Selective CO2 adsorption and Lewis acid catalytic activity towards naphthimidazole synthesis by a Zn-MOF

Article abstract of DOI:10.1016/j.poly.2020.114584

A two-fold interpenetrated, three dimensional Zn-based porous MOF, {[Zn(BPBA)Cl]?5H₂O}_n (1) [BPBA = 3,5-bis-(4-oxo-4H-pyridin-1-yl)-benzoate], has been synthesized at high temperature under solvothermal conditions by the in situ acidic hydrolysis of the tripodal ligand 3,5-bis-(4-oxo-4H-pyridin-1-yl)-benzonitrile (BPBN). The de-solvated MOF exhibited selective CO₂ adsorption at a temperature of 195 K and 1 bar pressure over N₂ and H₂. Interestingly, the four coordinated Zn(II) sites in the MOF exhibited high Lewis acidic heterogeneous catalytic activity for the synthesis of naphthimidazole in excellent yield without pre-activation of the MOF. The Zn(II) sites could directly coordinate to the substrate to catalyze the chemical transformation by an expansion of the coordination number. The π-π supramolecular interactions between the aromatic rings of the framework and the substrate molecule might help in the substrate activation.

Full text of DOI:10.1016/j.poly.2020.114584

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Selective CO Adsorption and Lewis Acid Catalytic Activity Towards Naph‐
2
thimidazole Synthesis by a Zn-MOF
Rashmi A. Agarwal, Dinesh De
PII:
S0277-5387(20)30241-2
DOI:
Reference:
https://doi.org/10.1016/j.poly.2020.114584
POLY 114584
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22 April 2020
Please cite this article as: R.A. Agarwal, D. De, Selective CO Adsorption and Lewis Acid Catalytic Activity
2
Towards Naphthimidazole Synthesis by a Zn-MOF, Polyhedron (2020), doi: https://doi.org/10.1016/j.poly.
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Selective CO Adsorption and Lewis Acid Catalytic Activity
2
Towards Naphthimidazole Synthesis by a Zn-MOF
a*
b
Rashmi A. Agarwal, Dinesh De
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, Kanpur,
India
Corresponding Author’s email: rashmi.a.agarwal@gmail.com
Abstract: A two-fold interpenetrated, three dimensional Zn-based porous MOF,
{
[Zn(BPBA)Cl]5H O} (1) [BPBA = 3,5-bis-(4-oxo-4H-pyridin-1-yl)-benzoate], has been
2
n
synthesized at high temperature under solvothermal conditions by the in situ acidic hydrolysis
of the tripodal ligand 3,5-bis-(4-oxo-4H-pyridin-1-yl)-benzonitrile (BPBN). The de-solvated
MOF exhibited selective CO adsorption at a temperature of 195 K and 1 bar pressure over N
2
2
and H . Interestingly, the four coordinated Zn(II) sites in the MOF exhibited high Lewis acidic
2
heterogeneous catalytic activity for the synthesis of naphthimidazole in excellent yield without
pre-activation of the MOF. The Zn(II) sites could directly coordinate to the substrate to catalyze
the chemical transformation by an expansion of the coordination number. The -
supramolecular interactions between the aromatic rings of the framework and the substrate
molecule might help in the substrate activation.
Keywords: Metal Organic Framework; Heterogeneous Catalysis; CO ; Single Crystal;
2
Naphthimidazole
1
. Introduction
Metal-organic frameworks (MOFs) are crystalline polymeric materials made up of metal ions
and multidentate bridging ligands [1]. These materials have a wide range of applications,
especially in gas adsorption [2,3] and heterogeneous catalysis [4], due to their structural
1

diversity, chemical functionality, large surface area, tuneability along with high thermal
stability.
Increasing concentrations of CO in the environment from coal fired power plants and burning
2
of fuel in automobiles create serious problems. Thus, there is an urgent need to sequestrate CO2
and reduce its excessive emissions to the atmosphere [5]. MOFs are excellent candidates for
CO capture and storage due to their unique features, such as structural diversity and permanent
2
porosity [6-9]. Presence of functional ligand moieties and open metal sites (OMSs) in the
architectures of MOFs not only enhances gas adsorption but also heterogeneous catalytic
activities. These free atoms or groups participate in making different types of non-covalent
interactions with the guest molecules [10,11]. Alternatively, the open coordination sites along
with the confined space of MOF interact with substrates and subsequently activates them to
form products.
Generally N-containing heterocyclic compounds have attracted the attention of many
researchers because of their utility as pharmaceutical and agrochemical agents due to their
biocompatibility [12-17]. Most commonly, these compounds are synthesized by the
condensation reaction of ortho-substituted aniline derivatives with carboxylic acids [18,19],
nitriles [20] and esters [21], or the oxidative cyclization of substrates with aldehydes [22,23]
and alcohols [24,25]. Recently benzimidazoles were synthesized by the reaction of 1,2-
arylenediamines with N,N-dimethylformamide (DMF) in highly acidic medium under
thermal/microwave conditions [26]. On the other hand, various benzimidazole derivatives have
been synthesized by utilizing a variety of o-phenylenediamines, N-substituted formamides and
a zinc catalyst in the presence of poly(methylhydrosiloxane) [27]. Very recently N-containing
heterocycles were obtained by CO promoted cyclization of ortho-substituted aniline
2
derivatives with DMF over a B(C F ) catalyst at 120 C [28]. Due to the requirement of toxic,
6
5 3
air-sensitive, costly reagents or highly acidic media, along with the multistep syntheses of the
2

pre-functionalized precursors, with limited success in terms of yield and selectivity, most of
the experimental procedures have disadvantages. Herein, we report for the first time a cheap
synthesis of naphthimidazole from 2,3-diaminonaphthalene and DMF at 120 C with an
excellent yield, using 1 as a Lewis acid heterogeneous catalyst.
2
. Experimental section
2
.1. Materials
Most of the reagent grade chemicals were purchased from Aldrich Chemical Company and
used as received without further purification. 4-Hydroxy pyridine was purchased from Avra
Chemicals and solvents were purchased from S. D. Fine Chemicals, India. Solvents were dried
before use.
2
.2. Physical measurements
–
1
Infrared spectra were obtained (KBr disk, 400-4000 cm ) using a Perkin-Elmer model 1320
1
spectrometer. The H NMR spectrum was recorded using a JEOL-ECX 500 FT (500 MHz and
1
25 MHz) instrument in CDCl with Me Si as the internal standard. Thermograms were
3 4
recorded on a Mettler Toledo (with a heating rate of 10 C/min) TGA instrument.
Microanalyses for the compounds were obtained using a CE-440 elemental analyser (Exeter
Analytical Inc.). Low-pressure gas adsorption measurements were performed on
Quantachrome Quadrasorb automatic volumetric instrument.
X-ray structural studies are provided in the Supporting Information.
2
.3. Synthesis of 3,5-bis-(4-oxo-4H-pyridin-1-yl)-benzonitrile (BPBN).
4
-Hydroxy pyridine (0.68 g, 7.20 mmol), 3,5-difluorobenzonitrile (0.5 g, 3.60 mmol), K CO
2
3
(1.73 g, 12.6 mmol) and DMF (15 ml) were taken in a 50 mL round bottom flask. The mixture
was stirred constantly at 80 °C (Scheme 1). After 48 h, heating was stopped and the reaction
mixture was allowed to cool down at room temperature. After that, the mixture was poured
into ice-cold water to obtain a white solid precipitate. It was filtered and air dried. Yield: 0.96
3

g, (92%). SI-MS: [M+H], m/z: 290.0934 (100%) (calcd for C H N O , 289.0851) (Fig. S1).
1
7
11
3
2
Anal. calcd. for C H N O : C, 70.59; H, 3.80; N, 14.53%. Found: C, 70.61; H, 3.82; N, 14.6%
1
7
11
3
2
–
1
IR (cm , KBr pellet): 3426 (m), 3044 (m), 2943 (m) 2245 (m), 1651 (s), 1599 (s), 1443 (s),
1
349 (s), 1248 (s), 1199 (s), 1090 (m), 892 (m), 843 (s), 690 (m), 557(m), 496 (m) (Fig. S2).
O
O
N
F
F
o
DMF, 80 C
N
2
+
N
K CO
2
3
OH
CN
CN
,5-Bis-(4-oxo-4H-pyridin-1-yl)-benzonitrile
4-pyridinol
3,5-Difluoro-benzonitrile
3
Scheme 1. Synthesis of the ligand BPBN.
.4. Synthesis of {[Zn(BPBA)Cl]5H O} (1).
2
2
n
A mixture of Zn(NO ) .6H O (0.12 g, 0.414 mmol) and BPBN (0.04 g, 0.138 mmol) was taken
3
2
2
in EtOH:H O (6 mL, 2:1 v/v) with 2 drops of dilute HCl, followed by heating at 180 C under
2
autogenous pressure in a Teflon-lined steel bomb for 3 days. Slow cooling was done to room
temperature. Colourless crystals were obtained and washed with ethanol. Yield ~68%. Anal.
calcd. for C H ClN O Zn: C, 40.98; H, 4.25; N, 5.61%. Found: C, 40.88; H, 4.2; N, 5.68%
1
7
21
2
9
–
1
IR (cm , KBr pellet): 3543 (m), 3430 (m), 3068 (w), 2924 (w), 1664 (s), 1592 (m), 1527 (s),
1
376 (s), 1193 (m), 854 (m), 577 (m) (Fig. S3).
2
.5. Procedure for the cyclization of ortho-substituted diaminonaphthalene to
naphthimidazole.
In a 50 ml round bottom flask, 2,3-diaminonaphthalene (200 mg), {[Zn(BPBA)Cl]5H O} (10
2
n
mg) and DMF (10 ml) were taken and equipped with a magnetic stirrer. The suspension was
heated at 120 C for two days. Reaction progress was checked through TLC. After completion
of the reaction, the mixture was allowed to cool down, followed by its filtration and the catalyst
was washed with DCM. The product was collected from the aqueous layer by extraction with
4

DCM. The organic layer was collected and evaporated, leaving the solid compound. The
product was recrystallized from methanol.
3
. Results and discussion
II
3
D porous Zn -framework 1 was obtained with 2-fold interpenetration through in situ acidic
hydrolysis of the BPBN ligand under solvothermal conditions at 180 C.
.1. Single crystal structure description of 1
3
Single crystal X-ray diffraction analysis revealed that compound 1 crystallized in the
monoclinic space group C2/c. The asymmetric unit consisted of one Zn(II) ion, one coordinated
chloride ion and one BPBA ligand. The nitrile group of BPBN was hydrolysed to a carboxylate
group through HCl hydrolysis. The free CN stretching of the ligand BPBN was observed at

1
2
245 cm (Fig. S2), which disappeared in the MOF. Five non-coordinated water molecules

1
were also present in the asymmetric unit. Broad bands at 3441 and 3548 cm revealed the
presence of lattice water molecules (Fig. S3). The Zn1 centre adopted a tetrahedral geometry
(
MO Cl), with coordination from two oxygen atoms of pyridine-1-ium-4-olate groups present
3
in the two different BPBA ligands and a third oxygen atom from a carboxylate group of a third
BPBA ligand (Fig. 1a). A1D zig-zag chain was formed by metal bonding with the oxygen atom
of pyridine-1-ium-4-olate, followed by formation of layered architecture by metal coordination
with one of the carboxylate oxygen atoms of the BPBN ligand. Both pyridine-1-ium rings were
perpendicular to the central benzene ring, leading to the structure’s third dimension. Hexagonal
channels were present with diameter of ~10.83 Å (considering the Van der Waals radii), as
shown in Fig. 1b, along the b axis. However, mutual interpenetration (Fig. 1c) gave rise to a
comparatively small void volume (28.72%), with a reduced diameter of ~6.3 Å of the channel
(considering the Van der Waals radii). The interpenetrated framework has been stabilised by

- non-covalent interactions between the parallel central benzene rings and between the
parallel pyridine-1-ium rings of two independent frameworks (Fig. 2). TOPOS software
5

topological analysis was performed, which revealed that Zn(II) ion has a 3-connected uninodal
3
net with point symbol 10 and topological type ths/ThSi2; 3/10/t4 (topos&RCSR.ttd) (Fig. 1d).
3
.2. Thermal stability
Thermogravimetric analysis (TGA) of compound 1 (Fig. S4) showed a sharp weight
loss of ~10.8%, ascribed to the loss of three lattice water molecules in the temperature range
092 °C. After that, a gradual weight loss of the lattice water molecule took place between 92
3
and 300°C. Above 365 °C, framework degradation started, signifying its high thermal stability.
The observed weight loss was found to be ~14.2% (calculated value ~14.4%), corresponding
to the loss of four solvent water molecules. PXRD patterns of the as-synthesized 1 showed
similar diffraction peaks compared to the simulated PXRD pattern, revealing phase integrity
of the framework (Fig. S5a and b).
(
c)
(
a)
(
b)
(
d)
Fig. 1. (a) Coordination environment around the metal centre, (b) 3D structure without
interpenetration (solvent molecules are omitted for clarity), (c) 3D structure with 2-fold
interpenetration and (d) 3-c uninodal net of 1 with the ths/ThSi2 topological type.
6

Fig. 2. - bonding interactions between parallel benzene rings and between pyridine-1-ium
rings in the 2-fold interpenetrated framework of 1.
3
.3. Gas adsorption studies
Before gas adsorption studies, activation of the sample was done by replacing all the solvent
molecules with low boiling DCM (dichloromethane) solvent molecules. To achieve this, the
crystals were immersed in DCM for 5 days, during which DCM was refreshed daily. After 5
days the framework was heated at 60 C under a high vacuum to remove the DCM solvent
molecules and to generate the activated or de-solvated compound 1a. PXRD data have been
collected for the activated compound 1a, which was similar to the as-synthesized PXRD
pattern, confirming the phase purity of the de-solvated compound as shown in Figure S5c.
Low pressure gas adsorption isotherms were measured at 77 K for N and H , and CO at 195
2
2
2
and 298 K temperatures. The de-solvated compound showed selective CO gas adsorption at
2
3
1
1
95 K, with a maximum uptake of 75 cm g along with a large hysteresis, as shown in Fig. 3.
7

2
−1
The BET surface area was found to be 153.710 m g , as calculated from the CO adsorption
2
isotherm at 195 K. In the 2-fold interpenetration, there are supramolecular - interactions
between two parallel benzene rings as well as between two parallel pyridine-1-ium rings of the
two independent frameworks (Fig. 2), which resist the reversible adsorption of CO . Extensive
2
π-π bonding interactions between the aromatic rings having exposed edges and faces stabilize
–
39
2
the CO quadrupole (CO quadruple moment 1.34 x 10 Cm ) through weak electron donation
2
2
towards CO molecules. On the other hand, dipole-quadrupole interactions take place between
2
the N atoms of the pyridine-1-ium rings and probe molecules [29]. Significant hysteresis was
observed at lower temperature (195 K) due to the compact packing of probe molecules in the
available voids, but at elevated temperature, the higher kinetic energy of CO hinders uptake
2
and dense packing in the cavities, leading to low gas adsorption with less hysteresis [30]. Due
to possessing a zero dipole moment, adsorption of H and N guest molecules did not take place
2
2
in the polar cavities of 1a because of the very weak interactions between the non-polar
adsorbate gas molecules (N and H ) and the adsorbent.
2
2
8

Fig. 3. Gas sorption isotherm of 1a at 1 atm pressure: CO at 195 and 298 K temperatures, N
2
2
and H at 77 K temperature.
2
Due to the larger void size compared to the kinetic diameters of the probe-adsorptive gas
species (CO = 3.3 Å, N = 3.64 Å and H = 2.8 Å), size selective gas uptake could be ruled
2
2
2
out [31]. The effective pore diameter (~6.3 Å) of the framework was relatively larger than the
kinetic diameter of any of the probe gases. It confirmed that the selective uptake of CO by 1a
2
was a combination of Van der Waals interactions and electrostatic interactions.
The literature reveals that modified mesoporous silica structures (with different pore
lengths) functionalized with triamine and polyethyleneimine (PEI) show higher as well as
faster CO adsorption over a very low range of CO concentrations compared to pure
2
2
mesoporous silica materials over a wide range of pressures and temperatures, as observed by
Sayari and co-workers [32-34]. CO adsorption in Na-A zeolite has been reported by Zukal et.
2
al. at 273333 K, with desorption at higher temperature due to the formation of surface
9

carbonates with a small portion of CO [35]. Zeolites are very difficult to tune according to
2
requirements.
Exceptionally high uptakes of CO have been shown by functionalized MOFs (Mg-MOF-74),
2
even in the presence of high humidity, by introducing a high density of free amine groups due
to the strong affinity of free amine groups towards CO , compared with non-functionalized
2
Mg-MOF-74 (CPO-27-Mg) with open metal sites (OMSs) under dry conditions (because in the
presence of moisture, water molecules are coordinated with the OMSs) [36-39]. Presence of
coordinatively unsaturated sites (CUS) in Cu-BTC MOF helps in CO gas uptake, accurately
2
calculated by a combined DFT-ab initio computational scheme [40]. In the present de-solvated
complex 1a, not only the higher kinetic energy of CO but also a slight contraction in the
2
3
1
framework at higher temperature (298 K) leads to gas adsorption of up to 55 cm g with a
small hysteresis. A number of MOFs display selective adsorption of CO by incorporating free
2
-N atoms, along with free carboxylate O atoms [41-43].
3
.4. Cyclization of ortho-substituted diaminonaphthalene to naphthimidazole
Naphthimidazole has important pharmaceutical properties and its derivatives have various
applications in labelling natural carbohydrates for capillary electrophoresis [44] and in mass
spectrometry detection for saccharide labelling with enhanced sensitivity [45]. Due to the
presence of the benzimidazole scaffold (N- containing heterocycles) in the structure,
naphthimidazoles have vital importance in medicinal chemistry because of various biological
activities: antiviral, antibacterial, anticancer, antihistaminic, antitubercular, antihypertensive
and anti-inflammatory agents, and also as plant growth regulators [46-51]. This is why the
synthesis of naphthimidazole is quite attractive. Various homogeneous catalysts, like strong
hydrochloric acid, polyphosphoric acid, boric acid, p-toluene sulfonic acid and some expensive
metal complexes, are generally used to catalyse the condensation reactions of aryl-1,2-diamine
and N,N-dimethylformamide (DMF)[26-28]. However, in all these cases the catalyst could not
1
0

be recovered and reused. Not only is a fresh catalyst required every time, also its removal needs
many steps to purify the compound.
In the present study, for the first time naphthimidazole has been synthesized by employing a
Zn-MOF as a heterogeneous catalyst. One most important point is that the MOF catalyst was
used as-synthesized and activation was not required. The presence of open Zn(II)-sites made 1
an excellent heterogeneous catalyst for the condensation reaction of 2,3-diaminonaphthalene
and DMF to afford naphthimidazole (Scheme 2). This is a very simple and single step reaction
towards the synthesis of naphthimidazole. The reaction has been carried out at 120 C, over 2
days in DMF solvent (10 ml) by utilizing the reactant 2,3-diaminonaphthalene (200 mg). The
progress of the reaction was checked through TLC. In the absence of catalyst 1, the reaction
did not proceed, even after 24 hrs (entry 1). TLC showed no new spot other than that of the
reactant. To check the real effect of the catalyst, the reaction has been carried out in the
presence of ZnCl . In this case also the reaction did not proceed appreciably (entry 2), but in
2
the presence of catalyst 1 (10 mg, 5 wt%) the reaction was initiated and could be completed
within 2 days with an excellent isolated yield (95%) (entry 5 and Fig. S6-S8). In the same way
higher temperature (120 C) was also found to be an essential requirement for this reaction.
We tried the reaction at room temperature as well as at 80 C, resulting in sluggish reactions
(entries 3 and 4).
Under the optimum reaction conditions, using 1,2- diaminobenzene as a substrate gave a
slightly higher yield (>99%) (entry 7).
Scheme 2. Synthesis of naphthimidazole in the presence of heterogeneous catalyst 1.
1
1

Table 1. Synthesis of naphthimidazole from 2,3-diaminonaphthalene and DMF utilizing
a
catalyst 1
Entry
Catalyst
Temperature
C)
Time (h)
% yieldb
(
1
2
No catalyst
120
120
25
24
24
24
48
48
48
48
8
15
12
31
95
85
>99
ZnCl2
3
1
1
1
4
80
5
120
120
120
th
6
1 after 4 run
7c
1
aCatalytic reactions have been done at 120 °C temperature and at atmospheric pressure in a 50 ml
round bottom flask for two days using 2,3-diaminonaphthalene (200 mg), DMF (10 ml) and
b
c
catalyst 1 (10 mg, 5 wt%). Yields were calculated by isolating the product. 1,2-diaminobenzene
was used as the substrate.
Recyclability tests have been carried out to prove the heterogeneous nature of catalyst 1. After
complete conversion of the reactant to the product (checked through TLC), the reaction mixture
was filtered, followed by washing several times with DCM to collect the catalyst. The solvent
was evaporated at room temperature due to its low boiling point, leaving regenerated catalyst
which could be used further for successive cycles of the catalysis. The catalyst 1 was reused
up to four times with 85% yield for fourth run, as shown in Fig. S9. Powder X-ray diffraction
patterns have been collected for the recycled catalyst, with the results displaying that
framework was completely intact, without any loss of its integrity. Sharp peaks of the recycled
catalyst matched well with the as-synthesized PXRD peak pattern (Fig. S10).
1
2

The MOF provided not only a confined space for the catalytic reaction but also a number of
interaction sites where DMF molecules covalently interacted with the open Zn(II)-sites. On the
other hand, 2,3-diaminonaphthalene was stabilised by - interactions. So, the nucleophilic
attack of the substrate with DMF was much easier, forming the formylated intermediate.
Dimethyl amine was liberated from DMF, followed by intramolecular cyclization and then a
dehydration reaction occurred to generate the product and the catalyst 1 was released.
4
. Conclusions
In summary, a three dimensional Zn(II)-MOF with 2-fold interpenetration has been synthesized
through the in-situ acidic hydrolysis of the tripodal ligand 3,5-bis-(4-oxo-4H-pyridin-1-yl)-
benzonitrile (BPBN) at high temperature. The activated framework showed selective uptake of
CO at low pressure (1 bar) and at 195 K temperature. In this first report, the cyclization of
2
ortho-substituted diaminonaphthalene to naphthimidazole has been carried out in a one pot
synthesis using the thermally stable as-synthesized Zn-MOF as a heterogeneous catalyst. This
catalyst was reusable in several catalytic cycles, maintaining its structural integrity.
Acknowledgments
R.A. Agarwal gratefully acknowledges IIT Kanpur for extending facilities and to the SERB
(DST) (YSS/2015/000691) New Delhi, India, for financial support.
Appendix A. Supplementary data
CCDC 1873571 contains the supplementary crystallographic data for 1. These data can be
obtained free of charge viahttp://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail:deposit@ccdc.cam.ac.uk.
1
3

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(
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9
Selective CO Adsorption and Lewis Acid Catalytic Activity Towards
2
Naphthimidazole Synthesis by a Zn-MOF
a*
b
Rashmi A. Agarwal, Dinesh De
Page No. 1-19
Graphical Abstract
1
9

DMF
Zn-MOF
Selective CO Adsorption and Lewis Acid Catalytic Activity Towards
2
Naphthimidazole Synthesis by a Zn-MOF
a*
b
Rashmi A. Agarwal, Dinesh De
Page No. 1-19
Graphical Abstract Legend
A three dimensional, as-synthesized Zn-MOF with 2-fold interpenetration exhibits excellent
Lewis acidic heterogeneous catalytic activity towards the synthesis of naphthimidazole for the
first time. It shows selective CO capture from flue gas.
2
2
0

DMF
Zn-MOF
Selective CO Adsorption and Lewis Acid Catalytic Activity Towards
2
Naphthimidazole Synthesis by a Zn-MOF
a*
b
Rashmi A. Agarwal, Dinesh De
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, Kanpur,
India
Highlights
1
2
3
4
) A 3D, Zn(II) based metal organic framework has been synthesized at high temperature.
) Four coordinated Zn(II) sites act as high Lewis acidic sites for catalytic activity.
) - supramolecular interactions are present in the MOF, facilitating substrate activation.
) The as-synthesized Zn(II) MOF converts diaminonaphthalene to the naphthimidazole
compound.
5
6
) Naphthimidazole is an important compound in the medical field.
) The de-solvated MOF exhibits selective CO adsorption at low temperature and pressure.
2
Credit Author Statement
2
1

Experimental part, data analysis, manuscript writing was done by the corresponding author R.
A. Agarwal. Minor part of introduction and catalysis was written by D. De.
2
2