Quantum-chemical, spectroscopic and X-ray diffraction studies of (E)-2-[(2-Bromophenyl)iminomethyl]-4-trifluoromethoxyphenol

Article abstract of DOI:10.1016/j.saa.2011.10.055

The Schiff base compound (E)-2-[(2-Bromophenyl)iminomethyl]-4- trifluoromethoxyphenol has been synthesised and characterised by IR, UV-vis, and X-ray single-crystal determination. The molecular geometry from X-ray determination of the title compound in th

Full text of DOI:10.1016/j.saa.2011.10.055

Spectrochimica Acta Part A 87 (2012) 15–24
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Quantum-chemical, spectroscopic and X-ray diffraction studies of
(E)-2-[(2-Bromophenyl)iminomethyl]-4-trifluoromethoxyphenol
Hasan Tanaka,∗, Ays¸ en Alaman Ag˘arb, Orhan Büyükgüngörc
a Department of Physics, Faculty of Arts and Sciences, Amasya University, 05100 Amasya, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
c Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 May 2011
Received in revised form 25 August 2011
Accepted 23 October 2011
The Schiff base compound (E)-2-[(2-Bromophenyl)iminomethyl]-4-trifluoromethoxyphenol has been
synthesised and characterised by IR, UV–vis, and X-ray single-crystal determination. The molecular geom-
etry from X-ray determination of the title compound in the ground state has been compared using the
Hartree–Fock (HF) and density functional theory (DFT) with the 6–311++G(d,p) basis set. The calculated
results show that the DFT and HF can well reproduce the structure of the title compound. Using the TD-
DFT and TD-HF methods, electronic absorption spectra of the title compound have been predicted and
good agreement with the TD-DFT method and the experimental determination was found. The predicted
nonlinear optical properties of the title compound are much greater than those of urea. In addition, DFT
calculations of the title compound, molecular electrostatic potential (MEP), natural bond orbital (NBO),
and thermodynamic properties were performed at B3LYP/6–311++G(d,p) level of theory.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Density functional theory
Electronic absorption spectra
Hartree–Fock
Molecular electrostatic potential
Schiff base
1. Introduction
[19,20] and N–H· · ·O in keto-amine [21,22] tautomers. Differ-
ent methods were used to show the presence of the enol-imine
Azomethines (known as Schiff-bases), having imine groups
(CH N) and benzene rings in the main chain alternately, and
being ␲-conjugated, exhibit interest as materials for wide spectrum
applications, particularly as corrosion inhibitors [1], catalyst car-
riers [2,3], thermo-stable materials [4–6], a metal ion complexing
agents [7] and in biological systems [8–10]. Schiff base ligands con-
sist of a variety of substituents with different electron-donating and
electron-withdrawing groups, and therefore may exhibit interest-
ing electro-chemical properties. The Schiff base compounds have
been also under investigation during last years because of their
potential applicability in optical communications and many of
them have NLO behavior [11,12].
Schiff base compounds display interesting photochromic and
thermochromic features in the solid state and can be classified in
terms of these properties [13]. Photo- and thermochromism arise
via H-atom transfer from the hydroxy O atom to the imine N atom
[14,15]. Such proton-exchanging materials can be utilized for the
design of various molecular electronic devices [16–18]. In gen-
eral, o-hydroxy Schiff bases display two possible tautomeric forms,
the enol-imine (OH) and the keto-amine (NH) forms (see Fig. 1).
Depending on the tautomers, two types of intramolecular hydro-
gen bonds are observed in Schiff bases: O–H· · ·N in enol-imine
and keto-amine forms, among them are UV–vis, IR, MS, 1H, 13C
NMR spectroscopy, and X-ray crystallography techniques [23–26].
Recently, we focused our attention on the synthesis and charac-
terization of various Schiff base derivatives [27–29] and studied
their special properties. To the best of our knowledge, neither the
synthesis nor theoretical studies of the title compound of (E)-2-[(2-
Bromophenyl)iminomethyl]-4-trifluoromethoxyphenol have been
available until now. After synthesizing this compound we deter-
mined its crystal structure.
Investigations into the structural stability of these compounds
using both experimental techniques and theoretical methods have
been of interest for many years. With recent advances in com-
puter hardware and software, it is possible to correctly describe
the physico-chemical properties of molecules from first principles
using various computational techniques [30]. In recent years, den-
sity functional theory (DFT) has been the shooting star in theoretical
modeling. The development of ever better exchange-correlation
functionals has made it possible to calculate many molecular prop-
erties with accuracies comparable to those of traditional correlated
ab initio methods, at more favorable computational costs [31]. Lit-
erature surveys have revealed the high degree of accuracy of DFT
methods in reproducing the experimental values in terms of geom-
etry, dipole moment, vibrational frequency, etc. [32–37].
In this paper, we wish to report the synthesis, charac-
terization and crystal structure of the Schiff base (E)-2-[(2-
Bromophenyl)iminomethyl]-4-trifluoromethoxyphenol as well as
∗
Corresponding author. Tel.: +90 358 218 01 60; fax: +90 358 218 01 04.
E-mail address: hasantanak@gmail.com (H. Tanak).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.10.055

16
H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
Fig. 1. Tautomeric forms of the title compound.
the theoretical studies on it by using the HF/6–311++G(d,p) and
B3LYP/6–311++G(d,p) methods. The interaction enegies, molecu-
lar electrostatic potential, thermodynamic and nonlinear optical
properties of the title compound were investigated at the
B3LYP/6–311++G(d,p) level. These calculations are valuable for pro-
viding insight into molecular properties of Schiff base compounds.
refinement was carried out using the full matrix least squares
method on the positional and anisotropic temperature parame-
ters of non-hydrogen atoms corresponding to 194 crystallographic
parameters. Atom H1 was located in a difference Fourier map and
refined isotropically, and the other H atoms were positioned geo-
metrically and treated using a riding model, fixing the bond lengths
˚
at 0.93 A for aromatic CH. The displacement parameters of the
H atoms were fixed at Uiso(H) = 1.2Ueq(C) of their parent atoms.
Details of the data collection conditions and the parameters of the
refinement process are given in Table S1 (Supporting Information).
2. Experimental and computational methods
2.1. Physical measurements
The melting point was determined using a Gallenkamp melt-
ing point apparatus. The IR spectrum of the title compound was
recorded in the range 4000–400 cm−1 using a Schmadzu FTIR-8900
spectrophotometer with KBr pellets. The spectrum was recorded
at room temperature with scanning speed of 10 cm−1 min−1 and
the spectral resolution of 4.0 cm−1. The ultraviolet absorption spec-
tra of the title compund were examined in the range 200–600 nm
using a Unicam UV–vis spectrophotometer equipped with a 10 mm
quartz cell. The UV pattern is taken from a 1 × 10−5 M solution of
the title compound, dissolved in ethanol at 20 ◦C.
2.4. Computational methods
The molecular geometry is directly taken from the X-ray diffrac-
tion experimental result without any constraints. In the next step,
the DFT calculations with a hybrid functional B3LYP (Becke’s three
parameter hybrid functional using the LYP correlation functional)
with the 6–311++G(d,p) basis set and Hartree–Fock calculations
with the 6–311++G(d,p) basis set using the Berny method [41,42]
were performed with the Gaussian 03W software package [43]. The
harmonic vibrational frequencies were calculated at the same level
of theory for the optimized structures. Vibrational band assign-
ments were made using the Gauss-View molecular visualisation
program [44]. Additionally, the calculated vibrational frequencies
were clarified by means of the potential energy distribution (PED)
analysis and assignments of all the fundamental vibrational modes
by using VEDA 4 program [45]. In order to investigate the atomic
charge behavior of the title compound in solvent media, we also car-
ried out optimization calculations in three solvents (ε = 78.39, H2O;
ε = 24.55, C2H5OH; ε = 4.9, CHCl3) at the B3LYP/6–311++G(d,p) level
using the Onsager [46] method. The electronic absorption spec-
tra were calculated using the time-dependent density functional
theory (TD-DFT) and Hartree–Fock (TD-HF) methods [47–50]. In
addition, the electronic absorbtion spectra were calculated in
ethanol solution with the Polarizable Continuum Model (PCM)
[51–54] method.
2.2. Synthesis
The
compound
(E)-2-[(2-Bromophenyl)iminomethyl]-4-
trifluoromethoxyphenol was prepared by reflux a mixture of a
solution containing 2-hydroxy-5-(trifluoromethoxy) benzalde-
hyde (0.019 g; 0.092 mmol) in 20 ml ethanol and
a solution
containing 2-bromoaniline (0.016 g; 0.092 mmol) in 20 ml ethanol.
The reaction mixture was stirred for 1 hunder reflux. The crystals of
(E)-2-[(2-Bromophenyl)iminomethyl]-4-trifluoromethoxyphenol
suitable for X-ray analysis were obtained from ethylalcohol by
slow evaporation (Yield: % 68; M.P, 357–359 K).
2.3. Crystal structure determination
To investigate the reactive sites of the title compound the MEP
were evaluated using the B3LYP/6–311++G(d,p) method. MEP, V(r),
at a given point r(x, y, z) in the vicinity of a molecule is defined
in terms of the interaction energy between the electrical charge
generated from the molecule’s electrons and nuclei and a positive
test charge (a proton) located at r. For the system studied the V(r)
values were calculated as described previously using the equation
[55],
A colourless crystal of the compound with dimensions of
0.04 mm × 0.18 mm × 0.45 mm was mounted on goniometer of a
STOE IPDS II diffractometer. Measurements were performed at
room temperature (296 K) using graphite monochromated Mo
˚
K␣ radiation (ꢀ = 0.71073 A). The systematic absences and inten-
sity symmetries indicated the monoclinic Pbca space group. A
total of 19,487 reflection (1132 unique) within the ꢁ range of
[1.5◦ < ꢁ < 26.5◦] were collected in the w scan mode. Cell parameters
were determined by using X-AREA software [38]. The intensi-
ties collected were corrected for Lorentz and polarization factors,
absorption correction (ꢂ = 3.00 mm−1) by integration method via
X-RED32 software [38]. The structure was solved by direct meth-
ods using SHELXS-97 [39]. The maximum peaks and deepest hole
ꢁ
ꢀ
ꢄ(rꢀ)
ZA
V(r) =
−
d3rꢀ
(1)
|RA − r|
|rꢀ − r|
where ZA is the charge of nucleus A, located at RA, ꢄ(rꢀ) is the
electronic density function of the molecule, and rꢀ is the dummy
integration variable. The linear polarizability and first hyperpo-
larizability properties of the title compound were obtained from
molecular polarizabilities based on theoretical calculations. In addi-
tion, the NBO analysis was performed at the B3LYP/6–311++G(d,p)
observed in the final ꢃꢄ map were 0.42 and −0.21 eA−3, respec-
˚
tively. The scattering factors were taken from SHELXL-97 [39].
The molecular graphics were done using ORTEP-3 for Windows
[40]. All non-hydrogen atoms were refined anisotropically. The

H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
17
˚
(6) A) bonds. The C9–O1 and C7–N1 bonds indicate single-bond
and a high degree of double-bond characters, respectively. Fur-
thermore, the H1 atom is located on atom O1, thus the title
compound exists in the enol-imine form in the solid state. Similar
results were observed for (E)-2-[(3-Fluorophenyl)iminomethyl]-4-
˚
(trifluoromethoxy) phenol (C–O = 1.343 (3) and C–N = 1.269 (5) A)
[59].
The title compound is stabilized by O–H· · ·N and O–H· · ·Br type
hydrogen bonds. There is a strong intramolecular O1–H1· · ·N1
hydrogen bond involving hydroxyl atom O1 and imine atom N1,
namely O1–H1· · ·N1, producing an S(6) ring motif [60] resulting
in approximate planarity of the molecular skeleton [O· · ·N = 2.600
˚
(6) A]. The crystal structure is further stabilized by intramolecular
O–H· · ·Br hydrogen bond, namely O1–H1· · ·Br1 and the details of
the hydrogen bonds are summarized in Table S2 (Supporting Infor-
mation). In addition, there is also ␲–␲ interaction between the Cg2
˚
ring in a neighboring molecule is 3.784 (4) A at (1/2 − x, 1/2 + x, z)
[Cg2 is the ring centroid of the C8/C13 ring]. A packing diagram of
the title compound is shown in Fig. S3 (Supporting Information).
3.2. Optimized geometries
B3LYP/6–311++G(d,p) and HF/6–311++G(d,p) calculations were
performed on the title compound. The atomic numbering scheme
the theoretical geometric structure of the title compound are
shown in Fig. 2b. Calculated geometric parameters are listed in
Table 1 along with the experimental data. When the X-ray structure
of the title compound is compared with its optimized counterpart
(Fig. S4; Supporting Information), conformational discrepancies
are observed. The most remarkable discrepancies are found in
the orientation of the bromophenyl ring of the title compound,
which is defined by the torsion angles C7–N1–C1–C2 [177.3(7)◦]
and C7–N1–C1–C6 [−3.3(9)◦]. These torsion angles have been cal-
culated at 133.18◦ and −49.90◦ for the HF/6–311++G(d,p) level,
141.52◦ and −41.81◦ for the B3LYP/6–311++G(d,p) level. Another
difference with respect to the optimized structures is observed
in the relative orientation of the trifluoromethoxy group. The
methoxy group is almost perpendicular with the attached ring with
C13–C12–O2–C14 and C11–C12–O2–C14 torsion angles of 90.0(8)◦
and −94.3(8)◦ for X-ray while the corresponding values are cal-
culated as 91.12◦ and −92.66◦ for HF and 90.04◦ and −94.26◦ for
B3LYP, respectively.
Fig. 2. (a) Ortep-3 diagram of the title compound. Displacement ellipsoids are drawn
at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
(b) The theoretical geometric structure of the title compound (B3LYP/6–311++G(d,p)
level).
level by means of the NBO 3.1 program within the Gaussian 03W
package [56].
3. Results and discussion
3.1. Description of the crystal structure
The title compound, an Ortep-3 view of which is shown in
Fig. 2a, crystallizes in the orthorhombic space group Pbca with
Z = 8 in the unit cell. The asymmetric unit in the crystal structure
contains only one molecule. The molecular structure of the title
compound is approximately planar. The dihedral angle between
the aromatic ring systems is 1.2(3)◦. The imino group is coplanar
with the hydroxyphenyl ring, as shown by the C9–C8–C7–N1 tor-
sion angle of 2.6(9)◦. It is also known that Schiff bases may exhibit
photochromism depending on the planarity or non-planarity,
respectively [57]. Therefore, the title compound may exhibit ther-
mochromic properties.
When the geometry of hydrogen bond in the optimized struc-
tures is examined, the proton donor group O1–H1 forms an
intramolecular interaction with nitrogen atom N1, with a bond
◦
˚
length of 1.91 A and a bond angle of 141.44 for HF and a bond length
◦
˚
of 1.76 A and a bond angle of 145.80 for B3LYP (Table S2; Sup-
porting Information). Similarly, another intramolecular H-bond,
◦
˚
O1–H1· · ·Br1, of length 3.49 A and bond angle 142.28 for HF and
◦
˚
of length 3.32 A and bond angle 138.67 for B3LYP is also observed.
The presence of the H-bond appears as an important property of
the molecule, stabilizing its conformation in the crystal; as shown
in the molecular modeling part, this is also visible in the model
obtained for the molecule discussed.
The tautomerism appears in ortho-hydroxylated Schiff bases
as a result of intramolecular proton transfer from oxygen atom
to nitrogen atom. This proton transfer is resulted in two tau-
tomeric structures as enol-imine and keto-amine forms in the
solid state. These tautomeric forms are related to two types of
intramolecular hydrogen bonds as O–H· · ·N in enol-imine form
and N–H· · ·O in keto-amine form (Fig. 1). The C7–N1 and C9–O1
bonds of the title compound are the most important indicators
of the tautomeric type. Because, the C2–O1 bond is of a double
bond for the keto-amine tautomer, whereas this bond displays
single bond character in enol-imine tautomer. In addition, the
C7–N1 bond is also a double bond in enol-imine tautomer and
of single bond lenght in keto-amine tautomer [58]. In the title
compound, the enol-imine form is favored over the keto-amine
It is well known that DFT-optimized bond lengths are usually
longer and more accurate than HF due to the inclusion of elec-
tron correlation. On the contrary, according to our calculations, the
HF method correlates well for the bond length compared with the
B3LYP method (Table 1). The biggest difference between experi-
˚
mental and calculated bond lengths is about 0.033 A for HF and
˚
0.055 A for B3LYP, the root mean square error (RMSE) is found
˚
˚
to be 0.015 A for HF and 0.026 A for B3LYP, indicating that the
bond lengths obtained by the HF method show a good correlation
with the experimental values. For bond angles, the opposite was
observed. As can be seen from Table 1, both the biggest difference
˚
form, as indicated by C9–O1 (1.328 (7) A) and C7–N1 (1.262

18
H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
Table 1
Selected molecular structure parameters.
Parameters
Experimental
Calculated 6–311++G(d,p)
HF
B3LYP
Bond lengths (Å)
C1–C2
C1–C6
C1–N1
C2–C3
C2–Br1
C3–C4
C4–C5
C5–C6
C7–N1
1.378 (6)
1.399 (7)
1.405 (6)
1.370 (7)
1.884 (5)
1.384 (8)
1.361 (8)
1.379 (7)
1.262 (6)
1.433 (7)
1.400 (8)
1.406 (8)
1.328 (7)
1.387 (8)
1.357 (9)
1.364 (8)
1.367 (8)
1.422 (7)
1.283 (8)
1.295 (8)
1.311 (8)
1.312 (8)
1.392
1.405
1.391
1.404
1.382
1.897
1.384
1.383
1.383
1.258
1.466
1.401
1.396
1.325
1.393
1.374
1.386
1.367
1.389
1.302
1.314
1.331
1.315
0.033
0.015
1.404
1.402
1.390
1.913
1.393
1.393
1.389
1.286
1.450
1.420
1.406
1.337
1.402
1.384
1.395
1.378
1.411
1.333
1.350
1.348
1.352
0.055
0.026
C7–C8
C8–C9
C8–C13
C9–O1
Fig. 3. FT-IR spectrum of the title compound.
C9–C10
C10–C11
C11–C12
C12–C13
C12–O2
C14–F2
C14–F1
C14–O2
C14–F3
Max. differencea
RMSE
and the RMSE for the bond angles obtained by the B3LYP method
are smaller than those determined by HF.
A logical method for globally comparing the structures obtained
with the theoretical calculations is by superimposing the molecular
skeleton on that obtained from X-ray diffraction, giving a RMSE of
˚
˚
2.229 A for B3LYP and 2.247 A for the HF method (Fig. S4; Support-
ing Information). According to these results, it may be concluded
that the HF calculation well reproduce the bond lengths, while
the B3LYP method is better at predicting the bond angles and 3-D
geometry of the title compound. In spite of the differences, cal-
culated geometric parameters represent a good approximation,
and they are the bases for calculating other parameters, such as
vibrational frequencies, electronic absorption spectra and molecu-
lar electrostatic potential, as described below.
Bond angles (◦)
C2–C1–C6
C2–C1–N1
C6–C1–N1
C3–C2–C1
C3–C2–Br1
C1–C2–Br1
C2–C3–C4
117.4 (5)
118.3 (4)
124.2 (5)
121.9 (5)
117.7 (4)
120.3 (4)
119.9 (6)
119.5 (6)
120.7 (5)
119.5 (6)
122.1 (6)
118.4 (6)
121.9 (6)
119.7 (6)
121.1 (6)
120.0 (6)
118.7 (6)
119.7 (6)
120.6 (5)
110.9 (7)
114.0 (7)
108.0 (6)
122.3 (5)
119.1 (5)
121.3 (5)
119.6 (5)
107.4 (8)
103.9 (7)
112.1 (6)
125.0 (5)
117.3 (5)
118.15
120.21
121.56
120.97
118.50
120.50
120.08
119.66
120.05
117.38
123.25
119.35
120.63
119.81
120.49
119.55
119.84
120.57
121.03
108.13
112.50
108.35
123.15
119.11
122.67
118.21
108.23
107.07
112.39
120.11
118.63
4.89
117.81
120.12
121.97
121.20
118.74
120.04
119.92
119.86
120.00
118.36
122.23
119.40
120.55
119.69
121.11
119.11
119.61
120.06
121.17
107.97
112.88
108.30
122.21
119.14
121.57
119.28
108.14
106.57
112.78
120.93
117.74
4.07
C5–C4–C3
C4–C5–C6
3.3. IR spectroscopy
O1–C9–C10
O1–C9–C8
C10–C9–C8
C11–C10–C9
C10–C11–C12
C11–C12–C13
C11–C12–O2
C13–C12–O2
C12–C13–C8
C5–C6–C1
F2–C14–O2
F1–C14–O2
F2–C14–F1
N1–C7–C8
C9–C8–C13
C9–C8–C7
C13–C8–C7
F2–C14–F3
F1–C14–F3
O2–C14–F3
C7–N1–C1
C14–O2–C12
Max. differencea
RMSE
Harmonic vibrational frequencies of the title compound
were calculated using the DFT/B3LYP and HF method with
6–311++G(d,p) basis set. The vibrational band assignments were
made using the Gauss-View molecular visualisation program. Fur-
thermore, theoretical vibrational spectra of the title compound
were interpreted by means of PEDs using VEDA 4 program [45].
In order to facilitate assignment of the observed peaks we have
analyzed some vibrational frequencies and compared our calcu-
lated results of the title compound with their experimental ones
and showed in Table 2. In order to improve the agreement between
the calculated and the experimentally observed values, the calcu-
lated harmonic frequencies have been scale down via introduction
of scaling factors. In this study four different scaling factors were
used. For wavenumbers less than 1700 cm−1, factors of 0.983 at
B3LYP level and 0.908 at HF level were used. For wavenumbers
higher than 1700 cm−1, factors of 0.958 at B3LYP level and 0.910 at
HF level were used [61].
The FT-IR spectra of the title compound were recorded in the
4000–400 cm−1 region using KBr pellets on a Schmadzu FT-IR 8900
spectrophotometer and given in Fig. 3. The O–H group gives rise
to three vibrations as stretching, in-plane bending and out-of-
plane bending vibrations. The OH group vibrations are likely to
be most sensitive to the environment, so they show pronounced
shifts in the spectra of the hydrogen-bonded species. The non-
hydrogen-bonded or a free hydroxyl group absorb strongly in the
3550–3700 cm−1 region [62]. Intramolecular hydrogen bonding
if present in sixmembered ring system would reduce the O–H
stretching band to 3200–3550 cm−1 region [63]. In the case of un-
substituted phenol it has been shown that the frequency of OH
stretching vibration in the gas phase is 3657 cm−1 [64]. In our case
1.56
1.29
Torsion angles (◦)
C2–C1–N1–C7
C6–C1–N1–C7
C13–C12–O2–C14
C11–C12–O2–C14
C8–C7–N1–C1
177.3 (7)
−3.3 (9)
90.0 (8)
−94.3 (8)
−178.8 (5)
2.2 (8)
133.18
−49.90
91.12
−92.66
177.93
−2.36
141.52
−41.81
90.04
−94.26
176.11
−2.95
N1–C1–C2–Br1
a
RMSE and maximum differences between the bond lengths and angles com-
puted using theoretical methods and those obtained from X-ray diffraction.
the experimental OH stretching mode was observed at 3417 cm−1
,

H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
19
Table 2
Comparison of the experimental and calculated vibrational frequencies (cm−1).
Experimental IR with KBr
Calculated at 6–311++(d,p)
HF
Assignments (%PEDa)
B3LYP
3417
–
–
3068
–
3576
3065
3062
3051
3048
3040
3028
2934
1703
1612
1602
1483
1465
1443
1379
1359
1312
1289
1275
1260
1223
1219
1037
1025
932
3121
3073
3069
3060
3055
3048
3038
2912
1639
1595
1579
1490
1476
1456
1405
1360
1295
1225
1201
1178
1165
1109
1022
983
892
883
816
751
730
696
666
651
605
597
476
458
ꢅ(O–H) (99)
ꢅs(C–H) R2 (99)
ꢅs(C–H) R1 (94)
ꢅas(C–H) R2 (98)
ꢅs(C–H) R2 (98)
ꢅas(C–H) R1 (96)
ꢅas(C–H) R1 (98)
ꢅaliphatic(C–H) (99)
ꢅ(C N) (44) + ꢅ(C C) R1 (10)
ꢅ(C C) R2 (16)
–
–
2898
1620
1586
1570
1489
1472
1441
1381
1354
1293
1257
1201
1172
1151
1030
965
943
900
884
826
755
735
680
651
622
605
570
486
435
ꢅ(C C) R1 (15)
(OH) (19) + (C–H) R1 (22)
(C–H) R1 (11) + ␥ (C–H) R2 (12)
␥(OH) (18)
ꢅ(C–C) R1 (30) + (OH) (27)
(C–H) (48)
aliphatic
ꢅphenol (C–O) (37) + (C–H) R1 (10)
ꢅs(C–F3) (20) + ꢅ(CO–CF3) (18) + ꢅ(C–N) (11)
ꢅ(C–C) R1 (14) + ꢅ(C–OCF3) (11) + ꢅ(C–N) (11)
ꢅ(CO–CF3) (31) + ꢅs(C–F3) (29)
␥(C–H) R2 (83)
ꢅas(C–F3) (64) + ı(FOFC) (20)
ꢅ(Br–C) (10) + ˇ(CCC) R2 (54)
ˇaliphatic(C–H)
ˇ(CCN) (10) + ꢆ(HCCC) R1 (10)
ꢆ(HCCC) R1 (51)
ꢆ(HOCC) R1 (69)
ω(C–H) R2 (59)
ꢆ(HCCC) R2 (10) + ꢆ(CCCC) R1 (38) + ı(OCCC) R1 (16)
ˇ(CCC) R2 (12)
ꢅ(C–F3) (16) + ˇ(COC) (10) + ω(FCF) (11) + ı(FOFC) (12)
ꢅ(Br–C) (10) + ˇ(CCC) R2 49
ı(FOFC) (44)
ˇ(CCC) R1 (13) + ω(FCF) (29)
ˇphenol (OCC) (16) + ω(FCF) (21) + ˇ(OCC) (15)
ꢆ(CCCC) R1 (18) + ı(BrCCC) (13)
900
850
761
741
725
698
646
623
602
481
464
a
Potential energy distribution (PED), less than 10% are not shown.
ꢅ, stretching; , rocking; ω, wagging; ˇ, bending; ꢆ, torsion; ı, out of plane bending; s, symmetric; as, asymmetric. Abbreviations: R1, trifluoromethoxyphenol ring; R2,
Bromophenyl ring.
which have been calculated with the B3LYP and HF at 3121 and
3576 cm−1, respectively. Generally, the OH in-plane bending vibra-
tion in phenols lie in the region 1300–1400 cm−1. The strong bands
at 1381–1489 cm−1 in the FT-IR spectra corresponds to in-plane-
bending vibration of OH group. The OH out-of-plane deformation
vibration in phenols, in general lies in the region 517–710 cm−1
[65]. The band at 826 cm−1 in the FT-IR spectra corresponds to out-
of-plane bending mode of hydroxyl vibration. The calculated values
of OH group vibrations show good agreement with the experimen-
tal results.
respectively [66]. The C–H aromatic stretching mode was observed
at 3068 cm−1 experimentally, and calculated at 3073–3038 cm−1
for B3LYP and at 3065–3028 cm−1 for HF. The band at 2898 cm−1
correspond to the aliphatic C–H stretching mode. The C–H in-
plane bending vibration computed at 1490, 1476, 1295, 1165
and 1124 cm−1 by B3LYP/6–311++G(d,p) method shows excel-
lent agreement with FT-IR bands at 1489, 1472, 1293, 1151 and
1043 cm−1. The bands observed at 884, 755 and 735 cm−1 in FT-IR
spectra are assigned to C–H out-of-plane bending vibration for the
title compound.
Another characteristic region of the Schiff bases derivative
spectrum is 1100–1400 cm−1, which is attributed to C–O stretch-
ing vibrations. The Car–OH stretching vibration was observed
at 1293 cm−1 which confirms the presence of phenol group in
the compound. Three strong infrared bands at 1257, 1172, and
1030 cm−1 are assigned to the C–F stretching modes. According
to the calculations, the first two bands are caused by symmetric
CF3 stretching modes and the latter is due to the asymmetric CF3
stretching mode. Furthermore, the medium bands at 651, 570 and
486 cm−1 in the IR spectrum of the title compund are assigned
to CF3 deformation modes. The C–Br vibrations are often found
over a wide range of 480–1290 cm−1 since its vibration is easily
affected by the adjacent atoms or groups [67,68]. In FT-IR spec-
trum of the title compound the medium bands at 965 and 622 cm−1
are assigned to C–Br stretching vibration coupled with ring defor-
mation. The other vibrational frequencies can be seen in Table 2.
The presence of O–H, C N and Car–O stretching vibrations strongly
The characteristic region of 1700–1500 cm−1 can be used to
identify the proton transfer of Schiff bases. Azomethine (C N) bond
stretching vibration was observed to be 1620 cm−1 experimentally,
while that have been calculated at 1703 cm−1 for HF and 1639 cm−1
for B3LYP. The benzene ring modes predominantly involve C
C
bonds and the vibrational frequency is associated with C C stretch-
ing modes of carbon skeleton [62]. The bands observed at 1620,
1586 and 1570 cm−1, which can be attributed to the C C stretch-
ing vibrations, were calculated at 1701, 1612 and 1602 cm−1 for HF
and at 1639, 1595 and 1579 cm−1 for B3LYP, respectively. The bands
observed at 570, 680 and 965 cm−1 in the FT-IR spectra are ascribed
to the vibration modes including the phenyl CCC angle bending.
The theoretically computed values of the angles bending vibration
modes show good agreement with the experimental values.
The aromatic C–H stretching, C–H in-plane bending and C–H
out-of-plane bending vibrations appear in 2900–3150 cm−1
1100–1500 cm−1 and 750–1000 cm−1
frequency ranges,
,

20
H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
Fig. 4. Correlation graphics of calculated and experimental frequencies of the title compound.
suggests that the title compound has the enol-imine form in the
solid state.
show a new band, especially in polar and nonpolar solvents, at
>400 nm [71–73]. In this study, any band belong to keto-amine
form was not observed with a value greater than 400 nm, which
indicates that the title compound is in enol form not in keto in
ethanol solvent.
To make a comparison with the experimental observations, we
present correlation graphs in Fig. 4 based on the calculations. As
we can see from correlation graphics in Fig. 4 experimental fun-
damentals are found to have a better correlation with HF than
B3LYP. Besides, the vibrational frequencies calculated by B3LYP
method are more compatible to experimental values with the
exception of O–H stretching mode which has the correlation coef-
ficient R2 = 0.99873.
Electronic absorption spectra were calculated using the TD-
DFT and TD-HF methods based on the B3LYP/6–311++G(d,p) and
HF/6–311++G(d,p) level optimized structures in gas phase, respec-
tively. The calculated results are listed in Table 3 along with the
experimental absorption spectra data. For TD-HF calculations, the
absorption wavelengths are obtained at 257, 220 and 179 nm. It
is obvious that these bands are not corresponding to the experi-
mental results. For TD-DFT calculations, the theoretical absorption
bands are predicted at 355, 280 and 215 nm and can easily be seen
that they correspond to the experimental absorption ones. In addi-
tion to the calculations in gas phase, TD-DFT calculations of the
title compound in ethanol solvent were performed using the PCM
model. The PCM calculations reveal that the calculated absorption
bands have slight blue-shifts (see Fig. 5) with values of 351, 278
and 214 nm comparing with the gas phase calculations of TD-DFT
method. Thus, the TD-DFT method in the gas phase and in solvent
media is convenient for predicting electronic absorption spectra.
According to the investigation on the frontier molecular orbital
(FMO) energy levels of the title compound, we can find that the
corresponding electronic transfers happened between the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO), HOMO−3 and LUMO, HOMO−1 and
LUMO+3 orbitals, respectively. Fig. 6 shows the distributions and
energy levels of the FMOs computed at the B3LYP/6–311++G(d,p)
level for the title compound. Molecular orbital coefficient analyses
based on optimized geometry indicate that, for the title com-
pound, the frontier molecular orbitals are mainly composed of
p-atomic orbitals, so aforementioned electronic transitions are
mainly derived from the contribution of the ␲ → ␲* band.
3.4. Electronic absorption spectra
The electronic absorption spectra of the title compound in
ethanol solvent were recorded within the 200–600 nm range and a
representative spectrum is shown in Fig. 5. As can be seen from the
figure, electronic absorption spectra showed three bands at 348,
272 and 212 nm. The maximum absorption wavelength is assigned
to intramolecular charge transfer band of the azomethine C
N
group. These values are similar to those found for related Schiff
base compounds [69,70].
The UV–visible spectrum of ortho-hydroxylated Schiff bases that
exist mainly as enol-imine structure indicate the presence of a band
at <400 nm, whereas compounds existing in the keto-amine form
3.5. Atomic charge distributions in gas-phase and in
solution-phase
The Mulliken atomic charges for the non-H atoms of
the title compound calculated at the HF/6–311++G(d,p) and
B3LYP/6–311++G(d,p) levels in gas-phase are presented in
Table S6 (Supporting Information). To investigate the solvent effect
for the atomic charge distributions of the title compound, based
on the B3LYP/6–311++G(d,p) model and Onsager reaction field
model, three kinds of solvent (chloroform, ethanol and water) were
Fig. 5. UV–vis spectra of title compound in ethanol solvent and the comparison
of calculated transitions in gas phase and ethanol solvent with the experimental
spectra.

H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
21
Table 3
Experimental and theoretical electronic absorption spectra values.
Experimental
TD-HF
TD-DFT
TD-PCM
Wavelength (nm)
Abs.
Wavelength (nm)
Oscillator strength
Wavelength (nm)
Oscillator strength
Wavelength (nm)
Oscillator strength
348
272
212
0.18
0.20
0.44
257
220
206
0.48
0.02
0.02
354
280
215
0.34
0.26
0.21
351
278
214
0.48
0.27
0.30
selected and calculated values are also listed in Table S6 (Support-
ing Information).
As can be seen from the figure, this molecule has several possi-
ble sites for electrophilic attack. Negative regions in the studied
molecule are found around the phenol O1 atom, O2, Br1 and the
fluor atoms of the CF3 group. Also, a negative electrostatic potential
region is observed around the N1 atom. The negative V(r) values are
−0.030 a.u. for O1, which is the most negative region, −0.019 a.u.
for O2, −0.011 a.u. for Br1, −0.011, −0.013 and −0.010 a.u. for F1,
F2 and F3 atoms, respectively, and −0.005 a.u. for N1 atom, which
is the least negative region. However, a maximum positive region
is localized on the C7–H7 bond with a value of +0.032 a.u., indi-
cating a possible site for nucleophilic attack. According to these
calculated results, the MEP map shows that the negative potential
sites are on electronegative atoms as well as the positive potential
sites are around the hydrogen atoms. These sites give informa-
tion concerning the region from where the compound can undergo
non-covalent interactions.
The Mulliken atomic charges show that the O2 atom, the Br atom
and the fluor atoms (F1, F2 and F3) have negative atomic charges
in gas phase. On the other hand, it is found that, in the solution
phase, the atomic charge values of the O2, Br1, F1 and F2 atoms
are bigger than those in gas phase and while the atomic charge
values will increase with increasing polarity of the solvent, the
value for F3 decreases with increasing solvent polarity. The coor-
dination of these atoms will changed in different solvents, which
may be helpful when one wishes to use the title compound to
construct interesting metal complexes with different coordinate
geometries [74]. This calculated result is not only consistent with
many reported experimental values [75–78], it also supports the
original idea of our synthesis.
The MEP is best suited for identifying sites for intra- and inter-
molecular interactions [82]. When an intramolecular interaction
takes place the electrostatic potential of the negative atom becomes
less negative and the positive region on the other atom becomes
less positive [82,83]. For the MEP surface in the studied molecule,
the weak negative regions associated with the N1 and Br1 atoms
and also the weak positive region by the nearby H1 atom are indica-
tive of intramolecular (N1· · ·H1–O1) and (Br1· · ·H1–O1) hydrogen
bondings.
3.6. Molecular electrostatic potential
The MEP is related to the electronic density and is a very useful
descriptor for determining the sites for electrophilic and nucle-
ophilic reactions as well as hydrogen bonding interactions [79].
The electrostatic potential V(r) is also well suited for analysing pro-
cesses based on the “recognition” of one molecule by another, as
in drug–receptor, and enzyme–substrate interactions, because it is
through their potentials that the two species first “see” each other
[80,81].
3.7. Natural bond orbital (NBO) analysis
To predict reactive sites for electrophilic and nucleophilic attack
for the investigated molecule, the MEP at the B3LYP/6–311++G(d,p)
optimized geometry was calculated. The negative (red and yellow)
regions of the MEP are related to electrophilic reactivity and the
positive (blue) regions to nucleophilic reactivity, as shown in Fig. 7.
NBO analysis provides an efficient method for studying intra-
and inter-molecular bonding and interaction among bonds, and
also provides a convenient basis for investigating charge transfer
or conjugative interaction in molecular systems [84]. The larger the
E(2) value, the more intensive is the interaction between electron
donors and electron acceptors, i.e., the more donating tendency
Fig. 6. Molecular orbital surfaces and energy levels given in parantheses for the
HOMO−3, HOMO−1, HOMO, LUMO and LUMO+3 of the title compound computed
at B3LYP/6–311++G(d,p) level.
Fig. 7. Molecular electrostatic potential map calculated at B3LYP/6–311++G(d,p)
level.

22
H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
from electron donors to electron acceptors and the greater the
extent of conjugation of the whole system. Delocalization of elec-
tron density between occupied Lewis-type (bond or lone pair)
NBO orbitals and formally unoccupied (antibond or Rydgberg) non-
Lewis NBO orbitals correspond to a stabilizing donor–acceptor
interaction.
ˇxzz, ˇyzz, ˇzzz, respectively. The components of the first hyperpo-
larizability can be calculated using the following equation [92]:
ꢂ
1
3
ˇi = ˇiii
+
(ˇijj + ˇjij + ˇjji
)
(5)
i =/ j
In order to investigate the intramolecular interactions, the sta-
bilization energies of the title compound were performed by using
second-order perturbation theory. To investigate the solvent effect
for the stabilization energies of the title compound, based on
B3LYP/6–311++G(d,p) model and PCM model, three kinds of sol-
vent were selected and calculated values were listed in Table 4. For
each donor NBO(i) and acceptor NBO(j), the stabilization energy E(2)
associated with electron delocalization between donor and accep-
tor is estimated as [85,86]
Using the x, y and z components of ˇ, the magnitude of the first
hyperpolarizability tensor can be calculated by:
ꢃ
ˇtot
=
(ˇx2 + ˇy2 + ˇz2)
(6)
The complete equation for calculating the magnitude of ˇ from
Gaussian 03W output is given as follows:
ꢄ
2
2
2
ˇtot
=
(ˇxxx + ˇxyy + ˇxzz
)
+ (ˇyyy + ˇyzz + ˇyxx
)
+ (ˇzzz + ˇzxx + ˇzyy
)
(7)
(Fij)2
i εj − εi
The calculations of the total molecular dipole moment (ꢂ), lin-
E(2) = −q
(2)
ear polarizability (˛) and first-order hyperpolarizability (ˇ) from
the Gaussian output have been explained in detail previously [94],
and DFT/B3LYP has been extensively used as an effective method to
investigate the organic NLO materials. To investigate the effects of
where qi is the donor orbital occupancy, εi, εj are diagonal ele-
ments (orbital energies) and Fij is the off-diagonal NBO Fock matrix
element.
basis sets on the NLO properties of the title compound, the ꢂtot
,
NBO analysis revealed that the n(N1) → ꢇ*(O1–H1) interac-
tions give the strongest stabilization to the system of the title
compound by 33.61 kcal/mol and strengthen the intramolecular
O1–H1· · ·N1 hydrogen bond in gas phase. As shown in Table 4,
the E(2) value due to the n(N1) → ꢇ*(O1–H1) orbital interaction
increases with increasing dielectric constant of solvent. The result
can be used to explain the enhancement of the O–H· · ·N hydro-
gen bond strength with increase of solvent polarity. There is
another NBO interaction of the n(Br1) → ꢇ*(O1–H1) imply the exis-
tence of O1–H1· · ·Br1 hydrogen bond which has the stabilization
energy 0.21 kcal/mol in gas phase. The stabilization energies of
the n(Br1) → ꢇ*(O1–H1) orbital interactions is almost a constant
as solvent polarity increases. Thus, it is apparent that O1–H1· · ·N1
and O1–H1· · ·Br1 interactions significantly influence crystal pack-
ing with this molecule.
˛
and ˇtot were calculated by B3LYP method with 6–31G(d),
tot
6–31+G(d), 6–31++G(d,p), 6–311+G(d), and 6–311++G(d,p) basis
sets and listed in Table S8 (Supporting Information).
From Table S8 (Supporting Information), we see that calculated
values of the ꢂtot, ˛tot and ˇtot slightly depend on the size of basis
sets. Obtained values of the ꢂtot and ˛tot with 6–31G(d) basis set
are smaller than those obtained with large size of basis sets. It is
found that the calculated results of the ꢂtot and ˛tot for the basis
sets from 6–31+G(d) to 6–311++G(d,p) have minor differences from
each other. Since there are not any reported experimental values for
the first hyperpolarizability of the title compound in the literature,
it is difficult to conclude which basis set computes reliable values
of ˇtot
.
Urea is one of the prototypical molecules used in the
study of the NLO properties of molecular systems. Therefore
it was used frequently as
tive purposes. The calculated values of ꢂtot, ˛tot and ˇtot for
a threshold value for compara-
3.8. Nonlinear optical effects
3
˚
the title compound are 3.560–3.749 D, 29.266–33.548 A and
Nonlinear optical (NLO) effects arise from the interactions of
electromagnetic fields in various media to produce new fields
altered in phase, frequency, amplitude or other propagation char-
acteristics from the incident fields [87]. NLO is at the forefront of
current research because of its importance in providing the key
functions of frequency shifting, optical modulation, optical switch-
ing, optical logic, and optical memory for the emerging technologies
in areas such as telecommunications, signal processing, and optical
interconnections [88–91].
3.445–3.946 × 10−30 cm5/esu, which are grater than those
3
˚
of urea (the ꢂtot, ˛tot and ˇtot of urea are 1.373 D, 3.831 A
and 0.3728 × 10−30 cm5/esu obtained by B3LYP/6–31G(d)
method). Although the calculated values of ˇtot are smaller
than that of 4-(2,3,4-trihydroxybenzylideneamino)antipyrine
(ˇtot = 10.012 × 10−30 cm5/esu calculated with B3LYP/6–31G(d)
method) [87] and 4-(2,3-dichlorobenzylideneamino)antipyrine
(ˇtot = 25.191 × 10−30 cm5/esu calculated with B3LYP/6–31G(d)
method) [95]. These results indicate that the title compound is a
good candidate of NLO material.
The non-linear optical response of an isolated molecule in an
electric field Ei(ω) can be presented as a Taylor series expansion of
the total dipole moment, ꢂtot, induced by the field:
To understand this phenomenon in the context of molec-
ular orbital theory, we examined the molecular HOMOs and
molecular LUMOs of the title compound. The calculated ener-
gies gaps are also listed in Table S8 (Supporting Infor-
mation). The HOMO–LUMO energy gaps were calculated as
3.981–4.074 eV for the title compound, 3.923 eV for 4-(2,3,4-
trihydroxybenzylideneamino)antipyrine [87], 3.903 eV for 4-(2,3-
dichlorobenzylidene amino)antipyrine [95]. It is also found as
8.205 eV for urea by B3LYP/6–31G(d) method.
As can be seen from the ˇtot values for these compounds, there
is an inverse relationship between first hyperpolarizability and
HOMO–LUMO gap, allowing the molecular orbitals to overlap to
have a proper electronic communication conjugation, which is a
marker of the intramolecular charge transfer from the electron
donating group through the ␲-conjugation system to the electron
accepting group [96,97].
ꢂtot = ꢂ0 + ˛ijEj + ˇijkEjEk + · · ·
(3)
where ˛ is the linear polarizability, ꢂ0 the permanent dipole
moment and ˇijk are the first hyperpolarizability tensor compo-
nents. The isotropic (or average) linear polarizability is defined as
[92]:
˛
xx + ˛yy + ˛zz
˛
tot
=
(4)
3
First hyperpolarizability is a third rank tensor that can be
described by 3 × 3 × 3 matrix. The 27 components of 3D matrix
can be reduced to 10 components due to the Kleinman symmetry
[93] (ˇxyy = ˇyxy = ˇyyx = ˇyyz = ˇyzy = ˇzyy ;. . . likewise other permu-
tations also take same value). The output from Gaussian 03 provides
10 components of this matrix as ˇxxx, ˇxxy, ˇxyy, ˇyyy, ˇxxz, ˇxyz, ˇyyz
,

H. Tanak et al. / Spectrochimica Acta Part A 87 (2012) 15–24
23
Table 4
Second-order perturbation theory analysis of the Fock matrix in NBO basis, calculated at B3LYP/6–311++G(d,p) level and PCM model.
Dielectric constant
Donor orbital (i)
Acceptor orbital (j)a
E(2) (kcal/mol)b
εj − εi (a.u.)c
Fij (a.u.)d
LP(1) N1
LP(2) Br1
BD*(1) O1–H1
BD*(1) O1–H1
33.61
0.21
0.50
0.42
0.127
0.010
Gas (ε = 1)
LP(1) N1
LP(2) Br1
BD*(1) O1–H1
BD*(1) O1–H1
34.35
0.22
0.50
0.43
0.128
0.010
Chloroform (ε = 4.9)
Ethanol (ε = 24.55)
LP(1) N1
LP(2) Br1
BD*(1) O1–H1
BD*(1) O1–H1
34.68
0.22
0.50
0.43
0.128
0.010
LP(1) N1
LP(2) Br1
BD*(1) O1–H1
BD*(1) O1–H1
34.71
0.22
0.50
0.43
0.128
0.010
Water (ε = 78.39)
a
BD*, antibonding orbital; LP, lone pair. For BD, (1) denotes ꢇ orbital. For LP, (1) and (2) denote the first and the second lone pair electron, respectively.
E(2) means energy of hyper conjugative interactions.
Energy difference between donor and acceptor i and j NBO orbitals.
b
c
d
Fij is the Fock matrix element between i and j NBO orbitals.
Table 5
with the DFT according to our calculations. However, the DFT
method seems to be more appropriate than the HF method for the
obtaining the bond angles and 3D geometry of the title compound.
For the calculation of vibrational frequencies, both the methods,
DFT and HF, can predict the IR spectrum of title compound well.
The TD-DFT calculations lead to much closer agreement with
the experimental absorption spectra, both in the gas phase and
in solvent media. Molecular orbital coefficient analyses suggest
that the electronic spectrum correspond to the ␲ → ␲* electronic
transition. The MEP map shows that the negative potential sites
are on electronegative atoms while the positive potential sites are
around the hydrogen atoms. These sites give information about
the region from where the compound can undergo non-covalent
interactions. NBO analysis revealed that the n(N1) → ꢇ*(O1–H1)
interaction gives the strongest stabilization to the system. The
predicted nonlinear optical (NLO) properties of the title compound
are much greater than those of urea. The title compound is a
good candidate as second-order nonlinear optical material. The
correlations between the thermodynamic properties Cp0,m, Sm0 , Hm0
and temperature T were also obtained. We hope our paper will be
helpful for the design and synthesis of new materials.
Thermodynamic properties at different temperatures at B3LYP/6–311++G(d,p) level.
T (K)
Hm0 (kcal/mol)
Cp0,m (cal mol−1 K−1
)
Sm0 (cal mol−1 K−1
)
200
250
298.15
300
350
6.00
8.80
48.70
59.35
69.32
69.69
79.37
88.17
96.04
120.51
132.97
144.63
145.07
156.86
168.31
179.39
12.00
12.13
15.96
20.25
24.96
400
450
3.9. Thermodynamic properties
To determine thermodynamical properties of the title com-
pound, the standard thermodynamic functions: heat capacity
(Cp0,m), entropy (Sm0 ), and enthalpy (Hm0 ) based on the vibrational
analysis at the B3LYP/6–311++G(d,p) level were obtained and are
listed in Table 5. The table shows that the standard heat capaci-
ties, entropies, and enthalpies increase at any temperatures from
200.00 to 450.00 K, because the intensities of the molecular vibra-
tion increase with increasing temperature.
The correlation equations between these thermodynamic prop-
erties and temperature T are as follows:
Appendix A. Supplementary data
Cp0,m=2.22995 + 0.28245T − 1.41884T2 × 10−4 (R2 = 0.99992)
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.10.055.
(8)
References
Sm0 = 67.30951 + 0.27953T − 6.7657T2 × 10−5 (R2 = 1)
(9)
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(10)
Based on these relationships, the values of Cp0,m, Sm0 , and Hm0 can
be obtained at any other temperatures and be helpful for the further
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4. Conclusions
(E)-2-[(2-Bromophenyl)iminomethyl]-4-
trifluoromethoxyphenol has been synthesised and characterised
by IR, UV–vis, and X-ray single-crystal diffraction. The X-ray, IR
and UV–vis spectral data for the title compound show that the
compound exists in the enol form, which is stabilized by the
intramolecular O–H· · ·N hydrogen bond. Although it is well known
that DFT optimized bond lengths are usually longer and more
accurate than HF because of inclusion of electron correlation,
the HF method correlates better for the bond length compared

24
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