Matrix isolation study of intermediates in the reaction of CrCl2O2 with CH3SH and (CH3)2S

Article abstract of DOI:10.1016/S0022-2860(01)00969-3

Initial and secondary intermediates in the reaction of CrCl₂O₂ with CH₃SH and (CH₃)₂S have been characterized by matrix isolation infrared spectroscopy and density functional calculations. Twin jet codeposition of these reagents led to a series of infrared absorptions that are assigned to the 1:1 molecular complexes CH₃SH·CrCl₂O₂ and (CH₃)₂S·CrCl₂O₂. The complexes were characterized by the shifts of Cr=O, Cr-Cl and S-H stretching modes. Irradiation of these matrices with light of λ > 300 nm led to complete destruction of the complexes, and for each system the growth of a number of new bands. For the CH₃SH/CrCl₂O₂ system, these are assigned to the ClCr(O)₂SCH₃ species, as well as to HCl arising from destruction of the complex. Identification of these species was supported by deuterium labeling as well as by density functional calculations. Good agreement was observed between the experimental and computed frequencies. For the (CH₃)₂S/CrCl₂O₂ system, photolysis product bands are tentatively assigned to CH₃Cl and ClCr(O)₂SCH₃.

Full text of DOI:10.1016/S0022-2860(01)00969-3

Journal of Molecular Structure 609 ꢀ2002) 149±157
www.elsevier.com/locate/molstruc
Matrix isolation study of intermediates in the reaction of
CrCl2O2 with CH3SH and ꢀCH3)2S
*
Susan R. Anderson, Bruce S. Ault
Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, OH 45221-0172, USA
Received 23 October 2001; revised 29 November 2001; accepted 29 November 2001
Abstract
Initial and secondary intermediates in the reaction of CrCl2O2 with CH3SH and ꢀCH3)2S have been characterized by matrix
isolation infrared spectroscopy and density functional calculations. Twin jet codeposition of these reagents led to a series of
infrared absorptions that are assigned to the 1:1 molecular complexes CH3SH´CrCl2O2 and ꢀCH3)2S´CrCl2O2. The complexes
were characterized by the shifts of CryO, Cr±Cl and S±H stretching modes. Irradiation of these matrices with light of
l . 300 nm led to complete destruction of the complexes, and for each system the growth of a number of new bands. For
the CH3SH/CrCl2O2 system, these are assigned to the ClCrꢀO)2SCH3 species, as well as to HCl arising from destruction of the
complex. Identi®cation of these species was supported by deuterium labeling as well as by density functional calculations.
Good agreement was observed between the experimental and computed frequencies. For the ꢀCH3)2S/CrCl2O2 system, photo-
lysis product bands are tentatively assigned to CH3Cl and ClCrꢀO)2SCH3. q 2002 Elsevier Science B.V. All rights reserved.
Keywords: Matrix isolation infrared spectroscopy; Chromyl chloride; Irradiation
1. Introduction
tion of reactive intermediates. This approach has been
applied to the study of a wide range of species, including
radicals,weaklyboundmolecularcomplexes,andmole-
cular ions. Recent studies [7±11] from this laboratory
have focused on the sequence of intermediates formed
in the reactions of OVCl3 and CrCl2O2 with small
organic substrates, including NH3 and CH3OH. In addi-
tion, a matrix isolation study of the reaction of OVCl3
with CH3SH was recently published [12]. While
CrCl2O2 is generally somewhat less reactive than
OVCl3, the origin of the differences between these two
compounds is not clear. Consequently, a study was
undertaken to identify and characterize initial and
secondary intermediates in the reaction of CrCl2O2
with CH3SH and ꢀCH3)2S, and to compare this system
to the previously studied systems. Density functional
calculations were also carried out in support of the
experimental observations.
CrCl2O2 is a strong oxidizing agent for a variety of
organic compounds [1,2]. It is used as a catalyst for
the polymerization of alkenes, the oxidation of hydro-
carbons, in the Etard reaction to produce ketones and
aldehydes and in the preparation of chromium coor-
dination complexes [3]. In many industries, selective
oxidation is important. Despite the importance of
these oxidation processes, the mechanism is not well
understood. This is because of the complexity of the
reactions themselves and also because of the lack of a
well-de®ned model.
The matrix isolation technique [4±6] was developed
tofacilitatethe isolation and spectroscopic characteriza-
* Corresponding author. Tel.: 11-513-556-9200.
E-mail address: bruce.ault@uc.edu ꢀB.S. Ault).
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860ꢀ01)00969-3

150
S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
2. Experimental details
locate energy minima, determine structures and calcu-
late vibrational spectra. Final calculations with full
geometry optimization employed the 6-311G basis
set, after initial calculations with smaller basis sets
were run to approximately locate energy minima.
Calculations were carried out on a Silicon Graphics
Indigo 2 workstation.
All the experiments in this study were carried out
on conventional matrix isolation apparatus that has
been described [13]. Chromyl chloride, CrCl2O2
ꢀAldrich), was introduced into the vacuum system as
the vapor above the room temperature liquid, after
puri®cation by freeze±pump±thaw cycles at 77 K.
CH3SH ꢀMatheson), CD3SD ꢀ99% D, Isotec) and
CH3SD ꢀ99% D, CDN isotopes) were introduced
from lecture bottles into a separate vacuum manifold
and were puri®ed by repeated freeze±pump±thaw
cycles at 77 K. ꢀCH3)2S and ꢀCD3)2S ꢀboth Aldrich)
were introduced into the vacuum system as the vapor
above the room temperature liquid, after puri®cation
by freeze±pump±thaw cycles at 77 K. Argon ꢀWright
Brothers) was used as the matrix gas in all experi-
ments, and was used without further puri®cation.
Matrix samples were deposited in both the twin jet
and merged jet modes. In the former, the two gas
samples were deposited from separate nozzles onto
the 14 K cold window, allowing for only a very
brief mixing time prior to matrix deposition. A
number of these matrices were subsequently warmed
to 33±36 K to permit limited diffusion and then
recooled to 14 K and additional spectra recorded. In
addition, most of these matrices were irradiated for
1.0 or more hours with the H2O/Pyrex ®ltered output
of a 200 W medium pressure Hg arc lamp, after which
additional spectra were recorded.
Several experiments were conducted in the merged
jet mode [14], in which the two deposition lines were
joined with an Ultratorr tee at a distance from the
cryogenic surface, and the ¯owing gas samples were
permitted to mix and react during passage through the
merged region. The length of this region was variable;
typically, a 30 cm length was employed. This region
could also be heated to as high as 300 8C to induce
further reaction, prior to deposition. In both twin and
merged jet, matrices were deposited at the rate of
2 mmol h21 from each sample manifold onto the
cold window. Final spectra were recorded on a
Perkin±Elmer Spectrum 2000 or a Bruker 113 Fourier
transform infrared spectrometer at 1 cm21 resolution.
Theoretical calculations were carried out on likely
intermediates in this study, using the gaussian-94
suite of programs [15]. Density functional calcula-
tions using the hybrid B3LYP function were used to
3. Results
Prior to any codeposition experiments, blank
experiments were run on each of the reagents used
in this study. In each case, the blanks were in good
agreement with literature spectra [16±21], and with
blanks run previously in this laboratory. However, the
spectra indicated that the purity of the CD3SD sample
was somewhat less than stated. Each blank experi-
ment was then irradiated by the H2O/Pyrex ®ltered
output of a 200 W Hg arc lamp for 1.0 or more
hours. No changes were observed in any of the
blank spectra as a result of irradiation. Weak bands
due to HCl impurity were noted in all of the CrCl2O2
blank experiments [22].
3.1. CrCl2O2 1 CH3SH
In an initial experiment, a sample of Ar=CH3SH ˆ
100 was codeposited with a sample of Ar=CrCl2O2 ˆ
150 in the twin jet mode. Initial concentrations of Ar/
CrCl2O2 of 100:1, 250:1 and 100:1 were codeposited
with Ar/CH3SH concentrations of 100:1, 100:1 and
250:1. The resulting spectra showed intense bands
due to the parent species along with new weaker
bands at 434, 537, 748, 927, 945, 962, 1182, 1390
and 2514 cm21. Upon annealing the matrix to 34 K,
the bands at 927, 945 and 962 cm21 increased slightly.
The rest of the bands remained unchanged. The
annealed matrix was then irradiated for 1 h with a
medium pressure Hg arc lamp and a H2O/Pyrex ®lter.
In the resulting spectra the bands at 927, 945 and
962 cm21 disappeared while the band at 2514 cm21
decreased slightly. The bands at 537, 748, 1182 and
1390 cm21 remained unchanged. The band at
434 cm21 was lost under new bands that grew in at
449, 438 and 436 cm21 that were very intense. Other
new bands grew at 415, 658, 668, 795, 939, 975, 1007,
1314, 1403, 1417, 2734 and 2752 cm21. Due to their
different behavior with respect to annealing and

S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
151
Fig. 1. Infrared spectra of the matrix formed by the twin jet codeposition of a sample of Ar/CH3SH with a sample of Ar/CrCl2O2. The top trace
shows the spectrum of the matrix upon initial deposition, the middle trace after annealing, and the bottom trace after irradiation with l .
300 nm: Bands marked with an asterisk are due to product species.
irradiation, the bands at 434, 927, 945 and 962 cm21
will be referred to as set A. The bands at 438, 658,
668, 932, 975, 1007, 1311, 1403 and 1417 cm21 that
formed upon irradiation will be referred to as group B
and the bands at 2752 and 2734 cm21 as group C. The
bands at 537, 748, 1182 and 1390 cm21 appear to be
independent of CH3SH and are therefore thought to
be due to an impurity. These bands will therefore not
be discussed further. Fig. 1 shows spectra for this pair
of reagents, after initial deposition, annealing and irra-
diation.
A number of additional twin jet experiments were
carried out with these two reagents, at several
different concentration combinations. The results
described previously were reproducible in all of
these experiments, with the same bands appearing.
Within each set, the bands maintained a constant
intensity ratio with respect to one another in all of
these experiments. In an additional experiment, irra-
diation times were varied at 15 min intervals from
15 min to 2 h. After 1 h, the spectra no longer
changed. In another experiment, irradiation was
done prior to annealing with the irradiated spectrum
essentially the same as all the other irradiated spectra.
Annealing after irradiation had no effect on this spec-
trum.
Samples of Ar/CrCl2O2 and Ar/CH3SH were code-
posited in a set of merged jet experiments, employing
the same concentration combinations as was used in
the twin jet experiments. The initial product bands
that were present in the twin jet experiments were
also present in the merged jet but were slightly more
pronounced. There were no additional new bands
present. The reaction zone of the merged system
was then heated in several of these experiments, to
100, 200 and 250 8C. Again, there were no new bands,
beyond those seen in the twin jet experiments.
Annealing had no effect on the merged jet experi-
ments, while irradiation of the matrices produced
the same bands as in the twin jet experiments.

152
S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
Fig. 2. Infrared spectra of the matrix formed by the twin jet codeposition of a sample of Ar/CH3SD with a sample of Ar/CrCl2O2. The top trace
shows the spectrum of the matrix upon initial deposition, the middle trace after annealing, and the bottom trace after irradiation with l .
300 nm: Bands marked with an asterisk are due to product species. Note particularly the bands near 1983 and 1995 cm21 due to photo-produced
DCl.
3.2. CrCl2O2 1 CD3SD
nated by group A are 424, 435, 920, 927, 940, 946 and
960 cm21 since these bands were destroyed by irradia-
tion. group Bbands are 437, 457, 980 and 1008 cm 21
,
Samples of Ar/CD3SD were codeposited with
samples of Ar/CrCl2O2 in a series of twin jet experi-
ments, using concentrations comparable to those used
in the abovementioned experiments with CH3SH.
New product bands formed upon initial deposition
were seen at 407, 424, 435, 518, 775, 804, 920, 927,
940, 946, 960, 990, 2508 and 2539 cm21; some of
these bands appeared as doublets or multiplets.
Annealing the matrix to 36 K had no discernable
effect on the spectra. Irradiation of the matrix created
bands at 437, 457, 977, 1008, 2424, 2442, 2563, 2574,
2685, 2726 and 2734 cm21; again, several of these
appeared as doublets or multiplets. At the same time
the initial product bands at 920, 927, 940, 946 and
960 cm21 were essentially destroyed. The bands at
424 and 435 cm21 were completely obliterated by
new, intense product bands in the same region so it
was dif®cult to determine their fate. The bands desig-
as these bands all grew uniformly upon irradiation.
New bands that also appeared upon irradiation but
had no counterpart in the undeuterated methanethiol
reactions were located at 2424, 2441, 2444, 2563,
2574 and 2685 cm21 and are referred to as group D.
These bands are in the range of the methanethiol
dimer and larger aggregates and are so assigned.
The bands at 2726 and 2734 cm21 are most likely
due to HCl formed from isotopically impure metha-
nethiol-d4.
A series of merged jet experiments were also
conducted with samples of Ar/CD3SD and Ar/
CrCl2O2. As in the experiments with the normal
isotope of methanethiol, no new bands were present
in the merged jet experiments ꢀthat were not present in
the twin jet experiments). Heating the reaction line
and annealing again had no effect on the bands

S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
153
Fig. 3. Infrared spectra of the matrix formed by the twin jet codeposition of a sample of Ar/ꢀCH3)2S with a sample of Ar/CrCl2O2. The top trace
shows the spectrum of the matrix upon initial deposition, the middle trace after annealing, and the bottom trace after irradiation with l .
300 nm: Bands marked with an asterisk are due to product species.
produced. Irradiation of the matrix produced the same
product bands as in the twin jet mode.
1983 and 1995 cm21 as set C. Fig. 2 shows spectra for
this pair of reagents, after initial deposition, annealing
and irradiation.
As with the two previous methanethiols, merged jet
experiments produced no new bands. Annealing the
matrix again had no effect on the spectra, while irra-
diation produced the same bands as in the twin jet
experiments.
3.3. CrCl2O2 1 CH3SD
Samples of Ar/CH3SD were also codeposited with
samples of Ar/CrCl2O2 in a series of twin jet experi-
ments. Product bands appearing upon initial deposi-
tion were located at 431, 800, 807, 920, 927, 957,
1392, 1417, 2071, 2074, 2510 and 2558 cm21
.
3.4. CrCl2O2 1 1CH3)2S
Annealing the matrix to 36 K again showed no
discernable effect on the spectrum. Irradiation of the
matrix for 1 h created new bands at 438, 476, 755,
932, 939, 948, 971, 980, 988, 991, 1008, 1405, 1983
and 1995 cm21. All of the product bands that appeared
upon initial deposition were essentially gone. The
bands at 431, 800, 807, 920, 927 and 957 cm21
again will be referred to as set A. The bands at 438,
476, 755, 932, 939, 948, 971, 980, 988, 991, 1008 and
1405 cm21 will be referred to as set Band the bands at
Initial twin jet experiments involving chromyl
chloride and dimethylsul®de ꢀDMS) were carried
out at the same concentrations as those used in the
chromyl chloride/methanethiol reactions. The
resulting spectra again showed intense bands due to
the parent species along with new weak bands at 432,
448, 918, 922, 946, 953 and 2268 cm21. Annealing
the matrix to 36 K had no effect on the band intensities
nor were any new bands formed. Irradiation for 1 h

154
S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
with the Hg arc lamp produced new bands at 436, 441,
452, 711, 933, 950, 1001, 1017 and 1022 cm21. The
band at 432 cm21 appeared to grow signi®cantly but
this was more likely due to the nearby intense band at
436 cm21 that grew in. The bands at 918, 922, 946 and
953 cm21 decreased tremendously while the band at
2268 cm21 exhibited no change. Again, due to the
different behavior, the bands at 432, 448, 918, 922,
946 and 953 cm21 will be referred to as group E, the
bands at 436, 441, 452, 711, 933, 950, 1001, 1017 and
1022 cm21 will be referred to as group F and the band
at 2268 cm21 as group G. Irradiation times were again
varied in 15 min intervals. After 1 h, no further
changes took place. Fig. 3 shows spectra for this
pair of reagents, after initial deposition, annealing
and irradiation.
Samples of Ar/ꢀCH3)2S and Ar/CrCl2O2 were
allowed to mix prior to deposition in a merged jet
system, using a 30 cm reaction zone. The resultant
spectra were essentially identical to those obtained
in the twin jet mode. Again, the reaction zone was
heated to 100, 200 and 250 8C in subsequent experi-
ments but no new bands occurred. Annealing had no
effect on the results, while irradiation of the matrix
produced the same results as the twin jet experiments
after irradiation.
These two reactants were also studied in several
merged jet experiments, with a 30 cm reaction zone.
The resultant spectra were essentially identical as in
the twin jet mode. Again, the reaction zone was heated
to 100, 200 and 250 8C in subsequent experiments but
no new bands were observed. Annealing had no effect
on the spectrum, while irradiation of the matrices led
to spectra that were identical to those obtained in the
twin jet experiments after irradiation.
4. Discussion
Twin jet and merged jet deposition led to identical
results for each of the systems studied here. In each
case, several product species are formed, based on the
band groupings and their behavior with respect to
irradiation. For the CH3SH/CrCl2O2 system, the
bands formed upon initial deposition were identi®ed
as group A, while the bands of group Bwere formed
upon irradiation, as the bands of group A were
destroyed. This strongly suggests sequential product
formation. It should also be noted that within a given
group, all of the bands maintained a constant intensity
ratio with respect to one another, strongly supporting
the idea that all of the bands within that group are due
to a single absorber.
Upon initial deposition of samples of Ar/CH3SH
and Ar/CrCl2O2, group A bands were formed. Since
in twin jet deposition the reactants mix only very
brie¯y on the surface of the matrix, group A may be
identi®ed with the initial intermediate in this system.
The yield in the twin jet was very low but increased
slightly with annealing. Merged jet yield was slightly
more intense but product formation was still very low.
Since this product forms upon initial deposition in the
twin jet mode, the barrier to formation must be very
low. Based on previous studies [7±9] of the reaction
of CrCl2O2 with CH3OH, ꢀCH3)2O and NH3, as well as
ab initio calculations, the species responsible for the
group A bands is identi®ed as the molecular complex
between the two reactants, CrCl2O2´HSCH3. Charac-
teristically, complexes form with essentially no acti-
vation barrier, and the formation of a complex is
indicated by the small shifts of the vibrational
modes of the two subunits. Based on the relatively
low sample concentrations used and analogy to
previous studies, the stoichiometry of the complex is
3.5. CrCl2O2 1 1CD3)2S
Samples of Ar/ꢀCD3)2S were substituted for DMS
in a series of experiments with CrCl2O2. Product
bands upon initial deposition were located at 435,
440, 757, 920, 946, 954, 1021 and 2265 cm21. No
changes were detected upon annealing the matrix to
36 K. Irradiation with the H2O/Pyrex ®ltered output of
a medium pressure Hg arc led to the formation of new
bands at 410, 417, 432, 446, 688, 832, 930, 962, 967,
972, 988, 995, 1002, 1027 and 1048 cm21. The initial
product bands at 435, 1021 and 2265 cm21 appeared
to increase with irradiation while the bands at 757,
920, 946 and 954 cm21 decreased or disappeared
with irradiation. Again due to the different behavior
of these bands with respect to irradiation, they can be
grouped as follows: group E consists of 435, 440, 757,
920, 946, 954 and 1021 cm21; group F consists of 410,
417, 432, 446, 688, 832, 930, 962, 967, 972, 988, 995,
1002, 1027 and 1048 cm21 and group G consist of
2265 cm21
.

S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
155
Table 1
Band positions ꢀcm21), assignments and comparison to theoretical calculations for ClCrꢀO)2SCH3
Band ꢀexpt.)
Band ꢀcalc.)a
D-shift ꢀexpt.)b
D-shift ꢀcalc.)
Assignment
438
448
454
469
2 1
1 9
±
2 2
0
S±Cr±Cl asym. st.
S±Cr±Cl sym. st.
S±C stretch
658, 668
932
620
988
±
±CH3 rock
939
975
1000
1072
1107
1393
1487
1502
±
±CH3 rock
1 2
1 1
±
1 1
1 1
OyCryO sym. st.
OyCryO asym. st.
±CH3 sym. bend
±CH3 asym. bend
±CH3 asym. bend
1007
1311
1403
1417
±
±
a
Unscaled frequency, from B3LYP/6-311G calculation.
Limited results were obtained with CD3SD; calculated shifts are only reported for those bands that were observed experimentally in the
b
CD3SD experiments.
very likely 1:1. For the CrCl2O2´HSCH3 complex, the
S±H stretch shifted from 2604 cm21 in the parent to
2514 cm21 in the complex, while the Cr±Cl stretches
near 500 cm21 shifted to 434 cm21 and the CryO
stretches between 981 and 1003 cm21 shifted to 920
and 960 cm21. The relatively large red shift of the S±
H stretching mode suggested that the structure of the
complex involves hydrogen bonding formation [23],
from the S±H group to either the oxo or chloride
groups on CrCl2O2. A red shift of the stretching
modes of the Lewis acid ꢀCrCl2O2) suggests some
transfer of electron density to the acid, and a slight
reduction in the stretching force constants.
The initial group A product bands were destroyed
by irradiation with the Hg arc lamp, leading to the
appearance of the bands in groups Band C. In
previous studies [7,8] of the photochemical reaction
of CrCl2O2 with CH3OH and NH3, and OVCl3 with
CH3OH, NH3 and CH3SH, in each case the initial
complex was destroyed by irradiation and HCl elim-
ination. However, the HCl that is formed is trapped
within the same matrix cage as the second photopro-
duct, and interacts weakly with that species. Conse-
quently, the absorption bandꢀs) of the photo-produced
HCl do not occur where isolated HCl has been
observed previously [24,25], but is shifted to lower
energy. For each of the previous systems, HCl
complexed to the photoproduct was observed between
2700 and 2800 cm21, near the group C bands in the
current study. Moreover, when CH3SD was employed,
the bands in the present study shifted to 1983 and
1995 cm21. This is precisely the shift anticipated for
HCl, and the shift observed previously [24,25]. Based
on the earlier studies, and this deuterium shift, the
bands in group C are assigned to HCl ꢀDCl) arising
through photoelimination from the initial molecular
complex.
The observation that the bands in groups Band C
grow in under the same conditions while the group A
bands were destroyed suggests that the bands in group
Bmay be assigned to the HCl elimination product
from the complex, namely ClCrꢀO)2SCH3. This is
consistent with all of the previous studies on similar
systems, including the OVCl3/CH3SH system. To
further support this identi®cation, density functional
calculations were carried out on this intermediate
species. These calculations converged to an energy
minimum, demonstrating that ClCrꢀO)2SCH3 should
be a stable species. Further, the calculations yielded a
theoretical infrared spectrum, for comparison to
experiment. As shown in Table 1, the agreement
between experiment and theory is quite reasonable,
particularly recognizing that calculations at the
B3LYP/6-311G level of theory are typically 3±4%
high. Consequently, the set Bbands in the CH SH/
3
CrCl2O2 experiments are assigned to the novel
ClCrꢀO)2SCH3 intermediate.
Further photolysis of the matrix, and the heating of
the reaction line in the merged jet experiments, did not
lead to any new species. This indicates that the
ClCrꢀO)2SCH3 species is relatively stable to photo-
chemical decomposition. This is in contrast to several

156
S.R. Anderson, B.S. Ault / Journal of Molecular Structure 609 12002) 149±157
of the previously studied systems, where further
thermal reaction and decomposition was seen.
second photoproduct in this system must be
regarded as tentative.
The sequence of product formation in the ꢀCH3)2S/
CrCl2O2 system was quite similar to that described
earlier for the CH3SH/CrCl2O2 system. Initial weak
product bands were formed upon twin jet deposition
ꢀgroup E). These were destroyed by Hg arc irradiation
as group F bands grew in. This observation, combined
with the argument presented above concerning the
formation of molecular complexes, strongly suggests
that the group E bands are due to the formation of the
isolated 1:1 complex, CrCl2O2´SꢀCH3)2. This complex
is characterized by the following shifts of the vibra-
tional modes of the two subunits: the Cr±Cl stretching
bands around 500 cm21 shifted to 434 cm21; the
CryO stretches between 981 and 1003 cm21 shifted
to 919 and 954 cm21; and the CH3 rocking band at
1030 cm21 shifted to 1021 cm21. In contrast to the
complex of CrCl2O2 with CH3SH, ꢀCH3)2S does not
have a hydrogen available for hydrogen bonding, and
the interaction is probably a classical coordination
compound, with the donation of a pair of electrons
from the sulfur to the Cr center.
Finally, the one band in group G at 2268 cm21 can
be assigned to the hydrogen bonded complex of HCl
with ꢀCH3)2S, ClH´´´SꢀCH3)2. This complex has been
described previously [27], the group G band matches
very well. Since HCl is a minor impurity in all experi-
ments containing CrCl2O2, the presence of this
complex is very reasonable. An analogous band, at
2514 cm21, was observed in the CH3SH/CrCl2O2
system, and is likewise assigned.
Acknowledgements
The National Science Foundation is gratefully
acknowledged for support of this research, through
grant CHE 9877076.
References
[1] K.B. Sharpless, A.Y. Teranishi, J.E. Backval, J. Am. Chem.
Soc. 99 ꢀ1977) 3120.
[2] G.K. Cook, J.M. Mayer, J. Am. Chem. Soc. 116 ꢀ1994) 1855.
[3] S. Buda Vari ꢀEd.), Merck Index 11th ed., 1989, p. 349.
[4] H.E. Hallam, Vibrational Spectroscopy of Trapped Species,
Wiley, New York, 1973.
The group E product bands were destroyed by irra-
diation with a Hg arc lamp, bringing about the appear-
ance of the bands in group F. Group F grows as group
E decreases which suggests that it is formed from the
initial product. While HCl elimination is less likely in
this case ꢀand no bands due to HCl formation were
observed), a hint as to the product comes from the
band at 711 cm21 in the ꢀCH3)2S/CrCl2O2 system
and the band at 688 cm21 in the ꢀCD3)2S/CrCl2O2
system. These bands fall very near the most intense
band of CH3Cl and CD3Cl, namely the C±Cl stretch
[26]. Unfortunately, the product yield was low and the
regions where other bands of CH3Cl might be
observed were obscured by parent band absorptions.
Nonetheless, these bands indicate the formation of
CH3ClꢀCD3Cl), which would be a potential and
reasonable elimination product from the initial
complex. The second photoproduct would be
ClCrꢀO)2SCH3, the same intermediate observed
for the CH3SH/CrCl2O2 system. Indeed, the
remainder of the set F bands was close to the
set Bbands, above. However, the product band
intensities and product yields were quite low,
less than that in the CH3SH/CrCl2O2 experiments.
Thus, the identi®cation of ClCrꢀO)2SCH3 as the
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