Molecular structures, spectral and computational studies on nicotinohydrazides

Article abstract of DOI:10.1016/j.saa.2010.06.031

The FT-IR and the high resolution ¹H and ¹³C NMR spectra have been recorded for N'-(2-methyl-3phenylallylidene)nicotinohydrazide (1) and N'-(2-methyl-3-phenylallylidene)isonicotinohydrazide (2) and analyzed.¹H-¹

Full text of DOI:10.1016/j.saa.2010.06.031

Spectrochimica Acta Part A 77 (2010) 687–695
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Short communication
Molecular structures, spectral and computational studies on nicotinohydrazides
A. Manimekalai , N. Saradhadevi , A. Thiruvalluvarb
a,∗
a
a
Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India
PG Research Department of Physics, Rajah Serfoji Government College (Autonomous), Thanjavur 613 005, Tamil Nadu, India
b
a r t i c l e i n f o
a b s t r a c t
The FT-IR and the high resolution 1H and 13C NMR spectra have been recorded for N -(2-methyl-3-
ꢀ
Article history:
Received 4 December 2009
Received in revised form 27 May 2010
Accepted 18 June 2010
ꢀ
phenylallylidene)nicotinohydrazide (1) and N -(2-methyl-3-phenylallylidene)isonicotinohydrazide (2)
1
1
and analyzed. H– H COSY spectra were also recorded for the hydrazides. The spectral studies reveal
that both the hydrazides exist in the keto form. Theoretical calculations were performed for some pos-
sible conformations of the hydrazide and the minimum energy conformers are predicted to be the one
in which the azomethine protons are syn to N–NH bond. From the optimized structures, HOMO–LUMO
energy gap and geometrical parameters were derived and these parameters were compared with the XRD
measurements of hydrazide 1. The vibrational frequencies in the ground state have been calculated using
DFT and HF methods and compared with the observed frequencies. Non-linear optical (NLO) behaviour of
the hydrazides was investigated by the determination of the electric dipole moment ꢀ, the polarizability
Keywords:
Nicotinohydrazides
Spectral
Theoretical studies
˛
and the hyperpolarizability ˇ using B3LYP method.
©
2010 Elsevier B.V. All rights reserved.
1
. Introduction
Hydrazones are a versatile class of ligands having great physio-
experimental studies have shown that large hyperpolarizabilities
generally arise from a combination of strong electron donor and
acceptor positioned at opposite ends of a suitable conjugation path
and the hyperpolarizability values depend not only on the strength
of donor and acceptor groups but also on the path length between
them [15,16]. Therefore, it is of considerable interest to synthesize
hydrazones derived from cinnamaldehyde since these compounds
are expected to exhibit wide range of biological activities and NLO
behaviour. To the best of our knowledge experimental data on
geometric structure and theoretical calculations on hydrazones
derived from nicotinohydrazide are not available in the literature.
Recently we report single crystal structure of hydrazone derived
from nicotinohyrdazide and trans-˛-methylcinnamaldehyde [17].
In this study we report, the synthesis, the spectral and computa-
tional study of hydrazones derived from nicotinohydrazide and
isonicotinohydrazide. The non-linear optical properties are also
addressed theoretically.
logical and biological activities and have been used as insecticides,
anticoagulants, antitumour agents, antioxidants and plant growth
regulators [1,2]. Their metal complexes have found applications
in various chemical processes like non-linear optics, sensors,
medicine, etc. [3]. Recently, second order NLO effects of organic
molecules have been extensively investigated for their advan-
tages over inorganic crystals. The organic NLO materials play an
important role in second harmonic generation, frequency mix-
ing and electro-optic modulation [4]. The single crystal structure
of a few hydrazones derived from o-aminobenzoylhydrazide and
2
-acetylthiophene-o-aminobenzoylhydrazide have been reported
[
5–8]. Theoretical study of molecular structure and vibra-
tional spectra of 2-acetylthiophene-o-aminobenzoylhydrazone
was made by Pekparlak and Atalay recently [9]. Aroylhy-
drazones such as N-2-hydroxy-4-methoxyacetophenone-N -4-
ꢀ
nitrobenzoylhydrazone and 2-hydroxyacetophenone nicotinic acid
hydrazone were characterized using spectral and single crys-
tal measurements [10,11]. Conformational analysis of hydrazones
from spectral studies were also reported in literature [10,12–14].
Organic molecules with conjugated ꢁ-electron system are
known to exhibit extremely large optical non-linear responses in
terms of their molecular hyperpolarizabilities. Both theoretical and
2
. Experimental
2.1. Synthesis of hydrazides 1 and 2
Sodium hydroxide (0.4 g, 0.01 mol) in a stoppered conical
flask was kept in an ice-cold environment. Ethanol (40 mL),
95%) was added to dissolve it and the mixture was stirred
(
continuously using a magnetic stirrer. An equimolar quantity
of nicotinohydrazide/isonicotinohydrazide (1.371 g, 0.01 mol) and
trans-˛-methylcinnamaldehyde (1.461 g, 0.01 mol) was added to
this mixture. The stirring was continued for 5 h in ice-cold con-
∗ Corresponding author. Tel.: +91 4144 238747; fax: +91 9486 283468.
E-mail address: profmeka1@gmail.com (A. Manimekalai).
1
386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.06.031

6
88
A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
Fig. 1. Structures of hydrazides 1 and 2.
ditions. The mixture was kept overnight in a refrigerator. The
mixture was then allowed to stand for 4 days under normal condi-
tions. A yellow solid was obtained. This was filtered, washed and
recrystallized from ethanol. Yield 2.2 g, 46% (1), 2.3 g, 46% (2). The
◦
◦
compounds 1 and 2 melted at 130 and 135 , respectively.
2
2
.2. Spectral measurements
.2.1. IR spectra
−
1
The FT-IR spectra were recorded in the range 400–4000 cm
−
1
−1
with a resolution of ± 4 cm and an accuracy of ± 0.01 cm on a
NICOLET AVATAR 360 FT-IR spectrometer. The sample was mixed
with KBr and the pellet technique was adopted.
2
.2.2. 1H and 13C NMR spectra
1H and 13C NMR spectra were recorded in DMSO-d6 at room
temperature on AMX 500 NMR spectrometer operating at 500 and
1
13
1
25 MHz for H and C NMR spectra, respectively. Samples were
prepared by dissolving about 10 mg of the sample in 0.5 mL of
DMSO-d6 containing 1% TMS for 1H NMR spectra. Proton spectra
have the following experimental parameters: number of scans 32;
spectral width 5682 Hz; acquisition time 2.88 s. Solutions for the
measurement of 1 C NMR spectra were prepared by dissolving 0.5 g
of the sample in 2.5 mL of DMSO-d6 containing a few drops of TMS
3
Fig. 2. FT-IR spectra of (a) hydrazide 1 and (b) hydrazide 2.
as internal reference. The solvent DMSO-d also provided the inter-
6
nal field frequency lock signal. The experimental parameters are:
spectral width 29,412 Hz; number of scans 1125; acquisition time
3
. Results and discussion
1
1
1
13
0.56 s. The H– H COSY and H– C COSY spectra were performed
The FT-IR spectra and the high resolution 1H and 13C NMR spec-
on a DRX-500 NMR spectrometer using standard pulse sequences.
ꢀ
tra of N -(2-methyl-3-phenylallylidene)nicotinohydrazide (1) and
N -(2-methyl-3-phenylallylidene)isonicotinohydrazide (2) (Fig. 1)
ꢀ
have been recorded and analyzed.
2.3. Computational study
−1
The prominent peaks around 3300, 1640 and 1600 cm in the
FT-IR spectra (Fig. 2) are attributed to ꢂN–H, ꢂC O and ꢂC N modes,
respectively. The observation of lower ꢂC O around 1640 cm is
Computational calculations are carried out initially at semi-
−1
empirical level (PM3) to predict the favoured conformation
minimum energy conformer). Further geometry optimizations
and vibrational frequencies of the favoured conformers were car-
due to extended conjugation of C O group with the nearby pyridine
ring. The C C stretching vibration of the aromatic ring appeared
(
−1
−1
around 1500 cm . The peaks around 1000 and 750 cm are due
to ꢂN–N and aromatic C–H out of plane bending vibrations, respec-
tively. The in plane bending vibration and rocking vibrations of
methyl group are characterized by bands in the range of 1400, 1150
ried out at basic DFT level using B LYP-6-31G(d,p) basis set and at
3
HFlevelusing6-31G(d,p) basisset available in Gaussian-03 package
[
18]. The total static dipole moments, the polarizability ˛ and first
order hyperpolarizability ˇ were calculated by finite field approach
using B LYP-6-31G* basis set.
and 1050 cm−1, respectively. The signals in the 1H NMR spectra
3
were assigned based on their positions, integrals and multiplici-
Fig. 3. Syn and anti-conformers of hydrazides.

A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
689
ties and these assignments were further confirmed from the results
1
1
1
13
derived from H– H COSY and H– C COSY spectra. Tables 1 and 2
1
13
report H and C chemical shifts of the hydrazides 1 and 2, respec-
tively.
3.1. Conformation of hydrazides
Since the hydrazides
are
derived
from
trans-˛-
methylcinnamaldehyde, they are having the structural moiety as
shown below.
There are two possible ways of attaching the hydrazide moiety
as shown in Fig. 3. In the conformation A the azomethine proton is
syn to N–NH bond whereas in B they are anti. The hydrazides may
exist in the enol form also. The possible conformations are shown
in Fig. 4.
3.1.1. Spectral studies
The possibility of existing in the enol form in solution as well as
in solid state is ruled out based on the observation of amide car-
13
bonyl peaks around 160 ppm in C NMR spectra and peaks around
−
1
1
630 cm in the IR spectra.
Generally in azines and hydrazides protons which are syn
to N–N bond are expected to resonate at upfield compared
to anti protons [19,20]. Comparison of the chemical shifts of
azomethine protons in N-2-hydroxy-4-methoxybenzaldehyde-
ꢀ
N -4-nitrobenzoylhydrazone (8.57 ppm) [21] with that of alde-
hydic proton of 4-methoxysalicylaldehyde (10.24 ppm) reveals
that conversion of aldehyde to hydrazides shields the CH
proton by 1.67 ppm. The conformation of N-2-hydroxy-4-
ꢀ
methoxybenzaldehyde-N -4-nitrobenzoylhydrazone is predicted
to be the one in which the azomethine proton is syn to N–NH bond.
Similar comparison of the chemical shifts of azomethine protons in
the hydrazides 1 and 2 [8.22 and 8.26 ppm] with that of aldehydic
proton of trans-˛-methylcinnamaldehyde (9.56 ppm) reveals that
conversion of aldehyde to hydrazides also shields the C–H proton
and the shielding magnitude is ≈1.3 ppm. From this it is concluded
that the favoured conformations of hydrazides 1 and 2 in solution
are predicted to be the one in which the azomethine protons are
syn to N–NH bond [conformation A].
3.1.2. Theoretical studies
Computational calculations were carried out initially at semi-
empirical level [PM ] for the possible conformations shown in
3
Fig. 4. The conformer in which heat of formation is minimum is
predicted to be the stable conformer and the heat of formation for
this conformer can be taken as zero and the values of the other con-
formers are reported as relative values with respect to this favoured
conformer. The relative heat of formations thus determined in this
manner for the hydrazides were displayed in Table 3 and the val-
ues reveal that the minimum energy conformers are 1A and 2A
same as those determined in solution. For 1A and 2A geometry opti-
mizations were also carried out according to DFT [B LYP functional]
3
and HF methods available in Gaussian-03 package using 6-31G(d,p)
basis set.
The optimized structures of the stable conformers by DFT
and HF methods for the hydrazides 1 and 2 are shown in
Fig. 5. For the hydrazide 1 single crystal measurements were
made recently (Figs.
6 and 7) and XRD indicates that the

6
90
A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
Table 2
1
3C Chemical shifts (ppm) of hydrazides 1 and 2.
Hydrazide
C(10)
C(11)
C(12)
C
O
C(21)
C(22)/C(26)
C(23)/C(25)
C(24)
C(2)
C(3)
C(4)
C(5)
C(6)
CH3
1
2
153.71
154.78
136.27
136.67
137.20
137.91
161.80
162.13
134.45
134.86
129.36
129.82
128.44
128.90
127.75
128.25
148.65
150.68
129.52
122.07
135.44
141.24
123.54
122.07
152.09
150.68
12.86
13.27
Fig. 4. Possible conformations of hydrazides 1 and 2.
Table 3
Relative heat of formation values (kcal/mol) of various conformers for hydrazides 1 and 2.
Hydrazide
Conformers
A
B
C
D
1
2
0
0
1.82
1.76
4.60
5.75
5.09
5.92

A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
691
Table 4
Selected geometric parameters (bond length, bond angle and torsional angle) in hydrazides 1 and 2.
Geometric parameters
1
2
XRD
DFT
HF
DFT
HF
Bond length (Å)
C21–C12
C12–C11
C11–C13
C11–C10
N9–C10
N9–N8
N8–C7
C7–O7
C7–C3
N8–H8
1.46
1.48
1.35
1.51
1.49
1.30
1.38
1.36
1.32
1.49
1.05
1.48
1.33
1.51
1.47
1.26
1.36
1.37
1.19
1.50
1.00
−
1.46
1.36
1.51
1.46
1.29
1.36
1.38
1.22
–
1.48
1.35
1.50
1.45
1.29
1.39
1.35
1.23
1.50
0.88
–
1.33
1.51
1.47
1.26
1.36
1.36
1.19
–
1.02
1.51
1.00
1.51
C7–C4
−
◦
Bond angle ( )
C22−C21−C12
C26−C21−C12
C21−C12−C11
C12−C11−C13
C13−C11−C10
C11−C10−N9
C10−N9−N8
N9−N8−C7
N8−C7−O7
N8−C7−C3
124.3
121.6
119.2
124.8
122.2
119.1
120.6
122.6
119.8
119.4
121.7
119.9
121.7
118.7
118.9
−
122.6
124.2
122.6
118.3
129.5
125.2
118.2
121.4
114.1
118.6
123.5
115.2
117.6
124.3
116.6
121.3
−
119.0
128.7
126.4
116.7
121.5
117.5
120.0
123.9
114.3
117.9
124.4
116.9
121.8
−
118.0
130.4
126.2
117.2
121.8
116.7
120.8
123.8
−
119.0
128.7
126.4
116.7
121.5
117.4
120.2
124.4
−
C7−C3−C2
−
−
C4−C3−C7
−
−
C12−C11−C10
O7−C7−C3
116.6
−
116.9
−
C7−C4−C3
117.6
124.6
114.1
121.5
118.1
123.7
114.1
122.1
C7−C4−C5
−
−
−
N8−C7−C4
−
−
−
O7−C7−C4
−
−
−
◦
Torsional angle ( )
C22−C21−C12−C11
C26−C21−C12−C11
C21−C12−C11−C13
C21−C12−C11−C10
C10−N9−N8−C7
N9−N8−C7−O7
N9−N8−C7−C3
N8−N9−C10−C11
C2−C3−C7−O7
C2−C3−C7−N8
C4−C3−C7−O7
C4−C3−C7−N8
H8−N8−C7−O7
C12−C11−C10−C9
N9−N8−C7−C4
C3−C4−C7−O7
C5−C4−C7−O7
C3−C4−C7−N8
C5−C3−C7−N8
−22.6
156.9
−1.4
178.6
179.3
−2.1
179.3
179.1
−23.9
154.8
156.4
−24.9
−
50.4
−132.8
3.1
45.4
137.3
2.9
27.2
−154.7
2.3
45.3
137.4
2.7
−177.0
178.2
−3.8
176.9
179.0
−26.7
152.6
151.2
−29.4
175.3
176.9
−
−178.3
170.5
−0.3
180.0
179.5
−27.8
151.9
150.1
−30.2
162.6
179.3
−
−178.8
175.0
−1.6
−
178.4
172.5
−0.1
−
179.7
−
179.7
−
−
−
−
−
−
−
169.3
−179.5
179.1
−24.2
153.9
155.1
−26.8
166.4
179.32
179.6
−30.4
148.3
149.3
−32.2
−177.0
−
−
−
−
−
−
−
−
−
−
−
−
−
hydrazide exists in the keto form in the solid state. Table 4
reports selected bond lengths, bond angles and torsional angles
in the optimized structures for the hydrazides along with
N8–C7–C3–C2, N8–C7–C3–C4, C2–C3–C7–O7 and C4–C3–C7–O7 in
hydrazide 1 and the torsional angles N8–C7–C4–C3, N8–C7–C4–C5,
C3–C4–C7–O7 and C5–C4–C7–O7 in hydrazide 2 also indicate the
twisting of the pyridine ring from the plane of the side chain
moiety.
The HOMO–LUMO energies were also calculated and the val-
ues and figures are listed in Table 5 and Fig. 8, respectively. The
energy gap (ꢃE) between HOMO and LUMO energies is higher for
the hydrazide 1 relative to 2. The HOMO energy of hydrazide 1
is less than that of hydrazide 2. The plot of HOMO–LUMO ener-
gies reveals that the HOMO orbitals are mainly derived from 2pz
orbitals of carbon atoms present in the cinnamaldehyde moiety
and nitrogen and oxygen atoms present in the hydrazide moiety.
LUMO orbitals are localized on the orbitals of the pyridine ring
and pz orbitals of nitrogen, carbon and oxygen present in the side
chain.
the values derived from single crystal measurement of
17].
The bond lengths derived from theoretical calculations are
1
[
closer to the values observed in XRD except in C7–O7 and N8–H8.
Low scattering factors of hydrogen atoms in the X-ray diffraction
experiment is responsible for the deviation observed in N8–H8. In
most of the cases the bond angles are slightly lower than the single
◦
crystal measurements. The maximum deviation is 8.5 . The tor-
sional angles especially C22–C21–C12–C11 and C26–C21–C12–C11
deviate to a greater extent compared to XRD measurements. These
values indicate that phenyl ring is distorted from the plane of
the side chain moiety and this distortion is predicted to have
large magnitude by theoretical calculations. The torsional angles

6
92
A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
Table 5
Calculated HOMO–LUMO energies (eV) of hydrazides 1 and 2.
Hydrazide
DFT
HF
LUMO
HOMO
Energy gap (ꢃE)
LUMO
HOMO
Energy gap (ꢃE)
1
2
1.864
−1.945
−8.181
−5.830
10.045
3.885
2.254
2.110
−8.227
−8.269
10.481
10.379
Table 6
Theoretical and experimental IR spectral data (cm−1) of hydrazides 1 and 2.
Wavenumber (cm 1
−
)
Hydrazide 1
Hydrazide 2
Observed
values
DFT
HF
Approximate
assignments
Observed
values
DFT
HF
Approximate
assignments
3444
3079
2860
−
3424
3020
2878
ꢂN–H
3452
3026
2969
−
3426
3038
2955
ꢂN–H
3085
2843
ꢂC–H (aromatic)
ꢂC–H (CH3)
3056
2996
ꢂC–H (aromatic)
ꢂC–H (CH3 symmetric
and asymmetric)
2
1671
1647
926
2907
−
2948
1664
1621
1580
1542
1433
1363
1
1
637
594
1609
1565
1615
1592
ꢂC
ꢂC
O
N
ꢂC
ꢂC
O
N
1611
1583
1500
1472
1336
1
600
1557
446
1
548
402
1555
1379
1539
1412
ꢂC
C
ꢂC C (aromatic)
1
1
Methyl in plane
bending vibration
N–H bending mode
ꢂC–N
1358
Methyl in plane
bending vibration
N–H bending mode
ꢂC–N
1300
1222
1147
1066
1018
970
1298
1249
1133
1082
997
1343
1248
1147
1057
1054
973
1296
1193
1152
1073
1022
958
1295
1220
1131
1074
1049
935
1249
1196
1141
1056
1039
974
CH3 rocking vibration
CH3 rocking vibration
ꢂN–N
ꢂN–N
989
The C–H out of plane
bending vibration of
benzene ring
The C–H out of plane
bending vibration of
benzene ring
9
8
7
24
48
53
907
867
754
900
828
738
920
860
752
908
820
742
688
663
905
851
749
703
668
703
6
89
707
697
Phenyl ring puckering
mode
625
Phenyl ring puckering
mode
5
–
20
–
–
513
–
519
471
515
−
511
451
–
–
Vibrational frequencies for the minimum energy conformer
were also calculated by HF and DFT methods. These values
were corrected using scale factor 0.9613 [DFT] and 0.8929
ments were summarized in Table 6 along with the observed
values. These values indicate that there is close agree-
ment between the calculated values and observed values.
The values calculated according to HF method are slightly
a
[
HF] [22] and the corrected frequencies and proposed assign-
Fig. 5. Minimum energy conformers of hydrazides 1 and 2.

A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
693
Table 7
−
24
esu) and the first hyperpolarizability ˇtot (×10−31 esu) of hydrazides 1 and 2.
The electric dipole moment ꢀ (D) the average polarizability ˛tot (×10
Hydrazide 1
Hydrazide 2
Hydrazide 1
Hydrazide 2
ꢀ
ꢀ
ꢀ
ꢀ
x
3.249
5.833
3.448
3.696
ˇxxx
−2062.453
−63.585
−63.519
154.381
83.694
−2909.720
−147.442
12.261
119.225
17.409
y
ˇxxy
z
−1.058
−0.624
ˇxyy
ˇyyy
ˇxxz
tot
6.760
5.093
˛
˛
˛
˛
˛
˛
xx
xy
yy
xz
yz
zz
411.715
4.739
181.954
4.509
427.814
22.586
189.598
3.434
10.694
78.680
232.031
ˇxyz
50.730
21.495
ˇyyz
−41.297
−22.840
ˇxzz
1.135
4.669
6.923
ˇyzz
8.565
−11.879
−0.264
86.323
226.664
33.592 × 10−
ˇzzz
−0.570
<
˛
˛>
tot (esu)
ˇtot
2127.500
2893.073
34
−34
−30
−30
34.387 × 10
ˇtot (esu)
18.380 × 10
24.994 × 10
higher than the DFT values and the observed values in some
cases.
method using B LYP/6-31G* basis set available in DFT package. To
3
calculate all the electric dipole moments and the first hyperpolar-
izabilities for the isolated molecules, the origin of the Cartesian
coordinate system (x, y, z) = (0, 0, 0) was chosen at own centre of
mass of each compound.
4
. Hyperpolarizability calculations
In Table 7 the results of the electric dipole moment ꢀ(i=x,y,z)
polarizability ˛ij and the first hyperpolarizability ˇijk for the
The polarizability ˛ and the hyperpolarizability ˇ and the elec-
tric dipole moment ꢀ of the hydrazides are calculated by finite field
hydrazides 1 and 2 are listed. It is seen that the electric dipole
moment of the hydrazide 1 has slightly greater value than the
hydrazide 2. The ˇtot value of hydrazide 2 obtained by numerical
second derivative of electric dipole moments according to the FF
approach is rather greater than that of hydrazide 1.
The highest value of dipole moment is observed for the com-
ponent ꢀy in both the hydrazides. The calculated polarizability ˛ij
is dominated by the diagonal components (˛xx, ˛yy, ˛zz) and the
hyperpolarizability ˇ is dominated by the longitudinal components
of ˇxxx, ˇxxy, ˇxyy, ˇyyy, ˇxxz, ˇxyz and ˇyyz. From this it is inferred
that a substantial delocalization of charges is noticed in these
directions.
In the present study the crystal structure of 1 has been
recognised as the space group P2 /c, with one molecule in the
1
Fig. 6. XRD structure of hydrazide 1.
asymmetric unit (centrosymmetric). The hydrazide 2 differs from
the hydrazide 1 in the position of nitrogen atom only and hence it
is also expected to have centrosymmetric structure. Lacroix et al.
have investigated crystal structure and molecular hyperpolarizabil-
ities of a Schiff base derived from 4-(diethylamino)salicylaldehyde
and 4-nitroaniline and its metal complexes [23]. The X-ray struc-
ture analysis of the Schiff base reveals the space group P2 /c with
1
one molecule in the asymmetric unit which is also centrosymmet-
ric. The polarizability associated with this Schiff base is explained
based on significant conjugation of the whole ꢁ-system and large
intramolecular charge transfer. The hydrazides 1 and 2 are also
polar molecules having non-zero dipole moment components and
such compounds may have large microscopic hyperpolarizability
and hence may have rather well microscopic NLO behaviour. The
higher dipole moment values are associated in general with even
larger projection of ˇtot quantities.
The NLO responses can be qualitatively understood by exam-
ining the energetics of frontier molecular orbitals [HOMO–LUMO]
of hydrazides 1 and 2. The HOMO–LUMO energy gap of hydrazide
1
is relatively higher than that of hydrazide 2 and shows lower ˇ
value than that of the hydrazide 2. It is evident that there should be
inverse relationship between HOMO–LUMO gap and the first order
hyperpolarizability [24].
5. Thermodynamic properties
Thermodynamic properties were calculated and the calculated
parameters are presented in Table 8. The hydrazides 1 and 2 have
same molecular formula but differ in the position of nitrogen atom
only. The hydrazide 2 is stabilized by an amount of −0.025187 a.u.
Fig. 7. Close packing of hydrazide 1.

6
94
A. Manimekalai et al. / Spectrochimica Acta Part A 77 (2010) 687–695
Fig. 8. HOMO–LUMO plots of hydrazides 1 and 2 (DFT).
Table 8
Theoretically computed energies (a.u.), zero-point vibrational energies (kcal mol 1), rotational constants (GHz), entropies (cal mol−1
−
K
−1
) and dipole moment (D) for
hydrazides 1 and 2.
Parameters
Hydrazide 1
Hydrazide 2
DFT
HF
DFT
HF
Total energy
Zero-point energy
−857.89523
−852.52564
188.37797
1.46215
0.09159
0.08760
137.223
42.624
−857.920417
175.61750
1.37309
0.09087
0.08594
141.773
42.624
−852.5249
188.37796
1.43492
0.09163
0.08758
137.273
42.624
174.00835
1
.63038
0.08820
.08478
Rotational constants
0
Entropy total
Translational
Rotational
133.728
42.624
34.532
56.571
34.571
60.628
34.660
64.489
34.589
60.060
Vibrational
(
DFT) and of −0.00074 a.u. (HF) over the hydrazide 1. The total
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2
entropy of hydrazide 2 is slightly higher than that of hydrazide 1
by both DFT and HF methods.
[
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order hyperpolarizabilities reveal that both hydrazides behave as
interesting NLO materials. Geometrical parameters derived from
theoretical investigations are compared with the single crystal
measurements for hydrazide 1. Vibrational frequencies were also
computed and the calculated vibrational frequencies are in good
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