Effects of molecular conformation on the spectroscopic properties of 4,4′-disubstituted benzylideneanilines

Article abstract of DOI:10.1016/j.molstruc.2015.09.035

The relationship between the molecular conformation and spectroscopic properties of unsymmetrical 4,4′-disubstituted benzylideneanilines, was explored by the combination of experiment and reference data. Crystal structure information and spectroscopic beh

Full text of DOI:10.1016/j.molstruc.2015.09.035

Journal of Molecular Structure 1104 (2016) 52e57
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Effects of molecular conformation on the spectroscopic properties of
0
4
,4 -disubstituted benzylideneanilines
a
,
*
a
a
b, **
, Xin Xie a
Zhengjun Fang , Feng Wu , Bing Yi , Chenzhong Cao
a
School of Chemistry and Chemical Engineering, Hunan Institute of Engineering, Xiangtan 411104, China
School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 August 2015
Received in revised form
The relationship between the molecular conformation and spectroscopic properties of unsymmetrical
0
4,4 -disubstituted benzylideneanilines, was explored by the combination of experiment and reference
data. Crystal structure information and spectroscopic behaviors of the seventeen samples p-XeC
6 4
H CH]
3
September 2015
NC , OMe, Me, Cl, CN, or NO , Y]NMe , OMe, Me, Cl, CN, or NO ) were provided for
6
H
4
ep-Y (X ¼ NMe
2
2
2
2
Accepted 29 September 2015
Available online 3 October 2015
this study. Among these seventeen compounds, nine ones were synthesized firstly, and five crystal
structures were determined and analyzed. It was observed that the twist angle of the aniline ring with
respect to the rest of the molecule (
The correlation results show that the UV maximum absorption in wavenumbers (
the substituent at the aromatic ring and the dihedral angle of the titled molecules, and a sine function
of (sin( )) is suitable to modify the substituent effects on the max. However, the dihedral angle has a
limited effect on the values of C NMR chemical shifts (C]N). The results indicate that the dihedral
angle has an significant effect on UV spectra of Schiff bases with different parent structure although
there is something different about the parameter metrics. While it has a relatively limited effect on the
values of (C]N) in both unsymmetrical and unsymmetrical Schiff bases. This study provides an suf-
ficient evidence of the molecular conformation on spectroscopic properties of Schiff bases.
t
) is systematically controlled by the substituent at the aromatic ring.
Keywords:
Dihedral angle
Absorption spectrum
y
max) is dependent on
t
NMR spectrum
t
t
y
t
0
13
4
,4 -disubstituted benzylideneanilines
d
C
t
d
C
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
an important role on the UV energy of symmetrical Schiff bases
derived from 1,4-Phenylenediamine and 1,4-Phthalaldehyde
[24,25]. The UV energy is dependent on the substituent at the an-
The spectroscopic behavior is known to be an important factor
for the optimal use of the optical materials and the design of new
candidates [1e5]. Understanding the quantitative structure-
property relationship (QSPR) helps to predict the optical proper-
ties of the target compounds [6,7]. Therefore, much attention has
been focused on the QSPR of the spectroscopic properties of con-
jugated organic compounds [8e10], including disubstituted ben-
zenes [11], disubstituted stilbenes [12,13], and disubstituted
benzylidene anilines [14].
iline ring and the dihedral angle
modify the substituent effects on the UV maximum absorption in
wavenumbers max. However, experimental investigations indicate
that the dihedral angle has a limited effect on the values of (C]
t, and the term sin(t) is suitable to
y
t
d
C
N). These studies provide an evidence of molecular conformation
effects on spectroscopic properties of symmetrical bis-Schiff bases.
However, research samples of these investigations are structurally
symmetrical, and in these samples the group at one end is identical
with that at the opposite end. It is known that the polarity is offset
in symmetrical systems, and in which the though-bond electronic
communication is different from that in unsymmetrical ones.
Therefore, a suggestion that the evidence of molecular conforma-
tion effects on spectroscopic properties in Schiff bases is insuffi-
cient if it only comes from symmetrical Schiff bases. Consequently,
it is a worthwhile work to explore the conformation effects in un-
symmetrical Schiff bases and provide a further proof for the effects
of molecular conformation on spectroscopic properties of Schiff
Schiff bases are receiving increasing attention in view of their
potential application as effective ligands for complexation [15,16].
Most importantly, they are used in the design of liquid crystals
[17e19] and nonlinear optical materials [20e23].
Recently, we have verified that the molecular conformation has
*
Corresponding author.
*
* Corresponding author.
E-mail addresses: fzj1001@163.com (Z. Fang), czcao@hnust.edu.cn (C. Cao).
http://dx.doi.org/10.1016/j.molstruc.2015.09.035
022-2860/© 2015 Elsevier B.V. All rights reserved.
0

Z. Fang et al. / Journal of Molecular Structure 1104 (2016) 52e57
53
2
bases.
least-squares method on F using the SHELXLe97 software [28]. All
of the non-hydrogen atoms were refined anisotropically, whereas
all hydrogen atoms were refined isotropically as a riding mode
using the default SHELXL parameters. A summary of the crystal
data and the structure refinements for the five compounds is
available in the Supporting Information.
We report herein the results of our systematic studies on the
conformation effects upon the Schiff bases. 4,4 -disubstituted
benzylideneanilines(i.e. XBAY, shown in Fig. 1) have simple struc-
ture and are representative, so they are applicable to fully prove the
effects of molecular conformation on spectroscopic properties of
Schiff bases if the samples are sufficient.
0
By means of computational study, Neuvonen and co-workers
3. Results and discussion
[
26] have proposed that the twist of the aniline ring with respect
13
of the plane of the C]N unit may affect the C NMR chemical shifts
of imine carbon in benzylideneanilines. However, Neuvonen's
conjecture has not been experimentally explored and still remains
complicated.
3.1. Description of the crystal structures
The reliability of the dihedral angle
t values is necessary for
research work in this paper. Experimental data available in the
literature were obtained in the different conditions, such as con-
dition of crystal test or cultivation. In addition, an analysis reveals
that the difference is relatively obvious between the calculated and
the experimental value of the same molecule (Table 1, column 10
and 11). Thus, to verify whether ambient conditions make a dif-
To clarify the effects of molecular conformation on the lmax and
C NMR chemical shifts d (C]N) of XBAY, we provided seventeen
C
samples of unsymmetrical Schiff bases XBAY in this work, and their
crystal structures information and spectroscopic properties were
obtained from the experimental values of our work or the Cam-
bridge Crystallographic Data Centre (CCDC). In XBAY, the sub-
13
ference on the
t value, we prepared five compounds including two
stituents X or Y include the most electron-donating group (NMe
2
)
compounds whose experimental data not available in the literature
and obtained their crystals. Crystal structures of them are shown in
Fig. 2.
A comparison of the X-ray crystal structures revealed a possible
role for the conformation of compounds 1e5 (Fig. 2). Compounds 1,
2 and 5 crystallized in the monoclinic space groups P2(1), while 3
and 4 crystallized in the orthorhombic space group Pbca. The C and
N elements in compounds 3 and 4 were observed to be disordered
because of the pseudo-symmetry in the structure of them. The
and the most electron-withdrawing one (NO ). The effects of the
2
molecular conformation on spectroscopic properties of XBAY were
quantified.
2
. Experimental methods
2.1. Sample preparation
Compounds were all prepared by solidesolid reactions [27]. The
results are in good agreement with the reference results [29e31].
0
pure p-substituted benzaldehyde and p-substituted aniline were
mixed in a 1:1 M ratio, and then the mixture was heated and
melted. The mixture was further stirred for several minutes before
being cooled to room temperature and purified by recrystallization
from absolute ethanol.
The dihedral angle
t
is defined by atoms C1eC7]N1eC1 .
3.2. Results of the conformation and spectra of compounds
Crystal structure informations of compounds come from our
works and CCDC. In all cases, the conformation observed for the
molecules is the anti-form with respect to the C]N bond. The
benzylidene ring of each compound is nearly co-planar with the
C1eC7]N1, whereas the aniline ring is twisted significantly from
2
.2. Spectral measurement
Absorbance spectra were collected on a LAMBDA-35 UVevis
ꢀ3
ꢀ5
0
spectrometer in a concentration range from 10 to 10 mol/L.
Ethanol used in absorption experiments were of spectroscopic
the C7]N1eC1 . Because of the slight deviation of the benzylidene
ring from the C1eC7]N1 plane, we discuss below the twist of the
grade and were used as purchased. The NMR chemical spectra of
aniline ring with respect of the plane of the C]N unit only. The
1
0
compounds were recorded in CDCl
3
at 293 K. The H NMR chemical
dihedral angle
t
is defined by atoms C1eC7]N1eC1 . The values of
shifts of the CH]N groups are expressed in ppm relative to CDCl
7.26 ppm). The detailed analytical data of compounds are available
in the Supporting Information.
3
t
t
in XBAY are listed in Table 1 (column 10 and 12). The value of
ꢁ
(
¼ 180 corresponds to the co-planarity of the aniline ring and the
0
C7]N1eC1 plane. As seen in Table 1, the dihedral angle
t
values of
compounds 1, 2 and 4 in our works are in accordance with the
experimental data available in the literature. This shows that the
data of t has a high reliability and it isn't restricted by the condition
2.3. X-ray crystallography
of crystal test or cultivation.
Crystals suitable for X-ray diffraction were obtained by slow
For the seventeen samples of XBAY, substituent X including
evaporation from a binary solvent mixture of petroleum ether e
chloroform (3:1). Colored crystals were obtained after a few days.
For compounds MeOBAH, MeOBAOMe, CNBACN, ClBACl and
Me
Me
2
N, MeO, Me, H, Cl, CN and NO
N, MeO, Me, H, Cl, CN and NO
2
, and substituent Y including
, the corresponding
2
2
y
max and
C
d (C]N) in model compounds are listed in Table 1, which come
NO
S Ultra, Oxford platform diffractometer. The crystals of them were
measured with Mo K monochromated radiation (
2
BAOMe, crystallographic analyses were performed on a Gemini
from previous or this work [32,33].
a
l
¼ 0.71073 Å).
3.3. Effects of substituents on the molecular conformation
An empirical absorption correction was applied. The structures
were solved using the direct method and refined by the full-matrix
It should be noted that is clearly affected by the substitution of
t
the aromatic ring. Among the seventeen compounds, the maximum
ꢁ
value of
found in HBAH (
in case X is NO
as the electron-withdrawing ability of the substituent Y improves.
In case Y is OMe, decreases as the electron-withdrawing ability of
the substituent X improves. While the regularity is not obvious in
t
occurs in NO
2
BANMe
2
(
t
¼ 172.9 ), and the minimum is
ꢁ
t
¼ 126.7 ). As seen in Table 1 (column 10 and 12),
2
, the twist of the ring increases (value of t decreases)
t
Fig. 1. General structures of compounds XBAY.

54
Z. Fang et al. / Journal of Molecular Structure 1104 (2016) 52e57
Table 1
Values of
max (cm 1) and
ꢀ
t
( ) for compounds XBAY.
ꢁ
lmax (cm),
y
Column
1
2
3
Y
4
5
6
7
8
9
10
11
12
13
14
(C]N)e
ex
cc
ex
cc
ta
tb
tc
d
No
X
s
(X)
s
(Y)
s
F
(X)
s
R
(X)
s
F
(Y)
s
R
(Y)
y
max
d
C
1
2
3
4
5
6
7
8
9
OMe
CN
OMe
Cl
H
ꢀ0.50
ꢀ0.70
ꢀ0.50
ꢀ0.22
ꢀ1.17
ꢀ1.81
ꢀ1.81
ꢀ1.81
ꢀ1.81
ꢀ0.17
ꢀ0.17
0.00
ꢀ0.22
ꢀ0.70
ꢀ1.17
ꢀ1.17
ꢀ1.17
0.00
0.29
0.51
0.29
0.42
0.65
0.15
0.15
0.15
0.15
0.01
0.01
0.00
0.42
0.51
0.65
0.65
0.65
ꢀ0.56
0.15
ꢀ0.56
ꢀ0.19
0.13
ꢀ0.98
ꢀ0.98
ꢀ0.98
ꢀ0.98
ꢀ0.18
ꢀ0.18
0.00
0.00
0.51
0.29
0.42
0.29
0.29
0.00
0.42
0.51
0.29
0.01
0.00
0.29
0.00
0.15
0.01
0
0.00
0.15
141.6
143.6
142.9
147.8
145.3
152.7
147.1
143.2
144.0
142.3
148.2
145.3
143.9
149.5
146.1
160.4
148.4
146.6
149.5
168.5
163.7
141.6
152.8
30113
30149
30162
31505
30211
27026
26580
25934
24013
31257
31452
32276
31373
31634
26954
30581
31646
159.64
160.21
157.88
159.11
154.76
158.65
160.21
160.51
161.86
158.46
159.58
160.34
156.68
157.82
151.51
156.32
157.33
CN
OMe
Cl
OMe
OMe
H
ꢀ0.70
ꢀ0.50
ꢀ0.22
ꢀ0.5
ꢀ0.56
ꢀ0.19
ꢀ0.56
ꢀ0.56
0.00
165.8
141.4
NO
2
NMe
NMe
NMe
NMe
Me
Me
H
Cl
CN
2
2
2
2
ꢀ0.50
0.00
166.3
137.7
140.5
137.1
162.1
140.3
126.7
160.7
149.5
172.9
152.1
142.5
Cl
ꢀ0.22
ꢀ0.70
ꢀ0.50
ꢀ0.17
0.00
ꢀ0.19
CN
OMe
Me
H
OMe
H
NMe
Me
H
0.15
10
11
12
13
14
15
16
17
ꢀ0.56
ꢀ0.18
0.00
ꢀ0.50
ꢀ0.19
ꢀ0.56
0.00
0.15
0.00
NO
2
NO
2
NO
2
2
ꢀ1.81
ꢀ0.17
0
0.13
0.13
0.13
ꢀ0.98
ꢀ0.18
0
ex
cc
s
,
s
F
R
and s are the excited-state parameter, inductive parameter and resonance parameter, respectively.
y
max is UV maximum absorption in wavenumbers.
(C]N) is the value of 1 C NMR chemical shifts of C]N.
3
d
C
a
The values were obtained via http://www. ccdc.cam.ac.uk/conts/retrieving.html (or from CCDC).
The values were taken from Ref. [26].
The experimental values of our work.
The values were taken from Ref. [32].
b
c
d
e
The values were taken from Ref. [33].
Fig. 2. Representative solid state molecular structures of compounds 1e5. Displacement ellipsoids are drawn at the 50% probability level, and H atoms are shown as small spheres of
0
arbitrary radii. Dihedral angle
t
is defined by atoms C1eC7]N1eC1 .

Z. Fang et al. / Journal of Molecular Structure 1104 (2016) 52e57
55
case X is NMe
correlations of
2
or Y is H. This behavior can be understood by the
versus and parameters ( and are the
are in good agreement with their experimental values. To allow
comparison, the errors of max have been converted to max. The
deviation ranges of the experimental and the predicted values are
shown in Fig. 4, in which the predicted max of seventeen samples,
the percentage of data points within 4.0 nm is 70.5%, within 6.0 nm
is 82.3%, with the maximum error being 9.8 nm. Both Figs. 3 and 4
confirm the reliability of Eqn (3). This demonstrates that molecular
conformation of benzylideneanilines with different parent struc-
ture has an significant effect on their absorption spectra, but there
is something different about the parameters of metrics.
t
s
F
s
R
s
F
s
R
y
l
inductive parameter and resonance parameter, respectively). The
correlation results are shown in Table 2. Good linear correlations
reveal that substituents have a remarkable and systematic elec-
tronic effect on the dihedral angle
Table 2, the signs in front of and
and Y is OMe, while in case X is NMe
alternated. Both and values are bigger in case X is NO
2
those in other three cases. From these preceding observations, it
can be inferred that the electronic effects on the molecular
conformation are different for the four cases, and the twist of the
l
t
in XBAY. It can be seen in
are the same in case X is NO
and Y is H, the signs are
than
r
F
r
R
2
2
r
F
r
R
3.5. Effects of molecular conformation on the NMR spectra
aniline ring is more sensitive in case X is NO
.4. Effects of molecular conformation on the absorption spectra
To give insight into the effects of molecular conformation on the
2
.
Table 1 summarizes the
d
C
(C]N) values of XBAY. As shown in
3
Table 1(column 14), the
to 161.86 ppm.
C
d (C]N) of compounds range from 151.51
To investigate the effects of molecular conformation on the NMR
0
0
absorption spectra in 4,4 -disubstituted benzylideneanilines, the
spectra in 4,4 -disubstituted benzylideneanilines, the
C
d (C]N)
ex
y
and
max values in Table 1 (column 13) were first correlated with s
values in Table 1 were first correlated with and parameters,
and Eqn (5) was obtained. The results are shown in Table 4. The
correlation results are excellent, and the deviation is only 0.44 ppm.
s
F
s
R
cc
ex
s
P
parameters (scc and
s
P
are the excited-state parameter and
), and
Eqn (1) was obtained. The results are shown in Table 3. The results
Hammett parameter parameter, respectively;
s
P
¼
s
R
þ
s
F
Is the twist of the aniline ring a factor influencing the
C
d (C]N) in
0
are average, and the correlation coefficient is 0.9719. In our previ-
unsymmetrical 4,4 -disubstituted benzylideneanilines? We modi-
ous researches, it was found that the
substituents at the benzylidene ring and the dihedral angle
symmetrical bis-Schiff bases, and the term sin( ) was suitable to
modify the substituent effects on the max [24,25]. Therefore,
n
max was dependent on the
fied the parameters
F R
s and s with the parameter sin(t). However,
t
of
unsatisfactory correlations were observed when the term sin(t)
t
was used to modify
(Eqn. (8)) (Table 4).
F R F R
s (Eqn. (6)), s (Eqn. (7)), or both s and s
n
ex
applying the term sin(
t
) to modify both scc and
s
p
, we carried out a
The behaviors described above can be understood by the
properties of (C]N). max depends on the HOMO-LUMO
correlation analysis once again (Eqn (2)). Surprisingly, the corre-
lation of Eqn (2) is much worse than that of Eqn (1), and its cor-
lmax and
d
C
l
gap, and a larger conjugation generally leads to a lesser gap. The
smaller the torsion of the C]N unit and the aniline ring is the
greater conjugation is. Thus, the absorbance energy is affected by
relation coefficient is only 0.9059. As further proof, the term sin(
t
)
ex
was used to modify
s
p
(Eqn (3)) and scc (Eqn (4)), respectively.
However, the correlation of Eqn (3) is much better than that of Eqn
C
the twist of an aniline ring. However, the d (C]N) value depends
ꢀ
1
(
1), and its standard error is only 268 cm , which is half of Eqn (1).
on the charge properties of imine carbon. The charge of imine
carbon depends on the whole molecular orbitals of molecules, not
just the frontier molecular orbitals. Therefore, the effects of aniline
ring torsion on electronic density of imine carbon are limited [24].
Further, to verify this result, LOO method was adopted [34,35].
The seventeen predicted d (C]N) values and the error between the
C
experimental and the predicted are available in the Supporting
Information.
Fig. 5 represents the correlation between the predicted and the
C C
experimental d (C]N), and it indicates that the predicted d (C]N)
of XBAY are in good agreement with their experimental values. The
deviation ranges of the experimental and the predicted values are
Correlation coefficient is only 0.8949 when sin( ) was used to only
t
ex
0
modify scc only (Table 3). This suggests that in 4,4 -disubstituted
benzylideneanilines, the effect of the twist of the aniline ring with
respect of the plane of the C]N unit is an important factor influ-
encing the substituent effects on the
scaled by modified the parameter
l
max, and the effects can be
s
p
with the term sin( ). The re-
t
sults are not in accordance with our previous studies [24,25].
The behaviors can be understood by the physical meaning of
s
p
ex
and scc . The parameter
s
p
expresses the electronic effects of
groups and reflects the degree of electronic communication. While
ex
the parameter scc is applied to measure the relative stability of free
radicals. It is known that the smaller the torsion of the C]N unit
and the aniline ring is beneficial to the communication of electrons.
C
shown in Fig. 6, in which the predicted d (C]N) of seventeen
samples, the percentage of data points within 0.5 ppm is 76.4%,
within 0.75 ppm is 88.2%, with the maximum error being 1.41 ppm.
Both Figs. 5 and 6 confirm the reliability of Eqn (5). This confirms
Thus, the twist of the aniline ring with respect of the plane of the
ex
C]N unit has greater impact on the
s
p
than that on the scc , and
sin( ) is suitable to modify the parameter
t
s
p
.
that the effects of the twist of aniline ring on the
C
d (C]N) values of
0
To further verify this result, Leave-One-Out method was applied
34,35]. For the seventeen compounds, there are seventeen pre-
unsymmetrical 4,4 -disubstituted benzylideneanilines are not
obvious.
[
dicted nmax values. The predicted ymax and the error between the
experimental and the predicted value are available in the
Supporting Information.
4. Conclusion
Fig. 3 represents the correlation between the predicted and the
Substituents have a remarkable and systematic electronic ef-
experimental
ymax, and it indicates that the predicted
ymax of XBAY
fects on the dihedral angle t, but the effects are not the same for
Table 2
Correlation results of
F R
t versus s and s parameters.
t
¼ Intercept þ
r
F
(Y)
(Y)
3.4
s
F
(Y) þ
r
R
(Y)
s
R
(Y)
t
¼ Intercept þ
r
F
(X)
s
F
(X) þ
r
R
(X)
R
s (X)
X
Intercept
r
F
r
R
(Y)
R
s
n
Y
Intercept
r
F
(X)
r
R
(X)
R
s
n
NMe
2
137.93
144.1
ꢀ42.8
ꢀ35.9
0.9338
0.9934
8.6
2.5
4
4
H
OMe
128.3
161.2
30.8
ꢀ8.7
ꢀ5.1
ꢀ8.4
0.8669
0.9361
5.8
2.7
5
5
NO
2
ꢀ40.1

56
Z. Fang et al. / Journal of Molecular Structure 1104 (2016) 52e57
Table 3
Correlation results of
ymax for model compounds.
Regression equation
R
R2
s
F
n
Eqns.
ex
ex
y
y
y
y
max ¼ 2269s (X) þ 2476s (Y) þ 1705
s
p
(X) e 1031
) þ 3351
(X)sin(
)ꢀ2158
) þ 1254 (X)ꢀ1414
s
p
(Y) þ 32426
(X)sin(
) þ 2648
(Y)sin(
) þ 32230
(Y) þ 32091
0.9719
0.9059
0.9956
0.8949
0.9643
8207
539
1210
268
81
17
17
17
17
(1)
(2)
(3)
(4)
cc
cc
ex
ex
max ¼ 2889s (X)sin(
t
) þ 8309s (Y) sin(
t
s
p
t
s
p
(Y)sin(
t
) þ 31867
130
338
12
cc
cc
ex
ex
max ¼ 2154s (X) þ 1739s (Y) þ 3416
s
p
t
s
p
t
0.9912
0.8008
cc
cc
ex
ex
max ¼ 3360s (X)sin(
t
) þ 8642scc (Y) sin(
t
s
p
s
p
1276
cc
Fig. 3. Plots of the predicted
XBAY compounds.
ymax using LOO method versus experimental values of the
Fig. 5. . Plots of the predicted
of the XBAY compounds.
C
d (C]N) using LOO method versus experimental values
Fig. 6. . Deviation ranges of the experimental and the predicted
d
C
(C]N) values.
Fig. 4. Deviation ranges of the experimental and the predicted lmax values.
Table 4
Correlation results of
C
d (C]N) for XBAY.
Regression equation
R
R2
s
F
n
Eqs.
d
d
d
d
C
C
C
C
(C]N) ¼ 160.51e5.05
s
s
s
F
(X) e 0.67
(X)sin( ) e 2.45
(X) e 0.08 (X) sin(
(X)sin( ) e 1.86 (X)sin(
s
R
(X) þ 2.84
(X) þ 5.00
) þ 5.97
) þ 2.18
s
F
(Y) þ 5.33
(Y)sin(
(Y) þ 13.03
(Y) þ 6.21
s
R
(Y)
) þ 12.89
(Y)sin(
(Y)
0.9880
0.7546
0.8810
0.9378
0.9760
0.5700
0.7761
0.8794
0.44
1.89
1.36
1.00
122.02
3.97
10.40
21.87
17
17
17
17
(5)
(6)
(7)
(8)
(C]N) ¼ 159.17e4.96
F
t
s
R
s
s
F
t
R
s (Y)
(C]N) ¼ 160.78e6.09
F
s
R
t
F
s
R
t
)
(C]N) ¼ 160.22e7.95
s
F
t
s
R
t
s
F
s
R

Z. Fang et al. / Journal of Molecular Structure 1104 (2016) 52e57
57
0
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The project was supported by the National Natural Science
Foundation of China (No. 21272063), the Scientific Research Fund of
Hunan Provincial Education Department (No. 15B055), the Doctoral
Scientific Research Foundation of Hunan Institute of Engineering
and the Scientific Research Fund of Hunan University of Science and
Technology (No. 14084). We thank Linjie Huang at Hunan Institute
of Engineering for the dealing with figures in article.
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2015.09.035.
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