Monothioether Complexes of Osmium: The trans-[OsBr4(SR2)2] Family and mer-[OsBr3(SR2)3] Precursors

Full text of DOI:10.1021/ic980142i

5678
Inorg. Chem. 1998, 37, 5678-5680
Monothioether Complexes of Osmium: The
trans-[OsBr4(SR2)2] Family and
mer-[OsBr3(SR2)3] Precursors
Kausikisankar Pramanik, Prasanta Ghosh, and
Animesh Chakravorty*
Department of Inorganic Chemistry, Indian Association for
the Cultivation of Science, Calcutta 700 032, India
ReceiVed February 6, 1998
Introduction
Simple monothioethers (R2S, R ) alkyl) have long been
known to have good affinity for platinum metal ions. Two of
the well-documented types of complexes are [MIIIX3(SR2)3] (M
) Ru, Rh, Ir; X- ) halide) and [MIVX4(SR2)2] (M ) Ir, Pt).1-5
In the case of osmium, just one compound of the former type
(but none of the latter type) is known.6 The difficulty lies in
the lack of availability of convenient synthetic methods. For
example, the reaction of R2S with [OsX6]2- salts failed to afford
tractable thioether complexes.7
A synthesis of mer-[OsBr3(SR2)3] via deoxygenation of R2-
SO by [OsBr6]2- was recently developed in this laboratory.8
The trivalent complexes have now provided facile access to the
hitherto unknown [OsBr4(SR2)2] family. The X-ray structures
of two of these are reported along with that of a mer-[OsBr3-
(SR2)3] precursor. This has provided an opportunity for
assessing the valence dependence of Os-SR2 back-bonding.
Metal reduction potentials are strongly dependent on the Br-:
R2S ratio.
Figure 1. ORTEP plot and atom-labeling scheme for trans-
[OsBr4{S(CH2Ph)2}2] (1b). All non-hydrogen atoms are represented
by their 30% probability ellipsoids.
Chart 1
Results and Discussion
A. Synthesis and Characterization. The dark colored
[OsIVBr4(SR2)2] complexes 1a-c having trans geometry (vide
infra; Chart 1) are furnished in good yield by the reaction of
mer-[OsIIIBr3(SR2)3],8 2a-c, with excess bromine in benzene
(1) (a) Jaswal, J. S.; Retting, S. J.; James, B. R. Can. J. Chem. 1990, 68,
1808. (b) Yapp, D. T. T.; Jaswal, J. S.; Retting, S. J.; James, B. R.;
Skov, K. A. Inorg. Chim. Acta 1990, 177, 199. (c) Sarma, U. C.;
Sarma, K. P.; Poddar, P. K. Polyhedron 1988, 7, 1737. (d) Fergusson,
J. E.; Karran, J. D.; Seevaratnam, S. J. Chem. Soc. 1965, 2627.
(2) (a) Allen, E. A.; Wilkinson, W. J. Chem. Soc., Dalton Trans. 1972,
613. (b) Anderson, S. J. Barnes, J. R.; Goggin, P. L.; Goodfellow, R.
J. J. Chem. Res. (M) 1978, 3601. (c) Kukushkin, Yu. N.; Rubtsova,
N. D.; Ivannikova, N. V. Zh. Neorg. Khim. 1970, 15, 1328. (d)
Fritzmann, E. K.; Krinitskii, V. V. J. Appl. Chem. (U.S.S.R.) 1938,
11, 1610.
(3) (a) Kauffman, G. B.; Tsai, J. H.-S.; Gubelmann, M. H.; Williams, A.
F. J. Chem. Soc., Dalton Trans. 1980, 1791. (b) Kauffman, G. B.;
Tsai, J. H.-S.; Fay, R. C.; Jørgensen, C. K. Inorg. Chem. 1963, 2,
1233. (c) Raˆy, P. C.; Adhikari, N.; Ghosh, R. J. Indian Chem. Soc.
1933, 10, 275.
(4) (a) Cipriano, R. A.; Levason, W.; Pletcher, D.; Powell, N. A.; Webster,
M. J. Chem. Soc., Dalton Trans. 1987, 1901. (b) Gulliver, D. J.;
Levason, W.; Smith, K. G.; Selwood, M. J.; Murray, S. G. J. Chem.
Soc., Dalton Trans. 1980, 1872.
(5) (a) Kukushkin, V. Yu. Coord. Chem. ReV. 1995, 139, 375 and
references therein. (b) Goggin, P. L.; Goodfellow, R. J.; Haddock, S.
R.; Knight, J. R.; Reed, F. J. S.; Taylor, B. F. J. Chem. Soc., Dalton
Trans. 1974, 523. (c) Kauffman, G. B.; Tsai, J. H-S.; Takahashi, L.
T. Inorg. Synth. 1966, 8, 245.
solution at room temperature. There is no indication that the
cis isomer of 1 is formed in this reaction. To our knowledge
1a-c represent the first examples of osmium(IV) complexes
of monodentate thioethers. A few osmium(IV) species incor-
porating bi/polythioethers chelation are known but none of these
have been structurally characterized.4b,7
Spectral and magnetic characterization data of the complexes
are listed in the Experimental Section. The type 1 species
display intense absorption near 500 nm presumably due to Br-/
SfOsIV charge transfer.1d,6 Significantly, in the less oxidized
type 2 species, the band system lies at higher energy, ∼450
nm. The magnetic moments (∼1.7 µB) of type 1 complexes
are low evidently due to high spin-orbit coupling.9
B. Structure. The X-ray structures of 1b and 1c have been
determined revealing centrosymmetric trans geometry. Molec-
ular views are shown in Figures 1 and 2, and selected bond
parameters are listed in Table 1. The S-Os-S axis is tilted
with respect to the normal to the OsBr4 plane, the tilt angle
being 8.4 and 5.7°, respectively for 1b and 1c.
(6) Aires, B. E.; Fergusson, J. E.; Howarth, D. T.; Miller, J. M. J. Chem.
Soc. A 1971, 1144.
(7) Ali, R.; Higgins, S. J.; Levason, W. Inorg. Chim. Acta 1984, 84, 65.
(8) Ghosh, P.; Pramanik, K.; Chakravorty, A. J. Chem. Soc., Chem.
Commun. 1995, 477.
(9) (a) Figgis, B. N.; Lewis, J. Prog. Inorg. Chem. 1964, 6, 165. (b) Chatt,
J.; Leigh, G. J.; Mingos, D. M. P.; Paske, R. J. J. Chem. Soc. A 1968,
2636.
10.1021/ic980142i CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/24/1998

Notes
Inorganic Chemistry, Vol. 37, No. 21, 1998 5679
Table 3. Electrochemical Dataa
E1/2,V (∆Ep,b mV)
E1/2,V (∆Ep,b mV)
OsIV/OsIII
OsIV/OsIII
compound
compound
1a
1b
1c
0.45 (120)
0.47 (110)
0.42 (110)
2ac
2bc
2cc
1.00 (110)
1.07 (130)
0.96 (140)
a In 5:1 dichloromethane-acetonitrile mixture at 298 K. b ∆Ep )
peak-to-peak separation. c OsIII/OsII E1/2 [V] (∆Ep [mV]) values: 2a,
-0.46 (110); 2b, -0.33 (130); 2c, -0.50 (140).
Figure 2. ORTEP plot and atom-labeling scheme for trans-[OsBr4-
{S(CH2)4}2] (1c). All non-hydrogen atoms are represented by their 30%
probability ellipsoids.
bonding (OsIII . OsIV). The back-bonding ability of OsIII has
been documented.10
C. Metal Redox: Valence Stability vis-a`-vis Br-:R2S
Ratio. Both 1 and 2 are electroactive and display quasirevers-
ible cyclic voltammograms in solution. Reduction potential data
are listed in Table 3. The osmium(IV)-osmium(III) couple
shifts dramatically from ∼0.4 to ∼1.0V vs SCE as the Br-:
R2S ratio changes from 4:2 (1) to 3:3 (2). The net result is
that under ambient conditions the Br4S2 and Br3S3 spheres
respectively stabilize the tetravalent and the trivalent states of
the metal. For type 2 complexes the osmium(III)-osmium(II)
couple is also observed (∼-0.4 V). The electrogenerated
[OsIIIBr4(SR2)2]- and [OsIVBr3(SR2)3]+ species are unstable and
could not be isolated.
Concluding Remarks
The main findings of the present work are as follows. The
first family of [OsIVX4(SR2)2] complexes incorporating mono-
thioethers and having centrosymmetric trans geometry has been
synthesized in good yield in the case of X ) Br via oxidative
bromination of mer-[OsIIIBr3(SR2)3]. In this transformation the
osmium(IV)-osmium(III) reduction potential is lowered by a
remarkable ∼0.6 V. The bond length trend (OsIV-Br < OsIII-
Br; OsIV-S > OsIII-S) among trans-[OsBr4(SR2)2] and mer-
[OsBr3(SR2)3] is indicative of relatively poor OsIV-SR2 back-
bonding in the former complexes.
Figure 3. Perspective view and atom-labeling scheme for mer-[OsBr3-
{S(CH2)4}3] (2c).
Table 1. Selected Bond Lengths (Å) and Angles (°) for 1b and 1c
1b
1c
Os-Br1
Os-Br2
Os-S1
2.472(2)
2.441(2)
2.420(4)
2.468(3)
2.455(3)
2.401(7)
Experimental Section
Br1-Os-Br2
Br1-Os-S1
Br2-Os-S1
90.3(1)
96.6(1)
95.1(1)
89.6(1)
94.8(2)
93.0(2)
Materials. The compound (NH4)2[OsBr6] was prepared from [OsO4]
(Arora-Mathey, India) by a reported procedure.11 Electrochemical grade
dichloromethane, acetonitrile, and tetraethylammonium perchlorate
(TEAP) were obtained as before.12 All other chemicals and solvents
were of analytical grade. Dimethyl sulfoxide (Merck, India), dibenzyl
sulfoxide (Fluka, Switzerland) and tetramethylene sulfoxide (Aldrich,
USA) were used.
Table 2. Selected Bond Lengths (Å) and Angles (°) for 2c
Os-Br1
Os-Br3
Os-S2
2.494(2)
2.518(3)
2.380(5)
Os-Br2
Os-S1
Os-S3
2.494(2)
2.383(5)
2.382(6)
Physical Measurements. A Hitachi 330 spectrophotometer was
used to record UV/visible/near-IR spectra. The EPR spectra were
obtained at X-band frequencies with a Varian E-109C spectrometer
fitted with a quartz Dewar. The calibrant was DPPH (g ) 2.0037).
Room-temperature magnetic susceptibilities were measured with a
model 155 PAR vibrating-sample magnetometer fitted with a Walker
Scientific L75FBAL magnet. A Perkin-Elmer 240C elemental analyzer
was used to collect microanalytical data (C, H). All electrochemical
measurements were performed under nitrogen atmosphere using a PAR
370-4 electrochemistry system as before:12b working electrode, platinum
disk; reference electrode, saturated calomel electrode (SCE); auxiliary
electrode, platinum wire; supporting electrolyte, NEt4ClO4 (0.1 M); scan
rate, 50 mV s-1; solute concentration 10-3 M. All potential reported
in this work are uncorrected for junction contribution.
Br1-Os-Br2
Br2-Os-Br3
Br2-Os-S1
Br1-Os-S2
Br3-Os-S2
Br1-Os-S3
Br3-Os-S3
S2-Os-S3
176.7(1)
91.4(1)
90.7(1)
91.8(1)
91.0(1)
88.4(1)
178.9(1)
89.1(2)
Br1-Os-Br3
Br1-Os-S1
Br3-Os-S1
Br2-Os-S2
S1-Os-S2
Br2-Os-S3
S1-Os-S3
90.5(1)
86.6(1)
90.0(1)
90.9(1)
178.1(2)
89.7(1)
89.9(2)
The X-ray structure of 2b was reported earlier (Os-Br,
2.495(2) and 2.497(2) Å, and Os-S, 2.398(3) and 2.387(5) Å).8
That of 2c has now been determined (Figure 3 and Table 2).
The data permits comparisons within the 1b-2b and 1c-2c
pairs.
In each pair the Os-Br length follows the order 1 < 2. This
is consistent with the electrostatic effect of the greater charge
on the tetravalent atom in 1. The implication is that the Os-
Br bond is primarily σ in character. The reversed order (1 >
2) of Os-S length is attributed to 5dπ(Os) f 3dπ(S) back-
(10) (a) Taube, H. Pure Appl. Chem. 1979, 51, 901. (b) Sekine, M.; Harman,
W. D.; Taube, H. Inorg. Chem. 1988, 27, 3604.
(11) Dwyer, F. P.; Hogarth, J. W. Inorg. Synth. 1957, 5, 204.
(12) (a) Lahiri, G. K.; Bhattacharya, S.; Ghosh, B. K.; Chakravorty, A.
Inorg. Chem. 1987, 26, 4324. (b) Chandra, S. K.; Basu, P.; Ray, D.;
Pal, S.; Chakravorty, A. Inorg. Chem. 1990, 29, 2423.

5680 Inorganic Chemistry, Vol. 37, No. 21, 1998
Notes
Preparation of Complexes. trans-[OsBr4(SMe2)2] (1a). To a
solution of mer-[OsBr3(SMe2)3] (60 mg, 0.095 mmol) in 40 mL of
benzene bromine (∼0.05 mL, 1.0 mmol) was added and magnetically
stirred. After 24 h another ∼0.05 mL of bromine was added and stirring
was continued for another 24 h. The color changed from orange to
deep red. After removing the volatiles under reduced pressure the
mixture was kept in vacuo overnight. Upon chromatographic purifica-
tion of the rasidue on neutral silica gel with 1:2 hexane/benzene mixture
as eluent, trans-[OsBr4(SMe2)2] was obtained. Yield 70%. Anal. Calcd
for C24H12S2Br4Os: C, 7.58; H, 1.91. Found: C, 7.5; H, 2.0. µeff
(solid, 298 K): 1.73 µB. Spectral data: UV/visible/near-IR in CH2Cl2
(λmax, nm (ꢀ, M-1 cm-1)), 503 (7600), 538 (7250), 676 (390), 835 (43),
1820 (82).
trans-[OsBr4{S(CH2Ph)2}2] (1b). This was prepared by the above
procedure using mer-[OsBr3{S(CH2Ph)2}3] as precursor complex. Yield
70%. Anal. Calcd for C28H28S2Br4Os: C, 35.83; H, 3.01. Found: C,
36.1; H, 2.9. µeff (solid, 298 K): 1.74 µB. Spectral data: UV/visible/
near-IR in CH2Cl2 (λmax, nm (ꢀ, M-1 cm-1)), 491 (6800), 570 (6100),
675sh (500), 840 (44), 1875 (105).
trans-[OsBr4{S(CH2)4}2] (1c). This was prepared similarly using
mer-[OsBr3{S(CH2)4}3] as starting material. Yield 65%. Anal. Calcd
for C8H16S2Br4Os: C, 14.00; H, 2.35. Found: C, 13.9; H, 2.4. µeff
(solid, 298 K): 1.71 µB. Spectral data: UV/visible/near-IR in CH2Cl2
(λmax, nm (ꢀ, M-1 cm-1)), 488 (8850), 550 (6350), 668 (440), 835 (38),
1810 (100).
mer-[OsBr3(SMe2)3] (2a). This was prepared from (NH4)2[OsBr6]
and Me2SO following the procedure described for 2b.8 Yield: 30%.
Anal. Calcd for C6H18S3Br3Os: C, 11.69; H, 2.94. Found: C, 11.8;
H, 3.1. µeff (solid, 298 K): 1.89 µB. Spectral data: UV/visible/near-
IR in CH2Cl2 (λmax, nm (ꢀ, M-1 cm-1)), 415 (5080), 460sh (4450), 715
(60), 900sh (28), 1540 (18). EPR in 1:1 CH2Cl2/toluene glass at 77 K
(g1, g2, g3), 2.79, 2.20, 1.72.
mer-[OsBr3{S(CH2)4}3] (2c). This was prepared from (NH4)2[OsBr6]
and (CH2)4SO. Yield: 25%. Anal. Calcd for C12H24S3Br3Os: C,
20.75; H, 3.48. Found: C, 20.6; H, 3.6. µeff (solid, 298 K): 1.91 µB.
Spectral data: UV/visible/near-IR in CH2Cl2 (λmax, nm (ꢀ, M-1 cm-1)),
415 (5000), 460sh (2850), 717 (70), 930sh (32), 1550 (24). EPR in 1:1
CH2Cl2/toluene glass at 77 K (g1, g2, g3), 2.74, 2.23, 1.71.
X-ray Structure Determination. Single crystals of 1b (0.11 × 0.20
× 0.21 mm3), 1c (0.08 × 0.15 × 0.24 mm3), and 2c (0.32 × 0.25 ×
0.18 mm3) were grown by slow diffusion of hexane into the respective
dichloromethane solutions. The cell parameters were determined by
least-squares fits of 30 machine-centered reflections (2θ, 14-28°). Data
were collected at 295 K by ω-scan technique for 1b (3 e 2θ e 50°), 1c
(3 e 2θ e 45°), and 2c (3 e 2θ e 45°), on a Nicolet R3m/V
diffractometer with graphite-monochromated Mo KR radiation (λ )
0.710 73 Å). Two check reflections measured after every 98 reflections
in each case showed no significant intensity reduction. Data were
corrected for Lorentz-polarization effects. An empirical absorption
correction based on ψ scan was applied in each case.13 The metal
atoms were located from Patterson maps and the rest of the non-
Table 4. Crystallographic Data for 1b, 1c, and 2c
1b 1c
2c
chem formula C28H28S2Br4Os C8H16S2Br4Os C12H24S3Br3Os
fw
938.5
686.2
694.4
space group
a, Å
P1h
P21/n
P21/c
6.792(3)
9.931(4)
11.792(5)
97.70(3)
104.19(4)
98.88(3)
755.0(6)
1
8.540(4)
7.423(4)
12.689(6)
7.278(2)
19.228(4)
13.791(4)
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
108.94(4)
100.81(2)
760.9(6)
2
22
1896.0(11)
4
T, °C
λ, Å
22
22
0.710 73
2.085
0.710 73
3.002
191.74
6.46
0.710 73
2.439
134.02
4.45
F
calcd, g cm-3
µ, cm-1
R,a%
97.66
5.47
Rw,b%
6.00
7.49
5.32
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
;
2
2
w-1 ) σ2(|Fo|) + g|Fc| ; g ) 0.0001, 0.001, and 0.0005 for 1b, 1c,
and 2c, respectively.
hydrogen atoms emerged from successive Fourier synthesis using I >
3σ(I) as observed. The structures were refined by full-matrix least-
squares procedures. All non-hydrogen atoms of 1b and 1c were refined
anisotropically. In the case of 2c all non-hydrogen atoms except C1,
C2, C6, and C7 were refined anisotropically. The S(CH2)4 ring
incorporating S1 displayed conformational disorder at C2. Hydrogen
atoms were included in calculated positions with fixed U ) 0.08 Å2 in
the final cycle of refinement. The highest difference Fourier peaks
were 1.53, 1.64, and 1.21 e Å-3 (in the vicinity of Os) for 1b, 1c, and
2c respectively. Significant crystal data are listed in Table 4. All
calculations were done on a MICROVAX II computer using the
SHELXTL-PLUS program package,14 and crystal structure plots were
drawn using ORTEP.15
Acknowledgment. Financial support was received from
Indian National Science Academy, Department of Science and
Technology, and Council of Scientific and Industrial Research,
New Delhi, are acknowledged. Affiliation with the Jawaharlal
Nehru Centre for Advanced Scientific Research, Bangalore,
India, is acknowledged.
Supporting Information Available: Tables of complete crystal-
lographic data, atomic coordinates, bond distances and angles, aniso-
tropic thermal parameters, and hydrogen atom positional parameters
for 1b, 1c, and 2c (16 pages). Ordering information is given on any
current masthead page.
IC980142I
(14) Sheldrick, G. M. SHELXTL-PLUS: Structure Determination Software
Programs; Siemens Analytical X-ray Instruments Inc.: Madison, WI,
1990.
(13) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr. 1968,
A24, 351.
(15) Johnson, C. K. ORTEP; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.