1:1 and 2:1 cocrystallizations of alkoxy-substituted naphthalene derivatives with octafluoronaphthalene through arene-perfluoroarene interactions

Article abstract of DOI:10.1016/j.jfluchem.2014.09.025

Naphthalene derivatives with laterally orientated short side chains readily form cocrystals with octafluoronaphthalene in which the position and the length of the lateral chain can control the 1:1 and 2:1 cocrystallization stoichiometries and overlapped a

Full text of DOI:10.1016/j.jfluchem.2014.09.025

Accepted Manuscript
Title: 1:1 and 2:1 Cocrystallizations of Alkoxy-Substituted
Naphthalene Derivatives with Octafluoronaphthalene through
Arene-Perfluoroarene Interactions
Author: Akiko Hori Haruhi Takeda J. Richard Premkumar G.
Narahari Sastry
PII:
S0022-1139(14)00289-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2014.09.025
FLUOR 8442
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
3-7-2014
10-9-2014
22-9-2014
Please cite this article as: A. Hori, H. Takeda, J.R. Premkumar, G.N. Sastry,
:1 and 2:1 Cocrystallizations of Alkoxy-Substituted Naphthalene Derivatives with
1
Octafluoronaphthalene through Arene-Perfluoroarene Interactions, Journal of Fluorine
Chemistry (2014), http://dx.doi.org/10.1016/j.jfluchem.2014.09.025
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1:1 and 2:1 Cocrystallizations of Alkoxy-Substituted Naphthalene Derivatives with
Octafluoronaphthalene through Arene-Perfluoroarene Interactions
a
a
b
b
Akiko Hori*, Haruhi Takeda, J. Richard Premkumar, and G. Narahari Sastry
a
Department of Chemistry, School of Science, Kitasato University, Kitasato 1-15-1, Minami-ku,
Sagamihara, Kanagwa 252-0373
b
CSIR-Indian Institute of Chemical Technology, Centre for Molecular Modelling, Hyderabad-
500607, India.
E-mail: hori@kitasato-u.ac.jp
HIGHLIGHTS
•
•
•
•
•
Alkoxy substituted naphthalenes were cocrystallized with octafluoronaphthalene.
Arene-perfluoroarene interaction is observed in the cocrystals.
The 2:1 cocrystal is rare example and each π-plane was highly overlapped.
Alkoxy groups at 2,7-position in naphthalene are effective for the cocrystallization.
Propoxy group is optimal to have possible CH···F interactions to give cocrystals.
ABSTRACT
Naphthalene derivatives with laterally orientated short side chains readily form cocrystals with
octafluoronaphthalene in which the position and the length of the lateral chain can control the 1:1
and 2:1 cocrystallization stoichiometries and overlapped areas of the π-planes, showing that the
systematic substitution patterns in the chains of molecules can be exploited to rationally designed
cocrystals.
Graphical Abstract
1
Page 1 of 16

Naphthalene derivatives with laterally orientated short side chains readily form unique 1:1 and 1:2
cocrystals with octafluoronaphthalene through arene-perfluoroarene interactions.
1. Introduction.
The control of weak bonds and interactions has developed several important fields of
supramolecular chemistry and crystal engineering in the last three decades [1,2]. Especially, the
control of the π-interaction is an important subject for chemistry and biology, because the π-
interactions behave as key interactions of molecular recognition events, self-assembly, and
conductive properties [1-4]. The precise control of the position and direction of π-conjugated
molecules is still challenging, because a rectangular orientation and a sliding orientation of the π···π
interactions are predominantly formed [5-8], and the gas-phase study of benzene clusters showed
that there is a competition between CH···π and π···π interactions [9a]. It also has been reported that
in presence of metal ion the strength of CH···π interaction will reduce and π···π interaction will be
enhanced for benzene dimer [9b]. However if the size of aromatic molecule increases, the stacking
interaction will be more preferred than CH…π interactions [10]. Thus, we have attempted to make
cocrystals through the arene-perfluoroarene interaction [3,11-15] in order to control the
arrangements of the aromatic compounds, and several fluorinated molecules have been synthesized
to create metal···metal [16] and metal···π [17] supramolecular associations through these
interactions.
In several cases, the arene-perfluoroarene interaction is an effective and powerful tool for the
formation of unique cocrystals [11-16], but, unfortunately, the interaction has several limitations;
e.g., two or more substitutions of the laterally orientated side chains in an aromatic moiety decrease
the strength of the interaction and flexible side chains hinder the cocrystallization. Thus, we
2
Page 2 of 16

examined the cocrystallization of flexible alkoxy-chain substituted naphthalene derivatives, which
increase the melting points and the strength of the arene-perfluoroarene interaction for comparison
with the corresponding benzene derivatives. The target compounds are dimethoxy (1), dipropoxy (2),
and dipentoxy (3) substituted naphthalenes, and the corresponding fluorinated naphthalenes 4-5, as
shown in Scheme 1. We successfully obtained new four cocrystals between alkoxy substituted
naphthalene and octafluoronaphthalene (C10
derivatives would produce steric repulsions in the crystal states. Furthermore, we discovered a 2:1
molecular ratio of the cocrystal of naphthalene derivative 2a and C10 , which is quite rare example,
and two π-planes of 2a and C10 are highly overlapped, compared with the cocrystal of the non-
substituted naphthalene, C10 , with C10 [18]. The results show that the systematic substitution
patterns in the lateral chains of the naphthalene derivatives can control the cocrystallization
behaviors; cocrystals were obtained between the alkoxynaphthalenes (1a-3a and 1b) and C10
through arene-perfluoroarene interactions, while no cocrystals were obtained using 2b and 3b.
Especially, the detailed structures of the 1:1 cocrystal of 1a•C10 , 2:1 cocrystal of (2a) , and
:1 cocrystal of 3a•C10 will be discussed along with those of the single-component crystals 1a-3a
by using the crystallographic and computational studies.
8
F ), while the alkoxy side chains on the naphthalene
F
8
F
8
H
8
F
8
F
8
F
8
2 8
•C10F
1
F
8
1
2
3
a: R =
OCH3
R1
R1
1
a: R =
O(CH ) CH3
1
2 2
a: R =
O(CH ) CH3
1
2 4
R2
1b: R =
OCH3
2
2
b: R =
O(CH ) CH3
2
2 2
R2
3b: R =
O(CH ) CH3
2
2 4
F
F
F
F
R3
R4
4
5
: R = H, R =
O(CH ) CH3
3
4
2 2
: R = R =
O(CH ) CH3
F
F
3
4
2 2
Scheme 1.
2. Experimental
2.1. General.
All the chemicals were of reagent grade and used without further purification. Compounds 1-
3
Page 3 of 16

5
were prepared as previously reported, using the corresponding dihydroxy naphthalene and
1
bromoalkane with K
2
CO
3
[19]. H NMR spectral data were recorded on a Bruker AVANCEIII-400
spectrometer. Infrared spectra were recorded on a Shimadzu IR 8400s in KBr disk. The results of
elemental analysis of C and H were collected by PerkinElmer PE2400 analyzer.
2.2. Preparations and characterization of cocrystals.
EtOH solutions of alkoxynaphthalene and C10
F
8
were combined to form the cocrystals.
(10 mmol) dissolved in EtOH (5 mL)
were combined at room temperature to produce colorless needle microcrystals to give cocrystals,
, (2a) , and single-components, 2b and 3b, respectively. They
were clearly characterized by single crystal X-ray crystallographic studies. The results of elemental
analysis show that C10 slowly removed by sublimation from the cocrystals at room temperature.
. mp 90 °C dec. (the crystals slightly decomposed at 90 °C, and then new colorless
prismatic crystals grew on the crystal surface, and the whole crystals melted at 135-138 °C). IR (KBr
Typically, 1-3 (10 mmol) dissolved in EtOH (5 mL) and C10F
8
1a•C10
F
8
2 8 8 8
•C10F 3a•C10F , 1b•C10F
F
8
1a•C10F
8
-1
disk, cm ): 3431, 3013, 2971, 2943, 1663, 1628, 1516, 1479, 1404, 1389, 1211, 1119, 1034, 945,
41, 775. Elemental analysis: Calcd for C22 (%): C 57.40, H 2.63; found: C 56.99, H 2.49.
2a) . mp 77-78 °C (A part of the crystals melted at 77-78 °C and the whole crystals
melted at 88-89 °C). IR (KBr disk, cm ): 2969, 2940, 2880, 1661, 1626, 1607, 1514, 1479, 1458,
404, 1213, 945, 858, 835.
. mp 51-52 °C (A part of the crystals melted at 51-52 °C and the whole crystals
8
12 8 2
H F O
(
2 8
•C10F
-1
1
3a•C10F
8
-1
melted at 62-63 °C). IR (KBr disk, cm ): 2959, 2945, 2872, 1661, 1626, 1518, 1479, 1406, 1389,
258, 1213, 1198, 1121, 1022, 945, 835, 785.
. mp 110 °C dec. (the crystals slightly decomposed at 110 °C, and then new
colorless prismatic crystals grew on the crystal surface, and the whole crystals melted at 133-156
1
1b•C10F
8
-1
°
C). IR (KBr disk, cm ): 3021, 2969, 2945, 2843, 1663, 1605, 1506, 1478, 1466, 1402, 1234, 1206,
1
2
12 8 2
159, 1117, 1032, 943, 856, 785, 590. Elemental analysis: Calcd for C22H F O (%): C 57.40, H
.63; found: C 57.13, H 2.52.
4
Page 4 of 16

2.3. X-ray crystallographic studies.
Single crystal X-ray structures were determined on a Bruker SMART APEX CCD
diffractometer with graphite monochrometer MoKa (l = 0.71073 Å) generated at 50 kV and 35 mA.
All crystals were coated by paraton-N and were measured at 100-233 K. For all compounds, cell
refinement and reduction were performed by Bruker SAINT program, the structure solution was
SHELXS97, the refinement was SHELXL97 [20]. Empirical adsorption corrections were applied
using the SADABS program [21]. All non-hydrogen atoms were refined anisotropically unless
otherwise stated and hydrogen atoms were constrained at idealized positions, with the C–H distances
of 0.95–0.99 Å. These data can be obtained free of charge from The Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_ request/cif.
1a•C10
F
8
(C22
H
12
F
8
O
2
1
: Mw = 460.32): monoclinic, P2 , T = 233 K, a = 6.9034(4) Å, b =
3
3
1
0
8.6158(10) Å, c = 7.2620(4) Å,  = 94.645(1)°, V = 930.19(9) Å , Z = 2, D = 1.643 g/cm , Rint =
c
.0185, No. reflns measured = 10505, No. independent = 4198, GOF = 1.043, R((I)>2(I)) = 0.0404,
2
o
wR(F
) = 0.1181, CCDC 875019.
1b•C10
F
8
(C22
H
12
F
8
O
2
: Mw = 460.32): triclinic, P-1, T = 100 K, a = 6.829(3) Å, b = 7.282(3)
3
Å, c = 9.671(4) Å,  = 68.235(3)°,  = 84.193(4)°,  = 84.599(4)°, V = 443.5(3) Å , Z = 1, D
c
=
3
1
.723 g/cm , Rint = 0.0182, No. reflns measured = 5067, No. independent = 1998, GOF = 1.044,
2
R((I)>2(I)) = 0.0321, wR(F
o
) = 0.0930, CCDC 875022.
: Mw = 760.74): monoclinic, P2
c
0.921(4) Å, c = 6.8154(13) Å,  = 103.496(2)°, V = 1804.4(6) Å , Z = 2, D = 1.400 g/cm , Rint =
(2a)
2
•C10
F
8
(C42
H
40
F
8
O
4
1
/c, T = 100 K, a = 13.014(3) Å, b =
3
3
2
0
.0305, No. reflns measured = 19819, No. independent = 4109, GOF = 1.151, R((I)>2(I)) = 0.0697,
2
o
wR(F
) = 0.2488, CCDC 875020.
3a•C10
F
8
(C30
H
28
F
8
O
2
: Mw = 572.52): triclinic, P-1, T = 233 K, a = 6.9574(12) Å, b =
3
1
4.683(3) Å, c = 14.743(3) Å,  = 110.379(2)°,  = 93.438(2)°,  = 101.820(2)°, V = 1367.7(4) Å , Z
3
=
2, D
c
= 1.390 g/cm , Rint = 0.0263, No. reflns measured = 15288, No. independent = 6079, GOF =
5
Page 5 of 16

2
1
.129, R((I)>2(I)) = 0.0779, wR(F
o
) = 0.2496, CCDC 875021.
3. Results and Discussion
3.1. Synthesis of cocrystals.
Compounds 1-3 were prepared using the corresponding dihydroxy naphthalene and
bromoalkane with K CO , based on previously reported procedures [19]. Single crystals 1-3 were
2
3
prepared from EtOH (CCDC 875014-875018 are deposited), and no intermolecular π···π stacking
was observed for the banana-shaped molecules of 1a-3a and rod-shaped ones of 1b-3b, because the
intermolecular CH···π interactions between the alkoxy chains and naphthalene centers are dominant
for all of the molecular packings, as shown in Fig. 1 (see Fig. S4 in Supporting Information).
However, arrangements of the molecules are dramatically changed in the cocrystals in which the π-π
stackings are clearly induced through the arene-perfluoroarene interactions, as shown below.
Fig. 1. Part of the crystal packing of (a) 1a and (b) 1b, showing the rectangular orientation of the
molecular planes. Color scheme: C, gray; H, white; O, black.
Compound 1 and C10
F
8
were combined to form the cocrystals. Typically, two EtOH (5 mL)
(58 mg, 10 mmol) were combined at room temperature,
solutions of 1 (43 mg, 10 mmol) and C10
F
8
and the mixture was slowly concentrated to produce colorless prismatic crystals. The results of the
GC-MS analysis of the first precipitated microcrystals indicated the formation of the 1:1 cocrystals,
8 8
1a•C10F and 1b•C10F , in which two compounds exist in the same ratio in the microcrystals. The
results of the elemental analysis also showed good agreements regarding the formation of the 1:1
6
Page 6 of 16

cocrystals. Melting points of the cocrystals, 1a•C10
significantly lower than the single-component crystals, 1a (138-139 °C) and 1b (152-153 °C), which
indicated the decomposition of the crystals by the elimination process of C10 (87 °C) [22]. The
8 8
F (90 °C dec.) and 1b•C10F (110 °C), were
F
8
results indicate that the flexibility of the side chains influenced the crystal stability, while the arene-
perfluoroarene interactions generally increase the melting points for cocrystallization [23]; the
cocrystal C10
compare with the single components of C10
The structures and the packing formations of the cocrystals of 1a•C10
shown in Fig. 2. In the crystal of 1a•C10 (Fig. 2a) [24], 1a and C10 are alternately aligned with
H
8
•C10
F
8
was highly stabilized through arene-perfluoroarene interaction (mp 132 °C) to
H
8
(80 °C) and C10 [18].
F
8
8 8
F and 1b•C10F are
F
8
F
8
face-to-face aromatic π-planes of the naphthalene moieties to form one dimer unit; the closest
distance of the centroids of the naphthalene ‘ten’ atoms, C1-C2-C3-C4-C5-C6-C7-C8-C9-C10 (x, y,
8
z) in 1a and C13-C14-C15-C16-C17-C18-C19-C20-C21-C22 (x, y, z + 1) in C10F , is 3.64 Å and the
corresponding mean separation between the two planes (i.e., the perpendicular distance from the ring
centroid to the adjacent planes) is 3.33 Å, showing the remarkable π-π stacking. The distance
between the corresponding two units, C1~C10 (x, y, z) in 1a and C13~C22 (x, y, z) in C10
Å and the corresponding distance of the π-π stacking is 3.43 Å. On the other hand, 1b and C10
the cocrystal 1b•C10 are alternately aligned with slightly twisted conformations because the π-
F
8
, is 3.68
F
8
in
F
8
planes of the naphthalene moieties overlap in a manner to avoid the side-chains (Fig. 2b). The
distance of the centroids of the naphthalene atoms, C1-C2-C3-C4-C5-C1a-C2a-C3a-C4a-C5a in 1b
and C7b-C8b-C9b-C10b-C11b-C7c-C8c-C9c-C10c-C11c in C10
π-π stacking is 3.34 Å. In comparison, the distance of the non-substituted naphthalene and
octafluoronaphthalene in the cocrystal (C10 ) [18] is longer, 3.73 Å, and the corresponding
8
F , is 3.64 Å and the distance of the
8 8
H •C10F
distance of the π-π stacking is 3.42 Å, indicating that the methoxy groups not only hindered the
supramolecular association through the arene-perfluoroarene interactions, but also closely arranged
between the two π-plane’s centroids.
7
Page 7 of 16

Fig. 2. The molecular structures of (a) 1a•C10
Displacement ellipsoids are drawn at the 30 and 50% probability levels for 1a•C10
(100 K), respectively. Symmetry transformation used to generate equivalent atoms show a
-x + 1, -y + 2, -z ), b (x, y + 1, z - 1), and c (-x + 1, -y + 2, -z + 1).
F
8
and (b) 1b•C10
F
8
, showing the numbering schemes.
F
8
(233K) and
1b•C10F
8
(
In contrast, the results of the cocrystallization were monitored by GC-MS analysis. Crystals
in a mixture of 2a-3a and C10 show the cocrystallization, while only the single components of 2b-
b are found in the crystals obtained from the mixtures of 2b-3b and C10 , for which the crystals are
F
8
3
F
8
quickly collected during the early crystallization stage. These results indicate that not only the
substitution numbers influence the cocrystallization behavior, but also the position of the alkoxy-
chains trigger the molecular association through the arene-perfluroarene interaction. It is pointed out
that no cocrystallization of the propoxy-attached perfluoronaphthalene, 4 and 5, was observed in the
corresponding experiments. The melting points of (2a)
again show a slightly lower temperature than the single-component crystals, 2a (81-82 °C) and 3a
53-54 °C).
In (2a)
give the 2:1 cocrystal (2a)
2 8 8
•C10F (77-78 °C) and 3a•C10F (51-52 °C)
(
2
•C10
F
8
, octafluoronaphthalene is wrapped and sandwiched by two molecules of 2a to
in which the π-planes of the three naphthalene moieties are highly
2
•C10F
8
overlapped (Fig. 3). To the best of our knowledge, this is a rare example of a 2:1 cocrystal through
an arene-perfluoroarene interaction, since the first example was reported by Marder et al. in 2004
[25,26]. A side-chain of each 2a molecule partially wraps around the central molecule of C10
8
F to
give the trimer, (2a) . The distance of the centroids of the naphthalene atoms, C1~C10 in 1a
2
•C10F
8
and C17d-C18d-C19d-C20d-C21d-C17e-C18e-C19e-C20e-C21e in C10
8
8
F , is 3.57 Å and the
Page 8 of 16

corresponding mean separation between the two planes is 3.31 Å. In the crystal packing, the three-
molecule aggregates form a zig-zag arrangement (Fig. 4b).
2 8
Fig. 3. ORTEP drawing of the crystal structure of (2a) •C10F at 100 K is shown with 50%
probability thermal ellipsoids. Symmetry transformation used to generate equivalent atoms show d (-
x + 1, -y + 1, -z + 1), e (x - 1, y, z - 1), and f (-x, -y + 1, -z).
Fig. 4. Crystal packing of (a) 1a•C10
8 2 8 8
F , (b) (2a) •C10F , and (c) 3a•C10F and the direction of
stacking toward the c, b, and c axis, respectively.
8 8
In the cocrystal 3a•C10F , 3a and C10F are also alternately aligned with the face-to-face
aromatic π-planes of the naphthalene moieties (Fig. 4c). The closest distance of the centroids of the
naphthalene atoms, C1-C10 in 3a and C21g-C25g-C21h-C25h (g: x, y + 1, z; h: -x + 2, -y + 1, -z +
9
Page 9 of 16

1
) in C10
F
8
, is 3.66 Å and the corresponding mean separation between the two planes is 3.36 Å. The
distance between C1-C10 (i) and C26c-C30c-C26i-C30i (i: x + 1, y, z - 1) is 3.75 Å and the distance
to the adjacent planes is 3.39 Å. The directions of the pentoxy groups in 3a•C10 and the methoxy
are alternately and regularly arranged, respectively, in each of the crystal
F
8
groups of 1a•C10F
8
packings.
3.2. Computational studies of cocrystals.
The experimental study showed that the arene-perfluoroarene mixture crystallizes in two
different ratios (1:1 or 2:1). To understand this cocrystallization behavior, we have carried out the
molecular modeling studies of the 1:1 and 2:1 stacked structures of the 1a (methoxy), 2a (propoxy),
and 3a (pentoxy) complexes of C10
(2:1), while the other two mixtures crystallize in the 1:1 ratio. Therefore, we evaluated the
crystal structures of the (1a) , (2a) , and (3a) and found a similarity in the 1a and
a alkyl group arrangements of the C10 complexes, that is, the alkoxy carbons and the naphthalene
8
F . The difference in the crystal formation ratio was found only in
2a:C10F
8
2
•C10
F
8
2
•C10
F
8
2 8
•C10F
3
F
8
ring are in a plane for 1a and 3a (Planar: P-conformation), but in 2a, the methoxy groups exist
up/down in the 2:1 cocrystal (Wrapped: W-conformation). Therefore, we modeled the P-
conformations of the dimers (this only found in crystal structure), then the P and W conformations
for the 2:1 trimers of 1a, 2a, and 3a with C10
conformations of (1a) and (3a) collapsed into the corresponding P-conformations. For
, the P-conformations are found to be energetically lower, and for
, as expected, the W-conformation is lower in energy than the P-conformation.
8
F were examined. The optimization of the W-
2
•C10
F
8
2 8
•C10F
(
1a)
2
2
•C10
•C10
F
8
8
and (3a)
2
•C10
F
8
(2a)
F
All the dimer and trimer energies were further improved by increasing the basis set from 6-
1G* to cc-pVTZ, which are shown in the Supporting Information. The binding energies of the
3
dimer and trimer can provide information about the trimerization energy. The binding energy can be
calculated by evaluating the difference in the total energy of the complex and the individual
monomers (in complexed state). In Table 1, we have listed the binding energy of the dimer (E
1
) and
trimer (E ) at the M06-2X/cc-pVTZ level of theory. The binding energies of the dimer and trimer
2
1
0
Page 10 of 16

increase as a function of the size of the alkyl chain, and as expected, the binding energy is found to
be higher for the trimer than for the dimer. The difference in the binding energies of the trimer and
dimer is called E
3
(E
3
= E
1
-E
2
), and E
complex requires 1.34 kcal/mol energy so it prefers to be a dimer
unit (1:1 ratio). The trimerization energy (E ) clearly explains the experimentally observed
:1 ratio for the 1a•C10 complex. In contrast to the experiment, the 2a•C10 complex prefers to be
= 0.11 kcal/mol) and the 3a•C10 complex prefers to be in the 2:1 ratio (E = -0.27
kcal/mol). For further understanding, we examined the relative energies of the W and P-
conformations for 2a•C10 and 3a•C10 . In the case of 3a•C10 , the W-conformation (partially
wrapped structure, experimentally observed one for (2a) ) is 1.81 kcal/mol higher in energy
1 3 4
-E is defined as the trimerization energy (E ). To attain a
trimer structure, the (1a)
2
•C10F
8
1a•C10
F
8
4
1
F
8
F
8
in a 1:1 ratio (E
4
F
8
4
F
8
F
8
F
8
2
•C10F
8
than the P-conformation. The question that then arises, is the W-conformation make the
crystallization as 2:1 ratio? If so, that type of conformation is higher in energy (not favorable) for the
3
2
a•C10
a•C10
F
8
8
structure due to steric reasons and so it prefers the 1:1 form. The P and W conformations of
are close in energy, however, the CH ···F interactions in 2a•C10 make the W-
F
3
F
8
conformation slightly lower in energy. The molecular electron density can be mapped through an
atoms in molecule’ procedure developed by Bader and coworkers [27]. To characterize the nature of
the CH ···F interaction, we have calculated the electron density at the (3,-1) intermolecular bond
critical point. The calculated intermolecular electron density at (3,-1) bond critical point (in between
CH ···F) is 0.004 a.u, considered to be a weak H-bond [28]. However, such a weak interaction is
found not only between CH ···F, but also between CH ···F as shown in Fig. 5. The recent
‘
3
3
3
2
computational study showed that CH…M interactions in metal-alkene complexes will increase
strength of the non bonding interaction [29]. Interestingly, we found that the length of the propoxy
group is optimal to have more possible CH···F interactions and this result explains the
8
cocrystallization behavior of 2a and C10F in the ratio of 2:1.
Table 1 The M06-2X/cc-pVTZ//M06-2X/6-31G* binding energy (kcal/mol) of the arene-
perfluoroarene complexes.
1
1
Page 11 of 16

R-group
dimer
trimer
(E
E
3
= E
2
-E
1
Trimerization energy
(E = E -E
(E
1
)
2
)
4
1
3
)
1
2
3
a
a
a
16.05
16.99
17.36
30.76
33.87
34.99
14.71
16.88
17.63
+1.34
+0.11
-0.27
2 8
Fig. 5. The AIM molecular graph for (2a) •C10F in the W-conformation calculated at the M06-
2X/6-31G* level of theory.
All the structures considered in this study were optimized at the M06-2X/6-31G* level of
theory without any symmetry constraint. The binding energies of the dimer and trimers were
calculated at the M06-2X/cc-pVTZ level on the M06-2X/6-31G* geometries. The geometry
optimization and the binding energy calculations have been done using the Gaussian 09 program
3
package [30]. To classify the strength of CH ···F interaction, we calculated the intermolecular (3,-1)
bond critical point on M06-2X/6-31G* wave function files using the AIM2000 package [31]. All the
optimized structure and principal geometries have been given in Supporting Information (Table S2
and Fig. S5-S11).
4. Conclusions
In conclusion, we found three types of cocrystals, 1:1 regular, 2:1 wrapped, and 1:1
1
2
Page 12 of 16

alternately arranged structures, depending on the lengths of the attached alkoxy chains. The
cocrystallization depends on the position of the flexible side chains, and the substitutions regulate the
crystal packings. The length of the propoxy group seems to be the governing factor for the special
arrangement between the alkoxyarene and perfluoroarene. The melting points of the cocrystals were
clearly decreased with the increase of the side chain length; C10
8 8 8
H •C10F (132 °C) [18] > 1a•C10F
(
90 °C dec.) > (2a) (77-78 °C) > and 3a•C10 (51-52 °C), which indicates that the heat
2
•C10
F
8
F
8
stability of the crystals decreases by longer flexible side chain. We correlated the distance between
the two centroids of naphthalene derivatives with the side chain lengths and found an optical point at
the propoxy group to give the 2:1 cocrystal; C10
H
8
•C10
F
8
(3.73 Å), 1a•C10
(3.66 Å). The remarkable short distance and highly overlapped structure of
are formed by the W-conformation which was supported by the CH ···F and CH ···F
8 2 8
F (3.68 Å), (2a) •C10F
(
3.57 Å), 3a•C10
2a)
F
8
(
2
•C10
F
8
2
3
weak interactions. Thus, suitable lengths of side chains stabilized the π-π interaction and formed
unique cocrystals, which independently works of the thermodynamic stability of the crystal systems.
Acknowledgements. A.H thank Prof. Hidetaka Yuge and Mr. Yuuki Akimoto of Kitasato
University for valuable discussion and helpful supports. G.N.S and J.R.P thank CSIR and DST, New
Delhi for financial support.
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[
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6 6 6 6
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8
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Page 16 of 16