Stabilization of Co(II) in an S2O2 Environment
Inorganic Chemistry, Vol. 39, No. 21, 2000 4823
(NEt4)Na[Zn(SC6H4COO)2]‚H2O (2). In an attempt to prepare the
(NEt4)2[Zn(SC6H4COO)2] complex, a solution of NEt4Cl in ethanol was
added to the filtrate of the previous synthesis. The amount of NEt4Cl
added was calculated on the basis of the zinc remaining in the filtrate
and assuming that a 2:1 NEt4+:Zn(II) molar ratio was needed. An
abundant white solid appeared almost immediately. The solvent was
partially removed by vacuum and the solid filtered, washed with ether,
and dried. The yield, based on the amount of zinc remaining in the
mother solution of the previous synthesis, was 0.09 g, 26.62%. Anal.
Calcd for C22H30NO5NaS2Zn: C, 48.30; H, 5.16; N, 2.41; S, 11.65.
Found: C, 48.85; H, 5.55; N, 2.59; S, 11.84. Ether diffusion into a
solution of this compound in acetonitrile/acetone gave suitable crystals
for X-ray diffraction.
soluble in most organic solvents, attempts to obtain crystals were
hindered by the ease of oxidation of Co(II) in solution.
The previous filtrate afforded dark green microcrystals, which were
recrystallized in diethyl ether under an open atmosphere. Analytical
and X-ray diffraction data showed that this solid corresponds to [Co-
(SC6H4COOMe)3] (7). Anal. Calcd for C24H21O6S3Co: C, 51.43; H,
3.75; S, 17.14. Found: C, 51.07; H, 3.67; S, 17.41.
(NEt4)2[Zn{Ph2C(S)COO}2] (8). To 5 mL of a 0.16 M solution
(0.8 mmol) of Ph2C(SH)COOH in diethyl ether was added 5 mL of a
0.32 M solution of NaMeO (1.6 mmol) in methanol. To this solution
was added dropwise 14 mL of a 0.03 M solution (0.4 mmol) of (Et4N)2-
[ZnCl4] in acetonitrile. After 30 min of stirring, the solvent was
removed, and the residue was extracted with the minimum amount of
acetonitrile. To the filtrate from the acetonitrile suspension was added
diethyl ether until separation of microcrystals, yield 0.16 g, 48%. Anal.
Calcd for C44H60N2O4S2Zn: C, 65.23; H, 7.41; N, 3.46; S, 7.90.
Found: C, 63.73; H, 7.50; N, 3.49; S, 7.83. Recrystallization of this
solid from acetonitrile by ether diffusion under a nitrogen atmosphere
afforded colorless crystals.
(NEt4)2Na[Co(SC6H4COO)3]‚2H2O (3). To a suspension of 0.20 g
(0.4 mmol) of (Et4N)2[CoCl4], 0.24 g (1.5 mmol) of HSC6H4COOH,
and 0.22 g (1.3 mmol) of NEt4Cl in 30 mL of ethanol at 0 °C was
added slowly with stirring 0.6 mL (3.1 mmol) of NaMeO in 20 mL of
ethanol. This addition was accompanied by a color change of the
mixture from yellow to blue and the appearance of a solid. Immediately
after filtration, washing, and drying, the solid was green, but it rapidly
turned to black, indicating the oxidation of cobalt. The remaining deep
blue filtrate was concentrated to dryness in a vacuum, the residue
redissolved in acetonitrile at room temperature, and the solution filtered.
While this solution was being stirred, it turned dark brown, despite
many attempts to maintain strict control of the anaerobic conditions.
After 2 days of stirring the solution was warmed to 50 °C and eventually
left open to the atmosphere. The resulting black solid and the crystals
obtained from the mother solution agree with the title compound.
However, solution of the crystal structure revealed not only that
oxidation had affected Co(II) totally but also that a fraction of thiolate
ligands have converted into sulfinate. The assumption that one-third
of the coordinated thiolate ligands, RS-, had oxidized into sulfinate,
RSO2-, afforded the best match between experimental and calculated
analytical data. Anal. Calcd for C37H56N2O10NaS3Co: C, 51.27; H, 6.46;
N, 3.47; S, 11.08. Found: C, 51.27; H, 6.46; N, 3.23; S, 11.08.
(NEt4)3Na3[{Co(SC6H4COO)3}2]‚6MeOH (4). In a manner analo-
gous to the preceding preparation, 0.4 mmol of (Et4N)2[CoCl4], 1.5
mmol of HSC6H4COOH, and 1.3 mmol of NEt4Cl in 30 mL of ethanol
were combined with 3.1 mmol of NaMeO in 10 mL of ethanol. The
same change of color of the solution was observed, and again the
isolated green solid turned to black. Immediately after filtration, the
deep blue filtrate was concentrated to dryness, the residue redissolved
in acetonitrile, and the solution filtered. To this solution were added 5
mL of MeOH and 5 mL of ether. After several days under nitrogen,
the solution had kept its blue color and the crystals formed were suitable
for X-ray diffraction. However, even though solution of the structure
showed that cobalt(II) had oxidized and the title compound was the
main product, analytical and X-ray data indicated the presence of some
Co(II) ions. Anal. Calcd for C72H108N3O18Na3S6Co2: C, 48.51; H, 6.30;
N, 2.68; S, 11.7. Found: C, 51.39; H, 6.42; N, 2.50; S, 11.42.
[Zn(SC6H4COOMe)2] (5). To a solution of 0.25 mL (1.8 mmol) of
HSC6H4COOMe in 8 mL of ethanol at room temperature was added
slowly with stirring 0.2 g (0.9 mmol) of Zn(CH3COO)2‚2H2O in 23
mL of warm ethanol, during which time the solution deepened its
initially yellow color. Stirring was continued until formation of an
abundant solid. The reaction mixture was concentrated to ca. 25 mL,
and the yellow solid was filtered, washed with warm ethanol, and dried;
yield 0.29 g, 80%. Despite the solubility of the solid in CH2Cl2 and
CHCl3, attempts to obtain single crystals were unsuccessful. Anal. Calcd
for C16H14O4S2Zn: C, 48.07; H, 3.50; S, 16.025. Found: C, 48.20; H,
3.60; S, 16.12.
Acetonitrile solutions of this complex developed a very light blue
color after several hours of their preparation. This solution turned yellow
if opened to the atmosphere. These findings were indicative of the
oxidation of a small fraction of the coordinated 2,2-diphenyl-2-
mercaptoacetic acid ligand to thiobenzophenone, which in turn oxidizes
to benzophenone in the presence of oxygen. This decomposition was
also accompanied by the appearance of an unidentified solid residue.
(NEt4)2[Co{Ph2C(S)COO}2] (9). This preparation followed closely
that of the zinc(II) analogue, and employed Ph2C(SH)COOH (0.8
mmol), sodium methoxide in methanol (1.6 mmol), and (Et4N)2[CoCl4]
(0.4 mmol). The deep blue filtrate was concentrated to dryness in a
vacuum, the residue redissolved in acetonitrile, and the solution filtered.
Ether was added until crystallization began; yield 0.19 g, 60%. Anal.
Calcd for C44H60N2O4S2Co: C, 65.75; H, 7.47; N, 3.48; S, 7.97.
Found: C, 62.75; H, 7.44; N, 3.39; S, 7.62. The compound was
recrystallized by ether diffusion into the acetonitrile solution under
nitrogen, giving deep blue crystals.
Unlike the Zn analogue, the light blue color indicating the oxidation
of the coordinated ligand in solutions of (NEt4)2[Co{Ph2C(S)COO}2]
to thiobenzophenone could not be visually observed because of the
intense blue color of the cobalt complex. However, a multiplet centered
at 8 ppm in the 1H NMR spectrum of the complex in CD3CN indicated
the presence of aromatic protons unaffected by the Co(II) paramagnetic
ion. As the presence of this cation only alters the chemical shift of the
protons of coordinated ligands, the signal at 8 ppm and the appearance
of a small solid residue were both indicative of a minor oxidative
decomposition of the ligand. In this case the 13C NMR spectrum of the
solution could not be recorded because of the presence of the Co(II)
ion.
Collection and Reduction of X-ray Data for Complexes 2-4 and
7-9. A summary of crystal data, data collection, and refinement
parameters for the six structural analyses is reported in Table 1. Crystals
were examined on a Bruker AXS SMART CCD area-detector diffrac-
tometer with graphite-monochromated Mo KR radiation (λ ) 0.71073
Å) and low-temperature equipment operating at 160 K. Cell constants
were obtained from a least-squares fit on the observed setting angles
of all significant intensity reflections. Intensities were integrated from
a series of 0.3° ω rotation frames covering at least a hemisphere of
reciprocal space, and were corrected for absorption by semiempirical
methods based on redundant and symmetry-equivalent reflections.9
The structures were solved by direct methods and were refined by
full-matrix least-squares on all unique F2 values, with anisotropic
displacement parameters for non-hydrogen atoms and with isotropic
H atoms constrained with a riding model.10 Disorder, particularly of
tetraethylammonium cations, was resolved in several of the structures
and was successfully refined with the aid of restraints on geometry
and displacement parameters. For the noncentrosymmetric structure of
[Co(SC6H4COOMe)n], n ) 2 (6), 3 (7). The following manipula-
tions were carried out under argon. To a solution of 0.22 mL (1.6 mmol)
of HSC6H4COOMe in 8 mL of ethanol at room temperature was added
slowly with stirring 0.20 g (0.8 mmol) of Co(CH3COO)2‚4H2O in 15
mL of ethanol, during which time the solution changed its color from
yellow to brown-green. The addition of the metal was concomitant with
the formation of an orange solid, which was eventually filtered and
dried. Analytical data for this solid agree well with [Co(SC6H4-
COOMe)2] (6). Anal. Calcd for C16H14O4S2Co: C, 48.85; H, 3.56; S,
16.28. Found: C, 48.35; H, 3.20; S, 16.25. Although the complex is
(9) Sheldrick, G. M. SADABS; Bruker AXS: Madison, WI, 1997.
(10) Sheldrick, G. M. SHELXTL, Version 5; Bruker AXS: Madison, WI,
1994.
Duran
