Molecular structure of 1,4-bis(substituted-carbonyl)benzene: A combined experimental and theoretical approach

Article abstract of DOI:10.1016/j.molstruc.2019.127633

The reaction of pyrazole derivatives (pyrazole (Pz), 3-methylpyrazole (MPz) and 3,5-dimethylpyrazole (DMPz)) with terephthaloyl dichloride (TD) in the presence of Et₃N afforded the desired products, 1,4-bis(pyrazolylcarbonyl)benzene (1), 1,4-bi

Full text of DOI:10.1016/j.molstruc.2019.127633

Journal Pre-proof
Molecular structure of 1,4-bis(substituted-carbonyl)benzene: A combined
experimental and theoretical approach
Ezzat Khan, Muhammad Khalid, Zarif Gul, Adnan Shahzad, Muhammad Nawaz
Tahir, Hafiz Muhammad Asif, Sumreen Asim, Ataualpa Albert Carmo Braga
PII:
S0022-2860(19)31742-9
DOI:
https://doi.org/10.1016/j.molstruc.2019.127633
MOLSTR 127633
Reference:
To appear in: Journal of Molecular Structure
Received Date: 29 September 2019
Revised Date: 19 December 2019
Accepted Date: 20 December 2019
Please cite this article as: E. Khan, M. Khalid, Z. Gul, A. Shahzad, M.N. Tahir, H.M. Asif, S. Asim,
A.A.C. Braga, Molecular structure of 1,4-bis(substituted-carbonyl)benzene: A combined experimental
and theoretical approach, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/
j.molstruc.2019.127633.
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The Reaction between terephthaloyl dichloride and 2-aminopyrazol derivatives give
corresponding compounds 1,4-phenylenebis(1H-pyrazol-1-yl)methanone (1), 1,4-
phenylenebis(3-methyl-1H-pyrazol-1-yl)methanone (2) and 1,4-phenylenebis(3,5-dimethyl-
1H-pyrazol-1-yl)methanone (3). All compounds are crystalline and their structures were
confirmed by single crystal X-ray diffraction. Detailed DFT calculations for compounds were
also carried out.

Molecular structure of 1,4-Bis(substituted-carbonyl)benzene: A combined Experimental
and Theoretical Approach
Ezzat Khan,a* Muhammad Khalid,d* Zarif Gul,a Adnan Shahzad,b Muhammad Nawaz Tahir,c
Hafiz Muhammad Asif,d Sumreen Asim,d Ataualpa Albert Carmo Bragae
aDepartment of Chemistry, University of Malakand, Chakdara, Lower Dir, Khyber
Pakhtunkhwa, 18800, Pakistan.
bInstitute of Chemical Sciences, University of Swat, Khyber Pakhtunkhwa, Pakistan.
cDepartment of Physics, University of Sargodha, 40100 Punjab, Pakistan.
dDepartment of Chemistry, Khwaja Farid University of Engineering & Information Technology,
Rahim Yar Khan-64200, Pakistan
eDepartamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av.
Prof. Lineu Prestes, 748, São Paulo, 05508-000, Brazil
*Corresponding authors, E-mail adresses: ekhan@uom.edu.pk (Ezzat Khan) and
khalid@iq.usp.br (Muhammad Khalid)
Abstract
The reaction of pyrazole derivatives (pyrazole (Pz), 3-methylpyrazole (MPz) and 3,5-
dimethylpyrazole (DMPz)) with terephthaloyl dichloride (TD) in the presence of Et3N afforded
the
desired
products,
1,4-bis(pyrazolylcarbonyl)benzene
(1),
1,4-bis(3-
methylpyrazolylcarbonyl)benzene (2) and 1,4-bis(3,5-dimethylpyrazolylcarbonyl)benzene (3).
Good quality crystals were isolated and diffraction data for single crystal were collected which
revealed that compounds 1-3 are monoclinic with space group P21/n, C2/c and P21/c,
respectively. These compounds were obtained as a result of C-N coupling reaction between the
acid chloride and pyrazol derivatives with the intent to explore their structure in solution as well
as solid state. Density function theory (DFT) calculations using B3LYP and CAM-B3LYP
functionals with 6-311G(d,p) basis set were performed to explore geometric and electronic
properties of compounds. The Root Mean Square Error (RMSE) has also been calculated for the
values of geometric parameters, indicating a good agreement with experimental findings.
Moreover, frontier molecular orbitals (FMOs) and natural bond orbitals (NBOs) analyses were

carried out through B3LYP/6-311G(d,p) level of theory. The linear polarizability (α) values of
nonlinear optical (NLO) analysis were calculated with the same level of theory and basis set as
FMO but under different solvent conditions. Time Dependent Density Functional Theory (TD-
DFT) study of these pyrazole substituted derivatives was performed aiming to investigate UV-
Visible behavior. The stability of molecule has been additionally analyzed by Hirshfeld surface
analysis in addition to NBO analysis. The calculated HOMO and LUMO energies from FMO
assisted in calculating global reactivity parameters (Chemical hardness, chemical softness,
electronegativity, EA, IP and electrophilicity). Natural population analysis (NPA) and Molecular
electrostatic potential (MEP) were also performed to obtain insights about the reactivity of
compounds 1-3. Theoretical calculations indicate that these compounds have considerable low
reactivity and can be used for development of coordination chemistry under optimum conditions.
Key words: C-N coupling reactions; terephthaloyl dichloride; x-ray diffraction; Time Dependent
Density Functional Theory; FMOs; NBOs.

1. Introduction
There is enormous interest in developing chemistry of acid chlorides and primary or secondary
amines. Primarily the reaction between acid chloride derivatives was carried out with ammonia
at low temperature under various reaction conditions and afterwards the same technique was
extended to saturated and unsaturated homologues [1]. This strategy leads to the formation of
amides which allow for simple and green operating procedure [2]. Pyrazole derivatives are easily
accessible [3], they possess various active reaction cites, accommodate a variety of functional
groups [4] and act as starting precursors in many reactions [5,6]. The NH function in the 5-
membered ring is of particular importance and the acidic nature of this group led to a number of
products for potential applications such as N-C coupling reactions for synthesis of carbonyl
derivatives [7,8].
On the other hand, acid chlorides for instance terephthaloyl dichloride is an active
ingredient in the synthesis of polymeric material. It has been reported that thiourea derivatives
containing terephthaloyl group are active antimicrobial agents [9]. On the basis of acid chloride
functional group at para position with respect to each other, this compound is suitable candidate
to bridge several molecules for a variety of applications [10].
Keeping in view a very rich chemistry of pyrazole derivatives and terephthaloyl
dichloride and in continuation to our previous work [8], Scheme 1, we carried out reactions
between these two with the intent to design multidentate ligands for possible polynuclear
coordination chemistry. The reaction of terephthaloyl dichloride with Pz, MPz and DMPz
afforded compounds 1-3, respectively. These compounds were isolated in crystalline form from
their respective solutions and their structures were determined by single crystal X-ray diffraction.
The compounds were explored theoretically using B3LYP and CAMB3LYP functionals with 6-
311G(d,p) basis set from data obtained by diffraction analyses. The Root Mean Square Error
(RMSE) has also been calculated for the geometric parameter data which disclosed a good
agreement between experimental and calculated structural parameters. Moreover, FMOs and
NBOs analyses were carried out to DFT method using B3LYP and CAM-B3LYP functional with
6-311G(d,p) basis set. The linear polarizability (α) values of nonlinear optical (NLO) analysis
were calculated with the same level of theory but under different solvent conditions. The
Hirshfeld surface of compounds 1-3 was calculated in order to determine the stability of these
derivatives. The calculated EHOMO and ELUMO were helpful in determining the global reactivity

parameters such as chemical hardness, softness, electronegativity, EA (electron affinity), IP
(ionization potential) and electrophilicity. The stability and electronic properties of compounds
1-3 are elaborated on the basis of insights obtained through DFT calculations.
Scheme 1: Compounds obtained by the reaction of acid chlorides with respective amines to
afford new precursors as a result of N-C bond formation.
2. Material and methods
2.1 General
Reactions were carried out in toluene (dried over benzophenone/Na), products were
obtained in reasonable quantity and were stored under aerobic conditions for prolonged period of
time. Trimethylamine (Et3N) was distilled prior to use. Other chemicals such as, pyrazole (pz), 3-
methylpyrazole (MPz), 3,5-dimethylpyrazole (DMPz) and terephthaloyl dichloride (TD) were
purchased from Sigma Aldrich and were used without further purification. Melting point of
compounds were uncorrected, measured by BIO-COT STUART-SMP10, Japan in sealed
capillary tubes. The FT-IR (ATR method, 400-4000 cm-1) were recorded by SHIMADZU model
1
13
8400s. H- and C-NMR were recorded on Bruker 300 MHz, in deuterated chloroform at room
temperature. The X-ray diffraction data were collected for compounds 1-3, at room temperature
(Bruker kappa APEXII CCD diffractometer, graphite-monochromator, Mo-Kα radiation, λ =
0.71073 Å). Resolution of structures and their refinements were accomplished by SIR97 [11],
SHELXL-97 [12], WinGX [13] and PLATON [14] programs.
2.2
Syntheses of 1,4-bis(pyrazolylcarbonyl)benzene (1), 1,4-bis(3-
methylpyrazolylcarbonyl)benzene (2) and 1,4-bis(3,5-dimethylpyrazolylcarbonyl)benzene
(3)
1. Following the literature procedure [8], toluene solution of pyrazole (2.30 mL, 28.0
mmol) was prepared followed by addition of triethylamine (4.0 mL, 28.0 mmol). The resulting

solution was allowed to stir for ca. 10 min. Stoichiometric amount of terephthaloyl dichloride
(3.00 g, 14.0 mmol) in toluene (20 mL) was dropwise added over a time of 20 min and reaction
contents were left stirring overnight. Precipitates of ammonium salt, [Et3NH]Cl were obtained,
washed with copious amount of water and the chloroform (organic) phase was collected
followed by slow evaporation at room temperature. After five days colorless needle-like crystals
appeared, were separated from the mother liquor and structure for a single crystal was confirmed
by X-ray diffraction. m.p. = 161-163°C, Yield = 80%; 1H-NMR
8.24-8.26 (m, 4H, Ph), 7.82 (d, 2H, CH-Pz), 6.58 (2, 2H, CH-Pz); 13C-NMR
127.9, 129.2, 145.5, 134.3, 162.9; FT-IR (ATR)
(cm-1) = 1725 (CO), 1564 (CN).
δ
(ppm) = 8.60 (d, 2H, CH-Pz),
(ppm) = 110.6,
δ
ν
2. Terephthaloyl dichloride (1.500 g, 7.0 mmol), 3-methylpyrazole, MPz (1.15 mL, 14.0
mmol) and two equivalents of Et3N. Crystals were grown in toluene solution. m.p. = 178-180°C,
Yield = 82%; 1H-NMR
δ(ppm) = 8.45 (d, 2H, CH-Pz), 8.23-8.26 (m, 4H, Ph), 6.52 (d, 2H, CH-
13
pz), 2.36 (s, 6H, Me); C-NMR
(ATR)
(cm-1) = 1728 (CO), 1556 (CN).
3. 3,5-dimethylpyrazole (2.30 mL, 28.0 mmol), slight excess of triethylamine (4.50 mL,
δ(ppm) = 12.0, 109.1, 128.8, 135.0, 137.9, 149.2, 164.7; FT-IR
ν
> 28 mmol) and terephthaloyl dichloride (3.12 g, 14.0 mmol). Crystals of the proposed
1
compound were grown in its chloroform solution. m.p. = 184-186°C, Yield = 86%; H-NMR
δ
δ
(ppm) = 2.23 (s, 6H, Me), 2.60 (s, 6H, Me), 6.12 (s, 2H, CH), 7.84-7.91 (m, 4H, Ph); 13C-NMR
(ppm) = 13.2, 14.0, 111.0, 129.1, 134.8, 141.5, 147.6, 165.4; FT-IR (ATR)
(cm-1) = 1723
ν
(CO), 1560 (CN).
2.3 Computational studies
Quantum chemical calculations for compounds 1-3 were carried out with the help of DFT
employing Gaussian 09 program package [15]. The SC-XRD data were used to build the
structure of compounds and the geometries were optimized. The complete geometrical
optimization was carried out without symmetry restrictions by applying DFT/B3LYP/6-311G
(d,p) and DFT/CAM-B3LYP/6-311G (d,p) levels of theory [16]. The frequency analysis based
on DFT/B3LYP/6-311G (d,p) and DFT/CAM-B3LYP/6-311G (d,p) levels of theory was used
for further confirmation of stability associated with optimized geometries. The NBO analysis
was also accomplished with the help of DFT/B3LYP level of theory at the same basis set [17].
The NLO analysis was performed at B3LYP/6-311G (d,p) level of theory. The FMOs, MEP and

the photophysical characteristics of compounds were determined employing TD-DFT/B3LYP/6-
311G (d,p) level of theory. The Hirshfeld surface analysis was conducted from their original
Crystallographic Information Files (CIF). Global reactivity parameters (GRP) were calculated
using the energies of FMOs and their respective energy gaps with the help of the given
equations, as discussed in the preceding text. The EA (electronic affinity, represented by A in the
equation) and IP (ionization potential, represented by I) values were calculated using equations 1
and 2, respectively [18].
ꢀ = −ꢁꢂꢃꢄꢃ
ꢅ = −ꢁꢆꢇꢄꢃ
Equation 1
Equation 2
Hardness (η) and electronegativity (X) were attained using equations 3 and 4 [19].
I-A
η
=
Equation 3
Equation 4
ꢈ
X= I+A
ꢈ
The chemical potential (µ) was calculated as below.
ꢊ
ꢎ ꢊ
ꢈ
ꢋꢌꢍꢌ
ꢏꢐꢍꢌ
ꢉ =
Equation 5
The magnitude of electrophilicity (
ω
) was calculated according Equation 6, which explain
the relation amongst energy variation and maximum electron transferred [20-22].
ꢒ
ꢑ
ω=
Equation 6
2
η
For calculating the value of softness (σ) equation 7 was used.
ꢔ
ꢓ = ꢈꢕ
Equation 7
All input files were organized with the help of Gaussview 5.0. Avogadro [23], Gauss view
5.0 [24], Gauss Sum [25], Argus Labs [26], Crystal Explorer [27] and Chemcraft [28] programs.
Moreover, same softwares were employed for the interpretation of the output files.
3. Results and discussion
3.1. General chemistry
Compounds 1-3 (Scheme 2, below) were synthesized as per literature protocol [7,8] with
the intent to explore their coordination chemistry with certain metal ions. When they were
treated with salts of Pd and Cu, extensive hydrolysis of the ligand was observed and only

complexes containing pyrazolyl ligands were obtained [29]. This study reveals that such
compounds undergo hydrolysis in the presence of metal salt and are converted into
corresponding acids and starting pyrazolyl moieties.
Scheme 2: Proposed structure of compounds 1-3.
Scheme 3: Cu(II) complexes of 3-methylpyrazole where the ligands adopts itself as 5-
methylpyrazole due to H exchange between two nitrogen atoms for the purpose to minimize
steric bulk near metal ion for efficient connectivity.
Compounds 1-3 were synthesized with the intent to explore their coordination chemistry.
Treatment of compound 2 with CuCl2 salt under reflux condition for three hours, afforded a
dinuclear copper (II) complex 4, Scheme 3. The formation of the complex was confirmed in
some solvents with varying polarity such as EtOH, MeOH and CH3Cl. Literature survey reveals
that complex 4 has been synthesized in a different way [6a]. When 3-methylpyrazole was treated
with CuCl2 under identical conditions, compound 5 was exclusively obtained [5]. These
reactions with copper (II) chloride salt did not allow further reactions to explore their
coordination chemistry. The hydrolysis of structurally analogues compounds was used as a tool
for the synthesis of coordination polymers with Cu(II) ion [8a] where as in this study we did not
isolate structurally novel complexes.

3.1.1. Structure description of 1,4-phenylenebis(1H-pyrazol-1-yl)methanone, 1
Crystal of suitable dimensions of compound 1 (shown in Figure 1) were selected and the
data were collected at room temperature. Structural parameters pertaining to crystal structure
determination and refinements are summarized in Table 1. The data indicate that compound 1
is monoclinic with space group P21/n. The C=O groups at para position of the phenylene ring
are oriented in a trans manner with respect to each other. The pyrazolyl and the respective
carbonyl moiety are coplanar while both the pyrazolyl rings across phenylene are arranged in
the space in a trans manner. Groups around C4 are arranged in trigonal manner and angles
ꢖ ꢀ
around it are collectively equal to 360° ( ∠O1 − C4 − N1 119.1 2 , ∠ O1 − C4 −
ꢁ ꢀ
C5 122.2 2 and ∠N1 − C4 − C5 118.7(18)). The bond lengths around C4 are C4-O1
1.206(2), C4-N1 1.402(2), C4-C5 1.487(3) Å (for comparison of bond lengths and angles see
Table 2) indicating that electron density is partially delocalized resulting in a comparatively
shorter bond length between C4 and C5 as compared to the reported structurally related
compound [8a]. All other bond lengths are within the expected regions. Pyrazolyl groups of the
molecule are co-planar with respect to each other while they are considerably twisted against
the phenylene ring (torsion angle N1C4C5C6 44.8° and N1C4C5C7 139.08°). The co-planarity
in compound 1 in solid state is probably attributed to intermolecular interactions as shown in
Figure 2. These intermolecular interactions also called secondary interactions are responsible
to arrange molecules in 2D supramolecular fashion. Separation distance between H of C6 and
N2 (H6-N2) is 2.701 Å, which is actually separation between two parallel layers. The
molecules in a parallel layer are linked through O1-H1 type hydrogen bonding with a distance
of 2.388 Å.

Figure 1: Molecular structure of compound 1, partial numberings are shown and hydrogen
atoms are omitted for clarity reasons. Selected bond lengths and angels are summarized in Table
2 also see Table S1 for more details.
Figure 2: Supramolecular 2D arrangements of molecules of compound 1, linked together with
the help of non-covalent interactions.
3.1.2. Structure
description
of
1,4-phenylenebis(3-methyl-1H-pyrazol-1-
yl)methanone, 2
The solid state structure of compound 2 is depicted in Figure 3, while data pertaining to
its structure refinements and solution are summarized in Table 1 and important structural
parameters are shown in Table 2. The molecule is monoclinic bearing space group C2/c.
geometry and orientation of various groups in the molecule are very close to each other with

negligible differences. The C4 is sp2 hybridized with trigonal planar geometry. The bond lengths
C4-O1 1.210(2), C4-N1 1.393(3) and C4-C2 1.484(3) Å are slightly different from compound 1.
It is evident that electron density is shifted towards pyrazolyl group thus making the C4-N1 bond
slightly shorter and C4-O1 bond longer in comparison to compound 1. Angles around C4 are
ꢁ
ꢂ
also in support with the trigonal planar geometry (∠O1 ꢀ C4 ꢀ N1 119.62 19 ∠ O1 ꢀ C4 ꢀ
ꢁ
ꢂ
C2 122.66 19 and ∠N1 ꢀ C4 ꢀ C2 117.73ꢁ16ꢂ°. In the same MePz (methylpyrazol) groups
are coplanar with respect to each other as well as with respective CO group with slight deviation
of 2.66°. Both the pyrazolyl moieties are twisted against phenylene ring (torsion angles N1-C4-
C2-C3 55.51° and N1-C4-C2-C1 128.73°).
In establishing the supramolecular structure of the compound methyl group plays an
important role. One of the H from CH3 group makes an interaction with the CO group with a
separation distance of 2.687 Å, affording a 2D architecture as depicted in Figure 4.
Figure 3: Molecular structure of compound 2, hydrogen atoms and numbering of some
structurally less important atoms are omitted for clarity reasons. Selected bond lengths and
angles are represented in Table 2 and for more details see Table S2.

Figure 4: View of 2D supramolecular structure of compound 2, hanging contacts are deleted for
clarity reasons.
3.1.3. Structure description of 1,4-phenylenebis(3,5-dimethyl-1H-pyrazol-1-
yl)methanone, 3
Solid state structure of compound 3 determined with the help of X-ray diffraction for its single
crystal is given in Figure 5. Its crystal structure refinements and solution parameters are
summarized in Table 1 and structural parameters in Table 2. The compound is monoclinic
having identical space group as compound 1 (P21/c). Carbonyl (C=O) moieties are oriented in
trans manner with respect to each other in a similar was as in compounds 1 and 2. Carbonyl
carbon (C6) is trigonal with angles around it, ∠C7 ꢀ C6 ꢀ N2 119.58, ∠ C7 ꢀ C6 ꢀ
O1 120.82 and ∠ N2 ꢀ C6 ꢀ O1 119.61°. These values are in agreement with trigonal planar
geometry of the C7C6N2O1 fragment. The bond length C6-O1 1.215, C6-C7 1.499 and C6-N2
1.398 Å, indicate that C=O bond gradually elongates. The C6-N2 bond is least affected and C6-
C7 bond becomes longer. These data indicate that the electron density is delocalized towards
dimethypyrazolyl group along O1-C6-N2 fragment. In the molecule dimethylpyrazolyl groups
are coplanar. The C=O groups are twisted by 163.85° with respect to DMP and by 28° with
respect to the phenylene ring. The DMP and phenylene rings are mutually twisted by ca. 40°.
There are several short ranged intermolecular interactions in compound 3, both Oxygen
atoms of the carbonyl groups interact with CH of DMP (distance 2.619 Å), H of one molecule

also interact with p-electrons of DMP (distance 2.891 Å). The CH3 protons of neighboring
molecules also interact with each other, stabilizing two molecules at a distance of 2.821 Å. These
interactions afford a 3D supramolecular structure of the compound.
Table 1: Crystal structure determination and refinements of compounds 1-3.
Compound Names
Chemical Formula
Mr
1
C14H10N4O2
266.26
2
C16H14N4O2
294.31
3
C18H18N4O2
322.36
Crystal System
Space group
Temperature(K)
a (Å)
Monoclinic
P21/n
Monoclinic
C2/c
Monoclinic
P21/c
296
296
296
3.9007(4)
11.0403(13)
14.955(2)
96.407(9)
3.9718(5)
15.299(3)
12.0601(18)
95.800(5)
4.1278(3)
14.7281(12)
13.1635(9)
94.682(4)
b (Å)
c (Å)
β
(°)
V(Å3)
640.02(13)
2
729.08(19)
2
Z
2
Radiatio type
Mo/Kα
0.10
Mo/Kα
0.09
Mo/Kα
0.09
µ (mm-1)
Crystal size
0.39×0.20×0.15 0.35×0.15×0.14 0.40×0.20×0.18
Reflections measured
Independent Reflections
Observed Reflection [I >2σ(I)]
Rint
(sinθ/λ)max (Å-1)
R[F2>2σ(F2)]
5614
6712
6660
1527
1738
1815
894
943
1439
0.041
0.659
0.058
0.139
1.02
0.047
0.660
0.050
0.132
1.01
0.032
0.649
0.044
wR(F2)
0.126
S
1.06
No. of Reflections/parameters
∆ρmax, ∆ρmin (eÅ-3)
1527/91
0.13, -0.16
1738/101
0.14, -0.21
1815/112
0.24, -0.22

Table 2: Summarized structural parameters of compounds 1-3, bond length (Å) and bond angles
(°).
Compound 1
Compound 2
Compound 3
Bond lengths
C4-O1
C4-N1
C4-C5
1.206(2)
C4-O1
1.210(2)
1.393(3)
1.484(3)
C6-O1
1.215(17)
1.398(18)
1.499(19)
1.402(2)
1.487(3)
C4-N1
C4-C2
C6-N2
C6-C7
Bond angles
O1-C4-N1
O1-C4-C5
C5-C4-N1
119.1(2)
122.2.(2)
118.7 (18)
O1-C4-N1 119.62(19)
O1-C4-C2 122.66(19)
N1-C4-C2 117.73(16)
O1-C6-N2 119.61(13)
O1-C6-C7 120.82(13)
N2-C6-C7 119.58(12)
Figure 5: Molecular structure confirmed by X-ray diffraction of compound 3, hydrogen atoms
are omitted for clarity, partial numbering is shown, for summarized structural features (bond
lengths and angles) see Table 2, for more details see Table S3.
3.1.4. Molecular geometric parameters
The geometry of compounds 1-3 was optimized by using two different level of theories
i.e., B3LYP and CAM-B3LYP with same basis set as 6-311G (d,p). The obtained parameters are
tabulated in detail in Table S1-S3 (Supplementary Information) and graphical representation of
molecular geometric parameters is presented in Figures 6, Figure S1 and S2, respectively.

Considering bond lengths, the experimental and calculated (DFT (B3LYP)) values, the
identical value was found to be 1.498 Å for (C6-C7) and (C18-C19) in compound 3. The least
deviated values were found to be 0.002 Å for (C3-C9), (C8-C9), (N13-C19) and (C18-C19) in 1,
0.002 Å for (O1-C7) and (O12-C18) in 2 and 0.001 Å for (C14-N22) in 3. However, the most
deviated values were 0.024 Å for (C2-C3) in 1, 0.026 Å for (N2-C7) and (N13-C18) in 2 and
0.018 Å for (C3-C4) and (C15-C16) in 3 (Figure 6 and Figures S1, S2, respectively).
While considering bond lengths, comparing the XRD and the DFT (CAM-B3LYP) values,
the least deviated values were found to be 0.002 Å for (C4-C10) and (N14-C20) in 1, 0.001 Å for
(N2-C8) and (N13-C19) in 2 and 0.001 Å for (C1-C2), (C7-C8), (C7-C9), (C13-C14), (C19-C20)
and (C19-C21) in 3. However, the most deviated values were 0.024 Å for (C1-C2) and (C11-
C12) in 1, 0.019 Å for (N2-N3), (N2-C7), (N13-N14) and (N13-C18) in 2 and 0.022 Å for (N10-
N11) and (N22-N23) in compound 3.
When considering bond angles, comparing the experimental and the DFT calculated
(B3LYP) values, the identical values were found for (C2-C3-C9) and (C12-N13-C19) in
compound 1, (N3-C10-C9) and (N14-C21-C20) in 2 and (C8-C7-C9) and (C20-C19-C21) in
compound 3. The least deviated values were found to be 0.1° for (C2-C1-C8), (C5-C4-C10),
(C5-C6-C17), (C7-C16-O15), (C12-C11-C18) and (O15-N14-C20) in compound 1, 0.1° for (N3-
C10-C11), (C9-C10-C11), (N14-C21-C22) and (C20-C21-C22) in 2 and 0.1° for (C3-C4-N11),
(C7-C8-C21), (C7-C9-C20), (C8-C21-C19), (C9-C20-C19) and (C15-C16-N23) in 3. However,
the most deviated values were 2.8° for (C1-C8-C4) and (C11-C18-N14) in 1, 2.8° for (C6-C5-
C7) and (C17-C16-C18) in 2 and 1.1° for (C1-C2-C3), (C2-N10-N11), (C13-C14-C15) and
(C14-N22-N23) in 3.
On the other hand, considering bond angles, comparing the actual experimental and the
DFT calculated (CAM-B3LYP) values, identical data were obtained for (C5-C6-C17), (C7-C16-
O15) and (C16-O15-C17) in 1 and (C3-C4-N11), (C5-C4-N11), (C15-C16-N23) and (C17-C16-
N23) in 3. The least deviated values were found to be 0.1° for (C2-C1-C8), (C2-C3-C9), (C12-
C11-C18) and (C12-N13-C19) in 1, 0.1° for (N3-C10-C9), (C9-C10-C11), (N14-C21-C20) and
(C20-C21-C22) in 2 and 0.1° for (C3-C4-C5), (C4-N10-N11), (C7-C9-C20), (C8-21-C19), (C15-
C16-C17) and (C16-N23-N22) in 3. However, the most deviated values were 2.8° for (C1-C8-

C4) and (C11-C18-N14) in 1, 2.7° for (C6-C5-C7) and (C17-C16-C18) in 2 and 1.2° for (C2-
N10-N11) and (C14-N22-N23) in 3.
The comparative analysis reveals that calculated bond angles and bond lengths are higher
than SC-XRD values as reflected in Tables S1-S3 and Figures 6, S1, S2. However, in few cases
the DFT values of bond angles and bond lengths were otherwise i.e., smaller than the XRD
values. The disagreement between DFT and experimental findings is predominantly because of
the medium effect (solid state and solution phase).
Figure 6: Comparative representation of Experimental and calculated bond lengths (Å) and bond
angles (°) for compound 1
For a fair comparison between the experimental and DFT study regarding optimization,
error was further calculated with the help of equations 8-10;
ꢝ
∑
|ꢊꢗꢘꢙꢚꢛꢜ|
ꢡ
ꢞꢟꢠ
Mean Absolute Deviation (MAD) =
Equation 8
Where, n is the total number of bond length or bond angle values considered, t is number
of bond length or bond angle values, “EXP” is the experimental based bond length or bond angle
value and “DFT” is the calculated bond length or bond angle value.
The mean absolute deviation (MAD) can be defined as the sum of absolute differences
between the experimental and calculated study-based values divided by the total number of bond
length or bond angle values taken.

ꢝ
ꢒ
∑
ꢖꢊꢗꢘꢙꢚꢛꢜ)
ꢡ
ꢞꢟꢠ
Mean Square Error (MSE) =
Equation 9
Mean square error is usually utilized error metric. It penalizes huge errors due to squaring
larger numbers consisting of a largest impact as compared to squaring smaller numbers.
ꢝ
ꢒ
Root Mean Square Error (RMSE) = ꢢ∑
ꢖꢊꢗꢘꢙꢚꢛꢜ)
ꢡ
ꢞꢟꢠ
Equation 10
The root mean square error (RMSE) can be calculated by taking the square root of MSE. It
is the most commonly used error metric and had been especially considered for compounds 1-3.
The RMSE approach is considered to be the most commonly used in structural
calculations, so, the RMSE approach has also been adopted for our investigated systems as given
in Table 3.
Table 3: Calculated standard error values for compounds 1-3.
1
2
3
CAM-
B3LYP
CAM-
B3LYP
CAM-
B3LYP
Level of Theory
B3LYP
B3LYP
B3LYP
RMSE for bond
lengths
0.0154
0.012
1.266
0.0146
0.0112
1.5362
0.00855
0.00845
0.5629
RMSE for bond
angles
1.2295
1.516
0.5472
The error calculations in terms of root mean square error gave an accurate comparison of
both the level of theories being applied, B3LYP and CAM-B3LYP. Both the level of theories
were in good agreement to one another.
3.1.5. Hirshfeld Surface Analysis
Moreover, to explore intermolecular interactions, Hirshfeld surface analysis for 1, 2 and 3
was performed [30-32]. The configuration of Hirshfeld surface for complete molecule of 1, 2 and
3 is shown in Figure 7. In Hirshfeld surface plot, strongest interactions are indicated by red
colour, intermediate interactions are indicated by white colour and almost negligible
intermolecular interactions are indicated by blue colour (shown in online version). Overall
interactions of compound 1 are given in Figure 8.

The intermolecular interactions can also be explored with the utilization of two-
dimensional fingerprint plots, which can be decomposed to quantify the individual contributions
of each intermolecular interaction involve in the structure. The overall two-dimensional
fingerprint plots are shown in Figure 8 (compound 1) and Figure S3 and S4 (compound 2 and 3,
respectively) [33-35]. These figures show the percent intermolecular contributions for various
interatomic contacts to the Hirshfeld surface and percentage contributions of an atom in
Hirshfeld surface with all other atoms present outside the surface to specify its role in crystal
packing.
Figure 7: Hirshfeld surfaces mapped over dnorm in the range from -0.2799 to 1.2890 a.u., 0.0079
to 1.3088 a.u. and -0.0748 to 1.1368 a.u. for compounds 1, 2 and 3 (left to right). 1 a.u. of
electron density = 6.748 eÅ-3

Figure 8: Two-dimensional fingerprint plots for compound 1.
Theoretical findings regarding crystal packing of compounds 1-3, show that the H…H
contacts appear to be the major contributor and was quantified as 38.3, 46.8 and 55.4%,
respectively. The role of hydrogen atoms is very crucial in the overall stabilization of structure
for these compounds and the percent contribution to intermolecular contacts is quite high. The
smallest contribution towards intermolecular interactions was observed for oxygen atom of C=O
group, its role in crystal packing was found as 1.3, 0.1 and 0%, respectively [36].
3.1.6. Natural Bond Orbital (NBO) Analysis
NBO analysis provides insights into intra- and inter-molecular interactions in filled and
virtual orbitals. Evaluation of the donor–acceptor interactions within the NBO analysis was
administered with the help of second-order Fock matrix [37]. For each donor (i) and acceptor (j),
the stabilization energy E(2) associated with the delocalization i→j was assessed according to
literature protocol, as given in equation 11 [38].
ꢥꢦ ꢨꢈ
ꢤ,ꢧ
ꢁꢖ ) = ꢣ
ꢈ
Equation 11
ꢤ ꢩ − ꢩꢤ
ꢧ
Where F(i.j) is the diagonal and ꢀj and ꢀi are the off-diagonal NBO Fock matrix elements
and qi is the donor orbital occupancy [39].

For finding out intra- and inter-molecular bonding and interaction among existing bonds,
natural bond orbital (NBOs) analysis is an efficient tool and it additionally provides a convenient
basis for investigating conjugative interactions or charge transfer in molecular systems [40,41].
The NBOs analyses were carried out for 1-3, the obtained data are given in supplementary file
(Table S4-S6, respectively). Selected values are represented in Table 4, and optimized structures
with complete numbering scheme are shown in Figure S5-S7.
Table 4: Representative values of NBOs analyses for 1, 2 and 3
i
Type
j (Acceptor) Type E(2)a
E(j)_E(i)b [a.u.] F(i;j)c [a.u.]
Entry
(Donor)
ꢪ∗
ꢪ∗
ꢪ∗
ꢪ∗
ꢫ∗
ꢫ∗
ꢫ∗
ꢪ∗
ꢪ∗
ꢫ∗
ꢪ∗
ꢪ∗
ꢪ∗
ꢪ∗
ꢫ∗
ꢫ∗
ꢪ∗
ꢫ∗
ꢪ∗
ꢪ∗
ꢪ∗
ꢫ∗
ꢫ∗
C1-C3
C16-C18
C5-N14
C20-N29
C18-C20
C3-C5
C5-N14
C20-N29
C1-C3
26.92
26.92
12.03
12.03
5.39
0.28
0.28
0.34
0.34
1.12
1.12
1.21
0.29
0.29
0.93
20.29
0.29
0.28
0.26
0.34
1.11
0.29
0.92
0.29
0.29
0.28
0.93
0.93
0.080
0.080
0.059
0.059
0.069
0.069
0.071
0.099
0.099
0.064
0.082
0.082
0.069
0.065
0.058
0.069
0.100
0.067
0.083
0.083
0.069
0.076
0.076
ꢪ
ꢪ
ꢪ
ꢪ
ꢫ
ꢫ
ꢫ
C16-C18
C16-H17
C1-H2
1
5.39
C5-N14
N13
C7-N13
C7-O15
C22-O30
C3-C5
5.03
37.49
37.49
5.39
LPꢖ1)
N28
LPꢖ1)
N14
LPꢖ1)
C10-C12
C28-C30
C6-C7
N3-C14
N21-C32
C22-C24
O1-C9
27.21
27.21
21.19
18.20
11.50
5.27
ꢪ
ꢪ
ꢪ
C6-C7
ꢪ
2
N3-C14
C30-C32
N2
C10- C12
C28-H29
O1-C9
ꢫ
ꢫ
LP(1)
38.76
6.06
N21
LP(1)
C30-C32
C5-N19
C26-N40
C14-C15
C8-N20
C29-N41
C6-C8
28.25
28.25
21.19
7.64
ꢪ
ꢪ
ꢪ
ꢫ
ꢫ
C27-C29
C35-C38
C9-H12
C30-H33
3
7.64

ꢫ∗
ꢫ∗
ꢪ∗
ꢫ∗
C6-C8
N20
C1-C5
5.12
38.45
38.45
5.91
1.13
0.28
0.28
0.93
0.068
0.099
0.099
0.067
ꢫ
C13-O21
C34-O42
C5-C6
LPꢖ1)
LPꢖ1)
LPꢖ1)
N41
N19
aE(2) represents “energy of hyper conjugative interaction (stabilization energy in kcal/mol)”.
bEnergy difference between i and j NBOs.
cF(i;j) is the Fock matrix element between i and j.
The probable transition consisting of enormous stabilization energies such as: π(C1-
C3)→π*(C5-C14) and π(C16-C18)→π*(C20-N29) contain 26.92 kcal/mol each for compound 1,
π(C10-C12)→π*(N3-C14) and π(C28-C30)→π*(N21-C32) has an energy value of 27.21
kcal/mol each for compound 2 and π(C6-C8)→π*(C5-N19) and π(C27-C29)→π*(C26-N40)
each with 28.25 kcal/mol for compound 3. Other important transitions in these compounds
pointing towards conjugation system are, π(C5-N14)→π*(C1-C3) and π(C20-N29)→π*(C16-
C18) in compound 1, π(C6-C7)→π*(C22-C24) and π(C6-C7)→π*(O1-C9) in compound 2 and
π(C35-C38)→π*(C14-C15) in compound 3 with stabilization energy values 12.03, 21.19 and
18.20 kcal/mol, respectively and 21.19 kcal/mol for 3. However, transitions such as π(C1-
C3)→π*(C5-C14), π(C10-C12)→π*(N3-C14) and π(C6-C8)→π*(C5-N19) demonstrated
highest stabilization energies of 26.92, 27.21 and 28.25 kcal/mol, respectively in compounds 1-3
(see supporting information Table S4-S6). Among all calculated stabilization energies, these
values were the leading one. The calculation of energy corresponds to π→π* interactions is
important to know about the existence of conjugation as well as charge transfer phenomenon in
compounds. Electronic transitions i.e., π(C20-N29)→π*(C16-C18), π(C6-C7)→π*(O1-C9) and
π(C35-C38)→π*(C14-C15) consisting of 12.03, 18.20 and 21.19 kcal/mol are associated with
least energy in 1-3, respectively. The interaction between the electron donor-acceptor moieties
lead to least energies. In contrast to π→π* the σ→σ* transitions are associated with very weak
donor (σ)-acceptor (σ*) interactions energies. The σ(C18-C20)→σ*(C16-C17), σ(C3-
C5)→σ*(C1-H2) transitions contained 5.39 kcal/mol each in compound 1, σ(N3-C14)→σ*(C10-
C12) contained 11.50 kcal/mol in 2 and σ(C9-H12)→σ*(C8-N20) and σ(C30-H33)→σ*(C29-
N41) contained 7.64 kcal/mol each in 3, showing higher stabilization energies among all σ→σ*
interactions. The σ(C5-N14)→σ*(C7-C13) transition associated with 5.03 kcal/mol energy in 1,
σ(C30-C32)→σ*(C28-H29) with 5.27 kcal/mol energy in 2 and σ(C6-C8)→σ*(C1-C5) with
5.12 kcal/mol in compound 3 were with least stabilization energy values (Table 4).

Interactions correspond to resonance were also observed in compounds 1-3, for example,
LP1(N13)→π*(C7-O15), LP1(N28)→π*(C22-O30), LP1(N2)→π*(O1-C9), LP1(N20)→
π*(C13-O21) and LP1(N41)→π*(C34-O42) produced 37.49, 37.49, 38.76, 38.45 and 38.45
kcal/mol in 1-3 and were the highest values. While LP1(N14)→σ*(C3-C5), LP1(N21)→σ*(C30-
C32) and LP1(N19)→σ*(C5-C6) produced 5.39, 6.06 and 5.91 kcal/mol which exhibited least
electron donating interactions energies in 1-3, respectively.
3.1.7. UV-Visible Analysis
The time dependent TD-DFT with B3LYP/6-311G (d,p) and CAM-B3LYP/6-311G (d,p)
levels of theory were used for theoretical calculations of UV-Visible spectral analysis. The
outcomes of UV spectrum of 1-3 are represented in Tables S7 and S8.
The theoretical results presented in Table S7 reveal that compound 1 gives absorbance at
274 and 297 nm with oscillator strength, f = 0.454 and 0.135, respectively. The same data for
compound 2 was observed as 283 and 295 nm with f = 0.303 and 0.191, respectively. Similarly,
3 gave 278 and 291 nm with f values 0.317 and 0.175, respectively. The aforesaid excitations of
1-3 are allowed transitions however, the known prohibited transitions are 289 and 294 for 1, 288
and 295 for 2 and 290 and 304 nm for 3 because they were found with zero magnitude of
oscillator strengths.
Tabulated data for compounds 1-3 (Table S8) reveal that compound 1 exhibits wavelength
250 and 234 nm with associated f values 0.539 and 0.115, compound 2 gives values at 251 and
266 nm with f 0.681 and 0.097 in the same way and two values 247 and 264 nm with f = 0.673
and 0.091 were observed for compound 3. The aforesaid excitations are allowed transitions
however, prohibited transitions are those with wavelength frequency of 235 and 269 (1), 237 and
268 (2) and 244 and 267 (3) because they possessed zero magnitude of oscillator strengths.
The calculated data represented in Tables S7 and S8 were based on B3LYP and CAM-
B3LYP, respectively. These give an easy understanding of comparison that B3LYP calculations
ended up with higher wavelengths and lower oscillator strengths while reverse was observed for
CAM-B3LYP.
3.1.8. Vibrational Analysis
As it is discussed that the DFT studies were carried out with the intent to have a clear
understanding of vibrational modes and stability (absence of imaginary frequency) for

compounds 1, 2 and 3 at B3LYP/6-311G(d,p) level of theory under solvent free conditions (gas
phase). The number of atoms in 1, 2 and 3 are 30, 36 and 42, respectively with symmetry point
group C1. Their FT-IR spectra are given in Figures S8-S10 (Supplementary Information), the
peaks observed corresponding to stretching frequencies of all-important bonds are within
expected regions.
3.1.9. Natural Population Analysis (NPA)
The Mulliken atomic charges of compounds 1-3 were determined with Time Dependent
DFT (TD-DFT) at B3LYP level of theory with basis set 6-311G (d,p) as presented in Figure 9
and Figures S11 and S12. Atomic charge transformation process normally takes place in
reactions and the electrostatic potential on external surface has to be calculated through theory
[42]. The bonding capacity and molecular confirmation are predicted on the basis of electronic
charges of respective atoms. The data pertaining to Mulliken population [43] reveal that unequal
distribution of electron density over the benzene ring is because of the presence of more
electronegative atoms O and N in compounds 1-3. Our concern is to describe the electron
distribution over the crystal and to explore the reactivity of the figured charges in the quantum
chemical approach [43].
Moreover, Mulliken population examination displays that there is no discrepancy in charge
distribution over H-atoms. The positive charges over H-atoms are because of the negative
charges of carbon atoms. The oxygen and nitrogen atoms present in entitled compounds
containing high negative charges and they enforce a large negative charge on some carbon atoms
because of resonance process.

Figure 9: Natural population analysis of compound 1, see Figures S11 and S12 for compounds 2
and 3.
3.1.10. Frontier Molecular Orbitals (FMOs)
The FMOs hold a significant place in the optical and electric properties and are used in
interpreting the chemical stability of species [45-50]. The energy gap of FMOs is an appreciated
parameter to get knowledge concerning the dynamic stability and chemical reactivity of species.
The HOMO/LUMO energies were obtained such as -7.36 /-2.61 eV, -7.24/-2.46 eV and -
6.93/-2.24 eV respectively for 1, 2 and 3. A chemical system contains a greater energy difference
between HOMO and LUMO orbitals might be less reactive as compared to that one which
contains a smaller gap. For compounds 1, 2 and 3, the calculated HOMO-LUMO energy gap was
4.75, 4.79 and 4.69 eV respectively, indicating that the compound 3 has more reactivity than 1
and 2.
Table 5: Frontier molecular orbitals energy calculated for compounds 1-3, units in eV.
Compounds
MO(s)
1
2
3
Energy
-7.36
-2.61
-7.39
-1.46
-7.46
∆
E
Energy
-7.24
-2.46
-7.26
-1.30
-7.32
∆
E
Energy
-6.93
-2.24
-6.94
-1.09
-7.12
∆E
HOMO
4.75
4.79
4.69
LUMO
HOMO-1
LUMO+1
HOMO-2
5.93
6.83
5.96
6.79
5.85
6.69

-0.63
-7.59
-0.48
-0.53
-7.36
-0.32
-0.43
-7.17
-0.23
LUMO+2
HOMO-3
LUMO+3
7.11
7.04
6.94
HOMO: Highest Occupied Molecular Orbital and LUMO: Lowest Unoccupied Molecular Orbital
HOMO (1)
LUMO (1)
HOMO (2)
LUMO (2)
HOMO (3)
LUMO (3)
Figure 10: FMOs of compounds 1-3.
The electron density in HOMO of compound 1 is dispersed on the 1,4-bis((1H-pyrazol-1-
yl)methyl)benzene fragment which is almost the whole structure except the carbonyl groups, in
the same way compounds 2 offers 1,4-bis((1H-pyrazol-1-yl)methyl)benzene fragment to take up
the electron density which is also almost the whole structure except the carbonyl groups and

methyl groups. However, it is different in case of 3, in which the electron density is dispersed on
the 5-methyl-1H-pyrazole fragment which is a minor portion of the structure (Figure 11).
3.1.11. Global Reactivity Parameters (GRPs)
The GRPs such as I (Ionization potential), A (electron affinity), X (electronegativity), η
(global hardness), ꢀ (chemical potential), ω (global electrophilicity) and σ (global softness) were
calculated using the FMOs energies for entitled compounds [50]. These chemical quantities can
be seen in Table 6.
Table 6: Global reactivity parameters (eV) of entitled derivatives 1, 2 and 3
Compounds
I
A
1.20
X
4.96
η
3.75
ω
3.27
σ
0.13
ꢉ
8.71
-4.96
1
2
3
6.93
8.83
2.24
1.35
4.59
5.09
2.34
3.74
-4.59
-5.09
4.49
3.46
0.21
0.13
In broad context, the electron donating and accepting capability of molecules is
distinguished with the help of ionization potential and electron affinity values, respectively. The
ionization potential values of 1-3 were established to be much greater than their electron affinity
values. The chemically hardness values were found to be 3.75, 2.34 and 3.74 eV for 1, 2 and 3
respectively. However, the chemically softness values were found to be 0.13, 0.21 and 0.13 eV
for 1, 2 and 3 respectively. These results indicate that investigated compounds have low
reactivity and show a good agreement with NBO and SC-XRD findings.
3.1.12. Density of States (DOS)
The DOS of compounds 1-3 were determined by the Gauss Sum software and the results
obtained therefrom are shown in Figure S13. The DOS spectrum provides enough informations
in relation to the population analysis per orbital in a certain energy range (energy range of the
spectrum is 0 to -20 eV). The CO groups and pyrazole rings are major contributors in high
energy range of -8 to -10 eV, which is the highest contribution and has substantial influence on
nonlinear optical properties of the material. The observation obtained are in close agreement with
FMOs analysis where the maximum electron density is spread over pyrazole substituents [51].

3.1.13. Non-Linear Optical Properties (NLO)
Electronic properties are accountable for the strength of optical response which rely on the
linear and nonlinear responses (polarizability, α and hyper polarizabilities, β and γ etc.) [52,54].
For the estimation of non-linear optical properties of 1-3, these linear and nonlinear responses
have to be evaluated. The <α> values were calculated by the set of theory as described above.
The average polarizability values of 1-3 accompanied by their major contributing tensors in three
different ways, with no solvent effect, with ethanol and acetonitrile as solvent. However, our
compounds are centrosymmetric, so, first hyper polarizabilities (β) values could not be
calculated.
Table 7: Dipole polarizabilities and major contributing tensors (a.u.) of compounds 1-3.
Solvent
Polarizability
1
2
3
304.516
182.685
81.649
339.12
214.15
102.03
218.43
413.62
298.55
132.22
281.46
415.061
300.767
133.278
283.036
356.079
248.925
125.964
243.656
431.296
341.882
166.574
313.251
432.780
344.313
168.009
315.034
αxx
αyy
αzz
αtotal
αxx
αyy
None
189.616
371.086
259.379
104.785
245.083
372.296
261.429
105.579
246.434
Ethanol
αzz
αtotal
αxx
αyy
αzz
αtotal
Acetonitrile
The data pertaining to the average <α> values and their tensors are represented in Table 7.
The dipole polarizabilities values obtained were 189.616, 218.43 and 243.656 a.u. for
compounds 1-3, respectively. Where the compound 3 exhibited higher value than the other
members of the 1 and 2. The HOMO/LUMO energy gap influences the molecular polarizability
and has an inverse relationship with linear polarizability. The compounds with small energy gap
endorse large linear polarizabilities. Compound 3 was found with smaller energy gap as
compared to 1 and 2 (Table 5). Subsequently, it shows more linear polarizability values (Table
7).
3.1.14. Molecular Electrostatic Potential (MEP)
The 3D plot of total electron density is also called molecular electrostatic potential (MEP).
The MEP is descriptor for elucidation of non-covalent interactions (NCIs) in molecules. The

MEP, a plot of electrostatic potential and constant electron density surface, is taken for
foreseeing sites and relative reactivity towards electrophilic or nucleophilic attack, in studies of
biological recognition, interactions between homo- or heterosynthons and in correlation and
prediction of scope of macroscopic properties. The color code is sorted from deep red to deep
blue, where blue indicates a nominal concentration of electrons and high density of electrons is
shown by red color in the figure. The charge contribution can be systematic in decreasing order
as, red > orange > yellow >green > blue.
It further elaborates that negative zones (red and yellow) are supposed to be favorite sites
for electrophilic attack and the positive zones (blue) can possibly allow nucleophilic attack. The
Figure S14 indicates a negative potential restrained over O and N atoms, whereas positive region
is located around H atoms for 1, 2 and 3.
4. Conclusion
Reaction between terethaloyl dichloride and pyrazole derivatives afford corresponding
products as a result of N-C coupling. The computed bond lengths as well as bond angles are in
close agreement with SC-XRD data. The error calculations of RMSE revealed that both CAM-
B3LYP and B3LYP functionals are in good agreement with respect to each other. The NBOs
analysis indicate that molecules are involved in the process of intra-molecular charge transfer.
The Hirshfeld surface analysis of the compounds support higher molecular stability.
Furthermore, NBOs based hyper conjugative interaction values were found with greater
magnitude which endorses the same molecular stability fact. For compounds 1,2 and 3, the
calculated HOMO-LUMO energy gap was 4.75, 4.79 and 4.69 eV, respectively, indicating that
the compound 3 is more reactivity than 1 and 2. The band gap of compound 3 is slightly smaller
than compounds 1 and 2 the smaller value is because of electron-donating ability of the attached
methyl groups. The global reactivity parameters have been calculated using the energies of
FMOs. The chemical hardness values of 1-3 were found greater as compared to their softness
values which indicated that the investigated compounds have low reactivity and show a good
agreement with NBOs and SC-XRD finding. Mutual comparison of compounds 1-3, indicates
that compound 3 has highest <α> values. The effect of solvent on the dipole polarizabilities of

compounds was determined and the higher average polarizabilities <α> values of 1-3 were found
in acetonitrile than ethanol and free solvent conditions.
Acknowledgement
EK, ZG and AS acknowledge the financial support from Higher Education Commission of
Pakistan under NRPU project No. 1488.
Supporting information
Supplementary information Figures and Tables pertaining to this work are given in a
separate file, available in online version of this paper. Crystal data (CIFs) have been submitted to
Cambridge Crystallographic Data Center CCDC No 19556722 (1), 1955620 (2) and 1955621 (3)
these data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK;
Fax: (+44) 1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk.
Conflict of interest
Authors declare no conflict of interest
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