Vibrational and conformational analysis on-N1-N 2-bis((pyridine-4-yl)methylene) benzene-1,2-diamine

Article abstract of DOI:10.1016/j.molstruc.2013.03.034

The molecule N¹-N²-bis((pyridine-4-yl)methylene) benzene-1,2-diamine (NBPMB) was synthesized and characterized by FT-IR, FT-Raman and UV-Vis., spectra. To identify the stable structure of the molecule meticulous conformational analys

Full text of DOI:10.1016/j.molstruc.2013.03.034

Journal of Molecular Structure 1042 (2013) 37–44
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Vibrational and conformational analysis on-N1-N2-bis((pyridine-4-yl)methylene)
benzene-1,2-diamine
e
e
S. Subashchandrabose a, C. Meganathan b, Y. Erdog˘du c, H. Saleem d, , C. Jajkumar , P. Latha
⇑
a Dept. of Physics, M.A.R. College of Engineering & Technology, Trichy, Tamil Nadu 621 316, India
b Dept. of Physics, G.K.M. College of Engineering & Technology, Perungalathur, chennai, Tamil Nadu 600 063, India
c Dept. of Physics, Ahi Evran University, Kirsehir 40040, Turkey
d Dept. of Physics, Annamalai University, Annamalai Nagar, Tamil Nadu 608 002, India
e Dept. of Chemistry, FEAT Annamalai University, Annamalai Nagar, Tamil Nadu 608 002, India
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Structural properties of NBPMB.
TED.
NBO analysis.
NLO.
Band gap energy.
a r t i c l e i n f o
a b s t r a c t
The molecule N1-N2-bis((pyridine-4-yl)methylene)benzene-1,2-diamine (NBPMB) was synthesized and
characterized by FT-IR, FT-Raman and UV–Vis., spectra. To identify the stable structure of the molecule
meticulous conformational analysis was performed. The observed (FT-IR and FT-Raman) spectral fre-
quencies were compared with harmonic wavenumbers. The vibrational assignments were performed
on the basis of the total energy distribution (TED). The optimized geometrical parameters are calculated
and compared with experimental results. The non-linear optical behavior NBPMB molecule is analyzed
using hyperpolarizability calculation. The charge transfer within the molecule and biological activity of
NBPMB were calculated.
Article history:
Received 16 December 2012
Received in revised form 17 March 2013
Accepted 17 March 2013
Available online 26 March 2013
Keywords:
FT-IR
FT-Raman
TED
Ó 2013 Elsevier B.V. All rights reserved.
NBO
Hyperpolarizability
HOMO–LUMO
1. Introduction
optical material, which were of great interest with good suscepti-
bilities have their application in the field of photonics and also
Schiff base which contain an azomethane group attracts much
interest in synthetic chemistry. Some donor atoms such as N, O,
S in Schiff bases have structural similarities with natural biological
systems and imports in elucidating the mechanism of transforma-
tions and racemisation reactions due to presence of imine
(AN@CHA) group [1]. It is also known to have biological activities
such as antibacterial [2,3], antifungal [4,5], antitumor [6,7], antiox-
idant [8] and anti-tuberculosis [9] activities. In organic molecules
the presence of AN@CA along with other functional groups form
more stable complexes compared to compounds with only
AN@CA coordinating moiety. Amino pyridine is a non-linear
many areas in chemistry. 4-N,N1-Dimethylaminopyridine has been
become one of the most popular catalyst for different process such
as acylations, alkylations, silylations, Baylis–Hilman reaction and
nucleophillic substitutions of alcohols and amines [10]. The vibra-
tional spectra of substituted pyridine have been the subject of
several investigations [11–14].
Pyridine is also called azabenzene and azine, is a heterocyclic aro-
matic tertiary amine characterized by a six membered ring structure
composed of five carbon atoms and one carbon–hydrogen atom in
the benzene ring being replaced by a nitrogen atom. Pyridine and
its related derivatives were found in the structure of many drugs.
It has been extensively studied from the spectroscopic point of view,
due in part to its presence in many chemical structures of high inter-
est in a variety of biomedical and industrial fields. To the best of our
⇑
Corresponding author. Tel.: +91 9443879295.
E-mail addresses: saleem_h2001@yahoo.com, sscbphysics@gmail.com (H. Saleem).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.03.034

38
S. Subashchandrabose et al. / Journal of Molecular Structure 1042 (2013) 37–44
knowledge neither quantum chemical calculations nor the vibra-
tional spectra of N1-N2-bis((pyridine-4-yl)methylene)benzene-1,2-
diamine (NBPMB) have been reported so for. Therefore, the present
investigation was undertaken to study the vibrational spectra of this
molecule and to identify the various modes with greater wavenum-
ber accuracy. In recent years, DFT calculations have been used
extensively for calculating a wide variety of molecular properties
such as equilibrium structure, charge distribution, FT-IR, NMR
spectra and provided reliable results which are in agreement with
experimental data [15]. In this research, Beck’s three-parameter
exchange functional [16] with Lee, Yang and Parr’s [17] correlation
functional (B3LYP) were used to perform the theoretical calculations
such as harmonic wavenumber, molecular polarizability, NBO anal-
ysis, thermodynamic properties and few quantum descriptors of the
title compounds.
It should be noted that Gaussian 03 W package was able to cal-
culate the Raman activity. The Raman activities were transformed
into Raman intensities using Raint program [22] by the expression:
1
mi
4
Ii ¼ 10ꢁ12 ꢂ ðm0
ꢁ
miÞ ꢂ ꢂ RAi
ð1Þ
where Ii is the Raman intensity, RAi is the Raman scattering activi-
ties, mi is the wavenumber of the normal modes and m0 denotes
the wavenumber of the excitation laser [23].
4. Results and discussion
4.1. Conformational stability
To find the stable conformers, a meticulous conformational
analysis was carried out for the NBPMB compound. Rotating 360
degree with intervals of 10° around the free rotation bonds, confor-
mational space of the title compound was scanned by molecular
mechanic simulations and then full geometry optimizations of
these structures were performed by B3LYP/6-31G(d,p) method.
Results of geometry optimizations were indicated that the title
compound may have at least three conformers as shown in
Fig. S1 (Supporting information). Ground state energies, zero point
corrected energies (Eelect.+ZPE), relative energies and dipole
moments of conformers were presented in Table S1 (Supporting
information). The conformer one is the most stable one and the
theoretical geometry of the title compound fairly well reproduce
the experimental one [24,25]. The results and discussion of this pa-
per is based on conformer one.
2. Experimental details
2.1. Synthesis
An ethanolic solution of o-phenylenediamine was refluxed with
4-pyridine carboxaldehyde [1:2 ratios] for about 5 to 6 h. The
volume of the solution was reduced to one third. The pale yellow
solid formed after 1 day and precipitation was filtered and then
recrystallized from ethanol.
2.2. FT-IR and FT-Raman spectra
The FT-IR spectrum of NBPMB was recorded in the region
400–4000 cmꢁ1 on an IFS 66 V spectrophotometer using the KBr
pellet technique. The spectrum was recorded at room temperature
with a scanning speed of 10 cmꢁ1 per minute and at the spectral
resolution of 2.0 cmꢁ1 in CISL Laboratory, Annamalai University,
Tamilnadu, India. The FT-Raman spectrum of title compound was
recorded using the 1064 nm line of a Nd:YAG laser as excitation
wavelength in the region 50–3500 cmꢁ1 on Bruker model IFS 66V
spectrophotometer equipped with an FRA 106 FT-Raman module
accessory and at spectral resolution of 4 cmꢁ1. The FT-Raman
spectral measurements were carried out from Sree Chitra Tirunal,
Institute of Medical Sciences and Technology, Poojappura, Thiruva-
nanthapuram, Kerala, India.
4.2. Molecular geometry
The optimized molecular geometry of NBPMB were calculated
by using DFT/B3LYP/6-31G(d,p) basis set which is given in
Table S2 (Supporting information). The numbering scheme of the
molecule is given in Fig. 1. The exact crystal structure of the title
compound is not yet discovered so that the optimized structure
can only be compared with other similar system, e.g. 2, 6-bis
[3-methoxysalicylidene)hydrazinocarbonyl] pyridine [25] and
5-(phenylazo)-N-(2-amino pyridine) salicylidene [24]. It is evident
from Table S2, the optimized bond lengths and bond angles were
3. Computational details
In order to establish the stable possible conformations, the
conformational space of NBPMB was scanned with molecular
mechanic simulations. This calculation was performed with the
Spartan 08 program [18]. For meeting the requirements of both
accuracy and computing economy, theoretical methods and basis
sets were considered. DFT has been proved to be extremely useful
in treating electronic structure of molecules. The entire calcula-
tions were performed at DFT level on a Pentium IV/3.02 G.Hz per-
sonal computer using Gaussian 03 W [19] program package,
invoking gradient geometry optimization [19,20]. In this study,
the conformer one is used for the geometry optimization. Initial
geometry generated from standard geometrical parameters was
minimized without any constraint in the potential energy surface
at DFT level, adopting the standard 6-31G(d,p) basis set. The opti-
mized structural parameters were used in the vibrational fre-
quency calculations at the DFT level to characterize all stationary
points as minima. Then vibrationaly averaged nuclear positions
of NBPMB were used for harmonic vibrational frequency calcula-
tions resulting in IR and Raman frequencies together with intensi-
ties and Raman depolarization ratios. The vibrational modes were
assigned on the basis of TED analysis using SQM program [21].
Fig. 1. The optimized molecular structure of NBPMB.

S. Subashchandrabose et al. / Journal of Molecular Structure 1042 (2013) 37–44
39
Table 1
Vibrational wave numbers obtained for NBPMB at B3LYP/6-31G(d,p) [harmonic frequency (cmꢁ1), IR , Raman intensities (km/mol), reduced masses (amu) and force constants
(mdynA°ꢁ1)].
Mode nos. Calculated frequencies (cmꢁ1
)
Observed frequencies (cmꢁ1
)
Intensities
Vibrational assignments TEDd (P10%)
b
c
Unscaled
Scaleda
FT-IR
FT-Raman
IIR
IRaman
1
2
3
4
5
6
7
8
25
27
32
61
64
24
25
30
58
61
0.03
0.30
0.31
0.02
0.06
0.23
3.79
8.88
2.74
0.01
0.00
0.86
3.84
0.42
0.16
3.18
0.01
0.03
4.34
6.20
33.62 dCCN(31) + dCNC(16)
1.91 CC12N11C1C2 (17) + CC12N11C1C6(12) + CC25N24C2C1(18) + CC25N24C2C3(12)
84.82 CCNCC(22) + CCCCH(15) + CCCCN(10)
20.69 dCNC(21) + CCNCC(15) + CCCCN(12)
0.22 CC14C12N11C1(18) + CC27C25N24C2(18)
6.84 dC12N11C1(14) + dC25N24C2(14)
38.35 CC12N11C1C2(11) + CC25N24C2C1(11)
18.68 CC12N11C1C2(11) + C C25N24C2C1(11)
2.07 dCCC(30) + CCCNC (10)
78
75
117
133
157
173
236
258
268
304
113
128
151
166
227
248
258
292
296
369
375
375
437
457
495
511
529
550
560
561
620
650
656
657
716
725
735
740
789
803
805
833
835
858
862
863
875
905
939
943
943
964
964
970
970
972
974
1032
1046
1046
1067
1068
1085
1141
1165
1172
1193
1196
1219
1224
1248
1249
1255
1282
1303
1305
116s
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
0.17 dCCN(18) + dCCC(18)
4.28 dC12N11C1(13) + dC25N24C2(13)
10.90 CCCCC(23) + CCCCN(16)
28.25 CCNCC(18)
0.40 dCCC(14) + CCCCN(10)
2.82 CCCNC(14) + dCCC(30)
308
384
390
0.12 dCCC(24) + CCCCC(20)
0.09 CN21C17C15C14(10) + CN34C32C29C27(10)
0.36 CN21C17C15C14(10) + CN34C32C29C27(10)
0.15 dCCN(16) + dCCC(16)
7.05 dCCN(12) + CCCCC(16)
1.94 dCCC(28)
0.42 CCNCC(16)
1.75 CCCNC(11)
0.33 dCCC(24)
2.64 CC6C5C4C3(15)
0.84 dC2C1N11(12) + d N24C2C1(12)
2.63 dC4C3C2(10) + dC1C6C5(10) + dCNC(12)
0.07 dCNC(24) + dCCN(10)
1.58 dCCC(28) + dNCC(32)
1.22 dCCC(27) + dNCC(31)
0.20 CCCCC(26) + CCNCC(16)
0.05 CCCCC(16) + CNCCC(20)
0.07 CCCCC(13)
391
455
476
515
531
550
572
583
583
645
677
683
683
745
755
765
770
821
836
837
867
869
893
898
899
911
942
978
981
982
1003
1004
1009
1010
1011
1014
1075
1089
1089
1111
1112
1129
1188
1212
1220
1242
1245
1268
1274
1299
1300
1306
1334
1356
1358
426w
465w
499w
25.04
2.34
17.80
10.83
4.09
1.72
10.30
4.11
0.41
0.49
0.06
2.73
0.06
39.10
13.76
31.03
4.70
5.88
7.20
3.35
0.74
0.18
4.42
4.27
0.15
0.10
0.28
0.49
0.26
5.22
4.94
3.93
7.10
3.81
4.57
3.48
4.66
0.24
15.58
0.06
17.86
35.92
0.77
8.27
0.76
0.00
0.63
8.98
6.06
7.47
4.78
12.50
537w
564w
618w
652w
670w
712 ms
743 ms
768 ms
1.55 CH8C4C3C2(14) + CC6C5C4H8(12) + CH9C5C4C3(12) + CC1C6C5H9(14)
1.50
mC2C1(37) + mCC(28) + mNC(14)
0.17 CHCCC(56) + CNCCH(18)
0.09 CHCCC(52)
0.98 CHCCC(22) + CCCCH(12)
812w
823w
1.07 dC5C4C3(12) + dC6C5C4(12)
6.73 CC(24) + dCNC(10) + dCCN(12)
851w
m
0.32 CHCCC(48) + CNCCH(22)
0.88 CHCCC(48) + CNCCH(16)
873w
904w
1.89
mCC(14) + dCNC(14) + dCCN(10)
0.39 CH8C4C3H7(20) + CH10C6C5H9(20)
0.34 CH23C19C16H20(16) + CH35C30C28H31(16)
0.51 CH23C19C16H20(15) + CH35C30C28H31(15)
0.44 CH8C4C3H7(16) + CH9C5C4H8(29) + CH10C6C5H9(16)
0.21 CH13C12N11C1(13) + CH26C25N24C2(13)
0.61 CHCNC(18) + CHCCH(20) + CCCCH (18) + CCCCH (18)
6.07 CH22C17C15H18(18) + CH36C32C29H33(18)
11.29 CHCCH(18) + CHCNC(10)
961w
1003w
1008w
1006 ms
0.57
4.43
3.73
0.38
0.70
0.50
0.96
2.74
m
m
m
m
m
m
m
m
CC(15) +
NC(17) + CHCCH(10)
C4C3(13) + C5C4(35) +
NC(21) + dHCC(30)
N21C17(7) + N21C19(4) +
mNC(26)
1024 m
1043 m
m
m
C6C5(13) + dCCH(20)
N34C30(4) + N34C32(7) + dHCC(30)
m
m
m
C19C16(11) +
C19C16(11) +
m
m
C30C28(11)
C30C28(11)
1094w
1137w
1156w
C4C3(11) + mC6C5(11) + dCCC (14) + dCCH (34)
1148w
1224w
10.41 dH8C4C3(16) + dC5C4H8(15) + dH9C5C4(15) + dC6C5H9(16)
14.11
87.72
1.36
2.45
6.64
0.40
0.53
5.66
6.31
10.86
m
m
m
m
m
m
m
m
m
m
CC(24) +
CC(36) +
NC(20) + dCCH(16) + dNCH(24)
NC(26) + dNCH(24) + dCCH(14)
m
m
NC(18) + dHCC(18)
NC(18)
1189 ms
1227 ms
C14C12(10) +
m
C27C25(10)
CC(18) + dHCN(10)
NC(36) + dHCC(12)
N21C19(13) +
NC(22) + dCCH(34)
C2C1(20) + C3C2(16) + mC5C4(10) + m
NC(18) +
CC(26) +
m
m
N21C17(10) +
m
m
N34C30(13) +
mN34C32(10)
1253 ms
1297 ms
1283 ms
1315 ms
m
C6C1(16)
1.39 dHCC(60)
2.74 dCCH(10) + dHCC(31)
(continued on next page)

40
S. Subashchandrabose et al. / Journal of Molecular Structure 1042 (2013) 37–44
Table 1 (continued)
Mode nos. Calculated frequencies (cmꢁ1
)
Observed frequencies (cmꢁ1
)
Intensities
Vibrational assignments TEDd (P10%)
b
c
Unscaled
Scaleda
FT-IR
FT-Raman
IIR
IRaman
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
1410
1411
1454
1454
1481
1516
1535
1537
1609
1609
1619
1631
1649
1649
1705
1707
3024
3025
3165
3165
3171
3171
3185
3192
3192
3193
3201
3212
3226
3226
1354
1355
1397
1397
1423
1457
1475
1477
1546
1546
1556
1567
1584
1585
1638
1640
2906
2906
3041
3041
3047
3047
3060
3067
3067
3068
3076
3086
3100
3100
1342w
8.74
4.92
8.02
19.93
5.34
12.08
1.28
2.71
0.00
47.79
0.26
5.95
41.59
35.33
0.91 dH13C12N11(16) + dH13C12C14(12) + dH26C25N24(16) + dH26C25C27(12)
0.14 dH13C12N11(18) + dH13C12C14(13) + dH26C25N24(18) + dH26C25C27(13)
1.37
0.75
m
m
CC(24) + dNCH(31)
CC(24) + dNCH(30)
1426s
1448s
1465w
1488w
1535w
1421w
1452s
4.46 dH8C4C3(10) + dC5C4H8(15) + dH9C5C4(15) + dC6C5H9(10)
28.32
2.07
m
m
C2C1(13)
NC(14) + dNCH(18) + dHCC(24)
1474s
1527 m
0.26 dHCC(22) + dNCH(18)
18.37
8.58
16.73
52.50
16.56
25.89
m
m
m
m
m
m
m
m
C15C14(11) +
C15C14(11) +
m
m
C16C14(10) +
C16C14(11) +
m
m
C29C27(11)
C28C27(11) + mC29C27(11)
C2C1(15) +
C3C2(13) +
m
m
C5C4(28)
C4C3(18) + mC6C1(13) + mC6C5(18)
1576 ms
1571s
1591s
C17C15(10) +
C17C15(10) +
C12N11(38) +
C12N11(38) +
m
m
C32C29(10)
C32C29(10)
1590w
1638w
1639w
40.69 100.0
m
m
C25N24(38)
C25N24(38)
(50)
100.00
31.82
34.95
47.61
1.04
10.97
33.03
1.13
29.31
1.63
3.32
13.49
20.49
1.44
47.23
0.39 mC12H13 (50) + mC25
H26
0.46 mC12H13 (50) + mC25H26 (50)
0.84 mC19H23 (41) + C30H35(39)
2985w
m
2.12 mC19H23 (39) + C30H35(41)
0.52 mC17H22 (47) + C32H36(47)
1.49 mC17H22 (47) + mC32H36 (47)
3042 ms
0.15
mC3H7(18) + mC4H8(32) + mC5H9(32) + mC6H10(18)
0.26 mC3H7 (18) + C6H10 (18) + C16H20 (22) + C28H31 (21)
2.01
m
C16H20(39) + mC28H31 (40)
C3H7(20) + mC6H10 (20) +
C4H8(18) +
C4H8(38) + mC5H9 (38) +
0.03 mC15H18 (47) + C29H33(50)
0.72 C15H18(50) + C29H33(46)
0.89
m
mC16H20(18) + mC28H31(18)
0.70 mC3H7 (32) +
2.58 C3H7(12) + m
m
m
C5H9(18) +
m
m
C6H10(32)
3085w
3165w
m
C6H10(12)
m
3.04
m
m
m
: Stretching, d: in-plane-bending,
C
: out-of-plane bending, vw: very week, w: week, m: medium, s: strong, vs: very strong.
a
Scaling factor: 0.9608 [28].
b
Relative IR absorption intensities normalized with highest peak absorption equal to 100.
Relative Raman intensities calculated by Eq. (2.1) and normalized to 100.
Total energy distribution calculated at B3LYP/6-31G(d,p) level.
c
d
slightly longer than the literature values because the molecular
states were different during the experimental and theoretical
process. The isolated molecule is considered as in gas phase during
theoretical calculation, while many packing molecules were
treated as in the condensed phase during the experimental
measurements.
In this study, the packing of the two pyridine rings through
N@CAH linkage on the benzene ring (at C1 and C2) cause some
changes in the CAC bond length. They vary by 0.024 Å in the most
extreme case within the same method of calculations. The benzene
ring is little distorted in which the C1AC2 (1.419 Å), and C1AC6/
C2AC3 (1.402 Å) bond lengths are longer than the bonds C3AC4,
C4AC5 and C5AC6 (ꢃ1.395 Å). The increasing of bond lengths at
C1AC2, C1AN11 and C2AN24 bonds is due to slightly irregular
hexagonal structure of the angles C2AC1AC6/C1AC2AC3 and
C2AC3AC4/C1AC6AC5 are 119.06° and 121.07° respectively. The
CAH bond lengths are found to be 1.086 Å in benzene ring, while
C12AH13/C25AH26 bond length is about 1.100 Å. The lengths
bond and bond angles of both pyridine rings are identical.
spectra have any imaginary wavenumbers, implying that the
optimizedgeometry is located at the local lowest point on the poten-
tial energy surface. Comparison of the frequencies calculated at
B3LYP with experimental assignments reveal the overestimation
of the calculated vibrational modes due to the neglect of anharmo-
nicity in the real system. We know that the ab initio HF and DFT
potentials systematically overestimate the vibrational wavenum-
bers. These discrepancies are corrected by computing anharmonic
corrections explicitly, by introducing a scaled field [26] or directly
scaling the calculated wavenumbers with the proper factor [27].
The scale factor 0.9608 [28] was used to bring the computed wave-
numbers close to the recorded frequencies. The combined experi-
mental and theoretical spectra are shown in Fig. 2 (FT-IR) and 3
(FT-Raman) (see Fig. 3).
4.3.1. CAH vibrations
The presence of one or more aromatic rings in a structure is nor-
mally readily determined from the CAH and C@CAC ring related
vibrations [29]. The CAH stretching vibration occurs above
3000 cmꢁ1 and is typically exhibited as multiplicity of the weak
to moderate bands, compared with the aliphatic CAH stretch
[30]. The heteroaromatic structure has shown the presence of
CAH stretching vibration in the region of 3100–3000 cmꢁ1 which
was the characteristic region for the ready identification of CAH
stretching vibrations [31].
4.3. Vibrational assignments
The NBPMB is a non-planar molecule and possesses C1 point
group symmetry. The molecule has 36 atoms and hence 102
normal modes of vibrations were possible, which were active in both
IR absorption and Raman scattering. The harmonic vibrational fre-
quencies were calculated at B3LYP level with 6-31G(d,p) basis set
and which are summarized in Table 1. In the last column of
Table 1, a detailed description of the normal modes based on the
TED is given. Furthermore, none of the predicted vibrational
In the present study, the harmonic CAH stretching vibrations
(benzene) are assigned in the range 3086–3060 cmꢁ1 (mode nos:
100, 99, 98, 95), while the observed FT-IR band is at 3085 cmꢁ1
.
Similarly the observed bands (FT-IR) 3165, 3042 cmꢁ1 and calcu-
lated frequencies lies in the range 3100–3041 cmꢁ1 (mode nos:

S. Subashchandrabose et al. / Journal of Molecular Structure 1042 (2013) 37–44
41
0.70
0.60
0.05
0.06
0.07
0.08
0.09
0.10
FT-IR
FT-Raman
0.50
0.40
0.30
0.20
0.10
0.00
0.60
1.00
0.80
0.60
0.40
0.20
0.00
IR/B3LYP
0.50
Raman/B3LYP
0.40
0.30
0.20
0.10
0.00
4000
3500
3000
2500
2000
1500
1000
500
-1
3500
1500
1000
500
Wavenumber (cm )
-1
Wavenumber (cm )
Fig. 2. The combined FT-IR and simulated IR spectra of NBPMB.
Fig. 3. The combined FT-Raman and simulated Raman spectra of NBPMB.
102, 101, 97, 96, 94–91) are assigned to
mCAH stretching for
wavenumbers. In this study, the CCAH modes are assigned at
743, 823 and 904 cmꢁ1 in FT-IR spectrum. These assignments
are in agreement with literature [33–35] and also within the
characteristic region. The mode numbers 48, 49 are belongs to
CCAH (C12AH13/C25AH26) modes.
pyridine rings. These assignments are shown as good correlation
with literature values [29], and also within the expected range.
As it is evident from the TED column, the mode nos: 102–91 is pure
stretching modes (<80%). The mode nos: 90 and 89 are assigned to
mCAH in methylene diamine linkage (C12AH3, C25AH26) with
100% TED. All the aromatic CAH stretching bands are found to be
weak and this is due to the decrease of the dipole moment caused
by the reduction of negative charge on the carbon atom.
4.3.2. CAN vibrations
The C@N stretching appears in the region 1670–1600 cmꢁ1 [36].
In the present study the band due to C@N stretching vibrations are
Inaromaticcompounds, the CAH in-plane bendingvibrations ap-
pear in the range 1000–1300 cmꢁ1 and the CAH out-of-plane bend-
ing vibrations appear in the range 750–1000 cmꢁ1 [32]. The bands
are sharp but weak to medium intensity. The weak and medium
intensity bands at 1137, 1156 and 1227, 1426 cmꢁ1 (strong) in FT-
IR spectrum are due to in-plane CAH bending of benzene ring. In-
plane bending of CAH bonds is recorded at 1148, 1224 and
1421 cmꢁ1. These recorded values are in parallel with the calculated
wavenumbers at 1141, 1165, 1224 and 1423 cmꢁ1 (mode nos: 60,
61, 66, and 77). Most of the vibrations were not pure but contains
a significant contribution from other modes. These assignments
were supported by literature values [33]. The FT-IR bands at 1043,
1189, 1315 cmꢁ1 and the FT-Raman bands 1253, 1297 cmꢁ1 are as-
signed to CAH in-plane bending vibrations of pyridine rings in
NBPMB. These assignments are comparable with harmonic wave-
numbers in range 1046–1305 cmꢁ1 (mode nos: 55, 56, 63, 64, 67,
69, 71, 72) and also find support from literature [34,35]. The mode
numbers 73, 74 are assigned to dCAH (C12AH13, C25AH26) modes.
These vibrations show considerable TED values.
recorded at 1639 and 1638 cmꢁ1
(mC12AN11, mC25AN24) in FT-IR and
their corresponding calculated values are about 1640 and
1638 cmꢁ1 (mode nos: 88, 87). The TED of this mode was shown
in such a way that they were moderately pure stretching mode
(78%). Karabacak et al. [37] observed the CAN stretching vibrations
at 1213 and 1189 cmꢁ1 (harmonic) for N-(2-methylphenyl) meth-
ane sulfonamide. In the present study, the observed FT-IR band
1189 cmꢁ1 (medium) is attributed to CAN stretching. The theoret-
ically calculated values of CAN (C1AN11; C2AN24) stretching
vibrations are 1196, 1193 cmꢁ1 (mode nos: 64, 63), in which mode
number 63 is in line with experimental data. In 1,3-bis (4-pyridyl)
propane [34], the CAN stretching bands were found to be 1038 and
1252 cmꢁ1
.
Based on the these factors, in the present work, the observed
frequency 1043 cmꢁ1/FT-IR and the predicted frequencies 1046,
1248, 1249 cmꢁ1 (mode nos: 55, 56, 67, 68) are due to CAN
stretching in pyridine rings. These assignments are further
supported from TED values. Erdog˘du et al. [34] observed dNCH
and dCNC vibration in the region 1215–1509 cmꢁ1 and at
826 cmꢁ1 respectively for 1,3 bis (4-pyridyl) propane. The DFT
Generally, the CAH out-of-plane deformations with the highest
wavenumbers have weaker intensity than those absorbing at lower

42
S. Subashchandrabose et al. / Journal of Molecular Structure 1042 (2013) 37–44
polarizability a0, the anisotropy of polarizability Da and the mean
first hyperpolarizability b0, using the x, y, z components are defined as
calculation gives the wavenumbers 1397, 1397, 1475, 1477 (mode
nos: 75, 76, 79, 80) are assigned to be NACAH in-plane bending
vibration (pyridine ring). While dN11@C12AH13/dN24@C25AH26 is
assigned to harmonic wavenumber 1354/1355 cmꢁ1 (mode nos:
73, 74) respectively. The harmonic frequencies at 620, 650 cmꢁ1
(mode nos: 27, 28) are attributed to dCANAC mode in both pyridine
rings. These assignments are supported by observed bands 1465,
1488, 1342, 618 in FT-IR and 1474, 652 cmꢁ1 in FT-Raman spectra.
1=2
l
¼ ðl2x
þ
þ
ly2
þ
lz2
Þ
ð3Þ
ð4Þ
axx
ayy
3
þ
azz
a0
¼
2
2
2
¼ 2ꢁ1=2½ðaxx
ꢁ
ayyÞ þ ðayy
ꢁ
azzÞ þ ðazz
ꢁ
axxÞ þ 6ða2xy
The harmonic frequencies of mode numbers 48, 49 (964, 964 cmꢁ1
)
D
a
1=2
a2yz
þ
a2xzÞꢄ
ð5Þ
are assigned to CN11@C12AH13/CN24@C25AH26 vibrations, whereas the
þ
frequency 961 cmꢁ1 in FT-IR spectrum supports the mode numbers
48 and 49.
1=2
b0 ¼ ðb2 þ b2 þ b2Þ
ð6Þ
x
y
z
4.3.3. CAC vibrations
Many organic molecules, containing conjugated
p
electrons
In general, the bands around 1600 and 1400 cmꢁ1 in benzene
are assigned to skeletal CAC stretching modes [38]. In this work,
the middle to strong bands are observed at 1576, 1448, 1283,
1094 cmꢁ1 in FT-IR and strong bands observed at 1571,
1452 cmꢁ1 in FT-Raman are assigned to aromatic CAC stretching
vibrations (benzene ring), which are good agreement with theoret-
ically calculated value at 1567–1085 cmꢁ1 (mode nos: 84, 83, 78,
70, 62, 59). These assignments find support from the work of
Fereyduni et al. [29] and are within the frequency intervals given
by Varsanyi [38]. Similarly the frequencies observed in FT-IR
spectrum at 1590, 1535, 1008, 873 cmꢁ1 are assigned to CAC
stretching vibrations for pyridine. The corresponding vibrations
were characterized by large values of molecular first order hyper
polarizabilities and analyzed by means of vibrational spectroscopy
[42–45]. The intra molecular charge transfer from the donor to
acceptor group through a single-double bond conjugated path
can induce large variations on both the molecular dipole moment
and the molecular polarizability making IR and Raman activity
strong at the same time [46].
The total molecular dipole moment (l) and mean first order
hyperpolarizability (b0) are given as 1.714 Debye and
1.117 ꢂ 10ꢁ30 esu, respectively. The total dipole moment of the
title compound is approximately higher and the first order
hyperpolarizability (b0) of the title molecule is three times greater
than that of urea, hence this molecule has considerable NLO
activity. The computation of the molecular polarizability of NBPMB
is shown in Table 2.
appear in the FT-Raman spectrum at 1591, 1527 and 1006 cmꢁ1
.
The computed values in the range 1585–875 cmꢁ1 (mode nos:
86, 85, 82, 81, 76, 75, 52, 43) shows good coherence with experi-
mental data and also in line with literature value [39]. These
assignments are also supported by TED values.
4.5. NBO analysis
The ring (benzene) in-plane deformation vibrations are ascribed
to the FT-IR band at 1094, 618 cmꢁ1 and harmonic bands at 1085,
835 and 620 cmꢁ1 (mode nos: 59, 39, 27). The CACAC out-of-plane
deformations (benzene) are found at 712, 564 cmꢁ1 FT-IR bands
and the harmonic bands at 735, 716, 560 cmꢁ1 (mode nos: 33,
31, 25). Similarly the CACAC in-plane-bending vibrations (pyri-
dine) are attributed to the harmonic bands in the range 657–
437 cmꢁ1 (mode nos: 30, 29, 21, 19) and the FT-IR bands at 670,
499, 426 cmꢁ1. The out-of-plane vibrations due to CACAC (pyri-
dine) are characterized by the harmonic bands at 725, 716, 375
and 248 cmꢁ1 (mode nos: 32, 31, 18, 17, and 12). These assign-
ments are supported by Sundaraganesan et al. [39], Erdog˘du
et al. [34] and Wang et al. [40] for pyridine and benzene rings.
The hyperconjugation may be given as stabilizing effect that
arises from an overlap between an occupied orbital with another
neighboring electron deficient orbital, when these orbitals are
properly orientated. This non-covalent bonding (antibonding)
Table 2
The molecular dipole moment (
l), polarizability (a) and
hyperpolarizability (b0) values of NBPMB.
Parameters
B3LYP/6-31G(d,p)
Dipole moment (l)
lx
ly
lz
l
0.0001
1.7143
ꢁ0.0001
1.7143 Debye
4.4. Hyperpolarizability calculations
Polarizability (a)
axx
axy
ayy
axz
ayz
azz
a
311.07
0.00
299.77
32.03
The first order hyperpolarizabilities (b0, a0 and Da) of NBPMB is
calculated using B3LYP/6-31G(d,p) basis set, based on the
finite-field approach. In the presence of an applied electric field,
the energy of a system is a function of the electric field. First hyper-
polarizability is a third rank tensor that can be described by a
3 ꢂ 3 ꢂ 3 matrix. The 27 components of the 3D matrix can be re-
duced to 10 components due to Kleinman symmetry [41]. It can
be given in the lower tetrahedral format. It is obvious that the
lower part of the 3 ꢂ 3 ꢂ 3 matrix is a tetrahedral. The components
of b are defined as the coefficients in the Taylor series expansion of
the energy in the external electric field. When the external electric
field is weak and homogeneous, this expansion becomes:
ꢁ0.01
109.67
6.47 ꢂ 10–30 esu
Hyperpolarizability (b0)
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
b0
ꢁ0.13
ꢁ837.08
0.07
ꢁ473.04
0.02
ꢁ53.46
0.02
0.00
E ¼ E0 ꢁ laFa ꢁ 1=2aabFaFb ꢁ 1=6ba FaFbFc
ð2Þ
b
c
17.48
0.00
where E0 is the energy of the unperturbed molecules, F is the field at
a
1.1167 ꢂ 10ꢁ30 esu
the origin, and la
moment, polarizability and the first order hyperpolarizabilities
respectively. The total static dipole moment the mean
,
aab, b
are the components of the dipole
a
bc
Standard
value
for
urea
l = 1.3732 Debye,
b0 = 0.3728 ꢂ 10ꢁ30 esu.
l,

S. Subashchandrabose et al. / Journal of Molecular Structure 1042 (2013) 37–44
43
p
(CAC) and pꢅ(CAC) the
Table 3
interaction is due to the overlap between
orbitals, which results in intra molecular charge transfer, appeared
in the molecular system [46].
The NBO results showing the following of Lewis and non-Lewis for orbitals for
NBPMB.
Bond (AAB) ED/e
EDA% EDB%
1.96151 50.00 50.00 0.7071sp1.85
ꢁ0.70773
+0.7071sp1.85
NBO
s%
p%
In the present study, the electron densities of the
r bonds are
higher than bonds. The lowering of the electron densities is
p
C1AC2
C
C
35.03 64.93
35.03 64.93
36.95 63.02
35.11 64.84
0.01 99.96
0.02 99.93
27.88 72.02
32.14 67.79
36.95 63.02
35.11 64.84
0.01 99.96
0.02 99.93
28.52 71.43
99.96
28.64 71.32
99.95 0.05
29.99 69.97
99.95 0.05
29.23 70.72
99.95 0.05
29.23 70.72
99.95 0.05
29.25 70.70
99.95
29.5
99.95
27.15 72.78
27.35 72.57
27.15 72.78
27.35 72.57
due to transfer of lone electron pair from donor to acceptor (anti
bonding) orbital. This is the evident from the Table S3 that the elec-
C1AC6
1.97074 51.01 48.99 0.7142sp1.71
C
ꢁ0.71752
ꢁ0.6999sp1.85
C
tron densities of
rC1AC2, C1AC6, C2AC3, C4AC5, and C5AC6 are
C1AC6(2)
C1AN11
C2AC3
1.6643
49.49 50.51 0.7035sp1.00
C
+0.7107sp99.99
C
about 1.962, 1.971, 1.971, 1.978 and 1.976 e respectively. Their
corresponding anti-bonding acceptor orbital is having weak elec-
tron densities with lesser hyperconjugative energy (E(2)). On the
ꢁ0.26823
1.97716 41.09 58.91 0.6410sp2.58
C
ꢁ0.77555
ꢁ0.7675sp2.11
N
1.97075 51.01 48.99 0.7142sp1.71
C
other hand, the occupancy of
pC1AC6, C2AC3 and C4AC5 are de-
ꢁ0.71752
+0.6999sp1.85
C
creased by increasing the electron densities of their corresponding
C2AC3(2)
C3AH7
1.66429 49.49 50.51 0.7035sp1.00
C
anti-bonding acceptor orbitals with maximum E(2) energy. The
ꢁ0.26823
ꢁ0.7107sp99.99
C
donor and acceptor interactions of
C4AC5, 11AC12);
(C2AC3) ? pꢅ(C1AC6, C4AC5,
(C4AC5) ? (C1AC6, C2AC3) revealed the maximum hyperconjugative
p
(C1AC6) ? pꢅ(C2AC3,
1.97788 60.48 39.52 0.7777sp2.50
C
H
ꢁ0.53209
+0.6287sp0.00
0.04
N
p
N24AC25) and
C4AH8
1.97941 60.36 39.64 0.7769sp2.49
C
p
ꢁ0.52857
ꢁ0.6296sp0.00
H
1.97777 61.59 38.41 0.7848sp2.33
C
interaction in benzene ring. It has been observed in both pyridine
C29AH33
C17AH22
C32AH36
C19AH23
C30AH35
LPN11
ꢁ0.6197sp0.00
H
rings.
ꢁ0.53174
1.98171 59.74 40.26 0.7729sp2.42
C
It is evident from the Table S3, the nApꢅ transition for N11, N21
,
+0.6345sp0.00H
N24 and N34 have maximum E(2) energy. In this study, the BDꢅ to
BDꢅ (anti-bond pꢅ interactions (BDꢅC19AN27 ? C14AC16
15AC17) and (BDꢅ C30AN34 ? C27AC28, C29AC32) reveal the maxi-
mum E(2) energy 1135.29, 616.86 and 1135.08, 616.81 kJ/mol
respectively. From the Table 3, the electron density of C1AC6 is
ꢁ0.53016
1.98171 59.74 40.26 0.77729sp2.42
C
H
A
pꢅ
)
,
1.98171
ꢁ0.6345sp0.00
1.98185 59.69 40.31 0.7726sp2.42
C
H
C
ꢁ0.53312
+0.6349sp0.00
0.05
70.70
0.05
1.98185 59.69 40.31 0.7726sp2.42
C
r
ꢁ0.53312
ꢁ0.6349sp0.00
H
1.970 e and the electron density value of C1 and C6 are 36.95
(s-orbital), 63.02 (p-orbital) and 35.11 (s-orbital), 64.84% (p-orbital)
respectively. In the pC1AC6 bond, the p-character for C1 and C6 are
99.9% on comparing with s-character. This clearly shows that
the higher values of p-character causes the interaction and hence
the charge transfer is more in the acceptor orbital with decreasing
occupancy in C1AC6 (1.664e).
1.87249
sp2.65
sp2.65
sp2.68
sp2.65
ꢁ0.35637
1.91459
LPN21
ꢁ0.34135
LPN24
1.87252
ꢁ0.35638
1.91459
LPN34
ꢁ0.34135
s, p – Are orbitals, A,B – denotes atoms, ED – electron density.
4.6. HOMO–LUMO analysis
Stability of the molecule depends on the band gap between the
highest filled and lowest unfilled orbitals. The lower band gap in-
creases the reactivity of the molecule while the higher band gap
decreases the reactivity. The HOMO and LUMO energy calculated
by B3LYP/6-31G(d,p) method has been shown in Table 4. In the
present study, band gap between HOMO and LUMO is calculated
about -3.9568 eV. The HOMO part is located over the benzene ring
and diamine bond (CAN@C). The LUMO is located over the each
atom of the molecule. On the basis of fully optimized ground-state
structure, TD-DFT/B3LYP/6-31G(d,p) calculation have been used to
determine the low-lying excited states of NBPMB. The calculated
results involving the vertical excitation energies, oscillator
strength (f) and wavelength are carried out and compared with
measured experimental wavelength. For NBPMB, the TD-DFT
interaction can be quantitatively described in terms of the NBO
analysis, which is expressed by means of the second-order pertur-
bation interaction energy (E(2)) [47–50]. This energy represents the
estimate of the off-diagonal NBO Fock matrix elements. It can be
deduced from the second-order perturbation approach [51]
2
Fði; jÞ
Eð2Þ
¼
D
Eij ¼ q
ð7Þ
i ej
ꢁ
ei
where qi is the donor orbital occupancy, ei and ej are diagonal
elements (orbital energies) and F(i,j) is the off diagonal NBO Fock
matrix elements. NBO analysis of NBPMB has been performed, in or-
der to explain the intra-molecular charge transfer and delocaliza-
tion of
p-electrons. The intra-molecular hyperconjugative
Table 4
The electronic transition of NBPMB.
Calculated at B3LYP/6-31G(d,p)
Oscillator strength and
excitation energies
Experimental band gap (nm)
Calculated band gap (eV/nm)
Excited state 1
Singlet-A/f = 0.0965
0.66888
382.21 nm/3.2439 eV
ꢁ3.9568
75 ꢁ >76 (HOMO–LUMO)
Excited state 2
Singlet-A/f = 0.0744
0.66932
336.47
306.43
336.18 nm/3.6880 eV
ꢁ4.3584
75 ꢁ >77 (HOMO–LUMO+1
Excited state 3
)
Singlet-A/f = 0.0123
0.45773
306.15 nm/4.0498 eV
ꢁ4.8749
72 ꢁ >76(HOMOꢁ3–LUMO)
73 ꢁ >77(HOMOꢁ2–LUMO+1
74 ꢁ >76(HOMOꢁ1–LUMO)
)
ꢁ0.28627
ꢁ5.2722
ꢁ0.41308
ꢁ4.6763

44
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200
300
400
500
600
Wavelength (nm)
Fig. 4. The experimental UV–Vis spectrum of NBPMB.
calculations predict the wavelengths 382, 336 and 306 nm are cor-
responding to transitions HOMO–LUMO, HOMO–LUMO+1 and
HOMOꢁ3–LUMO respectively. The observed band gaps 336.47
and 306.43 nm are in agreement with the calculated values
381.21 (E1), 336.18 (E2) and 306.15 nm (E3). The observed UV–Vis
spectra and HOMO and LUMO plots are shown in Fig. 4 and Fig-
ure S2 (Supporting information) respectively.
5. Conclusions
The observed FT-IR and FT-Raman spectral values were agreed
well with the calculated wavenumbers. For the prediction of accu-
rate vibrational assignments TED were calculated using SQM
method. The conformer one is more stable and hence the calcu-
lated bond length and bond angles were correlated well with the
experimental values. The NBO analysis reveals the occurrence of
hyperconjugative interaction and charge delocalization around
the bonds. It also reflects the charge transfer mainly due to
C
19AN21 and C30AN34 groups. The presence of C@N fused with
two pyridine rings, increases the molecular hyperpolarizability of
title compound about 1.116 ꢂ 10ꢁ30 esu, which is three times
higher than that of urea. The HOMO–LUMO energy gap indicates
the stability and reactivity of the title compound. Moreover,
HOMO-1, -2 are mainly located over N@C group.
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