Crystal structure, spectroscopic investigations and density functional studies of 4-(4-methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H)-one monohydrate

Article abstract of DOI:10.1016/j.saa.2012.02.054

The triazol compound 4-(4-methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H) -one monohydrate (I) has been synthesized and characterized by ¹H NMR, ¹³C NMR, IR, and X-ray single-crystal determination. The molecular geometry, vibration

Full text of DOI:10.1016/j.saa.2012.02.054

Spectrochimica Acta Part A 93 (2012) 106–115
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Crystal structure, spectroscopic investigations and density functional studies of
4-(4-methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H)-one monohydrate
Yavuz Köysala, Hasan Tanakb,∗
a Yes¸ilyurt Demir-C¸ elik Vocational School, Ondokuz Mayıs University, Samsun, Turkey
b Department of Physics, Faculty of Arts and Sciences, Amasya University, 05100, Amasya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The triazol compound 4-(4-methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H)-one monohydrate (I)
has been synthesized and characterized by 1H NMR, 13C NMR, IR, and X-ray single-crystal determination.
Received 4 November 2011
Received in revised form 22 January 2012
Accepted 14 February 2012
The molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13
C
NMR chemical shift values of (I) in the ground state have been calculated using the density functional
method (B3LYP) with the 6−31G(d) basis set. The calculated results show that the optimized geometry
can well reproduce the crystal structure, and the theoretical vibrational frequencies and chemical shift
values show good agreement with experimental values. The energetic behavior of (I) in solvent media
was examined using the B3LYP method with the 6−31G(d) basis set by applying the Onsager and the
polarizable continuum model (PCM). The predicted non-linear optical properties of (I) are greater than
ones of urea. In addition, DFT calculations of molecular electrostatic potentials, frontier molecular orbitals
and thermodynamic properties of (I) were carried out at the B3LYP/6−31G(d) level of theory.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
1,2,4-Triazole
Density functional theory
FT-IR
Non-linear optics
Molecular electrostatic potential
1. Introduction
photochemical transformations [15–18] and thermal decomposi-
tion products [19,20]. Many reports have appeared on the synthesis
The chemistry and structure of heterocyclic compounds has an
interesting field of study for a long time. The synthesis of 1,2,4-
triazoles and investigation of their chemical and biological behavior
have gained more importance in recent decades for biological,
medicinal and agricultural reasons. 1,2,4-triazole compounds pos-
sess important pharmacological activities such as antifungal and
antiviral activities. Examples of such compounds bearing the 1,2,4-
triazole residues are fluconazole [1], the powerful azole antifungal
agent as well as the potent antiviral N-nucleoside ribavirin [2]. Fur-
thermore, various 1,2,4-triazole derivatives have been reported as
fungicidal, insecticidal, antimicrobial as well as anticonvulsants,
antidepressants, and plant growth regular anticoagulants [3–8]. It
is known that 1,2,4-triazol moieties interact strongly with heme
iron, and aromatic substituents on the triazoles are very effective
for interacting with the active site of aromatase. Furthermore, it
was reported that compounds having triazole moieties such as
Vorozole, Anastrozole and Letrozole appear to be very effective
aromatase inhibitors very useful for preventing breast cancer.
The literature concerning the 1,2,4-triazole is rich and the
papers published cover such subjects as crystal structure determi-
nation [9–11], ab initio and DFT calculations on the tautomerism
and protonation sites [12–14], vibrational characteristics and
and characterization of novel triazole containing organic [21,22]
or metal coordination compounds [23,24] including spin-crossover
materials [25,26].
In recent years, density functional theory (DFT) has been exten-
sively used in theoretical modeling. The development of better
exchange–correlation functionals has made it possible to calcu-
late many molecular properties with comparable accuracies to
traditionally correlated ab initio methods, with more favorable
computational costs [27]. Literature survey has revealed that the
DFT has a great accuracy in reproducing the experimental values in
geometry, dipole moment, vibrational frequency, etc. [28–32].
The aim of this study is to investigate the energetic and
structural properties of the 1,2,4-triazole compound, 4-(4-
methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H)-one mono-
hydrate (Fig. 1), using density functional theory calculations. In
this study, the optimized geometry, vibrational spectra and assign-
ments, statistical thermodynamic parameters, natural bond orbital
analysis and nonlinear optical properties of (I) have been studied.
These calculations are valuable for providing insight into molecular
properties of 1,2,4-triazole compounds.
2. Experimental and computational methods
2.1. Synthesis
∗
Ethyl-2-(1-ethoxy-2-phenylethylidene)hydrazine
late (10 mmol) together with 2-(4-methoxyphenyl)ethylamine
carboxy-
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 © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.02.054

Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
107
Table 1
H2O
N
Crystal data and structure refinement parameters for the title compound.
H
N
Chemical formula
Formula weight
Temperature (K)
C18H21N3O3
327.38
296
N
˚
Wavelength (A)
0.71073
Monoclinic
P21/c
Crystal system
Space group
O
Unit cell parameters
˚
a, b, c (A)
6.7971(3), 32.0286(16), 9.1496(4)
90.00, 124.244(3), 90.00
1646.59 (13)
˛, ˇ, ꢃ (◦)
3
˚
Volume (A )
Z
4
Calculated density (Mg/m3)
1.321
0.09
ꢁ (mm−1
)
Absorption correction
F0 0 0
Crystal size (mm)
Index ranges
Integration (X-RED32)
696
O
0.700 × 0.483 × 0.270
−8 ≤ h ≤ 8, −40 ≤ k ≤ 40,
−11 ≤ l ≤ 11
CH3
Diffractometer/measurement
method
STOE IPDS II/rotation (ω scan)
Fig. 1. Chemical diagram of 4-(4-methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-
3(4H)-one monohydrate.
Theta range for data collection (◦)
Measured reflections
Independent/observed reflections
Rint
1.3 ≤ Â ≤ 26.8
11,228
3501/2637
0.059
(10 mmol) were heated without solvent in a sealed tube for 2 h
at 150–160 ◦C. Then, the mixture was cooled to r.t. and a solid
crude formed. The crude product was recrystallized using ethyl
acetate/petroleum ether (3:1) to afford the desired compound.
Yield: 196 mg (88%). Colorless crystals. M.P. 385 K.
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
R indices [I > 2ꢂ(I)]
R indices (all data)
Weighting scheme
Full-matrix least-squares on F2
2637/0/229
1.01
0.051
0.066
w = 1/[ꢂ2(Fo2) + (0.0756P)2];
P = (Fo2 + 2Fc2)/3
0.29, −0.49
3
˚
ꢄ
max, ꢄ
(e/A )
2.2. Physical measurements
min
The melting point was determined using a Gallenkamp melt-
ing point apparatus. The IR spectrum of (I) was recorded in the
range 4000–400 cm−1 using a Perkin-Elmer 1600 series FTIR spec-
trophotometer 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 1H and 13C nuclear magnetic
resonance spectra were recorded on a Varian-Mercury 200 MHz
spectrometer using TMS as standard and CDCl3 as solvent.
2.4. Computational methods
The molecular geometry was taken directly from the X-ray
diffraction 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 func-
tional) with the 6−31G(d) basis set using the Berny method [36,37]
were performed with the Gaussian 03W software package [38]. The
harmonic vibrational frequencies were calculated at the same level
of theory for the optimized structure and the obtained frequen-
cies were scaled by 0.9613 [39]. Vibrational band assignments were
made using the Gauss-View molecular visualization program [40].
In order to evaluate the energetic and atomic charge behavior of
(I) in solvent media, we also carried out optimization calculations
in five solvents (ε = 78.39, H2O; ε = 46.7, DMSO; ε = 24.55, C2H5OH;
ε = 10.36, CH2ClCH2Cl; ε = 4.9, CHCl3) at the B3LYP/6−31G(d) level
using the Onsager [41] and Polarizable Continuum Model (PCM)
[42–45] methods. To investigate the reactive sites of (I) the molec-
ular electrostatic potentials were evaluated using B3LYP/6−31G(d)
method. Molecular electrostatic potential, V(r), at a given point r(x,
y, z) in the vicinity of a molecule, is defined in terms of the inter-
action 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 [46],
2.3. Crystal structure determination
A
block
of
single
crystal
with
dimensions
0.80 mm × 0.57 mm × 0.41 mm was mounted on goniometer
and data collection was performed on a STOE IPDS II [33] diffrac-
tometer by the ω scan technique using graphite-monochromatic
˚
MoK˛ radiation (ꢀ = 0.71073 A) at 296 K. The intensity symmetries
indicate the monoclinic P21/c space group. A total of reflections
11,228 (3501 unique) were performed within 2Â range 1.27◦ and
26.75◦. Correction for absorption (ꢁ = 0.091), by comparison of
the intensities of equivalent reflections, was applied using X-RED
software [33] and cell parameters were determined by using
X-AREA software [33]. The initial partial solution obtained by
direct methods as implemented in the program SHELXS-97 [34]
was expanded and refined by means of the program SHELXL-97
[34]. The program ORTEP-3 for windows [35] has been used in the
preparation of the figures. All non-hydrogen atoms were refined
anisotropically. The refinement carried out by full matrix least
squares method on the positional and anisotropic temperature
parameters of non-hydrogen atoms corresponding to 229 crystal-
lographic parameters. All the H atoms were located geometrically
and refined using a riding model, except for H22, H33 and H44,
ꢁ
ꢀ
ZA
(rꢀ)
|rꢀ − r|
V(r) =
−
drꢀ
(1)
|RA − r|
A
where ZA is the charge of nucleus A, located at RA, (rꢀ) is the
electronic density function of the molecule, and rꢀ is the dummy
integration variable. The mean linear polarizability and mean first
hyperpolarizability properties of (I) were obtained from molec-
ular polarizabilities based on theoretical calculations. The NBO
analysis was performed at the B3LYP/6−31G(d) level by means of
the NBO 3.1 program within the Gaussian 03W package [47]. The
˚
˚
˚
fixing the bond lengths at 0.93 A, 0.96 A and 0.97 A for CH, CH3 and
CH2, respectively. The structure was refined to Rint = 0.0592 with
2637 observed reflections by the condition of I > 2ꢂ(I) threshold.
Details of the data collection conditions and the parameters of
refinement process are given in Table 1.

108
Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
Table 2
◦
˚
Hydrogen-bond geometry (A, ).
D
H· · ·A
D
H
H· · ·A
D· · ·A
D
H· · ·A
O3 H33· · ·O2i
O3 H44· · ·O2ii
N2 H22· · ·O3iii
0.90 (2)
0.88 (3)
0.93 (2)
1.87 (2)
1.94 (3)
1.92 (2)
2.7601 (16)
2.8233 (16)
2.8386 (16)
169.9 (19)
174 (2)
168.8 (17)
Symmetry codes: (i) −x + 1, −y + 1, −z; (ii) x + 1, y, z; (iii) x, y, −1 + z.
Fig. 3. Atom-by-atom superimposition of the structure calculated (red) over the X-
ray structure (black) for the title compound. (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of the article.)
conjugated C10 N1 and C11 N1 bonds. The molecular geometry of
the triazole ring is in agreement values with the structure 5-benzyl-
4-(3,4-dimethoxyphenethyl)-2H-1,2,4-triazol-3(4H)-one [50]. The
torsion angle around the (N1 C9 C8 C4) is −64.66(2)◦.
Structurally, the organic molecule forms O H· · ·O and N H· · ·O
types intermolecular hydrogen bonds (Table 2). The intermolec-
ular contacts are O3 H33· · ·O2i and O3 H44· · ·O2ii where atom
O2 accepts hydrogen bonds from O H donors [symmetry codes:
(I) −x + 1, −y + 1, −z; (ii) x + 1, +y, +z]. The H atoms of the water
molecule are engaged in hydrogen bonding with O2 atom of the
attached triazol system which link the molecules into discrete pairs
across crystallographic centers of symmetry. There is also short
intermolecular contact is namely N2 H22· · ·O3 [symmetry code:
(iii) x, y, −1 + z].
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/6−31G(d)
level).
thermodynamic properties of (I) at different temperatures were
calculated on the basis of vibrational analyses.
3. Results and discussion
3.1. Description of the crystal structure
The crystal structure of (I) is monoclinic and space group P21/c.
The molecular structure of (I) shown in Fig. 2a is not planar but
each ring system is planar individually. In the molecule of (I),
3.2. Optimized geometry
C
18H21N3O3, contains the 1,2,4-triazol ring, the methoxyphenethyl
The optimized parameters (bond lengths, bond angles, and
dihedral angles) of (I) were obtained using the B3LYP/6−31G(d)
method. The atomic numbering scheme of the theoretical geomet-
ric structure is shown in Fig. 2b. Calculated geometric parameters
are listed in Table 3 along with the experimental data. When the X-
ray structure of (I) is compared with its optimized counterparts (see
Fig. 3), slight conformational discrepancies are observed between
them. We note that the experimental results are for the solid phase
and the theoretical calculations are for the gas phase. In the solid
state, the existence of a crystal field along with the intermolecular
interactions connects the molecules together, which results in the
differences in bond parameters between the calculated and exper-
imental values. The most notable discrepancies are found in the
orientation of the benzyl ring of (I), which is defined by torsion
ring, benzyl ring. Triazol ring is oriented with respect to the
5-benzyl and 4-methoxyphenethyl rings at dihedral angles of
55.01(2)◦ and 35.88(2)◦, respectively. Triazol ring system is
˚
almost planar with the maximum deviation of 0.0015(1) A for
atom C11. The molecular geometry of the triazol ring is in
agreement with the values of structure 4-(3-Methoxyphenyl)-3-
[2-(4-methoxyphenyl)ethyl]-1H-1,2,4-triazol-5(4H)-one [48].
In the molecule of (I), the bond lengths and angles are within
normal ranges and they are comparable with those related struc-
ture [49]. Title compound, C18H21N3O3, containing the triazol ring
display the characteristic features of 1,2,4-triazol derivatives.
The interatomic distances within the triazole ring of (I) are
not equal. The N3 C11 is double bond and shorter than the

Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
109
Table 3
Selected molecular structure parameters.
Parameters
Experimental
B3LYP/6−31G(d)
˚
Bond lengths (A)
O2 C10
N1 C10
N1 C11
N1 C9
N2 C10
N2 N3
C11 N3
C11 C12
C9 C8
1.2413(17)
1.3738(17)
1.3790(17)
1.4605(16)
1.3388(18)
1.3826(17)
1.2960(17)
1.4914(19)
1.523(2)
1.386(2)
1.391(2)
1.505(2)
1.374(2)
1.417(2)
1.382(2)
1.385(2)
1.509(2)
1.385(2)
1.386(2)
1.388(2)
1.382(2)
1.384(2)
1.378(2)
1.368(3)
1.367(3)
1.238
1.393
1.388
1.457
1.363
1.376
1.303
1.503
1.544
1.397
1.406
1.512
1.364
1.419
1.399
1.398
1.515
1.395
1.398
1.394
1.399
1.403
1.388
1.395
1.396
C4 C5
C4 C3
C4 C8
O1 C1
O1 C7
C13 C18
C13 C14
C13 C12
C14 C15
C5 C6
C18 C17
C1 C6
C1 C2
Fig. 4. FT-IR spectrum of the title compound.
angles C11 C12 C13 C14 [−65.57(19)◦] and C11 C12 C13 C18
[117.29(16)◦]. These torsion angles have been calculated at −92.14
and 88.21◦ for B3LYP/6−31G(d) level. Another difference in the
optimized structure is observed in the relative orientation of the
triazole and methoxyphenethyl rings. The dihedral angle between
the triazole and methoxyphenethyl rings is 35.88(2)◦ for X-ray,
whereas the dihedral angle has been calculated as 48.31◦ for B3LYP.
A logical method for globally comparing the structures obtained
with the theoretical calculations is by superimposing the molec-
ular skeleton with that obtained from X-ray diffraction, giving a
C3 C2
C15 C16
C16 C17
Bond angles (◦)
C10 N1 C11
C10 N1 C9
C11 N1 C9
C10 N2 N3
N3 C11 N1
N3 C11 C12
N1 C11 C12
C11 N3 N2
N1 C9 C8
107.49(10)
122.63(11)
129.23(11)
112.53(11)
111.22(12)
126.31(12)
122.36(11)
104.48(11)
111.64(11)
117.15(14)
121.66(13)
121.11(13)
113.11(12)
118.18(13)
118.14(14)
119.99(14)
121.81(14)
115.53(11)
120.69(15)
129.36(13)
126.36(12)
104.28(11)
122.09(14)
120.79(15)
125.02(14)
115.40(14)
119.57(14)
121.60(14)
120.47(16)
120.13(14)
119.61(15)
119.42(14)
120.29(16)
107.65
122.08
130.23
113.45
111.45
125.25
123.27
104.51
113.23
117.59
121.34
121.04
114.20
118.23
118.86
120.37
120.76
113.69
120.69
129.81
127.26
102.92
121.81
120.60
124.87
115.72
119.39
121.50
120.05
120.07
119.64
119.61
120.13
˚
RMSE of 0.797 A for B3LYP/6−31G(d) (Fig. 3). This RMSE value is
quite large. This magnitude of RMSE can be explained by the fact
that the intermolecular Coulombic interaction with the neighbor-
ing molecules are absent in gas phase, whereas the experimental
result corresponds to interacting molecules in the crystal lattice
[28].
C5 C4 C3
C5 C4 C8
C3 C4 C8
C4 C8 C9
3.3. IR spectroscopy
C1 O1 C7
Harmonic vibrational frequencies of (I) were calculated using
the DFT/B3LYP method with 6−31G(d) basis set. The vibrational
band assignments were made using the Gauss-View molecular
visualization program. In order to facilitate assignment of the
observed peaks, we have analyzed the vibrational frequencies and
compared our calculation for (I) with the experimental results
(Table 4). The agreement between the experimental and calculated
frequencies is quite good in general.
C18 C13 C14
C18 C13 C12
C14 C13 C12
C11 C12 C13
C13 C14 C15
O2 C10 N2
O2 C10 N1
N2 C10 N1
C4 C5 C6
C13 C18 C17
O1 C1 C6
O1 C1 C2
C6 C1 C2
C2 C3 C4
The FT-IR spectra of (I) were recorded in the 4000–400 cm−1
region using KBr pellets on a Schmadzu FT-IR 8900 spectropho-
tometer and given in Fig. 4. 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]. Intra- and intermolecular hydrogen
bonding if present in the molecule would reduce the O H stretch-
ing band to 3000–3550 cm−1 region [51]. The IR spectra of (I)
has got an intense and relatively sharp band with a maximum at
3370 cm−1 was assigned to the stretching vibrations of the sub
group in the very weak intermolecular O H· · ·O hydrogen bonds
formed between the water molecule and the O atom of carbonyl
group. This band has been calculated at 3647 cm−1 for B3LYP level.
In the literature, some N H stretching modes observed for the dif-
ferent substituent-triazole ring are 3383 cm−1 [52] and 3417 cm−1
[53] as experimentally. In our study, the N H stretching mode was
observed at 3170 cm−1 which has a red shift and the cause of this
shift is the intermolecular N2 H22· · ·O3 hydrogen bonding. The
red shifting is further enhanced by the reduction in the N H bond
order values, occurring due to donor–acceptor interaction [54].
C16 C15 C14
C3 C2 C1
C17 C16 C15
C1 C6 C5
C16 C17 C18
Torsion angles (◦)
C3 C4 C8 C9
C5 C4 C8 C9
−88.91(17)
87.64(17)
−64.66(15)
95.36(17)
−74.24(17)
−165.67(13)
18.4(2)
−65.57(19)
117.29(16)
168.83(15)
−10.2(2)
−83.44
95.049
−64.25
102.31
−75.41
−176.85
4.51
N1 C9 C8 C4
C11 N1 C9 C8
C10 N1 C9 C8
N1 C11 C12 C13
N3 C11 C12 C13
C14 C13 C12 C11
C18 C13 C12 C11
C7 O1 C1 C2
−92.14
88.21
−179.62
−0.039
C7 O1 C1 C6

110
Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
computed at 1506, 1490 and 1102 cm−1 by B3LYP/6−31G(d)
method shows excellent agreement with FT-IR bands at 1513, 1496
and 1119 cm−1. The bands observed at 935, 892, 822 and 798 cm−1
in FT-IR spectra are assigned to ring C H out-of-plane bending
vibration for (I).
The stretching C O vibration gives rise to a band in the infrared
experimental spectrum at 1692 cm−1, while the calculated value
is predicted 22 cm−1 lower, at 1714 cm−1. Triazole (C N) bond
stretching vibration was observed to be 1582 cm−1 experimen-
tally, while that have been calculated at 1572 cm−1 for B3LYP. The
identification of C N vibrations is a very difficult task, since mix-
Table 4
Comparison of the experimental and calculated vibrational frequencies (cm−1).
Assignmentsa
Experimental B3LYP/6−31G(d)
IR with KBr
ꢅ(O H)
ꢅ(N H)
ꢅs(C H) of R2
ꢅs(C H) of R1
ꢅas(C H) of R1
ꢅas(C H) of R2
ꢅas(C H) of R1
ꢅas(C H) of R1
ꢅas(C H) of R2
ꢅs(C H3)
ꢅas(C H2)
ꢅas(C H2)
ꢅas(C H3)
ꢅs(C H2)
ꢅs(C H2)
ꢅs(C H2)
ꢅs(C H3)
ꢅ(C O)
ꢅ(C C)
ꢅ(C C)
ꢅ(C N) + ˇ(NCN)
ꢅ(C C)
ꢃ(C H) of R2 + ω(CH3)
ꢃ(C H) of R1
ω(C H3)
ꢅ(C N) of triazole + ꢅ(C C)
ꢃ(N H)
ˇ(C H2) + ꢆaliphatic (HCCC)
ꢅ(C C) of R2 + ˇ(C H2)
ꢅ(C C) of R2 + ω(C H2)
ˇ(C H2) + ω(CH3)
ꢅ(C O) + ꢃ(C C) of R2
ω(C H2) + ꢆaliphatic (HCNC) + ꢆaliphatic (HCCC)
ı(C H2) + ꢆaliphatic (HCCC)
ꢅ(C C) of R2 + ꢃ(C H) of R2 + ω(CH3)
ꢅ(N N)
3370
3170
3647
3404
3090
3084
3074
3064
3056
3053
3049
3037
3014
2987
2966
2963
2934
2913
2909
1715
1609
1603
1572
1567
1506
1490
1475
1413
1358
1341
1324
1311
1295
1250
1228
1161
1102
1065
1035
980
3060
ing of several bands is possible in this region. However, the C
N
stretching assignments are identified by the animation application
of Gauss-View 4.1.2 graphical interface for Gaussian output file. Sil-
verstein et al. [55] assigned C N stretching absorption in the region
3021
2947
1382–1266 cm−1 for aromatic amines. In benzotrizole, the C
N
stretchings are found to be present at 1382 and 1307 cm−1 [56].
We have predicted the same vibration at 1339 cm−1 in 5-benzyl-4-
(3,4-dimethoxyphenethyl)-2H-1,2,4-triazol-3(4H)-one [50]. In the
present study, a very strong band at 1433 cm−1 in FT-IR has
been assigned to triazole C N stretching vibration. These results
indicated some band shifts with regard to the different substituent-
triazole ring. The theoretically computed value of C N stretching
vibration is defined as 1413 cm−1. The C O stretching vibrations
were observed at 1245 and 1037 cm−1 which confirms the pres-
ence of methoxy group in the compound. These bands have been
calculated at 1250 and 1035 cm−1 for B3LYP level.
1692
1609
1582
1513
1496
1463
1433
1366
1349
1322
1302
1284
1245
1220
1181
1119
1085
1037
982
The benzene ring modes predominantly involve C C bonds and
the vibrational frequency is associated with C C stretching modes
of carbon skeleton [51]. The band observed at 1609 cm−1, which
can be attributed to the C C stretching vibration, were calculated
at 1609–1567 cm−1 for B3LYP. The bands observed at 538, 616 and
982 cm−1 in the FT-IR spectra are ascribed to the vibration modes
including the phenyl CCC angle bending. The theoretically com-
puted values of the angles bending vibration modes show good
agreement with the experimental values. The other vibrational fre-
quencies can be seen in Table 4.
ꢅ(O C)
ꢅ(C C) of R1 + ˇ(CCC) of R1
ω(C H) of R2 + ꢆ(CCCC) of R2
ω(C H) of R1 + ω(C H) of R1
ω(C H) of R2
935
925
892
893
822
810
ω(C H) of R2
798
796
ˇ(O H)
760
743
705
643
772
754
709
643
3.4. NMR spectra
ˇ(CNN) of triazole + ˇ(O H)
ꢆ(HNNC) of triazole
ˇ(OCN)
GIAO 1H and 13C chemical shift values (with respect to TMS)
were calculated using the B3LYP method with 6−31G(d) basis set
and generally compared to the experimental 1H and 13C chemical
shift values. The results of this calculation are shown in Table 5.
We have calculated 1H chemical shift values (with respect
to TMS) of 9.11–0.54 ppm at B3LYP/6−31G(d) level, whereas the
experimental results are observed to be 11.54–2.5 ppm. The OCH3
protons of (I) gave a singlet at 3.72 ppm. This was calculated
3.6–3.98 ppm at B3LYP level. The triplets observed at 3.42 and
3.54 ppm are assigned to C(8)H2 and C(9)H2 groups, respectively,
that have been calculated at 2.50–3.25 and 3.24–3.93 ppm. The aro-
matic C H signals were observed to be 7.26–7.34, 7.17, 6.93 and
6.85 ppm.
ˇ(CCC) of R1
616
580
538
527
612
602
547
517
ꢆ(CNNC) of triazole + ꢆ(CCCN) of triazole
ˇ(CCC) + ꢆ(CCCC) of R2 + out of plane (OCCC)
ˇ(OCN)
Out of plane (OCCC)
459
456
a
ꢅ, stretching; ꢃ, rocking; ω, wagging; ˇ, bending; ꢆ, torsion; ı, out of plane
bending; s, symmetric; as, asymmetric. Abbreviations: R1; phenyl ring; R2;
methoxyphenyl ring.
The theoretically calculated harmonic wavenumber at 3404 cm−1
by B3LYP/6−31G(d) shows little deviation on the higher side.
These differences of O H (277 cm−1) and N H stretching vibrations
(234 cm−1) occurred between the results of the experimental and
calculations are due to the consideration of the isolated molecules
(in gas phase) in the calculational method. Therefore, we can con-
clude that these differences can be explained by the existence of the
intermolecular interactions in molecular structure of (I). The aro-
matic 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 700–1000 cm−1 frequency ranges, respectively. The C H aro-
matic stretching mode was observed at 3060 cm−1 experimentally,
and calculated at 3049–3090 cm−1 for B3LYP. The bands at 3021
and 2947 cm−1 correspond to the asymmetric stretching CH2 and
CH3 modes, respectively. The C H in-plane bending vibrations
In differently substituent 1,2,4-triazole, the 1H chemical shift of
N
H were observed to be 11.33–13.56 ppm [57]. The NH hydrogen
of the 1,2,4-triazole ring appears at 11.54 ppm, and is deter-
mined computationally at 9.11 ppm. The signal assigned to protons
of the water molecule is observed at 2.5 ppm. This was calcu-
lated 0.54–4.06 ppm at B3LYP level. Because the intermolecular
hydrogen bonds in molecular structure of (I) are neglected in the
calculations, we can say that this difference between experimen-
tal and calculated chemical shifts is due to N H· · ·O and O H· · ·O
intermolecular interactions.
13C NMR spectra of (I) show signals at 158.67 and 155.68 ppm
due, respectively, to the C10 and C11 atoms of the triazole ring.

Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
111
Table 5
Table 6
Theoretical and experimental 1H and 13C isotropic chemical shifts (with respect to
TMS, all values in ppm) for the title compound.
Total energies and dipole moments of the title compound in different solvents.
Method
B3LYP
ε
Energy (a.u.)
ꢁ (Debye)
ꢄE (kJ/mol)
Atom
Experimental (ppm)
(CDCl3)
Calculated (ppm)
B3LYP/6−31G(d)
1
−1088.492542
2.949
Onsager
4.9
−1088.493075
−1088.493220
−1088.493308
−1088.493341
−1088.493357
3.850
4.049
4.150
4.203
4.215
−1.39939
−1.78009
−2.01113
−2.09778
−2.13978
C1
C2
C3
C4
C5
C6
C7
C8
146.93
114.57
129.42
130.46
129.42
114.57
55.65
33.80
42.89
158.67
155.68
31.97
136.04
130.41
129.33
127.62
129.33
130.41
6.85
150.39
112.25
123.28
123.6
125.66
103.43
52.56
35.21
45.67
146.35
140.33
33.37
126.71
123.78
121.15
120.07
121.16
123.93
6.8
10.36
24.55
46.7
78.39
PCM
4.9
−1088.509699
−1088.513893
−1088.516593
−1088.517447
−1088.518880
3.675
3.881
3.897
3.993
3.998
−45.0457
−56.0571
−63.1459
−65.3881
−69.1505
10.36
24.55
46.7
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
H2
78.39
ꢄE = ESolvation − EGas, ε = dielectric constant.
H3
6.93
7.16
H5
6.93
6.86
H6
6.85
6.43
H7A
H7B
H7C
H8A
H8B
H9A
H9B
H12A
H12B
H14
H15
H16
H17
H18
H22
H33
H44
3.72
3.72
3.72
3.42
3.42
3.54
3.54
3.62
3.98
3.6
3.69
3.25
2.50
3.24
3.93
2.95
2.40
6.9
7.1
7.08
7.06
6.49
9.11
4.06
3.62
7.17
7.26–7.34
7.26–7.34
7.26–7.34
7.17
11.54
2.50
Fig. 5. Energy difference between the gas phase and solvent media by polarizable
continuum model (PCM) and Onsager methods at B3LYP/6−31G(d) level of theory.
2.50
0.54
than those for the PCM method in the various solvents, and the
dipole moments obtained for the two solvation methods increase
with the increasing solvent polarity. Solvent effects improve the
charge delocalized in the molecules, therefore, inducing the dipole
moments to be raised. Ground-state dipole moment is an impor-
tant factor in measuring solvent effect, a large ground-state dipole
moment gives rise to strong solvent polarity effects [58,59].
These signals were calculated at 146.35 and 140.33 ppm, respec-
tively. The chemical shift values of C1 atom bounded OCH3 group
is observed as 146.93 ppm, whereas the corresponding value is
150.39 ppm for B3LYP level. While the C atom of the methoxy group
belonging to the benzyl ring is observed at 55.65 ppm, the aliphatic
CH2 (C8, C9, and C12) carbons are observed at 33.80, 42.89 and
31.97 ppm, respectively. The other calculated chemical shift values
can be seen in Table 5. As can be seen from Table 5, the theoretical
1H and 13C chemical shift results for (I) are generally closer to the
experimental 1H and 13C shift data.
3.6. Atomic charge distributions in gas-phase and in
solution-phase
3.5. Energetics and dipole moments
The Mulliken atomic charges for the non-H atoms of (I) calcu-
lated at the B3LYP/6−31G(d) level in gas-phase are presented in
Table 7. To investigate the solvent effect for the atomic charge dis-
tributions of (I), based on the B3LYP/6−31G(d) model and PCM
method, three solvents (chloroform, ethanol and water) were
selected and calculated values were also listed in Table 7. Mullikens
atomic charge plot has shown in Fig. 6.
The Mulliken atomic charges show that the N1, N2 and N3 atoms
of triazole ring, O1 atom of methoxy group and carbonyl O2 atom
have larger negative atomic charges in the gas phase. This behavior
may be the result of C10 O2 double bond character and electroneg-
ativity of triazole ring and methoxy group. On the other hand, it
is found that, in solution-phase, the atomic charge values of the
N2, N3 and O2 atoms are larger than those in gas-phase and while
their atomic charge values will increase with the increase of the
polarity of the solvent, that value of O1 and N1 decrease with the
In order to evaluate the total energy and dipole moment
behavior of (I) in solvent media, we carried out calculations in
five solvents (ε = 78.39, H2O; ε = 46.7, DMSO; ε = 24.55, C2H5OH;
ε = 10.36, CH2ClCH2Cl; ε = 4.9, CHCl3). The total energies and dipole
moments were calculated in solvent media at the B3LYP/6−31G(d)
level using the Onsager and PCM methods and the results are given
in Table 6. From this table, we can conclude that the obtained total
energy of (I) decreases with the increasing polarity of the solvent
so that the stability of (I) increases. The energy difference between
the gas phase and solvent media is shown in Fig. 5 for both meth-
ods. As can be seen from Fig. 5, the PCM method provides a more
stable structure than Onsager’s method (57.87 kJ/mol average). The
trend in the total energies is not observed in the dipole moments.
The dipole moments calculated by the Onsager method are larger

112
Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
Table 7
Atomic charges (e) of the title compound in gas phase and solution phase.
In gas phase
In solution phase B3LYP/6−31G(d)
B3LYP/6−31G(d)
Chloroform Ethanol
Water
(ε = 78.39)
(ε = 4.9)
(ε = 24.55)
C1
C2
C3
C4
0.373345
−0.028549
−0.069672
0.166487
0.374088
0.374571
0.374671
−0.021967 −0.019375 −0.018830
−0.066861 −0.065786 −0.065600
0.165773
0.165393
0.165327
C5
C6
C7
−0.053238
−0.058157
0.262345
−0.058844 −0.061174 −0.061636
−0.060721 −0.061843 −0.062031
0.263004
0.263643
0.263777
C8
C9
−0.031710
−0.032994 −0.033690 −0.033853
0.194114
0.195728
0.801408
0.542808
0.196198
0.801480
0.542502
0.196278
0.801523
0.542483
C10
C11
C12
C13
C14
C15
C16
C17
C18
N1
N2
N3
O1
0.800928
0.542730
−0.111282
−0.106845 −0.105069 −0.104720
0.187335
0.187326 0.187299 0.187308
−0.042730
0.000153
0.000941
−0.043008 −0.043099 −0.043209
0.001088
0.002690
0.001294
0.003410
0.001359
0.003574
−0.002467
−0.035382
−0.524079
−0.141158
−0.315725
−0.505933
−0.603430
−0.004867
−0.001510 −0.001071 −0.000978
−0.036108 −0.036537 −0.036557
−0.523677 −0.523536 −0.523520
−0.146340 −0.147364 −0.147640
−0.316532 −0.316754 −0.316811
−0.502989 −0.501604 −0.501347
−0.606152 −0.607883 −0.608143
−0.009365 −0.011005 −0.011427
O2
O3
Fig. 7. Molecular electrostatic potential map calculated at B3LYP/6−31G(d) level.
(For interpretation of the references to color in the text, the reader is referred to the
web version of the article.)
regions of the MEP are related to electrophilic reactivity and the
positive (blue) regions to nucleophilic reactivity, as shown in Fig. 7.
As can be seen from the figure, this molecule has several possi-
ble sites for electrophilic attack. Negative regions in the studied
molecule were found around the carbonyl O2 atom, N3 atom of tria-
zol ring and O1 atom. Also, a negative electrostatic potential region
is observed around the O3 atom of water. The negative V(r) val-
ues are −0.065 a.u. for O3 atom, which is the most negative region,
−0.062 a.u. for N3 atom, −0.054 a.u. for O2 atom and −0.032 a.u.
for O1 atom, which is a less negative region. However, a maximum
positive region is localized on the H44 atom of the water with a
value of +0.058 a.u. indicating 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 information about the region from where the compound can
have intermolecular interactions.
Fig. 6. Atomic charges of the title compound.
increasing polarity of the solvent. The coordination of these atoms
will changed in different solvents, which may be helpful when one
wishes to use (I) to construct interesting metal complexes with dif-
ferent coordinate geometries [60]. This calculated result is not only
consistent with many reported experimental values [61–63], it also
supports the original idea of our synthesis.
3.8. Natural bond orbital analysis
It is well-known that NBO analysis provides an efficient method
for studying intra- and inter-molecular bonding and interaction
among bonds, and also provides a convenient basis for investigat-
ing charge transfer or conjugative interaction in molecular systems
[67]. The larger the E(2) value, the more intensive is the inter-
action between electron donors and electron acceptors, i.e., the
more donating tendency from electron donors to electron accep-
tors and the greater the extent of conjugation of the whole system.
Delocalization of electron 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.
3.7. 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 [64].
The electrostatic potential V(r) is also well suited for analyzing 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
[65,66].
To predict reactive sites of electrophilic or nucleophilic attack for
the investigated molecule, the MEP at the B3LYP/6−31G(d) opti-
mized geometry was calculated. The negative (red and yellow)
In order to investigate the intermolecular interactions, the sta-
bilization energies of (I) were computed by using second-order
perturbation theory. For each donor NBO(i) and acceptor NBO(j),

Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
113
Fig. 8. Molecular orbital surfaces and energy levels given in parentheses for the HOMO−1, HOMO, LUMO and LUMO+1 of the title compound computed at B3LYP/6−31G(d)
level.
Table 8
some values in literature. For example, Grabowski [70] has esti-
Second-order perturbation theory analysis of the Fock matrix in NBO basis, calcu-
lated at B3LYP/6−31G(d) level.
Donor orbital (i) Acceptor orbital (j) E(2) (kcal/mol)a εj − εi (a.u.)b Fij(a.u.)c
mated the energy of the N H· · ·O hydrogen bond as 8.6 kcal/mol.
Furthermore, the intermolecular H· · ·O distance of the H22· · ·O3
˚
was observed to be 1.92(2) A. This distance is significantly shorter
than that of the van der Waals separation between O and H atoms
(2.72 A) [71]. This indicates the existence of the N2 H22· · ·O3 inter-
LP(1) O3
LP(1) O2
LP(2) O2
LP(3) O2
LP(1) O2
LP(2) O2
BD*(1) N2 H22
BD*(1) O3 H33
BD*(1) O3 H33
BD*(1) O3 H33
BD*(1) O3 H44
BD*(1) O3 H44
13.60
7.62
4.70
0.13
4.80
5.24
1.18
1.35
0.92
0.91
1.40
0.97
0.113
0.091
0.061
0.011
0.073
0.066
˚
molecular interaction for (I). There is another NBO interaction of the
n(O2) → ꢂ(O3 H33) imply the existence of O3 H33· · ·O2 hydro-
gen bond which has the total stabilization energy 12.45 kcal/mol.
The lone pairs of O2 also donate its electrons to ␴-type anti-
bonding orbital for O3 H44. The total stabilization energy of
O3 H44· · ·O2 intermolecular hydrogen bonding is 10.04 kcal/mol.
Thus, it is apparent that N H· · ·O and O H· · ·O interactions signif-
icantly influence crystal packing of this molecule.
a
E(2) means energy of hyper conjugative interactions.
Energy difference between donor and acceptor i and j NBO orbitals.
Fij is the Fock matrix element between i and j NBO orbitals.
b
c
the stabilization energy E(2) associated with electron delocalization
between donor and acceptor is estimated as [68,69]
3.9. Frontier molecular orbitals
(Fij)2
E(2) = −q
(2)
The frontier molecular orbitals play an important role in the
electric and optical properties, as well as in UV–vis spectra and
chemical reactions [72]. Fig. 8 shows the distributions and energy
levels of the HOMO−1, HOMO, LUMO and LUMO+1 orbitals com-
puted at the B3LYP/6−31G(d) level for (I).
i εj − εi
where qi is the donor orbital occupancy, εi, εj are diagonal elements
(orbital energies) and Fij is the off-diagonal NBO Fock matrix ele-
ment. The results of second-order perturbation theory analysis of
the Fock Matrix at B3LYP/6−31G(d) level of theory are presented
in Table 8.
The NBO analysis has revealed that the n(O3) → ꢂ(N2 H22)
interactions give the strongest stabilization to the system of (I) by
13.60 kcal/mol, and strengthen the intermolecular N2 H22· · ·O3
hydrogen bond. We can say that the energy of the N2 H22· · ·O3
hydrogen bond we obtained is reliable when it is compared with
As seen from Fig. 8, both in the HOMO and HOMO−1, electrons
are delocalized on the methoxyphenethyl fragment and triazole
ring as well as O2 atom. For the LUMO, electrons are mainly delo-
calized on the methoxyphenethyl ring and for the LUMO+1 the
electrons are delocalized on the benzyl ring. Both the highest
occupied molecular orbitals (HOMOs) and the lowest-lying unoccu-
pied molecular orbitals (LUMOs) are mainly localized on the rings,

114
Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
Table 9
indicating that the HOMO–LUMO are mostly the ␲-antibonding
type orbitals. The value of the energy separation between the
HOMO and LUMO is 5.673 eV. This large HOMO–LUMO gap auto-
matically means high excitation energies for many of excited states,
a good stability and a high chemical hardness for (I).
Thermodynamic properties at different temperatures at B3LYP/6−31G(d) level.
T (K)
Hm0 (kcal/mol)
Cp0,m(cal/mol/K)
Sm0 (cal/mol/K)
250
298.15
300
350
400
11.421
15.525
15.695
20.647
26.246
32.447
39.196
76.648
89.830
90.333
103.660
116.191
127.695
138.109
157.832
172.810
173.380
188.620
203.555
218.150
232.361
3.10. Nonlinear optical effects
450
500
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 [73]. 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 [74–77].
The calculations of the total molecular dipole moment (ꢁ), linear
polarizability (˛) and first-order hyperpolarizability (ˇ) from the
Gaussian output have been explained in detail previously [78], and
DFT has been extensively used as an effective method to investigate
the organic NLO materials.
Table 9 shows that the standard heat capacities, entropies, and
enthalpies increase at any temperature from 250.00 to 500.00 K,
because the intensities of molecular vibration increase with the
increasing temperature. The correlation equations between these
thermodynamic properties and temperature T are as follows:
Cp0,m = −6.30835 + 0.37306 T − 1.67959 × 10−5T2 (R2 = 0.99993)
Sm0 = 74.99195 + 0.34783 T − 6.61199 × 10−5 T2 (R2 = 1)
It is well known that from the literature, the B3LYP approach
provides fairly reliable values in electric hyperpolarizability cal-
culations when compared with accuracies of traditional ab initio
methods and this predictive capability of widely used B3LYP
method is of interest to a wide audience of computational scientists
[79,80]. In addition, taking into account reliability and the compu-
tational time required [28,81], the basis set 6−31+G(d) was chosen
for the calculations of the hyperpolarizability in this study.
The electronic dipole moment ꢁi(i = x, y, z), polarizability ˛ij
and the first hyperpolarizability ˇijk of (I) were calculated at
the B3LYP/6−31+G(d) level using Gaussian 03W program pack-
age. Urea is one of the prototypical molecules used in the
study of the NLO properties of molecular systems. Therefore
Hm0 = −0.9094 + 0.01816 T + 1.24201 × 10−4T2 (R2 = 0.99999)
These equations will be helpful for the further studies of (I).
4. Conclusions
4-(4-Methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H)-
one monohydrate has been synthesized and characterized by
FT-IR, NMR and X-ray single-crystal diffraction. The optimized
geometrical parameters, vibrational frequencies, chemical shift
values and some physicochemical properties have been calculated
using the DFT/B3LYP method with 6−31G(d) basis set. The X-ray
structure is found to be very slightly different from its optimized
counterpart, and the crystal structure is stabilized by N H· · ·O and
it was used frequently as
a threshold value for compara-
tive purposes. The calculated values of ˛tot and ˇtot for (I)
are, 335.218 A and 3.210 × 10−30 cm5/esu, which are greater
3
˚
O
H· · ·O hydrogen bonds. It was noted here that the experimental
3
˚
˛ and ˇtot of urea are 4.890 A
tot
than those of urea (the
results belong to solid phase and theoretical calculations belong
to gaseous phase. In the solid state, the existence of the crystal
field along with the intermolecular interactions have connected
the molecules together, which result in the differences of bond
parameters between the calculated and experimental values.
Despite the differences observed in the geometric parameters,
the general agreement is good and the theoretical calculations
support the solid-state structure. The vibrational frequencies and
1H and 13C NMR chemical shift values are precisely assigned to its
molecular structure with the aid of the theoretical calculations at
B3LYP/6−31G(d) level, in which the experimental and theoretical
results support each other. The total energy of (I) decrease with the
increasing polarity of the solvent and the stability of (I) increase
in going from the gas phase to the solution phase. The nonlinear
optical properties are also addressed theoretically. The predicted
NLO properties of (I) are much greater than ones of urea. (I) is
a good candidate as second-order NLO material. The MEP map
shows that the negative potential sites are on electronegative
atoms as well as the positive potential sites are around the hydro-
gen atoms. These sites give information about the region from
where the compound can have intermolecular interactions. NBO
analysis revealed that the n(O3) → ꢂ(N2 H22) interaction gives
the strongest stabilization to the system, and the major interaction
for the intermolecular O2· · ·O3 contact is n(O2) → ꢂ(O3 H33). The
correlations between the thermodynamic properties Cp0,m, Sm0 , Hm0
and temperatures T are also obtained. We hope our paper will be
helpful for the design and synthesis new materials.
and 0.49 × 10−30 cm5/esu obtained by B3LYP/6−31+G(d) method).
When it is compared with the similar triazole compound in
literature, the calculated value of ˇtot of (I) is bigger than
that of 4-(3-(1H-imidazol-1-yl)propyl)-5-methyl-2H-1,2,4-triazol-
3(4H)-one monohydrate (ˇtot = 1.7506 × 10−30 cm5/esu calculated
with B3LYP/6−31G(d) method) [14]. According to the magnitude
of the first hyperpolarizability, (I) may be a potential applicant in
the development of NLO materials.
To understand this phenomenon in the context of molec-
ular orbital picture, we examined the molecular HOMOs
and molecular LUMOs of (I) and showed in Fig. 8. The
HOMO–LUMO energy gaps were calculated as 5.673 eV for
(I), 6.35 eV for 4-(3-(1H-imidazol-1-yl)propyl)-5-methyl-2H-1,2,4-
triazol-3(4H)-one monohydrate [14] and 6.891 eV for urea by
B3LYP/6−31+G(d) method.
As can be seen from the ˇtot values for these compounds, the
larger value of first hyperpolarizability corresponds to the lower
HOMO–LUMO gap. This correlation is following with the inverse
relationship reported previously [82,83].
3.11. Thermodynamic properties
On the basis of vibrational analysis and statistical thermo-
dynamics, the standard thermodynamic functions: heat capacity
(Cp0,m), entropy (Sm0 ), and enthalpy (Hm0
B3LYP/6−31G(d) level and listed in Table 9.
) were obtained at

Y. Köysal, H. Tanak / Spectrochimica Acta Part A 93 (2012) 106–115
115
Supplementary material
M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. John-
son, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03, Revision E.01,
Gaussian, Inc., Wallingford, CT, 2004.
CCDC 796395 contains the supplementary crystallographic data
for the compound reported in this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre (CCDC), 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 0 1223 336033;
deposit@ccdc.cam.ac.uk].
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