Camphor sulfonic acid catalyzed facile and general method for the synthesis of 3,3'-(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones), 3,3'-(arylmethylene)bis(2-hydroxynaphthalene-1,4-diones) and 3,3'-(2-oxoindoline-3,3-diyl)bis(2-hydroxynaphthalene-1,4-dio

Article abstract of DOI:10.1080/00397911.2020.1856877

Camphor sulfonic acid catalyzed a straightforward, efficient, and general method has been developed for the synthesis of 3,3'-(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones), 3,3'-(arylmethylene)bis(2-hydroxynaphthalene-1,4-diones) and 3,3'-(2-oxoindoline

Full text of DOI:10.1080/00397911.2020.1856877

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Camphor sulfonic acid catalyzed facile and
general method for the synthesis of 3,3'-
(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones),
3,3'-(arylmethylene)bis(2-hydroxynaphthalene-1,4-
diones) and 3,3'-(2-oxoindoline-3,3-diyl)bis(2-
hydroxynaphthalene-1,4-dione) derivatives at
room temperature
Gurpreet Kaur , Diksha Singh , Arvind Singh & Bubun Banerjee
To cite this article: Gurpreet Kaur , Diksha Singh , Arvind Singh & Bubun Banerjee
(2020): Camphor sulfonic acid catalyzed facile and general method for the synthesis
of 3,3'-(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones), 3,3'-(arylmethylene)bis(2-
hydroxynaphthalene-1,4-diones) and 3,3'-(2-oxoindoline-3,3-diyl)bis(2-hydroxynaphthalene-1,4-
dione) derivatives at room temperature, Synthetic Communications, DOI:
10.1080/00397911.2020.1856877
To link to this article: https://doi.org/10.1080/00397911.2020.1856877
Published online: 09 Dec 2020.
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https://doi.org/10.1080/00397911.2020.1856877
Camphor sulfonic acid catalyzed facile and general method
for the synthesis of 3,3’-(arylmethylene)bis(4-hydroxy-2H-
chromen-2-ones), 3,3’-(arylmethylene)bis(2-hydroxynaphth
alene-1,4-diones) and 3,3’-(2-oxoindoline-3,3-diyl)bis(2-
hydroxynaphthalene-1,4-dione) derivatives at room
temperature
Gurpreet Kaur, Diksha Singh, Arvind Singh, and Bubun Banerjee
Department of Chemistry, Indus International University, Bathu, Himachal Pradesh, India
ABSTRACT
ARTICLE HISTORY
Received 12 October 2020
Camphor sulfonic acid catalyzed a straightforward, efficient, and
general method has been developed for the synthesis of 3,3’-(arylme-
thylene)bis(4-hydroxy-2H-chromen-2-ones),
3,3’-(arylmethylene)bis(2-
KEYWORDS
hydroxynaphthalene-1,4-diones) and 3,3’-(2-oxoindoline-3,3-diyl)bis(2-h-
ydroxynaphthalene-1,4-dione) derivatives in aqueous ethanol at room
temperature from the reactions of various aromatic aldehydes and
4-hydroxycoumarin or 2-hydroxynaphthalene-1,4-dione respectively.
Mild reaction conditions, use of metal-free organocatalyst, good to
excellent yields, high atom-economy, environmentally benign, easy iso-
lation of products, and no column chromatographic separation are
some of the major benefits of this developed protocol.
3,3’-(arylmethylene)bis(4-
hydroxy-2H-chromen-2-
one); 3,3’-
(arylmethylene)bis(2-hydrox-
ynaphthalene-1,4-dione);
3,3’-(2-oxoindoline-3,3-diyl)-
bis(2-hydroxynaphthalene-
1,4-dione); camphor sulfonic
acid; no column
chromatography
GRAPHICAL ABSTRACT
Introduction
4-Hydroxycoumarins (4-hydroxy-2H-chromen-2-one) and various coumarins annulated
heterocyclic scaffolds are very common in naturally occurring compounds[1] with a
broad spectrum of significant biological efficacies that include anti-bacterial,[2] anti-arth-
ritis,[3] anti-pyretic,[4] anti-inflammatory,[5] anti-viral,[6] analgesic,[7] anticoagulant,[8]
CONTACT Bubun Banerjee
banerjeebubun@gmail.com; bubun.banerjee@iiuedu.in
Department of Chemistry,
Indus International University, Distt. Una, V.P.O. Bathu, Himachal Pradesh-174301, India.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
G. KAUR ET AL.
anti-cancer[9] and many more[10,11] activities. Some of the synthetic 4-hydroxycoumarin
derivatives also possess antibiotic,[12] antifungal,[13] antitumor[14] and anti-HIV[15] activ-
ities. Moreover, few functionalized 4-hydroxycoumarin derivatives have gained signifi-
cant attention in the field of medicinal,[16] as well as agrochemicals[17] industries.
Figure 1 represents some of the drug molecules bearing 4-hydroxycoumarin as one of
the structural subunit.[18,19] Biscoumarins, the bridge-substituted dimers of 4-hydroxy-
coumarin, have also been found to exhibit significant phytochemicals activity.[20–23]
Recently, a series of synthetic biscoumarin derivaives have been evaluated to possess
potent HIV-1 integrase inhibitor,[24,25] antimicrobial[26] and cytotoxic[27] activities
(Figure 2). On the other hand, 2-hydroxy-1,4-naphthoquinone (Lawsone) is one of the
major chemical constituent of the medicinal plant Henna (Lawsonia inermis Linn.)[28]
Figure 1. Some of the drug molecules containing 4-hydroxycoumarin as an important struc-
tural subunit.
Figure 2. Glimpse of bioactive synthetic biscoumarin derivatives.

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3
Among many other derivatives of Lawsone, 3,30-(arylmethylene)bis(2-hydroxynaphtha-
lene-1,4-diones) particularly showed significant anti-cancer activity.[29]
Due to the these diverse applications, both 3,30-(arylmethylene)bis(4-hydroxy-2H-
chromen-2-one) and 3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) deriva-
tives have gained tremendous attention among the synthetic chemists to develop
efficient synthetic routes for those scaffolds. As a result a good number of methods are
already reported for the synthesis of 3,30-(arylmethylene)bis(4-hydroxy-2H-chromen-2-
one) (Table 1)[30–52] as well as 3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione)
derivatives (Table 2).[53–56] Although these available methodologies possess notable mer-
its, still they suffer from number of limitations such as use of toxic metal catalysts,
organic solvents, harsh reaction condition, expensive catalyst, longer reaction time etc.
Besides, these reported methods focused specifically on a particular scaffold i.e. either
synthesis of 3,30-(arylmethylene)bis(4-hydroxy-2H-chromen-2-one) or 3,30-(arylmethyle-
ne)bis(2-hydroxynaphthalene-1,4-dione) derivatives. Therefore, a search for more
efficient, cost-effective, environmentally-benign general route for the synthesis of both
3,30-(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones) as well as 3,30-(arylmethylene)-
bis(2-hydroxynaphthalene-1,4-dione) derivatives is still warranted.
In these environmentally conscious days, use of metal-free organo-catalysts increases
rapidly.[57–59] In recent times, among many others, camphor sulfonic acid has also
gained tremendous attention as an efficient organo-catalyst.[60]
As part of our continuing efforts to develop organo-catalyzed efficient synthetic pro-
tocols for some useful organic transformations,[61–64] herein we wish to report a simple,
straightforward, environmentally benign and high yielding general method for the one-
pot pseudo three-component synthesis of biologically relevant 3,30-(arylmethylene)bis(4-
hydroxy-2H-chromen-2-ones), 3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-diones)
and 3,30-(2-oxoindoline-3,3-diyl)bis(2-hydroxynaphthalene-1,4-dione) derivatives using
commercially available camphor sulfonic acid as inexpensive metal-free organo-catalyst.
Results and discussion
To optimize the reaction conditions, we conducted a series of trial reactions with 4-
methylbenzaldehyde (1a; 0.5 mmol) and 4-hydroxycoumarin (2; 1 mmol). Firstly, we
carried out the reaction in the absence of any catalyst as well as solvent at room tem-
perature which afforded only trace amount of yield after 24 hours (Table 2, entry 1).
Under catalyst-free conditions, the same reaction afforded 22% yield of the desired
product i.e., 3,30-(p-tolylmethylene)bis(4-hydroxy-2H-chromen-2-one) (3a) after 6 hours
in ethanol (Table 2, entry 2). After getting the poor yields under catalyst-free condi-
tions, we realized the necessity of some suitable catalyst to enhance the reaction rate as
well as yield of the product. We were interested to check the catalytic activity of cam-
phor sulfonic acid for this reaction. By employing camphor sulfonic acid as catalyst
(20 mol%) in ethanol, 78% of 3a was isolated after six hours (Table 2, entry 3). Using
the same amount of catalyst comparable yield was also obtained by using methanol as
solvent (Table 2, entry 4). Little bit lower yield (61%) was isolated by using water as
solvent Table 2, entry 5). Interestingly, excellent yield (94%) of 3a was obtained within
just two hours when we carried out the same reaction using 20 mol% camphor sulfonic

4
G. KAUR ET AL.
Table 1. Reported protocols for the synthesis of biscoumarin.
Entry
Catalyst (amount)
SDS (20 mol%)
SiO2Cl (75 mg)
[TMG][Ac] (0.75 mmol)
Cellulose sulfonic acid (0.02 g)
TSAT (10 mol%)
Nano TiO2 (5 mol%)
[P4VPy.BuSO3H]HSO4 (0.1 mmol)
EPZ-10 (20 mol%) Grinding
(H14[NaP5W30O110]).SiO2
PTTH (0.03 mol%)
TBAB (10 mol%)
[bmim]BF4 (4 mmol)
DBSA (25 mol%)
PFPA (40 mol%)
nano MgO (3 mol%)
CAN (10 mol%)
Mohr’s Salt hexahydrate (5 mol%)
Graphene oxide (5 g)
[PSebim][OTf] (10 mol%)
OBS (50 mol%)
CuO-CeO2 nanocomposite (0.05 g)
HAP/Fe3O4 NPs(III) (0.008 g)
Sulfanilic acid
Solvent
H2O
Temp.
Time
Yield (%)
1
2
3
4
5
6
7
8
60 ꢀC
2.5 h
2.5 h
3.5 h
2.0 h
8 min
8 min
0.9 h
10 min
30 min
90[30]
CH3Cl2
ꢁ
40 ꢀC
85[31]
25 ꢀC
96[32]
H2O
Reflux
90[33]
ꢁ
90 ꢀC
96[34]
H2O
Reflux
90 ꢀC
90[35]
toluene
neat
92[36]
RT
RT
85[37]
9
EtOH
H2O/neat
H2O/neat
TMSCl
EtOH-H2O
H2O
neat
H2O
H2O
H2O
90[38]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
80 ꢀC
8 min/5 min
50 min/40 min
3 h
78 min/ 6.5 min
80 min
27 min
8 h
90/80[39]
88/82[40]
83[41]
Reflux
60–70 ꢀC
Reflux/MW
Reflux
100 ꢀC
28–30 ꢀC
reflux
reflux
70 ꢀC
85/85[42]
89[43]
88[44]
82[45]
35 min
25 min
2.5 h
25 min
18 min
75 min
16 min
2 h
90[46]
90[47]
ꢁ
93[48]
H2O
reflux
reflux
90 ꢀC
78[49]
H2O
neat
H2O
EtOH-H2O
90[50]
98[51]
80 ꢀC
94[52]
CSA (20 mol%)
27–30 ꢀC
94[this work]
TMG: Tetramethylguanidium; TSAT: Triethylaminium-N-sulfonic acid tetrachloroaluminate; [P(4-VPH)ClO4]: Poly(4-vinylpyr-
idinium) perchlorate; PTTH: Propane-1,2,3-triyl tris(hydrogen sulfate); TBAB: Tetrabutylammonium bromide; DBSA: p-
Dodecylbenzenesulfonic acid; PFPA: pentafluoropropionic acid; CAN: Cerric ammonium nitrate; Mohrs salt: (ferrous
ammonium sulfate hexahydrate); [PSebim][OTf]: 1-ethyl-3-(3-sulfopropyl)-benzimidazolium trifluoromethanesulfonate;
OBS: o-benzenedisulfonimide
Bold values indicate the required catalyst amount.
acid as catalyst in aqueous ethanol as solvent at room temperature (Table 2, entry 6).
Lesser amount of 3a (86%) was isolated by using 15 mol% of camphor sulfonic acid as
catalyst in aqueous ethanol (Table 2, entry 7) whereas no significant improvement was
recorded in the reaction rate even by increasing the catalyst amount to 25 mol%
(Table 2, entry 8). From these preliminary experiments, 20 mol% of camphor sulfonic
acid in aqueous ethanol (1:1 v/v) at room temperature came out as the best suitable
conditions for the synthesis of 3,30-(p-tolylmethylene)bis(4-hydroxy-2H-chromen-2-one)
in terms of reaction time as well as product yield (Table 2, entry 6).
Under the optimized conditions, the reaction of 3-bromobenzaldehyde (1 b;
0.5 mmol), and 4-hydroxycoumarin (2; 1 mmol) afforded the desired product i.e., 3,30-
((3-bromophenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (3b) with 92% yield

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5
Table 2. Optimization of reaction conditions in the synthesis of 3,3’-(arylmethylene)bis(4-hydroxy-2H-
chromen-2-ones).
Entry
Catalyst (mol%)
No catalyst
No catalyst
CSA (20 mol%)
CSA (20 mol%)
CSA (20 mol%)
CSA (20 mol%)
CSA (15 mol%)
CSA (25 mol%)
Solvent
Time (h)
Yield(%)a,b
1
2
3
4
5
6
7
8
neat
EtOH
EtOH
MeOH
H2O
24
6
6
6
6
2
2
2
Trace
22
78
72
61
94
86
94
EtOH:H2O (1:1 v/v)
EtOH:H2O (1:1 v/v)
EtOH:H2O (1:1 v/v)
aReaction conditions: 4-methylbenzaldehyde (1a; 0.5 mmol), 4-hydroxycoumarin (2; 1 mmol) in the presence or
absence of camphor sulfonic acid in neat/4 mL of water/ethanol/methanol/ethanol-water at room temperature.
bIsolated yields.
Bold values indicates the optimized reaction condition.
within 2 h (Table 3, entry 2). 3,30-((3,4,5-Trimethoxyphenyl)methylene)bis(4-hydroxy-
2H-chromen-2-one) (3c) was isolated with 91% yield from the reactions of 3,4,5-trime-
thoxybenzaldehyde (1c) and 4-hydroxycoumarin (2; 1 mmol) (Table 3, entry 3). Various
heteroaryl aldehydes such as thiophene-2-carbaldehyde (1d), indole-3-carbaldehyde (1e)
and chromone-3-carboxaldehyde (1f) also underwent smoothly and produced the corre-
sponding products with good to excellent yields (Table 3, entries 4,5 & 6). To check the
generality as well as the effectiveness of our newly developed protocol, we were moti-
vated to synthesize 3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) derivatives
(5a–5b) by replacing 4-hydroxycoumarin (2) with 2-hydroxynaphthalene-1,4-dione (4)
under the same optimized conditions. At room temperature, 20 mol% camphor sulfonic
acid was also came out as an efficient catalyst for the synthesis of 3,30-(arylmethylene)-
bis(2-hydroxynaphthalene-1,4-dione) derivatives (5a–5b) in aqueous ethanol. Reactions
of syringaldehyde (1g; 0.5 mmol) or 2,4-dichlorobenzaldehyde (1 h; 0.5 mmol) with 2-
hydroxynaphthalene-1,4-dione (4; 1 mmol) were completed within three hours and
afforded the corresponding products with 82% (5a) or 84% (5b) yields respectively
(Table 3, entries 7 & 8). It is our delight to mention that under the same optimized
reaction conditions we were also able to synthesize 3,30-(2-oxoindoline-3,3-diyl)bis(2-
hydroxynaphthalene-1,4-dione) derivatives (7a–7b) with good yields (78–80%) from the
reactions of isatin (6a; 0.5 mmol) or 5-fluoroisatin (6b; 0.5 mmol) with 2-hydroxynaph-
thalene-1,4-dione (4; 1 mmol) (Scheme 1).
All the products were isolated pure just by simple filtration followed by subsequent
washing with aqueous ethanol; no tedious chromatographic purification was required.
All the synthesized products were fully characterized on the basis of physical as well as
1
detailed spectral studies including H NMR, 13C NMR and HRMS.

6
G. KAUR ET AL.
Table 3. Synthesis of 3,3’-(arylmethylene)bis(4-hydroxy-2H-chromen-2-one)
(3a-3f) and 3,3’-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) (5a-5b)
using camphor sulfonic acid as catalyst at room temperature.
Entry
1
2/4 Aldehydes
2
Products
Time (h)
2
Yield (%)a,b
94
2
3
2
2
2
92
91
2.5
4
5
2
2
3
3
86
77
6
2
3
73
7
8
4
4
3
3
82
84
aReaction conditions: aldehydes (1; 0.5 mmol) and 4-hydroxycoumarin (2; 1 mmol) or
2-hydroxynaphthalene-1,4-dione (4; 1 mmol) in the presence of 20 mol% camphor sulfonic
acid (0.023 g) as catalyst in aqueous ethanol at 27-30 ꢀC. bIsolated yields.

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Scheme 1. Synthesis of 3,3’-(2-oxoindoline-3,3-diyl)bis(2-hydroxynaphthalene-1,4-dione) derivatives.
Scheme 2. Plausible mechanism for the synthesis 3,3’-(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones).
Herein we propose a plausible mechanism for the formation of 3,30-(arylmethylene)-
bis(4-hydroxy-2H-chromen-2-ones) (Scheme 2). At first camphor sulfonic acid acts as a
Brønsted acidic catalyst to activate the carbonyl group of aldehydes which facilitates the
attack from C-3 position of 4-hydroxycoumarin (2) and generate the Knoevenagel inter-
mediate 8. Attack by the second molecule of 4-hydroxycoumarin (2) on 8 followed by
enolisation giving rise the desired product 3.
Experimental
General
Melting points were recorded on a Digital Melting Point Apparatus (Model No. MT-
1
934) and are uncorrected. TLC was performed on silica gel 60 F254 (Merck) plates. H

8
G. KAUR ET AL.
and 13C NMR spectra were obtained at 500 MHz Jeol (JNM ECX-500) NMR machines
with DMSO-d6 or CDCl3 as solvent. Mass spectra (TOF-MS ESþ) were measured on a
Bruker Impact HD QTOF Micro mass spectrometer.
General procedure for the synthesis of 3,3’-(p-tolylmethylene)bis(4-hydroxy-2H-
chromen-2-one) (3a)
In an oven-dried screw-cap test tube a magnetic stir bar, substituted 4-methylbenzalde-
hyde (1a; 0.5 mmol), 4-hydroxycoumarin (2; 1 mmol), a catalytic amount of camphor
sulfonic acid (20 mol%) and 4 mL of aqueous ethanol (1:1 v/v) were taken sequentially.
The reaction mixture was then stirred vigorously on a magnetic stirrer at room tem-
perature. Progress of the reaction was monitored by TLC. After completion of the reac-
tion, corresponding product (3a) was isolated pure just by simple filtration and
subsequent washing with aqueous ethanol (H2O:EtOH¼1:2). The structure of the syn-
1
thesized compound was determined by the detail spectral analysis including H NMR,
13C NMR and HRMS spectroscopy.
3,30-(p-Tolylmethylene)bis(4-hydroxy-2H-chromen-2-one) (3a): White solid; yield 94%;
1
mp 267–269 ꢀC (lit. 266 ꢀC)[38]; H NMR (500 MHz, DMSO-d6) d/ppm: 7.85 (2H, dd,
J ¼ 9.5 & 1 Hz, aromatic H), 7.57–7.53 (2H, m, aromatic H), 7.32 (2H, d, J ¼ 8.5 Hz,
aromatic H), 7.28 (2H, t, J ¼ 8.0 & 7.0 Hz, aromatic H), 6.99 (4H, s, aromatic H), 6.26
(1H, s, CH), 2.20 (3H, s, CH3); 13C NMR (125 MHz, DMSO-d6) d/ppm: 166.02 (2C),
165.32 (2C), 152.75 (2C), 137.53, 134.85, 132.30 (2C), 129.16 (2C), 127.14 (2C), 124.44
(2C), 124.18 (2C), 118.69 (2C), 116.43 (2C), 104.68 (2C), 36.14, 21.06; HRMS (ESI-
TOF) m/z: For C26H18O6 Calcd. [M þ H]þ 427.1182; Found [M þ H]þ 427.1332.
General procedure for the synthesis of 3,3’-((4-hydroxy-3,5-
dimethoxyphenyl)methylene)bis(2-hydroxynaphthalene-1,4-dione) (5a)
By following the above mentioned procedure, 3,30-((4-hydroxy-3,5-dimethoxyphenyl)-
methylene)bis(2-hydroxynaphthalene-1,4-dione) (5a) was synthesized from the reac-
tions of syringaldehyde (1 g; 0.5 mmol) and 2-hydroxynaphthalene-1,4-dione
(4; 1 mmol).
3,30-((4-Hydroxy-3,5-dimethoxyphenyl)methylene)bis(2-hydroxynaphthalene-1,4-dione)
(5a): Yellow solid; yield 82%; mp 219–221 ꢀC; 1H NMR (500 MHz, CDCl3) d/ppm:
8.11–8.07 (4H, m, aromatic H), 7.80–7.76 (1H, m, aromatic H), 7.73 (1H, t, aromatic
H), 7.68 (2H, t, J ¼ 7.5 & 7.4 Hz, aromatic H), 6.65 (1H, s, aromatic H), 6.53 (2H, s,
aromatic H), 6.35 (1H, s, aromatic H), 6.11 (1H, s, aromatic H), 5.27 (1H, s, CH), 3.81
(6H, s, 2 x –OCH3); 13C NMR (125 MHz, CDCl3) d/ppm: 185.08, 184.72, 181.46 (2C),
156.41, 154.58 (2C), 147.01, 135.39, 135.21, 133.34, 133.25, 132.76, 129.60 (2C), 127.27,
126.79 (2C), 126.60, 126.43, 122.91 (2C), 110.79 (2C), 105.70 (2C), 56.51 (2C), 38.03;
HRMS (ESI-TOF) m/z: For C29H20O9 Calcd. [M – H]þ 511.1029; Found [M –
H]þ 511.1432.

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9
Conclusions
In conclusion, we have developed a very simple, facile and general method for one-pot
pseudo three-component synthesis of pharmaceutically-interesting 3,30-(arylmethylene)-
bis(4-hydroxy-2H-chromen-2-ones), 3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-
diones) and 3,30-(2-oxoindoline-3,3-diyl)bis(2-hydroxynaphthalene-1,4-dione) derivatives
in the presence of a catalytic amount of camphor sulfonic acid in aqueous ethanol at
room temperature. Use of inexpensive and environmentally benign catalyst, mild reac-
tion conditions, good to excellent yields, clean reaction profiles, high atom-economy,
operational simplicity and absence of tedious purification procedures are some of the
salient features of this developed protocol.
1
Full experimental detail, scanned spectra including H-NMR, 13C-NMR and HRMS
of all the synthesized scaffolds are supplemented in supporting information. This mater-
ial can be found via the “Supplementary Content” section of this article’s webpage.’
Acknowledgments
Dr. B. Banerjee is thankful to the Indus International University, Una, Himachal Pradesh, India
and the Kartha Education Society, Mumbai, India for the support. Authors are grateful to
AMRC, IIT Mandi, Himachal Pradesh, India for the spectral measurements such as FTIR, NMR,
HRMS as well as single XRD data.
Disclosure statement
No potential conflict of interest was reported by the author(s).
ORCID
Bubun Banerjee
http://orcid.org/0000-0001-7119-9377
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