Isostructurality in the guest free forms and in the clathrates of 1,3,5-triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes

Article abstract of DOI:10.1021/cg2009144

Crystal structures of the guest free forms and some solvates of 1,3,5-triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes (1X, X = I, Br, Cl, F) have been studied. The guest free forms of 1I, 1Br, and 1Cl are isostructural, but the crystal structure of 1F is different from the heavier halogen analogues. An entirely different crystal structure of the Me analogue, which is known to be isosteric to the corresponding bromo compound, shows the importance of the electronic factors of the halogens in this series of structures. 1I and 1Br form four types of architectures in their solvates depending upon the inter-halogen interaction geometries. All these solvates are two dimensionally isostructural to the guest free form. 1Cl forms three different types of frameworks in its solvates, and the ethylacetate solvates of the 1I, 1Br, and 1Cl are isostructural. 1F forms only one type of solvate which is isostructural to the corresponding 1Cl solvate.

Full text of DOI:10.1021/cg2009144

Article
pubs.acs.org/crystal
Isostructurality in the Guest Free Forms and in the Clathrates of
1,3,5-Triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes
Published as part of the Crystal Growth & Design virtual special issue on Halogen Bonding in Crystal
Engineering: Fundamentals and Applications
Suman Bhattacharya and Binoy K. Saha*
Department of Chemistry, Pondicherry University, Puducherry 605 014, India
S
* Supporting Information
ABSTRACT: Crystal structures of the guest free forms and some solvates
of 1,3,5-triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes (1X, X = I, Br,
Cl, F) have been studied. The guest free forms of 1I, 1Br, and 1Cl are
isostructural, but the crystal structure of 1F is different from the heavier
halogen analogues. An entirely different crystal structure of the Me
analogue, which is known to be isosteric to the corresponding bromo
compound, shows the importance of the electronic factors of the halogens
in this series of structures. 1I and 1Br form four types of architectures in
their solvates depending upon the inter-halogen interaction geometries. All
these solvates are two dimensionally isostructural to the guest free form.
1Cl forms three different types of frameworks in its solvates, and the
ethylacetate solvates of the 1I, 1Br, and 1Cl are isostructural. 1F forms only
one type of solvate which is isostructural to the corresponding 1Cl solvate.
action into two subgroups, cis and trans.6 As far as the electron
INTRODUCTION
■
Halogen bonding1 is a class of weak noncovalent interactions
acceptance by a halogen is concerned, the tendency increases
down the Group 17 in the periodic table as F < Cl < B < I.7
that occurs in a system as A−Hal···B, when a halogen atom
approaches a Lewis base B possessing a lone pair. The most
This behavior could be attributed to the higher polarizability of
I compared to F. Although theoretically F could be a good
interesting aspect of the halogen bonding is that it is an
acceptor, because of its small size, poor polarizability, and high
interaction between two electronegative atoms that is expected
electronegativity, involvement of fluorine has been a matter of
to be repulsive but is in fact attractive in nature. Statistical
debate over the years. Recently, Guru Row and co-workers have
reports suggest that the halogen atoms, especially the heavier
reported a quantitative analysis of Cl···F and F···F interactions
in their work with 2-chloro-4-fluorobenzoic acid and 4-
fluorobenzamide.8 Investigations are also reported in the
literature regarding the preferential occurrence of halogen
bonding over hydrogen bonding in systems containing both
kinds of functional groups.9
Systems exhibiting halogen bonding have been designed that
show a wide range of applications. Nangia and co-workers have
reported a library of halogen substituted 2-halo-3-hydroxypyr-
idine, 2-halo-3-hydroxypyridine N-oxides, and 2-halo-3-amino-
pyridine where the inter-halogen interactions have been used as
a tool to promote crystallization of the compounds in non-
centrosymmetric space groups, producing models for studying
nonlinear optical (NLO) properties.10a Earlier, Thalladi et al.
reported a family of isotropic halogen containing 2,4,6-
triaryloxy-1,3,5-triazines as candidates for NLO studies.10b By
making use of the robust C−I···N interactions, Metrangolo et
ones, show a strong anisotropic shape in their electron cloud
owing to their polarization.2 The interaction energy of such
systems spans over a wide range, 10−200 kJ mol−1.3 In general,
halogens are thought to polarize in a manner that they are
electron deficient along the bond axis and electron rich in the
perpendicular direction to it. Thus, the approach of any system
with suitable complementarity along these vectors would result
in a stable interaction. The above facts suggest that so-called
halogen bonds, owing to their strong directionality and
strength, can be used as a tool for promoting specific crystal
packing motifs and thus could be a handy tool in crystal
engineering.4 In particular, the inter-halogen interactions too
have a directional feature which has been generalized by
Desiraju and Parthasarathi.5 According to them, halogen···hal-
ogen interactions are seen to be having two preferred
geometries, Type-I (θ1 ≅ θ2) and Type-II (θ1 ≅ 180°, θ2 ≅
90°). The type-I contact is merely a result of van der Waals
contact, whereas the type-II contact is a function of electrostatic
forces resulting from the polarization and anisotropy associated
with the electron cloud of the halogen. Recently, Guru Row
and co-workers have categorized type-I inter-halogen inter-
Received: July 16, 2011
Revised: November 1, 2011
Published: November 30, 2011
© 2011 American Chemical Society
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al. have designed poly(propylenimine) based dendrimers via
cocrystallization with bipyridine homologues.10c In an earlier
report, Resnati and co-workers investigated the possibility and
the potency of the halogen···N interaction in various organic
systems.10d Xu et al. used the halogen bonding as a steering
force in the synthesis of a new class of liquid crystalline
supramolecular polymers.10e Halogen bonds have also been
combined with hydrogen bonds in the engineering of desired
network structures.11
Isostructurality is the phenomenon in which two different
systems show similar kinds of structures.12 Study on
isostructurality opens up avenues for the study of periodicity
in chemical or physical properties of similar systems. There are
several reports where exchange of functional groups do not
alter the packing in a crystal structure.13 Halogen groups are
prone to show such behavior more frequently than all other
functional groups. Me/Cl and Me/Br exchange are also well-
known to produce isostructurality.14
Table 1. List of the Network Systems of the Halogenated
Compounds Crystallized from Different Solvents
Sl.
no.
solvents
acetonitrile
1I
1Br
1Cl
1F
1
GF1
GF1
GF1
NSC
GF1
GF2
NSC
GF2
HG5
HG5
HG5
HG5
NSC
GF2
NSC
NSC
NSC
a
c
2
benzene
HG1
HG1
HG2
HG2
HG2
HG2
HG2
HG2
HG3
HG3
HG3
HG1
HG3
HG2
HG2
HG2
HG1
HG2
HG2
HG3
NSC
NSC
3
pyridine
4
toluene
HG5
HG5
HG5
HG5
NSC
HG2
GF1
GF1
NSC
5
p-xylene
6
m-xylene
c
7
o-xylene
b
b
b
b
8
mesitylene
ethylacetate
chloroform
1,2-dibromoethane (DBE)
b
9
10
11
12
1,2-dichloromoethane
(DCE)
13
14
15
16
dioxane
HG3
HG3
HG3
HG3
HG4
HG6
NSC
NSC
GF1
NSC
NSC
NSC
GF2
Herein we report the crystal structures of the guest free
forms and some solvates of 1,3,5-triethyl-2,4,6-tris(4-
halophenoxy)methylbenzenes. We also have studied the Me
analogue of the compound to understand the importance of the
electronic factors of the halogens (Scheme 1).
tetrachloromethane (TCM) HG3
tetrahydrofuran (THF)
picoline
HG3
HG4
a
b
NSC: No single crystal obtained for X-ray diffraction. Squeezed.
c
Partially squeezed.
Scheme 1. The 1,3,5-Triethyl-2,4,6-tris(4-
halophenoxy)methylbenzene (1X, X = I, Br, Cl, F, Me)
Employed for the Study
One ethyl group of the molecule is disordered over two
positions. Halogen bonds play an important role in this crystal
structure. The crystal packing is guided by a type-II I···I
interaction involving two of the three halogens of a molecule
and a I···π halogen bond involving the third halogen to form a
one-dimensional (1-D) molecular tape running parallel to the
[110] direction (Figure 1b). The molecules also pair up in the
tape to form a Piedfort unit with small stacking offset.
Diffraction quality single crystals of the 1Br and 1Cl
compounds were obtained from the acetonitrile and chloroform
solutions respectively. Even though the bromo (1Br) and the
chloro (1Cl) analogues are isostructural to the 1I crystal
structure (GF1), they crystallize in the P21/c space group with
two and three molecules in the asymmetric units, respectively.
In the crystal structure of 1Br, all the three phenoxy groups in
one molecule are directed above the plane of the middle ring,
whereas in the other molecule, the arrangement of the phenoxy
groups is similar to the 1I molecule. On the other hand, in the
case of the 1Cl crystal structure, the conformations of the two
molecules are similar to the former 1Br molecule and the third
one is similar to the latter 1Br molecule. Hence, this is a case of
conformational isomorphism, the occurrence of different
conformers in the same crystal structure.15 Interestingly, 1I,
1Br, and 1Cl are isostructural in spite of different molecular
conformations, and the Z′ value also increases gradually from 1
to 3. This could be attributed to the increasing mosaicity in the
crystal structures from 1I to 1Cl. This fact suggests that this
type of crystal packing pattern (type GF1) could be more
suitable for the heavier halogen derivatives and beyond chlorine
this packing motif is not sustained. As a result, the crystal
structure of 1F (GF2) is different from these three analogues
(Figure 1c). The guest free form of 1F crystallizes from an
ethylacetate solution in a monoclinic space group P21/n and a
single molecule is present in the symmetry independent unit.
The intermolecular interactions in this type of structure (GF2)
are not so interesting. The F groups are involved in the weak
C−H···F interactions and the molecules also form Piedfort
units with a small offset in this crystal structure. The methyl
group is known to be isosteric to Br. Our calculation by the
RESULTS AND DISCUSSION
■
In this series of 43 crystal structures, there are six different types
of host architectures in the host−guest systems (HG1−6), and
three different types of structures in the guest free forms
(GF1−3) have been observed (Table 1). Among the six host
architectures, four forms (HG1−4) were obtained in the 1I
solvates, and two new forms (HG5 and 6) were obtained in the
1Cl solvates. The form HG2 is also present among the 1Cl
solvates. The 1Br and 1F solvates are isostructural to the 1I and
1Cl solvates, respectively. The guest free forms of 1I, 1Br, and
1Cl are isostructural (GF1), but the crystal structures of 1F
(GF2) and 1Me (GF3) are different from the heavier halogen
derivatives.
Guest Free Forms. The guest free form (type GF1, Figure
1a) of the 1I compound was obtained from an acetonitrile
solution of the compound which was solved in a monoclinic
space group P21/n with one molecule in the asymmetric unit.
The molecule is highly flexible in nature. Two of the phenoxy
groups are oriented above the plane of the middle aromatic
ring, and the third phenoxy group is oriented down the ring.
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structure of 1Me to compare with the halogenated compounds.
Diffraction quality single crystals of 1Me were obtained from a
dimethylformamide solution of the compound, and the system
crystallizes in the P21/n space group with one molecule in the
asymmetric unit. The crystal packing of 1Me (GF3) is entirely
different (Figure 1d) from the halogenated compounds (GF1
or 2), which suggests that interaction of the halogens plays an
important role in determining the self-assembly process of the
molecules in the crystal structures (GF1 and 2). Nangia and co-
workers have reported similar phenomena, where the
halogenated compounds formed a series of clathrate structures
guided by inter-halogen interactions,13a,16a but the correspond-
ing methyl derivative formed a close packed structure.16b
Solvates of 1I and 1Br. The solvates of 1X were obtained
by slow evaporation of the solvents from the solution of 1X in
the corresponding solvents at room temperature. There are
four different types of host networks (HG1−4) observed in the
1I and 1Br clathrates. Except the picoline solvates, which
crystallize in P21/n space group, all the other three types of
systems crystallize in the P1 space group with one molecule
̅
each of the host and the guest species in the asymmetric unit.
In all these crystal structures, two halogens are involved in a
type II inter-halogen interaction and the third halogen is
involved in a halogen···π interaction. The crystal structures of
the pyridine and benzene solvates of 1I (1I·pyridine,
1I·benzene) and the benzene and o-xylene solvates of 1Br
(1Br·benzene, 1Br·o-xylene) belong to the HG1 network type.
Similar to the guest free form, the host networks are guided by
a type II halogen dimer interaction and a halogen···π
interaction. In the case with the pyridine solvate, the system
is further stabilized by a N···I halogen bonds between the host
and the guest molecules (Figure 2a). Except the 1Br·o-xylene
solvate, the ethylacetate, toluene, o-xylene, m-xylene, p-xylene,
and mesitylene solvates of 1I and 1Br form a HG2 type of host
network. In these structures, the halogen···π interaction
remains intact, but the halogens form a “Z” shape halogen
tetramer (Figure 2b). We could not grow diffraction quality
single crystals of 1Br from 1,2-dibromoethane (DBE) and 1,2-
dichloroethane (DCE), except these two solvates of 1Br, the
chloroform, tetrachloromethane (TCM), DBE, DCE, dioxane,
and tetrahydrofuran (THF) solvates of 1I and 1Br along with
the 1Br·pyridine solvate adopt a HG3 type architecture. In
these structures, along with the halogen···π interaction, the
halogens are also involved in the formation of a cyclic halogen
tetramer synthon (Figure 2c). The interesting part in this type
of system is that the 1Br·pyridine does not adopt the structure
of 1I·pyridine, where the pyridine molecule forms a halogen
bond to the iodo group. This fact supports the idea that an iodo
group is a better candidate for halogen bonding over a bromo
group. The picoline solvates of 1I and 1Br are isostructural
(HG4) and crystallize in the monoclinic space group P21/n
with one molecule, each of the host and the guest species in the
asymmetric unit. Two of the halogens of a molecule are
involved in forming infinite helical chains with opposite
handedness, running parallel to the crystallographic b axis, via
type II inter-halogen interactions. Also in this structure the
third halogen is involved in a halogen···π interaction (Figure
2d,e). The guest molecules are hydrogen bonded via C−H···N
interactions to form a molecular chain, running through the
channel, generated in the host network, parallel to the b axis.
Solvates of 1Cl and 1F. The ethylacetate solvate of 1Cl
(1Cl·EtOAc) is isostructural to the HG1 framework and
Figure 1. Crystal packing in the guest free forms: (a) molecular
packing diagram in the crystal structure of 1I, (b) I···I, I···π halogen
bonds, and Piedfort unit directed molecular tape in 1I (GF1). (c)
Weak C−H···F hydrogen bond directed crystal packing in 1F (GF2).
(d) Packing of the 1Me molecules in a two-dimensional layer (GF3).
SPARTAN’10 (AM1) program shows that the volumes of the I,
Br, Cl, F, and Me groups are 32.0, 25.7, 21.1, 12.7, and 26.0 Å3,
respectively (volume of X = PhX−0.5(biphenyl); the dihedral
angle of the phenyl rings has been taken as 90° to avoid o-
hydrogen interactions). To understand the importance of the
electronic factor of the halogens, we have studied the crystal
crystallizes in the space group P1 with a host to guest ratio of
̅
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Figure 2. (a) I···I dimer and I···π halogen bonds directed HG1 type of open framework in 1I·pyridine. Pyridine molecules are connected to the host
molecules via I···N halogen bonds. (b) 1I molecules are assembled via “Z” shape iodo tetramer and I···π halogen bonds in the HG2 type of network
in 1I·p-xylene. (c) HG3 type of network formed by the 1I host molecules via cyclic iodo tetramer and I···π halogen bonds in 1I·dioxane system. (d)
Helical arrangement of the 1I host molecules via helical I···I interactions and I···π halogen bonds in the type HG4, 1I·picoline system. (e) The 1D
infinite right and left handed helices of type II I···I interactions along the b axis.
1:1. But the toluene, o-xylene, m-xylene, p-xylene, and the
dioxane solvates of 1Cl form different types of networks. The
first four solvates of 1Cl and 1F are isostructural (HG5) and
hydrogen bonded with the host network via weak C−H···O
and C−H···Cl interactions (Figure 3b). Interestingly, this
structure has close resemblance to the guest free form of the
1Cl compound (Figure 3c). After removal of the guest
molecules from the 1Cl·dioxane solvate, the system was
collapsed to the guest free form of 1Cl, as indicated by the
similarity between the simulated PXRD pattern of the guest
free form of 1Cl and the experimental PXRD pattern of the
apohost of 1Cl·dioxane solvate. The overlay diagram suggests
that the transformation needs very small reorientation of the
host molecules in the crystal lattice. The same guest free form
was also produced upon guest removal from the other two
types of solvates, namely, 1Cl·p-xylene and 1Cl·EtOAc (Figure
4).
crystallize in the space group P1. The host to guest ratio is
̅
found to be 1:2 in these systems. In this type of structure, the
halogens are involved only in the weak C−H···halogen type of
hydrogen bonds (Figure 3a) to form a square grid kind of
network where the guest molecules are incorporated inside the
cavities. The dioxane solvate of 1Cl (1Cl·dioxane) forms an
interesting framework (HG6) in this series. The system
crystallizes in a monoclinic space group P21/n with one
molecule of the host and a half molecule of the guest moieties
in the asymmetric unit. A molecular tape is formed via Cl···Cl
type-II interactions and Piedfort units. The guest molecules
occupy the cavities, generated within the tape, and are
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halogen interactions, a cyclic halogen tetramer motif is formed
in the HG3 type of networks. On the other hand, in the
network type HG4, the halogen dimers are connected via a
type-II inter-halogen interactions to form a 1-D helical chain.
Along with the inter-halogen interactions, the awkward shape of
the molecules is also important in their diverse inclusion
behavior in the solid state. In spite of the presence of several
flexible bonds, the molecules show some kind of semirigidity in
their “Y” shape conformation where the phenoxy planes are
approximately perpendicular to the middle benzene ring.
The influence of a solvent molecule in the crystallization
process is evident from the occurrence of polymorphism in a
substance crystallized from different solvents.18 It becomes
even more important when a solvent molecule is incorporated
in the crystal lattice.19 The size, shape, functional group, etc. of
a solvent could be a determining factor in the crystallization
outcome. Nevertheless, it is very difficult to rationalize the role
of a solvent molecule in terms of its property and the crystal
structure of the solute. In this series of crystal structures, the
systems more or less follow a general trend depending upon the
types of solvent molecules used for crystallization. Small solvent
molecules such as nitromethane, acetonitrile produced guest
free form (GF1, 2) of the halogenated compounds. In the
absence of a strong hydrogen bonding donor in the host
molecule, pyridine behaves like benzene for 1I host (HG1).
The HG2 type of network for the 1I/1Br hosts and the HG5
type of network for the 1Cl/1F hosts are generated when the
solvent systems are chosen as methylated benzenes (toluene, o/
m/p-xylene, mesitylene). The halogenated (chloroform, tetra-
chloromethane, dichloroethane and dibromoethane) and the
cyclic ether (tetrahydrofuran and 1,4-dioxane) solvent systems
produced an HG3 type of network for the 1I/1Br hosts. It is
interesting to note that the halogenated solvent systems are
quite different in sizes and shapes. On the other hand the
picoline molecules, which are connected via C−H···N hydro-
gen bonds along the channel, guided 1I and 1Br to adopt an
HG4 type of host network. Nevertheless, there are some
exceptions, such as 1Br·pyridine and 1Br·o-xylene, which have
chosen HG3 and HG1 networks instead of HG1 and HG2
types networks, respectively.
Isostructurality. Isostructurality is an important aspect in
the crystal structures of the halogenated compounds. Saha et al.
have performed a statistical analysis on the isostructurality in
analogous halogen containing organic compounds on CSD
version 5.26, February 2005 update.13b Herein we have
extended the search on CSD version 5.31, August 2010 update,
on reports of monovalent halogen (Cl, Br, and I) containing
compounds, which are single component, not polymeric, no
errors, no ions, no powder structures and R < 0.10 (Table S3,
Supporting Information). Data analysis shows that in a total of
101 hits where all the three halogen derivatives (Cl, Br, and I)
for the same compound are reported, 59.4% showed
isostructurality among I and Br homologues, followed by
70.3% cases of Br and Cl isostructurality, and 28.7% cases
showed a carryover of isostructurality in Cl, Br, and I analogues.
Interestingly, there are also three sets of structures which show
the isostructurality among all the four halogenated compounds.
We have further searched to find out the possibility of an
isostructurality in the clathrates of the halogenated compounds
present in this data set. Interestingly, there is no hit where the
guest free forms of the analogous chloro, bromo, and iodo
compounds are isostructural as well as the clathrates of these
compounds are also isostructural. Therefore, this is the first
Figure 3. (a) Inclusion of p-xylene guests inside the cavities formed by
1Cl molecules in 1Cl·p-xylene, type HG5 system. (b) Enclathration of
the dioxane guest molecules in the architecture of type HG6 made of
1Cl host molecules assembled via Cl···Cl dimer interactions in
1Cl·dioxane. (c) Overlay diagram of the guest free form of 1Cl (blue)
and 1Cl·dioxane solvate (red) systems.
Interestingly, in all four different types of structures, HG1−4
observed in the 1I and 1Br solvates, the guest molecules reside
inside the channel, which runs parallel to the crystallographic a
axis (along the b axis in the case of picoline solvates), and the
molecular tape, which is observed in the guest free form (GF1),
is also observed in these clathrates. As a result, all these
structures (GF1 and HG1−4) show two-dimensional (2-D)
isostructurality17 parallel to the ab plane, and they differ only in
the interlayer contacts around the halogens. In the guest free
form, GF1 and host−guest systems, HG1−4 and 6, the host
molecules are assembled through inter-halogen interactions.
The halogen groups form a type II dimer synthons in the GF1
and HG1 types of networks. When two such halogen dimers
are further connected via a type-I inter-halogen interactions, a
“Z” shape halogen tetramer synthon is formed in the HG2 type
of networks, but when they are linked via two type-II inter-
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Figure 4. The PXRD plots for the apohosts of (a) 1Cl·EtOAc, (b) 1Cl·p-xylene, (c) 1Cl·dioxane, and (d) the simulated plot of the guest free form of
1Cl.
report where the guest free forms of the chloro, bromo, and the
iodo compounds are isostructural and the clathrates of these
compounds are also isostructural.
xylene solvates of 1Cl. Therefore, the structural features and the
thermal analysis of the systems suggest that inter-halogen
interaction guided crystal packing is more favorable for the
heavier halogens compared to the lighter halogens, which rather
chooses C−H···hal hydrogen bond directed crystal packing as
expected. Carbon bound iodo group is a better candidate for
the halogen bonding compared to the other halogens, and the
strength and the frequency of occurrence of such interactions
decrease from iodo to fluoro gradually. Fluoro groups are
mainly involved in weak hydrogen bonds. Our studies showed
that the chloro group may behave like fluoro or heavier
halogens depending upon the nature of the solvent/guest
molecules. Similarities between the crystal structures of
different host molecules also depend upon the guest molecules
as shown in the cases of EtOAc, p-xylene, and pyridine
clathrates in this series of structures. The molecules form
several host architectures as well as easily form the guest free
forms at ambient conditions. The awkward shapes of the
molecules play an important role behind these interesting
features. There are several reports on the isostructurality among
the halogen compounds, but to the best our knowledge this is
the first report where the guest free forms of the chloro, bromo,
and iodo compounds are isostructural as well as a set of
inclusion compounds are also isostructural. Therefore, these
three halogens behave similarly in different packing arrange-
ments of the host molecules.
Thermal Analysis. Differential scanning calorimetry
(DSC) experiments were performed to investigate the relative
thermal stabilities of the different types of host−guest
systems.20 It is generally found that the thermal stability
gradually decreases from the heavier to the lighter halocom-
pounds.13a Among the isostructural 1:1 ethylacetate solvates in
this series, the thermal stability of the 1I and 1Br solvates are
comparable (desolvation temperature ∼ 86 °C), and as
expected it is comparatively very low (desolvation temperature
∼ 58 °C) for the 1Cl solvate (Figure 5). Interestingly, in the
cases of the dioxane and p-xylene solvates, not only the 1I
clathrates are thermally more stable than the isostructural 1Br
clathrates, but the structurally different 1Cl clathrates are also
slightly more stable.
CONCLUSION
■
Hydrogen bonds are robust but the inter-halogen interactions
are comparatively more flexible in nature. As a result, the
halogen bond geometries can be altered easily to modify the
voids which can accommodate guest molecules of different
sizes and shapes. Structural analysis shows that the 1-D
molecular tapes, which are guided by the inter-halogen
interactions, are always present in the 1I and 1Br systems.
On the contrary, this structural feature is present only in the
guest free form and in the ethylacetate solvate, partially present
in the dioxane solvate but absent in the toluene and o/m/p-
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Figure 5. (a) DSC plots for isostructural 1X·EtOAc solvates. (b) DSC plots for 1X·dioxane solvates (X = I and Br are visostrcutural). (c) DSC plots
for 1X.p-xylene solvates (X = I and Br are isostructural). The first endotherm in each case signifies desolvation of the system.
1Me. 1H NMR (CDCl3, 400 MHz) δ 1.245 (9H, t, 7.2 Hz), 2.328
EXPERIMENTAL SECTION
■
(9H,s), 2.847 (6H, q, 7.2 Hz), 5.060 (6H, s), 7.041 (6H, d, 8.0 Hz),
Synthesis: 1,3,5-Tris(bromomethyl)-2,4,6-triethylbenzene.
7.052 (6H, d, 8.0 Hz). 13C NMR δ 16.61, 20.64, 23.11, 64.29, 114.51,
1,3,5-Tris(bromomethyl)-2,4,6-triethylbenzene was prepared accord-
130.11, 130.3, 131.33, 146.23, 157.01. M.P. 142−144 °C.
Crystallization. Diffraction quality single crystals were obtained
by dissolving the compounds in a suitable solvent followed by slow
ing to the procedure mentioned in the literature.21
1,3,5-Triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes
(1X). KOH (5 equiv, 11.3 mmol, 655.4 mg) and 4-X-phenol (5 equiv,
evaporation of the solvent at room temperature. The solvates were
11.3 mmol) were dissolved in 100 mL of tetrahydrofuran and stirred
obtained from the corresponding solvents used for crystallization. The
for 1 h. 1 g (2.2 mmol) of 1,3,5-tris(bromomethyl)-2,4,6-
guest free forms of the 1I and 1Br compounds were obtained from
triethylbenzene was then added to the solution and stirred for 48 h
acetonitrile solvent, and the guest free forms of the 1Cl, 1F, and 1Me
under reflux. The solvent was removed in vacuo. Water (100 mL) was
compounds were obtained from chloroform, ethylacetate, and
added to the mixture and the 1X compound was extracted with
dimethylformamide solvents, respectively.
dichloromethane (3 × 50 mL). The dichloromethane was removed
under a vacuum to obtain the required compound. The compounds
X-ray Crystallography. X-ray crystal data were collected on a
Xcalibur Eos Diffraction Ltd. with Mo−Kα radiation (λ = 0.71073 Å).
are characterized by 1H and 13C NMR. The detailed characterization is
Empirical absorption correction using spherical harmonics, imple-
mented in SCALE3 ABSPACK scaling algorithm were applied.22
given as follows:
1I. 1H NMR (CDCl3, 400 MHz) δ 1.216 (9H, t, 7.6 Hz), 2.792
(6H, q, 7.6 Hz), 5.036 (6H, s), 6.820 (6H, d, 8.2 Hz), 7.593 (6H, d,
8.2 Hz). 13C NMR δ 16.53, 23.14, 64.42, 117.11, 130.96, 131.33,
138.53, 146.48, 158.91. M.P. 217−219 °C.
Structure solution and refinement were performed with SHELXS-9723
and XL,24 respectively. Wherever the highly disordered guest
molecules could not be modeled, the SQUEEZE routine of PLATON
was used to treat the residual electron density.25 Pertinent crystallo-
graphic data collection and refinement parameters of some
representative systems are shown in Table 2 and for the rest of the
systems and the intermolecular interaction parameters of the systems
are shown in Tables S1 and S2, respectively, in Supporting
Information.
1Br. 1H NMR(CDCl3, 400 MHz) δ 1.228 (9H, t, 7.6 Hz), 2.806
(6H, q, 7.6 Hz), 5.047 (6H, s), 6.920 (6H, d, 8.8 Hz), 7.430 (6H, d,
8.8 Hz). 13C NMR δ 16.54, 23.14, 64.55, 116.49, 129.05, 130.98,
132.55, 146.46, 158.13. M.P. 201−203 °C.
1Cl. 1H NMR(CDCl3, 400 MHz) δ 1.228 (9H, t, 7.6 Hz), 2.808
(6H, q, 7.6 Hz), 5.048 (6H, s), 6.960 (6H, d, 8.1 Hz), 7.286 (6H, d,
8.1 Hz). 13C NMR δ 16.56, 23.15, 64.59, 115.94, 129.06, 131.01,
134.81, 146.44, 157.61. M.P. 176−178 °C.
Powder Diffraction Experiments. The PXRD spectrum of the
apohosts of 1Cl clathrates were recorded at room temperature using
Cu Kα radiation (λ = 1.54056 Å) from X-ray diffractometer (model:
X-pert Panalytical). The spectrum was recorded with 2θ ranging from
2° to 45° and a step size of 0.02°. The apohosts of the 1Cl clathrates
were prepared by grinding the clathrate crystals manually in a mortar
pestle, followed by heating under a vacuum at 150−155 °C.
1F. 1H NMR(CDCl3, 400 MHz) 1.25 (9H, t, 7.6 Hz), 2.84 (6H, q,
7.6 Hz), 5.05 (6H, s), 6.98 (6H, dd, 8.8, 4.4 Hz), 7.03 (6H, t, 8.8 Hz)
13C NMR: 16.44, 20.94, 64.73, 115.42, 116.04, 128.9, 131.03, 146.19,
155.03. M.P. 155−157 °C.
175
dx.doi.org/10.1021/cg2009144 | Cryst. Growth Des. 2012, 12, 169−178

Crystal Growth & Design
Article
a
Table 2. Crystallographic Data for Some Selected Systems
system
1I (GF1)
1I·pyridine (HG1)
1I·EtOAc (HG2) (squeezed)
1I·dioxane (HG3)
1I·picoline (HG4)
formula
C33H33I3O3
858.29
C33H33I3O3·C6H5N1
937.39
C33H33I3O3·C4H8O2
946.40
C33H33I3O3·C4H8O2
946.40
C33H33I3O3·C6H7N
951.45
Mr
crystal system
space group
a (Å)
monoclinic
P21/n
triclinic
triclinic
triclinic
monoclinic
P21/n
P1
P1
̅
P1
̅
̅
9.9115(9)
13.3645(11)
24.952(3)
90.00
9.9646(6)
13.3987(7)
14.6107(8)
90.411(5)
107.322(5)
90.923(5)
1861.85(18)
298(2)
9.8411(3)
13.2260(5)
15.5234(6)
111.333(4)
94.651(3)
91.720(3)
1872.00(12)
298(2)
9.9745(8)
13.3547(8)
15.7276(13)
113.199(7)
97.615(7)
90.585(6)
1904.2(2)
298(2)
13.3699(7)
9.8382(6)
28.8159(18)
90.00
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
T (K)
Z
93.168(9)
90.00
90.815(6)
90.00
3300.2(6)
298(2)
3789.9(4)
298(2)
4
2
2
2
4
F(000)
μ (mm−1
1656
912
828
924
1856
)
2.871
2.553
2.531
2.500
2.510
ref collected/unique
parameters
9062/3014
374
10273/5020
428
10242/3479
364
10504/4776
398
9568/5424
436
final R indices [I > 2σ(I)]
R indices (all data)
goodness of fit on F2
system
R1 = 0.045
wR2 = 0.112
0.787
R1 = 0.066
wR2 = 0.174
1.039
R1 = 0.045
wR2 = 0.084
0.726
R1 = 0.072
wR2 = 0.231
1.031
R1 = 0.047
wR2 = 0.116
1.020
1Br (GF1)
1Br·EtOAc (HG2) (squeezed)
1Cl (GF1)
1Cl·p-xylene (HG5)
1Cl·dioxane (HG6)
formula
Mr
C33H33Br3O3
717.33
C33H33Br3O3·C4H8O2
805.43
C33H33Cl3O3
583.94
C33H33Cl3O3·(C8H10)2
690.14
C33H33Cl3O3·(C4H8O2)0.5
628.00
crystal system
space group
a (Å)
monoclinic
P21/c
triclinic
monoclinic
P21/c
triclinic
monoclinic
P21/n
P1
P1
̅
̅
19.1740(6)
13.3687(4)
25.1912(9)
90.00
9.8164(17)
13.4010(16)
14.992(3)
110.825(14)
92.594(15)
90.180(12)
1841.1(5)
298(2)
28.8875(11)
13.4670(4)
24.9657(11)
90.00
10.4401(10)
15.6190(13)
16.1505(15)
64.153(9)
71.764(9)
77.321(8)
2240.4(4)
298 (2)
10.1834(3)
13.5610(4)
23.4243(7)
90.00
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
T (K)
Z
109.733(4)
90.00
110.691(5)
90.00
91.118(3)
90.00
6078.1(3)
298(2)
9085.9(6)
298(2)
3234.21(17)
298 (2)
8
2
12
2
4
F(000)
μ (mm−1
2880
720
3672
844
1320
)
4.014
3.313
0.334
0.244
0.320
ref collected/unique
parameters
16564/6466
709
10058/2915
364
24827/6644
1064
10409/2108
503
7547/5689
382
final R indices [I > 2σ(I)]
R indices (all data)
goodness of fit on F2
system
R1 = 0.048
wR2 = 0.090
0.823
R1 = 0.054
wR2 = 0.144
0.818
R1 = 0.123
wR2 = 0.412
1.029
R1 = 0.062
wR2 = 0.126
0.737
R1 = 0.053
wR2 = 0.113
1.059
1Cl·EtOAc (HG2) (squeezed)
1F (GF2)
1Me (GF3)
formula
Mr
C33H33Cl3O3·C4H8O2
672.08
C33H33F3O3
534.59
C36H42O3
522.70
crystal system
space group
a (Å)
triclinic
monoclinic
P21/n
monoclinic
P21/n
P1
̅
9.7072(8)
13.4028(9)
14.6608(14)
110.951(7)
91.936(7)
90.081(6)
1780.1(3)
298 (2)
2
10.757(5)
18.021(7)
14.908(5)
90.00
10.3507(7)
19.1256(12)
15.2676(12)
90.00
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
T (K)
Z
104.84(4)
90.00
96.584(7)
90.00
2793.6(19)
298(2)
3002.5(4)
298(2)
4
4
F(000)
μ (mm−1
612
1128
1128
)
0.284
0.093
0.072
ref collected/unique
parameters
6339/3262
374
6099/1033
355
7019/2649
358
final R indices [I > 2σ(I)]
R1 = 0.078
R1 = 0.088
R1 = 0.074
176
dx.doi.org/10.1021/cg2009144 | Cryst. Growth Des. 2012, 12, 169−178

Crystal Growth & Design
Article
Table 2. continued
system
1Cl·EtOAc (HG2) (squeezed)
1F (GF2)
1Me (GF3)
R indices (all data)
goodness of fit on F2
wR2 = 0.263
wR2 = 0.115
wR2 = 0.195
1.008
0.774
0.991
a
The rest of the systems are given in Supporting Information.
Thermal Experiments. TG-DSC experiments were performed in
a TA Instruments. Crystals taken from the mother liquor were dried
on a tissue paper and placed in crimped but vented aluminum sample
pans for DSC experiment. The amount of sample taken varied from 4
to 7 mg in each case. The sample was heated from 30 to 250 °C for 1I
solvates, 30 to 220 °C for 1Br solvates, and 30 to 200 °C for 1Cl
solvates at a rate of 10 °C/min.
(4) (a) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G.
Angew. Chem., Int. Ed. 2008, 47, 6114−6127. (b) Smart, P.;
Espallargas, G. M.; Brammer, L. CrystEngComm 2008, 10, 1335−
1344. (c) Metrangolo, P.; Pilati, T.; Resnati, G.; Stevenazzi, A. Curr.
Opin. Colloid Interface Sci. 2003, 8, 215−222. (d) Crihfield, A.;
Hartwell, J.; Phelps, D.; Walsh, R. B.; Harris, J. L.; Payne, J. F.;
Pennington, W. T.; Hanks, T. W. Cryst. Growth Des. 2003, 3, 313−
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1675−1677. (f) Raatikainen, K.; Rissanen, K. Cryst. Growth Des. 2010,
NMR Experiments. 1H and 13C NMR spectra were recorded on a
400 MHz Bruker Avance-II spectrometer
̌ ́ ̌ ̌ ́
10, 3638−3646. (g) Cincic, D.; Friscic, T.; Jones, W. CrystEngComm
ASSOCIATED CONTENT
* Supporting Information
2011, 13, 3224−3231. (h) Metrangolo, P.; Meyer, F.; Pilati, T.;
Proserpio, D. M.; Resnati, G. Chem.Eur. J. 2007, 13, 5765−5772.
(i) Paton, A. S.; Lough, A. J.; Bender, T. P. CrystEngComm 2011, 13,
3653−3656.
■
S
Isostructural packing in the guest free forms and the clathrate
structures (Figure S1), ORTEP and crystallographic refinement
details for disordered molecules (Figure S2), crystallographic
data and refinement parameters (Table S1), the intermolecular
interaction parameters (Table S2), and CSD search on
isostructural halogenated organic molecules (Table S3) are
available. Crystallographic data in CIF are available. CCDC
856123−856165 contain the supplementary crystallographic
data for this paper. This material is available free of charge via
the Internet at http://pubs.acs.org.
(5) Desiraju, G. R.; Parthasarathy, R. J. Am. Chem. Soc. 1989, 111,
8725−8726.
(6) Nayak, S. K.; Reddy, M. K.; Guru Row, T. N.; Chopra, D. Cryst.
Growth Des. 2011, 11, 1578−1596.
(7) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G.
Angew. Chem., Int. Ed. 2008, 47, 6114−6127.
(8) Hathwar, V. R.; Guru Row, T. N. Cryst. Growth Des. 2011, 11,
1338−1346.
(9) (a) Aakeroy, C. B.; Fasulo, M.; Schultheiss, N.; Desper, J.; Moore,
̈
C. J. Am. Chem. Soc. 2007, 129, 13772−13773. (b) Corradi, E.; Meille,
S. V.; Messina, M. T.; Metrangolo, P.; Resnati, G. Angew. Chem., Int.
Ed. 2000, 39, 1782−1786.
AUTHOR INFORMATION
Corresponding Author
*E-mail: binoypu@yahoo.co.in.
■
(10) (a) Saha, B. K.; Nangia, A.; Nicoud, J. F. Cryst. Growth Des.
2006, 6, 1278−1281. (b) Thalladi, V. R.; Brasselet, S.; Weiss, H. C.;
Blaser, D.; Katz, A. K.; Carrell, H. L.; Boese, R.; Zyss, J.; Nangia, A.;
̈
Desiraju, G. R. J. Am. Chem. Soc. 1998, 120, 2563−2577.
(c) Metrangolo, P.; Meyer, F.; Pilati, T.; Proserpio, D. M.; Resnati,
G. Cryst. Growth Des. 2008, 8, 654−659. (d) Walsh, R. B.; Padgett, C.
W.; Metrangolo, P.; Resnati, G.; Hanks, T. W.; Pennington, W. T.
Cryst. Growth Des. 2001, 1, 165−175. (e) Xu, J.; Liu, X.; Lin, T.;
Huang, J.; He, C. Macromolecules 2005, 38, 3554−3557.
(11) (a) Zhu, S.; Xing, C.; Xu, W.; Jin, G.; Li, Z. Cryst. Growth Des.
2004, 4, 53−56. (b) García, M. D.; Blanco, V.; Iglesias, C. P.;
Peinador, C.; Quintela, J. M. Cryst. Growth Des. 2009, 9, 5009−5013.
(c) Mukherjee, A.; Desiraju, G. R. Cryst. Growth Des. 2011, 11, 3735−
3739.
ACKNOWLEDGMENTS
■
B.K.S. thanks DST (SR/FTP/CS-119/2006) and CSIR for
research funding, DST-FIST for X-ray facility, CIF, Pondicherry
University, for NMR, IR, and thermal data and Dr. R. N.
Bhowmik, Department of Physics, Pondicherry University, for
the PXRD data. S.B. thanks Pondicherry University for a
fellowship.
DEDICATION
■
Dedicated to Prof. T. N. Guru Row on the occasion of his 60th
birthday.
́ ́
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Cryst. Growth Des. 2011, 11, 2194−2204.
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