Polymorphs and solvates of 2-(1,4-dihydro-1,4-dioxonaphthalen-3-ylthio) benzoic acid

Article abstract of DOI:10.1021/cg300318u

Three conformational polymorphs of 2-(1,4-dihydro-1,4-dioxonaphthalen-3- ylthio) benzoic acid (L), an acetonitrile solvate of L, and cocrystal of L with 2,2′-bipyridine are structurally characterized. The two polymorphs I and II have Z′ = 1 and possess R₂²(8) type of dimeric structure in which the two aromatic rings are in trans disposition across the cyclic hydrogen bonded motifs. However, the dihedral angles between the aromatic ring and 2-methyl 1,4-naphthoquinone rings are -129.38° and 126.56°, respectively. The polymorph III has Z′ = 2; it shows R₂ ²(8) type of dimeric structures which are formed by two symmetry independent molecules. In its crystal lattice, the aromatic rings across the cyclic hydrogen bond motifs are in cis dispositions. Dihedral angles between the aromatic ring and 2-methyl 1,4-naphthoquinone ring in the two symmetry independent molecules are 114.82° and 125.27°, respectively. The acetonitrile solvate of 1 has Z′ = 3. In its crystal lattice, it has two symmetry independent molecules forming R₂²(8) hydrogen bonds to form dimeric assemblies and another cyclic R₂²(8) type hydrogen bond geometry between molecules which constitute the third set of symmetry independent molecules. The 2-(1,4-dihydro-1,4-dioxonaphthalen-3- ylthio)benzoic acid also forms a 2:1 cocrystal with 2,2′-bipyridine; in this cocrystal the two nitrogen atoms are trans to each other and they participate in hydrogen bonds with carboxylic acids.

Full text of DOI:10.1021/cg300318u

Article
pubs.acs.org/crystal
Polymorphs and Solvates of 2-(1,4-Dihydro-1,4-dioxonaphthalen-3-
ylthio)benzoic Acid
Bigyan R. Jali and Jubaraj B. Baruah*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
S
* Supporting Information
ABSTRACT: Three conformational polymorphs of 2-(1,4-dihydro-1,4-
dioxonaphthalen-3-ylthio) benzoic acid (L), an acetonitrile solvate of L, and
cocrystal of L with 2,2′-bipyridine are structurally characterized. The two
2
polymorphs I and II have Z′ = 1 and possess R2 (8) type of dimeric structure
in which the two aromatic rings are in trans disposition across the cyclic
hydrogen bonded motifs. However, the dihedral angles between the aromatic
ring and 2-methyl 1,4-naphthoquinone rings are −129.38° and 126.56°,
2
respectively. The polymorph III has Z′ = 2; it shows R2 (8) type of dimeric
structures which are formed by two symmetry independent molecules. In its
crystal lattice, the aromatic rings across the cyclic hydrogen bond motifs are in cis dispositions. Dihedral angles between the
aromatic ring and 2-methyl 1,4-naphthoquinone ring in the two symmetry independent molecules are 114.82° and 125.27°,
respectively. The acetonitrile solvate of 1 has Z′ = 3. In its crystal lattice, it has two symmetry independent molecules forming
2
2
R2 (8) hydrogen bonds to form dimeric assemblies and another cyclic R2 (8) type hydrogen bond geometry between molecules
which constitute the third set of symmetry independent molecules. The 2-(1,4-dihydro-1,4-dioxonaphthalen-3-ylthio)benzoic
acid also forms a 2:1 cocrystal with 2,2′-bipyridine; in this cocrystal the two nitrogen atoms are trans to each other and they
participate in hydrogen bonds with carboxylic acids.
INTRODUCTION
Polymorphism is the existence of the same chemical composition
in more than one crystalline modification, and solvates refer to
■
Figure 2. The crystal morphology of polymorphs I−III and acetonitrile
solvate IV.
We have shown that the packing pattern guided by weak
C−H···O interactions helps in the formation of different motifs
in sulfur-containing quinone compounds.7 Quinone compounds
having thiolate groups show conformational polymorphism.8 But
because of subtle energy differences among the polymorphic
structures only stable ones are generally isolated.7a Conforma-
tional polymorphs in quinonic type compounds such as
fuchsones are well documented, but the approach has not been
extended to quinones.9 Thus, we felt that introduction of a
functional group such as carboxylic acid capable of forming
hydrogen bonds in different ways may help in getting more
numbers of stable conformational polymorphs. Carboxylic acids
Figure 1. (a−d) Some dimeric hydrogen bonded motifs of carboxylic
acid.
the cases in which the same given substance includes solvent
during crystallization.1 The necessities to design crystalline solids
with desired structures and properties led to great progress in the
study of polymorphism.2 Controlling the formation of a specific
polymorph is a challenge3 in crystal engineering. The solvents
have an important role in the preparation of polymorphs.4
Polymorphism tends to be prominent in molecules that have
multiple options for hydrogen bond formation,5 which is
reflected in a number of active pharmaceutical ingredients.6
generally adopt the R2 (8) type10 of cyclic structure; puckering of
2
such structural motifs may lead to other orientations (Figure 1),
Received: March 7, 2012
Revised: May 2, 2012
Published: May 8, 2012
© 2012 American Chemical Society
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Scheme 1. Different Polymorphs, Solvates, and Cocrystals of L
Figure 3. (a) ORTEP diagram of polymorph I drawn with 50% thermal ellipsoids. (b) Cyclic H-bonding motif. (c) C−H···O and π-interactions in
polymorph I. (d) The packing diagram a-crystallographic axis.
which may be stabilized by the hydrogen bond interactions of the
carbonyl groups of quinone.
to a thiosalicylic acid part can be considered as a model
compound of medicine, in which a part having nutrient value is
attached to a medicinal component. With these points in mind,
we have synthesized a 2-methyl 1,4-naphthoquinone function-
alized carboxylic acid 2-(1,4-dihydro-1,4-dioxonaphthalen-3-
ylthio)benzoic acid (L) to study its polymorphs. During our
systematic investigation, we have obtained three conformational
polymorphs (I, II, and III), one acetonitrile solvate (IV), and one
cocrystal (V) with 2,2′-bipyridine of L as shown in Scheme 1. The
structural study of all these polymorphs is demonstrated.
Further to these, the study of the structural aspects of
2-methyl-naphthoquinone derivative such as L (Scheme 1) would
throw light on the assembling properties of thiosalicylic acid
derivatives that are used as active pharmaceutical ingredients.11
Moreover, the 2-methyl-napthoquinone part attached to the
thiosalicylic acid has some structural similarities to vitamin K, and
some of these compounds show interesting polymorphic
structures.12 Thus, a 2-methyl-naphthoquinone unit attached
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Table 1. Hydrogen Bond Parameters (Å, °) for Polymorphs I, II, III
polymorph
D−H···A
dD−H
dH···A
dD···A
∠D−H···A
I
O4−H4A···O3 [3 − x, 2 − y, −z]
C11−H11C···S1
C13−H13···O2 [−1 + x, y, z]
C16−H16···O4
O4−H4A···O3 [3 − x, 2 − y, −z]
C11−H11A···S1
C11−H11B···O1
0.82
0.96
0.93
0.93
0.82
0.96
0.96
0.93
0.93
0.82
0.82
0.93
0.93
0.93
0.96
0.96
0.93
0.93
1.84
2.69
2.44
2.36
1.84
2.77
2.38
2.48
2.40
1.82
1.81
2.58
2.56
2.57
2.77
2.36
2.58
2.66
2.66 (2)
3.14 (3)
3.29 (3)
2.70 (3)
2.64 (10)
3.08 (10)
2.81 (12)
3.13 (12)
2.73 (12)
2.63 (3)
2.62 (3)
3.30 (5)
3.17 (5)
3.18 (5)
3.12 (4)
2.74 (5)
3.37 (4)
3.19
173.4
109.2
152.5
132.2
168.0
100.1
107.0
127.4
101.0
175.4
171.5
134.9
123.8
123.2
103.0
103.0
143.8
116.9
II
C16−H16···O1 [1 + x, 1 + y, z]
C16−H16···O4
III
O3−H31···O7 [2 − x, 1/2 + y, 1/2 − z]
O8−H8···O4 [2 − x, −1/2 + y, 1/2 − z]
C2−H2···O4 [1 − x, −1/2 + y, 1/2 − z]
C3−H3···O6 [−1/2 − x, −y, −1/2 + z]
C4−H4···O6
C11−H11A···S1
C11−H11B···O1
C13−H13···O2 [−1 + x, y, z]
C20−H20···O5
Figure 4. (a) Structure polymorph II (50% thermal ellipsoids). (b) Dimeric H-bond motif. (c) Selected C−H···O, C−H···π interactions. (d) Packing
diagram of II.
leading to substituted naphthoquinones are well documented in the
literature.13 As illustrated in Scheme 1 from compound L we could
obtain three polymorphs I−III in unsolvated form and its acetonitrile
solvate. The crystal morphology of each polymorph is different and
the optical micrographs showing their crystal morphology are shown
in Figure 2.
RESULTS AND DISCUSSION
■
The 2-(1,4-dihydro-1,4-dioxonaphthalen-3-ylthio)benzoic acid
(L) was prepared by coupling of the 2-methyl 1,4-napthoquinone
with thiosalicylic acid in aerial condition. The reaction passes through
formation of 1,4-dihydroxy naphthalene derivative which gets quickly
oxidized under ambient conditions. Such coupling reactions directly
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Figure 5. (a) ORTEP diagram of polymorph III (50% thermal ellipsoids). (b) The arrangement of symmetry independent molecules in lattice (X red
and Y blue). (c) Weak interaction among molecules of polymorph III. (d) Packing diagram of III embracing of two molecules of one type of symmetry
by six molecules of another type.
Figure 6. Torsion angles of polymorph (a) I, (b) II, (c) III showing the orientation of the thiosalicylic acid part with respect to the 2-methyl 1,4-
naphthoquinone part.
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Crystallization of 2-(1,4-dihydro-1,4-dioxonaphthalen-3-
ylthio)benzoic acid L from different solvents such as THF/
acetone, methanol, and chloroform led to three different
polymorphs I−III. Polymorph I crystallizes in triclinic space
Polymorph II crystallizes in monoclinic space group P21/c
from a solution of L in methanol. The ORTEP diagram of the
polymorph II is shown in Figure 4a. Crystal packing of the
polymorph II shows that the carboxylic acids are engaged in
strong O4−H4···O3 interactions. Such interactions lead to the
group P1 from a solution L in mixed solvents of THF and
̅
acetone. In its crystal structure (Figure 3a), it is observed that the
sulfur atom bearing 2-methyl 1,4-naphthoquinone groups are
Table 3. Hydrogen Bond Geometries (Å, °) for Solvate IV and
Cocrystal V
trans to each other across a R2 (8) type of cyclic hydrogen bond
2
motif (Figure 3b). The carboxylic acid groups exhibit strong
O4−H4A···O3 interactions and form a cyclic hydrogen bond
architecture as shown in Figure 3b. Polymorph I forms a layered
1D polymeric structure in the lattice through C−H···O (Table 1)
interactions. Interestingly, polymorph I exhibits strong C18−
O3···S1 interactions in its lattice. The polymorph I also shows
π···π interactions between the phenyl moiety and the carboxylic
acid group containing a carbon atom with a distance
C13Phenyl···C18carboxy 3.379 Å as shown in Figure 3c.
solvate/
cocrystal
∠D−
D−H···A
O7−H7···O10
O9 −H9···O8
dD−H dH···A dD···A H···A
IV
0.82 1.86 2.68(3) 177.3
0.82 1.85 2.66(3) 172.9
O11−H11···O12 [−x, 1 − y, −z] 0.82 1.80 2.61(3) 173.9
C11−H11A···S1
C29−H29C···S2
C34 −H34···O9
C47− H47C···S3
C49−H49···O2 [x, −1 + y, z]
C56 −H56···O1 [−1 + x, y, z]
0.96 2.70 3.13(4) 108.5
0.96 2.68 3.15(4) 111.6
0.93 2.34 2.68(4) 101.5
0.96 2.64 3.13(3) 113.1
0.93 2.43 3.23(4) 144.9
0.96 2.33 3.15(5) 142.8
Table 2. Torsion Angles of Polymorphs I−III
C56−H56···O4 [1 − x, 1 − y, 1 − z] 0.96 2.31 3.25(5) 167.5
V
C11−H11B···S1
C13−H13···O3 [−1 + x, y, z]
C16−H16···O2
0.96 2.69 3.09
0.93 2.53 3.42
0.93 2.37 2.70
0.93 2.47 3.25
106.6
161.7
101.1
141.4
164.1
167.1
103.0
polymorph
dihedral angles
I
C6−C7−S1−C12, −129.38°; C8−C7−S1−C12, 57.82°
C6−C7−S1−C12, 126.56°; C8−C7−S1−C12, −62.88°
For X-set: C6−C7−S1−C12, 114.82°; C8−C7−S1−C12,
II
III
C19−H19···O1
C20−H20···O1 [1 − x, 1 − y, 1 − z] 0.93 2.60 3.49
C23−H23···O2 0.93 1.87 2.76
C23−H23···N1 [1 − x, −y, 1 − z] 0.93 2.48 2.83
−73.09°.
For Y-set: C24−C25−S2−C30, 125.27°; C26−C25−S2−C30,
−64.57°.
Figure 7. (a) ORTEP diagram of IV (drawn with 50% thermal ellipsoids). (b) The H-bond interactions to form dimeric assemblies among symmetry
independent molecules. (c) Weak interactions contributing to self-assembly formation in IV.
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formation of cyclic hydrogen bond architectures as shown in
Figure 4b. The packing pattern of the polymorph II is guided by
C16−H16···O1 and C2−H2···O2 interactions (Table 1). These
overall weak interactions help in generating a 1D polymeric
structure. Besides that, the structure of polymorph II extends to a
1D zigzag architectures by strong π···π interactions of the phenyl
moiety with the carbon atom of the carboxylic acid group
(C13Phenyl···C18carboxy 3.34 Å) as shown in Figure 4c.
The polymorph III is obtained from a solution of L in
chloroform; it crystallizes in orthorhombic space group P212121.
The structure of the polymorph III is shown in Figure 5a. Poly-
morph III has two symmetry independent molecules (X and Y)
in the crystallographic asymmetric unit as shown in Figure 5b.
From the crystal lattice, it is observed that sulfur atom bearing
2-methyl 1,4-naphthoquinone groups are cis to each other across
R2 (8) types of cyclic hydrogen bond motif architectures as
2
shown in Figure 5b. Both the molecules exhibit strong
O3−H3A···O7 and O8−H8···O4 (Table 1) interactions, leading
to formation of a cyclic hydrogen bond architecture. It is
observed that polymorph III assembles in the lattice through
C20−H20···O5 interactions. Oxygen atoms on quinones are
involved in bifurcated C3−H3···O6 and C4−H4···O6 interactions
to form a 1D linear architecture as shown in Figure 5c. Besides that
polymorph III adopts a 1D layered structure by strong π···π
interactions between phenyl moieties with the carboxylic
acid groups. The packing diagram of the molecules shown in
Figure 5d indicates that there are pair of molecules of one type of
symmetry get embraced by six molecules that have another type
of symmetry. If we compare the packing pattern of polymorph I
one can see an arrangement of head−head (Figure 3d), whereas
in polymorph II has head to tail arrangements (Figure 4d).
These make the lattice of these three polymorphs clearly
distinguishable.
From these structures, it is observed that the torsion angle of
C8−C7−S1−C12 and C6−C7−S1−C12 of polymorph II are
−62.88°, 126.56°, whereas in polymorph I the torsion angles of
C8−C7−S1−C12 and C6−C7−S1−C12 are 57.82° and
−129.38° (Figure 6), respectively, which shows the difference
between the conformation of the polymorphs I and II. Both
symmetry independent molecules of the polymorph III (X and Y)
show different torsion angles. The torsion angle for X-set,
namely, C8−C7−S1−C12, C6−C7−S1−C12 are −73.09° and
114.82°, respectively, whereas torsion angles of C26−C25−S2−
C30, C24−C25−S2−C30 for molecules designated as Y-set are
−64.57° and 125.27°, respectively. The torsion angles are shown
in Table 2.
Figure 8. Solid state IR (KBr, cm−1) spectra of in the region of 1800−
1200 cm−1 of polymorph I (top, blue line) and cocrystal V (bottom,
red line).
Figure 9. (a) Asymmetric unit of the cocrystal V. (b) O−H···N interactions in V. (c) Weak interactions in crystal lattice of V. (d) Crystal
morphology of V.
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molecules of L (X, Y, and Z) with one solvate molecule
(acetonitrile) in the crystallographic asymmetric unit (Figure
7a). In solvate IV, among the three symmetry independent L,
two of them, namely, the X and Y-set of molecules, are engaged in
R2 (8) type of cyclic hydrogen bond motif, whereas the Z-set of
2
molecules leads to the formation of a cyclic hydrogen bonding
architecture among themselves (Figure 7b). The hydrogen bond
parameters are listed in Table 3. Thus, the dimeric hydrogen
bonds are not broken by acetonitrile as guest molecules. It is
observed that sulfur atoms bearing 2-methyl 1,4-naphthoqui-
none groups are trans to each other. From the crystal lattice, it is
observed that solvate IV assembles through C−H···O
interactions between the quinonic moieties and solvent
molecules. This leads to the formation of a 1D zigzag
supramolecular polymeric structure.
Interestingly, the N atom of acetonitrile molecules exhibits
bifurcated C20−H20···N1 and C31−H31···N1 interactions
(Figure 7c). The solvate IV has an extended 1D layer supported
by strong lateral π···π interactions between phenyl moieties with
the carboxylic acid groups.
There are possibilities of formation of salt as well as cocrystal
of L with 2,2′-bipyridine. But when the compound L was reacted
with with 2,2′-bipyridine, we observed cocrystal formation
between them. The evidence comes from the IR spectra of the
cocrystal with compound L. For clarity if one looks at the IR
spectra of the cocrystal V and compares it with the IR spectra of L
(Figure 8), it is observed that the signature of the carbonyl
stretching of carboxylic acid at 1683 cm−1 is retained in the
cocrystal V. However, there is broadening occurring due to
additional peaks from cocrystal V. A salt formation would have
changed the position of this peak significantly supporting the
cocrystal formation in this case. Further, the O−H stretching of
the L and the cocrystals V have a very close resemblance; these
stretching frequencies appear as broad signals at 3444 cm−1 and
3452 cm−1, respectively (Supporting Information), confirming
the identity of V as a cocrystal.
Figure 10. Differential scanning calorimetry of polymorph I−III
(heating rate 5 °C per minute).
A 2:1 cocrystal of L with 2,2′-bipyridine, V crystallizes in
triclinic space group P1. The asymmetric unit of the cocrystal
̅
comprises one L along with the half of the 2,2′-bipyridine
molecule (Figure 9a). The 2,2′-bipyridine acts as a bridge
between the two carboxylic acid molecules. The two nitrogen
atoms are hydrogen bonded to carboxylic acids through O2−
H2···N1 interactions as shown Figure 9b. The nitrogen atoms of
the 2,2′-bipyridine are in a trans-disposition across the C−C
connecting the two rings. There are very weak C−H···O (Table 3)
interactions to provide rigidity to the assembly as shown in
Figure 9c. Participation of the C−H bond present at the ortho-
position of an aromatic ring is commonly encountered in
cocrystals of carboxylic acid with pyridine or quinoline
molecules.15 The 2,2′-bipyridine molecules are found to be
intercalated in the layers between the carboxylic acid molecules,
thereby making a sheetlike intercalated structure. It may be
mentioned that 4,4′-bipyridine forms salts with different aromatic
dithio aromatic acids,15a and in such cases the proton transfer
takes place to form ionic type of interactions. In our case, we
observe trans geometry of the 2,2′-bipyridine molecule which is
present in the parent molecule,16 and this shows that even
though there is possibility to adopt a cis-geometry through the
two nitrogen atoms via bifurcated hydrogen bonding to acidic
hydrogen atom it prefers to retain its original geometry. This
makes a distinction on conformation of 2,2′-bipyridine in a
supramolecular and coordination environments; in the latter case
the cis-geometry to form chelate is preferred.
The structures containing more than one molecule in the
crystallographic asymmetric unit are suggested to be important
for close inspection of the reaction coordinate of supramolecular
reactions.14a There are good numbers of examples of
polymorphic systems that have multiple Z′.14 In the present
polymophs I−III, we can clearly see a very close correlation
between the structures; namely, structures of I and III are
analogous to regio-isomers in organic chemistry. In this case, the
positions of the substituents across a rigid functionality formed
by supramolecular interactions (dimeric carboxylic acid part)
cause the differences in these structures, whereas polymorphs I
and II have slight orientation differences in the position of the
rings across the cyclic dimeric H-bonded motifs. This is revealed
in the torsion angle between the two aromatic rings present in
these polymorphs. The torsion angles between the aromatic ring
and 2-methyl 1,4-naphthoquinone ring in I and II are −57.04°
and 126.56°, respectively.
It is interesting to know while formation of the solvates the
original packing pattern of any of the polymorphs and the weak
interaction patterns of the polymorphs are retained in them or
not. Thus we have studied the structure of an acetonitrile solvate
of L and a cocrystal of 2,2′-bipyridine with L. Solvate IV
crystallizes in triclinic space group P1. The crystal structure of the
̅
IV is shown in Figure 7a. It has three symmetry independent
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Table 4. Crystallographic Parameters of I−V
compound no.
formulas
I
II
III
IV
V
C18H12O4S
324.25
C18H12O4S
324.25
C18H12O4S
324.25
C56H39NO12S3
1014.09
C23H16NO4S
402.44
formula wt
crystal system
space group
a (Å)
triclinic
monoclinic
P21/c
orthorhombic
P212121
4.903(3)
22.146(12)
27.486(14)
90.00
triclinic
triclinic
P1
P1
̅
P1
̅
̅
4.78 (4)
7.93 (5)
20.85 (15)
89.02
4.941(2)
10.113(5)
30.621(14)
90.00
7.7394(3)
13.4693(6)
24.0125(12)
103.506(12)
99.067(3)
96.329(3)
2375.18(18)
2
5.0244 (3)
9.5728 (6)
19.9981 (13)
82.573 (5)
84.043 (4)
85.488 (5)
946.56 (10)
2
b (Å)
C (Å)
α (°)
β (°)
γ (°)
V (Å3)
83.94
93.72 (3)
90.00
90.00
73.13
90.00
752.43 (10)
2
1527.0(12)
4
2985.0(3)
8
Z
density/Mg m−3
abs coeff /mm−1
F(000)
1.432
1.411
1.444
1.418
1.412
0.233
0.230
0.235
0.225
0.202
336
672
1344
1052
418
total no. of reflections
reflections, I > 2σ(I)
max 2θ/°
ranges (h, k, l)
7534
6844
26663
25441
4344
1635
1822
2486
5286
4318
50.00
49.66
50.00
48.46
54.90
−5 ≤ h ≤ 5
−9 ≤ k ≤ 9
−24 ≤ l ≤ 24
100.0
−5 ≤ h ≤ 5
−11 ≤ k ≤ 11
−36 ≤ l ≤ 36
98.6
−5≤ h ≤ 5
−26 ≤ k ≤ 26
−33 ≤ l ≤ 33
100.0
−8 ≤ h ≤ 8
−15 ≤ k ≤ 15
−27 ≤ l ≤ 27
95.8
−6 ≤ h ≤ 6
−12 ≤ k ≤ 12
−25 ≤ l ≤ 25
100.0
complete to 2θ (%)
data/restraints/parameters
GOF (F2)
2666/0/210
1.161
2596/0/210
1.091
3160/0/419
1.044
7652/0/656
1.007
4344/0/263
0.954
R indices [I > 2σ(I)]
R indices (all data)
0.0330
0.0431
0.1023
0.0296
0.0452
0.0492
0.2140
0.0357
0.0697
0.0493
Powder X-ray diffraction (PXRD) patterns of the samples
whose structures are presented can be indexed and comparable
to their respective simulated PXRD patterns to a satisfactory
extent (Supporting Information); there are few unassigned peaks
especially in the case of polymorph 2. So, we have recorded the
PXRD of the thiosalicylic acid to see if any amount is present in it
as an impurity (please see Supporting Information). Comparing
the PXRD of thisalicylic acid with the PXRD of polymorph II,
matching was not observed; thus, the additional peaks
encountered in the case of II may be attributed to the phase
impurity during crystallization. Differential scanning calorimetry
analyses show endothermic peaks in the cases of I−V.
The differential scanning calorimetry has been one of the key
methods to identify the monotropic and enantiotropic systems,17
and these are guided by Burger and Ramberger rules;17b
however, in our DSC the plots of each of I−III are independent
of each other and common endothermic processes as well as
reversibility on cooling are not observed in our case. DSC profiles
of the polymorphs I−III have clear distinctions and are shown
in Figure 10. Endothermic processes at 240 and 251 °C for I;
215.0 °C for II; at 205.9 °C and at 241.7 °C for III respectively
are observed. These corresponding to melting points followed by
phase transition are thus characteristic of the polymorphs and
clearly indicate the difference in packing patterns in the solid
state.
quinone tethered carboxylic acid to stabilize such conformational
changes across a supramolecular motif to observe polymorphs.
The weak interactions associated with the substituent on
quinone rings helps in stabilizing different supramolecular
structures. The salvation, as in the case of solvate IV and
cocrystals formation, as in the case of V, can lead to either
retention or disruption of hydrogen bonded dimeric assemblies
of carboxylic acid units.
EXPERIMENTAL SECTION
■
2-(1,4-Dihydro-2-methyl-1,4-dioxonaphthalen-3-ylthio)-
benzoic acid (L). A solution of 2-methyl-1,4-naphthoquinone (0.34 g,
2 mmol), thiosalicylic acid (0.30 g, 2 mmol) in methanol (20 mL) was
stirred for 3 h at room temperature. The color of the reaction mixture
slowly turned yellow followed by formation of yellow precipitate. The
precipitate was collected by filtration and dried in open air. Yield: 95%.
IR (KBr, cm−1): 3444 (m), 2922 (w), 2846 (w), 1683 (m), 1661 (s),
1589 (m), 1459 (w), 1417 (s), 1300 (m), 1283 (s), 1179 (w), 1035 (m),
955 (m), 842 (w), 787 (w), 741 (w), 710 (w), 650 (w). 1HNMR (400
MHz, DMSO-d6): 8.06 (d, J = 7.2 Hz, 1H), 7.92 (dd, J = 2.4 Hz, 1H),
7.85 (dd, J = 2.4 Hz, 1H), 7.83 (d, J = 7.2 Hz, 1H,), 7.32 (d, J = 6.0
Hz,1H), 7.29 (dd, J = 7.2 Hz, 2H), 7.23 (d, J = 6.0 Hz, 1H) 2.34 (s, 3H).
13C NMR (DMSO-d6): 182.7, 180.0, 167.5, 152.8, 142.5, 138.4, 134.1,
134.0, 132.4, 132.1, 132.0, 130.9, 128.9, 128.3, 126.5, 126.3, 125.3, 16.0.
Polymorph I. The polymorph I was obtained from a solution of L in
THF/acetone (1:1v ratio) after 7 days (yield >90%). IR (KBr, cm−1):
3444 (m), 2922 (w), 2846 (w), 1683 (m), 1661 (s), 1589 (m), 1459
(w), 1417 (s), 1300 (m), 1283 (s), 1179 (w), 1035 (m), 955 (m), 842
(w), 787 (w), 741 (w), 710 (w), 650 (w).
Polymorph II. The polymorph II was crystallized as red block from a
solution of L in methanol after 3 days (yield >40%).
Polymorph III. The polymorph III was obtained from a solution of L
in chloroform after 4 h (yield >70%).
Solvate IV. The solvate IV was obtained as yellow crystals from a
solution of L in acetonitrile after one week (yield ∼65%).
In summary, three conformational polymorphs of 2-(1, 4-
dihydro-1,4-dioxonaphthalen-3-ylthio) benzoic acid are demon-
strated. In each polymorph, the dimeric forms of carboxylic acids
are observed. Because of the orientation of the aromatic groups
across a hydrogen bond motif, different polymorphs I−III are
formed. Similar conformational polymorphs arise in fuchsones,9
but in this study we have tailor-made the effect of formation of
dimeric assemblies by carboxylic acid functional group of the
3121
dx.doi.org/10.1021/cg300318u | Cryst. Growth Des. 2012, 12, 3114−3122

Crystal Growth & Design
Article
Cocrystal V. A methanolic solution of 1:1 mixture of 2-(1,4-dihydro-
1,4-dioxonaphthalen-3ylthio)benzoic acid and 2,2′-bipyridyl was kept
undisturbed for crystallization. Yellow crystals were obtained after a day.
Yield: > 40% with respect to L. IR (KBr, cm−1): 3452 (bw), 3061 (w),
2922 (m), 2851 (w), 2432 (w), 1662 (s), 1589 (s), 1562 (m), 1462
(w),1435 (m), 1405 (m), 1371 (m), 1311 (w), 1281 (m), 1261 (m),
1214 (w), 1057 (w), 799 (m), 746 (w), 707 (w), 627 (w), 619 (w).
The X-ray single crystal diffraction data were collected at 296 K with
Mo Kα radiation (λ = 0.71073 Å) using a Bruker Nonius SMART CCD
diffractometer equipped with a graphite monochromator. The SMART
software was used for data collection and also for indexing the reflections
and determining the unit cell parameters; the collected data were
integrated using SAINT software. The structures were solved by direct
methods and refined by full-matrix least-squares calculations using
SHELXTL software.18 All the non-H atoms were refined in the
anisotropic approximation against F2 of all reflections. The H-atoms,
except those attached to oxygen atoms, were placed at their calculated
positions and refined in the isotropic approximation; those attached to
oxygen were located in the difference Fourier maps and refined with
isotropic displacement coefficients. The crystallographic parameters of
the compounds are tabulated in Table 4.
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ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files, powder XRD of I−V are available. These materials are
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: juba@iitg.ernet.in.
■
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors thank Council of Scientific and Industrial Research
(New Delhi) India for financial assistance.
■
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