Structure and photochemistry of a novel tetrazole-saccharyl conjugate isolated in solid argon

Article abstract of DOI:10.1016/j.molstruc.2012.04.081

A combined matrix isolation FTIR and theoretical DFT/B3LYP/6-311++G(3df, 3pd) study of the novel synthesised tetrazole-saccharyl conjugate 2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3(2H)-one 1,1-dioxide [1-TE-BZT] was performed. In the gas phase, at room temperature, the compound exists as a mixture of six isomeric forms (four conformers of 1H tautomer and two conformers of 2H tautomer). According to theoretical calculations, conformers 1H were the most stable and the relative energies among the three most stable forms are lower than 4 kJ mol^-1. These conformers benefit from stabilising intramolecular hydrogen bonds-like interactions involving the 1H of the tetrazole ring and the carbonyl oxygen of the saccharyl moiety. The photochemistry of 1-TE-BZT in solid argon was investigated and theoretical DFT/B3LYP/6-311++G(3df,3pd) calculations also helped in assignment of the experimental bands. A quick consumption of the compound occurred after irradiation of the matrix with UV laser light at λ = 275 nm. Three photofragmentation pathways were proposed, one leading to 2-[1-(1H-diaziren-3- yl)ethyl]-1,2-benzisothiazol-3(2H)-one 1,1-dioxide and molecular nitrogen, a second one giving 2-(1,1-dioxide-3-oxo-1,2-benzisothiazol-2(3H)-yl) propanenitrile and azide, and a third one involving loss of azide from the tetrazole ring and decarbonylation of the saccharyl ring of 1-TE-BZT to give acrylonitrile and 7-thia-8-azabicyclo[4.2.0] octa-1,3,5-triene 7,7 dioxide. The comparison of the relative intensities of the bands of the photoproducts obtained from the three channels allowed us to consider the latter pathway, involving an unprecedented photocleavage of the benzisothiazole (saccharyl) ring, as the preferred photodegradation channel of 1-TE-BZT.

Full text of DOI:10.1016/j.molstruc.2012.04.081

Journal of Molecular Structure 1025 (2012) 105–116
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structure and photochemistry of a novel tetrazole-saccharyl conjugate isolated
in solid argon
a,
A. Ismael a, A. Borba b, L. Duarte b, B.M. Giuliano b, A. Gómez-Zavaglia b,c, , M.L.S. Cristiano
⇑
⇑
a CCMAR and Department of Chemistry and Pharmacy, FCT, University of Algarve, P-8005-039 Faro, Portugal
b Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal
c Center for Research and Development in Food Cryotechnology (CIDCA), La Plata, Argentina
h i g h l i g h t s
"
"
"
"
"
A novel tetrazole-saccharyl conjugate (1-TE-BZT) was synthesised.
1-TE-BZT was isolated in argon matrices.
The photochemistry of 1-TE-BZT was investigated.
Three photofragmentation pathways involving both the cleavage of the tetrazole and the saccharyl moieties were proposed.
On the basis of quantum chemical calculations, the proposed photoproducts could be assigned.
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 8 May 2012
A combined matrix isolation FTIR and theoretical DFT/B3LYP/6-311++G(3df,3pd) study of the novel
synthesised tetrazole-saccharyl conjugate 2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3(2H)-one
1,1-dioxide [1-TE-BZT] was performed. In the gas phase, at room temperature, the compound exists as
a mixture of six isomeric forms (four conformers of 1H tautomer and two conformers of 2H tautomer).
According to theoretical calculations, conformers 1H were the most stable and the relative energies
among the three most stable forms are lower than 4 kJ molꢀ1. These conformers benefit from stabilising
intramolecular hydrogen bonds-like interactions involving the 1H of the tetrazole ring and the carbonyl
oxygen of the saccharyl moiety.
Keywords:
Saccharin
Tetrazole
Molecular structure
Matrix isolation
Photochemistry
The photochemistry of 1-TE-BZT in solid argon was investigated and theoretical DFT/B3LYP/
6-311++G(3df,3pd) calculations also helped in assignment of the experimental bands. A quick consump-
tion of the compound occurred after irradiation of the matrix with UV laser light at k = 275 nm. Three
photofragmentation pathways were proposed, one leading to 2-[1-(1H-diaziren-3-yl)ethyl]-1,2-ben-
zisothiazol-3(2H)-one 1,1-dioxide and molecular nitrogen, a second one giving 2-(1,1-dioxide-3-oxo-
1,2-benzisothiazol-2(3H)-yl)propanenitrile and azide, and a third one involving loss of azide from the
tetrazole ring and decarbonylation of the saccharyl ring of 1-TE-BZT to give acrylonitrile and 7-thia-8-
azabicyclo[4.2.0] octa-1,3,5-triene 7,7 dioxide. The comparison of the relative intensities of the bands
of the photoproducts obtained from the three channels allowed us to consider the latter pathway, involv-
ing an unprecedented photocleavage of the benzisothiazole (saccharyl) ring, as the preferred photodeg-
radation channel of 1-TE-BZT.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
tetrazoles, most of the applications derive from the acid/base prop-
erties of the tetrazolic acid fragment, ACN4H, which acts as a met-
Tetrazoles and benzisothiazoles are nitrogen heterocycles with
important applications in major areas, such as medicine, agricul-
ture, imaging technology and food chemistry. In the case of
abolically stable surrogate for the carboxylic acid group [1]. These
compounds can find wide applications in coordination chemistry,
as ligands. It has been demonstrated that the heterocycle tetrazole
is able to participate in at least nine distinct types of coordination
modes with metal ions, in the construction of novel metal–organic
frameworks. Furthermore, the coordination ability of the tetrazolyl
ligand through four nitrogen electron-donating atoms allows it to
serve as a bridging building block in supramolecular assemblies.
⇑
Corresponding authors. Address: Center for Research and Development in Food
Cryotechnology, La Plata, RA 1900, Argentina. (A. Gómez-Zavaglia).
E-mail addresses: angoza@qui.uc.pt (A. Gómez-Zavaglia), mcristi@ualg.pt
(M.L.S. Cristiano).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.04.081

106
A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
1,2-Benzisothiazole-3one 1,1-dioxide anions (deprotonated sac-
charines), also interact with metal centres, mostly through hydro-
gen bonding [2,3].
simplification is very useful for mechanistic elucidations and for
the study of intermediates that are unstable at room temperature
but that can be trapped in the matrices. Therefore, in this paper
we describe the structure and scrutinise the photochemistry of a
novel alkyl-linked tetrazole-saccharyl conjugate, 2-[1-(1H-tetra-
zol-5-yl)ethyl]-1,2-benzisothiazol-3(2H)-one (1-TE-BZT), isolated
in solid argon. The experimental results are supported by quantum
chemical calculations undertaken at the DFT(B3LYP)/6-
311++G(3df,3pd) level of theory. As detailed below, unprecedented
information concerning the matrix photochemistry of this tetra-
zole-saccharyl system was gathered.
Tetrazolyl and saccharyl ethers have particularly important
synthetic uses as intermediate compounds for reductive cleavage
of the CAO bond in allyl- benzyl- and naphthyl alcohols and phe-
nols catalysed by transition metals [4–7]. Much of the reactivity
of these ethers is ascribed to changes in bond lengths around the
central CHARAOACA ether bonds (HAR = heteroaromatic ring and
A = alkyl allyl, benzyl, phenyl or naphthyl group), caused by the
powerful electron-withdrawing effect of the benzisothiazole ring
system. The neat result of these electronic changes determines a
molecular structure in which the originally strong CAAO bond in
the alcohol or phenol lengthens becoming easily cleavable in the
ether whereas the CHARAO bond acquires a considerable degree
of double bond character. As such, thermal treatment of these com-
pounds leads to easy cleavage of the CAAO bond together with the
formation of a CHAR@O bond [8–12]. The thermally induced isom-
erisation of various allyloxy- and alkoxy-benzisothiazoles was
investigated and proved to involve intramolecular migration of
the allyl or alkyl groups from O to N and occur through an intramo-
lecular sigmatropic rearrangement.
2. Experimental and computational methods
2.1. Synthesis
The synthetic route to 2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-ben-
zisothiazol-3(2H)-one 1,1-dioxide (1-TE-BZT) is presented in
Fig. 1. Experimental details for the compounds prepared are as
follows.
2.1.1. 1-(1H-tetrazol-5-yl)ethanol, 2
Considering the wide interest demonstrated in tetrazole and
benzisothiazole heterocycles as multidentate nitrogen ligands
[13,14], efforts were made to prepare tetrazole-saccharyl conju-
gates with various linkers and to investigate their structure and
reactivity. Our previous works revealed that the bensizothiazole
moiety is photochemically stable whereas tetrazoles are highly
photoreactive [14–22]. Thus, combining the apparent photochem-
ical inertness of the benzisothiazole moiety with the high reactiv-
ity of the tetrazole moiety appeared to us as a challenge for this
investigation. If the benzisothiazole moiety proves photochemi-
cally inert upon photolysis, then new saccharyl derivatives result-
ing from photolysis of the tetrazole ring may be produced.
Alternatively, if conditions for photocleavage of the benzisothiaz-
ole moiety are established, photolysis of the tetrazole-saccharyl
conjugate will probably produce a set of new compounds, opening
ways for the development of synthetic pathways to new scaffolds.
Also, to the best of our knowledge the available information related
to the photochemistry of bensizothiazoles is still very scarce and
all published data report photochemistry in solution [23–26]. This
scenario prompted us to explore the photolysis of the benziso-
thiazolyl-tetrazole conjugate by matrix isolation FTIR spectros-
copy. The fact that in a cryogenic inert matrix the photochemical
processes are cage-confined (molecular diffusion is inhibited)
introduces a useful simplification to the study of the photochemi-
cal reactivity since no cross reactions can, in principle, take place
and only primary unimolecular reactions are expected. Such
Prepared from sodium azide (1.43 g; 22 mmol), zinc bromide
(4.50 g; 20 mmol) and 2-hydroxy-propanenitrile 1 (1.45 mL g;
20 mmol), in water (50 mL). The reaction mixture was refluxed
for 20 h with vigorous stirring. White amorphous powder (1.70 g;
75% yield). IR mmax (cmꢀ1): 3390 (OH), 1696, 1624, 1243, 1123;
1H NMR (CDCl3): d 7.55 (br, 1H), 7.22–7.35 (q, 1H), 7.35 (d, 3H);
MS (EI), m/z 115 (33%) [M+H]+, 1 m/z 132 (100%) [M+NH4]+. Acc.
Mass (CI): found, 115.1145; calcd. for C3H7N4O, 115.1134.
2.1.2. 3-Chloro-1,2-benzisothiazole 1,1-dioxide, 3
Prepared from saccharin (10.2 g; 56 mmol), and phosphorus
pentachloride (14.0 g; 66 mmol) heated at 180 °C. Colourless nee-
dles from trichloromethane (7.00 g; 63% yield), m.p. 143–145 °C.
IR
m
max: 1724, 1654, 1603 (C@C), 1346 (SO2), 775 (ArAH) and
692 (CACl) cmꢀ1
;
1H NMR (CDCl3): d 7.85 (4H, m, ArAH); Anal.
calcd. for C7H4NO2SCl: C, 41.7; H, 2.0; N, 7.0%, found: C, 41.5; H,
2.0; N, 6.9%; MS (EI), m/z 201 [M]+.
2.1.3. 2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3(2H)-one 1,1-
dioxide 5
A mixture of 1-(1H-tetrazol-5-yl)ethanol 2 (0.20 g; 1.75 mmol),
3-chloro-1,2-benzisothiazole 1,1-dioxide (0.35 g; 1.75 mmol) and
potassium tert-butoxide (0.65 g; 5.25 mmol, in dry THF (50 mL),
was stirred at 60 °C under a nitrogen atmosphere, until TLC analy-
sis (DCM/toluene 3:1) indicated the absence of starting material
(48 h). Work-up afforded a pale yellow powder (0.28 g; 58% yield),
m.p. 210–211 °C identified as 1-TE-BZT, 5. IR
mmax: 3091, 2974,
1721, 1593, 1463, 1336 (SO2), 1177 cmꢀ1 1H NMR (CDCl3): d
;
Table 1
8.05–8.08 (d, 1H), 7.91–7.95 (m, 2H), 7.86–7.90 (d, 1H), 5.26 (1H,
d), 1.39–1.41 (d, 3H); MS (EI), m/z 279 [M]+; Acc. Mass (CI):
found = 280.1089, calcd. for C10H10N5O3S: 280.1022.
Zero point corrected relative energies (
311++G(3df,3pd) level of theory of the various conformers of 1-TE-BZTa and average
energies (ꢀ
H/kJ molꢀ1) for intramolecular interactions involving the NH group in 1H
conformers of 1-TE-BZT, calculated using equations 1 and 2 (see text).b
D
E0/kJ molꢀ1) obtained at the DFT(B3LYP)/6-
D
2.2. Infrared spectroscopy and photochemical experiments
Tautomer Conformer
D
E0 DFT(B3LYP)/
NHꢁ ꢁ ꢁO@X
D
m
NH
ꢀ
DH
6-311++G(3df,3pd)
(nm)
(cmꢀ1
) )
(kJ molꢀ1
The infrared (IR) spectra of 1-TE-BZT were obtained using a
Nicolet 6700 Fourier transform infrared spectrometer equipped
with a deuterated triglycine sulphate (DTGS) detector and a
Ge/KBr beam splitter, with 0.5 cmꢀ1 spectral resolution. Matrices
were prepared by co-deposition, onto the cooled CsI substrate of
the cryostat, of the matrix gas (argon 99.9998%, obtained from
Air Liquide) and vapours of the compound under study produced
by evaporation in a specially designed temperature variable
mini-oven assembled inside the cryostat. The temperature of the
1H
G0Sk0
GSk0
G0Sk
GSk
0.0 (ꢀ3370201.670)c 0.2047
175.4 16.1
194.5 17.2
129.8 13.1
119.8 12.4
2.59
4.25
8.30
0.2012
0.2150
0.2179
2H
G0G0
GG0
7.12
8.60
Energies in kJ molꢀ1; conformers are depicted in Fig. 3.
See Fig. 1 for atom numbering.
Total energies with zero point vibrational energy contribution.
a
b
c

A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
107
Cl
N
S
CH3
N
O2
CH3
N
O
H3C
H
N
NH
N
NaN3/ZnBr2
water/reflux
3
HO
N
N
OH
N
N
N
S
1
O2
2
4
O
CH3
N
S
NH
N
O2
N
N
5
Fig. 1. Synthetic approach to 2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3(2H)-one 1,1-dioxide.
mini-oven used for evaporation of the compounds was ca. 335 K.
The low temperature experiments were done on the basis of an
APD Cryogenics close-cycle helium refrigeration system with a
DE-202A expander. The temperature of the CsI substrate during
deposition was 15 K.
The matrices were irradiated through the outer quartz window
of the cryostat, with the frequency-doubled signal beam of the
Quanta-Ray MOPO-SL pulsed (10 ns) optical parametric oscillator
(FWHM ꢂ0.2 cmꢀ1, repetition rate 10 Hz, pulse energy ꢂ2.5 mJ)
pumped with a pulsed Nd:YAG laser.
may occur through both [3,30]- and [1,30]-processes [8,10], the
relative proportion of isomerisation products depending on struc-
tural features of the starting ether such as electron density and ste-
ric hindrance on the allylic system, polarity of the reaction medium
and temperature. It was also observed that the saccharyl derivative
of the cyclic allyl alcohol myrtenol isomerises at room temperature
with exclusive formation of the [1,30]-product. This behaviour was
interpreted on the basis of steric constraints imposed by the cyclic
myrtenyl system, which destabilise the transition state required for
concerted [3,30]-migration, preventing its formation [10]. It was
further demonstrated that the [3,30]-products undergo inversion
to the thermochemically more favourable [1,30]-isomers upon ex-
tended heating [8]. It is not clear whether the [1,30]-rearrangement
in these ethers occurs through a fragmentation–recombination pro-
cess or through a pseudo-pericyclic mechanism. Recently, the ther-
mal isomerisation of neat 3-allyloxysaccharin was investigated in
the liquid phase, combining matrix-isolation FTIR spectroscopy, dif-
ferential scanning calorimetry and quantum chemical calculations.
From the results, a [3,30]-sigmatropic shift mechanism for the isom-
erisation in the liquid phase was proposed [36]. We have also dem-
onstrated that the isomerisation of 3-methoxy-saccharin in the
solid-state and in the gas phase occurs through a Chapman-type
mechanism [11,12]. Considering this scientific background, it was
reasonable to expect that compound 4 would easily isomerise to
the target conjugate 5, and a synthetic approach making use of this
reaction was therefore devised. Furthermore, migration of the alkyl
group from O to N in ether 4 was expected to be easier than in the
case of 3-methoxy-saccharin due to increased stabilisation of the
carbocation-like migrating moiety. In fact, ether 4 could not be iso-
lated because it readily isomerises to conjugate 1-TE-BZT, 5, as
could be demonstrated by FTIR and NMR (see Section 2.1.3).
2.3. Computational methods
The quantum chemical calculations were performed at the DFT
level of theory using the standard 6-311++G(3df,3pd) basis set
[27–31] and the three-parameter density functional abbreviated
as B3LYP, which includes Becke’s gradient exchange correction
[32] and the Lee, Yang, Parr correlation functional [33]. Geometri-
cal parameters were optimised using the Direct Inversion in the
Iterative Subspace (DIIS) method [34]. The optimisation of geome-
tries was followed by harmonic frequency calculation at the same
theory level. The nature of the obtained stationary points was
checked through analysis of the corresponding Hessian matrix.
Calculations were carried out using the Gamess program [35].
The calculated harmonic frequencies (scaled with the factor
0.978 [14]) were used to assist the analysis of the experimental
spectra and to account for the zero-point vibrational energy (ZPVE)
corrections.
3. Results and discussion
3.1. Synthesis of 2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-
3(2H)-one 1,1-dioxide
3.2. Geometries and energies of 1-TE-BZT
The synthetic route to 1-TE-BZT is presented in Fig. 1 and in-
volves a convergent strategy whereby the tetrazolyl and saccharyl
building blocks, 2 and 3, are prepared separately and then coupled
to form the ethyltetrazole-saccharyl ether 4 that subsequently
isomerises to the required target compound 5. Sigmatropic isomeri-
sation in saccharyl ethers has been studied by our groups. An earlier
investigation of the thermal isomerisation of allyl-saccharyl ethers
in solution, revealed that migration of the allyl group from O to N
Before the discussion of geometries and energies of 1-TE-BZT, it
must be underlined that for compounds containing sulphur–oxy-
gen linkages, such as bensizothiazoles, it is relatively difficult to
obtain reliable predictions of their fundamental properties. More
specifically, most of the standard computational methods and basis
sets have been found unable to correctly predict the values of the
S@O bond lengths and of the vibrational frequencies associated
with it [37–40]. To overcome this problem, we decided to use

108
A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
Tautomer 1H
O16) (see Fig. 1). All 1H conformers are close in energy and the
slight energy differences can be understood mainly by considering
the distances H28ꢁ ꢁ ꢁO@S or H28ꢁ ꢁ ꢁO@C. Table 1 shows the theoret-
ically calculated NHꢁ ꢁ ꢁO@X distances for all 1H conformers. Iogen-
sen, Rozenberg and coworkers proposed two empirical Eqs. (1) and
(2) allowing the estimation of the hydrogen bond or hydrogen
bond-like interaction strengths [42]. The first correlation (1) allows
13H
6
14O
O15
19CH20,21,22
12H
11H
3
1
2
5
S
7
C17
8
N
N25
N26
N
4
9
23
18H
3
estimating the redshift of the
mNH involved in hydrogen bonds or
24
N
hydrogen bond-like interactions.
16 O
27
H10
H28
2-[1-(1H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3 (2H)-one 1,1-dioxide
D
m
NH=cmꢀ1 ¼ 0:011½rHꢁꢁꢁH=nmꢃꢀ6:1
ð1Þ
Tautomer 2H
where
D
m
NH is the redshift induced by the hydrogen bond and
13H
14 O
rHꢁ ꢁ ꢁH is the hydrogen bond distance (NHꢁ ꢁ ꢁO@X in 1-TE-BZT). The
second Eq. (2) correlates the redshift estimated in equation 1 with
the interaction enthalpy, thus describing the energies of the intra-
molecular hydrogen bondings involving the NH group of 1H
conformers.
O15
19CH20,21,22
6
12 H
11 H
3
5
1
S
7
C17
8
N
N
25
4
9
23
2
18 H
N26
N27
H28
3
24 N
O16
H10
D
H2 ¼ 1:92 ꢄ ½
D
ðmNHÞ ꢀ 40ꢃ
ð2Þ
where
D
H is the interaction enthalpy (in kJ molꢀ1) and
D
m
NH),
2-[1-(2H-tetrazol-5-yl)ethyl]-1,2-benzisothiazol-3 (2H)-one 1,1-dioxide
the redshift obtained from Eq. (1). Table 1 also shows the values
corresponding to H. When compared the hydrogen
NH) and ꢀ
Fig. 2. Schematic representation of the two tautomeric forms of 1-TE-BZT with
adopted atom numbering.
D
m
D
bond energies of 1-TE-BZT with those of other compounds [42], it
can be concluded that hydrogen bonds in 1-TE-BZT are rather
weak. Eventhough, the hydrogen bond-like interactions in 1-TE-
BZT are the main factors contributing for the stabilisation of the
1H conformers, and the relative energies of 1H conformers can
be mainly explained in terms of hydrogen bonds distances. How-
ever, other factors such as repulsions between negatively charged
atoms or slight sterical hindrances (i.e.: the methyl group ad-
dressed to the SO2 is a slightly destabilising factor if compared with
the hydrogen atom) should also be considered.
According to preliminary calculations (not presented) per-
formed at a lower level of theory, all the barriers of interconversion
between the 1H conformers were higher than 30 kJ molꢀ1. Hence,
considering the low relative energies between the three most sta-
ble 1H conformers and the high barriers of interconversion, these
three forms can in principle be isolated experimentally in the ar-
gon matrices (note that due to the higher relative energy, 1H_GSk
form does not have experimental relevance).
the B3LYP functional together with an extensive set of polarisation
functions. As demonstrated in our previous work, this approach
correctly reproduces both the geometry and frequencies of the
hypervalent S@O bonds [41].
1-TE-BZT has a chiral centre, the two enantiomers (R and S
forms) being spectroscopically equivalent. In the present study
we will focus on the R form. The compound may exist in two tau-
tomeric forms (Fig. 2), both having two conformationally relevant
internal degrees of rotation, which are defined by the N8AC17
and C17AC23 bonds. Other tautomers, such as hydroxy benziso-
thiazole forms, could, in principle, be considered. These forms in-
volve transfer of H18 to O16 (the carbonyl oxygen in the saccharin
ring), forming and imino linkage between both heterocycles
(keto–enol tautomerisation). However, taking into account the
lower stability of enol forms and considering the high computa-
tional efforts required for the optimisation of bensizothiazole
derivatives, the enol tautomers have been a priori ruled out [16].
The theoretical calculations at the B3LYP/6-311++G(3df,3pd) le-
vel predicted a total of six minima on the ground state potential
energy surface of 1-TE-BZT. Four minima belong to the conformers
of 1H tautomer and the remaining two correspond to the two
conformers of 2H tautomer. The full set of conformers found for
each tautomer and their calculated relative energies (including
zero point energy corrections) are represented in Fig. 3 and Table
1. Geometrical parameters for the various isomers are given in Ta-
ble S1 (Supporting information). The following systematic rules
were used to attribute names to the different isomeric forms:
C9N8C17C23 is indicated by the first letter (G = gauche, ca. 60°;
G0 = gauche0, ca. ꢀ60°); N8C17C23N24 is indicated by the second
letters (Sk = skew, ca. 120°; Sk0 = skew0, ca. ꢀ120° in tautomer 1H
and G0 = gauche0, ca. ꢀ60° in tautomer 2H). 1H and 2H refer to the
position of H28 in the tetrazole ring.
As explained in the previous paragraph, none of the conformers
of 2H tautomer bears hydrogen bonds-like interactions. The posi-
tion of H28 in the tetrazole ring (2H position), oriented to the oppo-
site side of the bensizothiazole ring precludes the formation of
these stabilising forces, thus explaining the higher relative energies
of 2H conformers and consequently, their non-experimental
relevance.
3.3. Infrared spectra of the matrix-isolated compound
1-TE-BZT has 78 fundamental vibrations, all active in the infra-
red. The infrared spectrum of 1-TE-BZT isolated in an argon matrix
with the substrate kept at 15 K during the matrix deposition is pre-
sented in Fig. 4, together with the calculated spectrum of the
1H_GSk0 form. It must be considered that 1-TE-BZT is a molecule
composed of 28 atoms, 16 of them belonging to the rigid benziso-
thiazole ring. This explains the reason why the bands correspond-
ing to this ring are in general highly overimposed for the different
1H conformers, with the exception of the infrared modes relative
to the oxygen atoms, for which the position strongly depend on
the strength of the hydrogen bonds they establish. This fact makes
especially difficult the assignment of bands to each of the most
stable conformers. For this reason, we decided to simplify the
According to calculations, the conformers belonging to the 1H
tautomer were found to be the most stable forms. The stabilisation
of these forms results from the presence of an intramolecular
hydrogen bond-like (NHꢁ ꢁ ꢁO@X, where X = S, C), that is absent in
all the 2H conformers. The oxygens acting as electron donors are
those bound to C9 and S7 of the saccharine ring (O14, O15 and

A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
109
Tautomer 1H
1H_G'Sk'
0.00 kJ mol-1
(-66.0º; -129.0º)
1H_GSk'
2.59 kJ mol-1
(92.5º; -142.9º)
1H_GSk
1H_G'Sk
4.25 kJ mol-1
(-71.1º; 135.3º)
8.30 kJ mol-1
(73.7º; 118.8º)
Tautomer 2H
2H_GG’
8.60 kJ mol-1
2H_G’G’
7.12 kJ mol-1
(89.1º; -22.8º)
(-63.1º; -16.8º)
Fig. 3. DFT(B3LYP)/6-311++G(3pd,3df) optimised structures of the conformers of 1-TE-BZT. Two perspectives are provided, one with the viewpoint placed above the ring and
the other with the viewpoint along the major axis of the molecule. The C9AN8AC17AC23 and N8AC17AC23AN24 dihedral angles are indicated in parentheses and zero point
corrected relative energies are also shown.
assignments of bands in the freshly deposited matrix and, consid-
deposited compound in an argon matrix we performed the assign-
ment of experimental bands to this low energy form (Table 2). In
ering the nice fitting of the calculated 1H_GSk0 spectrum with the

110
A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
Calculated
0.12
0.10
0.08
0 06.
0.04
0 02.
0.00
Experimental
3600 3400 3200 3000
1800
1600
1400
1200
1000
800
600
Wavenumber / cm-1
Fig. 4. Experimental infrared spectra (3600–600 cmꢀ1 spectral range) of 1-TE-BZT in argon matrix (15 K), and DFT(B3LYP)/6-311++G(3pd,3df) calculated spectrum for
conformer (1H_GSk0). The calculated spectrum was simulated using Lorentzian functions with full width at half maximum of 5 cmꢀ1 with wavenumbers being scaled by
0.978.
agreement with the estimations reported in Section 3.2, the exper-
consumed reagent (1-TE-BZT) and the positive ones, to the
photoproducts.
imental observation of the mNH band at frequencies higher than
3400 cmꢀ1 (Table 2) also indicates that the hydrogen bond-like
interaction is relatively weak.
The calculated spectra for 1H_GSk0 and those of the photoprod-
ucts are also shown for comparison. A schematic summary of the
observed photoprocesses is given in Fig. 6. The following photo-
chemical pathways are proposed: (a) N2 extrusion with the
concomitant production of 2-[1-(1H-diaziren-3-yl)ethyl]-1,2-ben-
zisothiazol-3(2H)-one 1,1-dioxide (BZT-DZ); (b) production of
azide (N3H) and 2-(1,1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-
yl)propanenitrile (BZTC„N); (c) decarbonylation and ejection of
azide (N3H) to give 7-thia-8-azabicyclo[4.2.0] octa-1,3,5-triene
7,7 dioxide (TAOTD) and propene–nitrile. The complete assign-
ment of the bands observed for the different photoproducts is
given in Table 3, together with available previously reported values
for the isolated compounds [43–45] and calculated data.
It must be underlined that the conformation of 1-TE-BZT as re-
agent does not influence the nature of the photoproducts observed
after irradiation. Table S2 provides the complete set of frequencies
of all the 1-TE-BZT isomers.
3.4. UV-irradiation experiments
The photochemistry of different matrix isolated bensizothiaz-
oles and tetrazoles has been addressed by our groups. Photode-
composition of tetrazoles involves cleavage of the tetrazolyl ring,
leading to a variety of photoproducts, including azides, isocyanates
or aziridines. The photochemistry of tetrazoles was also shown to
be influenced by the chemical nature and conformational flexibil-
ity of substituents linked to the heterocycle, which may favour or
exclude certain reaction channels, and also determine the relative
amount of the final photoproducts [15–21].
In order to investigate the photochemical decomposition, the as-
deposited compound was irradiated with UV light as described in
Section 2.2 (Infrared spectroscopy and photochemical experi-
ments). The wavelength used for irradiation has been chosen on
the basis of the UV–Vis spectrum of 1-TE-BZT, which shows two
absorption maxima at 275 and 385 nm (see in Fig. S1, the UV–
Visible spectra of the compound in ethanol solution at room
temperature). Irradiation at 385 nm did not stimulate any
photofragmentation. After each irradiation, the sample was moni-
tored by recording its infrared spectrum.
In Pathway (a), 1-TE-BZT ejects molecular nitrogen to give BZT-
DZ. The ejection of molecular nitrogen is a common photodecom-
position pathway in tetrazoles isolated in rare gas matrices [15–
21]. BZT-DZ has two rotational axes [NAC, and CAC(N2H)] that
can give rise to at least six different conformers (I, II, III, IV, V,
VI), all of them with relative energies below 1.14 kJ molꢀ1 (Table
S3). The most distinctive bands of this photoproduct could be iden-
tified in the irradiated matrices. As mentioned before for 1-TE-BZT,
also in BZT-DZ, 16 out of 26 atoms belong to the bensizothiazole
ring. This means that 42 out of 72 vibrational modes are related
with this ring. This fact explains the high overlap of bands corre-
sponding to the different conformers of BZT-DZ, and also the over-
lap with bands corresponding to BZTC„N [produced in Pathway
(b)]. However, the observation of some bands in relatively clean re-
gions, such as those corresponding to m(N@N) of conformers I and
V, at 1822 and 1803 cmꢀ1 provides evidence for the photoproduc-
tion of BZT-DZ. Note also that the most intense band of the BZT-DZ
Irradiation at 275 nm induces a prompt decrease of the 1-TE-
BZT bands with a concomitant observation of other new bands
corresponding to the photoproduced species. Fig. 5 shows the
spectroscopic results, obtained by subtracting the spectrum of
the as-deposited matrix from the spectrum of the matrix irradiated
during 40 min with laser (k = 275 nm), when almost all reagent
was consumed. In Fig. 5, negative bands correspond to the
is that of
m(C@O) vibrational mode. This band fits nicely the
calculated spectrum and represents another proof of the presence
of BZT-DZ in the irradiated matrix. However, the low intensity of
the m(C@O) experimental band indicates that Pathway (a) is not a
major photodecomposition pathway of 1-TE-BZT. The assignment
of the most relevant bands corresponding to this photoproduct is

A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
111
Table 2
Experimental and calculated [B3LYP/6-311++G(3df,3pd); scaled by 0.978] vibrational frequencies (
m
; cmꢀ1) and calculated IR intensities (I, km molꢀ1) for the 1H_GSk0 form of
1 TE-BZT isolated in argon matrix.a
Approximate description
Calculated 1H_GSk0
Observedb
m
I
m
m
m
m
m
m
m
m
m
m
m
m
m
(NAH)
3468.5
3138.8
3135.8
3125.0
3112.9
3061.3
3058.8
3027.3
2983.8
1753.6
1595.3
1591.6
1531.1
1470.1
1464.4
1461.0
1456.5
1424.9
1388.9
1350.5
1332.7
1328.0
1318.1
1294.1
1282.6
1239.9
1236.3
1169.6
1165.8
1154.7
1140.2
1120.4
1086.3
1064.4
1056.6
1045.9
1038.2
1017.8
1003.3
994.3
262.6
4.2
0.1
2.2
1.3
8.1
5.8
4.3
5.0
302.4
1.7
9.6
39.2
3.5
8.0
3449.1/3445.6/3442.2
2995.3/2984.7
2939.2/2917.2
(CAH)ph
(CAH)ph
(CAH)ph
(CAH)ph
(CH3)as00
(CH3)as0
2913.0/2899.5
(CH18
)
(CH3)s
(C@O)
(CC)ph
(CC)ph
1766.9/1764.4
1602.0
1593.2
1573.1
1496.2
d(NAH) +
m
(C17AC23
)
c
(CH3)00
d(CAH)ph
d(CH3)as00
d(CAH)ph
sci(C23AC17AH18
d(CH3)s
1471.4/1470.3
1469.6
7.3
10.9
12.3
4.4
18.0
4.0
34.2
185.1
18.2
91.0
106.9
329.2
20.9
197.0
81.1
37.9
5.7
)
1463.4/1458.8
1445.0
1351.0
1334.0
1370.8
1368.4/1361.4
1304.5
1297.2/1295.5
1248.1/1245.2/1239.1
d(NAH) +
m(NN)t + d(CAH18
)
00
d(CAH18
d(CAH18) +
(SO2)as
)
+
m
(CC)ph + d(NAH)
m(CC)ph
m
0
d(CAH18
)
m
m
(CC)ph
(NN)t + d(NAH)
d(CAH)ph +
d(CAH)ph +
m
m
(C2AC9) +
(N8AC17)
m
(C9AN8)
1199.0/1189.1/1187.0
m(SO2)s + d(CAH)ph
d(CAH)ph +
d(CH3)as0
d(CH3)as00
d(CH3)as000 + d(NNN)
m
(SO2)s
1183.0/1180.6
1165.1/1161.3
1152.0
n.o.
1135.0/1132.6
1117.0
n.o.
1091.4
n.o.
n.o.
6.2
m
m
(NN)t + d(NNN)t
20.7
20.2
3.3
31.7
0.8
0.0
21.9
5.2
(NN)t + d(CH3)as000
d(CAC)ph
(NN)t
d(CAC)ph
m
c
c
m
c
(CAH)ph
(CH3)0
1025.0
1016.5
n.o.
(NN)t
(CAH)ph
986.4
968.4
0.4
d(C17C19C23H18
(CAH)ph
d Skeletal
)
928.5
886.9
865.6
38.4
0.2
3.8
868.6/867.1
n.o.
835.1
c
c
c
c
c
(CH)ph
(NAH28
(CAH)ph
(NN)t
785.9
766.3
750.4
746.2
734.0
691.4
683.1
675.4
660.0
632.0
573.2
534.8
526.7
497.5
8.4
786.0
753.9
751.9
749.3
733.4/727.7
704.3/703.3
674.3
)
38.3
34.1
13.0
13.8
5.2
13.4
18.9
7.7
12.7
52.6
38.0
41.8
14.7
d(CC)ph
d(CC)ph +
m
(CS)
c(NH28) +
c
(NN)t
d Skeletal
d Skeletal
d Skeletal
663.0
611.2/608.8
592.7
533.6
524.4
c(SO2)
x
s
(SO2)
Skeletal
d Skeletal
508.7
a
m
, stretching, d, bending,
c, rocking, s, torsion, x, wagging, sci, scissoring, s, symmetric, as, anti-symmetric, t, tetrazole ring, n.o., not observed. The infrared region below
500 cmꢀ1 was not investigated; extensively delocalised modes are designated generally as skeletal bending (d skeletal). See Fig. 2 for atom numbering.
also shown in Table 3. Due to the high overlap of bands, the assign-
ment of BZT-DZ has been performed only on the most stable form I.
Only in the regions where a doubtless assignment could be made,
the observation of the band due to the d(NAH) mode at ca.
1127 cmꢀ1. According to the literature [43], this band occurs at
1150 cmꢀ1 in the argon isolated azide. The deviation in the
observed azide d(NAH) band compared with the literature value
for the sole matrix-isolated compound indicates that once pro-
duced from fragmentation of 1-TE-BZT, azide interacts in the same
matrix cage with the other compounds produced in this path
(BZTC„N) and in Pathway (c), where azide is also produced. The
other forms were also considered [i.e.
m(C@N), m(C@O)]. In Pathway
(b), the most intense band of azide was observed in the irradiated
spectrum: 2142 cmꢀ1
: m(N@N@N)as. This band was observed in
the spectrum of azide isolated in argon matrix at 2140 cmꢀ1 [43].
The presence of azide in the photolysed matrix is reinforced by

112
A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
Calculated
Calculated
BZTC≡N conf G
BZTC≡N conf G‘
TAOTD
Azide
Propene-nitrile
BZT-DZ conf I
BZT-DZ conf V
BZTC≡N conf G
BZTC≡N confG'
Propene-nitrile
BZT-DZ confI
BZT-DZ confV
1-TE-BZT
2300
2200
2100
2000
1900
1800
1800
1750
1700
1650
1600
Experimental
0.010
0.005
0.000
Experimental
0.005
0.000
-
0.005
0.010
0.015
-
-
2300
2200
2100
2000
1900
1800
Wavenumber / cm-1
1750
1700
1650
1600
1550
Wavenumber / cm-1
Azide
BZTC≡N conf G
BZTC≡N conf G‘
TAOTD
Calculated
Propene-nitrile
BZT-DZ
1-TE-BZT
1500 1400 1300 1200 1100 1000 900
0.05
0.04
0.03
0.02
0.01
0.00
-0.01
-0.02
Experimental
1500 1400 1300 1200 1100 1000
900
Wavenumber / cm-1
Fig. 5. (Bottom) Infrared difference spectrum [(irradiated matrix by UV light; k = 275 nm; 40 min) minus (as-deposited matrix spectrum)] of 1-TE-BZT in an argon matrix.
Assignments for the bands due to photoproducts (pointing up) are given in Table 3. (Top) Simulation of the infrared difference spectrum shown in the bottom panel of the
figure, based on the DFT(B3LYP)/6-311++G(3pd,3df) calculated spectra for 1-TE-BZT (1H_GSk0; bands pointing down) and for its photoproducts [Azide, BZTC„N (conformer G
and conformer G0), TAOTD, propene–nitrile and BZT-DZ (conformer I and V)]. The intensities of the individual spectra were multiplied by different factors to obtain a better
simulation of the experimental difference spectra.

A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
113
O
O
hν
CH3
S
N
+
N2
Pathway a
NH
O
N
2-[1-(1H-diaziren-3-yl)ethyl]-1,2-benzisothiazol-
3(2H)-one 1,1-dioxide
BZT-DZ
O
O
O
O
CH3
N
S
CH3
S
hν
N
N
N3H
1-TE-BZT
+
H
N
Pathway b
O
O
N
N
N
2-(1,1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-
yl)propanenitrile
Azide
BZTC≡N
H2C
O
O
hν
S
N3H
+
+
+
CO
NH
Pathway c
N
Azide
Propene-nitrile
7-thia-8-azabicyclo[4.2.0]octa-1,3,5-triene 7,7-
dioxide
TAOTD
Fig. 6. Proposed reaction pathways resulting from irradiation of 1-TE-BZT monomer isolated in argon matrix.
hydrogen bonds connecting the different complexes, explain the
shift of the d(NAH) vibrational mode with regard to the matrix iso-
lated pure azide.
evident in the carbonyl region, where only products from (a) and
(b) are observed. In the region 1400–950 cmꢀ1, photoproducts
obtained in all the three pathways are observed. However, the
most intense bands observed in this region in the photolysed
matrices can be ascribed to photoproducts of Pathway (c) (Fig. 5
and Table 3). This fact allows us to consider this pathway as the
preferred photodecomposition channel for 1-TE-BZT.
The other photoproduct obtained in Pathway (b) is BZTC„N.
According to calculations at the DFT(B3LYP)/6-311++G(3df,3pd) le-
vel, only two conformers were found to correspond to minima
structures. They differ in the orientation of the CNCC dihedral
angle: G (CNCC = 91.7) and G0 (CNCC = ꢀ59.5). Their energies are
very close (the relative energies of G and G0 forms are 0 and
0.07 kJ molꢀ1, respectively) and the barrier of interconversion is
ca. 20 kJ molꢀ1. The bands at 2248 and 2241 cmꢀ1 can be assigned
4. Conclusions
In this work, the alkyl-linked saccharyl-tetrazole conjugate
1-TE-BZT has been synthesised and studied from the view point
of its molecular structure and vibrational spectra using matrix
isolation FTIR spectroscopy. All experimental results have been
supported by quantum chemical calculations at a high level of
theory [DFT(B3LYP)/6-311++G(3df,3pd)].
to the
and Table 3). Note that the low experimental intensity of bands
intrinsically strong [i.e. (C@O), (S@O) symmetric and asymmet-
m(C„N) vibrational mode of these two conformers (Fig. 5
m
m
ric], indicates that Pathway (b) is neither a major photodecompo-
sition Pathway.
In Pathway (c), 1-TE-BZT decarbonylates to give TAOTD,
propene–nitrile and azide. The carbon monoxide band is typically
observed at 2138 cmꢀ1 in argon matrices and in this case is over-
In 1-TE-BZT, the hydrogen atom bound to the tetrazole ring
gives rise to two different tautomers, 1H and 2H. In addition, the
two rotational axes of 1-TE-BZT can give rise to different conforma-
tional isomers within each tautomeric form. As a whole, the theo-
retical calculations led to the identification of four conformers 1H
and two conformers 2H. The experimental spectrum obtained from
the as deposited compound could be assigned to conformer
1H_GSk0.
The photochemistry of the saccharyl-tetrazole conjugate 1-TE-
BZT has also been addressed. However, the complexity of the stud-
ied compound makes difficult the analysis of the experimental
information, the interpretations not being conclusive. In this con-
text, considering the high reactivity of the tetrazole ring and the
photostability of the bensizothiazole moiety, three photolysis
pathways were proposed to interpret the photodecomposition
lapped with the m(N@N@N)as band of azide, produced in Pathway
(b) and also in this Pathway. The available information about
propene–nitrile isolated in argon matrices [44] and calculations
at the DFT(B3LYP)/6-311++G(3df,3pd) level of theory aided the
confirmation of propene–nitrile in the photolysed matrix (see for
example experimental bands at 975 and 973 cmꢀ1, ascribed to
the
x(CH2) vibrational mode. The opening of the bensizothiazole
ring gives TAOTD. The most intense bands of this compound occur
in the 1400–950 cmꢀ1 range and fit nicely the calculated spectrum.
The experimental intensity of the bands corresponding to the
photoproducts generated in Pathway (c) is higher than that of
the photoproducts of Pathways (a) and (b). This fact is particularly

114
A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
Table 3
Experimental and calculated [B3LYP/6-311++G(3df,3pd); scaled by 0.978] vibrational frequencies (
m
; cmꢀ1) and calculated IR intensities (I, km molꢀ1) for the observed
photoproducts of 1-TE BZT monomer isolated in argon matrix.a

A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
115
occurred upon matrix irradiation with UV k = 275 nm: (a) ejection
of molecular nitrogen to give at least six different conformers of
BZT-DZ; (b) cleavage of the tetrazole ring to give azide and
BZTC„N, and (c) decarbonylation of 1-TE-BZT to give propene–ni-
trile, azide and TAOTD. The comparison of the relative intensities of
the bands of the photoproducts obtained from the three channels
allowed us to conclude that Pathway (c) is the preferred one.
Although with low efficiency, this was the first time that
photocleavage of the bensizothiazole ring in rare gas matrices
was observed. The pathway proposed opens up several possibilities
in the interpretation of the molecular mechanisms leading to
photodecomposition of such stable aromatic compounds. The fact
that this particular saccharyl derivative is more prone to ring
photocleavage than the ones that we previously attempted to
photolyse, namely alkyl and allyl saccharyl ethers, may be ascribed
to the powerful electron-withdrawing effect of the tetrazole sub-
stituent which deviates electron density from the ring, weakening
the CAC bond to the carbonyl and subsequently favouring
a

116
A. Ismael et al. / Journal of Molecular Structure 1025 (2012) 105–116
[13] L.M.T. Frija, R. Fausto, R.M.S. Loureiro, M.L.S. Cristiano, J. Mol. Cat. A: Chem. 305
(2009) 142.
[14] A. Gómez-Zavaglia, A. Ismael, L.I.L. Cabral, A. Kaczor, J.A. Paixão, R. Fausto,
M.L.S. Cristiano, J. Mol. Struct. 1003 (2011) 103.
cleavage. We now aim at exploring further the photochemistry of
benzisothiazoles.
[15] A. Gómez-Zavaglia, I.D. Reva, L.M.T. Frija, M.L.S. Cristiano, R. Fausto, J. Phys.
Chem. A 109 (2005) 7967.
Acknowledgements
[16] A. Gómez-Zavaglia, I.D. Reva, L.M.T. Frija, M.L.S. Cristiano, R. Fausto, J.
Photochem. Photobiol. A 179 (2006) 243.
[17] A. Gómez-Zavaglia, I.D. Reva, L.M.T. Frija, M.L.S. Cristiano, R. Fausto, J. Mol.
Struct. 786 (2006) 182.
[18] A. Gómez-Zavaglia, I.D. Reva, L.M.T. Frija, M.L.S. Cristiano, R. Fausto, J.
Photochem. Photobiol. A 180 (2006) 175.
[19] L.M.T. Frija, I.D. Reva, A. Gómez-Zavaglia, M.L.S. Cristiano, R. Fausto, J. Phys.
Chem. A 111 (2007) 2879.
[20] L.M.T. Frija, I.D. Reva, A. Gómez-Zavaglia, M.L.S. Cristiano, R. Fausto,
Photochem. Photobiol. Sci. (PPS) 6 (2007) 1170.
[21] A. Gómez-Zavaglia, I.D. Reva, L.M.T. Frija, M.L.S. Cristiano, R. Fausto, Chem.
Phys. Res. J. 1 (2009) 221.
[22] A. Ismael, M.L.S. Cristiano, R. Fausto, A. Gómez-Zavaglia, J. Phys. Chem. A 114
(2010) 13076.
The authors are grateful to Fundação para a Ciência e Tecnologia
and FEDER (Projects PTDC/QUI/67674/2006 and PTDC/QUI/71203/
2006), bilateral cooperation grant (FCT-MinCyT PO/09/18) and
CYTED (Network 108RT0362) for financial support. A.G.Z. is mem-
ber of the Research Career CONICET, Argentina. A.B., B.M.G. and L.D.
acknowledge FCT for the award of postdoctoral and doctoral Grants
(SFRH/BPD/66154/2009, SFRH/BPD/44689/2008 and SFRH/BD/
62090/2009, respectively). We would also like to acknowledge
the Milipeia Computer Centre (University of Coimbra), research
project ‘‘Computação Avançada em Espectroscopia Molecular’’.
[23] I. Elghamry, D. Döpp, Tetrahedron Lett. 42 (2001) 5651.
[24] D.W. Cho, S.W. Oh, D.U. Kim, H.J. Park, J.Y. Xue, U.C. Yoon, P.S. Mariano, Bull.
Korean Chem. Soc. 31 (2010) 2453.
Appendix A. Supplementary material
[25] I. Elghamry, D. Döpp, G. Henkel, Synthesis 8 (2001) 1223.
[26] D. Döpp, Int. J. Photoenergy 3 (2001) 41.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2012.
04.081.
[27] R. Krishnan, J.S. Binkley, R. Seeger, J.A. Pople, J. Chem. Phys. 72 (1980) 650.
[28] A.D. McLean, G.S. Chandler, J. Chem. Phys. 72 (1980) 5639.
[29] M.J. Frisch, J.A. Pople, J.S. Binkley, J. Chem. Phys. 80 (1984) 3265.
[30] T. Clark, J. Chandrasekhar, G.W. Spitznagel, P.V.R. Schleyer, J. Comput. Chem. 4
(1983) 294.
[31] P.M.W. Gill, B.G. Johnson, J.A. Pople, M.J. Frisch, Chem. Phys. Lett. 197 (1992) 499.
[32] A.D. Becke, Phys. Rev. A 38 (1988) 3098.
[33] C.T. Lee, W.T. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[34] P. Pulay, J. Comput. Chem. 3 (1982) 556.
[35] GAMESS, version R1 (1-October-2010), M. Schmidt, K. Baldridge, J. Boatz, S.T.
Elbert, M.S. Gordon, J.H. Jensen, S. Koseki, N. Matsunaga, K.A. Nguyen, S.J. Su,
T.L. Windus, M. Dupuis, J. Montgomery, J. Comput. Chem. 14 (1993) 1347.
[36] A. Gómez-Zavaglia, A. Kaczor, R. Almeida, M.L.S. Cristiano, M.E.S. Eusébio,
T.M.R. Maria, P. Mobili, R. Fausto, J. Phys. Chem. A 113 (2009) 3517.
[37] I.G. Binev, B.A. Stamboliyska, E.A. Velcheva, Spectroc. Acta Part A – Mol.
Biomol. Spectrosc. 52 (1996) 1135.
[38] Y.I. Binev, C.T. Petkov, L. Pejov, Spectroc. Acta Part. A – Mol. Biomol. Spectrosc.
56 (2000) 1949.
[39] P. Naumov, G. Jovanovski, Struct. Chem. 11 (2000) 19.
[40] G. Jovanovski, S. Tanceva, B. Soptrajanov, Spectrosc. Lett. 28 (1995) 1095.
[41] A. Kaczor, R. Almeida, A. Gomez-Zavaglia, M.L.S. Cristiano, R. Fausto, J. Mol.
Struct. 876 (2008) 77.
References
[1] Y. Tamura, F. Watanabe, T. Nakatani, K. Yasui, M. Fuji, T. Komurasaki, H.
Tsuzuki, R. Maekawa, T. Yoshioka, K. Kawada, K. Sugita, M. Ohtani, J. Med.
Chem. 41 (1998) 640.
[2] H. Zhao, Z.-R. Qu, H-Y. Ye, R.-G. Xiong, Chem. Soc. Rev. 37 (2008) 84.
[3] E.J. Baran, V.T. Yilmaz, Coord. Chem. Rev. 250 (2006) 1980.
[4] M.L.S. Cristiano, R.A.W. Johnstone, P.J. Price, J. Chem. Soc. Perkin Trans. 1
(1996) 1453.
[5] N.C.P. Araújo, A.F. Brigas, M.L.S. Cristiano, L.M.T. Frija, E.M.O. Guimarães, R.M.S.
Loureiro, J. Mol. Catal. A: Chem. 215 (2004) 113.
[6] L.M.T. Frija, M.L.S. Cristiano, E.M.O. Guimarães, N.C. Martins, R.M.S. Loureiro, J.
Bikley, J. Mol. Catal. A: Chem. 242 (2005) 241.
[7] R.A.W. Johnstone, A.H. Wilby, I.D. Entwistle, Chem. Rev. 85 (1985) 129.
[8] J.V. Barkley, M.L.S. Cristiano, R.A.W. Johnstone, R.M.S. Loureiro, Sect. C: Cryst.
Struct. Commun. 53 (1997) 383.
[9] M.L.S. Cristiano, A.F. Brigas, R.A.W. Johnstone, R.M.S. Loureiro, P.C.A. Pena, J.
Chem. Res. (S) (1999) 704.
[10] N.C.P. Araújo, P.M.M. Barroca, J.F. Bickley, A.F. Brigas, M.L.S. Cristiano, R.A.W.
Johnstone, R.M.S. Loureiro, P.C.A. Pena, J. Chem. Soc. Perkin Trans. 1 (2002)
1213.
[11] R. Almeida, A. Gómez-Zavaglia, A. Kaczor, M.L.S. Cristiano, M.E.S. Eusébio,
T.M.R. Maria, R. Fausto, Tetrahedron 64 (2008) 3296.
[42] M. Rozenberg, G. Shoham, I. Reva, R. Fausto, Phys. Chem. Chem. Phys. 7 (2005)
2376.
[43] S. Shen, J.R. Durig, J. Mol. Struct. 661–662 (2003) 49.
[44] W.O. George, E.N. Lewis, D.A. Williams, W.F. Maddams, Appl. Spectrosc. 36
(1982) 592.
[45] F. Duvernay, T. Chiavassa, F. Borget, J.P. Aycard, Chem. Phys. 298 (2004)
241.
[12] A. Kaczor, L. Proniewicz, R. Almeida, A. Gómez-Zavaglia, M.L.S. Cristiano, A.M.
Matos Beja, M. Ramos Silva, R. Fausto, J. Mol. Struct. 892 (2008) 343.