Structural and spectroscopic characterization of 2-mesityl-1H-benzo[d] imidazol-3-ium chloride: A combined experimental and theoretical analysis

Article abstract of DOI:10.1016/j.saa.2012.01.069

The title molecular salt, 2-mesityl-1H-benzo[d]imidazol-3-ium chloride (C₁₆H₁₇N₂⁺·Cl), was synthesized unexpectedly from the reaction of N-[(1E)-mesitylmethylene]benzene- 1,2-diamine and CoCl₂·6H

Full text of DOI:10.1016/j.saa.2012.01.069

Spectrochimica Acta Part A 91 (2012) 51–60
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural and spectroscopic characterization of
2-mesityl-1H-benzo[d]imidazol-3-ium chloride: A combined experimental and
theoretical analysis
Namık Özdemir∗
Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
+
-
Article history:
Received 1 November 2011
Accepted 27 January 2012
The title molecular salt, 2-mesityl-1H-benzo[d]imidazol-3-ium chloride (C16H17N2 ·Cl ), was synthesized
unexpectedly from the reaction of N-[(1E)-mesitylmethylene]benzene-1,2-diamine and CoCl2·6H2O, and
characterized by elemental analysis, 1H NMR and FT-IR spectroscopies, and single-crystal X-ray diffrac-
tion technique. In addition, quantum chemical calculations employing density functional theory (DFT)
method with the 6−311++G(d,p) basis set were performed to study the molecular, spectroscopic and
some electronic structure properties of the title compound, and the results were compared with the
experimental findings. The computational result shows that the optimized geometry can well repro-
duce the crystal structural parameters. The intermolecular proton transfer process between the ionic
Keywords:
Crystal structure
DFT calculations
IR and NMR spectroscopy
Intermolecular proton transfer
Non-linear optical properties
+
-
(C16H17N2 ·Cl ) and nonionic forms (C16H16N2·HCl) of the title salt is investigated and found to be almost
barierless with an energy value of 0.20 kcal mol−1. The NLO properties of the compound are bigger than
those of urea.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
compounds driven by hydrogen-bonding interactions [28,29]. In
addition, benzimidazole-based organic ligands and their metal
Benzimidazoles are regarded as a promising class of bioactive
heterocyclic compounds that exhibit a range of biological activities.
Because of its synthetic utility and broad range of pharmacological
activities, the benzimidazole nucleus is an important heterocyclic
ring. Specifically, this nucleus is a constituent of vitamin-B12 [1].
This ring system is present in numerous antioxidant [2–4], antipar-
asitic [5,6], antihelmintics [7], antiproliferative [8], anti-HIV [9],
anticonvulsant [10], antiinflammatory [11,12], antihypertensive
[13,14], antineoplastic [15,16], antitrichinellosis [17], antimicrobial
[18,19], antihistaminic [20], antifungal [21,22], and anticancer [23]
activities. Owing to the immense importance and varied bioactivi-
ties exhibited by benzimidazoles, efforts have been made from time
to time to generate libraries of these compounds and screened them
for potential biological activities.
It is also well known that imidazole-containing molecules can
easily coordinate to metal ions as well as act as hydrogen-bond
acceptors or donors in supramolecular assembly reactions [24,25],
and thus their chemistry has been investigated extensively in
coordination chemistry [26,27]. The inclusion of benzimidazole
functional group can lead to different coordination modes and
may play a crucial role in the construction of supramolecular
complexes continue to attract interest as components in homo-
geneous catalysis [30]. These different applications have attracted
many experimentalists and theorist to investigate the spectro-
scopic and structural properties of benzimidazole [31–33] and
some of its derivatives [34].
Looking at the importance of benzimidazole nucleus, it was
thought that it would be worthwhile to design and synthesize some
new benzimidazole derivatives. In this study, I present results of a
detailed investigation of the synthesis and structural characteriza-
tion of the title compound using single crystal X-ray diffraction,
IR–NMR spectroscopy and quantum chemical methods. The calcu-
lations were performed at the DFT/B3LYP level of theory using the
6−311++G(d,p) basis function. These calculations are valuable for
providing insight into molecular parameters and the vibrational
and NMR spectra. The aim of this work is to explore the molecular
dynamics and the structural parameters that govern the chemi-
cal behavior, and to compare predictions made from theory with
experimental observations.
2. Materials and methods
2.1. General remarks
∗
All reagents were obtained from commercial suppliers and
used without further purification. The elemental analyses were
Tel.: +90 362 3121919/5256; fax: +90 362 4576081.
E-mail address: namiko@omu.edu.tr
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.01.069

52
N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
Table 1
determined on a Thermo Finnigan EA 1112 Series Flash Elemental
Analyser and Varian SpectrAA 220FS atomic absorption spectrom-
eter. The 1H NMR spectra were recorded on a Bruker 300 MHz
Ultrashield TM NMR spectrometer in CDCl3 with TMS as the
internal standard. Melting points were determined in open cap-
illary tubes on an Electrothermal 9100 melting point detection
apparatus. Thermal data were obtained by using Perkin-Elmer
Diamond Thermal Analysis. The TG–DTA measurements were
made between 20 and 1000 ◦C (in N2, 10 ◦C min−1). The infrared
spectra were measured by Perkin-Elmer Spectrum One FT-IR sys-
tem, and were recorded using universal ATR sampling accessory
(4000–550 cm−1).
Crystal data and structure refinement parameters for 2.
CCDC deposition no.
Color/shape
803481
Brown/leaf like plate
+
-
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell parameters
a, b, c (Å)
Volume (Å3)
C
16H17N2 ·Cl
272.77
296
0.71073 Mo K˛
Orthorhombic
Fddd (No. 70)
9.4482(6), 13.8602(10), 42.943(3)
5623.6(7)
16
1.289
Z
Dcalc (g/cm3)
ꢁ (mm−1
)
0.259
Absorption correction
Tmin, Tmax
Integration (X-RED32)
0.8428, 0.9782
2304
2.2. Syntheses
F000
2.2.1. N-[(1E)-mesitylmethylene]benzene-1,2-diamine (1)
1 was prepared by a modification of literature method [35].
A mixture of o-phenylenediamine (1.1 g, 10 mmol) and 2,4,6-
trimethylbenzaldehyde (1.51 ml, 10 mmol) in EtOH (30 ml) was
stirred at 5 ◦C for 2 h. In due course, a yellow suspension was
obtained, which was filtered to furnish the product as a yellow
solid. Yield: 2.2 g (93%). M.p.: 120–122 ◦C. Anal. Calc. for C16H18N2
(238.33 g): C, 80.63; H, 7.61; N, 11.75. Found: C, 80.66; H, 7.59; N,
11.85%. 1H NMR (300 MHz, CDCl3, 24 ◦C): 2.30 (s, 3H), 2.60 (s, 6H),
4.16 (b, 2H), 6.82 (d, J = 7.5 Hz, 2H), 6.97 (s, 2H), 7.03–7.13 (m, 2H),
8.95 (s, 1H).
Crystal size (mm3)
Diffractome-
0.80 × 0.41 × 0.06
STOE IPDS II/rotation (ω scan)
ter/measurement
method
Index ranges
−11 ≤ h ≤ 11, −17 ≤ k ≤ 17, −54 ≤ l ≤ 54
 Range for data collection (◦)
Reflections collected
Independent/observed
reflections
1.90 ≤ Â ≤ 26.81
15,097
1504/1220
Rint
0.0587
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢂ(I)]
R indices (all data)
ꢃꢄmax, ꢃꢄmin (e/Å3)
Full-matrix least-squares on F2
1504/0/91
1.021
R1 = 0.0443, wR2 = 0.1019
R1 = 0.0628, wR2 = 0.1105
0.16, −0.27
2.2.2. 2-Mesityl-1H-benzo[d]imidazol-3-ium chloride (2)
The title compound (2) was isolated by the following procedure
(Scheme 1). A solution of CoCl2·6H2O (0.1 g, 0.412 mmol) in 20 ml of
MeOH was added drop-wise to a solution of 1 (0.196 g, 0.824 mmol)
in 20 ml of MeOH. The resulting brown solution was refluxed for 2 h
and was concentrated (5 ml). Et2O was added with stirring to a final
volume of 20 ml causing a brown powder to precipitate. The pre-
cipitate was filtered off, washed with Et2O, and dried. X-ray quality
crystals were grown from a mixture of MeOH/Et2O. Yield: 240 mg
(68%). M.p.: 244 ◦C (dec.). Anal. Calc. for C16H17ClN2 (272.77 g): C,
70.45; H, 6.28; N, 10.27. Found: C, 70.44; H, 6.24; N, 10.45%. 1H NMR
(300 MHz, CDCl3, 24 ◦C): 1.87 (s, 3H), 2.18 (s, 6H), 6.53–6.79 (b, 4H),
7.11 (s, 2H).
2.4. Computational details
All geometries were fully optimized in the ground state using
the Berny algorithm [41] without symmetry restrictions and using
the default convergence criteria. The cartesian coordinates of the
X-ray structure were used as the starting geometry for the theo-
retical calculations. The calculations were performed by means of
the Gauss View molecular visualization program [42] and Gaussian
03 program package [43] using the spin-restricted hybrid density
functional theory (B3LYP) [44,45] method with the 6−311++G(d,p)
[46,47] basis set. A scale factor of 0.9668 [48] was used to cor-
rect the calculated vibrational frequencies. The 1H NMR chemical
shifts were calculated within the gauge-independent atomic orbital
(GIAO) approach [49,50] applying the same method and the basis
set as used for geometry optimization. The 1H NMR chemical shifts
were converted to the TMS scale by subtracting the calculated abso-
lute chemical shielding of TMS (ı = ˙0 − ˙, where ı is the chemical
shift, ˙ is the absolute shielding and ˙0 is the absolute shield-
ing of TMS), whose value is 31.96 ppm. The effect of solvent on
the theoretical NMR parameters was included using the default
model IEF-PCM (Integral-Equation-Formalism Polarizable Contin-
uum Model) [51] provided by Gaussian 03. Chloroform was used
as solvent. All the geometry optimizations were followed by fre-
quency calculations and no imaginary frequencies were found. That
is to say, the structures obtained from geometry optimization cor-
respond to stationary points in the potential surfaces and they are
stationary structures.
2.3. X-ray crystal structure determination
A suitable single crystal of 2 was chosen for the crystallo-
graphic study and then carefully mounted on goniometer of a STOE
diffractometer with an IPDS II image plate detector. All diffraction
measurements were performed at room temperature (296 K) using
˚
graphite monochromated Mo K˛ radiation (ꢀ = 0.71073 A) in ω-
scanning mode. The structure was solved by direct methods using
SHELXS-97 [36] implemented in WinGX [37] program suit. All non-
hydrogen atoms were refined anisotropically by the full-matrix
least squares procedure based on F2 using SHELXL-97 [38]. All H
atoms were positioned geometrically and treated using a riding
˚
model, fixing the bond lengths at 0.86, 0.93 and 0.96 A for NH, CH
and CH3 atoms, respectively. The displacement parameters of the
H atoms were fixed at Uiso(H) = 1.2Ueq (1.5Ueq for methyl) of their
parent atoms. The H atoms of the methyl group were disordered
about a twofold crystallographic axis, and were allowed for by plac-
ing six H atoms with equivalent half-occupancies. Data collection:
X-AREA [39], cell refinement: X-AREA, data reduction: X-RED32
[39]. Details of the data collection conditions and the parameters of
refinement process are given in Table 1. The general-purpose crys-
tallographic tool PLATON [40] was used for the structure analysis
and presentation of the results.
3. Results and discussion
Compound 1 was obtained from o-phenylenediamine and
2,4,6-trimethylbenzaldehyde. However, compound
unexpectedly from the reaction of compound 1 and CoCl2·6H2O
in 1:1 molar ratio, while I plan to synthesize the cobalt(II) com-
plex (see Scheme 1). The elemental analysis and atomic absorption
2 occurred

N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
53
Scheme 1. The formation of 2.
˚
spectrometer results of the compound being formed suggest the
formula C16H17ClN2. The TG–DTA curves of compound 2 show that
the compound starts decomposition at 244 ◦C (see Fig. S1 in the sup-
plementary material).
phthalate [1.339 and 1.394 A, respectively; [55]] and 2-amino-
˚
6-nitro-1H-benzoimidazol-3-ium chloride [1.340 and 1.387 A,
respectively; [56]].
The N1—C1 and N1i—C1 bond distances are equal to each other,
and show an intermediate character between single and double
bonds [57], indicating dispersion of positive charge over both N
atoms in the imidazole ring. In addition, a survey of the Cam-
bridge Structural Database (CSD, Version 5.31) [58] for only organic
compounds, which has been searched using ConQuest software
(Version 1.12) [59], revealed that the N1—C1—N1i angle [107.7(2)◦]
in the title compound has decreased when compared to those of the
non-protonated benzimidazoles groups [109.751–114.569◦].
The molecular structure does not exhibit any intramolecular
hydrogen bonds. In the crystal structure, the benzimidazole cation
is connected to the anion by means of N—H· · ·Cl hydrogen bond,
therefore, the C—N bonds mentioned above have intermediate
values between the expected single and double bond lengths. Prop-
agation of this hydrogen-bonding motif then generates a chain of
3.1. Crystallographic results
The title compound (2), a DIAMOND [52] view of which is shown
in Fig. 1, is a salt crystallizing in the orthorhombic space group Fddd
with Z = 16, and composed of a 2-mesityl-1H-benzo[d]imidazol-3-
ium cation and one chloride anion. Both ions are located on special
positions, allowing them to straddle a twofold rotation axis along
[0 0 1], so that the asymmetric unit contains the anion and one-half
of the cation. The twofold rotation axis bisects the benzimidazole
and mesityl rings, passing through C1, C5, C8 and C10 atoms. As a
result, the methyl group on the twofold axis is disordered.
The benzimidazole and benzene rings of the molecule are
not coplanar but rather have a dihedral angle of 56.78(8)◦; the
N1—C1—C5—C6i torsion angle is −55.80(11)◦. Furthermore, the
dihedral angle between the five- and six-membered rings of the
benzimidazole ring system is 1.34(14)◦, and the maximum devi-
ation from planarity is 0.0206(14) Å for atom N1, while the
crossed torsion angles at the junction, i.e. N1—C2—C2i—C3i and
N1i—C2i—C2—C3, are both equal to −178.24(15)◦.
¯
molecules running approximately along the [1 1 0] and [1 1 0] direc-
tions (Fig. 2). The full geometry of this intermolecular interaction
is given in Table 2. There are no other significant intermolecular
interactions in the crystal structure of 2.
3.2. Spectroscopic characterization
The N1—C1 and N1—C2 bond lengths in the imidazole ring
are significantly different, being 1.341(2) and 1.389(2) Å, respec-
tively. These distances are comparable with the average values
found for 2-amino-1H-benzo[d]imidazolium squarate [1.339 and
3.2.1. IR spectroscopy
The FT-IR spectra of componds 1 and 2 are presented in
Figs. 3 and 4, respectively, while the main vibrational bands are
given in Table 3. In the IR spectrum of 1, the (C O) stretching
band in the range of 1700–1750 cm−1 disappears due to the for-
mation of a C N bond between the amine and the aldehyde group,
˚
1.391 A, respectively; [53]], 2-(2-acetamido-4-methylthiazol-5-
yl)-1H-benzo[d]imidazol-3-ium chloride tetrahydrate [1.340 and
˚
1.387 A, respectively; [54]], 2-amino-1H-benzo[d]imidazol-3-ium

54
N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
Fig. 1. The molecular structure of 2 showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small
spheres of arbitrary radii. The dashed lines represent the Cl· · ·H contact. Only one orientation of the disordered methyl group is shown. (Symmetry code: i−x + 3/4, −y + 3/4,
z.).
¯
Fig. 2. Part of the crystal structure of 2, showing the formation of one-dimensional linear chains of molecules along [1 1 0] and [1 1 0]. For the sake of clarity, H atoms not
involved in the motif shown have been omitted.

N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
55
Fig. 3. FT-IR spectrum of 1.
while the (C N) stretching vibration is observed at 1598 cm−1
.
To make a comparison with experimental observations, I stud-
ied the correlation between the calculated and the experimental
data, and obtained correlation coefficients of 0.99969 and 0.9997
for compounds 1 and 2, respectively. These results show that there
is a good correlation between the theoretical and experimental
vibrational frequencies.
This band has been calculated at 1612 cm−1. The stretching, in-
plane and out-of-plane bending bands assigned to the methine
group are monitored at 2951, 1372 and 965 cm−1, which have been
appeared in 2947, 1378 and 964 cm−1 in the theoretical spectra. The
asymmetric and symmetric (N—H2) stretching bands are observed
at 3478 and 3377 cm−1, that have been calculated at 3540 and
3431 cm−1, respectively.
3.2.2. NMR spectroscopy
The solid phase of the compound includes various crystal
interactions. Benzimidazole derivatives are known to be strongly
associated through intermolecular hydrogen bonding. In the IR
spectrum of 2, the stretching band assigned to (N—H) is moni-
tored at 3551 cm−1, which is found to be 3530 cm−1 theoretically.
The region at 1660–1480 cm−1 is very characteristic of benzimi-
dazoles [60], in which the (C N) and (C C) stretching vibrations
were observed. The band observed at 1609 cm−1 is attributed to the
(C N) vibration, while the bands observed at 1574 and 1554 cm−1
can be attributed to the C C stretching vibrations. These bands
have been calculated at 1608, 1590 and 1552 cm−1, respectively.
All these data also agree with the results of the study of Sundara-
ganesan et al. [61].
The characterization of the compound was further enhanced
by the use of 1H NMR spectroscopy. The 1H NMR spectra of com-
ponds 1 and 2 are shown in Figs. 5 and 6. In addition, theoretical 1
H
NMR chemical shift values of the compounds have been computed
using the same method and the basis sets for the two optimized
geometries. The results of these calculations are tabulated in Table 4
together with the experimental values. Since experimental 1H
chemical shift values were not available for individual hydrogen
atoms of NH2 and CH3 groups, I have presented the average of the
computed values for these hydrogen atoms.
The 1H NMR spectrum of 1 shows two singlet signals assigned to
the CH3 protons at 2.30 (3H) and 2.60 (6H) ppm because of differ-
ent chemical environments, which have been computed as average
values of 2.42 and 2.62–2.75 ppm, respectively. These signals are
shifted upfield by 1.87 and 2.18 ppm in the spectrum of 2, while
the theoretical average value for these protons is determined as
2.50 and 2.27–2.62 ppm, respectively. The signals assigned to the
phenyl protons at the range 6.82–7.13 ppm in the spectrum of 1 are
shifted low frequencies in the spectrum of 2. When the 1H NMR
Table 2
Hydrogen bonding geometry for 2.
D—H· · ·A
D—H (Å)
0.86
H· · ·A (Å)
D· · ·A (Å)
D—H· · ·A (◦)
N1—H1· · ·Cl1
2.31
3.1254(13)
159

56
N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
Fig. 4. FT-IR spectrum of 2.
spectrum of 2 was compared to that of 1, the signals attributed to
the NH2 and CH N did not appear in the 1H NMR spectrum of 2.
This approves that the expected Co(II) complex compound did not
form as supported by the elemental analysis and atomic absorption
spectrometer results.
3.3. Quantum-chemical studies
3.3.1. Theoretical structure
The molecular structure of title compound was also studied
theoretically. The starting coordinates were those obtained from
the X-ray structure determination and were optimized by energy-
minimization with the density functional theory (DFT) method.
Some selected geometrical parameters experimentally obtained
and theoretically calculated are listed in Table 5.
As can be seen in Table 5, agreement between the calculated
structure and the experimentally determined X-ray crystal struc-
ture is satisfactory. However, when the X-ray structure of the title
compound is compared with its optimized counterpart (see Fig. 7),
some conformational discrepancies are observed between them.
The dihedral angle between the benzimidazole and benzene rings
of the title molecule is calculated at 61.606◦, while the dihedral
angle between the five- and six-membered rings of the benzimida-
zole ring system is computed at 0.022◦.
Fig. 5. 300 MHz 1H NMR spectrum of 1 in CDCl3.
A logical method for globally comparing the structure obtained
with the theoretical calculation is by superimposing the molecular

N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
57
Table 3
Comparison of the observed and calculated vibrational spectra of compounds 1 and
2.
Assignments
1
2
Exp. (cm−1
)
Calc. (cm−1
)
Exp. (cm−1
)
Calc. (cm−1
)
N—H
–
3478
3377
3063
3020
3002
2968
2951
2913
1598
–
–
3540
3431
3084
3050
3002
2973
2947
2920
1612
–
3551
–
3530
–
N—H2
as
N—H2
–
–
s
C—H (Ar)
3132
3058
2990
–
3102
3071
3005
–
s
C—H (Ar)
as
C—H3
as
C—H3
as
C—H (Mt)
–
–
C—H3
2889
1609
1574
–
1554
1502
1479
1451
1413
1393
–
2917
1608
1590
–
1552
1542
1484
1467
1427
1394
–
1367
1311
1258
–
–
1233
–
1136
1061
–
1029
993
–
838
786
745
730
–
s
C = N
C = C
˛ N—H2
C = C
1558
1494
–
1584
1538
–
C—C(NH)2 + ꢅ N—H
ꢅ N—H + ꢅ C—H
˛ C—H3
ꢅ N—H + ꢅ C—H
˛ C—H3
ꢅ C—H (Mt)
ω C—H3
ꢅ N—H + ꢅ C—H
C = C + ꢅ C—H (Ar)
C—NH2
C = C + ꢅ C—H (Ar)
ꢅ N—H + ꢅ C—H
C—N + ꢅ C—H (Ar)
ꢅ C—H (Ar)
ω N—H
–
–
1456
–
1429
1372
1317
–
1309
1291
1270
–
1153
1133
–
1463
–
1427
1378
1366
–
1309
1286
1274
–
1171
1142
–
1356
1293
1262
–
–
1222
–
1141
1046
–
1025
985
–
841
766
740
715
–
ꢅ N—H2 + ꢅ C—H (Ar) 1031
1046
–
ı C—H3
ꢅ C—H
ω C—H (Mt)
ı C—H (Ar)
Â
ω C—H (Ar)
ω C—H
ω N—H2
Â
–
–
–
Fig. 6. 300 MHz 1H NMR spectrum of 2 in CDCl3.
965
838
740
720
–
577
547
531
964
839
756
726
–
592
553
540
–
–
–
–
ˇ ring
def
Vibrational modes: , stretching; ˛, scissoring; ꢅ, rocking; ω, wagging; ı, twisting;
Â, ring breathing. Abbreviations: as, asymmetric; s, symmetric; Ar, aromatic; Mt,
methine.
Fig. 7. Atom-by-atom superimposition of the X-ray structure (black) of the title
compound and its DFT (red) optimized counterpart. Chloride anion and hydrogen
atoms omitted for clarity. (For interpretation of the references to color cited in the
figure legend, the reader is referred to the web version of the article.)
skeleton with that obtained from X-ray diffraction, giving an RMSE
of 0.052 A (Fig. 7). This value shows that there is a good correlation
˚
between the experimental and calculated structures. However, it
was noted here that the experimental 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 has connected the molecules together, which result
in the differences of bond parameters between the calculated and
experimental values.
3.3.2. Intermolecular proton transfer
The ionic (I), nonionic (II) and transition state (TS) geometries
of the title compound optimized at the B3LYP/6−311++G(d,p) level
are shown in Fig. 8, while selected structural parameters are listed
in Table 5.
Table 4
Experimental and theoretical 1H NMR chemical shifts ı(ppm) from TMS for compounds 1 and 2.
1
2
Atom
Experimental
Calculated
Atom
Experimental
Calculated
H1
4.16 (b, 2H)
4.32a
7.12
6.96–7.45
9.26
7.27–7.38
2.62a–2.75a
2.42a
H1
–
–
22.04
8.71
7.69–8.44
7.35–7.37
2.27a–2.62a
2.50a
H2, H5
H3, H4
H7
H10, H12
H14, H16
H15
7.03–7.13 (m, 2H)
6.82 (d, J = 7.5 Hz, 2H)
8.95 (s, 1H)
6.97 (s, 2H)
2.60 (s, 6H)
H1i
H3, H3i, H4, H4i
H7, H7i
H9, H9i
H10
6.53–6.79 (b, 4H)
7.11 (s, 2H
2.18 (s, 6H)
1.87 (s, 3H)
2.30 (s, 3H)
aAverage.
Note: The atom numbering according to Scheme 1 used in the assignment of chemical shifts of 1.
Note: The atom numbering according to Fig. 1 used in the assignment of chemical shifts of 2.

58
N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
Fig. 8. Optimized molecular structures of the ionic (I), nonionic (II) and transition state (TS) geometries of 2.
Here, the intermolecular proton transfer reaction II → TS → I
3.3.3. Molecular electrostatic potential
was examined in the gas phase. Due to the migration of a hydro-
gen atom from atom N1 to atom Cl1, some changes are observed
in the structure. The distance between atoms Cl1 and H1 decreases
upon the proton transfer II → TS → I. The N1—H1 and Cl1—H1 dis-
The 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 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 [62],
˚
˚
tances are found to be 1.360 A and 1.494 A for TS, respectively. It can
be concluded that the N1—H1 bond is broken, and a Cl1—H1 bond
˚
(ca. 1.380 A) is formed during the intermolecular proton transfer
ꢁ
ꢀ
ZA
ꢄ(rꢀ)
|rꢀ − r|
V(r) =
−
drꢀ
process in the compound. As can be seen from Table 5, in the pro-
ton transfer II → TS → I, very slight changes are observed in the
bond distances of the benzimidazole ring system. However, the
N1—C1—N1i and N1—C2—C2i angles contract as C1—N1—C2 angle
expands, approximately 2◦. In addition, the dihedral angle between
the benzimidazole and benzene rings is reduced from 68.279◦ to
61.606◦.
The tautomerization energy was calculated as the energy differ-
ences between the tautomers and the transition state. The energy
difference between the two tautomers (I and II) was calculated as
−0.13 kcal mol−1. So, it can be said that tautomer I is more stable
than tautomer II, but very little energy difference exists between
them. The relative energy of the TS with respect to tautomer II was
calculated to be 0.20 kcal mol−1. As a result, very low barrier height
was found for this intermolecular proton transfer reaction.
|RA − r|
A
where ZA is the charge of nucleus A located at RA, ꢄ(rꢀ) is the
electronic density function of the molecule, and rꢀ is the dummy
integration variable.
The molecular electrostatic potential (MEP) is related to the
electronic density and is a very useful descriptor in understand-
ing sites for electrophilic attack and nucleophilic reactions as well
as hydrogen-bonding interactions [63,64]. The electrostatic poten-
tial V(r) is also well suited for analyzing processes 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]. Being
a real physical property, V(r) can be determined experimentally by
diffraction or by computational methods [66].
To predict reactive sites for electrophilic and nucleophilic attack
for the title molecule, MEP was calculated by applying the same
method and the basis sets as used for geometry optimization. The
negative (red color) regions of MEP were related to electrophilic
reactivity and the positive (blue color) ones to nucleophilic reac-
tivity shown in Fig. 9. As can be seen from the figure, there is one
Table 5
Optimized and experimental geometries of 2 in the ground state.
Parameters
Experimental
Calculated
I
TS
II
Bond lengths (Å)
Cl1—H1
−
−
−
1.37946
1.31744
1.37383
1.38862
1.38560
−
N1—C1
1.341(2)
1.341(2)
1.389(2)
1.389(2)
0.86
1.32481
1.36358
1.38661
1.38991
1.16483
1.00806
1.47363
1.40511
1.32042
1.36917
1.38775
1.38741
−
N1i—C1
N1—C2
N1i—C2i
N1—H1
N1i—H1i
0.86
1.458(3)
1.394(3)
1.00790
1.47756
1.40775
1.00770
1.48009
1.40983
C1—C5
C2—C2i
Bond angles (◦)
N1—C1—N1i
N1—C1—C5
N1i—C1—C5
N1—C2—C2i
N1i—C2i—C2
N1—C2—C3
N1i—C2i—C3i
C1—N1—C2
C1—N1i—C2i
Torsion angles (◦)
N1—C1—C5—C6
N1i—C1—C5—C6i
N1—C1—C5—C6i
N1i—C1—C5—C6
107.7(2)
108.98595
127.09016
123.92359
107.73061
105.05774
130.85025
133.03278
108.92704
109.29822
110.13018
126.87332
122.99625
108.58430
104.82278
130.59522
133.02972
107.74765
108.71495
110.96735
126.67276
122.35970
109.22947
104.64727
130.38431
133.04019
106.87243
108.28336
126.15(11)
126.15(11)
106.11(8)
106.11(8)
132.26(15)
132.26(15)
110.04(14)
110.04(14)
124.20(11)
124.20(11)
−55.80(11)
−55.80(11)
118.47229
118.51635
−61.26036
−61.75101
114.57677
114.59789
−65.20502
−65.62032
111.80344
111.91596
−67.91335
−68.36725
Fig. 9. Molecular electrostatic potential map (in kcal mol−1) of 2 with an isodensity
value of 0.25 kcal mol−1. (For interpretation of the references to color cited in the
text, the reader is referred to the web version of the article.)
i
−x + 3/4, −y + 3/4, z.

N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
59
3.984 eV and this large energy gap indicates that the title structure
is quite stable.
3.3.5. Non-linear optical effects
Non-linear 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 [68]. 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 [69,70].
The calculations of the mean linear polarizability (˛tot) and the
mean first hyperpolarizability (ˇtot) from the Gaussian output have
been explained in detail previously [71]. The total molecular dipole
moment (ꢁtot), linear polarizability (˛tot) and first-order hyper-
polarizability (ˇtot) of the title compound were calculated at the
B3LYP/6−311++G(d,p) level. The calculated values of ꢁtot, ˛tot and
ˇtot are 10.735 D, 34.162 A3 and 5.379 × 10−30 cm5/esu. Urea is one
˚
of the prototypical molecules used in the study of the NLO prop-
erties of molecular systems. Therefore it was used frequently as a
threshold value for comparative purposes. The values of ꢁtot, ˛tot
3
and ˇtot of urea are 3.874 D, 5.042 A and 0.765 × 10−30 cm5/esu
˚
obtained at the same level. Theoretically, the first-order hyperpo-
larizability of the title compound is of ca. 7 times magnitude of urea.
According to these results, the title compound is a good candidate
of NLO material.
4. Conclusions
In this paper, I have reported the synthesis and characterization
of a novel benzimidazole salt compound (2) occurred unexpectedly,
together with the results of its electronic structure investigation
at the B3LYP/6−311++G(d,p) level. The major conclusions to be
gleaned from this work are the following:
Fig. 10. Molecular orbital surfaces for the HOMO and LUMO of 2. The positive phase
is red, and the negative phase is green. (For interpretation of the references to color
cited in the figure legend, the reader is referred to the web version of the article.)
possible site on the compound for electrophilic attack. The nega-
tive region is mainly localized on the chloride anion, Cl1, with a
maximum value of −47 kcal mol−1. However, a maximum positive
region is mainly over the benzimidazole nitrogen atom, N1, with a
maximum value of 53 kcal mol−1. So, Fig. 9 confirms the existence
of intermolecular N—H· · ·Cl interactions observed in the solid state.
1. The structure of 2 is verified by FT-IR, 1H NMR, elemental anal-
ysis and single crystal X-ray diffraction, as well as by atomic
absorption spectroscopy.
2. The structural parameters of the title molecule calculated in the
gas phase are in very good correspondence with X-ray experi-
mental data.
3. In the gas phase, the ionic form (I) of 2 is more stable than the
3.3.4. Frontier molecular orbitals
nonionic form (II), and very low barrier energy (0.20 kcal mol−1
)
The frontier molecular orbitals play an important role in the
electric and optical properties, as well as in UV–vis spectra. It is well
known that both the highest occupied molecular orbital (HOMO)
and lowest unoccupied molecular orbital (LUMO) are the main
orbital taking part in chemical reaction. The HOMO energy charac-
terizes the ability of electron giving, LUMO energy characterizes the
ability of electron accepting, and the gap between HOMO and LUMO
characterizes the molecular chemical stability [67]. Fig. 10 shows
the distributions and energy levels of the HOMO–LUMO orbitals
computed at the same level as used for geometry optimization for
the title compound.
is found for the intermolecular proton transfer reaction between
them.
4. The MEP map agrees well with the solid state interaction, and a
large HOMO–LUMO gap indicates a quite stable structure.
5. The predicted NLO properties of 2 are greater than ones of urea.
So, the title compound is a good candidate as second-order NLO
material.
Supplementary material
The calculations indicate that the compound has 72 occupied
molecular orbitals. As can be seen from the figure, the HOMO and
LUMO orbitals are localized on different parts of 2. The HOMO
orbitals are localized on the chloride anion, while the LUMO orbitals
are spread over the whole cation molecule. But, both of the high-
est occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) are mostly ␲-antibonding type orbitals.
The value of the energy separation between the HOMO and LUMO is
CCDC 803481 contains the supplementary crystallographic
data (excluding structure factors) for the structure reported
in this article. These data can be obtained free of charge
at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cam-
bridge Crystallographic Data Centre (CCDC), 12 Union Road,
Cambridge CB2 1EZ, UK. Fax: +44
deposit@ccdc.cam.ac.uk]
0 1223 336033; e-mail:

60
N. Özdemir / Spectrochimica Acta Part A 91 (2012) 51–60
Acknowledgments
[31] S. Mohan, N. Sundaraganesan, J. Mink, Acta Part A 47 (1991) 1111–1115.
[32] T.D. Klots, P. Devlin, W.B. Collier, Spectrochim. Acta Part A 53 (1997) 2445–2456.
[33] M.A. Morsy, M.A. Al-Khaldi, A. Suwaiyan, J. Phys. Chem.
9196–9203.
[34] S¸ . Yurdakul, C. Yılmaz, Vib. Spectro. 21 (1999) 127–132.
[35] A.W. Kleij, D.M. Tooke, A.L. Spek, J.N.H. Reek, Eur. J. Inorg. Chem. 22 (2005)
4626–4634.
[36] G.M. Sheldrick, SHELXS-97 Program for the Solution of Crystal Structures, Uni-
versity of Göttingen, Germany, 1997.
A 106 (2002)
I wish to thank Prof. Dr. Orhan Büyükgüngör for his help with the
data collection and acknowledge the Faculty of Arts and Sciences,
Ondokuz Mayıs University, Turkey, for the use of the STOE IPDS II
diffractometer (purchased under grant No. F-279 of the University
Research Fund).
[37] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837–838.
[38] G.M. Sheldrick, SHELXL-97 Program for Crystal Structures Refinement, Univer-
sity of Göttingen, Germany, 1997.
Appendix A. Supplementary data
[39] Stoe, Cie, X-AREA Version 1.18 and X-RED32 Version 1.04, Stoe & Cie, Darm-
stadt, Germany, 2002.
[40] A.L. Spek, Acta Crystallogr. D65 (2009) 148–155.
[41] C. Peng, P.Y. Ayala, H.B. Schlegel, M.J. Frisch, J. Comput. Chem. 17 (1996) 49–56.
[42] R. Dennington II, T. Keith, J. Millam, Gauss View, Version 4.1.2, Semichem Inc.,
Shawnee Mission, KS, 2007.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2012.01.069.
References
[43] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheese-
man, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P.
Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Strat-
mann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K.
Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich,
A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari,
J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Ste-
fanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith,
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.
[1] M.J. O’Niel, M. Smith, P.E. Heckelman, The Merck Index, 13th ed., Merck & Co.
Inc., New Jersey, 2001, P-1785, Monograph Number, p. 10074.
[2] G. Ayhan-Kılcıgil, C. Kus¸ , E.D. Özdamar, B. Can-Eke, M. Is¸ can, Arch. Pharm. 340
˙
(2007) 607–611.
˙
[3] C. Kus¸ , G. Ayhan-Kılcıgil, B. Can-Eke, M. Is¸ can, Arch. Pharm. Res. 27 (2004)
156–163.
[4] Z. Ates¸ -Alagöz, C. Kus¸ , T. C¸ oban, J. Enzyme Inhib. Med. Chem. 20 (2005) 325–331.
[5] G. Navarrete-Vázquez, R. Cedillo, A. Hernández-Campos, L. Yépez, F.
Hernández-Luis, J. Valdez, R. Morales, R. Cortés, M. Hernández, R. Castillo,
Bioorg. Med. Chem. Lett. 11 (2001) 187–190.
[6] S.K. Katiyar, V.R. Gordon, G.L. McLaughlin, T.D. Edlind, Antimicrob. Agents
Chemother. 38 (1994) 2086–2090.
[7] E. Ravina, R. Sanchez-Alonso, J. Fueyo, M.P. Baltar, J. Bos, R. Iglesias, M.L. San-
martin, Arzneim. -Forsch./Drug Res. 43 (1993) 689–694.
[8] L. Garuti, M. Roberti, M. Malagoli, T. Rossi, M. Castelli, Bioorg. Med. Chem. Lett.
10 (2000) 2193–2195.
[9] A. Rao, A. Chimirri, E. De Clercq, A.M. Monforte, P. Monforte, C. Pannecouque,
M. Zappalá, Il Farmaco 57 (2002) 819–823.
[10] A. Chimirri, A. De Sarro, G. De Sarro, R. Gitto, M. Zappalá, Il Farmaco 56 (2001)
821–826.
[11] P.A. Thakurdesai, S.G. Wadodkar, C.T. Chopade, Pharmacologyonline 1 (2007)
314–329.
[12] H.-T. Le, I.B. Lemaire, A.-K. Gilbert, F. Jolicoeur, L. Yang, N. Leduc, S. Lemaire, J.
Pharmacol. Exp. Ther. 30 (2004) 146–155.
[13] B. Serafin, G. Borkowska, J. Główczyk, I. Kowalska, S. Rump, Pol. J. Pharmacol.
Pharm. 41 (1989) 89–96.
[14] K. Kubo, Y. Inada, Y. Kohara, Y. Sugiura, M. Ojima, K. Itoh, Y. Furukawa, Y.K.
Nishikawa, T. Naka, J. Med. Chem. 36 (1993) 1772–1784.
[15] A. Abdel-monem Abdel-hafez, Arch. Pharm. Res. 30 (2007) 678–684.
[16] S. Ram, D.S. Wise, L.L. Wotring, J.W. McCall, L.B. Townsend, J. Med. Chem. 35
(1992) 539–547.
[17] A.Ts. Mavrova, P. Denkova, Y.A. Tsenov, K.K. Anichina, D.I. Vutchev, Bioorg. Med.
Chem. 15 (2007) 6291–6297.
[18] G. Ayhan-Kılcıgil, N. Altanlar, Il Farmaco 58 (2003) 1345–1350.
[19] S. Özden, D. Atabey, S. Yıldız, H. Göker, Bioorg. Med. Chem. 13 (2005)
1587–1597.
[44] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652.
[45] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789.
[46] R. Krishnan, J.S. Binkley, R. Seeger, J.A. Pople, J. Chem. Phys. 72 (1980) 650–654.
[47] M.J. Frisch, J.A. Pople, J.S. Binkley, J. Chem. Phys. 80 (1984) 3265–3269.
[48] P.M. Anbarasan, M.K. Subramanian, P. Senthilkumar, C. Mohanasundaram, V.
Ilangovan, N. Sundaraganesan, J. Chem. Pharm. Res. 3 (2011) 597–612.
[49] R. Ditchfield, J. Chem. Phys. 56 (1972) 5688–5691.
[50] K. Wolinski, J.F. Hinton, P. Pulay, J. Am. Chem. Soc. 112 (1990) 8251–8260.
[51] E. Cancès, B. Mennucci, J. Tomasi, J. Chem. Phys. 107 (1997) 3032–3041.
[52] K. Brandenburg, DIAMOND Demonstration Version 3.2.f, Crystal Impact GbR,
Bonn Germany, 2006.
[53] O.Z. Yes¸ ilel, M. Odabas¸ og˘lu, O. Büyükgüngör, J. Mol. Struct. 874 (2008) 151–158.
[54] E.B. Usova, E.Y. Kambulov, V.E. Zavodnik, G.D. Krapivin, Chem. Heterocycl.
Comp. 35 (1999) 231–239.
[55] T.-F. Tan, J. Han, M.-L. Pang, H.-B. Song, Y.-X. Ma, J.-B. Meng, Cryst. Growth Des.
6 (2006) 1186–1193.
[56] Y.-S. Chen, K. Zhang, S.-Q. Zhao, Acta Crystallogr. E65 (2009) o1926.
[57] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R. Taylor, J. Chem.
Soc., Perkin Trans. II 12 (1987) S1–S19.
[58] F.H. Allen, Acta Crystallogr. B58 (2002) 380–388.
[59] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P. McCabe, J. Pearson,
R. Taylor, Acta Crystallogr. B58 (2002) 389–397.
[60] J. Yin, R.L. Elsenbaumer, J. Org. Chem. 70 (2005) 9436–9446.
[61] N. Sundaraganesan, S. Ilakiamani, P. Subramani, B.D. Joshua, Spectrochim. Acta
A 67 (2007) 628–635.
[62] P. Politzer, J.S. Murray, Theor. Chem. Acc. 108 (2002) 134–142.
[63] F.J. Luque, J.M. Lopez, M. Orozco, Theor. Chem. Acc. 103 (2000) 343–345.
[64] N. Okulik, A.H. Jubert, Internet Electron. J. Mol. Des. 4 (2005) 17–30.
[65] P. Politzer, P.R. Laurence, K. Jayasuriya, Environ. Health Perspect. 61 (1985)
191–202.
[66] P. Politzer, D.G. Truhlar, Chemical Applications of Atomic and Molecular Elec-
trostatic Potentials, Plenum, New York, 1981.
[67] I. Fleming, Frontier Orbitals and Organic Chemical Reactions, Wiley, London,
1976.
[20] N. Terziog˘lu, R.M. van Rijn, R.A. Bakker, I.J.P. De Esch, R. Leurs, Bioorg. Med.
Chem. Lett. 14 (2004) 5251–5256.
[21] H. Küc¸ ükbay, R. Durmaz, E. Orhan, S. Günal, Il Farmaco 58 (2003) 431–437.
[22] N.M. Agh-Atabay, B. Dülger, F. Gücin, Eur. J. Med. Chem. 38 (2003) 875–881.
[23] M. Andrzejewska, L. Yépez-Mulia, R. Cedillo-Rivera, A. Tapia, L. Vilpo, J. Vilpo,
Z. Kazimierczuk, Eur. J. Med. Chem. 37 (2002) 973–978.
[24] S.E. Castilo-Blum, N. Barba-Behrens, Coord. Chem. Rev. 196 (2003) 3–30.
[25] K.K. Mothilal, C. Karunakaran, A. Rajendran, R. Murugesan, J. Inorg. Biochem.
98 (2004) 322–332.
[26] J.B. Wright, Chem. Rev. 48 (1951) 397–541.
[27] P.N. Preston, Chem. Rev. 74 (1974) 279–314.
[28] X.-L. Zheng, Y. Liu, M. Pan, X.-Q. Lü, J.-Y. Zhang, C.-Y. Zhao, Y.-X. Tong, C.-Y. Su,
Angew. Chem. Int. Ed. Engl. 46 (2007) 7399–7403.
[29] D.-Q. Qi, G.-G. Hou, J.-P. Ma, R.-Q. Huang, Y.-B. Dong, Acta Crystallogr. C65 (2009)
o85–o87.
[68] Y.-X. Sun, Q.-L. Hao, W.-X. Wei, Z.-X. Yu, L.-D. Lu, X. Wang, Y.-S. Wang, J. Mol.
Struct. THEOCHEM 904 (2009) 74–82.
[69] V.M. Geskin, C. Lambert, J.-L. Brédas, J. Am. Chem. Soc. 125 (2003) 15651–15658.
[70] D. Sajan, H. Joe, V.S. Jayakumar, J. Zaleski, J. Mol. Struct. 785 (2006) 43–53.
[71] G.A. Babu, P. Ramasamy, Curr. Appl. Phys. 10 (2010) 214–220.
[30] W.A. Herrmann, Angew. Chem. Int. Ed. Engl. 41 (2002) 1290–1309.