Control of relationship between conformational and color polymorphs of achiral 2-methyl-3-arylthio-1,4-naphthalenediones

Article abstract of DOI:10.1016/j.molstruc.2010.07.032

The achiral compound 2-methyl-3-(4-bromophenylthio)-1,4-naphthalenedione shows conformational and color polymorphism. The relationship between the conformational and color polymorphs (chirality and color) of 2-methyl-3-arylthio-1,4-naphthalenediones can c

Full text of DOI:10.1016/j.molstruc.2010.07.032

Journal of Molecular Structure 982 (2010) 16–21
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Control of relationship between conformational and color polymorphs of achiral
2-methyl-3-arylthio-1,4-naphthalenediones
Takafumi Kinuta a, Tomohiro Sato a, Takunori Harada b, Nobuo Tajima c, Reiko Kuroda b,d
,
Yoshio Matsubara a, , Yoshitane Imai a,
⇑
⇑⇑
a Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
b JST ERATO-SORST Kuroda Chiromorphology Team, 4-7-6, Komaba, Meguro-ku, Tokyo 153-0041, Japan
c Graduate School of Pure and Applied Sciences, Tsukuba University, 1-1-1 Tenodai, Tsukuba, Ibaraki 305-8571, Japan
d Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2010
Received in revised form 22 July 2010
Accepted 22 July 2010
Available online 29 July 2010
The achiral compound 2-methyl-3-(4-bromophenylthio)-1,4-naphthalenedione shows conformational
and color polymorphism. The relationship between the conformational and color polymorphs (chirality
and color) of 2-methyl-3-arylthio-1,4-naphthalenediones can change according to the type of arylthio
group.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Chiral
Crystal-engineering
Naphthoquinone
Polymorphism
1. Introduction
2-methyl-3-arylthio-1,4-naphthalenedione by using 2-methyl-3-
(4-chlorophenylthio)-1,4-naphthalenedione (2) and 2-methyl-3-
In the field of solid-state chemistry, polymorphism has at-
tracted much attention because the polymorphs of a compound
show unique physical and chemical properties in the solid-state
[1]. Recently, we have reported that the achiral compound 2-
methyl-3-(2-naphthalenylthio)-1,4-naphthalenedione (1) shows
conformational and color polymorphism (Fig. 1) [2]. One of the
polymorphs (IA) is a deep orange and achiral crystal, and the other
(IB) is a reddish purple and chiral crystal. Interestingly, the rela-
tionship between these polymorphs can be controlled by changing
the crystallization conditions.
In general, it is difficult to predict whether a compound can
show polymorphism or not. It is more difficult to control the rela-
tionship between conformational and color polymorphs of com-
pounds of the same series. In other words, it is more difficult to
produce 2-methyl-3-arylthio-1,4-naphthalenedione with two
polymorphs (chiral deep orange crystal and achiral reddish purple
crystal) as compared to 1.
(4-bromophenylthio)-1,4-naphthalenedione (3).
2. Experimental
2.1. General methods
Crystallization solvents were purchased from Wako Pure Chem-
ical Industry. These solvents were used directly as obtained
commercially. Diffuse reflectance spectra (DRS) of crystals were
measured with a HITACHI U-4000 Spectrometer. The circular dichro-
ism (CD) and absorption spectra were measured using a Jasco
J-800KCM spectrophotometer. X-ray powder diffraction (XRPD) pat-
terns of crystals were collected on a Rigaku RINT2500. 1H NMR
spectra were recorded with a Varian Mercury M300 spectrometer
in chloroform-d using tetramethylsilane as an internal standard
(300 MHz). 13C NMR spectra were recorded with a Varian Mercury
M300 spectrometer in chloroform-d using tetramethylsilane as an
internal standard (75 MHz).
In this paper, we attempted to control the relationship
between the conformational and color polymorphs of achiral
2.2. Synthesis of 2-methyl-3-(4-bromophenylthio)-1,4-naphthalenedi-
one (3)
⇑
Corresponding author. Tel.: +81 06 6730 5880x5241; fax: +81 06 6727 2024.
** Corresponding author. Tel.: +81 06 6730 5880x5241; fax: +81 06 6727 2024.
E-mail addresses: y-matsu@apch.kindai.ac.jp (Y. Matsubara), y-imai@apch.
kindai.ac.jp (Y. Imai).
Compound
3
was synthesized following the literature
method for related compounds with some modification [2].
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.07.032

T. Kinuta et al. / Journal of Molecular Structure 982 (2010) 16–21
17
Fig. 1. Photographs of crystals IA and IB. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
2-Methyl-1,4-naphthoquinone oxide (175 mg, 0.93 mmol) and 4-
bromobenzenethiol (175 mg, 0.93 mmol) were dissolved in iso-
propanol (30 mL). After that, 15% potassium hydroxide (0.05 mL)
solution was added to the iso-propanol solution. The reaction mix-
ture was stirred at room temperature for 3 h. The mixture was
evaporated under vacuum. A diethyl ether (100 mL) was added.
The combined organic layers were washed with brine, dried over
Mg2SO4, and evaporated under vacuum to give the crude sulfide
compound. Compound 3 was purified by crystallization from
diethyl ether in 51% yield. 1H NMR (300 MHz, CDCl3): d = 2.39 (s,
3H), 7.24 (dd, J = 6.6 Hz, J = 1.8 Hz, 2H), 7.41 (dd, J = 6.6 Hz,
J = 1.8 Hz, 2H) 7.69–774 (m, 2H), 8.92 (dd, J = 6.8 Hz, J = 2.2 Hz,
1H), 8.12 (dd, J = 6.8 Hz, J = 2.2 Hz, 1H). 13C NMR (75 MHz, CDCl3):
d = 16.3, 31.2, 121.7, 127.0, 127.3, 132.3, 132.5, 132.7, 133.5, 134.0,
134.1, 145.0 149.8, 180.5, 183.2. HR-MS (EI): m/z [M]+ calcd for
C17H11BrO2S: 357.9663; found: 357.9682.
2.3. X-ray crystallographic study of crystal
Table 1
Crystal data and structure refinement details.
X-ray diffraction data for single crystals were collected using a
BRUKER APEX instrument. The crystal structures were solved by di-
rect methods [3] and refined by full-matrix least-squares using
SHELXL97 [3]. The diagrams were prepared using PLATON [4].
Absorption corrections were performed using SADABS [5]. Nonhy-
drogen atoms were refined with anisotropic displacement param-
eters, and hydrogen atoms were included in the models in their
calculated positions in the riding model approximation. Crystallo-
graphic data and details of measurements are summarized in
Table 1. The CSD reference number of crystals II, IIIA, and IIIB is
763,247, 763,248, and 763,249, respectively. Crystallographic data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB21EZ, UK; fax:+ 44 1223
336 033; deposit@ccdc.cam.ac.uk).
II
IIIA
IIIB
Formula
Formula
C
17H11ClO2S
C17H11BrO2S
359.23
C17H11BrO2S
359.23
314.77
weight
Temperature
Radiation
Crystal
115(2) K
115(2) K
115(2) K
) 0.71073 Å Mo(K
Mo(K
a
) 0.71073 Å Mo(K
a
a
) 0.71073 Å
Monoclinic
Orthorhombic
Triclinic
system
Space group
Unit cell
dimensions
P21/n
a = 7.2691(13) Å
P212121
a = 5.8375(6) Å
P-1
a = 7.6398(6) Å
b = 24.185(4) Å
c = 7.8234(14) Å
b = 13.3827(14) Å
c = 17.8321(18) Å
b = 11.3688(8) Å
c = 17.5044(13) Å
a
= 90.00°
b = 91.438(3)°
= 90.00 °
a
= 90.00°
b = 90.00°
= 90.00°
a
= 74.7520(10)°
b = 83.2300(10)°
= 82.8380(10)°
c
c
c
Volume (Å3)
Z, density
(g/cm3)
1374.9(4)
4, 1.521
1393.1(2)
4, 1.713
1449.62(19)
4, 1.646
3. Results and discussion
l
(mmꢀ1
)
0.430
648
3.101
720
2.980
720
F (0 0 0)
Crystal size
(mm)
Theta range
Reflection
collected/
unique
0.45 ꢁ 0.35 ꢁ 0.10 0.40 ꢁ 0.30 ꢁ 0.25 0.40 ꢁ 0.35 ꢁ 0.10
Compounds 2 [6] and 3 were prepared in the same manner as 1.
Reaction of 2,3-epoxy-2-methyl-1,4-naphthoquinone with 4-chlo-
robenzenethiol (or 4-bromobenzenethiol) and 15% potassium
hydroxide solution produced 2 or 3 in 71% and 51% yields, respec-
tively (Scheme 1).
In order to investigate the polymorphism of these compounds, 2
and 3 were crystallized from [diethyl ether and dichloromethane
(CH2Cl2)]. For 2, the same orange color crystals (II) were obtained
from the two solutions. On the other hand, it was found that 3
had two different colored crystals and the relative proportion of
these two crystals depended on the type of the solvent used for
slow evaporation. When the diethyl ether solution was used as a
solvent, deep orange crystals (IIIA) were obtained, but when
CH2Cl2 was used as a solvent, reddish purple crystals (IIIB) were
1.68–27.86
8220/3127
1.90–27.89
8476/3176
1.87–27.93
9009/6318
Data/
3127/191
1.047
3176/191
6318/381
parameters
S (on F2)
0.925
1.037
R [I > 2.0
R [all data]
wR [I > 2.0
(I)]/wR
[all data]
CCDC
r
(I)]/ 0.0463/0.0565
0.0258/0.0289
0.0376/0.0440
0.1149/0.1216
763,247
0.0501/0.0507
763,248
0.0972/0.1014
763,249
r
Scheme 1.

18
T. Kinuta et al. / Journal of Molecular Structure 982 (2010) 16–21
obtained (Fig. 2). These two crystals did not contain any other mol-
ecules such as those of the crystallization solvent.
The colors of these conformational polymorphs were different,
as shown in Fig. 2. Solid-state diffuse reflectance spectra (DRS) of
IIIA and IIIB were measured (Fig. 3).
As expected, the solid-state DRS of IIIA and IIIB were markedly
different; the absorption edges were located at ca. 520 and 570 nm,
respectively.
To investigate the chirality of these polymorphs, solid-state cir-
cular dichroism (CD) spectra of these crystals were measured by
using a KBr pellet. Only IIIA showed CD. The solid-state CD and
absorption spectra of IIIA, as shown in Fig. 4, indicate that IIIA
has chirality.
compound 3 has conformational and color polymorphs, each of
which exhibits different optical properties.
In order to study the structures of these polymorphs, X-ray
crystallographic analyses were performed. IIIA obtained from
diethyl ether solution was analyzed first. Its structure is shown
in Fig. 5. It is composed of only 3 without the crystallization sol-
vent. As expected, this crystal belongs to the chiral space group
P212121. The torsion angle is -65.9° [C(3)-C(2)-S(12)-C(13)], shifted
from the vertical value (Fig. 5a). In one crystal, all bromobenzene
rings incline in the same direction with respect to the naphthalen-
edione ring. That is, only one handedness of 3 exists in one crystal.
This chiral crystal is formed by the self-assembly of molecules of 3
through three types of interactions (Fig. 5b and c) [7]. One type is
Peaks originating from the naphthalenedione ring were ob-
served in the CD spectrum at 438 and 504 nm. The circular anisot-
CH–p interactions (2.63 Å, indicated by red A arrows in Fig. 5b),
and the other is benzene-naphthalene edge-to-face interactions
(2.88 Å, indicated by blue B arrows in Fig. 5b). Moreover, there
are one CH–O hydrogen bond (2.60 Å, indicated by black C arrow
in Fig. 5b) and one CH–S hydrogen bond (2.84 Å, indicated by black
D arrow in Fig. 5b).
ropy (gCD = D
OD/OD) factor of the Cotton effect (kCD = 504 nm) was
approximately 8.3 ꢁ 10ꢀ4. These results suggest that the achiral
The crystal structure of IIIB obtained from the CH2Cl2 solution is
shown in Fig. 6.
It is composed of only 3 without the crystallization solvent. This
crystal belongs to the achiral space group P–1. A characteristic fea-
ture of the structure is the presence of two independent molecules,
3a and 3b, which have different torsion angles around the sulfur
atom in an asymmetric unit (Fig. 6a and b, indicated in blue color
for 3a and green color for 3b). The torsion angles of these mole-
cules are 133.9° for 3a [C(3)-C(2)-S(12)-C(13)] and 124.6° for
3b [C(23)-C(22)-S(32)-C(33)]. This achiral crystal is formed by
Fig. 2. Photographs of crystals IIIA and IIIB. (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
the stacking of these molecules along the a-axis through p–p inter-
0
actions (indicated by the red circle, 3.46 and 3.66 ÅA, in Fig. 6d) [8].
Moreover, there are three CH–O hydrogen bonds (2.36, 2.59, and
2.56 Å, indicated by red A, blue B, and black C arrows, respectively,
in Figs. 6c and 6d) and one CH–Br hydrogen bond (2.88 Å, indicated
by black D arrow in Fig. 6c) [7].
For comparison, the crystal structure of II is shown in Fig. 7.
This crystal belongs to the achiral space group P21/n. The tor-
sion angle is 159.5° [C(3)-C(2)-S(12)-C(13)] (Fig. 7a). 2 forms a
columnar unit (indicated by the red dotted rectangle in Fig. 7b)
0
along the c-axis through CH–
p (2.80 ÅA, indicated by red A arrows
in Fig. 7b) and CH–O hydrogen bond (2.39 Å, indicated by blue B ar-
row in Fig. 7b) interactions [7]. This achiral crystal is formed by the
self-assembly of this columnar unit (indicated by the0 red dotted
circle in Fig. 7c) through CH–O hydrogen bond (2.45 ÅA, indicated
by black C arrows in Fig. 7c) [7].
The two conformational polymorphs of 3 showed different opti-
cal properties. Therefore, the difference in the colors of crystals IIIA
and IIIB may be attributed to the different conformations or pack-
ing arrangements of 3 in these crystals. To verify this, excited
states of the molecules in IIIA and IIIB were calculated by the ZIN-
DO method [9,10]. The excitation energies of 3 in IIIA were calcu-
lated as 2.58, 2.63, 3.62, 4.07, and 4.12 eV, and those in IIIB were
calculated as 2.59, 2.67, 3.66, 4.11, and 4.15 eV. These values indi-
cate that the conformational polymorphs of 3 in IIIA and IIIB
should have similar energy absorption; however, the DRS spectra
indicate that the latter has lower energy absorption than the for-
mer (Fig. 3). Therefore, the reason for the difference in the colors
of IIIA and IIIB can not be explained simply on the basis of the
molecular geometry. It is likely that the excited states of 3 are af-
fected rather strongly by the intermolecular interactions in these
crystals.
Fig. 3. Diffuse reflectance spectra (DRS) of crystals IIIA (red line) and IIIB (black
line). (For interpretation of the references to color in this figure legend, the reader is
referred to the web version of this article.)
In order to study the control of polymorphism and examine the
reversible switching between the two conformational polymorphs
(IIIA and IIIB) in bulk products, the polymorphism of 3 was inves-
tigated by X-ray powder diffraction (XRPD) analyses. When crys-
tals IIIA were dissolved in the CH2Cl2 solution and crystallized,
Fig. 4. Solid-state CD and absorption spectra of crystal IIIA (KBr pellet).

T. Kinuta et al. / Journal of Molecular Structure 982 (2010) 16–21
19
Fig. 5. Crystal structure of IIIA. Oxygen and sulfur atoms are shown in red and orange, respectively. (a) Structure of extracted single molecule 3. (b) Packing structure
observed along the a-axis. (c) Packing structure observed along the b-axis. Red A, blue B, and black C (or D) arrows indicate CH– , benzene-naphthalene edge-to-face, and
p
hydrogen bond interactions, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 6. Crystal structure of IIIB. Oxygen and sulfur atoms are shown in red and orange, respectively. (a) Structure of extracted single molecule 3a. (b) Structure of extracted
single molecule 3b. (c) Packing structure observed along the b-axis. Red A, blue B, and black C (or D) arrows indicate hydrogen bond interactions. (d) Packing structure
observed along the a-axis. The red circle shows a p–p interaction. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of
this article.)
reddish purple crystals were obtained from the solution. XRPD pat-
terns of these crystals showed that they were the same as crystals
IIIB (Fig. 8). In the same way, when crystals IIIB were dissolved in
the diethyl ether solution and crystallized, orange crystals identical
to crystals IIIA were obtained from the solution (Fig. 8). Moreover,
the rotational barrier for the dione ring of 3 around the thioether
bond is calculated as 4.5 kcal/mol by the RHF method using the
6–31G basis set [11]. These results show that the polymorphism
of this system can be perfectly and reversibly controlled by chang-
ing the crystallization conditions.
During crystallization from solution, 3 is crystallized through
intermolecular interactions with the crystallization solvent. In par-
ticular, two carbonyl groups of 3 interact with the crystallization
solvent. It is thought that the steric difference between the aryl
ring and the 1,4-naphthoquinone ring may be the cause for the chi-
ral crystallization of 3.

20
T. Kinuta et al. / Journal of Molecular Structure 982 (2010) 16–21
Fig. 7. Crystal structure of II. Oxygen and sulfur atoms are shown in red and orange color, respectively. (a) Structure of extracted single molecule 2. (b) Packing structure of
columnar unit of 2 along the c-axis. (c) Packing structure of columnar unit observed along the c-axis. Red A arrows show CH– interactions. Blue B and black C arrows indicate
p
hydrogen bond interactions. Red dotted rectangle and circle show a columnar unit. (For interpretation of the references to color in this figure legend, the reader is referred to
the web version of this article.)
Fig. 8. XRPD spectra of crystals IIIA and IIIB. (a) X-ray powder diffraction pattern of crystals. (b) Simulated X-ray powder pattern of the crystals, calculated from the crystal
structure data.
bromophenylthio)-1,4-naphthalenedione has chiral deep orange
crystals and achiral reddish purple crystals. We believe that the
results of this study will be useful for the systematic design of a no-
vel organic compound that shows conformational and color
polymorphism.
4. Conclusions
We found that the achiral compound 2-methyl-3-(4-bromophe-
nylthio)-1,4-naphthalenedione has two conformational and color
polymorphs. These polymorphs show different optical properties
and the relationship between the two can be controlled by chang-
ing the crystallization conditions. In particular, by crystallization
from the diethyl ether solution, this compound shows chirality in
the crystalline state without any external chiral source. In the 2-
methyl-3-arylthio-1,4-naphthalenedione system, the relationship
between chirality and color in the two polymorphs can be con-
trolled by the type of arylthio group. 2-methyl-3-(2-naphthalenyl-
thio)-1,4-naphthalenedione has achiral deep orange crystals and
chiral reddish purple crystals. On the other hand, 2-methyl-3-(4-
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Re-
search (No. 22750133) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan, and a research Grant from
TEPCO Research Foundation. T.K. is grateful to JSPS Research Fel-
lowships for Young Scientists.

T. Kinuta et al. / Journal of Molecular Structure 982 (2010) 16–21
21
[6] L.F. Fieser, R.H. Brown, J. Am. Chem. Soc. 71 (1949) 3609–3614.
[7] It is determined by PLATON geometry calculation.
Appendix A. Supplementary data
[8] Distance between the nearest centers of intermolecular 6-memebered rings of
3.
[9] (a) J.E. Ridley, M.C. Zerner, Theor. Chim. Acta 32 (1973) 111–134;
(b) J.E. Ridley, M.C. Zerner, Theor. Chim. Acta 42 (1976) 223–236;
(c) M.C. Zerner, G.H. Lowe, R.F.U.T. Kirchner Mueller-Westerhoff, J. Am. Chem.
Soc. 102 (1980) 589–599.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.07.032.
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