Polymorphism in chloro derivatives of 1,4-naphthoquinone: Experiment and density functional theoretic investigations

Article abstract of DOI:10.1016/j.molstruc.2016.05.022

Molecular interactions underlying polymorphs of chlorine containing 1,4-naphthoquinone derivatives have been investigated by employing single crystal X-ray, ¹H NMR, FTIR and electronic spectra experiments combined with density functional theory. Two polymorphs of 2,3-dichloro-1,4-naphthoquinone possessing (i) triclinic space group P-1(A1 and A3), and (ii) orthorhombic with Pb2₁a (A2) space group were obtained. The polymorph A3 has two molecules in its asymmetric unit which facilitate [Formula presented] interactions engendeing polymeric planar sheets. The two polymorphs of 2-amino-3-chloro-1,4-naphthoquinone reveal monoclinic forms with Pc (B1) and C_2/C (B2) space groups. A tetramer of B2 molecule possess [Formula presented] interactions. The polymorphs of 2-chloro-3-hydroxy-1,4-naphthoquinone crystallizes in monoclinic space groups Pc (C1) and Pn (C2). Polymeric chain of C2 molecules results via [Formula presented] interactions and the chains further are connected through [Formula presented] and π-π stacking interactions those arise from benzenoid and quinonoid centroid. Moreover A3 facilitates the dimer via the halogen bonding interactions. Furthermore hydrogen bonding renders stability to the dimer C2. On the other hand compound B2 does not favor dimer formation. These inferences based on experimental observations are rationalized through the use of the dispersion corrected M06-2x functional based density functional theory. Further time dependent density functional theory has been used to assign the electronic transitions in UV–visible spectra of A3, B2 and C2.

Full text of DOI:10.1016/j.molstruc.2016.05.022

Journal of Molecular Structure 1120 (2016) 281e293
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Polymorphism in chloro derivatives of 1,4-naphthoquinone:
Experiment and density functional theoretic investigations
,
Dinkar Chaudhari a, Shridhar P. Gejji a **, Dipali N. Lande a, Debamitra Chakravarty b,
,
*
Sunita Salunke-Gawali a
a Department of Chemistry, Savitribai Phule Pune University, Pune 411007, India
b Central Instrumentation Facility, Department of Chemistry, Savitribai Phule Pune University, Pune 411007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Molecular interactions underlying polymorphs of chlorine containing 1,4-naphthoquinone derivatives
have been investigated by employing single crystal X-ray, 1H NMR, FTIR and electronic spectra experi-
ments combined with density functional theory. Two polymorphs of 2,3-dichloro-1,4-naphthoquinone
possessing (i) triclinic space group P-1(A1 and A3), and (ii) orthorhombic with Pb21a (A2) space group
were obtained. The polymorph A3 has two molecules in its asymmetric unit which facilitate CeH/O
interactions engendeing polymeric planar sheets. The two polymorphs of 2-amino-3-chloro-1,4-
naphthoquinone reveal monoclinic forms with Pc (B1) and C2/C (B2) space groups. A tetramer of B2
molecule possess NeH/O interactions. The polymorphs of 2-chloro-3-hydroxy-1,4-naphthoquinone
crystallizes in monoclinic space groups Pc (C1) and Pn (C2). Polymeric chain of C2 molecules results
Received 22 March 2016
Received in revised form
6 May 2016
Accepted 9 May 2016
Available online 12 May 2016
Keywords:
Polymorphism
Naphthoquinone
via OeH/O interactions and the chains further are connected through CeH/Cl and
p-p stacking in-
p-p stacking
teractions those arise from benzenoid and quinonoid centroid. Moreover A3 facilitates the dimer via the
halogen bonding interactions. Furthermore hydrogen bonding renders stability to the dimer C2. On the
other hand compound B2 does not favor dimer formation. These inferences based on experimental
observations are rationalized through the use of the dispersion corrected M06-2x functional based
density functional theory. Further time dependent density functional theory has been used to assign the
electronic transitions in UVevisible spectra of A3, B2 and C2.
Hydrogen bonding
Dichlone
TD-DFT
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
The biological applications of quinone molecules include as
antibiotics [5], anticancer [6,7], vitamin [8], antibacterial [9],
Polymorphism in crystalline solids or materials has same
chemical composition with different lattice structures and/or
different molecular conformations. Molecular arrangement in
crystalline solids are facilitated through noncovalent interactions
fungicide [10] etc. Innumerable quinone compounds studied by
crystallography revealed hydrogen bonding interactions. The weak
molecular interactions engender polymorphic structures in qui-
nones [11e16]. Molecular interactions responsible for drug action
in particular, those between drug or biomolecules have been of
fundamental importance. With this motif the polymorphs of chloro
derivatives of 1,4-naphthoquinones viz., 2,3-dichloro-1,4-
naphthoquinone(polymorphs A1 to A3), 2-amino-3-chloro-1,4-
naphthoquinone (polymorphs B1 and B2) and 2-chloro-3-
hydroxy-1,4-naphthoquinone (polymorphs C1 and C2) (Table 1)
have been investigated in the present work. Interestingly 2,3-
dichloro-1,4-naphthoquinone commonly known as dichlone was
first synthesized by Graebe [19] in 1867 and described by Car-
stanjen [20] in following year finds applications as algicide [17] and
fungicide [18]. Besides dichlone serves as DNA methyl transferase
inhibitor [21] and can be exported as starting material for synthesis
such as hydrogen bonding, van der Waals interactions, p-p stacking
and electrostatic interactions [1]. Hydrogen bonding has been one
of the key factors toward noncovalent binding that has been
explored for molecular recognition [2,3]. Such non covalent in-
teractions control the chemical stability, solubility and the
bioavailability of the active pharmaceutical ingredients [4] in
pharmaceutical solids.
* Corresponding author.
** Corresponding author.
E-mail addresses: spgejji@chem.unipune.ac.in (S.P. Gejji), sunitas@chem.
unipune.ac.in (S. Salunke-Gawali).
http://dx.doi.org/10.1016/j.molstruc.2016.05.022
0022-2860/© 2016 Elsevier B.V. All rights reserved.

282
D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
Table 1
Details of polymorphs A1 to A3, B1, B2 and C1, C2.
Compound
Molecular structure
Polymorph
Space group
Reference
2,3-dichloro-1,4-naphthoquinone (Dichlone)
A1
A2
A3
Triclinic P-1
Orthorhombic Pb21a
Triclinic P-1
[26]
[27]
Present work
O
8
9
1
Cl
Cl
7
6
2
3
10
4
5
O
2-amino-3-chloro-1,4-naphthoquinone
B1
B2
Monoclinic Pc
Monoclinic C2/c
[31]
Present work
O
8
9
1
NH2
Cl
7
6
2
3
10
4
5
5
O
O
2-chloro-3-hydroxy-1,4-naphthoquinone (Chlorolawsone)
C1
C2
Monoclinic Pn
Monoclinic C2/c
[29]
Present work
4
10
9
3
OH
Cl
6
7
2
1
8
O
of numerous compounds of biological significance [22]. Dichlone
further has been utilized in nucleophilic substitution reactions
[23,24] and also in synthesis of numerous heterocyclic compounds
[25]. The crystal structure of dichlone was elucidated in 1961 [26],
the crystals grown in toluene revealed triclinic space group (A1)
(Table 1). On the other hand, the crystals grown from the com-
pound melt showed orthorhombic space group (A2) [27]. The
works of Hauw et al. [29] further concluded that in alkaline and
neutral solutions dichlone hydrolyzes to form 2-chloro-3-hydroxy-
1,4-naphthoquinone [28]; the single crystal X-ray data of which
was elucidated only in 1965 (C1). Fries et al. [30] carried out the
synthesis of 2-amino-3-chloro-1,4-naphthoquinone the structure
of which was known since 1965 (B1) [31].
2.2. Synthesis of 2-amino-3-chloro-1,4-naphthoquinone; B2
Modified procedure have been used for synthesis of 2-amino-3-
chloro-1,4-naphthoquinone [33]. Recrystallized 2,3-dichloro-1,4-
naphthoquinone, (0.5 g, 2.2 mM) was suspended in 20 ml of
ethanol and 25 ml ammonium hydroxide solution was added to the
solution of dichlone with constant magnetic stirring. The mixture
was refluxed for 3 h at 60 ꢁC. Red color precipitate was obtained,
which was filtered and washed with diethyl ether and dried in
vacuum. The product was further purified by column chromatog-
raphy (silica column, 60e120 mesh) and eluted with pet ether/
ethyl acetate.
All three compounds studied in present investigation were used
to synthesize several compounds those find application in phar-
macology and in medicinal chemistry. Despite of all these experi-
mental studies the reports on the molecular interactions in
different polymorphs of these compounds are rather limited. The
present work precisely focuses on this aspect and outlines analysis
of structural and spectral characteristics of biologically as well as
synthetically important chlorine containing 1,4-naphthoquinone
derivatives (Table 1).
2.3. Synthesis of 2-chloro-3-hydroxy 1,4-naphthoqinone; C2
Modified procedure [28] has been used for synthesis of com-
pound ‘C2’. Recrystallized 2,3-dichloro-1,4-naphthoquinone (0.5 g,
2.2 mM) have been added in 10 ml of water. To this suspension,
10 ml aqueous solution of KOH (0.247 g, 4.4 mM) was added with
constant magnetic stirring. This reaction mixture was heated for
~1 h at 70 ꢁC. Red color solution was obtained. Unreacted dichlone
was extracted with dichloromethane from aqueous reaction
mixture and was acidified by adding a few drops of concentrated
hydrochloric acid till pH of the reaction mixture becomes acidic
(pH ¼ 2). Yellow color precipitate thus obtained was filtered and
washed with diethyl ether and dried in vacuum. This yellow color
residue was further purified by column chromatography (silica
column, 60e120 mesh) and eluted with ethyl acetate/pet ether
(1:9). X-ray quality crystals were obtained after recrystallization of
solid product in methanol.
2. Experimental section
2.1. General materials and methods
The materials used viz., 2,3-dichloro-1,4-naphthoquinone was
purchased from Sigma-Aldrich and used as received. KOH pellets
and aqueous ammonia was obtained from Merck chemicals.
Analytical grade solvents used such as dichloromethane, toluene,
methanol, pet ether, ethyl acetate were purchased from Merck
Chemicals. Solvents were distilled by standard methods [32] and
dried wherever necessary. FT-IR spectra were recorded between
4000 and 400 cmꢀ1 as KBr pellets on SHIMADZU FT 8400 Spec-
trophotometer. Melting points of compounds were determined
using (Make-METTLER). 1H (500 MHz) and 13C (125 MHz) NMR of
compound B2 was recorded in DMSO-d6, on Varian 500 MHz
NMR instrument. TMS (tetramethylsilane) was used as the
reference. UVevisible spectra of all compounds in methanol were
recorded from 200 nm to 800 nm on Shimadzu UV 1800
spectrophotometer.
2.4. Characterization
2-amino-3-chloro-1,4-naphthoquinone; B2. Red crystal, Yield:
0.342 g (79.93%). m. p 195e196 ꢁC. FT-IR (KBr, nmax(cmꢀ1)): 3403,
3293, 2322, 2287, 1678,1590, 1553, 1305, 1268, 711, 685, 592, 521.1H
NMR (500 MHz, DMSO-d6,
d
(ppm)): 8.17 (d, 1H, J ¼ 7.5 Hz), 8.16 (d,
1H, J ¼ 7.5), 7.7 (t, 1H, J ¼ 7.5), 7.65 (t, 1H, J ¼ 7.65), 5.5 (s, 2H). 13
C
NMR (125 MHz, DMSO-d6, d(ppm)): 176, 145, 134, 132, 132, 129, 126,
126. UVevis (lmax (nm), methanol): 284, 332, 449.
2-hydroxy-3-chloro-1,4-naphthoqinone; C2. Yellow Solid, Yield:
0.400 g (87.14%). m. p. 206e207 ꢁC. FT-IR (KBr, nmax(cmꢀ1)): 3269,
1668, 1639, 1585, 1454, 1363, 1330, 1298, 1273, 1219, 1128, 1008,

D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
283
Fig. 1. ORTEP plot of compound A3, B2 and C2. The ellipsoid was drawn with 50% probability.
Table 2
Crystallography parameters of A3, B2 and C2.
A3
B2
C2
CCDC
1426674
20H8 Cl4 O4
454.06
1426672
C10 H6Cl NO2
207.61
1426673
C10 H5Cl O3
208.59
Empirical formula
Formula weight
Temperature
C
296(2) K
296(2) K
296(2) K
Wavelength
0.71073 Å
0.71073 Å
0.71073 Å
Crystal system, space group
Unit cell dimensions
Triclinic, P-1
a ¼ 7.32790(10) Å,
Monoclinic, C2/c
a ¼ 13.7381(3) Å,
Monoclinic, P n
a ¼ 8.25530(15) Å,
a
¼ 89.7690(6)ꢁ
a
¼ 90.0ꢁ
a
¼ 90.0ꢁ
b ¼ 8.27650(10) Å,
b ¼ 7.57140(10)Å,
b ¼ 3.90730(7)Å,
b
¼ 82.5420(10)ꢁ
b
¼ 110.7030(7)ꢁ
b
¼ 100.4200(8)ꢁ
c ¼ 16.1368(3) Å,
c ¼ 18.2389(3) Å,
c ¼ 13.4222(2) Å,
g
¼ 67.0180(10)ꢁ
g
¼ 90.0ꢁ
g
¼ 90.0ꢁ
Volume
892.22(2) Å3
2, 1.690 Mg/m3
0.690 mmꢀ1
1774.64(5)Å3
8, 1.554 Mg/m3
0.397 mmꢀ1
425.806(13)Å3
2, 1.627 Mg/m3
0.420 mmꢀ1
Z, Calculated density
Absorption coefficient
F(000)
456
848
212
Crystal size
Theta range for data collection
Limiting indices
0.49 ꢂ 0.48 ꢂ 0.27 mm
0.492 ꢂ 0.473 ꢂ 0.264 mm
0.49 ꢂ 0.47 ꢂ 0.26 mm
2.905e28.400ꢁ
3.123e28.405ꢁ
3.086e28.328ꢁ
ꢀ9 ꢃ h<¼9, ꢀ11 ꢃ k<¼10, ꢀ21 ꢃ l<¼21 ꢀ18 ꢃ h<¼18, ꢀ10 ꢃ k<¼10, ꢀ24 ꢃ l<¼24 ꢀ10 ꢃ h<¼11, ꢀ5 ꢃ k<¼5, ꢀ17 ꢃ l<¼17
Reflections collected/unique
30738/4409 [R(int) ¼ 0.0500]
32282/2225 [R(int) ¼ 0.0975]
99.9%
MULTI SCAN
0.9024 and 0.8285
Full-matrix least-squares on F2
1558/0/128
10250/2114 [R(int) ¼ 0.0534]
99.9%
Semi-empirical from equivalents
e
Full-matrix least-squares on F2
2225/0/127
1.05
Completeness to theta ¼ 30.49 99.9%
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
Refinement method
0.830 and 0.720
Full-matrix least-squares on F2
4409/0/254
Data/restraints/parameters
Goodness-of-fit on F2
1.023
0.998
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 ¼ 0.0474, wR2 ¼ 0.0922
R1 ¼ 0.0911, wR2 ¼ 0.1107
0.268 and ꢀ0.346 e.Aꢀ3
R1 ¼ 0.0497, wR2 ¼ 0.0980
R1 ¼ 0.0970, wR2 ¼ 0.1172
0.271 and ꢀ0.209 e. Aꢀ3
R1 ¼ 0.0351, wR2 ¼ 0.0570
R1 ¼ 0.0510, wR2 ¼ 0.0602
0.185 and ꢀ0.153 e. Aꢀ3

284
D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
Table 3
2.5. X-ray crystallography
Hydrogen bonding interactions of A2, A3, B2 and C2.
Compound D_H/A
A3
C(8)eH(8)/Cl(2)(i)
D/H(Å) H/A(Å) D/A(Å) D_ H/A(º)
The X-ray quality yellow-green crystals of compound ‘A3’ was
obtained from the unreacted fraction from the column of the re-
action between 2,3-dichloro-1,4-naphthoquinone and 2-
aminophenol. A red block crystal of ‘B2’ was obtained after evap-
oration of red fraction of the column and a yellow block crystal of
‘C2’ was obtained after evaporation of methanol solution. Crystals
of appropriate size were chosen for data collection.
0.929
0.930
0.931
0.930
0.930
0.930
0.930
0.930
0.930
0.860
2.827
2.612
2.847
2.868
2.882
2.643
2.868
2.887
2.883
2.408
2.323
2.810
2.331
2.890
2.546
2.046
2.639
2.701
2.606
2.937
3.252
3.169
3.159
3.736(3) 166.0
3.450(4) 150.1
3.727(3) 157.9
3.704(3) 165.1
3.805(3) 172.6
3.490(4) 151.6
3.704(4) 150.2
3.808(4) 170.7
3.789(4) 165.1
3.167(2) 147.5
3.153(2) 162.5
3.643(2) 149.6
3.187(3) 152.7
3.563(3) 130.1
3.295(3) 137.8
2.770(2) 147.0
C(70)eH(70)/O(1)(ii)
C(60)eH(60)/Cl(1)(ii)
C(7)eH(7)/Cl(2)(iii)
C(5)eH(5)/Cl(20)(iv)
C(6)eH(6)/O(20)(iii)
C(7)eH(7)/Cl(20)(iii)
C(50)eH(50)/Cl(1)(i)
C(80)eH(80)/Cl(1)(v)
N(1)eH(1B)/O(2)(vi
Data for all three compounds have been collected on D8 Venture
PHOTON 100 CMOS diffractometer using graphite mono-
B2
chromatized Mo-Ka radiation (
l
¼ 0.7107 Å) with exposure/
N(1)eH(1A)/O(2)(vii) 0.860
frame ¼ 8 s, 15 s and 10 s for A3, B2 and C2 respectively. The X-ray
generator was operated at 50 kV and 30 mA. An initial set of cell
constants and an orientation matrix were calculated from total 24
frames. The optimized strategy used for data collection consisted
C(8)eH(8)/Cl(1)(viii) 0.930
C(5)eH(5)/O(1)(vi)
C(5)eH(5)/Cl(1)(ix)
C(8)eH(8)/O(3)(x)
O(2)eH(2)/O(1)(xi)
C(6)eH(4)/O(1)(xii)
0.931
0.930
0.931
0.820
0.917
C2
A2
different sets of
f and u f/u. Crystal to
scans with 0.5ꢁ steps in
3.391
3.592
3.337
3.751
139.7
143.4
137.8
135.4
151.6
166.3
167.9
C(16)eH(2)/O(2)(xiii) 1.040
detector distance was 5.00 cm with 512 ꢂ 512 pixels/frame, Oscil-
lation/frame ꢀ0.5ꢁ, maximum detector swing angle ¼ ꢀ30.0ꢁ,
beam centre ¼ (260.2, 252.5), in plane spot width ¼ 1.24. Data
integration was carried out by Bruker SAINT program and empirical
absorption correction for intensity data were carried out by Bruker
SADABS. The programs are integrated in APEX II package [34]. The
data were corrected for Lorentz and polarization effect. The struc-
ture was solved by Direct Method using SHELX-97 [35]. The final
refinement of the structure was performed by full-matrix least-
squares techniques with anisotropic thermal data for non-
hydrogen atoms on F2. The non-hydrogen atoms were refined
anisotropically whereas the hydrogen atoms were refined at
calculated positions as riding atoms with isotropic displacement
parameters. Molecular diagrams were generated using ORTEP-3
[36] and Mercury programs [37]. Geometrical calculations were
performed using SHELXTL [35] and PLATON [38].
C(17)eH(7)/O(4)(xiv) 0.909
C(16)eH(2)/Cl(1)(v)
C(3)eCl(2)/O(4)(xv)
1.040
1.726
C(12)eCl(3)/O(1)(xvi) 1.694
C(2)eCl(1)/O(2)(xvii) 1.701
(i) x,ꢀ1þy,z; (ii) x,1þy,z (iii) x,1þy,1þz; i½v) x,y,1þz ; v) x,y,z, vi) ꢀ½þx,ꢀ½þy,z;
vii) ½ꢀx,ꢀ ½þy, ½ꢀz; viii) x,2ꢀy,ꢀ½þz; ix) ꢀ1þx,1þy,z ; x) ꢀ½þx,ꢀy,ꢀ½þz; xi)
ꢀ½þx,1ꢀy,ꢀ½þz; (xii) ꢀ½þx,y,z; (xiii) ½þx,y,ꢀ1ꢀz; xiv) ½þx,y,z; xv) x,y,ꢀ1þz;
xvi) ½ꢀx,ꢀ½þy,ꢀ1þz; xvii) ½þx,yꢀ1,ꢀ1ꢀz.
856, 727, 682, 599, 538. 1H NMR (400 MHz, DMSO-d6,
8.00 (dd, 2H), 7.86e7.74 (m, 2H), 3.89 (s, 1H). 13C NMR (100 MHz,
DMSO-d6, (ppm)): 180.74, 178.26, 158.53, 135.22, 133.79, 132.30,
d (ppm)):
d
130.10, 126.77, 126.59, 126.11. UVevis (lmax (nm), methanol): 287,
321, 473.
Fig. 2. Dichlone molecules of triclinic space group P-1 (A1) showing a)
p-p stacking and b) Cl∙∙∙O close contacts down b-axis.

D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
285
Fig. 3. Dichlone molecules of orthorhombic space group (Pb21a)(A2) showing polymer of dimeric units of ‘X1’ and ‘Y1’ down c-axis.
2.6. Computational details
bonding parameters are reported in Table 3. The molecular in-
teractions of A3, B2 and C2 together with respective known poly-
morphs in literature are outlined below.
Optimized structures of A3, B2 and C2 were derived within the
framework of M06-2x based density functional theory employing
the Gaussian-09 program [39]. The internally stored 6-31G basis set
with diffuse functions being added on all the heavy atoms (desig-
nated as 6-31þþG(d,p) basis) have been used for optimizations
[40e42]. The stationary point structures were confirmed to be local
minima on the potential energy surface through vibrational fre-
quency calculations. Frontier orbital were computed in the same
framework of theory.
3.2. Polymorphs A1 to A3
Two polymorphic structures of dichlone were known prior to
this report. These polymorphs are designated by A1 [26] and A2
3. Result and discussion
3.1. Molecular interactions in polymorphs A1eA3, B1eB2 and
C1eC2
The ORTEP plots of polymorphs A3, B2 and C2 are shown in
Fig. 1. The crystallographic data is presented in Table 2. Hydrogen
Fig. 5.
p
$$$
p
stacking of symmetry equivalent molecule X (green, 3.532 Å) and Y (Blue,
&ctdot stacked
3.509 Å) molecules down b-axis. The interlayer spacing between
p
p
molecules; green (centroid separation being 4.619 Å), blue (centroid distance being
4.173 Å).
Fig. 4. Planar polymeric sheets of Dichlone in triclinic P-1 space group (A3) formed by
CeH/O and CeH/Cl interactions of ‘X’ and ‘Y’ molecules.
Fig. 6. Polymeric chain p-p stacked chains of compound ‘B1’ formed by NeH/O
interaction down a-axis.

286
D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
Fig. 7. Tetramer unit of compound ‘B2’ formed by NeH/O and CeH/O interaction down b-axis.
ꢀ
[27]. The structure given by Metras [26] showed that the crystal
belongs to the triclinic P-1, space group (A1). The crystals were
obtained from toluene, showed the cell parameters, a ¼ 18.18 Å
alternate molecule revealed p-p stacking interactions (~3.50 Å)
between the symmetry equivalent molecules when viewed down
b-axis (Fig. 2a). The molecules possess Cl∙∙∙O close contacts
(Fig. 2b) as well. Orthorhombic polymorph (A2) with space group
(a
¼ 112ꢁ 300), b ¼ 8.29 Å (
b
¼ 73ꢁ) and c ¼ 7.35 Å (
g
¼ 117ꢁ 300).
There are two molecules in unit cell and the centroid of every
Fig. 8. Chlorolawsone polymorph ‘C1’ (Pc) molecules down c-axis.
Fig. 9. p-p stacking of symmetry equivalence polymorph C2 chains down a-axis.

D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
287
Pb21a obtained from the melt of dichlone by Ikemoto et al. [27] in
are a ¼ 8.11(2)Å, b ¼ 3.93(2)Å, (
b
¼ 113ꢁ) and c ¼ 14.84(2)Å. When
1977. The cell parameters turns out to be a ¼ 16.204(12)Å,
viewed down a-axis (Fig. 6) molecules showed NeH/O interaction
(N(1)∙∙∙O(1) ¼ 2.849 Å). The polymeric chain further extends via
b ¼ 26.686(17) Å (
b
¼ 113ꢁ) and c ¼ 3.830(2) Å. Molecules are
denoted by ‘X1’ and Y10(Fig. S1 in ESIy). Chlorine, Cl(1) and Cl(2) of
molecule ‘X1’ showed Cl∙∙∙O close contacts, while molecule Y1
only Cl(3) facilitate Cl∙∙∙O close contacts (Fig. 3). Dimeric chains of
X1 and Y1, formed by CeH/O, CeH/Cl interaction and Cl/O close
contacts engendering extended polymeric chain as be viewed
down the c-axis.
p-p stacking (3.567 Å).
A polymorph of B2 obtained in the present work (polymorph
B2) by reaction of dichlone and aqueous ammonia and purified by
column chromatography with ether-ethyl acetate as eluent solvent
(named as B2). As may be noticed ‘B2’ crystallizes in monoclinic C2/
c space group (Fig. 1) with eight molecules in its unit cell. Each
molecule is in vicinity to six neighbouring molecules via NeH/O,
Polymorph of dichlone in the present work (A3) was obtained
from the unreacted fraction (of the column chromatography) of the
reaction of 2-aminophenol and dichlone, with toluene and meth-
anol as eluents. A parrot green color crystals belongs to triclinic
space group P-1(A3) with cell parameters being a ¼ 7.3279(1) Å,
(
a
¼
89.769(1)ꢁ),
b
¼
8.2765(1) Å,
(
b
¼
82.542(1)ꢁ) and
c ¼ 16.1368(3) Å (
g
¼ 67.0180(6)ꢁ). The cell parameters differed
ꢀ
from those of Metras [26]. Two molecules in the asymmetric unit
are denoted by ‘X’ and ‘Y’.
Molecules ‘X’ and ‘Y’ differ with respect to intermolecular
hydrogen bonding. Each molecule of ‘X’ is in close contact with four
‘Y’ and other two ‘X’ molecules. Further each molecule ‘Y’ in vicinity
to four ‘X’ and two other ‘Y’ molecules. The X and Y molecules
differed with respect to intermolecular CeH/O hydrogen bonding
interactions from.
C(6)eH(6)$$$O(20) in molecule X and C(70)-H(70)$$$O(1) in
molecule Y. The interactions from the O(2) and O(10), respectively of
X and Y are absent.
The CeH/O and CeH/Cl interactions in both molecules (X and
Y) form a planar sheet (Fig. 4) and
noticed on viewing down the b-axis in Fig. 5. The centroid sepa-
rations of stacked X$$$X molecules turned out to be 3.53 Å and
p-p stacked interactions can be
p-p
3.50 Å in Y/Y molecules. The interlayer spacing of symmetry
equivalent molecules varies and the centroid distance was turned
out to be 4.619 Å between ‘X’ molecules and 4.173 Å for ‘Y’ mole-
cules (Fig. 5).
Molecular structure of polymorph of B1 was reported by Hauw
et al. [31] in 1965 (polymorph B1). The crystals obtained in acetic
acid revealed monoclinic space group, Pc and the cell parameters
Fig. 10. Polymeric chain formed by OeH/O and CeH/O of ‘C2’ polymorph also
showed inter chain CeH/Cl interaction down b-axis.
Fig. 11. Optimized structures of monomer (a) A3, (b) B2 (c) C2. Atomic labeling scheme
is also shown along with.

288
D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
CeH/O and CeH/Cl (Fig. S2 in ESIy) intermolecular interactions.
Oxygen O(2) as well as the H(11A) and H(11B) showed bifurcated
NeH/O interaction. Polymeric chain is facilitated by N(11)
eH(1B)/O(2) and C(5)eH(5)$$$O(1) interactions. A tetrameric unit
of molecules was resulted from NeH/O interactions with
NeH(11A)∙∙∙O(2)(1/2 þ x, 1/2 þ y,z) and NeH(11B)/O(2) (1/
2ꢀx,ꢀ1/2 þ y, 1/2ꢀz) from the two parallel chains running in
opposite directions when viewed down the b-axis. The tetrameric
units are further joined by CH/Cl interactions (Fig. 7) viz., N(11)-
H(1A)∙∙∙O(2) (1/2ꢀx, ½þy, ½ꢀz) and C(8)eH(8)∙∙∙Cl(1) (x,2ꢀy, 1/
2 þ z).
Crystal structure of chlorolawsone has been known since 1965
by Hauw et al. [29] (polymorph C1). The crystals obtained by sub-
limation of the solid showed monoclinic space group Pc with one
molecule in asymmetric unit. The cell parameters are a ¼ 8.25(2) Å,
b ¼ 3.92(2) Å (
b
¼ 113.20ꢁ) and c ¼ 14.39(3) Å. The molecules
showed polymeric chain formed via OeH/O interaction, when
viewed down c-axis (Fig. 8) with O(1)$$$O(3) separations being
2.750 Å. The neighbouring polymeric chains reveal
p-p stacking
interactions between quinonoid and benzenoid ring with centroid
being separated by 3.561 Å.
The crystals of C2 were obtained in methanol in our laboratory
belong to monoclinic crystal system and the space group is Pn
(Fig. 1). The cell parameters are a ¼ 8.25530(15), b ¼ 3.90730(15),
c ¼ 13.4222(2) and
b
¼ 100.4200(8)ꢁ and there is one molecule in
the asymmetric unit. Each molecule is in vicinity to eight neigh-
bouring molecules facilitating OeH/O, CeH/O and CeH/Cl in-
teractions besides
p-p stacking. Thus polymeric chain extends
Fig. 12. Optimized structures of dimer (a) A3, (b) C2. Atomic labeling scheme is also
shown along with.
through O(2)eH(2)$$$O(3) and C(8)eH(8)$$$O(3) interactions
(Fig. 9) when viewed down a-axis. The polymeric chains are con-
nected by C(5)eH(5)$$$Cl(1)) interactions (Fig. 10) can be seen
down b-axis. The neighbouring chains are stabilized owing to p-p
stacking interactions (Fig. 9) between benzenoid and quinonoid
rings.
well with those observed in the X-ray crystal data (cf Table 4). To
understand interplay between halogen and hydrogen bonding we
delve into dimer formation by ‘A3’, ‘B2’ and ‘C2’ conformers. Opti-
mized dimers are shown in Fig. 12.
3.3. DFT investigations
The present theoretical calculations revealed that ‘A3’ and ‘C2’
tend to form dimer species; the corresponding binding energies
turned out to be 7.0 kJ molꢀ1 and 17.5 kJ molꢀ1, respectively. As
opposed to this the conformer ‘B2’ does not favor dimer formation
and calculated binding energies turn out to be largely negative
(ꢀ63 kJ molꢀ1). These inferences are in consonance with the X-ray
crystal structure experiments. Noteworthy enough, the dimer ‘A3’
possess Cl$$$O close contacts (the separation being 3.1 Å). The
dimer C2 on the other hand, are rendered with the OeH/O
(2.20 Å) hydrogen bonding. The density functional theoretic
structures thus corroborate inferences drawn from the single
crystal X-ray diffraction experiments. To simulate the influence of
Optimized structures of monomer ‘A3’, ‘B2’ and ‘C2’ from the
density functional theory are portrayed in Fig. 11. The net atomic
charges derived from the population analyses based on Hirshfeld
partitioning scheme are given in parentheses. Structural parame-
ters of local minima on the potential energy surface agree fairly
Table 4
Selected bond distances (in Å) in A3 and C2 dimer in the gas phase and in methanol.
A3
C2
Gas
Methanol
Gas
Methanol
CeCl(1)
CeCl(2)
CeCl(3)
CeCl(4)
C¼O(1)
C¼O(2)
C¼O(3)
C¼O(4)
CeH(1)
CeH(2)
CeH(3)
CeH(4)
CeH(5)
CeH(6)
CeH(7)
CeH(8)
OeH(5)
OeH(6)
1.718
1.712
1.708
1.727
1.210
1.215
1.218
1.222
1.087
1.082
1.087
1.082
1.083
1.089
1.085
1.081
1.709
1.713
1.703
1.706
1.204
1.205
1.204
1.209
0.929
0.931
0.930
0.929
0.929
0.930
0.930
0.930
1.76
1.76
1.76
1.76
Table 5
The comparison of experimental and calculated vibrational frequencies (scaled by
0.9657) in cmꢀ1 of A3, B2 and C2. The experimental values are given in parenthesis.
1.258
1.258
1.258
1.258
1.070
1.070
1.070
1.070
1.070
1.070
1.070
1.070
0.96
1.258
1.257
1.258
1.258
1.070
1.070
1.070
1.070
1.070
1.070
1.070
1.070
0.96
A3(dimer)
3165, 3127
B2 (monomer)
C2(dimer)
n(CH)
3121(3294)
3111(3109, 2977)
1646(1678)
1819
3199(3268)
3110
1733
1760(1865)
1704(1765)
1698(1699, 1669, 1640)
1636(1584)
n
n
n
n
n
n
(C]O1)
(C]O2)
(C]O3)
(C]O4)
(C]C)
1776(1776)
1747(1703)
1730(1678)
1704
1634
1656(1591, 1552)
3618(3474)
3612
(NH2)
n
n
(O3H)
(O6H)
3627(3736)
3538(3674)
0.96
0.96

D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
289
a)
b)
2000
100
1500
1000
500
3500
3000
2500
0
100
0
90
80
70
500
1000
1500
200
400
B2 Simulated
B2 observed
B2 Simulated
B2 observed
2000
1500
1000
500
Wavenumber(cm-1)
Wavenumber(cm-1)
c)
2000
1500
1000
500
4000
0
3500
3000
2500
100
0
500
80
60
40
20
80
500
60
1000
1500
1000
1500
40
Monomer
Dimer
Monomer
Dimer
C2 Observed
20
C2 observed
2000
1500
1000
500
4000
3500
3000
2500
Wavenumber(cm-1)
Wavenumber(cm-1)
Fig. 13. Optimized and observed IR spectra of a) ‘A3’, b) ‘B2’ and c) ‘C2’.
solvent on the structure of these dimers we further carried out the
SCRF-PCM calculations using methanol as the solvent. The struc-
tural parameters obtained are displayed in Table 4. Structural
ramifications of such interactions in vibration frequencies can
further be probed through the normal vibration analysis. A com-
parison of calculated vibrational frequencies (scaled by a factor of
0.9657) of the monomer ‘B2’ and dimers ‘A3’ and ‘C2’ with those
observed has been given in Table 5. Theoretical computed spectra
are also compared with those measured in experiment in Fig. 13.
1H NMR chemical shifts in monomers as well as those in dimers
in DMSO were simulated through the SCRF-PCM theory at the M06-
2x/6-31þþG(d,p) level of theory. Overall the calculated dH values
(Table 6) are in consonance with experiments and generally exhibit
larger deshielding relative to those measured in the experiment.
Frontier orbitals HOMO and LUMO of A3, B2, C2 dimers portrayed in
Figs. 14 and 15 revealed the electron-rich regions localized exclu-
sively on one of the monomer. The complementarily of electronic
distributions can be noticed in these orbital’s. Moreover, the Time
Dependent Density Functional Theory (TDDFT) calculations
revealed several bands in the electronic spectra of ‘A3’, ‘B2’ and ‘C2’
in the gas phase and in methanol agree well with experiment. The
MO’s and assignments of electronic transitions in the UV spectra of
Table 6
1H chemical shift (in ppm) in DMSO for monomer and dimer values. The experi-
mental values are given in parenthesis.
A3 monomer B2 monomer C2 monomer A3 dimer C2 dimer
H(1) 9.4(8.18)
H(2) 8.9(7.8)
H(3)
H(4)
H(5)
9.2(8.16)
9.2(7.65)
9.5(7.70)
9.4(8.17)
6.2(5.5)
9.2
9.2
9.5
9.6
8.2
9.1
9.5
9.3
10.3
9.5
9.1
9.2(8.00)
8.9(7.86-7.74)
9.2(8.00)
10.7(7.86-7.74)
8.5(3.89)
10.7
H(6)
6.8(5.5)
H(7)
8.9
9.4
H(8)
9.5
9.5
H(9)
9.6

290
D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
Fig. 14. Frontier orbital’s (HOMO and LUMO) in monomer (a) A3 (b) B2 and (c) C2.
Fig. 15. Frontier orbital’s (HOMO and LUMO) in dimer (a) A3 and (b) C2.

D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
291
Fig. 16. MO diagram explaining the electronic spectra of A3 monomer (left) and A3 dimer (right).
Fig. 17. MO diagram explaining the electronic spectra of B2 monomer.
A2, B2 and C2 from the TDDFT theory has been shown in
Figs. 16e18. The wavelength maxima (lmax), oscillator strength (f)
along with excitation energies (Eex) of A3 and C2 are summarized in
Tables 7a and b. The absorption band near 307 nm of the dimer A
arises from the (HOMO-2) to LUMO transition.
polymorphs monoclinic Pc (B1) and C2/C (B2). Compound C: 2-
chloro-3-hydroxy-1,4-naphthoquinone crystallizes as two poly-
morphs in triclinic Pc (C1) and Pn (C2). Structural parameters,
spectral characteristics observed in infrared, 1H NMR, UVevisible
spectra are presented. The dispersion corrected M06-2x density
functional calculations showed that the compound A3 possesses
halogen bonding interactions while the crystalline network in C2
extends through hydrogen bonding interactions. Compound B2
void of both such interactions does not favor dimer formation.
TDDFT has been used to assign the transitions in the electronic
spectra.
4. Conclusions
Compound A: 2,3-dichloro-1,4-naphthoquinone possess three
polymorphs viz. triclinic P-1 (A1 and A3), orthorhombic; Pb21a (A2).
Compound B: 2-amino-3-chloro-1,4-naphthoquinone showed two

292
D. Chaudhari et al. / Journal of Molecular Structure 1120 (2016) 281e293
Fig. 18. MO diagram explaining the electronic spectra of C2 monomer (left) and C2 dimer (right).
Table 7a
Wavelength maxima (lmax, nm), oscillator strengths (f) and assignments of bands in the electronic spectra of the monomer A3, B2, and C2 in methanol from TDDFT. The
experimental values are given in parenthesis.
Transition
A3
B2
C2
Eex(eV)
lmax (nm)
(f)
Eex(eV)
lmax (nm)
(f)
Eex(eV)
lmax (nm)
(f)
Homo/Lumo
3.7
4.2
4.8
6.6
333(339)
302(289)
261
0.0069
0.1047
0.3885
0.3050
3.1
4.3
4.7
5.3
404(449)
291(332)
265(284)
234
0.0611
0.0943
0.2971
0.4588
3.5
4.2
4.7
5.6
361(321, 472)
297(287)
263
0.0293
0.1121
0.3565
0.4596
Homo-1/ Lumo
Homo-2 /Lumo
Homo/ Lumoþ1
188
220
Table 7b
Wavelength maxima (lmax), oscillator strengths (f) and assignments of bands in the electronic spectra of the dimer A3, and C2 in methanol from TDDFT. The experimental
values are given in parenthesis.
Transition
A3
C2
Eex(eV)
lmax(nm)
(f)
Eex(eV)
lmax(nm)
(f)
Homo / Lumo
4.5
4.7
274(287)a
261
0.0877
0.2516
Homo-4 / Lumoþ1
Homo-2 / Lumo
Homo / Lumoþ1
Homo-1 / Lumo
Homo-2 / Lumoþ1
5.0
4.0
3.7
263
307 (289)
335(339)
0.5003
0.1292
0.0082
3.5
3.4
4.2
356(321)
365
296
0.0213
0.0284
0.1214
a
Experimental values.
Acknowledgements
Appendix A. Supplementary data
SSG is grateful to ISRO Project 136 (“Naphthoquinone containing
metal polypyridyl complexes for Solar Cells: Computational and
experimental Study”) India for financial support. DC acknowledge
University Grants Commision (UGC), New Delhi, India for Merito-
rious fellowship. SPG acknowledges the support from the Board of
Research in Nuclear Sciences, India in the form of the research
project (37(2)/14/11/2015-BRNS). DNL is thankful to Savitribai
Phule Pune University for the award of research fellowship through
the University of potential excellence scheme from the UGC, New
Delhi, India.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.05.022.
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