Structural and computational studies of geometric isomers of 2-(4-methoxystyryl)-1,3-benzothiazole and preparation of their complexes with zinc halides

Article abstract of DOI:10.1016/j.molstruc.2009.09.013

The 2-(4-methoxystyryl)-1,3-benzothiazole (MeO-sbt) and its complexes with zinc halides of general formula [ZnX₂(MeO-sbt)₂], X = Cl, Br, I, are prepared. Crystal structure of both geometric isomers cis-2-(4-methoxystyryl)-1,3-benzoth

Full text of DOI:10.1016/j.molstruc.2009.09.013

Journal of Molecular Structure 938 (2009) 125–132
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural and computational studies of geometric isomers of 2-(4-methoxystyryl)-
1,3-benzothiazole and preparation of their complexes with zinc halides
a
b
a
c,
ˇ
ˇ
*
´
ˇ
´
´
Marijana Ðakovic , Helena Cicak , Zeljka Soldin , Vesna Tralic-Kulenovic
a Laboratory of General and Inorganic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia
b Laboratory of Organic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia
c
´
Department of Applied Chemistry, Faculty of Textile Technology, University of Zagreb, Prilaz baruna Filipovica 30, HR-10000 Zagreb, Croatia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 July 2009
Received in revised form 7 September 2009
Accepted 11 September 2009
Available online 18 September 2009
The 2-(4-methoxystyryl)-1,3-benzothiazole (MeO-sbt) and its complexes with zinc halides of general for-
mula [ZnX2(MeO-sbt)2], X = Cl, Br, I, are prepared. Crystal structure of both geometric isomers cis-2-(4-
methoxystyryl)-1,3-benzothiazole 1a and trans-2-(4-methoxystyryl)-1,3-benzothiazole 1b are reported.
Optimized structures of isomers 1a and 1b are consistent with X-ray structures. By comparison of calcu-
lated and experimental IR spectra as well as experimental NMR data it has been concluded that trans-iso-
mer 1b was initial product. Quantum–mechanical calculations have shown that thermal isomerization in
the singlet ground state is not possible at room temperature, but isomerization could be initiated by high
temperature or photochemically which had not been studied in this work.
Keywords:
cis- and trans-2-(4-Methoxystyryl)-1,3-
benzothiazole
Ó 2009 Elsevier B.V. All rights reserved.
Zn complexes
Crystal structure
Weak interactions
DFT and HF calculations
1. Introduction
various derivatives of benzothiazole were investigated in order to
find compounds that would be a good enough substitute to cis-
Various natural and synthetic compounds with benzothiazole
moiety have versatile pharmaceutical and industrial applications.
Benzothiazole and its derivatives exhibit diverse biological proper-
ties such as antitumor, antibacterial, antifungal, antiinflammatory
and antiallergic activity [1–4]. Some benzothiazole derivatives
have interesting photochemical properties due to presence of
two different chromophores in their molecule, namely benzothia-
zole moiety and the substituted aromatic ring [5]. Furthermore,
substituted benzothiazoles are of significant interest in design
and synthesis of organic luminescent materials [6].
[Pt(NH3)2Cl2] [9–14].
As a part of our comprehensive investigation of the coordina-
tion chemistry of the 12th group metals with various benzothia-
zole derivatives [15–18] we undertook this investigation. In this
paper, we report the synthesis, structural characterization of cis-
and trans-2-(4-methoxystyryl)-1,3-benzothiazole and our results
on coordinating ability of MeO-sbt towards zinc(II) ion. In addition
we made a computational study on isomers 1a and 1b which have
included equilibrium geometries optimization, vibrational analysis
and consideration of isomerization process possibility.
Beside the abovementioned applications, benzothiazole and its
derivatives are of substantial coordination interest as well. In addi-
2. Experimental
tion to
p-aromatic systems, these molecules have two endocyclic
heteroatoms with pronounced donor abilities, e.g. S and N, and
consequently possess significant coordination potential. Coordina-
tion polymers have been investigated mostly with respect to their
properties and potential technological value in areas of catalysis,
chirality, conductivity, luminescence, magnetism [7]. Discovery of
the antitumor activity of cis-[Pt(NH3)2Cl2] [8] aroused interest in
synthesis of new metal(II) complexes which might show improved
activity and lowered toxicity. Several platinum(II) complexes with
2.1. Materials and physical measurements
All reagents were supplied by Aldrich Chemical Co. and were
used as received without further purification. The CHNS-microa-
nalyses were performed by the Chemical Analytical Service of the
-
´
Ruder Boškovic Institute, Zagreb. Infrared spectra were obtained
from KBr pellets within the range 4000–400 cmꢀ1 with a Perkin-El-
mer FTIR spectrometer 1600 Series. The one-dimensional 1H and
13C spectra were recorded by a Bruker AV 600 spectrometer. Sam-
ples were measured in DMSO-d6 solution and chemical shifts
(ppm) were referred to TMS.
* Corresponding author.
E-mail address: vtralic@ttf.hr (V. Tralic´-Kulenovic´).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.09.013

´
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
126
2.2. Preparation of compounds
benzene, filtered off and dried. Yield: 0.23 g (62%). Anal. Calcd.
for C32H26ZnBr2N2O2S2 (759.93): C, 50.57; H, 3.45; N, 3.69; S,
8.44%. Found: C, 51.04; H, 3.46; N, 3.78; S, 8.30%. IR data (KBr pel-
let, cmꢀ1): 2927(w), 1622(w), 1596(vs), 1511(vs), 1464(m),
1435(m), 1286(w), 1256(vs), 1201(w), 1173(s), 1027(m), 953(w),
933(w), 816(m), 757(m), 727(m), 690(w), 545(w), 473(w).
2.2.1. cis- and trans-2-(4-Metoxystyryl)-1,3-benzothiazole (MeO-sbt)
To a mixture of p-anisaldehyde (1.36 g, 10 mmol) and 2-
methyl-1,3-benzothiazole (1.49 g, 10 mmol), anhydrous ZnCl2
(0.5 g, 3.67 mmol) was added in one portion and heated for 3 h
at 130 °C (Scheme 1). After cooling, the reaction mixture was trit-
urated with petrol–ether (100 mL) and the obtained yellow solid
was filtered off and crystallized from methanol. Yield: 1.9 g
(70%), mp 140–142 °C (literature mp 145 °C) [19]. Anal. Calcd. for
C16H13NOS (267.34): C, 71.87; H, 4,91; N, 5.24; O, 5.98; S, 11.99%.
Found: C, 71.75; H, 4.96; N, 5.22; O, 5.89; S, 12.10%. IR data (KBr
pellet, cmꢀ1): 3057(w), 3027(w), 2994(w), 2939(w), 2837(w),
1600(s), 1571(w), 1559(w), 1513(w), 1482(m), 1468(w),
1457(m), 1435(m), 1419(m), 1306(m), 1296(m), 1281(m),
1257(vs), 1233(s), 1219(m), 1192(m), 1174(vs), 1125(w),
1111(m), 1030(s), 1014(m), 963(m), 957(m), 932(w), 872(m),
859(w), 826(s), 809(s), 759(s), 729(s), 686(w), 664(w), 514(w),
466(w). 1H NMR (300 MHz, DMSO-d6): d = 3.82 (s, 3H, H-OCH3),
7.01 (t, 1H, J = 8.8 Hz, H-Ph), 7.42 (t, 1H, J = 8.1 Hz, H-Bt), 7.48 (d,
1H, J = 16.2 Hz, H-CH), 7.51 (t, 1H, J = 8.3 Hz, H-Bt), 7.62 (d, 1H,
J = 16.2 Hz, H-CH), 7.74 (d, 2H, J = 8.7 Hz, H-Ph), 7.96 (d, 1H,
J = 8.1 Hz, H-Bt), 8.07 (d, 1H, J = 8.1 Hz, H-Bt). 13C NMR (75 MHz,
DMSO-d6): 55.2 (q), 114.4 (d, 2C), 119.4 (d), 121.9 (d), 122.3 (d),
125.1 (d), 126.4 (d), 127.7 (s), 129.3 (d, 2C), 133.9 (s), 137.3 (d),
153.5 (s), 160.4 (s), 166.8 (s).
2.2.4. Preparation of ZnI2(MeO-sbt)2 (4)
A solution of MeO-sbt (0.29 g, 1.08 mmol) in chloroform (5 mL)
was added slowly to an ethanol solution of zinc iodide (0.16 g,
0.50 mmol in 10 mL). The reaction mixture was stirred and re-
fluxed for 6 h then left at room temperature to evaporate. Obtained
pale orange product was washed with small portions of benzene,
filtered off and dried. Yield: 0.25 g (59%). Anal. Calcd. for
C32H26ZnI2N2O2S2 (853.93): C, 45.00; H, 3.07; N, 3.34; S, 7.51%.
Found: C, 45.37; H, 3.19; N, 3.28; S, 7.85%. IR data (KBr pellet,
cmꢀ1): 2920(w), 2833(w), 1620(w), 1596(vs), 1512(vs), 1458(w),
14348(m), 1417(m), 1317(w) 1284(w), 1255(vs), 1203(w),
1171(s), 1111(w), 1031(m), 958(m), 948(m), 930(w), 814(m),
801(m), 756(s), 726(m), 690(m) 505(w).
2.2.5. Reaction of ZnBr2 with MeO-sbt in hydrothermal conditions
Suspension of zinc bromide (0.06 g, 0.27 mmol) and MeO-sbt
(0.15 g, 0.56 mmol) in ethanol (20 mL) was sealed in a Teflon-lined
stainless-steel vessel and heated for 5 h at 140 °C. After cooling, the
mother liquor was left to stand at room temperature and in a few
days pale yellow crystalline product was obtained. The crystals
suitable for single crystal X-ray diffraction experiment were fil-
tered off, washed with ethanol and dried. Attempt to obtained me-
tal complex failed. Pale yellow product was proved to be trans-
MeO-sbt 1b.
The recrystallization of the final product from the ethanol gave
a few crystals of cis-2-(4-methoxystyryl)-1,3-benzothiazole 1a of
suitable quality for the X-ray experiment. Good quality single crys-
tals of trans-2-(4-metoxystyryl)-1,3-benzothiazole 1b were ob-
tained unexpected by unsuccessful attempt of hydrothermal
complexation of MeO-sbt and ZnBr2 (see Section 2.2.5).
2.3. X-ray crystal structure analysis
2.2.2. Preparation of ZnCl2(MeO-sbt)2 (2)
A solution of MeO-sbt (0.20 g, 0.75 mmol) in chloroform (5 mL)
was added slowly to an ethanol solution of zinc chloride (0.05 g,
0.37 mmol in 10 mL). The reaction mixture was stirred and re-
fluxed for 6 h then left at room temperature to evaporate. Obtained
pale orange product was washed with small portions of benzene,
filtered off and dried. Yield: 0.10 g (40%). Anal. Calcd. for
C32H26ZnCl2N2O2S2 (671.03): C, 57.27; H, 3.91; N, 4.17; S, 9.56%.
Found: C, 56.99; H, 3.85; N, 4.11; S, 9.67%. IR data (KBr pellet,
cmꢀ1): 2926(w), 2836(w), 1598(vs), 1512(vs), 1466(w), 1455(w),
1436(m), 1308(w), 1287(w), 1255(s), 1202(w), 1172(s), 1111(w),
1027(m), 992(w), 955(m), 934(w), 817(m), 760(s), 728(w),
713(w), 690(w), 511(w).
The general and crystal data and summary of intensity data col-
lection and structure refinement for isomers 1a and 1b are col-
lected in Table 1.
Data were collected at 296 K on an Oxford Diffraction Xcalibur
four-circle kappa geometry single-crystal diffractometer with Sap-
phire-3 CCD detector, by applying CrysAlisPro Software system
[20]. The compounds were measured with Mo K
ated by a fine-focus sealed tube using a graphite monochromator.
Scans were performed in and 1° frames were collected. A crystal-
a radiation gener-
x
detector distance was 50 mm. Data reduction, including absorption
correction, was done by CrysAlice RED program [20].
The structures were solved by direct methods implemented in
the SHELXS-97 program [21]. The coordinates and the anisotropic
thermal parameters for all non-hydrogen atoms were refined by
the least-squares methods based on F2 using SHELXL-97 program
[21]. In each structure, the methylene and aromatic hydrogen
atoms were placed in geometrically idealized positions and con-
strained to ride on their parent C atom at distances of 0.93 Å with
Uiso(H) = 1.2Ueq(C). The methyl H atoms were constrained to an
2.2.3. Preparation of ZnBr2(MeO-sbt)2 (3)
A solution of MeO-sbt (0.30 g, 1.12 mmol) in chloroform (5 mL)
was added slowly to an ethanol solution of zinc bromide (0.11 g,
0.49 mmol in 10 mL). The reaction mixture was stirred and re-
fluxed for 12 h then left at room temperature to evaporate. Ob-
tained orange product was washed with small portions of
Scheme 1. Preparation of trans-MeO-sbt (1b).

´
127
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
Table 1
double zeta basis sets) to confirm the connection of that transition
sate with the two investigated isomers.
Crystal data and details of the structure refinement for 1a and 1b.
Complex
1a
1b
Empirical formula
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
C16H13NOS
267.34
296
0.71073
Triclinic
C16H13NOS
267.34
296
0.71073
Triclinic
3. Results and discussion
3.1. Synthesis
Initially prepared MeO-sbt is trans-isomer what was concluded
on only nine signals in 1H NMR spectrum and JHC value of 16.2 Hz
which is characteristic for trans spin–spin coupling of olefinic pro-
tons. A few crystals of cis-MeO-sbt 1a suitable for X-ray diffraction
analysis were obtained by recrystallization from the ethanol solu-
tion. Good quality crystals of trans-MeO-sbt 1b were obtained
unexpected from the reaction mixture of MeO-sbt and ZnBr2 in
hydrothermal conditions. Generally, zinc complexes were prepared
by refluxing of chloroform solutions of corresponding zinc halide
and MeO-sbt.
6.6595(2)
8.4857(3)
12.2033(5)
100.825(3)
101.872(4)
92.942(3)
659.95(4)
2
9.5492(3)
9.9437(3)
15.0343(4)
106.374(3)
90.881(2)
99.632(2)
1347.41(7)
4
b [Å]
c [Å]
a
b [°]
b [°]
[°]
c
Volume [Å3]
Z
qCalcd [g/cm3]
F(0 0 0)
1.345
280
1.318
560
Crystal size [mm]
Reflections collected
Unique reflections
0.13 ꢁ 0.29 ꢁ 0.41
0.31 ꢁ 0.56 ꢁ 0.59
14338
17731
2885
173
0.0414; 0.0310
0.0857; 0.0821
0.0464, 0.0387
1.067
4706
346
0.0586; 0.0495
0.1316; 0.1261
0.0619; 0.7799
1.026
3.2. IR spectra
Parameters
R1,all data, R1 [I > 2
a
r
(I)]
r(I)]
b
wR2,all data, wR2 [I > 2
The IR spectral data for MeO-sbt and its zinc complexes exhibit
very similar solid state IR spectra, so we could not unambiguously
assign shifts of absorption bands due to metal coordination. There-
fore, we can give just general assignation of absorption maxima
according to the literature [30,31]. Absorption bands in the range
of 1625–1400 cmꢀ1 can only be associated with olefinic double
bond and overall ring-skeletal (benzene and thiazole ring) stretch-
ing modes. Ring breathing and CH in-plane deformations are ob-
served in the range of 1330–930 cmꢀ1 and CH out-of-plane
deformations fall into range 865–720 cmꢀ1. Absorption band at
about 680 cmꢀ1 can be associated with CAS stretching frequency.
g1, g2 in wc
Sd on F2
e
D
rmin/max [e Åꢀ3
]
ꢀ0.16/0.19
ꢀ0.25/0.65
P
P
a
b
c
R ¼ jjFoj ꢀ jFcjj= jFoj.
P
P
2
2 1=2
wR ¼ ½ ðF2o ꢀ Fc2Þ = wðF2o Þ ꢂ
.
2
w ¼ 1=½r2ðF2o Þ þ ðg1PÞ þ g2Pꢂ where P ¼ ðFo2 þ 2F2c Þ=3 .
P
2
1=2
S ¼ ½wðF2o ꢀ F2c Þ =ðNobs ꢀ NparamÞꢂ
.
d
ideal geometry [CAH = 0.96Å and Uiso(H) = 1.5Ueq(C)], but were al-
lowed to rotate freely about the CAC bonds.
Graphical work has been performed by the programs ORTEP-3
for Windows [22] and Mercury 1.4.1 [23]. The thermal ellipsoids
are drawn at the 50% probability level.
3.3. Structural description
A survey of the Cambridge Structural Database (CSD) accom-
plished on version 5.30 (including update 3, May 2009) [32] using
ConQuest [33] (version 1.8) has revealed a total of seven entries
that contain the 2-styryl-1,3-benzothiazole fragment. Apart from
(benzo-15-crown-5)-1,3-benzothiazole [34], structurally charac-
terized are unsubstituted 2-styryl-1,3-benzothiazole [18] and five
of its derivatives with one, two and three substituents on phenyl
group; 2-(N-carbazolylstyryl)styryl-1,3-benzothiazole [35], 2-
(3,4-dimethoxystyryl)-1,3-benzothiazole [36], 2-(3,4-dichlorosty-
ryl)-1,3-benzothiazole [37], 2-(2-bromo-5-nitrostyryl)-1,3-ben-
2.4. Computational methods
Density functional theory (DFT) and Hartree–Fock (HF) calcula-
tions were performed with the Gaussian 03 program package [24].
B3LYP and mPW1PW91 hybrid DFT methods with standard 6-
311++G(d,p) and 6-311+G(2d,p) basis sets and tight convergence
criteria were employed for the calculations of geometries of cis/
trans-isomers 1a and 1b. B3LYP uses Becke’s three-parameter ex-
change functional and Lee, Yang and Parr’s gradient-corrected cor-
relation functional (B3LYP) [25] while mPW1PW91 uses the
Perdew–Wang (1991) exchange functional as modified by Adamo
and Barone and Perdew and Wang’s (1991) gradient-corrected cor-
relation functional [26]. 6-311++G(d,p) and 6-311+G(2d,p) are two
valence triple zeta basis sets augmented with additional set(s) of
diffuse and polarization functions.
The equilibrium molecular geometries of cis/trans-isomers 1a
and 1b were fully optimized in vacuo and the harmonic vibrational
analysis was performed at all used levels of theories to verify there
are no imaginary vibrational frequencies and to confirm them as
minima. In order to compare the calculated and experimental IR
spectra, the calculated vibrational wavenumbers have been scaled
by the factor 0.96 [27].
zothioazole
[38]
and
2-(2,4-dichloro-5-nitrostyryl)-1,3-
benzothiazole monohydrate [39]. In all these, trans arrangement
of benzothiazolyl and phenyl groups is found. To the best of our
knowledge, 1 is the first 2-styryl-1,3-benzothiazole for which both
geometric isomers are structurally characterized. The molecular
and crystal structures of isomers 1a and 1b are depicted in Figs.
1 and 2 and the pertinent molecular geometry parameters are
listed in Table 2.
The main differences in molecular geometries of two isomers,
cis 1a and trans 1b, are observed in spatial orientation of the
methoxyphenyl moieties. Furthermore, 1b crystallizes with two
symmetrically independent molecules, the feature already ob-
served in 2-(3,4-dimethoxystyryl)-1,3-benzothiazole [36] and 2-
(2,4-dichloro-5-nitrostyryl)-1,3-benzothiazole monohydrate [39].
Two molecules of 1b (1: S11/N11/O11/C11AC16; 2: S21/N21/
O21/C21AC26) are both reasonably planar, with dihedral angles
between the benzothiazolyl and methoxy-containing aryl rings
with the olefinic groups of 9.0 (2) and 4.6 (2)° in (1), and 7.0 (2)
and 6.2 (3)° in (2). Having cis- instead of trans-positioned benzo-
thiazolyl and methoxyphenyl groups, the molecule of 1a is not pla-
nar so far. The planarity is retained only in vinyl-benzothiazole
Hartree–Fock (HF) ab initio method [28] with 6-311+G(2d,p) ba-
sis set was used for the calculation of the transition state of cis–
trans isomerization. Transition structure was fully optimized in va-
cuo and the harmonic vibrational analysis gave one imaginary
vibrational frequency, which confirms it as the first order saddle
point. The intrinsic reaction coordinate (IRC) calculation [29] was
also employed at the HF/3-21G level of theory (3-21G is valence

´
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
128
Fig. 2b. Perspective view of crystal packing of 1b. Hydrogen bonds are presented by
dashed lines.
Fig. 1a. The ORTEP-3 drawing of cis-2-(4-methoxystyryl)-1,3-benzothiazole 1a
with the atom numbering scheme of the asymmetric unit.
derivatives [18,34–39]. The differences in the CAC bonds within
benzene ring are usual for such fused rings.
The olefinic C@C bond is somewhat shorter in 1b [1.314 (4) and
1.303 (4) Å, in 1 and 2, respectively] than in 1a [1.325 (2) Å]. Fur-
thermore, the values in both isomers are among the shortest of
substituted (1.341 (2) and 1.342 (2) Å in [36]; 1.330 (6) Å in [37],
1.316 (5) Å in [38], 1.341 (8) and 1.340 (8) Å in [39]), but very close
to the same in unsubstituted 2-styryl-1,3-benzothiazole (1.314
(4) Å in [18]).
In the crystal structures of both isomers hydrogen bonds are not
pronounced. Moreover, no classic hydrogen bonds were found,
only weak CAHꢃ ꢃ ꢃO and CAHꢃ ꢃ ꢃN hydrogen bonding and CAHꢃ ꢃ ꢃ
p
interactions are present. The details of geometries are given in Ta-
bles 3 and 4. In 1a, methoxy oxygen and thiazole nitrogen atoms
act as hydrogen bond acceptors for vinyl (H9) and benzothiazole
(H3) hydrogen atoms, respectively, forming acentric hydrogen
bonded rings of the graph-set motif of R22(17). These rings are fur-
ther fused to each other, thus forming endless supramolecular
chains running in [1 0 0] direction. The crystal structure is addi-
Fig. 1b. Perspective view of crystal packing of 1a. Hydrogen bonds are presented by
dashed lines.
part of molecule [dihedral angle: 7.4 (1)°], while the methoxy-con-
taining aryl ring is turned out of the plane drawn through the rest
of the molecule for 71.3 (1)°, probably due to minimization of ste-
ric repulsion. The benzothiazole moieties of all three molecules un-
der consideration are almost ideally planar, with the largest
deviations from the bt planes being that of the atoms S1
[0.0198(6) Å] in 1a, C11 [0.043 (2) Å] and C21 [0.024 (2) Å] in 1b.
In all three molecules, the two CAS bonds of the thiazole rings
[e.g. S1AC1 and S1AC2 in 1a, S11AC11 and S21AC21 in 1b] differ
with respect to each other, but both are within two border cases,
single SAC [1.82 Å] and double S@C [1.56 Å] bond [40]. The bond
angles around the S atom are within the range found in the five-
membered thiazole rings of 2-styryl-1,3-benzothiazole and its
tionally stabilized by only one weak CAHꢃ ꢃ ꢃ
the methoxy-containing phenyl ring hydrogen atom (H14) and
benzene -system of the benzothiazole moiety. In 1b, two sym-
p interaction between
p
metrically related molecules are interconnected by two identical
CAHꢃ ꢃ ꢃN interactions forming centrosymmetrical R22(22) dimers
[41,42] which are further fused by R44(16) rings forming extended
2D supramolecular sheets in (1–10) plane (Fig. 2c). Interestingly,
there are no hydrogen bonds between symmetrically independent
molecules. The weak CAHꢃ ꢃ ꢃ
p interactions are, as well, more pro-
nounced in trans than in cis-isomer. These are mostly established
Fig. 2a. The ORTEP-3 drawing of trans-2-(4-methoxystyryl)-1,3-benzothiazole 1b with the atom numbering scheme of the asymmetric unit.

´
129
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
Fig. 2c. Hydrogen bond motifs of R22(22) and R44(16) formed between symmetrically related molecules.
between aromatic CAH groups and
and phenyl rings.
p
-systems of fused benzene
levels of theory, B3LYP/6-311++G(d,p), B3LYP/6-311+G(2d,p) and
mPW1PW91/6-311+G(2d,p), gave geometries which are in good
agreement with the X-ray structures. The average absolute devia-
tions (AAD) of the theoretical structural parameters from experi-
mental ones are given in Table 5. The mPW1PW91/6-
311+G(2d,p) model gave the best geometries matching with AADs
of 0.0090 Å, 0.486° and 4.02° for bond distances, valence angles
3.4. Computational studies
DFT calculations have been performed for the isomers 1a and
1b starting from their X-ray molecular structures. All three used
Table 2
Selected bond distances (Å) and angles (°) for isomers 1a and 1b. Theoretical values are calculated at mPW1PW91/6-311+G(2d,p) level of theory.
Isomer 1aa
C8AC9
Experimental
1.325(2)
Theoretical
1.3400
Isomer 1bb
Experimental
Theoretical
C18AC19
C28AC29
C11AC18
C21AC28
C19AC110
C29AC210
S11AC11
S21AC21
S11AC12
S21AC22
N11AC11
N21AC21
N11AC17
N21AC27
O11AC113
O21AC213
1.313(4)
1.302(4)
1.454(4)
1.465(4)
1.466(3)
1.467(3)
1.758(3)
1.766(3)
1.723(2)
1.737(2)
1.278(3)
1.286(3)
1.408(3)
1.389(3)
1.357(3)
1.356(3)
1.418(4)
1.418(3)
89.2(1)
1.3413
1.4464
1.4520
1.7676
1.7338
1.2959
1.3718
1.3507
1.4109
88.989
111.598
122.432
114.893
122.675
129.287
109.094
115.426
125.202
118.164
116.025
124.577
180.000
0.000
C1AC8
1.451(2)
1.447(2)
1.758(1)
1.728(1)
1.298(2)
1.384(2)
1.361(2)
1.421(2)
89.20(6)
111.34(11)
123.87(10)
115.06(10)
120.98(12)
129.17(10)
109.49(9)
114.90(11)
125.77(12)
118.4(1)
115.3(1)
125.2(1)
ꢀ5.7(3)
1.4504
1.4664
1.7645
1.7324
1.2977
1.3705
1.3523
1.4102
89.090
C9AC10
S1AC1
S1AC2
N1AC1
N1AC7
O1AC13
O1AC16
O11AC116
O21AC216
C1AS1AC2
C1AN1AC7
S1AC1AC8
S1AC1AN1
N1AC1AC8
S1AC2AC3
S1AC2AC7
N1AC7AC2
N1AC7AC6
C13AO1AC16
C12AC13AO1
C14AC13AO1
C1AC8AC9AC10
S1AC1AC8AC9
C8AC9AC10AC11
C14AC13AO1AC16
C11AS11AC12
C21AS21AC22
C11AN11AC17
C21AN21AC27
S11AC11AC18
S21AC21AC28
S11AC11AN11
S21AC21AN21
N11AC11AC18
N21AC21AC28
S11AC12AC13
S21AC22AC23
S11AC12AC17
S21AC22AC27
N11AC17AC12
N21AC27AC22
N11AC17AC16
N21AC27AC26
C113AO11AC126
C213AO21AC226
C112AC113AO11
C212AC213AO21
C114AC113AO11
C214AC213AO21
C11AC18AC19AC110
C21AC28AC29AC210
S11AC11AC18AC19
S21AC21AC28AC29
C18AC19AC110AC111
C28AC29AC210AC211
C114AC113AO11AC116
C214AC213AO21AC216
89.2(1)
111.785
124.721
114.697
120.385
129.308
109.169
115.254
125.217
117.993
115.951
124.573
ꢀ7.952
ꢀ11.951
133.645
0.515
109.7(2)
110.6(2)
121.8(2)
122.5(2)
116.5(2)
115.6(2)
121.7(3)
121.8(2)
129.0(2)
130.1(2)
109.1(2)
108.5(2)
115.5(2)
116.1(2)
125.7(2)
124.6(2)
118.8(2)
118.2(2)
115.5(2)
115.8(2)
125.3(2)
124.9(2)
177.1(2)
ꢀ176.3(2)
5.3(4)
ꢀ4.3(2)
ꢀ4.7(4)
177.5(2)
ꢀ175.4(3)
0.7(3)
116.7(2)
1.4(2)
180.000
0.000
ꢀ6.1(3)
a
The average absolute deviations of the theoretical bond distances of benzene ring in methoxyphenyl moiety is 0.0099 Å and in benzothiazole moiety is 0.0060 Å.
The average absolute deviations of the theoretical bond distances of benzene ring in methoxyphenyl moiety is 0.0073 Å and in benzothiazole moiety is 0.0079 Å.
b

´
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
130
Table 3
the two isomers is within 24.0 and 25.6 kJ/mol depending on the
Hydrogen-bonding (Å and °) for isomers 1a and 1b.
calculation model, whereas the trans-isomer 1b is more stable
one. The thermal cis–trans isomerization in the singlet ground state
does not occur at the room temperature. The energy barrier for
rotation around the olefinic double CAC bond is very high
(296.2 kJ/mol at HF/6-311+G(2d,p) level of theory related to the
DAHꢃ ꢃ ꢃA
Isomer 1a
DAH
HꢃꢃꢃA
DꢃꢃꢃA
\DHA
Symmetry code
C3AH3ꢃ ꢃ ꢃN1
0.93
0.93
2.64
2.71
3.534(2)
3.395(2)
165
131
x + 1, y, z
x ꢀ 1, y, z
C9AH9ꢃ ꢃ ꢃO1
trans-isomer 1b) mostly due to the p-bond breaking. Earlier inves-
Isomer 1b
C19AH19ꢃ ꢃ ꢃS11
C29AH29ꢃ ꢃ ꢃS21
C15AH15ꢃ ꢃ ꢃO11
C25AH25ꢃ ꢃ ꢃO21
C116AH16Aꢃ ꢃ ꢃN11
C216AH21Bꢃ ꢃ ꢃN21
0.93
0.93
0.93
0.93
0.96
0.96
2.69
2.75
2.65
2.57
2.64
2.58
3.148(3)
3.195(3)
3.445(3)
3.426(3)
3.549(3)
3.428(4)
112
110
144
153
158
148
–
–
tigations showed that such torsional pathway in stilbene deriva-
tives was the only possible thermal isomerization mechanism
[43]. The corresponding transition structure is shown in Fig. 4.
The dihedral angle amounts 106.49°. The harmonic normal mode
calculation of transition structure gave imaginary frequency of
x, y, ꢀ1 + z
x, y, ꢀ1 + z
ꢀx, ꢀy, 1 ꢀ z
1 ꢀ x, ꢀy, 1 ꢀ z
1440i cmꢀ1. The
p-bonds of both isomers and frontier orbitals
(HOMO and LUMO) of transition state for rotation process are
shown in Fig. 5. The possibility of photochemical isomerization
was not considered in this study.
and dihedral angles, respectively. These structures and selected
structural parameters are shown in Fig. 3 and Table 2, respectively.
The small differences between X-ray and calculated structures are
consequence of different states of matter: during the theoretical
calculation single isolated molecule is considered in vacuo, while
many molecules are treated in solid state during X-ray diffraction.
However, all the calculated geometric parameters, obtained by
three used models, represent good approximations and they can
be applied as groundwork for prediction and exploring the other
properties of the isomers.
The theoretical IR spectra of two isomers and the comparison
with the experimental FTIR spectrum of initial reaction product
MeO-sbt are shown in Fig. 6(a–c). Generally, calculated spectra of
both isomers are very similar. In the region above 1700 cmꢀ1 spec-
tra are simple and only CAH bond stretching bands around
3000 cmꢀ1 are present. The region below 1700 cmꢀ1 is much more
complicated because it consists of stretching and bending vibra-
tions bands. Bands around the 1600 cmꢀ1 correspond to the C@C
stretching vibrations. In the region below 1600 cmꢀ1, which is
mostly fingerprint region, calculated spectra show only few differ-
Trans-isomer 1b is planar (Cs point group), while cis-isomer 1a
has no symmetry (C1 point group). The energy difference between
Table 4
CAHꢃ ꢃ ꢃ
p interactions for isomers 1a and 1b.
CAHꢃ ꢃ ꢃCga
Hꢃ ꢃ ꢃCg
cb (°)
CAHꢃ ꢃ ꢃCg (°)
Cꢃ ꢃ ꢃCg (Å)
Symmetry operation on Cg
Isomer 1a
C14AH14ꢃ ꢃ ꢃCg(C2 ? C7)
2.97
9.11
144
3.765(2)
x, ꢀ1 + y, z
Isomer 1b
C116AH12Bꢃ ꢃ ꢃCg(S21, N21, C21, C22, C27)
C13AH13ꢃ ꢃ ꢃCg(C210 ? C215)
C23AH23ꢃ ꢃ ꢃCg(C12 ? C17)
2.98
2.98
2.68
2.96
2.82
2.98
2.85
17.11
20.93
7.97
12.31
11.36
6.49
154
126
136
135
130
126
130
3.861(3)
3.609(3)
3.410(3)
3.681(3)
3.488(2)
3.605(2)
3.519(2)
1 ꢀ x, ꢀy, 1 – z
1 ꢀ x, 1 ꢀ y, 1ꢀz
1 + x, y, z
C26AH26ꢃ ꢃ ꢃCg(C12 ? C17)
x, y, z
C111AH111ꢃ ꢃ ꢃCg(S21, N21, C21, C22, C27)
C112AH112ꢃ ꢃ ꢃCg(C22 ? C27)
C211AH211ꢃ ꢃ ꢃCg(C110 ? C115)
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
1 + x, y, z
5.27
a
Centre of gravity of the aromatic ring. CAHꢃ ꢃ ꢃp interactions are selected on criteria Hꢃ ꢃ ꢃCg < 3.4 and c < 30°.
b
c
= angle defined by a line connecting centre of gravity of the aromatic ring with H atom and the normal to the aromatic ring.
Table 5
Average absolute deviations of theoretical structural parameters from the experimental ones.
B3LYP/6-311++G(d,p)
B3LYP/6-311+G(2d,p)
mPW1PW91/6-311+G(2d,p)
Bonds/Å
Valence angles/°
Dihedral angles/°
0.0137
0.564
4.58
0.0121
0.552
4.43
0.0090
0.486
4.02
Fig. 3. Optimized structures at mPW1PW91/6-311+G(2d,p) level of theory of isomers 1a (a) and 1b (b).

´
131
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
Fig. 4. Optimized structure of transition state at HF/6-311+G(2d,p) level of theory (two different views).
Fig. 5.
p-Bonds (HOMO) of isomer 1a (a) and isomer 1b (b). Frontier orbitals of transition state (HOMO (c) and LUMO (d)) for rotation around central CAC bond. (MO surface
isovalue = 0.02).
ences each other (marked by small orange circles in Fig. 6(c)) and
most of the corresponding bands are present in the experimental
spectrum. The only exception is band at 1370 cmꢀ1 in cis-isomer
1a which is not found in experimental spectrum. This band corre-
sponds to the HAC@CAH synchronous in-plane bending (wag-
ging). Analogous band in trans-isomer 1b is observed at
1215 cmꢀ1 (also marked in Fig. 6(c). The rest of the marked bands
at 995, 677, 648 and 474 cmꢀ1 correspond to the in-plane bendings
involving trans-olefinic double bond.
observed in spatial orientation of methoxyphenyl moieties. While
trans 1b is essentially planar, in cis 1a methoxy-containing aryl
ring closes the dihedral angle of 71° with the rest of the molecule.
In both, 1a and 1b, weak CAHꢃ ꢃ ꢃO, CAHꢃ ꢃ ꢃN and CAHꢃ ꢃ ꢃ
p interac-
tions are found to be main supramolecular tool in crystal forma-
tion. Transition state for thermal cis–trans isomerization in the
singlet ground state was calculated. Calculations showed that bar-
rier for that interconversion is too high to occur at the room tem-
perature, mostly due to the
p-bond breaking. Comparison of
By calculated IR spectra and their comparison with experimen-
tal FTIR, it has been confirmed that experimental spectrum belongs
to trans-isomer 1b.
calculated and experimental IR spectra was also made, which gave
confirmation that trans-isomer 1b was initially synthesized. Cis-
isomer 1a was prepared by recrystallization of 1b from ethanol.
4. Conclusion
5. Supplementary material
The crystal structures of two isomorphs 1a and 1b are deter-
mined by X-ray diffraction analysis at room temperature and their
molecular structures are confirmed by DFT calculations. Apart from
being only cis and trans, main difference between two isomers is
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
No. 739225 for complex 1a and 739226 for complex 1b. Copies
of this information may be obtained from the Director, CCDC, 12

´
M. Ðakovic et al. / Journal of Molecular Structure 938 (2009) 125–132
132
Union Road, Cambridge CB2 1EZ, UK (fax: +44 (0) 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk or website: http://www.ccdc.
cam.ac.uk).
Acknowledgements
This research was supported by Ministry of Science, Education
and Sports of the Republic of Croatia (Grant Nos. 119-1193079-
1332, 119-1191342-1339 and 117-0000000-3283).
References
[1] R.H. Goldfarb, R.P. Kitson, K.W. Yoshino, N. Horohita, Y. Kotera, Y. Inoue, M.
Ohashi, Anticancer Res. 19 (1999) 1663.
[2] E.A. Sener, O.T. Arpaci, I. Yalcin, N. Altanlar, Farmaco 55 (2000) 397.
[3] A.B. Nadkarn, R.V. Kamath, G.B. Khadse, Indian J. Heterocycl. Chem. 9 (2000)
309.
[4] L. Racané, V. Tralic´-Kulenovic´, L. Fišer-Jakic´, D.W. Boykin, G. Karminski-Zamola,
Heterocycles 55 (2001) 2085.
[5] I. Petkov, T. Deligeorgiev, I. Timtcheva, Dyes Pigments 35 (1997) 171.
[6] H.Y. Fu, X.Y. Sun, X.D. Gao, F. Xiao, B.X. Shao, Synthetic Metals 159 (2009) 254.
[7] C. Janiak, Dalton Trans. (2003) 2781.
Fig. 6a. Unscaled calculated IR spectra of isomers 1a (cis-calc) and 1b (trans-calc).
[8] B. Rosenberg, L. Van Camp, J.E. Trosko, V.H. Mansour, Nature 222 (1969) 385.
[9] J.A. Muir, G.M. Gomez, M.M. Muir, O. Cox, M.E. Cadiz, Acta Crystallogr. C43
(1987) 1258.
[10] J.A. Muir, G.M. Gomez, M.M. Muir, M.E. Cadiz, O. Cox, Acta Crystallogr. C44
(1988) 803.
[11] G.M. Gomez, M.M. Muir, J.A. Muir, O. Cox, Acta Crystallogr. C44 (1988) 1554.
[12] M.M. Muir, G.M. Gomez, M.E. Cadiz, J.A. Muir, Inorg. Chim. Acta 168 (1990) 47.
[13] C.M. Lozano, M.M. Muir, X. Tang, Y. Li, J. Chem. Crystallogr. 24 (1994) 639.
[14] C.M. Lozano, O. Cox, M.M. Muir, J.D. Morales, J.L. Rodríguez-Cabán, P.E. Vivas-
Mejía, F.A. Gonzales, Inorg. Chim. Acta 271 (1998) 137.
ˇ
[15] Z. Popovic´, D. Mrvoš-Sermek, Z. Soldin, V. Tralic´-Kulenovic´, Acta Crystallogr.
C57 (2001) 20.
ˇ
ˇ
[16] Z. Popovic´, Z. Soldin, G. Pavlovic´, D. Matkovic´-Calogovic´, D. Mrvoš-Sermek, M.
Rajic´-Linaric´, Struct. Chem. 13 (5/6) (2002) 425.
ˇ
[17] Z. Popovic´, G. Pavlovic´, Z. Soldin, V. Tralic´-Kulenovic´, L. Racané, Acta
Crystallogr. C59 (2003) m4.
ˇ
´
´
´
´
[18] G. Pavlovic, Z. Soldin, Z. Popovic, V. Tralic-Kulenovic, Polyhedron 26 (2007)
5162.
[19] S. Ried, J.L. Hinschung, Ann. Chem. 600 (1956) 47.
[20] Oxford Diffraction, CrysAlisPro Version 171.32, Oxford Diffraction Ltd.,
Abingdon, Oxfordshire, England, 2007.
Fig. 6b. Experimental FTIR spectrum of MeO-sbt (exp).
[21] G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112.
[22] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[23] I.J. Bruno, J.C. Cole, P.R. Edgington, M.K. Kessler, C.F. Macrae, P. McCabe, J.
Pearson, R. Taylor, Acta Crystallogr. B58 (2002) 389.
[24] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
et al., Gaussian 03, Revision C02, Gaussian Inc., Pittsburgh, PA, 2004.
[25] R.G. Parr, W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford
University Press, Oxford, 1989.
[26] (a) C. Adamo, V. Barone, J. Chem. Phys. 108 (1998) 664;
(b) B.J. Lynch, Y. Zhao, D.G. Truhlar, J. Phys. Chem. A 107 (2003) 1384.
[27] Available from: http://cccbdb.nist.gov/.
[28] C.C.J. Roothaan, Rev. Mod. Phys. 23 (1951) 69.
[29] K. Fukui, Acc. Chem. Res. 14 (1981) 363.
[30] N.B. Colthup, L.H. Daly, S.E. Wiberley, Introduction to Infrared and Raman
Spectroscopy, Academic Press, New York, 1964.
[31] C.N.R. Rao, R. Venkataraghavan, Can. J. Chem. 42 (1964) 43.
[32] H.F. Allen, W.D.S. Motherwell, Acta Crystallogr. B58 (2002) 380.
[33] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kesser, C.F. Macrae, P. McCabe, J. Pearson,
R. Taylor, Acta Crystallogr. B58 (2002) 389.
[34] S.P. Fedorov, O.A. Fedorova, E.N. Andryukhina, S.P. Gromov, M.V. Alfimov, L.G.
Kuzmina, J.A.K. Howard, J.-J. Aaron, New J. Chem. 27 (2003) 280.
[35] D.-X. Cao, Q. Fang, D. Wang, Z.-Q. Liu, G. Xue, G.-B. Xu, W.-T. Yu, Eur. J. Org.
Chem. (2003) 3625.
[36] L.G. Kuzma, O.A. Fedorova, E.N. Andryukhina, M.M. Mashura, S.P. Gromov, M.V.
Alfimov, Kristallographiya (Russ.) (Crystallogr. Rep.) 51 (2006) 467.
[37] J. Yin, P. Kumar, J.R. Dimmock, J.W. Quail, Acta Crystallogr. C51 (1995) 2700.
[38] J.A. Muir, O. Cox, L.A. Bernerd, M.M. Muir, J. Crystallogr. Specrtrosc. Res. 22
(1992) 695.
[39] O. Cox, M. Cordero, S. Pineiro, S.D. Huang, Acta Crystallogr. C53 (1997) 310.
´
[40] N. Trinajstic, Tetrahedron Lett. 12 (1968) 1529.
Fig. 6c. Scaled calculated IR spectra of isomers 1a (cis-calc) and 1b (trans-calc) and
experimental FTIR spectrum of MeO-sbt (exp) in the 1750–450 cmꢀ1 region. (Larger
differences between cis-calc and trans-calc are marked by small orange circles.) (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this paper.)
[41] J. Bernstein, R.E. Davies, L. Shimoni, N.-L. Chang, Angew. Chem. Int. Ed. Engl. 34
(1995) 1555.
[42] M.C. Etter, Acc. Chem. Res. 23 (1990) 120.
[43] A. Cembran, F. Bernardi, M. Garavelli, L. Gagliardi, G. Orlandi, J. Am. Chem. Soc.
126 (2004) 3234.