Photochemical reaction channels of OCS with Cl2, ICI, or IBr isolated together in an argon matrix: Isolation of syn-iodocarbonylsulfenyl bromide

Article abstract of DOI:10.1021/jp056135e

The photolytically induced reactions of a dihalogen XY (= Cl₂, ICl, or IBr) with OCS isolated together in an Ar matrix at about 15 K lead to different photoproducts depending on the natures of X and Y. In addition to the known species ClCO, OCCl₂, syn-ClC(O)SCl, syn-ClC(O)SSCl, IC(O)Cl, IC(O)Br, and ^n-BrC(O)SBr, syn-iodocarbonylsulfenyl bromide, yyn-IC(O)SBr, has thus been identified for the first time as'a photoproduct of the reactions involving IBr. The first product to be formed in the reactions with Cl ₂ or ICI is the C1CO radical which reacts subsequently with halogen or sulfur atoms or other matrix guests to give the corresponding carbonyl dihalide (OCCl₂ and IC(O)Cl), syn-ClC(O)SCl or syn-ClC(O)SSCl. The analogous reaction with IBr affords syn-BrC(O)SBr, IC(O)Br, and syn-IC(O)SBr. The changes have been followed, the products characterized experimentally by IR measurements, and the spectra analyzed in the light of the results of appropriate theoretical calculations.

Full text of DOI:10.1021/jp056135e

2674
J. Phys. Chem. A 2006, 110, 2674-2681
Photochemical Reaction Channels of OCS with Cl2, ICl, or IBr Isolated Together in an
Argon Matrix: Isolation of syn-Iodocarbonylsulfenyl Bromide
†
†,‡
,†
,†,‡
Yeny A. Tob o´ n, Laura I. Nieto, Rosana M. Romano,* Carlos O. Della V e´ dova,* and
Anthony J. Downs§
CEQUINOR (UNLP-CONICET) and Laboratorio de SerVicios a la Industria y al Sistema Cient ´ı fico
(
UNLP-CIC-CONICET), Departamento de Qu ´ı mica, Facultad de Ciencias Exactas, UniVersidad Nacional de
La Plata, 47 esq. 115, (1900) La Plata, Argentina, and Inorganic Chemistry Laboratory, UniVersity of Oxford,
South Parks Road, Oxford, OX1 3QR, U.K.
ReceiVed: October 25, 2005; In Final Form: December 7, 2005
The photolytically induced reactions of a dihalogen XY () Cl
2
, ICl, or IBr) with OCS isolated together in an
Ar matrix at about 15 K lead to different photoproducts depending on the natures of X and Y. In addition to
•
the known species ClCO , OCCl
syn-iodocarbonylsulfenyl bromide, syn-IC(O)SBr, has thus been identified for the first time as a photoproduct
of the reactions involving IBr. The first product to be formed in the reactions with Cl
or ICl is the ClCO•
radical which reacts subsequently with halogen or sulfur atoms or other matrix guests to give the corresponding
carbonyl dihalide (OCCl and IC(O)Cl), syn-ClC(O)SCl or syn-ClC(O)SSCl. The analogous reaction with
2
, syn-ClC(O)SCl, syn-ClC(O)SSCl, IC(O)Cl, IC(O)Br, and syn-BrC(O)SBr,
2
2
IBr affords syn-BrC(O)SBr, IC(O)Br, and syn-IC(O)SBr. The changes have been followed, the products
characterized experimentally by IR measurements, and the spectra analyzed in the light of the results of
appropriate theoretical calculations.
1
. Introduction
had hitherto eluded detection; unlike its chloro counterpart, but
in keeping with the results of earlier, sophisticated quantum
In the pursuit of new species and elucidation of the
7
chemical calculations, this is most aptly formulated as a weakly
photochemical reaction channels open to a dihalogen XY in
the presence of OCS, we became interested in the specific cases
where XY ) Cl2, ICl, or IBr. An earlier study of the matrix
.
bound van der Waals complex engaging CO to a Br atom. All
these antecedents are relevant to the current study, mainly
because carbonyl sulfide, OCS, is dissociated into CO and S
1
photochemistry of chlorocarbonylsulfenyl bromide, ClC(O)SBr,
8
atoms upon broad-band UV-vis photolysis.
has served as the basis for subsequent research. Broad-band
UV-vis irradiation of ClC(O)SBr leads not only to partial
transformation of the more stable syn into the anti form of the
molecule but also to the formation of its isomer BrC(O)SCl, as
well as the photoevolution of the fragments BrCl, BrSCl, CO,
Here, we report on some photolytically initiated reactions
involving a dihalogen molecule XY () Cl2, ICl, or IBr) and
OCS isolated together in a solid Ar matrix at about 15 K. Under
broad-band UV-vis photolysis, the reaction pathways lead to
the formation of one or more carbonyl dihalides, OCXY, and/
or halogenosulfenylcarbonyl halides, XC(O)SY, where X, Y )
Cl, Br, or I may be the same or different atoms. Hence, syn-
iodocarbonylsulfenyl bromide, syn-IC(O)SBr, has finally been
produced by the photoreaction of OCS with IBr; this is the first
example of a molecule containing the hitherto unidentified IC-
1
and OCS. The mechanisms proposed for the various processes
imply active rather than passive roles for the stable products
CO and OCS. Hence, it has already been shown, for example,
that hitherto unknown compounds such as BrC(O)SBr can be
formed under matrix conditions by photoactivation of Br2 in
the presence of OCS.2
This experience has served to point the way to a means of
completing the carbonyl dihalide family when the matrix
photoreactions of IBr and ICl with CO were shown to afford
(
O)S- group. syn-IC(O)SBr as well as the known species
•
ClCO , OCCl2, IC(O)Cl, syn-ClC(O)SCl, syn-ClC(O)SSCl, and
IC(O)Br, formed in similar reactions involving the relevant
halogen atoms, have been characterized experimentally by their
IR spectra and theoretical calculations.
3
4,5
IC(O)Br and IC(O)Cl, respectively. As reported recently,
trapping XY and CO together in an Ar matrix results, prior to
photolysis, only in the formation of a weakly bound adduct XY‚
2
. Experimental Section
‚
‚CO. The first product of photolysis when either X or Y ) Cl
•
6
Commercial samples of ICl and IBr (ex Aldrich) were purified
is the familiar radical ClCO , which subsequently takes up a
second halogen atom to form the appropriate carbonyl dihalide
XC(O)Cl (X ) Cl, Br, or I). By contrast, the photoinduced
by repeated trap-to-trap condensation in vacuo, mainly to remove
I2 impurity, the presence of which hampered photochemical
studies by its inherently high absorption cross-section throughout
much of the visible and UV regions. Cl2 (again ex Aldrich)
and OCS were used without any further purification. Gas
mixtures of the dihalogen (XY), OCS, and Ar, typically with
the composition XY/OCS/Ar ) 0.5:1:200, were prepared by
standard manometric methods. Each such mixture was deposited
on a CsI window cooled to ca. 15 K by a Displex closed-cycle
•
reaction with Br2 gives rise initially to the radical BrCO which
*
To whom correspondence should be addressed. E-mail:
carlosdv@quimica.unlp.edu.ar.
†
CEQUINOR, Universidad Nacional de La Plata.
Laboratorio de Servicios a la Industria y la Sistema Cient ´ı fico,
‡
Universidad Nacional de La Plata.
§
Inorganic Chemistry Laboratory, University of Oxford.
1
0.1021/jp056135e CCC: $33.50 © 2006 American Chemical Society
Published on Web 02/04/2006

Isolation of syn-Iodocarbonylsulfenyl Bromide
J. Phys. Chem. A, Vol. 110, No. 8, 2006 2675
refrigerator (Air Products, model CS202) using the pulsed
TABLE 1: Wavenumbers and Assignments of the IR
Absorptions Appearing after Broad-Band UV-Vis
Photolysis of an Ar Matrix Containing a Mixture of OCS
deposition technique.9,10
The IR spectrum of each matrix sample was recorded at a
and Cl
2
at ca. 15 K
-
1
resolution of 0.5 cm , with 256 scans and a wavenumber
wavenumber
reported
previously
-
1
accuracy of (0.1 cm , using a Nicolet Magna-IR 560 FTIR
Ar matrix
assignment
vibrational mode
instrument equipped with either an MCTB or a DTGS detector
ν (cm-1
)
molecule
-1
-1
(
for the ranges 4000-400 cm or 600-250 cm , respectively).
a
2140.6
2137.9
1877.1
OC‚‚‚Cl
2
ν(CdO)
ν(CdO)
ν(CdO)
2140.7
2138.2
1876.7
Following deposition and IR analysis of the resulting matrix,
the sample was exposed to broad-band UV-vis radiation (200
e λ e 800 nm) issuing from a spectral energy Hg-Xe arc lamp
operating at 800 W. The output from the lamp was limited by
a water filter to absorb IR radiation and so minimize any heating
effects. The IR spectrum of the matrix was then recorded at
different times of irradiation and scrutinized closely for signs
of decay of the absorptions due to the reactants and growth of
absorptions due to the respective products. Experiments involv-
ing more selective photolysis were unsuccessful, the much
reduced light flux resulting in little or no detectable change.
All of the quantum chemical calculations were performed
a
free CO
b
ClCO‚
c
1840.6
1834.6
1840.61
1834.71
1810.12
OCCl
2
ν
2
+ ν
5
+ ν
6
}
}
c
1
1
1
8
8
810.0
772.9
010.2
47.5
40.4
OCCl
2
ν(CdO)
d
syn-ClC(O)SSCl ν(CdO)
1795
c
OCCl
Cl /OCCl
2
ν
ν
2
+ ν
as(Cl-C-Cl)
6
1010.08
e
2
2
847.8
c
837.36
837.20
OCCl
2
ν
5
as(Cl-C-Cl) (ν )
}
}
837.4
812.2
f
syn-ClC(O)SCl
syn-ClC(O)SSCl
ν
ν
as(Cl-C-S)
as(Cl-C-S)
812.4
795
d
8
03.8
c
c
581.21
5
81.2
OCCl
2
δ
4
oop (ν )
580.88
11
}
}
using the Gaussian 98 program system under the Linda parallel
execution environment using two coupled PCs. HF, density
functional theory (DFT), and MP2 methods were tried, in
combination with a 6-31+G* basis set for C, O, and Cl atoms
and a LANL2DZ basis set12 including an effective core potential
580.56
568.29
564.75
572.5
OCCl
2
ν
s
(CCl
2
2
) (ν )
561.12
5
5
5
47.9
17.5
15.8
syn-ClC(O)SSCl
ν
ν
ν
s
(Cl-C-S)
35
35
g
SCl
SCl
2
as( Cl-S- Cl)
517.5
515.2
490
(
ECP) for Br and I atoms. The ECP chosen is that proposed by
35
37
g
2
s
( Cl-S- Cl)
13
d
Hay and Wadt which incorporates the mass velocity and
Darwin relativistic effects. Representative levels of approxima-
tion are cited throughout this paper. Geometry optimizations
were sought using standard gradient techniques by simultaneous
relaxation of all the geometrical parameters. The calculated
vibrational properties correspond in all cases to potential energy
minima for which no imaginary vibrational frequency was
found.
490.2
456.3
syn-ClC(O)SSCl ν(S-S)
syn-ClC(O)SSCl ν(S-Cl)
}
4
45.3
a
Reference 5. b Reference 6. c Reference 15. d Reference 16 (liquid
IR). e Reference 17. Reference 18. Reference 19.
f
g
3
. Results and Discussion
i) Cl2 + OCS. A mixture of Cl2, OCS, and Ar in different
(
proportions, for example, 1:2:200, 1:1:200, or 2:1:200, formed
a solid matrix at ca. 15 K which displayed only IR absorptions
-
1 8,14
attributable to free OCS (at 2049.8 cm );
in addition, the
presence of a weakly bound van der Waals complex OCS‚‚‚
Cl2 was revealed by some changes in the patterns of the
fundamental bands associated with the parent OCS molecule.
Subsequent irradiation of the matrix with broad-band UV-
vis light (200 e λ e 800 nm) led, however, to drastic changes
in the IR spectrum. Table 1 lists the wavenumbers of all the
new absorptions observed to develop under these conditions,
together with the literature data for the OC‚‚‚Cl2 van der Waals
-
1
Figure 1. FTIR spectra in the 2000-900 cm region for an Ar matrix
containing Cl and OCS (Cl
2
2
/OCS/Ar ) 1:1:200) immediately after
deposition (bottom) and after 5 h of photolysis (top).
its wavenumber must arise from the free CO molecule resulting,
together with S atoms, from the photodissociation of OCS. As
reported recently, the CO interacts with the Cl molecules to
form the weakly bound van der Waals complex OC‚‚‚Cl2.
Figures 1 and 2 show two different regions of the IR spectra of
such a matrix, first immediately after deposition and then after
broad-band UV-vis irradiation for 5 h.
Once formed by interaction of the photoproducts CO and Cl ,
the products OCCl and ClCO gave absorptions whose intensi-
ties varied with photolysis time, as previously reported, in a
way suggesting that the radical is an intermediate stage in the
formation of OCCl (see Figure 3). The results imply that the
reactions depend on the photodissociation of Cl2 and the
subsequent addition of the resulting Cl atoms variously to either
S atoms, CO, or ClCO , with little contribution from concerted
5
5
•
6
15
8
complex, the free CO molecule, the ClCO radical, OCCl2,
1
6
17
4,5
syn-ClC(O)SSCl, the OCCl2‚‚‚Cl2 complex, syn-ClC(O)-
2
SCl,1 and SCl2; with the single exception of syn-ClC(O)-
SSCl, for which literature data are scarce, all these products
have previously been characterized by their IR spectra under
comparable conditions. Four of the new bands, centered near
8
19
-
1
1
810, 840/837, 581, and 572 cm , are recognizable as the
2
•
fundamentals ν1, ν5, ν4, and ν2, respectively, and two others,
2
-
1
3
near 1841/1835 and 1010 cm , as combinations or overtones
of the OCCl2 molecule.15 This was formed in what appeared to
be a relatively efficient matrix reaction involving, first, the
2
8
photoproduction of CO and S atoms from OCS and, second,
•
the subsequent photoreaction of CO and Cl2. All the bands
showed a significant structure due in part to isotopic splitting
•
3
5
37
9
(
from Cl/ Cl) and in part to matrix site effects.
addition of Cl to CO.
2
First to appear after broad-band UV-vis photolysis, however,
To distinguish the bands corresponding to the different species
formed in the matrix, and help determine the sequence of the
-
1
was a band centered near 2138 cm which on the evidence of

2676 J. Phys. Chem. A, Vol. 110, No. 8, 2006
Tob o´ n et al.
SCHEME 1: Products Formed after Broad-Band UV-
Vis Photolysis of an Ar Matrix Containing a Mixture of
Cl2 and OCS at ca. 15 K
-
1
Figure 2. FTIR spectra in the 900-400 cm region for an Ar matrix
containing Cl and OCS (Cl /OCS/Ar ) 1:1:200) immediately after
2
2
deposition (bottom) and after 5 h of photolysis (top).
SCHEME 2: Products Formed after Broad-Band UV-
Vis Photolysis of an Ar Matrix Containing a Mixture of
Br2 and OCS at ca. 15 K
changes, the integrated intensities of the new bands have been
plotted as a function of irradiation time, as depicted in Figure
•
3. Besides the bands belonging to OCCl2, SCl2, CO, and ClCO ,
a new set of bands with a common growth pattern and
-
1
wavenumbers near 1773, 804, 548, 490, and 456 cm was
tentatively assigned, respectively, to the ν(CdO), νas(Cl-C-
S), νs(Cl-C-S), ν(S-S), and ν(S-Cl) normal modes of syn-
ClC(O)SSCl. This assignment is based on comparisons with
2
Br2/OCS. Whereas with Br2, syn-BrC(O)SBr is formed as a
1
6
the IR spectra reported for ClC(O)SSCl as a liquid film and
major product, the photochemical changes evolve rather dif-
ferently with Cl2 (see Schemes 1 and 2).
(ii) ICl + OCS. Similar studies were carried out with
matrixes formed by mixtures of ICl, OCS, and Ar, typically in
the proportion 2:1:200. The IR spectrum of such a matrix
measured immediately after deposition was dominated by the
absorptions of OCS, with evidence of some perturbation due
to the interaction of OCS with ICl to form one or more van der
Waals complexes OCS‚‚‚ICl. Irradiation with broad-band UV-
vis light led to significant changes, as illustrated in Figure 4
for three different regions of the spectrum. Table 3 lists the
wavenumbers of the absorptions seen to develop in these
conditions, as well as the proposed assignments. As in the
experiment with Cl2, the reaction is initiated by the photodis-
1
9
in CDCl3 solution, although no more than three fundamentals
were then identified. The other two bands, not reported
previously, are in accordance with the results of theoretical
calculations, as revealed in Table 2. The calculated vibrational
spectrum corresponds to a syn structure for the molecule that
was found to be the energy minimum over the potential energy
surfaces.21
8,14
The yield of OCCl2, the major product formed in these
experiments, was found to increase as the concentration of Cl2
increases. An excess of Cl2 relative to the OCS leads to an
increased yield of syn-ClC(O)SCl, SCl2, and syn-ClC(O)SSCl.
A remarkable difference is thus revealed between the matrix
photochemistry of the system Cl2/OCS and that of the system
8
sociation of OCS to give CO and S atoms. The subsequent
•
Figure 3. Plots as a function of irradiation time of the intensities of the bands assigned to (a) OCCl
syn-ClC(O)SSCl in the IR spectrum of a matrix with the initial composition Cl /OCS/Ar ) 1:1:200.
2
, (b) SCl
2
, (c) CO and ClCO , and (d)
2

Isolation of syn-Iodocarbonylsulfenyl Bromide
J. Phys. Chem. A, Vol. 110, No. 8, 2006 2677
TABLE 2: Comparison of the Wavenumbers and Intensities of the IR Bands Due to the Photoproduct Believed to Be
a
syn-ClC(O)SSCl with Previous Reports and with the Results of Theoretical Calculations with Different Models
vibrational mode
Ar matrix IR (cm-1)
CDCl
3
solnb
filmc
HF/6-31+G*d
B3LYP/6-31+G*d
MP2/6-31+G*d
ν(CdO)
1772.9 (97)
803.8 (100)
1780
780
1795
795
1840.2 (65)
854.3 (100)
574.5 (2)
566.1 (13)
523.3 (2)
494.0 (7)
436.5 (1)
1866.3 (57)
796.1 (100)
567.0 (1)
1795.3 (43)
857.7 (100)
574.1 (1)
593.6(24)
536.8 (1)
497.8 (9)
441.5 (2)
ν
as(Cl-C-S)
δ(Cl-C-S)
ν
s
(Cl-C-S)
547.9 (1)
490.2 (2)
456.3 (4)
445.3 (?)
554.1 (3)
ν(S-S)
490
495.4 (<1)
450.1 (13)
414.3 (4)
ν(S-Cl)
δ(OdCsS)
a
Relative intensities given in parentheses. b Reference 20. c Reference 16. d Wavenumbers scaled by a factor of 0.9.
SCHEME 3: Products Formed after Broad-Band UV-
Vis Photolysis of an Ar Matrix Containing a Mixture of
ICl and OCS at ca. 15 K
Figure 4. FTIR spectra of an Ar matrix containing ICl and OCS (ICl/
OCS/Ar ) 0.5:1:200) immediately after deposition (bottom) and after
2
40 min of photolysis (top).
interaction of CO and ICl gives products, which display IR
TABLE 3: Wavenumbers and Assignments of the IR
Absorptions Appearing after Broad-Band UV-Vis
Photolysis of an Ar Matrix Containing a Mixture of OCS
and ICl at ca. 15 K
bands in the ν(CdO) region at 2157/2155, 2145, 2141, 2138,
-
1
5
2
137, and 2128 cm . As described previously, these can be
attributed to the species OC‚‚‚ICl, OC‚‚‚ClI, OC‚‚‚Cl2, free CO,
CO‚‚‚ClI, and CO‚‚‚ICl, respectively. The appearance of not
wavenumber
reported
•
Ar matrix
ν (cm-1)
assignment
vibrational mode
only the adduct OC‚‚‚Cl2 but also the radical ClCO and OCCl2
molecule
previously
merits some comment.
a
As in the experiments with Cl2, bands characteristic of OCCl2
2
2
2
156.8
154.6
145.0
2157.0
2154.0
2145.6
OC‚‚‚ICl
OC‚‚‚ClI
ν(CdO)
ν(CdO)
-1 15
•
}
}
(near 1815 and 840 cm ) and the ClCO radical (1876.9
a
-1 6
cm ) were clearly in evidence. In the absence of Cl2 in the
}
•
2
144.2a
initial deposit, the intermediacy of Cl atoms is plainly indicated
2140.8
2138.1
2136.6
2128.4
1876.9
OC‚‚‚Cl
2
ν(CdO)
ν(CdO)
ν(CdO)
ν(CdO)
ν(CdO)
2140.7
2138.2
by the evolution of these products and of the adduct OC‚‚‚Cl2.
New bands belonging, on the evidence of a common growth
pattern, to a single product were also observed near 1799 and
a
free CO
CO‚‚‚ClI
CO‚‚‚ICl
ClCO‚
2136.5a
2128.4a
-1
35
37
1876.7b
751 cm . The wavenumbers and evidence of Cl/ Cl isotopic
c
1815.58
splitting suggest a molecule incorporating a ClsCdO fragment,
1
1
1
815.2
814.1
810.3
1814.78
1814.26
1813.56
and the most plausible conclusion is that it is the carbonyl iodide
chloride, IC(O)Cl.
OCCl
2
ν(CdO)
3
}
}
}
Once again, the primary reaction involves UV photodisso-
1810.12
8
d
ciation of OCS into CO and S atoms; there is then competition
1
1
799.1
796.7
1801.5
1799.2
IC(O)Cl
ν(CdO)
between the halogen atoms generated by the dissociation of ICl
and the S atoms to add to the CO either to form species such
as OCCl2, IC(O)Cl, syn-ClC(O)SCl, syn-ClC(O)SSCl, and
}
1
796.7
e
1
772.4
syn-ClC(O)SSCl ν(CdO)
1795
c
8
8
8
8
8
8
37.36
37.20
36.38
36.22
35.37
•
ClCO or to regenerate OCS (see Scheme 3). No trace of the
molecules ClC(O)SI, IC(O)SCl, ISCl, or SI2 came to light in
the spectra.
8
40.3
OCCl
2
ν
as(Cl-C-Cl)
}
Figure 5 shows how the various bands grow as a function of
irradiation time. Thus, bands originating in OCCl2, IC(O)Cl,
35.23
f
812.3
02.8
syn-ClC(O)SCl
syn-ClC(O)SSCl
ν
as(Cl-C-S)
as(Cl-C-S)
812.4
•
free CO, ClCO , and syn-ClC(O)SSCl show similar behavior
8
ν
795e
in the way they evolve with time. This analysis seems therefore
to confirm our interpretation, including the formation of the
disulfide species syn-ClC(O)SSCl. No photolability signs of syn-
ClC(O)SSCl have been found so far.
d
7
7
7
7
54.2
53.1
51.4
50.1g
7
51.3
IC(O)Cl
ν
ν
as(I-C-Cl)
}
3
5
35
5
17.2
SCl
2
as ( Cl-S- Cl)
517.5
(
iii) IBr + OCS. Similar experiments were carried out with
a
Reference 5. b Reference 6. Reference 15. Reference 3. e Ref-
c
d
Ar matrixes doped with IBr and OCS, typically in the propor-
f
g
erence 16 (liquid IR). Reference 18. Reference 19.
tions IBr/OCS/Ar ) 0.5:1:200. The most prominent features in

2678 J. Phys. Chem. A, Vol. 110, No. 8, 2006
Tob o´ n et al.
•
Figure 5. Plots as a function of irradiation time of the intensities of the bands assigned to (a) OCCl
2
, (b) IC(O)Cl, (c) CO and ClCO , and (d)
syn-ClC(O)SSCl in the IR spectrum of a matrix with the initial composition ICl/OCS/Ar ) 0.5:1:200.
Figure 7. 800-400 cm- region of the FTIR spectra of an Ar matrix
containing IBr and OCS (IBr/OCS/Ar ) 0.5:1:200) immediately after
deposition (bottom) and after 240 min of photolysis (top).
1
Figure 6. 1850-1750 cm-1 region of the FTIR spectra of an Ar matrix
containing IBr and OCS (IBr/OCS/Ar ) 0.5:1:200) immediately after
deposition (bottom) and after 240 min of photolysis (top).
the IR spectrum of the initial deposit were again confined to
the OCS regions.8,14 They showed, in addition to the absorptions
characteristic of free OCS, some perturbation of the these
contours arising, we presume, from the presence of one or more
One such product, characterized by bands at 1801/1799 and
58 cm , is readily identified on the basis of the results of
-1
7
earlier studies of the photoinduced matrix reaction between Br2
2
and OCS as the sulfenyl bromide syn-BrC(O)SBr. A second
5
adducts formed by OCS and IBr. Subsequent irradiation of such
-1
product, responsible for the band at 1805 cm and a weak band
-
1
a matrix with broad-band UV-vis light produced several
changes in the spectrum. These can be interpreted for the most
part in terms of the formation of the known van der Waals
complexes OC‚‚‚IBr, OC‚‚‚BrI, and CO‚‚‚IBr, together with free
CO, IC(O)Br, syn-BrC(O)SBr, and SBr2. In addition, however,
the spectrum witnessed the growth of new bands that can be
attributed to the hitherto unknown molecule syn-IC(O)SBr; this
is noteworthy for incorporating, apparently for the first time,
the IC(O)S- group (see Figures 6 and 7 and Table 4).
Identification of the different products was aided by scrutiny
of how the new bands grow as a function of irradiation time
correlating with it at 657 cm , is then most likely to be the
3
mixed carbonyl dihalide BrC(O)I. A third product, readily
-
1
identified by its absorption at 419 cm , is the triatomic
2
2
molecule SBr2. On the basis of the results of our quantum
chemical calculations, the set of bands occurring near 1790,
-
1
700, and 423 cm is identified with the new molecule syn-
IC(O)SBr. None of the experiments gave any sign of the band
-
1
3
at 2045.7 cm associated with the Br‚‚‚CO radical, but with
the generally rather low concentrations of photoproducts, we
attach no particular significance to this apparent omission.
Scheme 4 details some of the feasible reactions of the photo-
reaction between IBr and OCS.
(Figures 8 and 9).

Isolation of syn-Iodocarbonylsulfenyl Bromide
J. Phys. Chem. A, Vol. 110, No. 8, 2006 2679
Figure 8. Plots as a function of irradiation time of the intensities of the bands assigned to (a) syn-BrC(O)SBr, (b) syn-IC(O)SBr, (c) SBr
IC(O)Br in the IR spectrum of a matrix with the initial composition IBr/OCS/Ar ) 0.5:1:200.
2
, and (d)
TABLE 4: Wavenumbers and Assignments of the IR
Absorptions Appearing after Broad-Band UV-Vis
Photolysis of an Ar Matrix Containing a Mixture of OCS
and IBr at ca. 15 K
wavenumber
reported
previously
Ar matrix
ν (cm-1)
assignment
vibrational mode
molecule
OC‚‚‚IBr
OC‚‚‚BrI
free CO
CO‚‚‚BrI
IC(O)Br
2
2
2
2
1
1
1
1
1
1
7
7
6
6
6
6
4
4
150.8
145.0
138.0
136.4
805.0
801.2
799.4
792.6
789.9
787.1
58.3
09.4
99.2
89.8
74.3
56.8
22.7
19.2
ν(CdO)
ν(CdO)
ν(CdO)
ν(CdO)
ν(CdO)
2150.8a
a
2145.5
2138.2a
a
2136.5
1806b
c
1801.0
1799.4
syn-BrC(O)SBr
ν(CdO)
}
}
syn-IC(O)SBr
ν(CdO)
this work
}
syn-BrC(O)SBr
ν
ν
ν
as(Br-C-S)
as(I-C-S)
as(I-C-Br)
758.2b
syn-IC(O)SBr
this work
}
IC(O)Br
658b
syn-IC(O)SBr
ν(S-Br)
ν(S-Br)
this work
SBr
2
418d
a
Reference 5. b Reference 3. c Reference 2. d Reference 22.
The dimensions and vibrational properties of syn-IC(O)SBr
have been calculated by ab initio, DFT methods, and perturba-
tion theory in combination with a 6-31+G* basis set for C, O,
and S and a LANDL2DZ pseudopotential for I and Br, with
the results set out in Tables 5 and 6.
Figure 9. Plots as a function of irradiation time of the intensities of
the bands due to the van der Waals complexes OC‚‚‚BrI, OC‚‚‚IBr,
and CO‚‚‚BrI and free CO in the IR spectrum of a matrix with the
initial composition IBr/OCS/Ar ) 0.5:1:200.
The most intense IR absorptions are predicted to occur near
-
1
1
800, 700, and 420 cm , in persuasive agreement with the
features observed for the new photoproduct. On the evidence
of the calculated wavenumbers and IR intensities, there was
significantly less chance of locating any of the other funda-
mentals under the conditions prevailing in our experiments.

2680 J. Phys. Chem. A, Vol. 110, No. 8, 2006
Tob o´ n et al.
TABLE 5: Experimental and Calculated Values for syn-IC(O)SBra
Ar matrix
theoretical calculations
vibrational
mode
HF/6-31+G*-
LANL2DZ
B3LYP/6-31+G*-
MP2/6-31+G*-
LANL2DZ
ν (cm-1)
792.6
LANL2DZ
1
1
1
7
6
6
6
789.9 (100)
787.1
ν(CdO)
1836.6 (100)
744.2 (84)
1871.9 (100)
706.8 (62)
1785.6 (100)
}
09.4
99.2
89.8
74.3
(80)
νas(I-C-S)
770.4 (95)
}
ν
s
(I-C-S)
oop(I-C-S)
ν(S-Br)
522.8 (5)
504.4 (1)
426.0 (7)
537.0 (6)
499.0 (<1)
398.5 (14)
554.7 (5)
518.3 (<1))
379.9 (6)
δ
4
22.7 (15)
a
Relative intensities are given in parentheses.
3
SCHEME 4: Possible Mechanisms of the Photochemical
atom (and presumably also an I atom), the low stability of
which causes it to have little or no influence in directing the
course of the matrix reactions between OCS and XBr (X ) Br
or I) that are set in train by broad-band UV-vis irradiation.
Reaction between IBr and OCS in an Ar Matrix at ca. 15
K
Acknowledgment. The authors acknowledge a British
Council-Fundaci o´ n Antorchas award for British-Argentine
cooperation. C.O.D.V. and R.M.R. thank Jesus College Oxford,
the Consejo Nacional de Investigaciones Cient ´ı ficas y T e´ cnicas
(CONICET) (PIP 4695), the Comisi o´ n de Investigaciones
Cient ´ı ficas de la Provincia de Buenos Aires (CIC), and the
Facultad de Ciencias Exactas, Universidad Nacional de La Plata
for financial support. R.M.R. is also grateful to the Fundaci o´ n
Antorchas and to the Royal Society of Chemistry for a grant
for international authors. In addition, A.J.D. is indebted to the
EPSRC for support allowing the purchase of equipment, while
Y.A.T. acknowledges a Deutscher Akademischer Austausch
Dienst (DAAD) award. C.O.D.V. especially acknowledges the
DAAD for its generous sponsorship of the DAAD Regional
Program of Chemistry of the Republic of Argentina (supporting
Latin-American students for a Ph.D. program in La Plata).
TABLE 6: Geometrical Parameters for syn-IC(O)SBr
Calculated with Different Theoretical Approximations Using
a 6-31+G* Basis Set for C, O, and S and a LANL2DZ
Pseudopotential for Br and I
geometrical
parameter
HF
B3LYP
MP2
r(CdO)
1.1592
2.1842
1.7718
2.1839
1.1833
2.2406
1.7654
2.2337
104.9
123.7
131.4
1.2025
2.1941
1.7544
2.2915
r(C-I)
References and Notes
r(C-S)
r(S-Br)
(
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R(I-C-S)
R(IsCdO)
R(OdCsS)
R(C-S-Br)
109.0
107.4
122.4
128.6
102.1
123.6
129.1
102.4
(
2001, 2638-2639.
103.3
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have been shown to give rise to one or more carbonyl dihalide
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•
of the ClCO radical which is formed from OCS and XCl (X )
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Isolation of syn-Iodocarbonylsulfenyl Bromide
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