Synthesis and supramolecular organization of 5-(4-Alkylphenyl)isatin

Article abstract of DOI:10.1021/cg200700r

The synthesis of a homologous series of 5-(4-alkylphenyl)isatin derivatives, as well as the crystal structure and DFT studies of the respective hexyl derivative are presented, constituting the first examples of a new family of supramolecular bilayer forming isatin derivatives, which reveal a new type of molecular strand-a molecular arrangement also supported by quantum chemical calculations.

Full text of DOI:10.1021/cg200700r

ARTICLE
pubs.acs.org/crystal
Synthesis and Supramolecular Organization of 5-(4-Alkylphenyl)isatin
Jan H. Porada,†,‡ J€org Neud€orfl,† and Dirk Blunk*,†
†Universit€at zu K€oln, Department f€ur Chemie, Greinstrasse 4, 50939 K€oln, Germany
S Supporting Information
b
ABSTRACT: The synthesis of a homologous series of 5-(4-alkylphenyl)isatin derivatives, as well
as the crystal structure and DFT studies of the respective hexyl derivative are presented,
constituting the first examples of a new family of supramolecular bilayer forming isatin
derivatives, which reveal a new type of molecular strand—a molecular arrangement also
supported by quantum chemical calculations.
’ INTRODUCTION
draw analogy conclusions about the situation in the liquid crystal
phase of similar but slightly different isatin derivatives published
earlier.10 Though the prediction of the supramolecular architec-
ture of a compound in its liquid crystalline phase on the basis of
its crystal structure cannot be done, it is nonetheless reasonable
to assume that dominant molecular interactions such as
H-bonds, which are present in the crystal phase, may also exist
in the mesophase.11
Supramolecular organization of chromophores is essential
for many high-tech applications, such as laser technology,1 non-
linear optics,2,3 or supramolecular photochemistry.4
Common approaches to achieve a desired supramolecular
alignment are the following: embedding of chromophoric guests
in polymeric, crystalline, or liquid-crystalline host matrices, as
well as covalent insertion of chromophoric monomers into the
main-chain or into side-chains of polymers.2,3
Within our interest in the anisotropic order of nonpolymeric,
chromophoric molecules in their condensed phases, we synthe-
sized a number of new isatin derivatives with the aim to elucidate
the nature of the supramolecular architecture and interactions in
this new chromophoric family.
With respect to its molecular structure, isatin is best suited to
serve as a highly variable tecton5,6 for the construction of supra-
molecular assemblies because of its remarkable hydrogen bond
acceptor/donor abilities and a comparably large molecular dipole
moment. Two chemically different carbonyl oxygens resemble two
hydrogen bond acceptor functions pointing toward different
spatial directions, and the hydrogen attached to the amide nitro-
gen constitutes the hydrogen bond donor.
From a synthetic point of view, it is advantageous that all four
peripheral positions of the isatin phenyl ring can be addressed by
substitution in a straightforward way, each starting from the
respective regioisomer of, for example, bromoisatin. The latter
are synthetically easily accessible.7À9 All the above-mentioned
features make isatin exceedingly interesting for supramolecular
engineering. In this contribution, we describe the synthesis and
an unconventional crystal structure with a hydrogen bond
supported chain formation of 5-(4-alkylphenyl)isatin derivatives.
By analyzing its interesting crystal structure, we can cautiously
’ EXPERIMENTAL SECTION
Syntheses. The synthesis of the new 5-(4-alkylphenyl)isatin deri-
vatives 3aÀe (Scheme 1) was accomplished in a straightforward
manner: To probe an alternative approach to 1-bromo-4-alkylbenzenes,
which usually are synthesized by a sequence of FriedelÀCrafts acylation
and subsequent WolffÀKishner reduction,12 we applied a modern iron
mediated cross-coupling reaction13 of alkyl bromides with phenyl
magnesium chloride followed by bromination. This sequence leads to
1:3 mixtures of the respective ortho- and para-bromo alkyl benzenes,
the tedious separation of which was omitted at this point. Rather, the
products were converted to the respective boronic acids via bromine
lithium exchange and quenching with trimethyl borate. At this stage,
the 4-alkylphenyl boronic acids 2aÀe could be separated by column
chromatography. However, considering the selectivity problems and the
chromatographic separation of the 4-alkylphenyl boronic acids, our new
method provides no significant advantage compared to the traditional
sequence. The boronic acid intermediates 2aÀe were coupled with
5-bromoisatin (1) under SuzukiÀMiyaura conditions to the desired
5-(4-alkylphenyl)isatins 3aÀe.
Received: June 3, 2011
Published: June 21, 2011
r
2011 American Chemical Society
3648
dx.doi.org/10.1021/cg200700r Cryst. Growth Des. 2011, 11, 3648–3652
|

Crystal Growth & Design
ARTICLE
Scheme 1. SuzukiÀMiyaura Coupling Yielding the
5-(4-Alkylphenyl)isatin Derivatives 3aÀe
Table 1. Yields of the SuzukiÀMiyaura Coupling and
Thermal Dataa of the Fusion Point of the Products 3aÀe
ΔHfus
ΔSfus
compd
R
yield (%)
mp (°C)
(kJ/mol)
(J/(K mol))
3a
3b
3c
3d
3e
C6H13
C8H17
C10H21
C12H25
C14H29
32
39
32
34
24
174.2
169.3
165.9
159.6
154.8
17.7
19.9
20.6
21.0
22.1
39.6
45.0
46.9
48.5
51.6
a Thermal data obtained by differential scanning calorimetry.
As can be seen from Table 1, the yields of this SuzukiÀMiyaura
coupling were only moderate but delivered enough material for the
further studies. The complete reaction sequence and all relevant
analytical data are compiled in the Supporting Information.
Figure 1. (a) Molecular strand in the crystal structure of 3a. Dotted
lines represent hydrogen bonds (dNHÀO = 1.94(2) Å, yellow, forming
the C(4) motif, and dCHÀO = 2.29(1) Å, blue, forming the C(7) motif).
(b) Crystal structure of 3a showing parts of two adjacent strands. The
molecules of both chains are associated via πÀπ-interactions and by
weak hydrogen bonds between the lateral phenyl groups with a
hydrogenÀcentroid distance of 2.96(3) Å (green dashed lines). In this
way, each of the lateral phenyl rings is linked with both adjacent chains
(in the front and in the back).
Experimental Molecular and Crystal Structures. To our
initial disappointment, the 5-(4-alkylphenyl)isatins 3aÀe do not show
enantiotropic liquid crystalline behavior.14 Rather, they melt directly
into the isotropic liquid with the phase transition parameters given in
Table 1, but to our edification they permit a detailed insight into the
supramolecular organization principles of this class of compounds,
which is discussed below and which could not be obtained from other
derivatives, e.g. from their alkoxy analogues. Apart from a new form of
strand formation, hitherto not observed with isatin derivatives, this
insight is valuable for the interpretation and understanding of the liquid
crystalline behavior of the respective previously published 5-(4-alkyloxy-
phenyl)isatin derivatives, from which it was not possible to grow single
crystals suitable for X-ray analysis.10
nomenclature, a layer in the crystals of 3a would be called a network,
made up mainly by two different motifs forming a basic graph set of
N1dC(4)C(7), describing the chains including either four or seven
atoms before iteration (i.e., walking through the chain following the
yellow dotted lines for C(4) or the blue dotted lines for C(7),
respectively, in Figure 1). Both motifs combine to a complex graph set
of N2dR33(14), which describes a ring structure of H-bonds between
three donors and three acceptors involving 14 atoms.
The determining factor for the first dimension—the formation of the
strand (cf. Figure 1a)—is the C(4)18,19 hydrogen bond motif formed
between the amide hydrogen and the 2-carbonyle function of the next
molecule (dNHÀO = 1.94(2) Å, yellow in Figure 1). At this hydrogen
bond supported interface of the strand, the molecules are arranged
syndiotactically; that is, their hydrophobic tails point out of the strand
alternating to the opposite sides.
Figure 1 shows the highly interesting crystal structure15 of 5-(4-
hexylphenyl)isatin (3a), which could be resolved and related to density
functional theory calculations. The crystals were obtained by slow
evaporation from a saturated chloroform solution.
The crystals of 3a are organized in layers, and these are formed by
antiparallel arranged, slightly tilted strands of molecules. According to
the Cambridge Structural Database (CSD),16 the supramolecular
strands found in the case of 3a constitute a new type with respect to
isatin derivatives.17 Both half strands are very slightly different. But due
to the only tiny differences, it is reasonable to discuss the structure with
averaged values (standard deviation based on entire population given in
parentheses).
The crystal structure of 3a reveals five different factors determining
the three-dimensional crystal architecture: three different types of
hydrogen bonds, dipole compensation, and πÀπ-interactions.
For the topological description of hydrogen bond networks in organic
crystals, a nomenclature based on graph theory has been developed and
proven as a powerful tool to describe and compare them.18,19 Following this
In such a strand, all the isatin headgroups point in the same direction;
that is, in Figure 1a, all carbonyl functions point to the right while all the
amine nitrogen atoms point to the left. This leads to an anticlinic setup
causing a polar character of each strand.
A second, weak hydrogen bond motif is formed between the
6-hydrogen of 3a and the 3-carbonyl function of the next but one
3649
dx.doi.org/10.1021/cg200700r |Cryst. Growth Des. 2011, 11, 3648–3652

Crystal Growth & Design
ARTICLE
molecule of the same strand, which is the next molecule on the same side
of the strand (dCHÀO = 2.29(1) Å, blue in Figure 1a). This second C(7)
hydrogen bond motif additionally stabilizes the strand.
Both motifs together lead to a complex graph set describing a R33(14)
ring structure in which the C(4) motif contributes two H-bonds, while
the C(7) motif participates with only one H-bond.
The second dimension of the supramolecular setup of 3a is opened by
the formation of layers by juxtaposition of the above-discussed strands,
cf. Figure 1b. Here, the organizing factors are the shape anisotropy of the
strands, nanophase segregation of the polar aromatic heads from the
apolar alkyl chains, and the polarity of each strand. The latter leads to an
antiparallel alignment of adjacent strands so that their polarities cancel
out and the overall layer is macroscopically not dipolar. In the adjacent
strands of one layer, the molecules lie on top of each other (but with the
above-described opposite orientation) with a face-to-face distance
between the isatin head groups of 3.26(1) Å, which is close enough to
allow πÀπ-interactions between them.
While the planes of all the isatin bicycles in the crystal structure of 3a
are arranged parallel to each other, the lateral phenyl rings organize in a
fishbone-like manner in such a way that two (partially positively
charged) hydrogen atoms of each phenyl ring point toward the
(negatively charged) π-electron cloud of the lateral phenyl ring of a
neighbored molecule in an adjacent strand. This third, weak hydrogen
bond motif is a further cross-linking factor between adjacent chains and
was not considered in the graph set analysis performed above.
The third dimension of the crystal is formed by stacking the above-
described bilayers on top of each other. At the interface between these
layers, the alkyl chains point toward each other in a synclinic manner.
Within the layers, the plane of the strands is tilted by 14° with respect
to the layer normal. Together with the polar order of the strand, this
could lead to supramolecular chirality even from achiral molecules.
Examples for such spontaneous formation of chirality are the so-called
“banana”- or “bent-core”-liquid crystals.20À23 However, since in the case
of 3a the neighboring polar strands are oriented into opposite directions,
a supramolecular racemic situation is developed within the layers. But,
the supramolecular chiral character of each tilted single strand in this
crystal architecture possibly opens an opportunity to discriminate
between both polar orientations (i.e., the “enantiomers”) by introducing
a molecular chirality and thus converting the enantiomeric situation of the
antiparallel tilted strands into a diastereomeric and, thus, energetically
distinct situation.
Figure 2. (a) Section of a molecular strand of 3a calculated under
periodic boundary conditions (PBC), showing the C(4) hydrogen bond
motif but lacking the C(7) one found in the crystal structure, cf.
Figure 1a. (b) Calculated dimer of 3a showing the same hydrogen bond
motif as found in the crystal structure26 of unsubstituted isatin.
Table 2. Calculated (B3LYP/6-311G(d)) Energetic Data of
5-(4-Hexylphenyl)isatin (3a) and Isatina
compd
Etot (Hartree)
ΔEtot (kJ/mol)
3a
monomer
dimer
À980.223062416
À1960.47197137
À1960.48711830
À513.18639588
À1026.39866586
À1026.41370584
0
À67.9
À107.6
0
3a
3a
strand
isatin
isatin
isatin
monomer
dimer
À67.9
À107.4
strand
a In each case of the calculated structures of 3a, several conformers are
possible with respect to, for example, the orientation of the alkyl chain at
the heterocycle or the relative arrangement of different molecules. Only
the energetically most favored one is reported here.
program. For the monomers and dimers, the ground state character of the
stationary points has been proven by frequency calculations, confirming the
absence of any negative eigenvalues in the Hessian matrix. Unfortunately, the
latter type of calculation is not possible with G03 under periodic boundary
conditions(PBC), whichwereemployedforthecalculationsofthestrand. All
computed structures are listed in detail in the Supporting Information.
In a preliminary theoretical DFT study, both primary organization
models, the C(4)-strand (Figure 2a) and R22(8) dimers (Figure 2b),
could be reproduced.
For 5-(4-hexylphenyl)isatin (3a) and isatin, both types of organiza-
tion constitute local minima. For both compounds, the energy gain
ΔE is calculated to be about À68 kJ/mol for the dimerization and about
À107 kJ/mol for the strand formation (see Table 2); that is, in both cases,
the strands are calculated to be favored by about ΔΔE ≈ 40 kJ/mol
compared to the dimers in these “gas-phase structures” (all values refer to
the simple difference of the computed total energy without consideration of
zero point energies or basis set superposition errors—which are not available
for the PBC structures). That the energetic results for 3a and isatin are so
similar is not surprising, since the computable intermolecular interactions
are very similar in both cases and the only difference, the additional residue
in 3a, is located far away from the direct molecular interaction.
The formation of such hydrogen bond supported bilayers strongly
recalls the formation of bilayers in smectic liquid crystals. Thus, we are
confident that the experimental and theoretical findings described here
for the 5-(4-alkylphenyl)isatins 3aÀe can be applied to the rational
design of isatin derived liquid crystals as well.
Despite the numerous isatin derivatives described in the literature,24
only 16 crystal structures of 8 different compounds are registered in the
CSD.16 The tendency of isatin derivatives to form polymorphs is well
described for the case of 7-fluoroisatin, exhibiting three different crystal
structures with dimeric and tetrameric hydrogen bond motifs.25 From
the above-mentioned 16 crystal structures, the vast majority of 10
structures describe dimers; also, the stem compound isatin shows this
type of organization.26 In general, such homodromic dimers with a
R22(8) graph set, as, for example, the well-known dimers of carboxylic
acids, are of frequent occurrence in nature.18,19 Among the remaining six
crystal structures, only one describes a strand, but which is of a different
type compared to the one described here. In this other type of strand, the
hydrogen bond linkage proceeds from the NH-group to the 3-carbonyl,
forming a C(5) motif.27
Computational Structures. All calculations have been performed
by employing the Becke three-parameter hybrid functional28 with the
correlation functional of Lee, Yang, and Parr29 (B3LYP) in combination
with the 6-311G(d) basis set as implemented in the Gaussian 0330 (G03)
However, regarding the experimental crystal structure of isatin, the
calculated result is obviously untenable. But it has to be kept in mind that
in these provisional calculations still a lot of molecular interactions are
3650
dx.doi.org/10.1021/cg200700r |Cryst. Growth Des. 2011, 11, 3648–3652

Crystal Growth & Design
ARTICLE
Table 3. Characteristic Measures from Computed (B3LYP/
6-311G(d)) and X-ray Structures of the Different Aggregates
of 5-(4-Hexylphenyl)isatin (3a) and Isatina
interactions which are effective between the molecules and which
will help for the rational design of new functional materials (e.g.,
in the field of liquid crystals or crystal engineering) on the basis of
this structural motif. The presented DFT studies support the
experimentally found supramolecular basic units, i.e. dimers and
strands, in a qualitative manner. However, at the level of theory
chosen here, only the strongest hydrogen bonds could be
reproduced in the calculated structures while all the weaker
interactions remained neglected. For this reason, the quantitative
energetical results of calculations at this level of theory concern-
ing the supramolecular assemblies of isatin and its derivatives are
not expressive for a deeper interpretation of the polymorphic
variations.
The parallel spatial alignment of the chromophoric parts of the
substituted isatins 3, the formation of supramolecular polar
strands, and the high molecular dipole moment of the isatin
headgroup might be technically applicable because of their
anisotropy, possibly already with such crystalline compounds
as 3, but particularly in derivatives which may form liquid
crystalline, i.e. fluid, phases. Respective works are ongoing and
will be reported elsewhere.
dNHÀO
dNÀO
dCOÀH
dC2ÀN
compd
(Å)
(Å)
(Å)
(Å)
3a
strand, X-ray
1.94
1.85
1.89
2.04
1.84
1.88
2.79
2.84
2.89
2.93
2.83
2.89
2.29
2.51
6.84
6.80
3.62
3.58
6.82
3.62
3a
strand, computed
dimer, computed
dimer, X-ray26
3a
isatin
isatin
isatin
strand, computed
2.54
dimer, computed
a dNH-O, distance between the hydrogen atom of the H-bond and the
acceptor oxygen; dNÀO, distance between the donor group nitrogen and
the acceptor oxygen of the next molecule; dCO-H, distance between the
3-carbonyl oxygen and the phenyl 6-hydrogen of the adjacent molecule;
d
C2ÀN, distance between C-2 and the nitrogen of the neighboring
molecule located at the same half side.
not considered, e.g. the dipolar interactions between adjacent strains or
dimers, van der Waals interactions, as well as any entropic influences or
crystal packing effects (e.g., minimization of excluded volume etc.).
On the other hand, the calculated strand of 3a, computed under periodic
boundary conditions, reproduces the structure found in the crystal quite
well; a collection of characteristic measures, comparing the DFT calcula-
tions with the crystal structures of 3a and isatin is compiled in Table 3.
Differences between the computed and the X-ray determined struc-
tures appear with respect to the second, weak C(7) hydrogen bond motif
in the strands of 3a, which is not described properly by the DFT
calculations. A second difference is that in the calculations the isatin
heads of adjacent molecules (dimers and strands) lie exactly in the same
plane, while in the crystal structures an offset occurs, leading to a little
“step” between the molecules.
A very good agreement was found regarding the out-of-plane twist of
the lateral phenyl groups of 3a, for which the angle is 38.4° in the
computed structure and, thus, only 1.7° smaller than the measured one.
At this stage of our study we concentrated on the supramolecular
organization with respect to the first dimension only. Interactions between
adjacent dimers or between adjacent strands have not yet been studied,
since conventional DFT is known to perform only poorly with respect to
weak intermolecular interactions, such as, for example, van der Waals or
πÀπ interactions.31,32 Therefore, the calculations presented here resemble
just a qualitative measure for possible supramolecular aggregates.
Regarding the computed structures, a clear difference between the liquid
crystalline alkoxyphenyl-substituted isatin derivatives10 and the alkylphenyl
derivatives of series 3is that, in the case of the alkoxyphenyl substituents, the
alkyloxy chain is situated in plane with the phenyl ring while, in the case of
the alkylphenyl derivatives, the alkyl chain is arranged nearly perpendicular
to the plane of the phenyl ring. These predilections for the orientation of the
alkyl- or alkyloxy-chain can also be one reason for the different behavior of
the two series with regard to their thermomesomorphism.
Concerning the melting process, it is reasonable to assume that the
weakest H-bond, i.e. the C(7) pattern, breaks first, which gives the
molecules a certain rotational freedom and opens the possibility of a
dynamic equilibrium between the (almost infinite) C(4) strand, shorter
but still linear fragments of it, cyclic structures, and the R22(8) dimers. All
these architectures differ in their degrees of freedom and, thus, in their
entropic situation, in which the dimers are most favored.
’ ASSOCIATED CONTENT
S
Supporting Information. Instrumentation, synthetic pro-
b
cedures and analytical data (refraction index, IR-, H-, 13C
1
NMR), crystal structure data including crystallographic informa-
tion files (CIF), and DFT-computed structures. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: d.blunk@uni-koeln.de. Telephone: +49-221-470 5213.
Fax: +49-221-470 3064.
Present Addresses
‡Department of Chemistry and Biochemistry, 215 UCB, University
of Colorado, 80309 Boulder, CO, USA.
’ ACKNOWLEDGMENT
The generous provision of computing time at the Regional
Computing Centre RRZK, Cologne, Germany, and within the
D-GRID initiative is gratefully acknowledged. This work was
partly funded by the Federal Ministry of Education and Research
(BMBF) Project MoSGrid, reference no. 01IG09006A.
’ REFERENCES
(1) Preiswerk, H. P.; Lubanski, M.; Kneub€uhl, F. K. Appl. Phys. B:
Laser Opt. 1984, 33, 115–131.
(2) Ostroverkhova, O.; Moerner, W. E. Chem. Rev. 2004, 104,
3267–3314.
(3) Kajzar, F.; Lee, K.-S.; Jen, A. K.-Y. Polymeric materials and their
orientation techniques for second-order nonlinear optics. In Polymers for
Photonics Applications II; Springer-Verlag Berlin: Berlin, 2003; Vol. 161,
pp 1À85.
(4) Ariga, K.; Kunitake, T. Supramolecular Chemistry—Fundamentals
and Applications; Springer Verlag: Berlin, Heidelberg, New York, 2006.
(5) Simard, M.; Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113,
4696–4698.
’ CONCLUSION
The crystal architecture of the newly synthesized 5-(4-hex-
ylphenyl)isatin (3) reveals a number of important intermolecular
(6) Su, D.; Wang, X.; Simard, M.; Wuest, J. D. Supramol. Chem.
1995, 6, 171–178.
3651
dx.doi.org/10.1021/cg200700r |Cryst. Growth Des. 2011, 11, 3648–3652

Crystal Growth & Design
ARTICLE
(7) Borsche, W.; Jacobs, W. Ber. Dtsch. Chem. Ges. 1914, 47, 354–363.
(8) Sandmeyer, T. Helv. Chim. Acta 1919, 2, 234–242.
(9) Sadler, P. W. J. Org. Chem. 1956, 21, 169–170.
(10) Blunk, D.; Porada, J. ChemPhysChem 2009, 10, 3260–3264.
(11) Haase, W.; Athanassopoulou, M. Crystal Structures of LC
Mesogens. In Liquid Crystals I; Mingos, D., Ed.; Springer: Berlin/
Heidelberg, 1999; Vol. 94, pp 139À197.
(12) Gray, G. W.; Hird, M.; Lacey, D.; Toyne, K. J. J. Chem. Soc.,
Perkin Trans. 2 1989, 2041–2053.
(13) Nakamura, M.; Matsuo, K.; Ito, S.; Nakamura, B. J. Am. Chem.
Soc. 2004, 126, 3686–3687.
(14) Using polarization microscopy, we could observe a monotropic
liquid crystalline phase far below the respective melting point of the
5-(4-alkylphenyl)isatin homologues with an alkyl chain of octyl or
longer . This phase could not be caught by DSC due to preceding
recrystallization.
(15) CCDC 722527 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(16) CSD Version 5.30, Update 3.
(17) Unsubstituted isatin and several derivatives form dimers in their
crystals. Some halogen substituted isatin derivatives form molecular
chains of a different type, in which the amide hydrogen bond is linked to
the oxygen atom of the 3-carbonyl group.
(18) Etter, M. C.; Macdonald, J. C.; Bernstein, J. Acta Crystallogr.,
Sect. B: Struct. Sci. 1990, 46, 256–262.
(19) Bernstein, J.; Davis, R. E.; Shimoni, L.; Chang, N. L. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1555–1573.
(20) Link, D. R.; Natale, G.; Shao, R.; Maclennan, J. E.; Clark, N. A.;
Korblova, E.; Walba, D. M. Science 1997, 278, 1924–1927.
(21) Reddy, R. A.; Tschierske, C. J. Mater. Chem. 2006, 16, 907–961.
(22) Takezoe, H.; Takanishi, Y. Jpn. J. Appl. Phys., Part 1 2006,
45, 597–625.
(23) Tschierske, C. Curr. Opin. Colloid Interface Sci. 2002, 7, 69–80.
(24) As of September 2010, CAS lists 1768 isatin derivatives as single
compounds in which the heterocycle, both carbonyl functions, and the
NH-group are neither substituted nor modfied.
(25) Mohamed, S.; Barnett, S. A.; Tocher, D. A.; Price, S. L.;
Shankland, K.; Leech, C. K. CrystEngComm 2008, 10, 399–404.
(26) Palenik, G. J.; Koziol, A. E.; Katritzky, A. R.; Fan, W. Q. J. Chem.
Soc., Chem. Commun. 1990, 715–716.
(27) Garden, S. J.; Pinto, A. C.; Wardell, J. L.; Low, J. N.; Glidewell, C.
Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2006, 62, O321–O323.
(28) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(29) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37,
785–789.
(30) Frisch, M. J.; et al. Gaussian 03, Revision D.02; Gaussian Inc.:
Wallingford, CT, 2004.
(31) Szalewicz, K.; Patkowski, K.; Bogumil, J. Intermolecular Inter-
actions via Perturbation Theory: From Diatoms to Biomolecules. In
Intermolecular Forces and Clusters II; Springer-Verlag: Berlin, Heidelberg,
2005; Vol. 116, pp 43À117.
(32) Wu, X.; Vargas, M. C.; Nayak, S.; Lotrich, V.; Scoles, G. J. Chem.
Phys. 2001, 115, 8748–8757.
3652
dx.doi.org/10.1021/cg200700r |Cryst. Growth Des. 2011, 11, 3648–3652