged by Fluorinated
Benzenethiolates
Guillermina Rivera,† Sylvain Berne`s,‡ Cecilia Rodriguez de Barbarin,§ and Hugo Torrens*,†
DEPg., F. Qu´ımica, UNAM, Ciudad Universitaria, 04510 Me´xico D.F., Mexico, Centro de Qu´ımica,
IC-UAP, Blvd. 14 Sur 6303, San Manuel, 72570 Puebla Pue., Mexico, and F. Ciencias Qu´ımicas,
UANL, Ciudad Universitaria, 66451 S. Nicolas de los Garza, Nuevo Leon, Mexico
ReceiVed April 6, 2001
A variable-temperature 19F NMR study of the homoleptic bimetallic anionic complexes X2[Pt2(µ-SC6F5)2(SC6F5)4]
(X ) K+, 1a; Bu4N+, 1b), X2[Pt2(µ-p-SC6HF4)2(p-SC6HF4)4] (X ) K+, 2a; Bu4N+, 2b), and X2[Pt2(µ-p-SC6F4-
(CF3))2(p-SC6F4(CF3))4] (X ) K+, 3a; Bu4N+, 3b) demonstrates the occurrence of dynamic processes that give
rise to several stereoisomeric species in solution. Experimental evidence suggests that both inversion of configuration
at the sulfur bridging atoms and hindered rotation about the carbon-sulfur bond are involved in generating the
observed isomers. The solid-state X-ray diffraction structures of compounds 1b, 2b, and 3b show that all three
complexes contain planar [Pt2(µ-S)2] rings with an anti configuration.
Introduction
X-ray diffraction studies have shown that solid-state interac-
tions between fluorine atoms on neighboring groups could be
responsible for the restriction of the C-S bond rotation.12-14
Inversion of configuration at metal-bridging sulfur atoms has
been examined, and it was found that the activation energy
Binuclear complexes of d8 transition metal ions of the type
[M2(µ-SR)2(L)4] display a variety of molecular conformations.
The particular molecular conformation depends on a number
of factors, such as whether the complexes incorporate a bent or
a planar [M2(µ-S)2] ring,1 the relative orientation of the
substituents (R) at the sulfur bridging atoms,2 and the extent of
hindered rotation about the R-sulfur bond.3
involved in this process is in the range 40-80 kJ mol-1 15,16
.
The binuclear complexes K2[Pt2(µ-SC6F5)2(SC6F5)4]2- 1a and
K2[Pt2(µ-p-SC6HF4)2(p-SC6HF4)4]2- 2a have been reported
previously.17 In these studies the existence of isomers in solution
was noted and attributed to sulfur inversion, although this
phenomenon was not studied in greater depth.17,18
Conversion between each of these isomers is accomplished
either by flipping of the [M2(µ-S)2] ring,4 hindered rotation about
the R-sulfur bond,5 inversion of configuration at tricoordinated
pyramidal sulfur atoms,6,7 or a combination these processes.2
Theoretical and experimental studies have shown that the
energy differences between planar and bent structures are
relatively small (ca. 40 kJ mol-1), and it has been pointed out
that, in some cases, the steric repulsion between terminal ligands
or packing forces can ultimately affect the structural choice.8
On the other hand, variable-temperature NMR studies of
complexes bearing pentafluorothiophenolate rings have shown
that, as one would expect, C-S bond rotation is frequently
restricted. The activation energies associated with this process
are in the range 30-50 kJ mol-1, and these values are larger
than those found for comparable nonfluorinated compounds.9-11
In this paper we report the synthesis of the new perfluorinated
compounds X2[Pt2(µ-p-SC6F4(CF3))2(p-SC6F4(CF3))4]2- (X )
K+, 3a; X ) Bu4N+, 3b) as well as the variable-temperature
19F NMR study and the crystal and molecular structures of
(Bu4N)2[Pt2(µ-SC6F5)2(SC6F5)4] 1b, (Bu4N)2[Pt2(µ-p-SC6HF4)2-
(p-SC6HF4)4] 2b, and (Bu4N)2[Pt2(µ-p-SC6F4(CF3))2(p-SC6F4-
(CF3))4] 3b.
Experimental Section
All manipulations were carried out under dry oxygen-free dinitrogen
atmospheres using Schlenk-tube techniques. Solvents were dried and
degassed using standard techniques.19 Thin-layer chromatography (TLC)
† UNAM, Ciudad Universitaria.
‡ IC-UAP.
(11) Davidson, J. L.; McIntosh, C. H.; Leverd, P. C.; Lindsell, W. E.;
Simpson, N. J. J. Chem. Soc., Dalton Trans. 1994, 2423-2429.
(12) Arroyo, M.; Berne`s, S.; Brianso, J. L.; Mayoral, E.; Richards, R. L.;
Rius, J.; Torrens, H. J. Organomet. Chem. 2000, 599, 170-177.
(13) Wan Abu Bakar, W. A.; Davidson, J. L.; Lindsell, W. E.; McCullough,
K. J. J. Organomet. Chem. 1987, 322, C1-C6.
§ UANL, Ciudad Universitaria.
(1) Aullo´n, G.; Ujaque, G.; Lledo´s, A.; Alvarez, S. Chem. Eur. J. 1999,
5, 1391-1410.
(2) Brown, M. D.; Puddephat, R. J.; Upton, C. E. E. J. Chem. Soc., Dalton
Trans. 1976, 2490-2494.
(3) Dixon, K. R.; Moss, K. C.; Smith, M. A. J. Chem. Soc., Dalton Trans.
1974, 971-977.
(14) Castellanos, A.; Garcia, J. J.; Torrens, H.; Bailey, N.; Rodriguez de
Barbarin, C. O.; Gutierrez, A.; del Rio, F. J. Chem. Soc., Dalton Trans.
1994, 2861-2866.
(4) Dias, A. R.; Green, M. L. H. J. Chem. Soc. A 1971, 1951-1956.
(5) Agh-Atabay, N. M.; Davidson, J. L. J. Chem. Soc., Dalton Trans.
1992, 3531-3539.
(15) Shaver, A.; Morris, S.; Turrin, R.; Day, V. M. Inorg. Chem. 1990,
29, 3622-3623.
(6) Abel, E. W.; Bush, R. P.; Hopton, F. J.; Jenkins, C. R. Chem. Commun.
1966, 58-59.
(16) Abel, E. W.; Bhargava, S. K.; Orrell, K. G. Prog. Inorg. Chem. 1984,
32, 1-118.
(7) Haake, P.; Turley, P. C. J. Am. Chem. Soc. 1967, 89, 4611-4616.
(8) Aullo´n, G.; Ujaque, G.; Lledo´s, A.; Alvarez, S. Inorg. Chem. 1998,
37, 804-813.
(17) Garcia, J.; Mart´ın, E.; Morales, D.; Torrens, H. Inorg. Chim. Acta
1994, 207, 93-96.
(18) Uso´n, R.; Fornie´s, J.; Uso´n, M. A.; Apaolaza, J. A. Inorg. Chim. Acta
1991, 187, 175-180.
(9) Meaking, P.; Ovenall, D. W.; Sheppard, W. A.; Jesson, J. P. J. Am.
Chem. Soc. 1975, 97, 522-528.
(19) Riddick, J. A.; Bunger, W. B.; Sakaro, T. K. Organic SolVents:
Physical Properties and Methods of Purification, 4th ed.; Techniques
of Chemistry, Volume II; Wiley-Interscience: New York, 1970.
(10) Wan Abu Bakar, W. A.; Davidson, J. L.; Lindsell, W. E.; McCullough,
K. J. J. Chem. Soc., Dalton Trans. 1989, 991-1001.
10.1021/ic010437n CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/22/2001

5576 Inorganic Chemistry, Vol. 40, No. 22, 2001
Rivera et al.
Table 1. Crystallographic Data for Complexes 1b, 2b, and 3b
complex
1b
2b
3b
chem formula
fw
space group
a/Å
b/Å
C68H72F30N2Pt2S6
2069.82
P21/n
14.1703(17)
19.2766(18)
14.763(3)
94.362(11)
4020.8(9)
C68H78F24N2Pt2S6
1961.86
P21/n
13.6707(8)
19.276(2)
15.6448(15)
109.012(7)
3897.9(6)
C74H72F42N2Pt2S6
2369.88
P21/n
14.282(4)
22.526(4)
15.2241(19)
90.406(18)
4897.6(17)
2
3.099
1.607
25
0.71073
c/Å
â/deg
V/Å3
Z
2
2
µ/mm-1
3.741
1.709
25
0.71073
R1 ) 4.11%, wR2 ) 9.54%
R1 ) 6.28%, wR2 ) 10.91%
3.843
1.672
25
0.71073
R1 ) 5.61%, wR2 ) 14.56%
R1 ) 8.92%, wR2 ) 17.03%
F
calcd/(g cm-3
)
temp/°C
λ/Å
R indices (I > 2σ(I))a
R indices (all data)a
R1 ) 7.21%, wR2 ) 15.31%
R1 ) 15.98%, wR2 ) 19.05%
a Rint ) ∑|Fo - Fo |/∑Fo , R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑w(Fo - Fc2)2/∑w(Fo )2], S ) [∑w(Fo - Fc2)2/(m - n)].
2
2
2
2
2
2
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1ba
(Merck, 5 × 7.5 cm2 Kiesegel 60 F254) was used when possible to
monitor the progress of the reaction under study.
Pt1-S3
Pt1-S1
S1-C1
S2-C7
2.3115(18)
2.3217(16)
1.785(7)
Pt1-S2
Pt1-S1′
S1-Pt1′
S3-C13
2.2984(18)
2.3164(16)
2.3164(16)
1.760(7)
Complexes were characterized by FTIR spectra recorded over the
4000-200 cm-1 range on a Perkin-Elmer 1600 spectrophotometer, and
the samples were prepared as CsI pellets. Data are expressed in
wavenumbers (cm-1) with relative intensities (s ) strong, m ) medium,
w ) weak).
1.752(7)
S3-Pt1-S2
S2-Pt1-S1
S2-Pt1-S1′
C1-S1-Pt1
Pt1-S1-Pt1′
C13-S3-Pt1
89.43(7)
173.37(6)
97.52(6)
105.7(2)
97.26(6)
105.9(2)
S3-Pt1-S1
S3-Pt1-S1′
S1-Pt1-S1′
C1-S1-Pt1′
C7-S2-Pt1
90.78(6)
172.16(7)
82.74(6)
109.5(2)
108.5(2)
1H and 19F NMR spectra were measured with a Varian spectrometer
operating at 299.7 and 282.0 MHz, respectively. 195Pt NMR spectra
were measured with a Bruker spectrometer operating at 64.5 MHz.
Chemical shifts are relative to TMS [δ ) 0 (1H)], CFCl3 [δ ) 0 (19F)]
and Na2[PtCl6]/D2O [δ ) 0 (195Pt)]. A standard variable-temperature
unit was used to control the probe temperature, and this was checked
periodically using a thermocouple to ensure that temperature readings
were within (1 °C. Complexes were dissolved in deuterated acetone.
Elemental analyses were determined by Galbraith Labs. Inc., USA.
K2[Pt2(µ-SC6F5)2(SC6F5)4] 1a,17 K2[Pt2(µ-p-SC6HF4)2(p-SC6HF4)4]
2a,17 and [PtCl2(COD)]20 were prepared according to the literature
methods.
Pb(p-SC6F4(CF3))2. To a solution of Pb(CH3COO)2 (0.66 g, 2 mmol)
in water (50 cm3) was added H-p-SC6F4(CF3) (1.00 g, 4 mmol). A
yellow precipitate formed, and this was filtered off and dried in vacuo
to give Pb(p-SC6F4(CF3))2. The lead salt was recrystallized from
acetone. Yield: 80%. Mp: 230 °C dec. C14F14S2Pb: Anal. Calcd (%):
C, 23.84; S, 9.09. Found (%): C, 23.8; S, 9.06. IR (cm-1): 1642s,
1474vs, 1325vs, 1179vs, 1156vs, 1137vs, 977vs, 830vs, 715vs. 19F
NMR: δ -56.74 (pseudotriplet, p-CF3), δ -133.57 (multiplet, o-F), δ
-146.54 (multiplet, m-F).
K2[Pt(p-SC6F4(CF3))4]. To a solution of KOH (0.27 g, 4.82 mmol)
in water (10 cm3) was added H-p-SC6F4(CF3) (1.21 g, 4.82 mmol),
and the mixture was heated to 50 °C. After 30 min a solution of K2-
[PtCl4] (0.5 g, 1.2 mmol) in water (10 cm3) was added dropwise, and
the mixture was stirred for 2 h. The solution was then filtered and the
filtrate dried in vacuo to give K2[Pt(p-SC6F4(CF3))4] as a red solid.
Yield: 74%. Mp: 240 °C dec. Anal. Calcd for C28F28K2PtS4 (%): C,
26.49; S, 10.1. Found (%): C, 26.4; S, 10.0. IR (cm-1): 1644s, 1469vs,
1328vs, 1181s, 1139s, 969vs, 827s, 714s. 19F NMR: δ -54.64
(pseudotriplet, p-CF3), δ -130.98 (multiplet, o-F), δ -147.86 (multiplet,
m-F).
[Pt(p-SC6F4(CF3))2(COD)]. To a suspension of [PtCl2(COD)] (0.10
g, 0.27 mmol) in acetone (25 cm3) was added a solution of Pb(p-SC6F4-
(CF3))2 (0.19 g, 0.27 mmol) in acetone. A white solid precipitated from
the resulting yellow solution, and this was filtered off and washed with
acetone. The filtrate was evaporated to dryness under reduced pressure
to afford pale yellow microcrystals of [Pt(p-SC6F4(CF3))2(COD)].
Yield: 93%. Mp: 247 °C dec. Anal. Calcd for C22H12F14PtS2 (%): C,
32.97; H, 1.51; S, 8.0. Found (%): C, 32.8; H, 1.5; S, 8.1. IR (cm-1):
1643m, 1476vs, 1430m, 1386m, 1323vs, 1175s, 1144s, 976vs, 830s,
a Primed atoms are generated by inversion through a center of
symmetry occupied by Pt1. For the Pt1 coordinates given in the
Supporting Information for 1b, the transformation to generate the
primed atoms is -x + 2, -y, -z.
714s. 19F NMR: δ -57.21 (pseudotriplet, p-CF3), δ -132.06 (multiplet,
o-F), δ -145.46 (multiplet, m-F).
K2[Pt2(µ-p-SC6F4(CF3))2(p-SC6F4(CF3))4] 3a. To a solution of K2-
[Pt(p-SC6F4(CF3))4] (0.10 g, 0.079 mmol) in acetone (25 cm3) was added
a solution of [Pt(p-SC6F4(CF3))2COD] (0.06 g, 0.079 mmol) in acetone
(25 cm3). The reaction mixture was heated under reflux, and the course
of the reaction was followed by thin-layer chromatography (TLC). After
63 h the solvent was distilled off under vacuum. The solid product
was washed with benzene to give K2[Pt2(µ-p-SC6F4(CF3))2(p-SC6F4-
(CF3))4] 3a. Yield: 86%. Mp: 245 °C dec. Anal. Calcd for C42F42K2-
Pt2S6 (%): C, 26.76; S, 10.21. Found (%): C, 26.7; S, 10.1. IR (cm-1):
1643m, 1475vs, 1178s, 1327vs, 976s, 828m, 715s.
(Bu4N)2[Pt2(µ-p-SC6F4(CF3))2(p-SC6F4(CF3))4] 3b was obtained
after treatment of 3a with (Bu4N)Cl in acetone at room temperature.
Yield: 91%. Mp: 119-120 °C. Anal. Calcd for C74H72F42N2S6Pt2
(%): C 37.51; H, 3.06; S, 8.12. Found (%): C, 37.4; H, 3.1; S, 8.2. IR
(cm-1): 2965m, 1641s, 1478vs, 1384m, 1324vs, 1177s, 1141vs, 977s,
826m, 714s.
X-ray Diffraction Data. Suitable single crystals of complexes 1b,
2b, and 3b were obtained by slow evaporation of solutions and were
found to be stable in air. Pertinent crystal data and other crystallographic
parameters are listed in Table 1. The diffraction data were collected at
295 K on a Bruker P4 diffractometer21 using graphite-monochromated
Mo KR radiation (λ ) 0.71073 Å) and a θ/2θ or ω scan mode with
variable scan speed. Absorption corrections were applied using ψ-scans.
For all three complexes the non-H atoms were refined anisotropically
without restraints on thermal parameters, regardless of the disordered
fragments. Structures were solved and refined using routine proce-
dures.22
For the anion, due to the large atomic displacement parameters of
the ligand C13‚‚‚C18, the corresponding ring was refined as an idealized
(21) Fait, J. XSCANS Users Manual; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1991.
(20) Drew, D.; Doyle, R. J. Inorganic Synthesis; Angelici, R. J., Ed.; J.
(22) Sheldrick, G. M. SHELX97 Users Manual; University of Go¨ttingen:
Go¨ttingen, Germany, 1997.
Wiley & Sons: 1990; Vol. 28, p 346.

Dynamic Study of Homoleptic Bimetallic Pt(II) Complexes
Inorganic Chemistry, Vol. 40, No. 22, 2001 5577
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2ba
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 3ba
Pt1-S3
Pt1-S1
S1-C1
S2-C7
2.3012(17)
2.3174(16)
1.774(5)
Pt1-S2
Pt1-S1′
S1-Pt1′
S3-C13
2.3141(16)
2.3271(16)
2.3271(15)
1.782(5)
Pt1-S2
Pt1-S3
S1-C1
S2-C8
2.306(4)
2.325(4)
1.776(14)
1.765(15)
Pt1-S1′
Pt1-S1
S1-Pt1′
S3-C15
2.323(3)
2.326(3)
2.323(3)
1.759(14)
1.731(6)
S3-Pt1-S2
S2-Pt1-S1
S2-Pt1-S1′
C1-S1-Pt1
Pt1-S1-Pt1′
C13-S3-Pt1
84.07(6)
169.37(5)
95.41(6)
110.3(2)
97.09(6)
108.77(17)
S3-Pt1-S1
S3-Pt1-S1′
S1-Pt1-S1′
C1-S1-Pt1′
C7-S2-Pt1
98.77(6)
173.59(5)
82.91(6)
107.3(2)
111.6(2)
S2-Pt1-S1′
S1′-Pt1-S3
S1′-Pt1-S1
C1-S1-Pt1′
Pt1′-S1-Pt1
C15-S3-Pt1
169.37(15)
91.74(13)
82.74(13)
107.6(5)
97.26(13)
103.8(5)
S2-Pt1-S3
S2-Pt1-S1
S3-Pt1-S1
C1-S1-Pt1
C8-S2-Pt1
88.06(14)
98.75(14)
170.68(14)
111.4(5)
110.5(5)
a Primed atoms are generated by inversion through a center of
symmetry occupied by Pt1. For the Pt1 coordinates given in the
Supporting Information for 2b, the transformation to generate the
primed atoms is -x + 1, -y + 2, -z + 2.
a Primed atoms are generated by inversion through a center of
symmetry occupied by Pt1. For the Pt1 coordinates given in the
Supporting Information for 3b, the transformation to generate the
primed atoms is -x + 1, -y + 2, -z.
hexagon and the four C-F bond lengths were restrained to 1.34(2) Å.
Finally, in the case of 3b, all terminal CF3 groups are disordered, a
situation that is common for this fragment. F73/F74 and F143/F144
were refined with occupation factors of 0.5, while F211/F212/F213
are disordered, as are F214/F215/F216, the occupation factors being
0.67 and 0.33, respectively.
Complex anions 1-3 were characterized by single-crystal
X-ray diffraction of complexes containing the bulky cation
Bu4N+. All complexes show the same space group, but they
are not isomorphous (see Table 1). The asymmetric unit of the
three structures contains one cation and one metal atom bonded
to three thiolate ligands. This latter fragment lies close to an
inversion center of space group P21/n, which yields a cen-
trosymmetric dianion including a planar [Pt2(µ-S)2] skeleton (see
Figures 1-3). Sulfur atoms of terminal thiolate ligands are
located in the plane defined by the metallic core.
Selected geometric parameters for 1b, 2b, and 3b are listed in Tables
2, 3, and 4, respectively.
Results and Discussion
Complex anions 1-3 were prepared according to reactions
1 and 2:
The most interesting structural feature is the configuration
of the thiolate rings. The bridging ligand displays an anti
configuration in all cases. However, the terminal ligands adopt
a different configuration with respect to the bridging thiolates.
For 1b and 3b, ligand S2 is almost parallel to the bridging ligand
while ligand S3 is almost perpendicular to the bridge (see
Figures 1 and 3). In complex 1b, the angle between the mean
planes of ligands S1 and S2 is 12.1° whereas the angle between
planes S1 and S3 is 95° (mean planes are calculated through
the six C atoms of the aromatic rings). In the case of anion 3b,
these angles are 2.5° and 92.5°, respectively. Unexpectedly, the
configuration is different for 2b, where both terminal ligands
S2 and S3 are almost parallel to the bridging ligand (see Figure
2): the dihedral angles between the aromatic rings are 15.7°
and 22.7° for the S1/S2 and S1/S3 moieties, respectively. In all
cases the spatial arrangement of the thiolates does not allow
strong intramolecular interactions between the aromatic groups.
K2[Pt(SR)4] + [Pt(SR)2(COD)] f
K2[Pt2(µ-SR)2(SR)4] + COD (1)
R ) C6F5 1a, p-C6HF4 2a, p-C6F4(CF3) 3a;
COD ) 1,5-cyclooctadiene
K2[Pt2(µ-SR)2(SR)4] + 2(N(C4H9)4)Cl f
(N(C4H9)4)2[Pt2(µ-SR)2(SR)4] + 2KCl (2)
R ) C6F5 1b, p-C6HF4 2b, p-C6F4(CF3) 3b
Reaction 1 suggests the possibility of preparing mixed
complexes of the type [Pt2(µ-SR′)2(SR)4] (R′ * R). However,
the only products isolated after reacting [Pt(SR)2(COD)] and
K2[Pt(SR′)4] were the corresponding homoleptic compounds K2-
[Pt2(µ-SR)2(SR)4] and K2[Pt2(µ-SR′)2(SR′)4] [R and R′ ) C6F5,
p-C6HF4, or p-C6F4(CF3)], as shown in reaction 3. This fact
indicates that ligand rearrangement is a highly favored process
during this reaction.
In a search for intramolecular interactions that could restrict
rotation of the thiophenolate ring (vide infra), we examined the
nearest 12 Pt-F distances for the three anions. The shortest
Pt‚‚‚F distance found is 3.249 Å whereas the sum of van der
Waals radii for Pt and F is ca. 3.22-3.3 Å.23,24 These
intramolecular interactions could, therefore, restrict the orien-
tational freedom of the ligands. This situation may explain the
fact that different configurations are observed for 1b and 2b,
even though the ligands are very similar. The Pt‚‚‚F interactions
probably give rise to a relatively high energy barrier between
one configuration and the other in the lattice, thus precluding
the possibility of switching in the solid state. In the case of
anion 1b, diffraction data for three crystals obtained from three
different attempts at crystallization resulted in the same con-
figuration for the anion. These findings corroborate the idea
that intramolecular interactions are important in stabilizing the
observed configurations.
3K2[Pt(SR′)4] + 3[Pt(SR)2(COD)] f
K2[Pt2(µ-SR)2(SR)4] + 2K2[Pt2(µ-SR′)2(SR′)4] + 3COD
(3)
R and R′ ) C6F5, p-C6HF4, or p-C6F4(CF3);
COD ) 1,5-cyclooctadiene
Complexes 1-3 are yellow-orange crystalline solids that are
relatively stable in air. Complexes 1a, 2a, and 3a are soluble
in acetone whereas compounds 1b, 2b, and 3b are soluble in
acetone, dichloromethane, chloroform, and ethanol.
Crystal and Molecular Structures of 1b, 2b, and 3b. The
molecular structures of (Bu4N)2[Pt2(m-SC6F5)2(SC6F5)4] 1b,
(Bu4N)2[Pt2(m-p-SC6HF4)2(p-SC6HF4)4] 2b, and (Bu4N)2[Pt2-
(m-p-SC6F4(CF3))2(p-SC6F4(CF3))4] 3b are shown in Figures
1-3, respectively. Selected bond distances and angles are
collected in Tables 2-4, respectively.
(23) Altomare, A.; Cascarno, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. SIR97 Users Manual; University of
Bari: Bari, Italy, 1997.
(24) Bondi, A. J. Phys. Chem. 1964, 68, 441-444.

5578 Inorganic Chemistry, Vol. 40, No. 22, 2001
Rivera et al.
Figure 1. Structure of anion 1b showing 20% probability displacement ellipsoids.
Figure 2. Structure of anion 2b showing 20% probability displacement
Figure 3. Structure of anion 3b showing 20% probability displacement
ellipsoids. Note the thermal agitation for ligand S3.
ellipsoids. Note the thermal agitation for ligand S3.
Variable-Temperature NMR Studies. Room temperature
1H and 19F NMR data for compounds 1b, 2b, and 3b have been
deposited as Supporting Information.
complexes are therefore expected to include bridge and terminal
absorptionsswith a 1(bridge):2(terminal) ratiosfor each ortho,
meta, and para substituent.
195Pt NMR spectra for compounds 1b, 2b, and 3b, (-3202.6,
-3178.8, and -3178.3 ppm, respectively), acquired at room
temperature, each show a relatively broad (ca. 2100 Hz at half-
height) signal only, suggesting the presence of several species.
The expected magnetic systems for the fluorinated rings C6F5,
p-C6HF4, and p-C6F4(CF3) can be described as AA′BB′C,
AA′BB′X, and AA′BB′X3, respectively. All three systems share
ortho (A ) F) and meta (B ) F) fluorine nuclei but bear
different para substituents, namely, C ) F, X ) H, and X3 )
CF3. In each anion 1-3 there are two bridging and four terminal
ligands and the room temperature 19F NMR spectra of these
The experimental data at room temperature show that bridging
ligands give rise to relatively broad absorptions since they are
particularly sensitive to variations in the configuration. The lack
of definition for these signals precludes an accurate measurement
of coupling constants. The terminal ligands, however, give rise
to more defined absorptions, and the corresponding coupling
constants were measured.
The complexes [Pt2(µ-SC6F5)2(SC6F5)4] 1 and [Pt2(µ-p-SC6F4-
(CF3))2(p-SC6F4(CF3))4] 3 belong to the still uncommon family
of perfluorinated metal complexes and, as such, the study of
their fluxional behavior is confined to the study of 19F nuclei.

Dynamic Study of Homoleptic Bimetallic Pt(II) Complexes
Inorganic Chemistry, Vol. 40, No. 22, 2001 5579
assigned to ortho, para, and meta fluorine atoms of terminal
thiolates and a second set with three relatively broad absorptions
(δ ) -130.7, -167.6, and -161.6 ppm; ratio 2:1:2; total
intensity ) 1) corresponding to ortho, para, and meta fluorine
nuclei of the bridging thiolate groups.
An increase in the temperature of the 19F NMR experiments
to 50 °C (see Figure 5) gave rise to sharper signals for both the
terminal and bridging thiolate ligands. However, complete
definition, particularly regarding the bridging signals, was not
reached, and therefore the condition of a fast exchange process
is not attained.
As the temperature of the experiments was decreased, the
bridge fluorine signals became broader, and at ca. -30 °C the
absorption due to the terminal o-fluorine nuclei becomes two
separate signals, as shown in Figure 5. This phenomenon
indicates the presence of syn and anti isomers (relative intensity
1:10), which are in equilibrium through a sulfur inversion
Figure 4. Room temperature 19F NMR spectrum of (Bu4N)2[Pt2(µ-
SC6F5)2(SC6F5)4] 1b.
process for which a value of ∆Gq ) 56.82 ( 1 kJ mol-1
298
was estimated. Errors in ∆Gq were calculated from the standard
deviation term |σ(∆Hq) - Tσ(∆Sq)| as described by Binsch and
Kessler.30
On the other hand, the NMR spectrum of a fluxional molecule
depends on the rate of exchange, the difference in resonance
frequency of the exchanging species, and the frequency of the
observed nucleus within the molecule. For example, in the case
reported here, the observed 19F nuclei (ortho and meta) are
separated by ca. 10.45 kHz and the resolution of each signal
varies considerably. For this reason, the following discussion
is focused mainly on the o-fluorine region of the 19F NMR
spectrum, which shows better definition at all temperatures.
Simulated spectra were obtained using the program gNMR-
3.25 The values of ∆Gq298 for the fluxional processes found were
calculated according to the Eyring equation using curve
fitting.26-29
With the exception of the p-fluorine nuclei, decreasing the
temperature of the NMR experiments caused the broad signals
of the bridging thiolate ligands to separate into two pairs of
absorptions. At the lowest experimental temperature (-90 °C)
the 19F NMR spectra of both syn and anti isomers show 1:1
doublets for the o-fluorine nuclei (syn, δ ) -121.6, -134.6
ppm, and anti, δ ) -125.6, -136.4 ppm), indicating that
restricted rotation about the S-C6F5 bond makes the o-fluorine
atoms nonequivalent. At -90 °C the spectrum consists of two
overlapping subspectra corresponding to the syn and anti
isomers, as shown in Figure 6.
It is worth mentioning at this point that, as noted previously,11
signals assigned to p-fluorine nuclei on rotating rings do not
show significant changes in shift nor in signal width upon
changing the temperature. Hindered ring rotation around the
S-C bond does, however, affect the ortho and meta fluorine
(Bu4N)2[Pt2(µ-SC6F5)2(SC6F5)4] 1b. As shown in Figure 4,
the room temperature 19F NMR spectrum of the compound
(Bu4N)2[Pt2(µ-SC6F5)2(SC6F5)4] exhibits two sets of absorp-
tions: one set with three relatively sharp signals (δ ) -133.3,
-166.7, and -168.7 ppm; ratio 2:1:2; total intensity ) 2)
Figure 5. Variable-temperature 19F NMR spectra of (Bu4N)2[Pt2(µ-SC6F5)2(SC6F5)4] 1b.

5580 Inorganic Chemistry, Vol. 40, No. 22, 2001
Rivera et al.
-143.5 ppm; ratio 1:1, total intensity ) 2) assigned to the o-
and m-fluorine nuclei of terminal thiolate ligands and two broad
signals (δ ) -128.6 and -142.1 ppm; ratio 1:1, total intensity
) 1) corresponding to o- and m-fluorine nuclei of the bridging
thiolate groups.
As in the cases discussed above, increasing the temperature
up to 50 °C gave rise to sharper signals for both the terminal
and bridging thiolates, but only the terminal absorptions show
an incipient fine structure.
As found for compound 1b, decreasing the temperature down
to -30 °C causes the absorption due to the terminal o-fluorine
nuclei to split into two signals. Once again this indicates the
presence of syn and anti (relative intensity 1:4) isomers that
are in equilibrium through a sulfur inversion process, for which
∆Gq ) 54.72 ( 0.4 kJ mol-1. At lower temperatures the
253
spectra consist of the two overlapping (syn and anti) subspectra
described above.
At the lowest experimental temperature (-90 °C), the 19F
NMR spectra of both syn and anti isomers show 1:1 doublets
for the o-fluorine nuclei (syn, δ ) -121.06, -132.66 ppm, and
anti, δ ) -124.8, -133.97 ppm). These data also indicate that
rotation about the S-C6HF4 bond is restricted, a fact that renders
the o-fluorine atoms nonequivalent.
The calculated activation energies for the restricted carbon-
sulfur bond rotation are syn, ∆Gq ) 55.53 ( 0.5 kJ mol-1
,
298
and anti, ∆Gq ) 41.41 ( 0.5 kJ mol-1
.
298
(Bu4N)2[Pt2(µ-p-SC6F4(CF3))2(p-SC6F4(CF3))4] 3b. The room
temperature 19F NMR spectra of compound 3b show two triplets
(δ ) -55.47 and -55.04 ppm; relative intensities 1:2), which
have been assigned to the fluorine atoms of the p-CF3 groups
of the bridging and terminal thiolate ligands, respectively.
Furthermore, two sharp signals (δ ) -130.83 and -145.91
ppm, ratio 1:1, total intensity 2) have been assigned to ortho
and meta fluorine nuclei of the terminal thiolates and two broad
signals (δ ) -127.28 and -143.67 ppm, ratio 1:1, total intensity
1) assigned to the ortho and meta fluorine nuclei of the bridging
thiolate groups.
Figure 6. Subspectra in the variable-temperature 19F NMR of (Bu4N)2-
[Pt2(µ-SC6F5)2(SC6F5)4] 1b, showing syn and anti isomers with frozen
rings at the bridging thiolate ligands.
nuclei, which eventually give rise to two different ortho and
two distinct meta fluorine signals upon lowering the temperature.
As expected, the energies involved in the carbon-sulfur bond
rotation are different for each of the syn and anti isomers. The
A decrease in the acquisition temperature to -30 °C causes
the absorption due to the terminal p-CF3 groups to split into
two signals, which again indicates the presence of syn and anti
isomers (relative intensity 1:5). The calculated energy for this
corresponding calculated activation energies are syn, ∆Gq
)
298
59.87 ( 0.5 kJ mol-1, and anti, ∆Gq298 ) 41.85 ( 0.4 kJ mol-1
.
Molecular modeling strongly suggests that the steric interac-
tions involved in an anti configuration are much less significant
than in the syn configuration. This situation implies that the
former configuration should be more abundant. On the basis of
this assumption, the relative population of isomers, as obtained
from the experimental spectrum, should be anti 10:syn 1.
(Bu4N)2[Pt2(µ-p-SC6HF4)2(p-SC6HF4)4] 2b. The room tem-
perature 19F NMR spectrum of the compound (Bu4N)2[Pt2(µ-
p-SC6HF4)2(p-SC6HF4)4] exhibits two signals (δ ) -131.7 and
sulfur inversion process is ∆Gq ) 58.32 ( 0.7 kJ mol-1
.
298
At the lowest experimental temperature (-90 °C) the 19F
NMR spectra of both syn and anti isomers show 1:1 doublets
for the o-fluorine nuclei (syn, δ ) -119.4, -132.5 ppm, and
anti, δ ) -123.96, -133.97 ppm), indicating that restricted
rotation of the S-C6F4CF3 bond renders the o-fluorine nuclei
nonequivalent. Calculated activation energies for these processes
are syn, ∆Gq ) 60.00 ( 0.6 kJ mol-1, and anti, ∆Gq
)
298
298
43.18 ( 0.4 kJ mol-1
.
(25) Budzelaar, P. H. M. gNMR-3.6; Cherwell Scientific Publishing
Limited: Oxford, UK, 1995.
(26) Sandstro¨m, J. Dynamic NMR Spectroscopy; Academic Press: New
York, 1982.
Acknowledgment. We are grateful to DAGAPA-IN121698
and CONACYT-25108E for their support for this research.
(27) Friebolin, H. Basic One and Two-Dimensional NMR Spectroscopy;
VCH Publishers: New York, 1995.
(28) Abel, E. W.; Bhargava, S. K.; Orrell, K. G. Prog. Inorg. Chem. 1984,
32, 1-118.
(29) Orrell, K. G. Coord. Chem. ReV. 1989, 96, 1-48.
(30) Binsch, G.; Kessler, H. Angew. Chem., Int. Ed. Engl. 1980, 19, 411-
428.
Supporting Information Available: X-ray crystallographic files
1
in CIF format for complexes 1b, 2b, and 3b and a table with H and
19F NMR parameters for complexes 1b, 2b, and 3b. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC010437N