Crystal engineering of a liquid crystalline piperazinedione

Article abstract of DOI:10.1021/ol035365d

(Matrix presented) A molecule designed to self-assemble via hydrogen bonding, arene-arene, and van der Waals interactions and expected to possess thermotropic liquid crystalline properties has been synthesized and characterized. Results support the validi

Full text of DOI:10.1021/ol035365d

ORGANIC
LETTERS
2003
Vol. 5, No. 20
3683-3686
Crystal Engineering of a Liquid
Crystalline Piperazinedione†,‡
Robin A. Kloster, Michael D. Carducci, and Eugene A. Mash*
Department of Chemistry, The UniVersity of Arizona, Tucson, Arizona 85721-0041
emash@u.arizona.edu
Received July 22, 2003
ABSTRACT
A molecule designed to self-assemble via hydrogen bonding, arene-arene, and van der Waals interactions and expected to possess thermotropic
liquid crystalline properties has been synthesized and characterized. Results support the validity of an assembly paradigm based on incorporation
of chemically orthogonal and spatially independent recognition elements in the molecular building blocks.
Understanding and harnessing noncovalent interactions is of
universal importance to biology, chemistry, and materials
science.1 We postulated that crystal packing might be
controlled by incorporation of three chemically orthogonal
molecular recognition elements that are also spacially
independent of each other and designed a family of pipera-
zinedione-containing molecules to test this hypothesis (Figure
1).2 The central piperazine-2,5-dione ring should favor
formation of supramolecular one-dimensional tapes through
reciprocal amide-to-amide hydrogen bonding.3 Control of
second and third dimensional order depends on arene-to-
† Dedicated to Professor E. J. Corey on the occasion of his 75th birthday.
‡ Organic Crystal Engineering with Piperazine-2,5-diones. Part 5.
(1) (a) Kitaigorodsky, A. I. Molecular Crystals and Molecules; Academic
Press: New York, 1973. (b) Desiraju, G. R. Crystal Engineering: The
Design of Organic Solids; Elsevier: Amsterdam, 1989. (c) Wright, J. D.
Molecular Crystals, 2nd ed.; Cambridge University Press: Cambridge, 1995.
(d) Lehn, J.-M. Supramolecular Chemistry; VCH: Weinheim, Germany,
1995. (e) The Crystal as a Supramolecular Entity; Desiraju, G. R., Ed.;
John Wiley & Sons, Ltd.: Chichester, England, 1996. (f) Crystal Engineer-
ing: The Design and Application of Functional Solids; Seddon, K. R.;
Zaworotko, M., Eds; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1999. (g) Organised Molecular Assemblies in the Solid State;
Whitesell, J. K., Ed.; John Wiley & Sons, Ltd.: Chichester, England, 1999.
(h) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural
Chemistry and Biology; Oxford University Press: Oxford, 1999. (i) Steed,
J. W.; Atwood, J. L. Supramolecular Chemistry; John Wiley & Sons, Ltd.:
Chichester, England, 2000, and references cited therein.
Figure 1. Assembly paradigm: molecular units incorporating three
geometrically and chemically independent recognition elements
might assemble predictably into a solid.
arene interactions and van der Waals contacts. Arene
interactions have been recognized as important, from the
packing of small molecules to the stabilization of protein
tertiary structures.4 van der Waals attractive interactions
contribute significantly to crystal lattice organization as is
evidenced by the tendency of organic compounds to achieve
closest packing in the solid state.1,5
10.1021/ol035365d CCC: $25.00
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We have previously observed that the crystal packing of
compound 1 follows the assembly paradigm given in Figure
1. Hydrogen-bonded tapes (Figure 2, one tape is shown in
Figure 4. Conformers present in the crystal structure of 2.
Figure 2. Cross section perpendicular to the hydrogen bonding
axis from the crystal structure of compound 1. Molecular recogni-
tion elements include hydrogen-bonded tapes (red), arene edge-to-
face interactions (blue), and van der Waals contacts (green).
Figure 5. View of the unit cell (shown) from the crystal struc-
ture of 2 illustrating hydrogen bonding and arene edge-to-face
interactions between conformers A (red) and D (dark blue).
Conformers B and C, which coreside with A and D, and the dodecyl
chains of conformers A and D have been omitted for clarity.
red) associate via arene edge-to-face interactions (blue) to
give sheets that maximize van der Waals contacts (green)
in the solid.2a Other piperazinediones with topology similar
to 1 pack similarly.2b
Poly(methylene) chains longer than butyl generally adopt
an extended zigzag conformation and pack in either a parallel
or an antiparallel fashion in the crystalline state.6 Given this
fact and the observed packing in the crystal of 1, we
(2) (a) Williams, L. J.; Jagadish, B.; Kloster, R. A.; Lyon, S. R.; Carducci,
M. D.; Mash, E. A. Tetrahedron, 1999, 55, 14281-14300. (b) Williams,
L. J.; Jagadish, B.; Lansdown, M. G.; Carducci, M. D.; Mash, E. A.
Tetrahedron 1999, 55, 14301-14322. (c) Jagadish, B.; Williams, L. J.;
Carducci, M. D.; Bosshard, C.; Mash, E. A. Tetrahedron Lett. 2000, 41,
9483-9487. (d) Jagadish, B.; Carducci, M. D.; Bosshard, C.; Gu¨nter, P.;
Margolis, J. I.; Williams, L. J.; Mash, E. A. Cryst. Growth Des. 2003, 3,
0000-0000.
(3) Many examples of “ladder-like” tapes have been reported. See:
MacDonald, J. C.; Whitesides, G. M. Chem. ReV. 1994, 94, 2383-2420.
(4) (a) Waters, M. L. Curr. Opin. Chem. Biol. 2002, 6, 736-741. (b)
Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Am. Chem. Soc. 1994, 116, 3500-
3506. (c) Jorgensen, W. L.; Severance, D. L. J. Am. Chem. Soc. 1990, 112,
4768-4774. (d) Burley, S. K.; Petsco, G. A. J. Am. Chem. Soc. 1986, 108,
7995-8001. (e) Karlstro¨m, G.; Linse, P.; Wallqvist, A.; Jo¨nsson, B. J. Am.
Chem. Soc. 1983, 105, 3777-3782. (f) Ribas, J.; Cubero, E.; Luque, F. J.;
Orozco, M. J. Org. Chem. 2002, 67, 7057-7065. (g) Nakamura, K.; Houk,
K. N. Org. Lett. 1999, 1, 2049-2051. (h) Kim, E.; Paliwal, S.; Wilcox, C.
S. J. Am. Chem. Soc. 1998, 120, 11192-11193. (i) Umezawa, Y.;
Tsuboyama, S.; Honda, K.; Uzawa, J.; Nishio, M. Bull. Chem. Soc. Jpn.
1998, 71, 1207-1213. (j) Paliwal, S.; Geib, S.; Wilcox, C. S. J. Am. Chem.
Soc. 1994, 116, 4497-4499.
(5) (a) Depero, L. E. AdV. Mol. Struct. Res. 1995, 1, 303-337. (b)
Perlstein, J. NATO Sci. Ser. C 1999, 538, 23-42. (c) Desiraju, G. R. Nature
Mater. 2002, 1, 77-79. (d) Organic zeolites are exceptions; see: Feldman,
K. S.; Liu, Y.; Saunders, J. C.; Masters, K. M.; Campbell, R. F. Heterocycles
2001, 55, 1527-1554 and references therein.
Figure 3. Hypothetical tape cross section and anticipated crystal
packing viewed perpendicular to the hydrogen bonding axis for
compound 2.
3684
Org. Lett., Vol. 5, No. 20, 2003

Figure 6. View of sheet interdigitation from the crystal structure of 2 looking down the hydrogen-bonded tape axis. For clarity, only con-
formers B (pink) and C (light blue) are shown in the top sheet and only conformers A (red) and D (dark blue) are shown in the bottom
sheet.
postulated that tapes with elongated cross sections would
pack via reciprocal hydrogen bonding, arene edge-to-face
interactions, and van der Waals-driven interdigitation of the
alkyl tails in extended conformations (Figure 3). Such
molecules should exhibit liquid crystalline properties.
Compound 2 was prepared as depicted in Scheme 1.
Experimental details for the synthesis of 2 are given in
Supporting Information.
Microcrystals of 2 were grown at room temperature by
evaporation of a 2-propanol solution and the structure deter-
mined by X-ray diffraction at 100 K at the Advanced Photon
Source at Argonne National Laboratory.7
Four conformers were present in the crystal of 2 (Figure
4). Conformers A and B are similar and coreside at a general
position in the unit cell, while conformers C and D are similar
and coreside at a position with inversion of symmetry.
Figure 7. Modulated DSC curve for compound 2. Heating and
cooling rate was 5 °C/min.
Despite the greater conformational complexity, the crystal
packing of 2 follows the anticipated assembly paradigm:
piperazinediones engage in reciprocal hydrogen bonding to
form tapes (Figure 5), lateral neighbor tapes associate via
arene edge-to-face interactions to form sheets (Figure 5), and
sheets nest to maximize van der Waals contacts in the solid
(Figure 6).
The melting behavior of 2 was examined by modulated
differential scanning calorimetry (Figure 7). Reversible phase
Org. Lett., Vol. 5, No. 20, 2003
3685

Scheme 1. Synthesis of Piperazinedione 2
transitions were noted near 35 °C (solid to liquid crystal)
Grant DMR-9304725, and the State of Illinois through the
Department of Commerce and the Board of Education
Grant IBHE HECA NWU 96. Use of the Advanced Photon
Source was supported by the U.S. Department of Energy,
Basic Energy Sciences, Office of Science, under Contract
No. W-31-109-Eng-38. We thank DND-CAT staff for their
help.
and 195 °C (liquid crystal to isotropic). These transitions
were also observed by optical microscopy under cross-
polarized light.
Solid-state structure and bulk properties are inextricably
linked. Design of compounds that exhibit expected properties
from a predictable crystal packing is a primary goal of crystal
engineering. The assembly paradigm given in Figure 1 was
employed in the design of 2. The validity of this paradigm
is supported by experimental results with 2.
Supporting Information Available: Synthetic procedures
for the preparation of 2, X-ray crystallographic information
file (CIF) for 2, PDF files for Figures 2 and 6, and pho-
tographs depicting the temperature-dependent birefringence
of 2. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. This work was supported by the
Office of Naval Research through the Center for Advanced
Multifunctional Nonlinear Optical Polymers and Molec-
ular Assemblies, by the National Science Foundation
(CHE-9610374), by Research Corporation, and by the
University of Arizona through the Materials Characteriza-
tion Program and the Office of the Vice President for
Research. Portions of this work were performed at the Du
Pont-Northwestern-Dow Collaborative Access Team (DND-
CAT) Synchrotron Research Center located at Sector 5 of
the Advanced Photon Source. DND-CAT is supported by
the E.I. Du Pont de Nemours & Co., The Dow Chemical
Company, the U.S. National Science Foundation through
OL035365D
(6) For example, the hydrocarbon tails of stearic acid pack in a parallel
fashion, producing a sheet structure that resembles a lipid bilayer. Adjacent
sheets associate by carboxylic acid dimer formation. See: Kaneko, F.;
Sakashita, H.; Kobayashi, M.; Kitagawa, Y.; Matsuura, Y.; Suzuki, M. Acta
Crystallogr., Sect. C 1994, 50, 247-250.
(7) Crystal data for 2: C68H114N2O6; M ) 1055.61 g/mol, monoclinic,
P21/c, colorless prism measuring 0.02 × 0.03 × 0.07 mm, T ) 100(2) K,
a ) 21.981(4), b ) 18.298(4), c ) 24.801(5) Å, â ) 108.72(3)°, V )
9447(3) Å3, Z ) 6, Dc ) 1.113 Mg/m, µ ) 0.069 mm-1, Tmax ) 1.0000,
Tmin ) 0.5915, GOF on F2 ) 1.098, R1 ) 0.1160, wR2 ) 0.2971 for all
25086 independent observed reflections.
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Org. Lett., Vol. 5, No. 20, 2003