An efficient synthesis, structural (SC-XRD) and spectroscopic (FTIR, 1HNMR, MS spectroscopic) characterization of novel benzofuran-based hydrazones: An experimental and theoretical studies

Article abstract of DOI:10.1016/j.molstruc.2020.128318

Herein, the benzofuran-based hydrazones derivatives such as N’-(1-(benzofuran-2-yl)ethylidene)isonicotinohydrazide (BEINH), N’-(1-(benzofuran-2-yl)ethylidene)nicotine-hydrazide (BFENH) and N’-(1-(benzofuran-2-yl)ethylidene)-2-chlorobenzohydrazide (BECBH)w

Full text of DOI:10.1016/j.molstruc.2020.128318

Journal of Molecular Structure 1216 (2020) 128318
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
An efficient synthesis, structural (SC-XRD) and spectroscopic (FTIR,
1HNMR, MS spectroscopic) characterization of novel
benzofuran-based hydrazones: An experimental and theoretical
studies
, c,
Muhammad Khalid a, Muhammad Nadeem Arshad b **, Muhammad Nawaz Tahir d,
,
Abdullah M. Asiri b c, Muhammad Moazzam Naseer e, Muhammad Ishaq f,
,
*
Muhammad Usman Khan g, Zahid Shafiq f
a Department of Chemistry, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan, 64200, Pakistan
b Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah, 21589, Saudi Arabia
c Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, P.O. Box 80203, Jeddah, 21589, Saudi Arabia
d Department of Physics, University of Sargodha, Sargodha, 40100, Pakistan
e Department of Chemistry, Quaid-i-Azam University, Islamabad, 45320, Pakistan
f Institute of Chemical Sciences, Bahauddin Zakariya University, Multan, 60800, Pakistan
g Department of Applied Chemistry, Government College University, Faisalabad, 38000, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein, the benzofuran-based hydrazones derivatives such as N’-(1-(benzofuran-2-yl)ethylidene)iso-
nicotinohydrazide (BEINH), N’-(1-(benzofuran-2-yl)ethylidene)nicotine-hydrazide (BFENH) and N’-(1-
(benzofuran-2-yl)ethylidene)-2-chlorobenzohydrazide (BECBH)were synthesized and characterized us-
ing FTIR, 1HNMR, MS spectroscopic and SC-XRD techniques. Furthermore, the structural geometrical
parameters, vibrational bands, natural bond orbitals (NBOs), natural population analysis (NPA), molec-
ular electrostatic potential (MEP), linear and nonlinear optical (NLO) properties of the BEINH, BFENH and
BECBH were rationalized applying B3LYP level of density functional theory (DFT) inclusive of 6-
311þG(d,p) basis set. Consequently, an excellent complement between the experimental data and the
DFT based results was attained. The most dominant hyper conjugative interactions with associated
stabilization energies of 67.52, 59.61 and 48.35 kcal/mol were found for BEINH, BFENH and BECBH
respectively which may become the cause of their stability. The band gaps (Egap) of BEINH, BFENH and
BECBH were rationalized to be 3.814, 3.903 and 3.727eV respectively which can be efficiently polarized
the chemical structures. The descending order of average linear polarizability for title compounds is as:
BECBH> BEINH>BFENH. It was conferred that highest value of btot was obtained for BEINH as 3591.872
(a.u) and the smallest value was obtained for BECBH i.e. 2242.707 (a.u) among title compounds. The
overall decreasing order of btot was observed as: BEINH> BFENH> BECBH. Additionally, NLO properties
of title compounds were found larger than reference material.
Received 21 March 2020
Received in revised form
21 April 2020
Accepted 21 April 2020
Available online 25 April 2020
Keywords:
Benzofuran-based hydrazones
SC-XRD
Spectroscopic data
DFT
Optical exploration
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
characteristics of heterocyclic compounds have made them one of
the cornerstones of medicinal chemistry. Among the oxygen het-
The innate versatility and distinctive physicochemical
erocycles, medicinal chemists appraise benzofuran as central
pharmacophores due to its wide spectrum of pharmacological
properties and structure activity relationships [1,2]. Benzofurans
consists of furan ring fused to benzene and is a major group in
nature’s assembly of pharmacologically active heterocycles. Recent
studies have reported the biological activities of benzofuran-based
scaffold including anti-cancer [3,4], anti-tubercular and anti-
* Corresponding author.
** Corresponding author. Chemistry Department, Faculty of Science, King Abdu-
laziz University, P.O. Box 80203, Jeddah, 21589, Saudi Arabia.
E-mail addresses: mnachemist@hotmail.com (M.N. Arshad), zahidshafiq@bzu.
edu.pk (Z. Shafiq).
https://doi.org/10.1016/j.molstruc.2020.128318
0022-2860/© 2020 Elsevier B.V. All rights reserved.

2
M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
bacterial [5,6] antioxidant [1], antimicrobial [7,8] anti-Alzheimer
[9], anti-hyperlipidemic [10], ant-inflammatory and anti-
convulsant [11], anti-viral [12] and anti-pyretic [13].The medicinal
importance of benzofuran or 2,4-dihydrobenzofuran scaffold can
be conceived by the fact that presently benzofurans and its ana-
logues are culminated as leads for numerous diseases and are in-
tegrated in more than 34 FDA (Food and Drug Administration)
approved drugs [14].Other than being a pharmacologically signifi-
cant scaffold, benzofuran is regarded as an important moiety in
material sciences as well [15,16]. In recent studies, benzofuran and
its derivatives have been used to form highly fluorescent copolymer
materials [17], nonlinear optical (NLO) materials [18], solar cells
donor materials [19], high-performance non-fullerene electron
acceptors for heterojunction organic solar cells [20,21] and organic
2.3. N’-(1-(benzofuran-2-yl)ethylidene)isonicotinohydrazide
(BEINH)
Off-white powder, yield: 94%, M.P: 240e242 ꢀC, 1H NMR
(DMSO‑d6),
d
(ppm): 2.41 (s, 3H); 7.28 (t, 1H, J ¼ 6.9 Hz), 7.37e7.40
(m, 1H), 7.49 (s, 1 H) 7.64e7.79 (m, 4H); 8.76 (d, 2H, J ¼ 7.4 Hz), 11.01
(brs, NH, 1H) see Fig. S5; EIMS; C16H13N3O2 279 (Mþ, 100%): 264,
173, 132, 116, 106, 78; Anal. Calcd. for C16H13N3O2: C, 68.81; H, 4.69;
N, 15.05. Found: C, 68.98; H, 4.88; N, 15.15.
2.4. N’-(1-(benzofuran-2-yl)ethylidene)nicotinohydrazide (BFENH)
White powder, yield: 75%, M.P: 194e196 ꢀC, 1H NMR (DMSO‑d6),
d
(ppm): 2.41 (s, 3H); 7.25e7.71 (m, 5H), 7.37e7.40 (m, 1H), 8.23
light emitting diodes (OLED) [22]. Hydrazone is
a well-
(dd, 1 H, J ¼ 7.8, 1.8 Hz), 8.75 (d, 1H, J ¼ 3.9 Hz), 9.03 (s, 1H), 11.03
(brs, NH, 1H) see Fig. S6; EIMS; C16H13N3O2 279 (Mþ,100%): 264
(100%), 173, 132, 115, 106, 78; Anal. Calcd. for C16H13N3O2: C, 68.81;
H, 4.69; N, 15.05. Found: C, 68.96; H, 4.91; N, 15.23.
acknowledge skeleton in organic synthesis. The imine-forming
reaction conducted between hydrazine and carbonyl group of an
aldehyde or a ketone provides a simple and modifiable conjugation
strategy. Hydrazones have vast applications in medicinal chemistry,
chemical biology, biomaterials and hydrogels, dynamic combina-
torial chemistry and polymer chemistry [23]. Pharmacological
properties such as anticonvulsant, analgesic, antituberculosis,
antifungal, antibacterial, antituberculosis, antimalarial and anti-
cancer have been attributed to Acyl hydrazones [24].
In a recent study, 2-acetyl benzofuran based hydrazones are
prepared as leads for Alzheimer’s disease [25] and various Benzo-
furan hydrazones are also reported to be promising candidates as a-
glucosidase inhibitors [26]. Moreover, for development of multi-
functional drugs, Ethyl benzofuran-2-carboxylate hydrazones have
been reported potential scaffolds; expressing photoprotective,
antioxidant and antiproliferative properties [27].
2.5. N’-(1-(benzofuran-2-yl)ethylidene)-2-chlorobenzohydrazide
(BECBH)
Light yellow powder, yield: 90%, M.P: 182e183 ꢀC, 1H NMR
(DMSO‑d6),
3 H), 8.50e9.19 (m, 4 H), 12.46 (brs, NH, 1H) see Fig. S7; EIMS;
17H13ClN2O2 312 (Mþ): 312 (100%), 297, 173, 139, 132, 104; Anal.
d (ppm): 2.5 (s, 3H); 6.90e6.96 (m, 2H), 7.31e7.80 (m,
C
Calcd. for C17H13ClN2O2: C, 65.29H, 4.19 N, 8.96. Found: C, 65.44H,
4.31 N, 8.81.
3. Results and discussion
2. Experimental
3.1. Chemistry
2.1. Materials and methods
Towards our interest to explore molecular structural aspects, we
have synthesized three hydrazone scaffolds (BEINH, BFENH and
BECBH) by combining 2-acetylbenzofuran (1) with corresponding
hydrazides (2a-c) as shown in the Scheme1.
Melting points were taken on a Fisher-Johns melting point
apparatus and are uncorrected. Elemental analyses were performed
on a Leco CHNS-9320 (USA) elemental analyzer. Infrared spectra
(KBr discs) were run on Shimadzu Prestige-21 FT-IR spectrometer.
The1H NMR spectra were recorded in CDCl3 or DMSO‑d6 on Bruker-
300 MHz & 400 MHz spectrometer using TMS as an internal
The reaction was carried out in refluxing ethanol under the
catalysis of p-TsOH. The course of the reaction was monitored
through TCL under UV light and upon completion, the solid product
was crystallized. The synthesized hydrazones (BEINH, BFENH and
BECBH) were analyzed by FTIR spectrophotometer. The IR spectra
of all compounds showed the lack of bands at 1700-1750 cmꢁ1 due
to carbonyl group of ketone BEINH, and at 3500-3300 cmꢁ1 due to
eNH stretching vibration of primary amine, while a new band
appeared at 1633-1611 cmꢁ1 assigned to the azomethine (C]N)
association. The band due to carbonyl (C]O) of amide group was
present at 1683-1645 cmꢁ1. In the 1H NMR spectrum of hydrazones
BEINH synthesized from isoniazid, the eNH proton appeared at
standard. 1H chemical shifts are reported in
d/ppm and coupling
constants in Hz. The electron impact mass spectra (EIMS) were
determined with JEOL MS Route mass spectrometer. The progress
of the reaction and purity of the products were checked by TLC
plates coated with Merck silica gel 60 GF254, and the spots were
visualized under ultraviolet light at 254/366 nm and/or spraying
with iodine vapors.
2.2. Preparation of hydrazones (BEINH, BFENH and BECBH)
d
11.01 ppm. The ¼ CH proton appeared as a singlet at
and methyl protons as a singlet at 2.41 ppm. All other aromatic
protons appeared between 7.28e8.76 ppm. In case of hydrazones
derivative BFENH obtained from nicotinic acid hydrazide, the signal
for eNH proton appeared at 11.03 ppm and methyl protons at
2.41 ppm. The aromatic protons appeared in the range between
7.25e9.03 ppm. The 1H NMR spectrum of hydrazones BECBH
12.46 ppm while the aromatic
7.21e7.92 ppm. The EIMS
d 7.49 ppm
d
To a hot stirred ethanolic solution of corresponding hydrazide
(2a-c) (1 mmol) was added ethanolic solution of 2-
acetylbenzofuran (1) (0.16g, 1 mmol). After 10 min, catalyst (p-
TsOH) was added into the reaction mixture. Precipitation started
after 30 min. The resultant mixture was then heated at reflux
temperature for 2 h. The reaction was monitored via thin layered
chromatography. On completion, the reaction muddle was cooled
at room temperature. The product was assembled by filtration,
rinsed with warm ethanol and dried up. Re-crystallization of
product was done in chloroform and dioxane. The structure of
synthesized Schiff’s bases (BEINH, BFENH and BECBH) was deter-
mined through IR, Mass, 1H NMR spectra and X-ray crystallography.
d
d
d
d
showed singlet for eNH proton at
protons appeared in the range of
d
d
(Electron Ionization Mass Spectroscopy) data confirmed the for-
mation of the hydrazones (BEINH, BFENH and BECBH). The mo-
lecular ion peak at m/e 279 in BEINH and at m/e 312 in BECBH was
also the base peak. The other fragmentation data was found to be
well synchronized with the fragments obtained in EIMS.

M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
3
Scheme1. The synthetic route of hydrazone scaffolds (3a: BEINH, 3b: BFENH and 3c: BECBH).
3.2. Crystallographic discussion
[dihedral angles (ꢀ): O(1)-C(8)-C(9)-N(1) 13.3(3), N(2)-C(11)-C(12)-
C(13) ꢁ32.5(3), C(9)-N(1)-N(2)-C(11) ꢁ168.2(2)] (Fig. 1). This is
most probably due to the different levels of conjugation of lone pair
present on central amide nitrogen atom N(2) to the neighboring
imino and carbonyl moieties. It is worth mentioning here that the
conjugation of nitrogen lone pair towards imino side lead to the
extension of conjugation involving benzofuran ring. The bond
distances between O(2)eC(11) 1.227(2) Å in BEINH, 1.228(3) Å in
BFENH and 1.215(3) Å in BECBH, N(2)eC(11) 1.349(3) Å in BEINH,
1.348(3) Å in BFENH and 1.344(4) Å in BECBH, N(1)eN(2) 1.381(2)
Å in BEINH, 1.387(2) Å in BFENH and BECBH and 1.376(3) Å in
BECBH, N(1)eC(9) 1.284(3) Å in BEINH, 1.287(3) Å in BFENH and
1.285(3) Å in BECBH clearly highlight the different level of
conjugation.
As shown in Fig. 1, the central N-iminoamide moiety adopts
trans-conformation providing hydrogen bond donor and acceptor
sites on opposite sides. Owing to this conformation, the crystal
packing of BEINH, BFENH and BECBH is dominated by 1D-supra-
molecular chains (Fig. 2). These chains are formed mainly by means
of NeH/O [N(2)-H(2A)$$$O(2) 2.265 Å], CeH/O [C(2)eH(2)$$$
The structures of benzofuran-based hydrazones BEINH, BFENH
and BECBH were unambiguously proved by X-ray diffraction
analysis. Good quality single crystals of BEINH, BFENH and BECBH
(Table 1) suitable for X-ray diffraction analysis were obtained by
slow evaporation of their solutions in CHCl3/dioxan at room tem-
perature. The benzofuran-based hydrazones BEINH and BECBH
both crystallized in the monoclinic crystal lattice with Pc and Cc
space groups, respectively, whereas BFENH crystallized in the
orthorhombic crystal lattice with Pbca space group.
The molecular structures (ORTEP diagrams) of benzofuran-
based hydrazones BEINH, BFENH and BECBH along with crystal-
lographic numbering schemes are shown in Fig. 1. The nicotinyl
moiety and 2-chlorobenzyl moiety in BEINH and BECBH, respec-
tively that are linked to thebenzofuran ring through central
hydrazone moiety are tilted and present nearly at right angle to
each other [dihedral angles (ꢀ): O(1)-C(8)-C(9)-N(1) ꢁ18.6(3) and
3.2(4), N(2)-C(11)-C(12)-C(13) ꢁ51.8(3) and 115.4(3), C(9)-N(1)-
N(2)-C(11) 171.11(18) and 178.0(2) in BEINH and BECBH respec-
tively. However the two aromatic rings i-enicotinyl moiety and
benzofuran are present nearly in the same plane in case of BFENH
O(1) 2.646 Å] and CeH$$$p [C(13)eH(13)$$$C(14) 2.825 Å] in-
teractions in 1, NeH/O [N(2)-H(2A)$$$O(2) 2.171 Å], CeH/O
Table 1
X-ray crystallographic data of BEINH, BFENH and BECBH.
Crystal data
BEINH
BFENH
BECBH
CCDC
1956018
1956017
1956019
Chemical formula
Mr
C
16H13N3O2
C16H13N3O2
279.29
C17H13ClN2O2
312.74
279.29
Crystal system, space group
Temperature (K)
a, b, c (Å)
Monoclinic, Pc
296
11.0648 (8), 7.7788 (6), 7.8939
Orthorhombic, Pbca
296
11.002 (2), 8.4435 (14), 29.137
Monoclinic, Cc
296
9.9593 (10), 18.8724 (18), 8.1103
(5)
(5)
e
(6)
b
(ꢀ)
94.860 (4)
676.99 (8)
2
92.793 (3)
1522.6 (2)
4
V (Å3)
2706.7 (8)
8
Z
Radiation type
Mo K
0.09
a
Mo K
0.09
a
Mo Ka
0.26
m
(mmꢁ1
)
Crystal size (mm)
Data collection
0.40 ꢂ 0.30 ꢂ 0.27
0.42 ꢂ 0.32 ꢂ 0.28
0.32 ꢂ 0.22 ꢂ 0.18
Diffractometer
Absorption correction
Bruker Kappa APEXII CCD
Multi-scan (SADABS; Bruker,
2005)
Bruker Kappa APEXII CCD
Multi-scan (SADABS; Bruker,
2005)
Bruker Kappa APEXII CCD
Multi-scan (SADABS; Bruker, 2005)
Tmin, Tmax
0.940, 0.980
0.944, 0.984
0.934, 0.974
No. of measured, independent and observed [I > 2
s(I)]
5425, 1547, 1410
14972, 3164, 2083
6240, 2804, 2247
reflections
Rint
0.017
0.649
0.049
0.657
0.018
0.641
(sin
Refinement
R[F2 > 2 (F2)], wR(F2), S
q/l) )
max (Åꢁ1
s
0.031, 0.085, 1.06
0.058, 0.126, 1.07
0.033, 0.084, 1.03
No. of reflections
No. of parameters
No. of restraints
H-atom treatment
1547
191
2
3164
191
2
2804
200
2
H-atom parameters constrained H-atom parameters constrained H-atom parameters constrained
0.15, ꢁ0.16 0.20, ꢁ0.17 0.14, ꢁ0.16
D
Dmax, D )
Dmin (e Åꢁ3

4
M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
Fig. 2. Showing 1D-supramolecular chain along b-axis, BEINH; BFENH and BECBH.
Fig. 1. The molecular structures (ORTEP diagram) of benzofuran-based hydrazones
BEINH, BFENH and BECBH respectively.
Similarly, the analysis with respect to FMO and NLO was also
conducted by applying B3LYP/6-311þG(d,p). Moreover, the photo-
physical properties of BEINH, BFENH and BECBH were determined
by making use of UVeVis analysis based on TD-DFT at B3LYP/6-
311þG(d,p) level. The input files were organized by GaussView5.0
[33]. The interpretation of output files was furnished through
Avogadro [34],GaussView 5.0 [31] and Chemcraft program [35].
[C(13)eH(13)$$$O(2) 2.655 Å &C(19)-H(16A)$$$O(2) 2.598 Å] and
CeH$$$
[N(2)-H(2A)$$$O(2) 2.320 Å], NeH/N [N(2)-H(2A)$$$N(1) 2.615 Å]
and CeH$$$ [C(2)eH(2)$$$C(8) 2.885 Å] interactions in BECBH
p [C(2)eH(2)$$$C(7) 2.807 Å] interactions in 2, and NeH/O
p
(Fig. 2aec). These chains are further connected to the neighboring
chains by various non-covalent interactions, providing an overall
3D-networks in benzofuran-based hydrazones BEINH, BFENH and
BECBH (Fig. 3).
3.4. Molecular geometric parameters
The comparison of DFT based structural aspects was made to
that of structural aspects of compounds obtained through experi-
mental data of SC-XRD. Moreover, it could be noticed that the non-
covalent interactions (NCIs) are existed within crystal structures
and crystals are free from solvent molecules. The bond angles and
bond lengths of BEINH, BFENH and BECBH were obtained from DFT
and X-ray diffraction as can be seen in Tables S1eS3 (Supplemen-
tary Information).In the case of BEINH, the bond lengths of O1eC1,
O1eC8 and O2eC11 were found to be 1.363, 1.373 and 1.210 Å (DFT)
as well as 1.375, 1.381 and 1.227 Å (EXP) respectively. The bond
lengths of N1eN2, N1eC9, N2eC11, N3eC14 and N3eC15 were
obtained to be 1.355, 1.291, 1.388, 1.335 and 1.338 Å (DFT) and also
1.381, 1.283, 1.349, 1.324 and 1.331 Å (EXP) respectively. The bond
angles among carbon and oxygen atoms likewise C1eO1eC8,
O1eC1eC2, O1eC1eC6, O2eC11eN2 and O2eC11eC12 were
found to be 106.8ꢀ, 126.0ꢀ, 110.4ꢀ, 124.1ꢀ and 122.1ꢀ(DFT)respec-
tively. While SC-XRD obtained the values of same bond angles as
3.3. Computational procedure
The computational calculations were conducted with the help of
Gaussian 09 program package [28] by making use of DFT [29e32].
For this purpose, SC-XRD crystal structures were used to regain the
initial geometries of BEINH, BFENH and BECBH. The optimization
for BEINH, BFENH and BECBH was accomplished without applying
symmetry restrictions by B3LYP level of DFT and 6-311þG(d,p)
basis set. The frequency analysis with DFT/B3LYP/6-311þG(d,p)
functions was performed to confirm the stability associated to
optimized geometries. The true minimum for the optimized ge-
ometries of BEINH, BFENH and BECBH were achieved as indicated
by the absence of negative eigen values in all the calculated fre-
quencies. The same level of DFT with embedded package of NBO 3.1
program was used for the analysis of natural bond orbitals (NBOs).

M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
5
N1eC9eC8 were containedas 116.6, 118.4 and 116.3 (SC-XRD) and
118.0, 120.5 and 117.0 (DFT), respectively (Fig. S1).
In BECBH, the bond lengths of O1eC1, O1eC8 and O2eC11 were
found to be 1.363, 1.373 and 1.211 Å (DFT) and 1.369, 1.376 and
1.216 Å (EXP) respectively. The bond lengths for N1eN2 and N1eC9
were found to be 1.355 and 1.291 Å (DFT) as well as 1.377 and
1.285 Å (EXP) respectively. The bond angles among carbon and
oxygen atoms such as C1eO1eC8, O1eC1eC2, O1eC1eC6,
O1eC8eC7, O1eC8eC9 and O2eC11eN2were calculated through
DFT which were found to be 106.8ꢀ, 126.0ꢀ, 110.4ꢀ, 110.9ꢀ, 117.6ꢀ and
124.0ꢀ respectively. On the contrary, SC-XRD based bond angles
were observed as 106.0ꢀ, 125.5ꢀ, 110.6ꢀ, 110.2ꢀ, 117.4ꢀ and 123.7ꢀ
respectively. Further, the bond angels among nitrogen and carbon
atoms as N2eN1eC9, N1eN2eC11, N1eC9eC8, N1eC9eC10 and
N2eC11eC12 were calculated viaDFT with 117.7ꢀ, 120.6ꢀ, 117.0ꢀ,
124.5ꢀ and 114.9ꢀvalues respectively; SC-XRD based bond angles
were observed as 117.1ꢀ, 118.2ꢀ,116.0ꢀ 125.8ꢀand 113.6ꢀrespectively
(Fig. S1).
The evaluation and comparison of the experimental and theo-
retical data with respect to bond angles and bond lengths reflect a
good agreement between the data with a few error deviations as
can be seen in Table 2. The calculated geometrical parameters have
still good validity and approximation even by considering the de-
viations. However, the observed deviations might be attributed due
to the involvement of intermolecular and intramolecular in-
teractions in solid phase.
3.5. Natural bond orbitals (NBO) analysis
The sound and clear understanding of orbital based facts
regarding the molecular phenomena like inter and intra molecular
hydrogen bonding, conjugation and charge transfer in electron rich
and electron deficient moieties can be achieved by NBO analysis
[36].Moreover, the shifting of charge density from a filled bonding
molecular orbital to non-bonding orbitals (empty orbitals) can be
easily elucidated with the help of NBO analysis [37].In this situa-
tion, second order perturbation theory could be applied to char-
acterize the stabilization energy which associated to
donoreacceptor interactions [38]. In this analysis, NBO(i) repre-
sents the donor orbital and NBO(j) represents the acceptor orbital
and the stabilization energy on account of electronic delocalization
was represented by E(2)as can be obtained by following equation.
Fig. 3. The 3D-molecular packing of benzofuran-based hydrazones; BEINH, BFENH
and BECBH.
105.5ꢀ, 125.4ꢀ, 110.7ꢀ, 124.3ꢀ and 120.5ꢀ, respectively. The bond
angels of carbon atoms: C3eC4eC5, C4eC5eC6, C6eC7eC8,
C7eC8eC9 and C5eC6eC7 were found to be 121.3ꢀ, 118.3ꢀ, 106.7ꢀ,
131.5ꢀ and 135.8ꢀ respectively (DFT). Whereas, aforesaid bond
angle values were observed as 121.8ꢀ, 118.1ꢀ, 106.5ꢀ, 131.4ꢀ and
135.9ꢀ(SC-XRD), respectively as can be seen in Fig. S1.
For BFENH, the bond lengths for O1eC1, O1eC8 and O2eC11
were acquired to be 1.363, 1.373 and 1.210 Å (DFT) as well as 1.377,
1.387 and 1.228 Å (EXP) respectively. The N1eN2, N1eC9, N2eC11,
and N3eC15 bond lengthswere achieved to be 1.354, 1.290, 1.392,
and 1.338 Å (DFT) and 1.387, 1.287, 1.348, and 1.335 Å (EXP),
respectively.The bond angles among carbon and oxygen atoms:
ꢀ
ꢁ
2
Fi;j
Eð2Þ ¼ q
(1)
iεj ꢁ εi
Whereas, qi stands for orbital occupancy, εI stands for diagonal NBO
Fock matrix elements and Fi,j stands for the off-diagonal NBO Fock
matrix elements respectively [39].
The NBO analysis had been carried out for BEINH, BFENH and
BECBH and elaborated in Tables S4eS6. Nevertheless, some
selected values were given in Table 3.
C1eO1eC8,
O1eC1eC2,
O1eC1eC6,
O2eC11eN2
and
Table 2
O2eC11eC12 were calculated through DFT which were found to be
106.8ꢀ, 126.0ꢀ, 110.4ꢀ, 123.9ꢀ and 122.5ꢀ respectively. While SC-XRD
based bond angles among former atoms were observed as 105.8ꢀ,
125.6ꢀ, 110.3ꢀ, 122.9ꢀ and 120.5ꢀrespectively. Further, the bond
angels among carbon atoms: C3eC4eC5, C4eC5eC6, C6eC7eC8,
C7eC8eC9 and C5eC6eC7 were calculated to be 121.3ꢀ, 118.3ꢀ,
106.7ꢀ, 131.5ꢀ and 135.8ꢀ (DFT) respectively. While SC-XRD based
bond angles among former atoms were observed as 121.1ꢀ, 118.5ꢀ,
107.3ꢀ, 131.6ꢀand 135.8ꢀ respectively. Furthermore, bond angels
among nitrogen and carbon atoms: N2eN1eC9, N1eN2eC11 and
Calculated error deviations by geometric parameters of title compounds.
Compounds
BEINH
Parameter
MAD
RMSE
MAPE
Bond Lengths
Bond Angles
Bond Lengths
Bond Angles
Bond Lengths
Bond Angles
0.0121
0.8742
0.015
0.7032
0.0187
1.1394
0.0149
1.2818
0.0179
0.9942
0.0227
1.8055
0.8838
0.7384
1.0886
0.5948
1.3402
0.9546
BFENH
BECBH
MAD ¼ Mean Absolute Deviation, RMSE ¼ Root Mean Square Error, MAPE ¼ Mean
Absolute Percentage Error.

6
M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
Table 3
NBO representative values of entitled derivatives.
Compounds
BEINH
Donor(i)
Type
Acceptor(j)
20eC21
C7eC
8
C9eC10
Type
E(2)a [kJ/mol]
E(j)_E(i)b [a.u.]
F(i,j)c [a.u.]
N5eC19
C6eC11
C6eC11
C6eC11
C9eC10
C9eC10
p
p
p
p
s
p
p
p
s
LP(2)
LP(1)
p
p
p
p
p
p
p
s
s
LP(2)
LP(1)
p
p
p
p
p
s
p
p
s
LP(2)
LP(1)
C
p
p
p
p
*
*
*
*
20.62
17.87
18.59
15.63
5.12
0.39
0.29
0.29
0.27
1.21
0.28
0.26
0.28
4.81
0.66
0.31
0.38
0.29
0.29
0.28
0.29
0.28
0.28
1.17
4.67
0.66
0.32
0.29
0.29
0.31
0.28
0.29
1.21
0.28
0.29
4.5
0.081
0.065
0.067
0.06
C
C
12eC13
11eC12
s
*
0.07
C7eC
p
p
p
*
*
*
19.4
0.067
0.062
0.074
0.509
0.125
0.107
0.085
0.065
0.067
0.071
0.065
0.066
0.067
0.071
0.472
0.125
0.106
0.065
0.067
0.060
0.071
0.065
0.070
0.067
0.063
0.448
0.124
0.112
8
C20eC21
C20eC21
C21eH34
N5eC19
18.41
24.33
67.52
28.61
44.3
23.97
17.92
18.62
21.26
18.41
18.03
19.38
5.32
59.61
28.93
42.76
17.97
18.64
13.87
21.18
18.32
5.11
19.32
16.64
48.35
27.57
48.72
C
C
17eC18
20eH33
s
s
*
*
O2
N4
N4eC16
O2eC16
p
p
p
p
p
p
p
p
*
*
*
*
*
*
*
*
BFENH
N6eC33
C7eC16
C7eC16
C8eC10
C8eC10
C
29eC31
C8eC10
12eC14
C7eC16
12eC14
C
C
C12eC14
C12eC14
C26eC33
C33eH34
C7eC16
C8eC10
C
C
27eH28
31eH32
s
s
s
*
*
*
O2
N4
N4eC25
O2eC25
C8eC10
p
p
p
p
p
p
*
*
*
*
*
*
BECBH
C7eC16
C7eC16
C7eC16
C8eC10
C8eC10
C
C
12eC14
17eC19
C7eC16
C
C
12eC14
16eC17
C12eC14
C12eC14
C17eC19
C34eH35
s*
C8eC10
N4eC20
C32eC34
N5eC25
O3eC25
p
p
p
*
*
*
O3
N5
s
*
0.67
0.31
p
*
a
E(2) means energy of hyper conjugative interaction (stabilization energy).
Energy difference between donor and acceptor i and j NBO orbitals.
F(i,j) is the Fock matrix element between i and j NBO orbitals.
b
c
In this work, the most dominant transitions for
*C20eH33) in BEINH, (C33eH34)/ *(C31eH32) in BFENH and
(C34eH35)/ *(C32eC34) in BECBH were found with associated
s
(C21eH34)/
s
*(N4eC25) and LP(1)(N4)/p* (O2eC25) with 28.93 and 42.76 kcal/
s
s
s
s
mol respectively were observed for BFENH. Similarly, LP(2)(O3)/
*(N5eC25 and LP(1)(N5)/ *(O3eC25 contained 27.57 and
s
s
)
p
)
stabilization energies of 67.52, 59.61 and 48.35 kcal/mol respec-
tively. Moreover, for BEINH, *interactions were seen as
(N5eC19)/ *(C20eC21), (C9eC10)/
*(C9eC10), (C20eC21)/ *(N5eC19),
(C6eC11)/ *(C12eC13) with stabili-
48.72 kcal/mol respectively for BECBH(Table 3). The obtained en-
ergy values were attributed to the phenomenon of resonance and
the same is responsible for stabilization energy of investigated
compounds. The NBO data presented herein just representative
values which show very conclusive and precise for the existence of
charge transfer, hyperconjugation and extended conjugation.
Furthermore, the combined effect of extended conjugation and
charge transfer leads to NLO character and red shift behavior of the
entitled compounds.
p/p
p
p
p
(C20eC21)/
p
*(C17eC18),
(C6eC11)/
p
p
p
p
p
p
*(C7eC8),
p
p
(C6eC11)/
p
*(C7eC8) and
p
zation energy values of 24.33, 20.62, 19.4, 18.59, 18.41,17.87and
15.63 kcal/mol respectively (Table 3).Further transitions like
p
p
p
(N6eC33)/
p
*(C29eC31),
(C7eC16)/
p*(C12eC14)were also observed for BFENH reflected
p
(C8eC10)/
p
*(C7eC16),
p
(C12eC14)/
*(C8eC10),
p
p
*(C12eC14), (C12eC14)/
p
p*(C7eC16)and
(C8eC10)/
the stabilization energiesas 23.97, 21.26, 19.38, 18.62, 18.03 and
18.41 kcal/mol respectively (Table 3). Similarly, the energy values
associated to the stabilization were found to be 21.18, 18.64, 18.32,
3.6. FT-IR analysis
17.97, 19.32 and13.87 kcal/mol due to
p
(C8eC10)/
*(C12eC14),
*(C8eC10) and (C7eC16)/
p
p
p
*(C7eC16),
(C7eC16)/
*(C17eC19
p(C7eC16)/p*(C12eC14),
p
(C8eC10)/
p
The molecular vibrations, especially those associated with the
absorption frequencies of characteristic bonds and groups in FT-IR
spectroscopy have been considered of great significance by the
experimental and theoretical chemists. The investigations
regarding the nature of modes of vibration with respect to BEINH,
BFENH and BECBH were conducted by experimental FT-IR along
with DFT based vibrational analysis. The calculations for theoretical
vibrational spectra were conducted in gas phase. The vibrational
modes for the compounds under study were assigned by making
use of animation option of Avogadro software. The findings of
theoretical vibrational and experimental FT-IR vibrations of BEINH,
BFENH and BECBH were placed in Tables S7eS9.
p*(C8eC10),
p
(C12eC14)/
p
p
)
transitions respectively which ultimately reflect conjugation in
BECBH (Table 3).The stabilization energy values associated with
s
/
s
*
transitionswere found very weakthan
because of very poor donors( )-acceptors( *) transitions. So,the
stabilization energy values as 5.12, 5.32 and 5.11 kcal/mol could be
attributed for (C9eC10)/ *(C11eC12), (C26eC33)/ *(C27eH28
and (C12eC14)/ *(C16eC17) for BEINH, BFENH and BECBH
respectively. Moreover, the other transitions like LP(2)(O2)/
*(N4eC16) and LP(1)(N4)/ * (O2eC16) with 28.61, and 44.3 kcal/
mol respectively were found in BEINH. Transitions: LP(2)(O2)/
p/p*transitions
s
s
s
s
s
s
)
s
s
s
p

M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
7
3.7. CeH stretching vibration
reactivities and electromagnetic spectra are well-known observ-
ables of any chemical system which have direct association to
atomic charges of that chemical system [44]. The atomic charges
based on natural population of BEINH, BFENH and BECBH were
determined by adopting B3LYP level with 6-311þG(d,p) basis set.
The natural charge distribution of BEINH, BFENH and BECBH were
shown in Fig. 4. NPA of the BEINH indicates that the O1, N3, N4 and
some carbon atoms were positively charged. While the O2, N5, C6,
C7 and C16 atoms have high negative charges. The other atoms of
BEINH could be seen in Fig. 4. In the case of BFENH, NPA details
were shown in Fig. 4. As can be seen in Fig. 4 that O1, N3 and N4
contained positive charges. The nitrogen atom as N5 contained
negative charge. The carbon atoms like C6 and C17 were extremely
negative charged while C11 and C18 were extremely positive
charged atoms (see Fig. 4). The chloro atom (Cl), O2 and N5 of
BECBH were positively charged. While, the nitrogen and carbon
atoms as N5, C16 and C19 consisted of negative charge. The carbon
atoms C11and C19 were highly positively charged (see Fig. 4).
Generally, heteroaromatic organic compounds and their de-
rivatives exhibited CeH vibrations very close to CeH vibrations in
benzene ring which were consisted of multiple weak bands ranging
from 3100 to 3000 cmꢁ1 [40]. In our study, experimental IR
stretching vibrations of BEINH, BFENH and BECBH were found in
the range of 3056e2999 cmꢁ1 (Figs. S2eS4). While, DFT based
vibrational values of carbon-hydrogen(CeH) stretching vibrations
in BEINH, BFENH and BECBH showed symmetric modes at 3205-
3017 cmꢁ1. The DFT based rocking modes were found to be 1333,
1485 and 1488 cmꢁ1 for BEINH, BFENH and BECBH respectively.
Similarly, the experimental IR carbon-hydrogen (CeH) frequencies
were found to be 1278.55, 1473.28 and 1488.74 cmꢁ1 for BEINH,
BFENH and BECBH respectively (Figs. S2eS4). Whereas, the
calculated scissoring frequencies were observed at 1172, 1172 and
1174 cmꢁ1 for BEINH, BFENH and BECBH, respectively. A reason-
able agreement was found between experimental and DFT based
values (see Tables S7eS9).
3.13. Frontier molecular orbital analysis
3.8. Methyl group vibration
The optoelectronic properties of a molecule, its reactivity and
potential to absorb light could be easily unveiled by considering the
frontier molecular orbitals (FMOs) analysis. The kinetic stability and
chemical reactivity of a molecule is directly related to the energy
difference between HOMO and LUMO orbitals [45,46]. The electron
donation is an attribute of HOMO orbital which the electronically
filled orbital whereas the acceptance of electrons is an attribute of
LUMO orbital which is the unfilled or empty orbital [47]. The
smaller energy difference between HOMO and LUMO orbitals,
greater will be the chance of intramolecular charge transfer and
more polarizable the molecule will be obtained and vice-versa [48].
In present study, B3LYP/6-311þG(d,p) basis sets have been
employed for energies associated to HOMO and LUMO orbitals for
BEINH, BFENH and BECBH as tabulated in Table 4. We displayed
FMOs likewise HOMO, HOMO-1 and HOMO-2, LUMO, LUMOþ1,
LUMOþ2 of BEINH, BFENH and BECBH in Fig. 5. The DFT based
calculations for the molecular orbitals and their respective energy
gaps are listed in Table 4.
In HOMO, the charge density was mainly accumulated on the N-
(benzofuran-2-ylmethylene) acetohydrazide; whereas, in LUMO,
the charge density was accumulated somehow on the complete
molecule (BEINH). Similarly, in BFENH, for HOMO, the charge
density was mainly accumulated on the N-(benzofuran-2-
ylmethylene) acetohydrazide; while, in context of LUMO, the
charge density was accumulated on the complete molecule.
Moreover, for BECBH, in terms of HOMO, the charge density was
mainly accumulated on the 2-chlorobenzohydrazide; however, in
case of LUMO, the charge density moves to the chlorobenzene
(Fig. 5).
Usually, CeH stretching vibrations of methyl were generally
observed in the region of 3000e2800 cmꢁ1 [41,42]. Experimental
IR carbon-hydrogen (CeH) stretching vibrations of BEINH, BFENH
and BECBH were found in the range of 3023.08e2999.27 cmꢁ1
(Figs. S2eS4). DFT based symmetric vibrational stretching modes
were found at 3023-3018 cmꢁ1 for BEINH, BFENH and BECBH
respectively (see Tables S7eS9).
3.9. Stretching vibration associated to NeH bond
The experimental IR frequencies for nitrogen-hydrogen (NeH)
were found to be 3566.06e3150.00 cmꢁ1 for BEINH, BFENH and
BECBH respectively (Figs. S2eS4). The calculated NeH stretching
vibrations for BEINH, BFENH and BECBH were appeared in the
range of 3542e3254 cmꢁ1. The calculated rocking vibrational
modes of NeH group were appeared at 1544,1540 and 1597 for
BEINH, BFENH and BECBH respectively. The experimental IR fre-
quencies for nitrogen-hydrogen (NeH) were found to be
1557.60e1507.61 cmꢁ1 for BEINH, BFENH and BECBH respectively
(Figs. S2eS4).
3.10. C¼O vibrations
A strong C]O stretching vibration is found at 1850-1550 cmꢁ1
which is a characteristic peak of carbonyl group [43]. In our study,
the experimental IR frequencies for carbonyl (C]O) group were
found to be 1748.65, 1748.69and 1771.51 cmꢁ1 for BEINH, BFENH
and BECBH respectively. The calculated C]O vibrational bands
were found as 1769, 1768and 1762 cmꢁ1 for BEINH, BFENH and
BECBH respectively which show a well agreement with experi-
mental data (see Tables S7eS9).
The band gaps (Egap) of BEINH, BFENH and BECBH were
calculated to be 3.814, 3.903 and 3.727eV respectively. The ob-
tained data demonstrated that the compound (BECBH) contained
less energy gap as compared to BEINH and BFENH. The lower Egap
illustrated that the BECBH would have strong intramolecular
charge transfer capability and larger NLO properties than BEINH
and BFENH.
3.11. CeC vibrations
The CeC stretching vibrations were appeared in
1652e1505 cmꢁ1 for BEINH, BFENH and BECBH respectively (see
Tables S7eS9). The experimental IR frequencies for (CeC) vibra-
tions were found to be in the span of 1683.06e1517.61 cmꢁ1 for
BEINH, BFENH and BECBH respectively (see Figs. S2eS4).
EHOMO, ELUMO and energy gaps (DE) associated to FMOs were
effectively employed to predict global reactivity descriptors
[49e52] which assisted in a clear description of the chemical
reactivity, internal charge transfer, and stability of BEINH, BFENH
and BECBH. The results were summarized in Table 5.
3.12. Natural population analysis (NPA)
Ionization potential energies were calculated to be
6.131(HOMO/LUMO), 6.847 (HOMO-1/LUMOþ1) and 7.416
(HOMO-2/LUMOþ2) for BEINH and 6.085 (HOMO/LUMO),
NMR chemical shifts, dipole moments, electric potentials,

8
M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
Fig. 4. The natural charge distribution of BEINH, BFENH and BECBH.
Table 4
a molecule with high energy gap could be considered as hard, non-
reactive, stable species and vice versa [54,55]. Taking into account
of these information, it could be concluded that BFENH is hard,
non-reactive and stable which also supports to our calculated
global hardness values: 1.907, 1.951 and 1.863 eV (HOMO/LUMO)
for BEINH, BFENH and BECBH respectively (Table 5).The reactivity
and stability of any chemical system could be predicted with the
help of chemical potential value. The chemical compound contains
higher chemical potential energies might be taken into account as
more stable and vice versa. The chemical potential for BEINH,
BFENH and BECBH were obtained: ꢁ4.224, ꢁ4.133 and ꢁ8.051 eV
(HOMO/LUMO) respectively. The global softness values were
found to be 0.262 (HOMO/LUMO), 0.190 (HOMO-1/LUMOþ1)
and 0.159 eV (HOMO-2/LUMOþ2) for BEINH. Similarly, for
BFENH these values: 0.256 (HOMO/LUMO), 0.190 (HOMO-
1/LUMOþ1) and 0.166 eV(HOMO-2/LUMOþ2). Whereas, in case
of BECBH, these values were: 0.268 (HOMO/LUMO),
0.175(HOMO-1/LUMOþ1) and 0.159 eV (HOMO-2/LUMOþ2).
These values were found greater in magnitude as compared to their
Frontier molecular orbital energies of BEINH, BFENH and BECBH.
BEINH
BFENH
BECBH
MO(s)
HOMO
LUMO
HOMO-1
LUMOþ1
HOMO-2
LUMOþ2
E(eV)
D
E
E(eV)
D
E
E(eV)
DE
ꢁ6.131
ꢁ2.317
ꢁ6.847
ꢁ1.577
ꢁ7.416
ꢁ1.125
ꢁ6.085
ꢁ2.182
ꢁ6.812
ꢁ1.556
ꢁ7.290
ꢁ1.281
ꢁ9.915
ꢁ6.188
ꢁ10.207
ꢁ4.476
ꢁ10.484
ꢁ4.190
3.814
5.27
3.903
5.256
6.01
3.727
5.731
6.294
6.291
E ¼ energy,
D
E(eV) ¼ ELUMO-EHOMO; MO(s): molecular orbitals, HOMO: highest
occupied molecular orbital; LUMO: lowest unoccupied molecular orbital.
6.812 (HOMO-1/LUMOþ1) and 7.29 (HOMO-2/LUMOþ2) for
BFENH. Likewise, BECBH contains IP values:9.915(HOMO/LUMO),
10.207(HOMO-1/LUMOþ1) and 10.484 (HOMO-2/LUMOþ2).
The electron affinity values were found to be 2.317, 2.182 and
6.188 (HOMO/LUMO) for BEINH, BFENH and BECBH respectively.
The electron affinity values for other levels could be seen in Table 5.
Since ionization potential and electron affinity values could be used
to describe the electron releasing and accepting capability of
investigated molecules which were directly related to the energy of
HOMOs and LUMOs [53]. The ionization potential values were
observed larger in some extent as compared to electron affinity
values describing the better electron acceptance capability of
investigated molecules. The order of electron acceptance capability
of investigated molecules was: BECBH > BFENH > BEINH. Usually,
global hardness values. The global electrophilicity (u) was found to
be 4.678 (HOMO/LUMO), 3.366 (HOMO-1/LUMOþ1) and
2.899 eV(HOMO-2/LUMOþ2) for BEINH. Similarly, for BFENH
these values are: 4.377 (HOMO/LUMO), 3.330(HOMO-
1/LUMOþ1) and 3.056 eV (HOMO-2/LUMOþ2).Whereas, in
case of BECBH, these valueswere: 17.394(HOMO/LUMO),
9.405(HOMO-1/LUMOþ1) and 8.553 eV (HOMO-2/LUMOþ2).
The afore mentioned results revealed that all investigated

M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
9
molecules were characterized with greater kinetic stability.
3.14. Nonlinear optical (NLO) properties
The NLO behavior of organic molecules has become the inter-
ested topic of discussion in the recent research among many fields
[56,57]. The low dielectric constants along with faster electronic
responses are the significant features of organic NLO materials
which ultimately enhance their demand and utilization in a num-
ber of optoelectronic applications. The utilization of organic ma-
terials in optical fiber telecommunication sector is also based on the
delocalized electronic systems and the capability of intramolecular
charge transfer (ICT) [58e62]. The non-centrosymmetric nature of
the molecules along with their molecular architecture is respon-
sible for NLO behavior of the molecule. The features required for
NLO behavior of the molecules can be met by keeping the donor
and acceptor units at appropriate distance and variation in frame
work of conjugated system [63].The synthesized compounds
(BEINH, BFENH and BECBH) were subjected to B3LYP/6311þG(d,p)
basis set for the evaluation of their NLO behavior. The diagonal
elements of equation (2) were considered for estimating the
average polarizability (a).
ꢂ ꢀ
ꢁ
<
a
> ¼ 1 3 axx
þ
ayy
þ
azz
(2)
First hyperpolarizability (btot) has been obtained from equation
(3) by considering the x, y and z-direction tensors.
ꢃ
ꢃ
ꢃ
btot
¼
bxxx
þ
bxyy
þ
bxzz byyy
þ
bxxy
þ
byzz bzzz
þ
bxxz
þ
byyz
ꢄ
ꢃ
ꢀ
i
1=2
ꢁ
2
bzzz
þ
bxxz
þ
byyz bzzz
þ
bxxz
þ
byyz
(3)
The values of linear polarizabilities associated to BEINH, BFENH
and BECBH were placed in Table 6. However, calculated results with
respect to linear polarizability (atotal) and first hyperpolarizability
(second-order NLO; btotal) were placed in Tables 6 and 7 respec-
tively. The dipole moment data of BEINH, BFENH andBECBH re-
flected charge distribution in all directions. The highest dipole
moment was found in BFENH as 7.0564 D and the smallest 5.1544 D
was present in BECBH. So, the decreasing order of dipole moment
was BFENH > BEINH>BECBH.
The most cited molecule for comparative analysis with respect
to dipole moment and polarizability in literature is urea molecule
[64]. The dipole moments for BEINH, BFENH and BECBH were
found as 5.4538, 7.0564 and 5.1544D respectively. The obtained
values of dipole moment for all the investigated compounds were
greater than that of urea (1.3732 D) [64].The largest value of linear
polarizability was obtained for BECBH (271.234 a.u.) and values for
BEINH and BFENH were obtained as 253.2853 and 253.1556 a.u.
respectively. The order of decrease in total linear polarizability for
compounds was as BECBH> BEINH> BFENH.
The results of btot and the associated contributing tensors along
x, y, and z directions were placed in Table 7. It was observed that the
dominant transition which contributedfor btot were along x-axis
direction for BEINH, BFENH and BECBH. The highest value of btot
was obtained for BEINH as 3591.872 (a.u) among the title com-
pounds.Whereas, least contribution of dominant x-axis transitions
led to the smallest value of btot for BECBH i.e. 2242.707 (a.u). The
decreasing
order
for
the
value
of
btot
was
as
BEINH> BFENH>BECBH.The results were further analyzed in
comparison with standard urea molecule (btot (urea) ¼ 43 a.u). So,
the title compounds (BEINH, BFENH and BECBH) showed greater
btot values in comparison to urea molecule. On comparative basis,
btot values of BEINH, BFENH and BECBH have been estimated as
Fig. 5. Frontier molecular orbitals of entitled compounds.

10
M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
Table 5
Ionization potential (IP), electron affinity (EA), electro negativity (X) chemical potential (
m
) global hardness (
h
) global softness (S) and global electrophilicity (u).
GRP
BEINH
A
BFENH
A
BECBH
B
C
B
C
A
B
C
IP
EA
X
6.131
2.317
4.224
ꢁ4.224
1.907
0.262
4.678
6.847
1.577
4.212
ꢁ4.212
2.635
0.190
3.366
7.416
1.125
4.270
ꢁ4.270
3.145
0.1589
2.899
6.085
2.182
4.134
ꢁ4.133
1.951
0.256
4.377
6.812
1.556
4.184
ꢁ4.184
2.628
0.190
3.330
7.29
9.915
6.188
8.051
ꢁ8.051
1.863
0.268
17.394
10.207
4.476
7.341
ꢁ7.341
2.865
0.175
9.405
10.484
4.19
1.281
4.286
ꢁ4.285
3.005
0.166
3.056
7.337
ꢁ7.337
3.147
0.159
8.553
m
h
S
u
A ¼ HOMO & LUMO; B¼ HOMO-1 & LUMOþ1; C¼ HOMO-2 & LUMOþ2; units in eV.
Table 6
The linear polarizability (
a
) units in a. uand dipole moments (m) units in Debyeof the
studied compounds.
Linear polarizability
BEINH,
BFENH BECBH
axx
ayy
azz
424.452
213.701
121.704
253.286
426.484
210.119
122.866
253.156
443.689
227.161
142.853
271.234
< a >
Dipole moment
mx
BEINH,
1.9401
5.0675
ꢁ0.5476
5.4538
BFENH
0.8604
6.9825
0.5453
7.0564
BECBH
1.7655
4.0846
ꢁ2.6014
5.1544
my
mz
mtotal
Table 7
The computed second-order polarizabilities (btot) and major contributing tensors
(a.u) of the studied compounds.
Polarizability
BEINH,
BFENH
BECBH
bxxx
bxxy
bxyy
byyy
bxxz
byyz
bxzz
byzz
bzzz
btotal
3569.325
ꢁ187.182
105.140
69.748
26.152
8.005
2556.934
ꢁ143.806
141.641
107.050
25.885
2110.406
184.323
137.399
ꢁ8.476
39.614
9.366
33.594
ꢁ83.971
ꢁ55.719
ꢁ16.284
ꢁ8.554
75.319
28.731
38.773
10.924
3591.872
ꢁ13.034
2642.950
2242.707
50.39, 68.84 and 42.58 times greater than that of urea.
3.15. Molecular electrostatic potential (MEP)
The chemical and physical aspects of any chemical system could
be explored with the help of MEP plot. Usually, MEP plot could be
employed to comprehend the plausible attacking of electrophilic or
nucleophilic at suitable sites on chemical structures. MEP surface
contains several standard colors likewise orange, red, yellow, blue
and green which revealed the magnitude of electrostatic potential.
The order of magnitude of electrostatic potential in terms of
decreaseing was found to be blue > green > yellow > orange > red.
The segment highlited with red color was engaged to communicate
the negative potential value which could be supportive for elec-
trophilic attack. On the contrary, the nucleophile enticing site by
most positive potential could be displayed through blue color. MEP
was charaterized using Equation (4).
Fig. 6. MEPs and color scheme of the studied compounds: BEINH,BFENH and BECBH.
for BEINH, BFENH and BECBH were presented in Fig. 6. From Fig. 6,
it could be seen that the pure red color zone on MEP was presented
on the oxygen atoms of furan ring and carbonyl group of BEINH,
BFENH and BECBH molecules. Therefore, this area was the
electron-rich zone and related to the chance of electrophilic attack.
The colors as green and blue were usually displayed for hydrogen
and some carbon atoms which define an electron-deficient area
which could be favorable sites for attacking of nucleophilic species.
ꢅ
ꢆ
ð
4. Conclusions
X
ZA
RA
pðr’Þ
(4)
’
VðrÞ ¼
ꢁ r
ꢁ
’
=
ðr ꢁ rÞdr
This study emphasizes on the synthesis, characterization, and
quantum chemical calculations of novel benzofuran-based hydra-
zones (BEINH, BFENH and BECBH). The chemical structures of the
In this equation, ZA indicated the nucleus charge which was
placed at RA and (r’) indicated the electron density. MEP surfaces
r

M. Khalid et al. / Journal of Molecular Structure 1216 (2020) 128318
11
novel series of 3-benzofuran-5-aryl-1-pyrazolyl-pyridylmethanone and 3-
benzofuran-5-aryl-1-pyrazolylcarbonyl-4-oxo-naphthyridin analogs, Eur. J.
Med. Chem. 45 (2010) 3831e3839.
investigated products (BEINH, BFENH and BECBH) have been
characterized by FT-IR, 1H NMR and EIMS. The SC-XRD analysis
disclosed that the BEINH, BFENH and BECBH compounds crystal-
lized in monoclinic, orthorhombic and monoclinicsystems with
space group Pc, Pbca and Cc, respectively. Moreover, SC-XRD study
revealed that the crystal packing of BEINH, BFENH and BECBH is
dominated by 1D-supramolecular chains. These chains are further
connected to the neighboring chains by various non-covalent in-
teractions, providing overall 3D-networks in BEINH, BFENH and
BECBH. The NBO analysis also pointed out that hyper conjugative
interactions play a vital role for the cohesion as well as stabilization
of the network of entitled compounds. The calculated bond lengths
and angles have been compared to the experimental values
revealing a nice agreement in both findings. The FTIR measure-
ments are also predicted by adopting DFT theory, subsequently,
compared to the experimental FT-IR spectra with a nice agreement.
MEP descriptor indicated that oxygen atoms in all title compounds
are prone to electrophilic attack, while carbon atoms of aromatic
rings are prone to nucleophilic attack. The HOMO and LUMO energy
values and their energy bands were acquired and GRP were
accomplished which confess the chemical stability of BEINH,
BFENH and BECBH. The btot values of BEINH, BFENH and BECBH
were explored as 50.39, 68.84 and 42.58 times greater in compar-
ison of urea, respectively. These findings are promising for the
BEINH, BFENH and BECBH which can be used as NLO material in
the photonic based devices.
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Author statement
MM, MI and ZS involved in synthesis and spectroscopic studies
along with their writeup. MNA, MNT and AMA involved in crys-
tallographic experiment, solution and compilation. MK and MUK
performed computational experiment and write-up. So, all authors
have equal contribution in this manuscript.
[18] S. Satheeshchandra, D. Haleshappa, S. Rohith, A. Jayarama, N. Shetty, Novel
benzofuran based chalcone material for potential nonlinear optical applica-
tion, Phys. B Condens. Matter 560 (2019) 191e196.
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donor-acceptor polymer for fullerene-free solar cells, Eur. Polym. J. 120 (2019)
109205.
Declaration of competing interest
[20] J. Yang, F. Chen, J. Hu, Y. Geng, Q. Zeng, A. Tang, X. Wang, E. Zhou, Planar
benzofuran inside-fused perylenediimide dimers for high VOC fullerene-free
organic solar cells, ACS Appl. Mater. Interfaces 11 (2019) 4203e4210.
[21] X. Wang, K. Dou, B. Shahid, Z. Liu, Y. Li, M. Sun, N. Zheng, X. Bao, R. Yang,
Terpolymer strategy toward high-efficiency polymer solar cells: integrating
symmetric benzodithiophene and asymmetrical thieno[2,3-f]benzofuran
segments, Chem. Mater. 31 (2019) 6163e6173.
The authors declare that they have no conflict of interest.
Acknowledgments
This Project was funded by the Deanship of Scientific Research
(DSR), King Abdulaziz University, Jeddah, under grant No. (DF-488-
130-1441). The authors, therefore, gratefully acknowledge DSR for
technical and financial support.
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Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2020.128318.
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