1200 J. Am. Chem. Soc., Vol. 123, No. 6, 2001
Zmolek et al.
dopability.1
9-27
Polysulfur nitride, for example, is superconduc-
Experimental Section
tive below 1 K and polythiophene compounds are semiconduc-
tors that become conductive after doping.28 Plasma-polymerized
General Methods. All chemicals were used as received unless
otherwise specified. THF was freshly distilled from sodium benzophe-
none ketyl and carbon disulfide was distilled under vacuum from P O .
2 5
Elemental analyses were performed by Desert Analytics Laboratory,
Tucson, Az.
carbon disulfide has been used as a cathode material in
rechargable batteries; however, the material made by this process
is contaminated with free sulfur.13 Because of minimal con-
tamination by free sulfur, CS2 photopolymers14 may be viable
alternatives to the plasma-polymerization materials.
NMR Experiments. NMR data were collected with 250, 300, or
5
00 MHz spectrometers and chemical shifts are reported relative to
Photopolymerization of gas-phase CS2 also provided a novel
1
13
TMS in H spectra and to CHCl
3
(δ 77.0 ppm) in C spectra. Magic
1
5,18
13
example of a mass-independent sulfur isotope fractionation,
angle spinning (MAS) solid-state C spectra were acquired at room
temperature with a Varian Unity 300-MHz H NMR spectrometer at a
which was similar to those of astrophysical origin.29-33 Carbon
disulfide is an important component of gaseous nebula and
primitive planetary atmospheres. Photopolymerization of CS2
1
sample frequency of 75.426 MHz with a Doty Scientific Inc. probe.
Samples (∼100 mg, referenced externally to tetrakis(trimethylsilyl)-
2
silane at δ 0.0 ppm) were placed in an airtight 7 mm ZrO rotor and
may represent an important gas-to-particle process in the presolar
nebulae.15 Although gas-phase photopolymerization of 13CS2
spun at 1.5 kHz.
1
3
Electron Paramagnetic Resonance (EPR) Measurements. Spectra
were recorded with a Brucker ElexSys E500 spectrometer operating at
X-band frequency. Temperatures of approximately 6 ( 1 K were
obtained with an Oxford helium cryostat. Samples were prepared by
yields the ( CS2)x photopolymer with an anomalously high
3
3
34
36
enrichment in S, S, and S, liquid-phase photolysis yields
solid material of different composition with a normal isotopic
1
8
signature.
2 x x
placing acetonitrile suspensions of finely divided (CS ) or (CS) into
The structure of Bridgman’s Black carbon disulfide was first
quartz EPR tubes and then removing the solvent under vacuum for
several hours. Spectral simulations employed the WINEPR SimFonia
program from Bruker Instruments.
probed by Whalley in 1960.34 Using IR spectroscopy, he
-
1
assigned a strong absorption at 1063 cm to a CdS (thiocar-
bonyl) stretch, and suggested the simple linear polymer structure
3 5
X-ray Diffraction Studies. Single-crystal X-ray data of all the (C S )
-
[C(dS)S]x-. Later, Chan and Jonscher proposed a more
compounds were collected with a Siemens R3m/V four-circle diffrac-
tometer using Mo KR radiation and the low-temperature accessory.
Data collection and crystal parameters are only reported for the new
7
complicated structure based on a more detailed IR spectrum.
In 1995 the vapor-phase-prepared photopolymers (CS2)x and
1
3
14
isomer R-(C S )(C(O)C H ) in the Supporting Information. Each of
(
CS2)x were reported. The (CS2)x photopolymer exhibits an
3
5
6
5 2
the structures was solved by direct methods (SHELXTL PLUS). All
non-hydrogen atoms were refined anisotropically, while the hydrogens
were calculated and fixed in idealized positions (d(C-H) ) 0.96 Å).
Tables of positional parameters, bond lengths, bond angles, and
anisotropic thermal parameters of the complex cations are available in
the Supporting Information. Powder X-ray diffraction measurements
were performed with a Scintag XDS-2000. Samples were prepared by
placing about 3-5 mg of the finely divided film onto zero background
quartz slides.
IR spectrum nearly identical with that for Bridgman’s Black. It
was concluded that the structure of (CS2)x aerosol was similar
to the one proposed by Chan and Jonscher for Bridgman’s
Black, but with thiocarbonyl end groups.
This work describes the characterization of a new carbon-
sulfur polymer of approximate stoichiometry (CS)x, prepared
by the photoirradiation of liquid-phase carbon disulfide. Isotopic
labeling studies and comparison of IR spectral features with
model compounds reveal the presence of C-C, CdC, and S-S
bonds in both (CS)x and (CS2)x. Thermochemical arguments
favor C-C coupling during the polymerization process and a
mechanism for polymer formation based on a S2CdCS2
intermediate is proposed.
Vibrational Spectroscopy. IR measurements were taken with the
use of a Nicolet 510 FT-IR spectrometer equipped with a liquid nitrogen
-
1
cooled MCT detector that was optimized for the 4000-800 cm
spectral region. The sample chamber was purged with N to remove
atmospheric CO and H O. A Nicolet Magna-IR 550 was used for
analyzing the spectral region below 800 cm . Samples contained 2-3
mg of dried (CS , (CS) , or model compound and 150 mg of IR grade
2
2
2
-1
(
(
19) Farges, J. P. Organic Conductors; Marcel Dekker: New York, 1994.
20) Br e´ das, J. L.; R. L., E.; Chance, R. R.; Silbey, R. J. Chem. Phys.
)
2 x
x
KBr, and were ground under nitrogen in an agate mortar and pestle.
Finally, the mixture was pressed in a hand-held KBr die assembly.
Liquid-phase spectra were measured in CCl solvent. Raman spectros-
4
copy measurements were taken with use of a liquid nitrogen cooled
CCD spectrometer (Princeton Instruments Model EUV-1143) and a
10 mW HeNe laser (MWK Industries) tuned to a wavelength of 632.85
nm. The laser was focused onto a powdered sample at a 45° angle
from horizontal. Raman light was captured by a simple collector lens
attached to a quartz fiber optic cable and transmitted to the CCD.
Reflected laser light was removed by a holographic notch filter.
1
983, 78 (9), 5656-5662.
21) Br e´ das, J. L.; Silbey, R. Conjugated Polymers; Br e´ das, J. L., Silbey,
R., Eds.; Kluwer Academic: Dordrecht, The Netherlands, 1991.
22) Crayston, J. A.; Iraqi, A.; Walton, J. C. Chem. Soc. ReV. 1994, 23,
(
(
1
47-153.
(
23) Little, W. A. Phys. ReV. A 1964, 134, 1416-1424.
(24) Whangbo, M.-H.; Hoffmann, R.; Woodward, R. B. Proc. R. Soc.
London, A 1979, 366, 23-46.
25) Whangbo, M. H. Extended Linear Chain Compounds; Plenum: New
York, 1982.
(
(26) Jerome, D.; Auban, P.; Kang, W.; Cooper, J. R. The Physics and
Organic Chemistry of Organic Superconductors; Jerome, D., Auban, P.,
Kang, W., Cooper, J. R., Eds.; Springer-Verlag: Tokyo, 1989; Vol. 51, pp
Electron Microscopy. Images were acquired with use of a Cam-
bridge 360 SEM at an accelerating voltage of 200 kV. For (CS
.8 cm glass disks were placed inside a 2 L quartz Schlenk flask and
were coated with the (CS aerosol photopolymer that settled out during
photolysis. Samples were sputter-coated with gold to a thickness of
300 Å to ensure adequate conductivity. For (CS) a small piece of the
2 x
) several
2
-7.
27) Korshak, Y. V.; Medvedeva, T. V.; Ovchinnikov, A. A.; Spector,
V. N. Nature 1987, 26, 370-372.
28) Greene, R. L.; Street, G. B.; Suter, L. J. Phys. ReV. Lett. 1975, 34,
77.
29) Wieler, R.; Anders, E.; Baur, H.; Lewis, R. S.; Signer, P. Geochim.
Cosmochim. Acta 1991, 55, 1709-1722.
30) Rees, C. E.; Thode, H. G. Geochim. Cosmochim. Acta 1977, 41,
679-1682.
31) Gao, X.; Thiemens, M. H. Geochim. Cosmochim. Acta 1993, 57,
171-3176.
32) Gao, X.; Thiemens, M. H. Geochim. Cosmochim. Acta 1993, 57,
159-3169.
33) Gao, X.; Thiemens, M. H. Geochim. Cosmochim. Acta 1991, 55,
671-2679.
34) Whalley, E. Can. J. Chem. 1960, 38, 2105-2108.
1
(
2 x
)
(
5
x
(
2
thin film photopolymer (∼3-4 mm ) was placed, via acetonitrile
suspension, on a 1.8 cm glass disk attached to an aluminum mounting
post. It was then dried under vacuum for several hours and sputter-
coated with gold to a thickness of 300 Å.
(
1
3
3
2
(
Atomic Force Microscopy. Images were obtained with use of a
model MMAFM-2 multimode SPM (Digital Instruments, Inc.) in
tapping mode. Silicon tips were purchased from Olympic Optical Co.
and had a radius of curvature from 5 to 10 nm. They were rated at a
resonance frequency of 300 kHz and a spring constant of 42 N/m. Scan
(
(
(