Synthesis, molecular structure, spectroscopic and theoretical studies on E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol

Article abstract of DOI:10.1016/j.molstruc.2015.02.001

Synthesis, crystallographic characterization, spectroscopic (FT-IR) and density functional modelling studies of a new Schiff base E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol C₁₇H₁₉NO₃ have been reported. The molecular structure obtained from X-ray single-crystal analysis of the investigated compound in the ground state has been compared using Hartree-Fock (HF) and density functional theory (DFT), B3LYP and B1B95 functional with the 6-311++G(d,p) basis set. In addition to the optimized geometrical structures, atomic charges, molecular electrostatic potential (MEP), natural bond orbital (NBO), nonlinear optical (NLO) effects and thermodynamic properties of the compound have been investigated by using DFT calculations. The electronic properties of the title compound in solvent media were also examined using the DFT calculations. The potential energy surface (PES) scans about important torsion angles are performed by using B3LYP/6-311++G (d,p) level of theoretical approximation for the compound. The experimental (FT-IR) and calculated vibrational frequencies (using DFT calculations) of the title compound have been compared. The predicted NLO properties of the compound which calculated by the B3LYP method with 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-311++G(d,p) basis sets are greater than ones urea. The standard thermodynamic functions were obtained for the title compound with the temperature ranging from 200 to 450 K.

Full text of DOI:10.1016/j.molstruc.2015.02.001

Accepted Manuscript
Synthesis, molecular structure, spectroscopic and theoretical studies on E-2-
ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol
Celal Tuğrul Zeyrek, Gökhan Alpaslan, Hamit Alyar, Mustafa Yıldız, Nefise
Dilek, Hüseyin Ünver
PII:
S0022-2860(15)00073-3
DOI:
http://dx.doi.org/10.1016/j.molstruc.2015.02.001
MOLSTR 21299
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
28 November 2014
30 January 2015
2 February 2015
Please cite this article as: C.T. Zeyrek, G. Alpaslan, H. Alyar, M. Yıldız, N. Dilek, H. Ünver, Synthesis, molecular
structure, spectroscopic and theoretical studies on E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol, Journal of
Molecular Structure (2015), doi: http://dx.doi.org/10.1016/j.molstruc.2015.02.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis, molecular structure, spectroscopic and theoretical studies on E-2-
ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol
Celal Tuğrul Zeyreka*, Gökhan Alpaslanb, Hamit Alyarc, Mustafa Yıldızd, Nefise Dileke, Hüseyin Ünverf**
aAnkara Nuclear Research and Training Center, Turkish Atomic Energy Authority, TR-06100 Besevler-Ankara,
Turkey.
bDepartment of Medical Services and Techniques, Vocational School of Health Services, Giresun University, TR-
28200 Giresun, Turkey.
cDepartment of Physics, Science and Art Faculty Karatekin University, TR-18100 Çankırı, Turkey.
dDepartment of Chemistry, Faculty of Sciences and Arts, Çanakkale Onsekiz Mart University, TR-17100 Çanakkale,
Turkey.
eDepartment of Physics, Faculty of Sciences and Arts, University of Aksaray, TR-68100, Aksaray, Turkey.
fDepartment of Physics, Faculty of Sciences, University of Ankara, TR-06100 Besevler-Ankara, Turkey.
Corresponding author. Tel.: +90-312-2126230; fax: +90-312-2226421
E-mail address: zeyrek@taek.gov.tr, ctzeyrek@gmail.com
**Corresponding author. Tel.: +90-312-2126720 - 1106; fax: +90-312-2232395
E-mail address: unverh@ankara.edu.tr, huseyinunverr@gmail.com
1

Abstract
Synthesis, crystallographic characterization, spectroscopic (FT-IR) and density functional
modelling studies of a new Schiff base E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol
C17H19NO3 have been reported. The molecular structure obtained from X-ray single-crystal
analysis of the investigated compound in the ground state has been compared using Hartree-Fock
(HF) and density functional theory (DFT), B3LYP and B1B95 functional with the 6-311++G(d,p)
basis set. In addition to the optimized geometrical structures, atomic charges, molecular
electrostatic potential (MEP), natural bond orbital (NBO), nonlinear optical (NLO) effects and
thermodynamic properties of the compound have been investigated by using DFT calculations.
The electronic properties of the title compound in solvent media were also examined using the
DFT calculations. The potential energy surface (PES) scans about important torsion angles are
performed by using B3LYP/6-311++G (d,p) level of theoretical approximation for the compound.
The experimental (FT-IR) and calculated vibrational frequencies (using DFT calculations) of the
title compound have been compared. The predicted NLO properties of the compound which
calculated by the B3LYP method with 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-
311++G(d,p) basis sets are greater than ones urea. The standard thermodynamic functions were
obtained for the title compound with the temperature ranging from 200 to 450 K.
Keywords: Schiff base; Crystal structure; PES scan; Density functional theory; FT-IR, Nonlinear
optical effects.
2

1. Introduction
Schiff-bases are known azomethines and they having a double C=N bond and usually
synthesized from the condensation of primary amines and active carbonyl groups. Schiff bases
exhibit mainly interest as corrosion inhibitors, catalyst carriers, thermo-stable materials, metal
complexion agents and in biological systems and they have a wide range of applications, such as
dyes and pigments [1–9]. Several Schiff bases have nonlinear optical (NLO) behavior [10-13].
They have been under investigation the last years, since their potential applicability in optical
communications. We reported previously the spectroscopic studies, nonlinear optical (NLO)
properties and crystal structures of several Schiff base compounds [14-20]. Density functional
theory (DFT) is widely used methods in the computational quantum chemistry by using ab initio
calculation of electronic structures of many-particle systems. Many molecular properties are
calculated and revealed according to the development of better and better exchange-correlation
functional method [21]. In the literature, the DFT calculations has a great accuracy in reproducing
the experimental values in geometry, dipole moment, vibrational frequency, excited states of
organic compounds [21-23]. Recently, the synthesis, structure, spectroscopic and DFT modelling
studies of 1-[(4-ethoxyphenylimino)methyl]napthalene-2-ol has been studied by our research
group [20]. In the present work, firstly we present the synthesis, crystal structure and Fourier
transform infrared spectroscopy (FT-IR) of
a
new Schiff base E-2-ethoxy-4-[(4-
ethoxyphenylimino)methyl]phenol. The molecular structure, the potential energy surface (PES)
scans, vibrational frequencies assignments, atomic charges, molecular electrostatic potential
(MEP), natural bond orbital (NBO), nonlinear optical (NLO) effects and thermodynamic
properties of the compound have been investigated by using DFT calculations. Theoretical
geometrical parameters and frequencies were compared with the corresponding experimental
results.
3

2. Materials and methods
2.1 General techniques
Elementary analyses were performed on a Vario EL III CHNS elemental analyzer. The
infrared spectra of the investigated compound were recorded in the 4000–400 cm-1 region using
KBr pellets on a MATTSON-1000 model FT-IR spectrometer. A suitable single crystal of the title
compound was mounted on goniometer and data were collected at 296 K on a Bruker Kappa
APEXII CCD diffractometer using graphite monochromated MoKα radiation (λ=0.71073 Å).
2.2. Synthesis of the compound
3-Ethoxy-4-hydroxybenzaldehyde, 4-ethoxyaniline, CHCl3, n-pentane and ethanol were
purchased from Merck (Germany). A solution of 3-ethoxy-4-hydroxybenzaldehyde (0.005 mol,
0.83 g) in 50 mL pure ethanol was prepared and heated to the boiling temperature. 4-
Ethoxyaniline (0.005 mol, 0.69 g) was dissolved in 60 mL hot ethanol. A mixture of the two
solutions was then refluxed for 1 h. The yellow crystals were formed during the reflux. The yellow
precipitate was collected by filtration, and then washed with cold ethanol. It was recrystallized
from CHCl3 : n-pentane (3:1). C17H19NO3 (285.14): calcd. C 71.54; H 6.66; N, 4.90; found C
71.53, H 6.67, N 4.90. The chemical diagram of the molecule is shown in Figure S1
(supplementary material). The suitable single crystals were obtained directly from the synthesis of
the compound. Formula; C17H19NO3, Yield; 92 %. Carbon, nitrogen and hydrogen analyses were
within ±0.4% of theoretical values.
2.3. X-ray structure determination
Cell parameters of the compound were determined by using SAINT software [24].
Absorption correction ( = 0.08 mm-1) was obtained by the multi-scan method via SADAPS
V2012/1 [25] software. Details of the data collection conditions and the parameters of the
4

refinement process are given in Table 1. The compound is solved by direct methods using
SHELXS-97 [26] and refined with SHELXL-97 [27]. The molecular figures are prepared by the
help of Mercury and ORTEP3 program packages [28, 29]. The atoms of ethoxy groups are
disordered over two positions. For C1A, C2A, C33A, C34A, O2A and O6A atoms the site
occupancy factor is 0.656(9) and for C1B, C2B, C33B, C34B, O2B and O6B atoms the site
occupancy factor is 0.344(9). Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as
Supplementary Publication No. CCDC 10360311.
2.4.Calculation details
The molecular geometry of the compound is directly taken from the X-ray diffraction
experimental result of the geometry optimization. This result was used at in the Gaussian 09
software package and the Gauss-view visualization program [30,31] for the DFT calculations with
Becke’s Three-parameter Hybrid Functional Using the Lee-Yang-Parr (LYP) Correlation
Functional B3LYP at the 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-311++G(d,p)
basis sets by using the Berny method [32, 33]. The optimized structure parameters of the title
compound were calculated by using Hartree-Fock (HF) and density functional theory (DFT) with
the functional B3LYP and B1B95 using the 6-311++G(d,p) basis set.
The Mulliken atomic charges and natural population analysis (NPA) for the included H
atoms of the compound were calculated at B3LYP/6-311++G(d,p) level by NBO analysis [34].
In order to investigate the solvent effect selected five kinds of solvent ( =4.9, chloroform;
=10.36, dichloroethane; =24.55, ethanol; =46.7, dimethylsulfoxide and =78.39 water), the
atomic charge distributions of the compound were also calculated at B3LYP/6-311++G(d,p) level
by using a Polarized Continuum (PCM) model [35].
5

To investigate the reactive sites and to identify sites of intra- and intermolecular
interactions of the compound, molecular electrostatic potential surface was evaluated by using
B3LYP/6-311++G(d,p) method.
The HOMO and LUMO are the main orbitals taking part in chemical stability. The
HOMO represents the ability to donate an electron, LUMO as an electron acceptor representing
the ability to obtain an electron. The total molecular energies, HOMO and LUMO energies and
HOMO-LUMO band gaps were predicted by the B3LYP/6-311++G(d,p) level.
The chemical hardness is useful to rationalize the relative stability and reactivity of
chemical compounds. There are large HOMO–LUMO gap in the hard compounds and more
stable and less reactive than soft compounds having small HOMO–LUMO gap [36]. The
definitions of universal concepts of molecular structure stability and reactivity can be provided by
using DFT method [37]. For definition of hardness η, following equation developed [38, 39];
1
(1)
  (I  A)
2
In the equation (1) I is the vertical ionization energy and A stands for the vertical electron
affinity. According to the Koopmans theorem [40], the ionization energy and electron affinity can
be equalized through HOMO and LUMO orbital energies:
EA  HOMO
(2)
IP  LUMO
According to the equation (2), the hardness corresponds to the gap between the HOMO and
LUMO orbitals. Hence, the larger the HOMO-LUMO energy gaps the harder molecule.
1
(3)
  (LUMO HOMO
)
2
For the title compound, the chemical hardness (η) were calculated with the B3LYP/6-311++G(d,p)
base sets.
The stabilization energies of the compound were computed by using second-order
perturbation theory for examined the intra- and intermolecular interactions among bonds and also
6

investigated charge transfer and conjugative interactions in the molecular system of the
investigated compound. The stabilization energy E(2) connected with electron delocalization
between donor NBO(i) and acceptor NBO(j) were estimated as [41]
(F )2
ij
E(2)  qi
(4)
 j i
where qi is the donor orbital occupancy, i, j are diagonal elements (orbital energies) and Fij is the
off-diagonal NBO Fock matrix element. B3LYP/6-311++G(d,p) level was used for second-order
perturbation theory analysis of the Fock matrix.
Thanthiriwatte and Nalin de Silva were explained in detail previously that how is the
calculations of the total dipole moment (μtot), linear polarizability (αij), and the first-order
hyperpolarizability (βijk) from the Gaussian output file [42]. The total molecular dipole moment
(μtot), linear polarizability (αij), and the first-order hyperpolarizability (βijk) was predicted by the
B3LYP method with different base sets 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-
311++G(d,p) for investigating the effects of basis sets on the NLO properties.
The natural bond orbital (NBO) analysis of the title compound was fulfilled at the
B3LYP/6-311++G(d,p) level by means of the NBO 3.1 program within the Gaussian 09 package
[43].
It is well-known that the vibrational wavenumbers obtained by DFT computations usually
overestimate than their experimental counterpart. These discrepancies can be corrected either by
computing anharmonic corrections or by introducing a scaled field. In order to compensate these
systematic errors and also to get precise vibrational wavenumbers for the investigated compound
in solid phase, we calibrated the vibrational wavenumbers by using a scale factor group for
individual primitive internal coordinates at B3LYP/6-311++G(d,p) level of theory. The scale
factor values used in the scaled quantum mechanics force field (SQMFF) methodology [44]. The
assignments of each vibrational mode were defined from their potential energy distributions
7

(PED) which were calculated by using SQM program [45]. The visual check for the vibrational
band assignments were also performed by using Gauss-View molecular visualization program.
Finally, the standard thermodynamic functions were obtained from statistical
thermodynamics based on the vibrational frequency analysis at B3LYP/6-311++G(d,p) level at the
Gaussian 09 software package.
3. Results and discussions
3.1. Description of the crystal structure
The title compound, an Ortep-3 view which is shown in Figure 1, crystallizes in the
monoclinic space group Pbca with Z = 16 in the unit cell. The asymmetric unit of the title
compound contains two independent molecules, namely (I) and (II), which are linked by a O–
H···N hydrogen bond. Both the molecules have an E conformation about the central C=N bond.
While molecule (I) in the asymmetric unit is non-planar, molecule (II) is almost planar. The
dihedral angles between the two phenyl ring systems are 27.79(6) and 5.07(7), respectively, for
molecules (I) and (II). In the azomethine groups, the N1–C9 distance is 1.269(3) Å for molecule
(I) and N2–C26 distance is 1.271(3)Å for molecule (II). The bond lengths and bond angles of the
title compound are in a good agreement with those of the related structures [46-50]. The obtained
geometric parameters from X-ray study are given in Table 2. In crystal structure of the title
compound, there are two intermolecular hydrogen bonds. The donor and acceptor distances are
3.454(3) Å for C12–H12···O3i [symmetry code (i): -x, -y+3, -z,] and 2.958(3) Å for O4–H4···N1ii
[symmetry code (ii): x, y-1, z.], respectively (Figure 2 and Figure 3). The details of the hydrogen
bonds are summarized in Table 3.
3.2. Optimized molecular structure
The molecular structure of E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol has been
experimentally determined. The optimized structure parameters such as bond lengths, bond angles,
8

and dihedral angles of the title compound were calculated by using Hartree-Fock (HF) and
density functional theory (DFT) with the functional B3LYP and B1B95 using the 6-311++G(d,p)
basis set. The calculated bond distances, bond angles and selected torsion angles are compared
with the experimental values of the title compound (Table 2). The conformational discrepancies
between the X-ray structure and optimized counterparts by using Hartree-Fock (HF), the B1B95
and the B3LYP functional with 6-311++G(d,p) basis set can be seen from Figure S2
(supplementary material).
As seen from Table 2 and Figure S2 (supplementary material), when the X-ray structure of
the title compound is compared with its optimized counterparts, slight conformational
discrepancies are observed between them. The most significant structural disparities are found in
the orientation of 3-Ethoxy-4-hydroxybenzaldehyde ring (ring1) in the compound. This structural
disparity is defined by torsion angles C5–C9–N1–C10 [172.97(19)o], C9–N1–C10–C15 [-
17.9(3)o], and C6–C5–C9–N1 [173.4(2)o] for experimentally. These torsion angles are the
orientation of the aldehyde ring (ring1) part with respect to the 4-ethoxyaniline ring (ring2) part,
and have been calculated for the investigated compound at 178.236, -43.252, 178.626o for the
HF/6-311++G(d,p) level, 176.454, -38.543, and 178.013o for the B1B95/6-311++G(d,p) level and
176.661, -37.503, and 178.460o for the B3LYP/6-311++G(d,p) level.
The ring1 part and ring2 part are inclined at the angle of 27.8(1) with respect to one
another for experimentally, whereas this angle has been calculated as 44.1(6)o for the HF/6-
311++G(d,p) level, 41.1(6)o for the B1B95/6-311++G(d,p) level, and 39.2(6)o for the B3LYP/6-
311++G(d,p) level.
The bond lengths of C9–N1 [1.269(3) Å] and C26–N2 [1.271(3) Å] have a double bond
character. These bond lengths are predicted by the bond lengths of 1.2538 Å for HF, 1.2735 Å for
B1B95 and 1.2791 Å for B3LYP level.
It is well known that DFT-optimized bond lengths are usually longer and more accurate
than HF due to the inclusion of electron correlation [19, 20, 51]. According to our calculations
9

(Table 2), the biggest difference between experimental and calculated bond lengths is about
0.0242 Å for HF, 0.0320 Å for B1B95, and 0.0390 Å for B3LYP level, while the root mean square
error (RMSE) is found to be 0.0235 Å for HF, 0.0252 Å for B1B95, and 0.0226 Å for B3LYP.
According to the RMSE value, the bond lengths obtained by the B3LYP level show a good
correlation with the experimental values. For bond angles, the opposite was observed. As can be
seen from Table 2, both the biggest difference and the RMSE for the bond angles obtained by the
DFT calculations (B1B95 and B3LYP level) are bigger than those determined by HF. A logical
method for globally comparing the structures obtained from theoretical calculations is by
superimposing the molecular skeleton on that obtained from X-ray diffraction [Figure S2
(supplementary material)]. According to these results, it may be concluded that the B3LYP
calculation well reproduces the bond lengths, while the HF method is better at predicting the bond
angles and 3D geometry of the title compound.
Whereas the most of the calculated bond lengths are slightly longer than the experimental
values, as seen from Table 2, the calculated bond lengths and angles are in good agreement with
the experimental values of the title compound and also similar compounds in the literature [19, 20,
46-50].
We noted that the experimental results belong to the solid phase whereas theoretical
calculations belong to the gas-phase. The result in the differences of bond parameters between the
calculated and experimental values depend on the existence of the crystal field along with the
inter-molecular interactions connects the molecules together in the solid state [52]. The presence
of the intermolecular hydrogen bonds (Table 3) appears as an important property of the title
compound, stabilizing its conformation in the crystal, so the NBO analysis is also discussed as
follows.
10

3.3. Potential energy surface (PES) scan
To investigate the conformational stability of the title compound, the potential energy
surface (PES) scans about the link fragments of the aldehyde ring (ring1) part with respect to the
4-ethoxyaniline ring (ring2) part in the whole molecule (Figure 1). For this reason, the torsion
angles T1(C9–N1–C10–C15) and T2(C6–C5–C9–N1) are relevant coordinates for conformational
flexibility of the investigated molecule. The scans were obtained by minimizing the potential
energy using B3LYP/6-311++G(d,p) level of theory in all geometrical parameters by varying the
torsion angles at a step of 10o in the range of 0-360o rotation around the bond. The variations of
potential energy change from its equilibrium with the torsional perturbation are presented in
Figure S3 (supplementary material). Potential energy surface (PES) scan for torsion angles T1
o
show five minima positions at 37.503, 147.503, 217.503, 327.503 and -37.503 and T2 shows
three minima positions at -178.460, 1.540 and 181.540o. Among these the deepest minima values
correspond to the optimized molecular geometry [T1(C9–N1–C10–C15) = -37.503 and T2(C6–
C5–C9–N1) = 178.460o using B3LYP/6-311++G(d,p) level] of the compound which is directly
taken from the X-ray diffraction experimental result. The energy of the most stable conformation
is -939.91536142 Hartree, respectively.
3.4.Vibrational spectra
The vibrational band assignments were performed at B3LYP/6-311++G(d,p) theory level
combined with scaled quantum mechanics force field (SQMFF) methodology [44] to compare the
experimental (FT-IR) and calculated vibrational frequencies of the title compound (Figure 4). The
compound E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol consists of N=40 atoms and hence
114 (3N-6) normal modes of vibrations. We have analyzed the normal vibrational frequencies and
compared our calculated results of the investigated compound with the experimental ones on the
basis of potential energy distributions (PED) and given in Table 4. The infrared spectra of the
11

investigated compound have some characteristic bands of the vibrations of the O – H, C – H, C =
N, C – O, C – C, C – H3 and C – H2 groups.
O–H vibrations
The characteristic region of the O – H group vibrations spectrum in the Schiff bases, which
have a free hydroxyl group or non-hydrogen bonded, is 3550 – 3700 cm-1 [53]. In this study, the
experimental O–H stretching vibration was observed at 3735 cm-1. The O – H stretching vibration
was calculated at 3582 cm-1 for B3LYP/6-311++G(d,p) level with the 100% contribution of PED.
The experimental and theoretically predicted frequency for O–H vibration by B3LYP/6-311G(d,p)
level shows excellent agreement with recorded spectrum as well as the literature data and also find
support from PED values [54, 55]. The strong hydrogen bonding if present in the Schiff bases
composed with 2-hydroxy-1-napthaldehyde system would reduce the O–H stretching band shifting
to lower wavenumber 2900 cm-1 [20, 36]. The in plane O–H bending vibration modes occur
1350± 50 cm-1, while the out-of plane O–H bending vibration modes is 650±50 cm-1 [56]. The in-
plane O–H bending vibration modes is observed at 1371 experimentally and calculated at 1355
cm-1. The out-of-plane OH deformation appears at 456 experimentally and calculated at 448 cm-1.
C–H vibrations
The aromatic structure shows the presence of C–H stretching vibrations in the region 3000
– 3125 cm-1, which is the characteristic region for the identification of υ(CH) stretching vibrations
[36]. But in this region, the bands are not appreciable affected by the nature of the substituent [57].
In the FT-IR spectrum of the title compound, symmetric C–H stretching vibrations are observed at
3223 and 3268 cm-1. The calculated values of these symmetric C–H stretching vibrations are 3076,
3066, 3059 and 3058 cm-1. The calculated values the asymmetric C–H stretching vibrations are
3043, 3038 and 3033 cm-1. The asymmetric and the symmetric modes are almost pure modes with
the 90-100% contribution of PED. Substitution sensitive C–H in-plane bending vibrations lie in
12

the region 1000 – 1300 cm-1 [54]. In the title compound, four infrared bands at 1286, 1240, 1178
and 1123 cm-1 with medium, very strong and very weak intensities are assigned to C–H in-plane
bending vibrations. These vibrations are corresponding to 1296, 1239, 1180 and 1130 cm-1 of
calculated values. The C–H out-of-plane bending vibrations appear in the range 1000 – 675 cm-1
[54, 58, 59]. The observed vibrations are 971, 946, 917 and 793 cm-1 for the C–H out-of-plane
bending vibrations. The bands at 940, 917, 908, 906, 875, 830, 808, 797 and 785 cm-1 are assigned
to the C–H out-of-plane bending vibrations for the investigated compound. As seen in Table 4, the
C–H out-of-plane bending vibrations are assigned as mixed and pure modes, respectively.
C–H2 vibrations
For the assignments of CH2 group frequencies, basically six fundamentals can be
associated to each CH2 group namely, υs(CH2)-symmetric stretch, υas(CH2)-asymmetric stretch,
sci(CH2)- scissoring, and ρ(CH2)-rocking modes which belong to in-plane vibrations. In addition
to that w(CH2)-wagging and Tw(CH2)-twisting modes of CH2 group would be expected to be
out‐of‐plane bending vibrations. The asymmetric CH2 stretching vibration is generally observed at
the 2926±10 cm‐1, while the CH2 symmetric stretch will appear 2855±10 cm‐1, cm‐1 [56]. The CH2
asymmetric and symmetric stretching vibrations computed by B3LYP/6-311++G(d,p) at 2906 and
2873 cm‐1 are assigned to CH2 asymmetric stretching and symmetric pure modes with the 98 and
99% contribution of PED. The calculated band at 2966 cm‐1 is assigned to CH2 asymmetric
stretching mix modes with 68% contribution of PED. The other fundamental CH2 group vibrations
which are sci(CH2)- scissoring, ρ(CH2)-rocking, w(CH2)-wagging and Tw(CH2)-twisting modes
appear in the expected wavenumber region of 1475-875 cm‐1 [60, 61]. In the investigated
compound, scaled vibrational frequencies computed at 1514 and 1380 cm‐1 are assigned to
sci(CH2)-scissoring mix modes, while observed at 1564 cm‐1in FT-IR spectrum. The computed
wavenumbers at 1390 and 1366 cm‐1 are assigned to w(CH2)-wagging vibration. The Tw(CH2)-
twisting vibration observed 1286 cm‐1 as a very strong band in FT-IR spectrum is assigned to CH2
13

twisting vibration. The calculated value of Tw(CH2)-twisting vibration is 1278 cm‐1, respectively.
The ρ(CH2)-rocking mode appear at 846 cm-1 experimentally and calculated at 818 cm-1. The
assignments of CH2 group frequencies show good agreement with literature [60-62].
C–H3 vibrations
The υs(CH3)-symmetric stretching, υas(CH3)-asymmetric stretching, δ(CH3)s-symmetric
bending deformation (umbrella mode), δ(CH3)as-asymmetric bending deformation, and ρ(CH3)-
rocking frequencies are assigned for the CH3 group in the investigated compound. The υas(CH3)-
asymmetric stretching vibration is generally observed at the 2962±10 cm‐1, while the υs(CH3)-
symmetric stretching will appear 2872±10 cm‐1 [56]. The υs(CH3)-symmetric stretching vibrations
are observed at 2909 and 2806 cm‐1, and assigned at 2911 and 2910 cm‐1 as pure modes with the
100% contribution of PED by B3LYP/6-311++G(d,p) level. The υas(CH3)-asymmetric stretching
modes are assigned at 2991, 2982, 2973, and 2971 cm‐1. The δ(CH3)s-bending deformation
(umbrella mode) show up at 1375±10 cm‐1, while δ(CH3)as-asymmetric bending deformation show
up at 1460±10 cm‐1 [56]. In our present study, the δ(CH3)s-bending deformation (umbrella mode)
vibrations are assigned at 1409, 1405, and 1380 cm‐1, whereas δ(CH3)as-asymmetric bending
deformation modes are assigned at 1496, 1495, 1493, 1486, and 1483 cm‐1. The δ(CH3)as-
asymmetric bending deformation is observed at 1472 cm-1 as experimentally. The rocking
vibrations of CH3 group usually appear in region 1070-1010 cm-1 [63]. The FT‐IR spectrum at
1178 and 1123 cm‐1 are assigned to CH3 rocking vibration. The rocking vibrations of CH3 group
are calculated at 1180, 1167, 1154, and 1115 cm-1 by B3LYP/6-311++G(d,p) level.
C=N vibrations
The C=N stretching vibrations were assigned in the region 1500-1600 cm-1 by Silverstein
[63]. In the present study, the C=N stretching vibration band observed at 1616 in FT-IR. This band
14

is calculated at 1621 cm-1 with B3LYP/6-311++G(d,p) level. The PED for this mode is 51%. The
PED for this mode suggests that this is a mixed mode (Table 4).
C–C and C=C vibrations
The ring C=C stretching vibrations for aromatic group generally appear 1430-1625 cm-1
[64] and usually assigned to C=C stretching modes in 1400-1650 cm-1 [65]. For title compound,
the C–C and C=C stretching vibrations are observed at 1616, 1564, 1427, and 1371 and 1286 cm-1
in FT-IR spectrum. The mean difference between theoretical and experimental frequencies is
about 7 cm-1. It shows the good agreement between theoretical and experimental the ring C–C and
C=C stretching vibrations for aromatic group.
C–O vibrations
The C–O stretching vibrations appear in the spectral range 1168-1310 [66]. The C–O
stretching vibrations are observed at 1240, 1178 and 1123 cm-1 in FT-IR spectra respectively, and
assigned values of these modes are 1239, 1180 and 1130 cm-1 by the DFT calculations. The C–O
stretching vibrations are also calculated at 1222, 1130, 115, 1027, 963 and 917 cm-1 with 10-43%
contributions of PED. The phenolic C–OH stretching vibration was observed at 1291 cm-1 and
calculated at 1273 cm-1 [20]. For title compound, the phenolic C–OH stretching vibration is
observed at 1240 cm-1 and assigned at 1239 cm-1 with 25% contributions of PED.
The calculated values of other group vibrations show good agreement with the
experimental results. The other experimental and calculated vibrational values can be seen in
Table 4. To make a comparison with the experimental observation, we present correlation
graphics in Figure S4 (supplementary material). The relations between the calculated unscaled
(ucal) and experimental (exp) wavenumbers and also the calculated scaled (cal) and experimental
(exp) wavenumbers are linear and described by the following equations:
(5)
15

(6)
According to the fitting results of the equation (1) and (2), the general scale factor value
was found to be 0.96287 for 6-311++G(d,p). As a result, the scaled fundamental vibrationals are
in good consistency with experimental results and are found a good agreement above the predicted
literature.
3.5. Atomic charge distributions, energy and dipole moment behavior in the gas and the
solution phases
The calculation of atomic charges plays a significant role in the application of quantum
mechanical calculations to molecular systems because of atomic charges affect some properties of
molecular systems including dipole moment and molecular polarizability. The atomic charges
have been also used to describe the MEP surfaces [20, 67, 68]. The total atomic charges of the
Mulliken population analysis and the natural population analysis (NPA) were listed in Table S1
(supplementary material). The calculated Mulliken atomic charges for gas and solvent phase were
illustrated in Figure S5 (supplementary material). According to the calculated Mulliken atomic
charges and, the C5 atom has a largest positive atomic charge and C8 atom has a largest negative
atomic charge. As can be seen in Figure S5 and Table S1 (supplementary materials), all of the
hydrogen atoms have net positive charge. The obtained atomic charge was showed that the H10
atom has bigger positive atomic charge (0.30164) than the other hydrogen atoms. The imine N1
atom has positive atomic charge and O1, O2 and O3 atoms have a large negative atomic charge in
the gas phase. These behavior may be result of the intermolecular N–H···O hydrogen bond. On
the other hand, as shown in Figure S5 and Table S1 (supplementary materials), the negative
atomic charge values of the O atoms in solution phase are becoming more negative while the
positive atomic charge of N1 is decreasing with the increase of the polarity of the solvent.
16

According to these results, NBO’s net charges (NPA) are slightly longer than Mulliken charges.
The intention is to accurately model partial charge magnitude and location within a molecule.
The total energies and dipole moments of the compound calculated with B3LYP/6-
311++G(d,p) level for five solvents ( =4.9, chloroform; =10.36, dichloroethane; =24.55,
ethanol; =46.7; dimethylsulfoxide and =78.39 water), in order to evaluate the difference of total
energy and dipole moment behavior of the title compound in solvent media. The results are given
in Table 5. As can be seen from Table 5 and Figure S6 (supplementary material), the dipole
moments which are calculated by the PCM method in the various solvents increase with
increasing solvent polarity. The energy difference between the gas phase and solvent media and
dipole moments are shown in Figure S6 (supplementary material). According to the results, we
can say that the obtained total energy of the compound decreases with the increasing polarity of
the solvent. The lessening in total energy of the title molecule increases the stability. We can
conclude that according to the results, the investigated molecule in the gas phase more reactive
than in the solution phase.
3.6. Molecular electrostatic potential surface
To investigate reactive sites for electrophilic and nucleophilic attack, the regions of the
MEP for the title compound was composed by DFT calculation using the optimized geometry at
the B3LYP/6-311++G(d,p). As shown Figure S7 (supplementary material), red and yellow colors
indicated for the negative regions of the MEP are related to electrophilic reactivity, while blue
colors indicated for positive regions to nucleophilic reactivity. As can be seen from Figure S7
(supplementary material), the compound has three possible sites for electrophilic attack. The
oxygen atoms O1 of the aldehyde ring and the N1 and O3 atoms of the 4-ethoxyaniline ring have
negative region. The maximum negative molecular electrostatic potential value is 0.033 a.u. for
the mainly region of the O1 atom. The H10 atom of the O1 have positive region to nucleophilic
attack with a maximum value. According to these calculated results, the region of MEP shows that
17

the negative potential sites are on electronegative atoms as well as the positive potential sites are
around the hydrogen atoms. The determining of MEP region is best suit for identifying sites for
intra- and intermolecular interactions [69]. According to the MEP surface of the compound, the
weak negative region associated with O1 atom and also the weak positive region by the nearby
H10 atom. It can be indicative of an intermolecular (O1–H10…N2) hydrogen bonding in the
compound (Figure 2 and Figure 3).
3.7. Relation between the HOMOs –LUMOs gap and the chemical hardness
The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) are the very important parameters for quantum chemistry. These orbitals play an
important role in the electric properties and determine the way the molecule interacts with other
species [70–72]. Both the HOMO and the LUMO are the main orbital taking part in chemical
reaction. While the energy of the HOMO is directly related to the ionization potential, LUMO
energy is directly related to the electron affinity. Frontier molecular orbitals (HOMO and LUMO)
may be used to predict the adsorption centers of the inhibitor molecule for corrosion of metal
surfaces [73]. To provide a reasonable qualitative indication of the excitation properties, HOMO
and LUMO for the title compound were investigated. The total molecular energies, HOMO and
LUMO energies and HOMO-LUMO band gaps were predicted by the B3LYP method with 6-
311++G(d,p). The calculated values of HOMO and LUMO energies and HOMO-LUMO band
gaps of the title compound were listed in Table 5. The HOMO–LUMO energy gap value was
found to be 3.9288 eV at B3LYP/6-311++G(d,p) in gas phase. The frontier molecular orbital
distributions and energy levels of the HOMO and LUMO, which computed at B3LYP/6-
311++G(d,p) level of the title compound are shown in Figure S8 (supplementary material). The
frontier molecular orbital shows π molecular orbital characteristics and visualized in Figure S8
(supplementary material). Except for ethoxy group atoms in the aldehyde and aniline rings of the
18

structure, the LUMO is mainly localized on the whole structure, whereas except for CH2 and CH3
atoms in the structure, the HOMO is localized on the whole structure as seen from Figure S8
(supplementary material). The HOMO and LUMO are mostly the π-antibonding type molecular
orbitals in the structure.
The chemical hardness is useful to rationalize the relative stability and reactivity of
chemical compounds. For the title compound, the chemical hardness (η) were calculated with the
B3LYP/6-311++G(d,p) base sets The results are given in Table 5. The value of energy separation
between the HOMO and LUMO is 3.9288 eV and the value of hardness is 1.9644 eV for the title
molecule. From Table 5, in going from the gas phase to the solvent phase, the chemical hardness
increases in parallel with the increasing value of the energy gap and molecule becomes more
stable. These results are in a good agreement with those of the related structures [74-76].
3.8. Natural Bond Orbital (NBO) Analysis
The natural bond orbital occupancies of the title compound are listed in Table S2
(supplementary material). The double bond character of the N1–C9 has revealed by the NBO
analysis. In the aniline ring, consist of C3, C4, C5, C6, C7 and C8 atoms and rings of the aldehyde
part, consist of C10, C11, C12, C13, C14 and C15 atoms are typically single-double arrangement
that form the conjugate structure. Also, as seen from Table S2 (supplementary material), the NBO
occupancies of single O2–C2 and O3–C16 are same level in the ethoxy part. The calculated
results from the NBO analysis are consistent with the obtained from X-ray structure analysis of
the compound. So, NBO analysis can be a very useful method for molecular modelling.
The results of second-order perturbation theory analysis of the Fock matrix at B3LYP/6-
311++G(d,p) level of theory and the stabilization energies larger than 12.55 kJ/mol are given
Table S3 (supplementary material). The stabilization energy E(2) value increases with the strong
interaction between electron donors and electron acceptors. Also, the larger stabilization energy
E(2) values, the greater the extend of the conjugation of the whole system. As seen from Table S3
19

(supplementary material), the strong intramolecular hyperconjugative interaction of the  and 
electrons of C – C to the anti C – C bond of the aromatic rings results to stabilization of some part
of the rings, such as the intramolecular hyperconjugative interaction of the (C13 – C14)
distribute to *(C13 – C12) stabilization of 16.95 kJ/mol. This enhanced further conjugate with
antibonding orbitals * of the C12 – C11 and C15 – C10 which results to strong delocalization of
69.20 and 86.94 kJ/mol, respectively. The results from the NBO analysis indicate that the C12 –
C11, C10 – C15, C6 – C5, C8 – C7 and C4 – C3 bonds have the same kind interaction, as seen
from Table S3 (supplementary material).
The donor orbitals LP(2) of O1 and O3 have strongest interaction energies resulting
stabilization of 120.92 and 122.47 kJ/mol. This important interaction reveals the existence of
intermolecular hydrogen bonding in the compound. The N1 LP(1) with antibonding orbital *(C9
– H9) causes to moderate stabilization of 54.73 kJ/mol, respectively.
The NBO analysis provides an efficient method for studying intra- and intermolecular
bonding such as O–H…N and C – H…O interactions. These interactions and bonds significantly
influence the crystal packing of this molecule.
3.9. Nonlinear Optical (NLO) Effects
To investigate the nonlinear optical properties of the molecules is very important because
of the key functions of frequency shifting, optical modulation, optical switching, optical logic and
optical memory for the emerging technologies in areas such as in telecommunications, signal
processing and optical interconnections [77].
The total molecular dipole moment (µ), linear polarizability (α), and the first-order
hyperpolarizability (β) were calculated by the B3LYP method with each of 6-31G(d), 6-
31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-311++G(d,p) basis sets to investigate the effects of
basis sets on the NLO properties. The calculated values of the µtot, αtot and βtot are listed in Table
9. From the Table 9, it can be seen that the calculated values of the µtot, αtot and βtot slightly depend
20

on the size of basis sets. The obtained values of the µtot, αtot and βtot with 6-31G(d) basis set are
smaller than those obtained with the large size of basis sets. It was found that the calculated results
for the basis sets from 6-31+G(d) to 6-311++G(d,p) have minor differences from each other.
It can be seen from the Table 9, the calculated values of βtot for the title compound are
greater than urea (the βtot of urea is 0.373x10-30 cm5/esu obtained by using B3LYP/6-31G(d) basis
set). When it is compared with the similar Schiff base compounds in the literature, the calculated
values of βtot in the compound are larger than that of N-(2,5-methylphenyl)salicylaldimine (I) (βtot
=3.752x10-30 cm5/esu) [19], while smaller than that of 2-[2,4-dimethylphenyl)iminomethyl]-3,5-
dimethoxyphenol]
(βtot
=8.256x10-30
cm5/esu)
[78]
and
1-[(4-
ethoxyphenylimino)methyl]napthalene-2-ol (βtot =33.231x10-30 cm5/esu) [20] calculated with
B3LYP/6-311++G(d,p) method. The calculated value of βtot =7.0934x10-30 cm5/esu in the gas
phase, which is greater than that of urea (βtot =0.592x10-30 cm5/esu obtained by using B3LYP/6-
311++G(d,p) method). Especially, the first-hyperpolarizability value of the investigated compound
is 11.98 times more than that of urea at the same level B3LYP/6-311++G(d,p) base set.
3.10. Thermodynamic Properties
0
0
Cp,m
The standard thermodynamic functions: heat capacity (
), entropy ( ) and enthalpy (
Sm
Hm0
) based on the vibrational analysis using the B3LYP/6-311++G(d,p) level to investigate
thermodynamical properties of the title compound were calculated and listed in Table 10. The
standard heat capacities, entropies, and enthalpies increase at any temperatures from 200 to 450 K
for the compound, by reason of the intensities of the molecular vibration increase with increasing
Sm0
and
0
Cp,m
temperature. The correlations between the thermodynamic properties
, entropy
Hm0
enthalpy
and temperatures T are described and shown in Figure S9 (supplementary material),
according to the data in Table S5 (supplementary material).
21

The correlation equations between these thermodynamic properties and temperature T are
as follows:
(R2=1)
(7)
(8)
(9)
(R2=0.99991)
(R2=1)
Sm0
Hm0
can easily be obtained at any temperatures using these
0
Cp,m
The values of
,
and
relationships and these results will be helpful for the further studies of the title compound.
4. Conclusion
E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol
has
been
synthesized
and
characterized by FT-IR and X-ray single crystal diffraction. DFT studies of the Schiff base ligand
have been also reported in this study. The calculated geometric parameters by using the Hartree-
Fock (HF) and density functional theory (DFT) with the 6-311++G(d,p) basis set are in good
agreement with the X-ray structure, in spite of the observed differences, in general. The result in
the differences of bond parameters between the calculated and experimental values depend on the
existence of the crystal field along with the inter-molecular interactions connects the molecules
together in the solid state. The potential energy surface (PES) scans two torsion angles are
performed by using B3LYP/6-311++G (d,p) level of theoretical approximation for the compound.
The energy of the most stable conformation is -939.91536142 Hartree. The total molecular
energies obtained by the PCM method decrease with the increasing polarity of the solvent and the
stability of the title compound increase in going from the gas phase to the solution phase. The
lessening in total energy of the title molecule increases the stability. We can conclude that
according to the results, the investigated molecule in the gas phase more reactive than in the
solution phase.
22

The vibrational band assignments were performed at B3LYP/6-311++G(d,p) theory level
to compare the experimental (FT-IR) and calculated vibrational frequencies of the title compound.
The calculated vibrations show good agreement with the experimental results. The Mulliken
atomic charges for the included H atoms of the compound were calculated at B3LYP/6-
311++G(d,p) level . The obtained atomic charge was showed that the H10 atom has bigger
positive atomic charge (0.301642) than the other hydrogen atoms. The imine N1 atom has positive
atomic charge and O1, O2 and O3 atoms have a large negative atomic charge in the gas phase.
These behaviors may be result of the intermolecular dipole-dipole interactions once again because
of the partial positive hydrogen (H10) and partial negative nitrogen (N) atoms. According to the
MEP surface of the compound, the weak negative region associated with O1 atom and also the
weak positive region by the nearby H10 atom. It can be indicative of an intermolecular (O1–
H10…N2) hydrogen bonding in the compound. The HOMO–LUMO energy gap value was found
to be 3.9288 eV at B3LYP/6-311++G(d,p) in gas phase. The frontier molecular orbital shows π
molecular orbital characteristics. According to the value of energy separation between the HOMO
and LUMO and the value of hardness is 1.9644 eV for the title molecule, in going from the gas
phase to the solvent phase, the chemical hardness increases in parallel with the increasing value of
the energy gap and molecule becomes more stable. The bond characters and inter-intramolecular
interactions of the investigated molecule has revealed by the NBO analysis. The calculated results
from the NBO analysis are consistent with the obtained from X-ray structure analysis of the
compound. The total molecular dipole moment (µ), linear polarizability (α), and the first-order
hyperpolarizability (β) were calculated by the B3LYP method with different basis sets to
investigate the effects of basis sets on the NLO properties. Our computational results yield that βtot
for the title compound is greater than those of urea. So the HOMO-LUMO gap is also related to
the polarizability of a molecule and the investigated compound is a good candidate as a nonlinear
0
Sm
0
m
0
Cp,m
optical material. The thermodynamic properties heat capacity (
), entropy ( ), enthalpy (H
)
and temperatures T were also obtained. The results show that the standard thermodynamic
23

functions increase at any temperatures from 200 to 450 K, because the intensities of the molecular
vibration increase with increasing temperature.
We hope that the synthesis, crystallographic and spectroscopic characterization and DFT
studies of E-2-ethoxy-4-[(4-ethoxyphenylimino)methyl]phenol will be helpful for the design and
synthesis of new materials.
Acknowledgements
The authors are grateful to the Ankara University Grants Commission for a research grant
(Project No. : 2014H0430005).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in the online version, at
http://dx.doi.org/
Note
1. Further information may be obtained from: Cambridge Crystallographic Data Center
(CCDC), 12 Union Road, Cambridge CB21EZ, UK, by quoting the depository number
CCDC 1036031, e-mail: deposit@ccdc.cam. ac.uk.
References
[1] I. Danaee, O. Ghasemi, G.R. Rashed, M. Rashvand Avei, M.H. Maddahy, J. Mol. Struct. 1035
(2013) 247–259.
[2] R. Drozdzak, B. Allaert, N. Ledoux, I. Dragutan, V. Dragutan, R. Verpoort, Coord. Chem.
Rev. 249 (2005) 3055-3074.
[3] C. J. Yang, S. A. Jenekhe, Macromolecules 28 (1995) 1180-1196.
24

[4] S. Destri, I. A. Khotina, W. Porzio, Macromolecules 3 (1998) 1079-1086.
[5] C. T. Zeyrek, A. Elmali, Y. Elerman, Z. Naturforsch 60b (2005) 520-516.
[6] D.R. Larkin, J. Org. Chem. 55, 1563-1568 (1990).
[7] J. Vanco, O. Svajlenova, E. Racanska, J. Muselik, J. Valentova, J. Trace Elem. Med. Biol. 18
155-161 (2004).
[8] A. E. Taggi, A.M. Hafez, H. Wack, B. Young, D. Ferraris, T. Lectka, J. Am. Chem.Soc. 124
(2002) 6626-6635.
[9] R. Ramnauth, S. Al-Juaid, M. Motevalli, B.C. Parkin, A.C. Sullivan, Inorg. Chem. (2004) 43
4072.
[10] H. Ünver, A. Karakas¸ A. Elmali, J. Mol. Struct. 702 (2004) 49-54.
[11] H. Ünver, A. Karakas¸ A. Elmali, T. N. Durlu, J. Mol. Struct. 737 (2005) 131-137.
[12] A. Karakaş, A. Elmali, H. Ünver, I. Svoboda, J. Mol. Struct. 702 (2004) 103-110.
[13] A. Karakaş, H. Ünver, A. Elmali, J. Mol. Struct. 877 (2008) 152-157.
[14] H. Unver, A. Elmali, A. Karakas, H. Kara, E. Donmez, J. Mol. Struct. 800 (2006) 18-22.
[15] A. Karakas, H. Ünver, Spectrochimica Acta Part a-Molecular and Biomolecular Spectroscopy
75 (2012) 1492-1496.
[16] H. Ünver, M. Yıldız, B. Dülger, Ö. Özgen, E. Kendi, T. N. Durlu, J. Mol. Struct. 737 (2005)
159-164.
[17] H. Ünver, M. Yıldız, H. Özay, T.N. Durlu, Spectrochim. Acta A 74 (2009) 1095–1099.
[18] H. Ünver, M. Yıldız, A. Kiraz, N.O. İskeleli, A. Erdönmez, B. Dülger, T.N. Durlu, J. Chem.
Crystallogr. 36 (2006) 229-237.
[19] C. T. Zeyrek, J. Korean Chem. Soc. 57 (2013) 461-471.
[20] C. T. Zeyrek, N. Dilek, M. Yıldız, H. Ünver, Mol. Phys., 112 19 (2014) 2557.
[21] E. Kavitha, N. Sundaraganesan, S. Sebastian, M. Kurt, Spectrochim. Acta. Part A 77 (2010)
612-619.
25

[22] Y. X. Sun, Q. L. Hao, Z. X. Yu, W. X. Wei, L. D. Lu, X. Wang, Mol. Phys. 107 (2009) 223-
235.
[23] I. Seiji, F. Hiroo, K. Hidetoshi, I. Makoto, K. Nobuaki, Bull. Chem. Soc. Jpn. 76(4) (2003)
733-742.
[24] Bruker, APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA (2012).
[25] Bruker, SADABS, Bruker AXS Inc., Madison, Wisconsin, USA, 2005.
[26] G. M. Sheldrick, SHELX-97, Program for the solution of crystal structures, University of
Göttingen, Germany (1997).
[27] G. M. Sheldrick, SHELXL-97, Program for the refinement of crystal structures, University
of Göttingen, Germany (1997).
[28] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M.Towler, J.
Van de Streek, J. Appl. Crystallogr. 39 (2006) 453–457.
[29] L. J. Farrugia, J. Appl. Crystallogr. 45(2012) 849-854.
[30] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V.
N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S.
Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz,
J. Cioslowski, and D. J. Fox, Gaussian 09, Revision D.01 (Gaussian, Inc., Wallingford CT, 2009).
[31] R. Dennington, T. Keith, J. Millam, GaussView, Version 5, (Semichem, Inc., Shawnee
Mission, KS, 2009).
26

[32] H.B. Schlegel, J. Comput. Chem. 3 (1982) 214-218.
[33] C. Peng, P.Y. Ayala, H.B. Schlegel, M.J. Frisch, J. Comput. Chem. 17 (1996) 49-56.
[34] R.S. Mulliken, J. Chem. Phys. 23 (1955) 1833-1840.
[35] J. B. Foresman, T. A. Keith, K. B. Wiberg, J. Snoonian, and M. J. Frisch, J. Phys. Chem. 100,
16098-16104 (1996).
[36] N. Özbek, G. Kavak, Y. Özcan, S. İde, N. Karacan, J. Mol. Struct. 919 (2009) 154-159.
[37] P. Geerlings, F. De Proft, W. Langenaeker, Chem. Rev. 103 (2003) 1793-1873.
[38] R. G. Pearson. J. Chem. Ed. 64 (1987) 561-567.
[39] R. G. Parr, P. K. Chattaraj, J. Am. Chem. Soc. 113 (1991) 1854-1855.
[40] T. Koopmans, Physica 1 (1933) 104-113.
[41] E. Scrocco, J. Tomasi, Adv. Quant. Chem. 11(1978) 115.
[42] K. S. Thanthiriwatte, K. M. Nalin de Silva, J. Mol. Struct. (Theochem), 617 (2002) 169-175.
[43] E. D. Glendening, J. K.Badenhoop, A. E. Reed, J. E. Carpenter, F. Weinhold, F. NBO
Version 3.1, Theoretical Chemistry Institute, University of Wisconsin, Madison, (1995).
[44] G. Fogarasi, P. Pulay, Ab initio calculation of force fields and vibrational spectra, Vibrational
Spectra and Structure: a Series of Advances, vol. 14 (Chapter 3), 125–219, Elsevier, Amsterdam,
(1985).
[45] SQM version 1.0, Scaled Quantum Mechanical, Green Acres Road, Fayetteville, Arkansas,
72703, (2013).
[46] A. D. Khalaji, M. Weil, K. Gotoh, H. Ishida, Acta Crystallogr. E65 (2009) o436.
[47] A. D. Khalaji, K. Fejfarová, M. Dušek, Acta Crystallogr. E68 (2012) o2646.
[48] J. Li, Z.P. Liang, X.S. Tai, Acta Crystallogr. E64 (2008) o2319.
[49] A. Özek, B. Koşar, Ç. Albayrak, O. Büyükgüngör, Acta Crystallogr. E66 (2010) o684.
[50] E. Soydemir, O. Büyükgüngör, Ç. Albayrak, O. Büyükgüngör, M. Odabaşoğlu, Acta
Crystallogr. E67 (2011) o599.
27

[51] C. T. Zeyrek, H. Ünver, Ö. T. Arpacı, K. Polat, N. O. İskeleli, M. Yıldız, J. Mol. Struct. 1081
(2015) 22-37.
[52] F.F. Jian, P.S. Zhao, Z.S. Bai, L. Zhang, Struct. Chem. 16 (2005) 635-639.
[53] A. Teimouri, A. N. Chermahini, K. Taban, and H. A. Dabbagh, Spectrochim. Acta A 72
(2009) 369-377.
[54] C. Arunagiri, A. Subashini , M. Saranya , P. Thomas Muthiah , K. Thanigaimani, I. Abdul
Razak, Spectrochim. Acta. Part A 135 (2015) 307-316.
[55] Y. Wang, Z. Yu, Y. Sun, Y. Wang, L. Lu, Spectrochim. Acta A 79 (2011) 1475-1482.
[56] Brian C. Smith, Infrared Spectral Interpretation: A Systematic Approach, CRC Press, New
York, 1999.
[57] A. Teimouri, A. N. Chermahini, K. Taban, H. A. Dabbagh, Spectrochim. Acta A 72 (2011)
369-377.
[58] Y. Erdogdu, M. Tahir Gulluoglu, Spectrochim. Acta A 74 (2009) 162-167.
[59] N. Sundaraganesan, B. Dominic Joshua, K. Sethu, Spectrochim. Acta A 66 (2007) 381-388.
[60] H. Alyar, A. Ünal, N. Özbek, S. Alyar, N. Karacan, Spectrochim. Acta A 91 (2012) 39-47
[61] S. P. V. Chamundeeswari, E. R. J. J. Samuel, N. Sundaraganesan, European Journal of
Chemistry 2 (2) (2011) 136‐145
[62] V. Arjunan, S. Subramanian, S. Mohan, Turk J. Chem 27 (2003), 423-431.
[63] R.M. Silverstein, F.X. Webster, Spectroscopic Identification of Organic Compounds, sixth
ed., John wiley & Sons Inc., New York, 2003.
[64] Govindarajan, K. Gansan, S Periandy, S. Mohan, Spectrochim. Acta A76 (2010) 12.
[65] D. Michalska, D.C. Bienko, A.J.A. Bienko, Z. Latajaka, J. Phys. Chem. 100 (1996) 1186-
1193.
[66] A.R. Berenji, S.F. Tayyari, M. Rahimizadeh, H. Eshghi, M. Vakili, A. Shiri, Spectrochim.
Acta Part A 102 (2013) 350-357.
[67] V.L. Abramenko, V.S. Sergienko, Russ. J. Inert. Chem 47 (2002) 905-911.
28

[68] V. Balachandran, K. Parimala, Spectrochim. Acta A 96 (2012) 340.
[69] P. Politzer, M.C. Concha, J.S. Murray, Int. J. Quantum Chem. 80 (2000) 184-192.
[70] M. Govindarajan, S. Periandy, K. Carthigayen, Spectrochim. Acta A 97 (2012) 411-422.
[71] M. Govindarajan, M. Karabacak, Spectrochim. Acta A 96 (2012) 421-435.
[72] C. Ravikumar, I.H. Joe, V.S. Jayakumar, Chem. Phys. Lett. 460 (2008) 552-558.
[73] R. M. Issa, M. K. Awad, F. M. Atlam, Materials and Corrosion, 61(8) (2010) 709-714.
[74] H. Tanak, A. A. Ağar, O. Buyukgungor, Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy 118 (2014) 672–682.
[75] A. A. Ağar, M. Yavuz, H. Tanak, Molecular Physics Vol. 108, No. 13, 10 July 2010, 1759–
1772.
[76] B. Koşar, Ç. Albayrak, Spectrochimica Acta Part A 78 (2011) 160–167.
[77] C. Andraud, T. Brotin, C. Garcia, F. Pelle, P. Goldner, B. Bigot, A. Collet, J. Am. Chem. Soc.
116 (1994) 2094-2102.
[78] H. Tanak. J. Mol. Struct. (Theochem), 950 (2010) 5-12.
29