Structural, spectral, and theoretical investigations of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid

Article abstract of DOI:10.1007/s11164-015-2292-y

The present research work has focused on combined experimental and theoretical studies of one of the biologically important pyrazole-4-carboxylic acid derivatives, viz. 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid (C₁₁H₁₀N₂

Full text of DOI:10.1007/s11164-015-2292-y

Res Chem Intermed
DOI 10.1007/s11164-015-2292-y
Structural, spectral, and theoretical investigations
of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid
1
2
•
Shivapura Viveka
1
•
Gowda Vasantha
3
•
Dinesha
•
Shivalingegowda Naveen
Neratur Krishnappagowda Lokanath
Gundibasappa Karikannar Nagaraja
4
•
1
Received: 9 July 2015 / Accepted: 21 September 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract The present research work has focused on combined experimental and
theoretical studies of one of the biologically important pyrazole-4-carboxylic acid
derivatives, viz. 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid (C H N O ).
1
1 10 2 2
The starting material 5-methyl-1-phenyl-1H-4-pyrazolecarboxylate (1) was
obtained by the cyclocondensation of ethyl acetoacetate, N,N-dimethylformamide
dimethyl acetal (DMF-DMA), and phenylhydrazine, which upon basic hydrolysis
yielded the corresponding acid (2). The target compound (2) was characterized by
1
13
H and C NMR (solution in DMSO), Fourier transform infrared (FT-IR) spec-
troscopy, thermo gravimetric analysis, and by single-crystal X-ray diffraction
technique. The single crystals of compound (2) were obtained at room temperature
by slow evaporation of ethanol as solvent and crystallized in the space group P2 /
1
1
n of monoclinic system. The experimental FT-IR and H and C NMR chemical
13
shifts have been compared to those calculated by means of density functional theory
(DFT) at the B3LYP/TZ2P level of theory. The continuum-like screening model
was used for geometry optimization of a single molecule and for subsequent cal-
&
Gundibasappa Karikannar Nagaraja
nagarajagk@gmail.com
1
2
3
4
Department of Studies in Chemistry, Mangalagangotri, Mangalore University, Konaje 574199,
India
Chemistry of Interfaces, Division of Chemical Engineering, Lule a˚ University of Technology,
9
7187 Lule a˚ , Sweden
Institution of Excellence, Vijnana Bhavana, Manasagangotri, University of Mysore,
Mysore 570006, India
Department of Studies in Physics, Manasagangotri, University of Mysore, Mysore 570006,
India
123

S. Viveka et al.
culations of NMR shielding constants in solution (DMSO). Finally, the HOMO–
LUMO energy levels were also constructed to study the electronic transition within
the molecule by time-dependent TD-DFT method.
Keywords Pyrazole Á Crystallization Á FT-IR spectrum Á Thermo gram Á Crystal
structure Á NMR Á DFT
Introduction
Pyrazoles have been studied for more than a century as an important class of
heterocyclic compounds. Pyrazoles are the most important privileged scaffolds
found in biologically active molecules and agrochemicals [1]. The pyrazole ring
occurs as the core moiety in a variety of leading drugs such as Celebrex, Viagra, and
Rimonabant, etc. [8]. Pyrazole, and most of its analogues, have been applied to treat
inflammatory [2, 3], diabetic [4], cancer [5], bacterial [6], and analgesic [7] diseases.
This class of compounds and its derivatives have been described as useful synthons
of various heterocycles and has led to widespread interest in developing new
strategies to access these valuable structures. Modification of the structural profile
by altering the 1-, 3-, or 4-position substituent in the pyrazole ring affects some
bioactivities remarkably [9–11]. The incorporation of acid group into organic
molecules, including pyrazole derivatives, has a potential to modify the bioactiv-
ities. The presence of this specific functional group opens up a wide range of
possibilities for further modification. Moreover, acid functional groups have played
a crucial part in the development of theory of heterocyclic compounds, and also they
are used extensively in organic synthesis [8, 12–14].
In continuation of our work on the synthesis and discovery of pyrazole
derivatives [6, 15, 25–27], herein we describe the synthesis and structural
investigations of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid (2). The com-
pound (2) was synthesized by the base hydrolysis of the corresponding ester (1)
[
25]. In our earlier work, we reported the structural analysis of the ester (1) by
single-crystal X-ray diffraction and thermo-gravimetric analysis (TGA) techniques
along with the molecular and electronic structure analysis using DFT methods [15].
In order to comprehend and understand the experimental studies, further theoretical
studies need to be carried out aiming to describe the fundamental properties of the
present acid.
In order to understand the molecular/electronic structure and properties of
pyrazole derivative, we present combined experimental and theoretical investiga-
tions of our target acid and the results are compared with our previous work on the
corresponding ester [15]. We also present our results on the differential scanning
calorimetry (DSC) analysis, which gives information of the heat flow associated
with material transition as a function of time and temperature [16], and thermo-
gravimetric analysis (TGA), which measures the amount and rate of change in the
mass of the sample as a function of temperature [17] of the compound (2).
1
23

Structural, spectral and theoretical investigations of…
Experimental
Materials and methods
All reagents were purchased from Spectrochem Pvt. Ltd., India, and used
without further purification. Infrared spectra was recorded on a Shimadzu FT-IR
-
1
spectrophotometer in the range of 400–4000 cm using the KBr pellets. TGA
and DSC were measured using a PerkinElmer Thermal Analysis Instrument and
Netzsch Instrument, respectively. Elemental analysis was carried out by using a
VARIO EL-III (Elementar 10 Analysensysteme GmBH) instrument. Melting
1
points were determined in open capillary tubes and were uncorrected. The H
NMR spectra was recorded on a Bruker AV III 400 NMR spectrometer with a
5-mm PABBO BB-1H probe using dimethyl sulfoxide (DMSO-d ) as solvent.
6
The X-ray intensity data were collected at a temperature of 296 K on a Bruker
Proteum2 CCD diffractometer equipped with an X-ray generator operating at
˚
4
5 kV and 10 mA, using Cu-K radiation of wavelength 1.54178 A. Data were
a
collected for 24 frames per set with different settings of u (0° and 90°), keeping
the scan width of 0.5°, exposure time of 5 s, the sample-to-detector distance of
4
5.10 mm, and 2h value at 46.6°. A complete data set was processed using
SAINT PLUS [18]. The parameters of the molecular geometry, electronic
structure, and harmonic frequency calculations were calculated using the
Amsterdam Density Functional package (ADF 2014.01) [19, 20]. In all of our
calculations, we have used generalized gradient approximation (GGA) with
Perdew–Burke–Ernzerhof (PBE) or hybrid B3LYP density functionals [21]. The
coordinates from the X-ray diffraction data were used as the starting structure for
geometry optimization by DFT method. The geometry was fully optimized at the
PBE/TZ2P (triple-f basis set with two sets of polarization functions) basis set
level followed by the vibrational frequency calculations (no imaginary frequen-
cies). The analytical frequency calculations are fully parallelized and linearly
1
13
scaled. The H and C NMR shielding constants and the Frontier molecular
orbitals (FMOs) were obtained for the fully optimized monomer of the titled
compound at the scalar relativistic ZORA (zeroth-order regular approximation)
level of theory using B3LYP/TZ2P methods and the orbitals are plotted using
the ADF view program.
Synthesis of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid (2)
The synthesis of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylate (1) is described in
our previous report [25]. In the present work (Scheme 1), a mixture of compound
(
1) (1.29 g, 5 mmol) and potassium hydroxide (0.28, 5 mmol) in ethanol (25 ml)
was heated under reflux for 5 h and the solvent was distilled in vacuo. The residual
mass was poured over crushed ice and neutralized the alkaline solution with 10 %
hydrochloric acid. The precipitated crude product was filtered, washed with water,
dried, and recrystallized from ethanol to give white crystals of compound (2). Yield
1
.10 g, (85 %). m.p. 168–170 °C.
123

S. Viveka et al.
O
N
O
O
N
O
OEt
O
O
OH
DMF-DMA
Ph-NH-NH2
NaOH
H+
OEt
OEt
N
N
N
(
1)
(2)
Scheme 1 Proposed reaction scheme for the formation of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic
acid (2)
Elemental analysis for C H N O (%): C (65.34); H (4.98); N (13.85). Found:
1
1 10 2 2
C (65.39); H (4.95); N (13.90).
Results and discussions
Thermal analysis (DSC-TGA)
The thermal properties of the 8.07 mg of 5-methyl-1-phenyl-1H-pyrazole-4-
carboxylic acid (2) were investigated in the 25–500 °C temperature range under
nitrogen atmosphere at a heating rate of 20 °C/min. The descending TGA thermal
curve (Fig. 1) of 8.07 mg of indicates the stages of decomposition at intervals in the
Fig. 1 Thermal analysis of compound 2
1
23

Structural, spectral and theoretical investigations of…
temperature range 20 °C up to 500 °C. The decomposition of the crystal was
observed in the temperature range of 220–300 °C. There was no weight loss up to
the decomposition temperature, which indicates the absence of moisture in the
crystal. The major weight loss that appears in the TGA curve is reflected in the
second endothermic peak of the DSC curve. From the DSC curve, the melting point
of the material was observed at 171 °C. The sharpness of exothermic peak showed
the existence of a good degree of crystallinity and purity of the sample. Further, it
indicates that there exists no phase transition before this temperature. Conversion
from ester to acid in a 5-methyl-1-phenyl-1H-pyrazole increases the thermal
stability of the pyrazole (ester decomposes within 271 °C).
1
13
H and C NMR spectral analysis
1 13
The H and C NMR spectra of compound (2) are shown in Figs. 2 and 3,
1
respectively. In the H NMR spectrum, a singlet at d 2.49 ppm (s, 3H) and the
multiplets (m, 5H) in the range of d 7.48-7.58 ppm can be assigned to methyl and
phenyl protons, respectively. The downfield shifted peak at d 7.96 ppm (s, 1H) can
be assigned to the pyrazole proton. The comparatively sharp resonance line for OH
proton of the acid at higher d 12.42 ppm (s, 1H) value is due to the relatively high
energy intermolecular H-bonding interactions between acid. The high-resolution
1
3
C NMR spectrum clearly distinguishes all non-equivalent carbons of compound
2). For example, the most downfield-shifted resonance line (164.52 ppm) can be
assigned to the carboxylic acid carbon without any ambiguity. The resonance lines
(
1
Fig. 2 H NMR (400 MHz) spectrum of compound 2 (solution in DMSO)
123

S. Viveka et al.
1
Fig. 3 C NMR (100 MHz) spectrum of compound 2 (solution in DMSO)
3
2
in the range of d 112.97–143.21 ppm are similarly assigned to the sp hybridized
carbons. The atom-wise assignment of H and C chemical shifts for the titled
compound (2) is given in Table 1. The regression plot showing the correlation
1
13
1
3
between the calculated and the experimental C chemical shift is depicted in Fig. 4.
The slope, lower than 1, indicates deviation from the linearity of the calculated
values with respect to the experimental results. These discrepancies could be
attributed to the fact that there is a strong intermolecular hydrogen bonding between
the acids in solution, which was neglected during both the geometry optimization
and the NMR chemical shift calculations.
Table 1 Experimental and
DFT (B3LYP/TZ2P) calculated
13
1
C chemical shifts
H chemical shifts
1
13
H and C chemical shifts for
title compound (2)
Atoms
Expt.
Calc.
Atoms
Expt.
Calc.
C7
164.52
143.21
141.61
138.6
163.7
147.8
140.2
138.9
128.2
128.2
125.0
111.3
12.2
–OH
12.44
7.96
12.0
8.4
C5
Py–H
Ar–H
C3
7.46–7.57
2.49
7.8–8.0
2.3
C10
–CH
3
C12, C14
C13
129.28
128.53
125.32
112.97
11.53
C11, C15
C4
C6
1
23

Structural, spectral and theoretical investigations of…
B3LYP/TZ2P/COSMO
200
150
100
y = 0.9363x - 2.0526
R² = 0.9981
50
0
0
50
100
150
200
13C Experimental chemical shiꢀ (ppm)
13
Fig. 4 Experimental versus calculated C chemical shifts for compound (2) in DMSO solution
FT-IR spectral analysis
The theoretical and experimental FT-IR spectrum of compound (2) is shown in
Fig. 5. The experimental IR vibrational frequencies are assigned as follows (DFT
calculated values are within parenthesis).
Pyrazole acid dimers are identified by the bonded O–H stretching absorption at
-
1
419 (3632) cm . The band at 2978 (2968–3100) cm can be assigned to the
-1
3
symmetric and asymmetric C-H (methyl and phenyl) stretching frequencies of the
compound. In addition, due to the monomer–dimer equilibrium, the intramolecular
-
1
hydrogen bonding resulted in lowering of C=O 1712 (1715) cm
frequency, which depends upon the degree of hydrogen bonding. The stretching and
stretching
-
1
bending vibrations for pyrazole ring C–C and C–N bonds appeared at 1531 cm
1542).
Comparison of the vibrational frequencies calculated at PBE/TZ2P shows
reasonably good agreement with experimental values with minor exceptions. For
(
-
1
example, the calculated O–H stretching vibration is about 200 cm away from the
-
experimental value. Similarly, the vibrational peaks at around 2300 and 1600 cm
1
are not seen in the calculated spectrum. These discrepancies between the calculated
and experimental vibrational frequencies are because the calculations were
performed on a single molecule in the gaseous state unlike the experimental result,
which was obtained for the powdered sample and also the molecules are
characterized by strong intermolecular interactions. In evidence, the X-ray structure
reveals the presence of strong intermolecular hydrogen bonding (O–HÁÁÁO) forming
dimers in solid state. On the other hand, the DFT-optimized structure (monomer)
has slightly different geometry than the experimental one.
Single-crystal X-ray diffraction
A colorless, rectangular-shaped single crystal of dimensions 0.3 9 0.27 9 0.25 mm
of the title compound was chosen for an X-ray diffraction study. The structure was
123

S. Viveka et al.
Fig. 5 Experimental (FT-IR spectra using KBr) and theoretical vibrational spectrum (PBE/TZ2P theory
level) of the compound 2
2
solved by direct methods and refined by full-matrix least-squares method on F
using SHELXS and SHELXL programs [22]. All the non-hydrogen atoms were
revealed in the first-difference Fourier map itself. All the hydrogen atoms were
positioned geometrically and after several cycles of refinement, the final-difference
Fourier map showed peaks of no chemical significance and the residuals saturated to
0
.0505. The geometrical calculations were carried out using the program PLATON
23]. The molecular and packing diagrams were generated using the software
[
MERCURY [24].
The details of the crystal structure and data refinement are given in Table 2. The
list of bond lengths and bond angles of the non-hydrogen atoms, together with DFT
1
23

Structural, spectral and theoretical investigations of…
calculated values, are given in Tables 3 and 4, respectively. Figure 6 represents the
ORTEP diagram of the molecule with thermal ellipsoids drawn at 50 % probability.
A detailed analysis of the molecule shows that all the bond lengths and angles are
within the expected ranges. The molecule is non-planar. The bond lengths and bond
angles are normal and the molecular conformation is characterized by a dihedral
angle of 64.05 (13)°, which is much higher than the reported value of 56.69(10)° for
ethyl 5-methyl-1-phenyl-1H-pyrazole-4-carboxylate [15]. The carbonyl group at C7
is oriented in a ?syn-periplanar conformation as indicated by the torsion angle
value of 3.3(4)° for O8–C7–C4–C5, indicating that it lies in the plane of the
pyrazole ring.
The crystal structure is stabilized by the intermolecular O–HÁÁÁO hydrogen bond
˚
(
dimers. The packing of the molecules when viewed down along the c axis indicates
O9—H9ÁÁÁO8, 1.81 A, 165°) (Fig. 7), which links the molecules to form inverted
that these inverted dimers run into zig zag chains (Fig. 8).
Table 2 Crystal data and structure refinement table of compound (2)
Parameter
Value
CCDC deposit no.
Empirical formula
Formula weight
1047065
11 10 2 2
C H N O
202.21
293(2) K
Temperature
˚
Wavelength
1.54178 A
1
Monoclinic, P2 /n
Crystal system, space group
Unit cell dimensions
˚
a = 5.6872(5) A, b = 26.979(2) A
˚
˚
c = 6.7978(6) A
b = 105.379(6)°
3
˚
1005.66(15) A
Volume
3
Z, Calculated density
Absorption coefficient
4, 1.336 Mg/m
0.775/mm
F
(000)
424
Crystal size
0.30 9 0.27 9 0.25 mm
3.28–63.97°
-6 B h B 5, -31 B k B 30, -7 B l B 7
Theta range for data collection
Limiting indices
Reflections collected/unique
Refinement method
7821/1648 [R(int) = 0.0660]
2
Full-matrix least squares on F
Data/restraints/parameters
2
Goodness-of-fit on F
1648/0/137
1.101
Final R indices [I [ 2r(I)]
R indices (all data)
R1 = 0.0505, wR2 = 0.1331
R1 = 0.0678, wR2 = 0.1575
-
3
˚
0.166 and -0.228 e A
Largest diff. peak and hole
123

S. Viveka et al.
PBE/TZ2P
˚
Table 3 Bond lengths (A)
Atoms
Length
PBE/TZ2P
Atoms
Length
N1–C5
N1–N2
N1–C10
N2–C3
C3–C4
C4–C5
C4–C7
C5–C6
1.353(3)
1.375(3)
1.436(3)
1.320(3)
1.401(4)
1.390(3)
1.447(3)
1.484(3)
1.373
1.368
1.424
1.324
1.419
1.400
1.459
1.489
C7–O8
1.261(3)
1.274(3)
1.375(4)
1.381(3)
1.375(4)
1.381(4)
1.371(4)
1.385(4)
1.222
1.371
1.399
1.399
1.395
1.395
1.397
1.393
C7–O9
C10–C15
C10–C11
C11–C12
C12–C13
C13–C14
C14–C15
Table 4 Bond angles (°)
Atoms
Angle
PBE/TZ2P
Atoms
Angle
PBE/TZ2P
C5–N1–N2
C5–N1–C10
N2–N1–C10
C3–N2–N1
N2–C3–C4
C5–C4–C3
C5–C4–C7
C3–C4–C7
N1–C5–C4
N1–C5–C6
C4–C5–C6
113.5(2)
127.8(2)
118.6(2)
103.4(2)
112.5(2)
105.5(2)
127.8(2)
126.4(2)
105.0(2)
122.8(2)
132.1(2)
112.8
128.9
118.2
104.7
111.9
105.2
128.0
126.3
105.3
125.0
129.6
O8–C7–O9
122.5(2)
120.7(2)
116.8(2)
120.9(2)
119.1(2)
119.9(2)
119.3(2)
120.5(2)
119.6(2)
120.6(3)
119.1(2)
121.7
126.4
111.9
120.4
118.8
120.9
119.6
120.2
119.6
120.4
119.7
O8–C7–C4
O9–C7–C4
C15–C10–C11
C15–C10–N1
C11–C10–N1
C12–C11–C10
C11–C12–C13
C14–C13–C12
C13–C14–C15
C10–C15–C14
Gas-phase geometry optimization and electronic structure–property
calculations
To compare the structural parameters obtained from the theoretical calculations and
the single-crystal X-ray diffraction, we performed geometry optimizations of both
the monomeric and dimeric molecules of compound (2) (Fig. 9). The analytical
frequency calculations on the X-ray diffraction structures (both monomer and
dimer) resulted in imaginary frequency values, which is due to the negative
vibrational force constants. However, the fully optimized structures resulted all
vibrational force constants positive and no imaginary frequency has appeared. In
other words, the optimized structures were sitting at a true minimum at the potential
energy surface. The theoretical bond lengths and bond angles for the monomer are
given in Tables 3 and 4 together with the experimental values. The experimental
bond parameters were well reproduced by the calculations with few exceptions. The
1
23

Structural, spectral and theoretical investigations of…
Fig. 6 ORTEP of the molecule with thermal ellipsoids drawn at 50 % probability
Fig. 7 A view of the crystal packing of the title compound showing inverted dimers
˚
bond lengths were overestimated by ca 0.01 A for all phenyl C–C bonds whereas
the variations of bond angles were all uneven. The largest deviations were observed
˚
for C–O bond length (0.1 A) and O–C–C bond angles (4°–6°).
TD-DFT calculations
In order to study the characteristics of electronic transition and oscillator strength
(
F) of compound (2), a single-point, time-dependent DFT calculation of lowest
singlet–singlet transitions were performed by employing the B3LYP functional at
scalar-relativistic ZORA level. The results are listed in Table 5.
Figure 10 lists the energies and percentage composition of few FMOs viz.
LUMO?1, LUMO, HOMO, and HOMO-1, calculated using PBE and B3LYP
density functionals. It is a known fact that pure GGA functionals such as PBE
generally underestimate the band gap. The calculated energy difference between
HOMO and LUMO for the title complex is 4.18 eV (PBE) and 5.48 eV (B3LYP).
The HOMO is mostly composed of both phenyl and pyrazole carbons as well as the
pyrazole nitrogens with small contributions from the oxygen atoms whereas the
LUMO is almost spread over the entire molecule. The two major electronic
transitions for the compound exhibiting a large oscillator strength and assigned to
123

S. Viveka et al.
Fig. 8 Packing of the molecules when viewed along the c axis. The dotted lines represent inter-
molecular hydrogen bonds linking the molecules into zig zag chains
Fig. 9 The DFT optimized structure overlaid with monomer of the X-ray diffraction structure (PBE/
TZ2P level of theory)
1
23

Structural, spectral and theoretical investigations of…
Table 5 TD-DFT calculation
TD-DFT state
E/a.u.
E/eV
F
of excitation energies (E) and
oscillator strength (F) of the
S
0
S
1
S
2
S
3
S
4
S
5
S
6
S
7
S
8
S
9
0.18153
0.18484
0.18854
0.19277
0.20548
0.20723
0.21196
0.21235
0.21980
0.22574
4.93979
5.02965
5.13031
5.24552
5.59127
5.63888
5.76760
5.77835
5.98108
6.14278
0.410400
0.003989
0.002504
0.033990
0.000107
0.039050
0.106900
0.172400
0.000239
0.032760
lowest excited singlet–singlet
states
Orbitals
Frontier molecular orbitals (FMOs)
Energy
C%
N%
-
O%
-
LUMO+1
-
(
1.774
92.1
-0.947)
(90.4)
LUMO
-
(
2.249
77.1
4.6
8.5
-1.478)
(76.2)
(5.8)
(7.6)
HOMO
-
(
6.266
74.7
16.4
2.3
-6.925)
(72.8)
(15.3)
(1.3)
HOMO-1
-
(
6.428
40.5
26.9
16.8
(4.8)
-7.221)
(50.4)
(31.6)
Fig. 10 Frontier molecular orbital (FMO) analysis, energies, and percent atomic contribution to the
frontier molecular orbitals of the title compound at the PBE and B3LYP (within parenthesis) scalar
relativistic ZORA level with TZ2P basis set
123

S. Viveka et al.
S –S , which corresponds essentially to the HOMO–LUMO, HOMO-1-LUMO,
0
1
HOMO–LUMO?1, HOMO–LUMO?2, HOMO-2-LUMO excitations. HOMO-
shows orbital contributions from the pyrazole ring alone whereas LUMO ? 1 is
1
composed of orbitals of phenyl ring (except C8 and C11). The HOMOs are
generally of bonding character, while the LUMOs are mostly antibonding in nature
and essentially delocalized over the entire molecule.
Conclusions
The present study reports the successful synthesis and single-crystal X-ray
diffraction analysis of 5-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid. The titled
compound was crystallized in the space group P2 /n of monoclinic system and
1
structure was stabilized by the intermolecular O–HÁÁÁO hydrogen bond. The DFT-
1
13
based H and C NMR chemical shift calculations were in good agreement with the
experimental results. The assignments of most of the fundamental vibrational modes
of the title compound were made based on the results of the DFT calculations. Both
HOMO and LUMO is delocalized over the phenyl and pyrazole group with small
contributions from the oxygen atoms whereas the HOMO-1 and LUMO?1 are
composed of either phenyl or pyrazole groups, respectively. All the experimental
results are successfully compared with our previous reports of 5-methyl-1-phenyl-
1
H-4-pyrazolecarboxylate.
Acknowledgments The authors are grateful to the Institution of Excellence, Vijnana Bhavana,
University of Mysore, India, for providing the single-crystal X-ray diffractometer facility. The authors
gratefully acknowledge the DST-PURSE for the financial assistance. The authors thank Mangalore
University for IR, DSC and TGA instrumental facilities. We are grateful to the Indian Institute of Science,
Bangalore, for the NMR facility.
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