Journal of Chemical Crystallography, Vol. 36, No. 1, January 2006 (C 2006)
DOI: 10.1007/s10870-005-9028-6
Crystal structure of
2,8,14,20-tetranaphthylpyrogallol[4]arene
Cesar H. Zambrano,(1) Jorden P. Kass,(1) Eric Efrain Dueno,(1)∗
Yanxiong Ke,(2) and Hong-Cai Zhou(2)
Received March 14, 2005; accepted September 27, 2005
Published Online December 23, 2005
The aromatic derivative 2,8,14,20-tetranaphthylpyrogallol[4]arene was synthesized by the
acid catalyzed condensation of 2-naphthaldehyde and pyrogallol in refluxing aqueous
ethanol. Single crystal X-ray analysis revealed that the molecule crystallizes in a triclinic
space group P1(bar) No. 2, with a = 11.3396(7) Å, b = 15.9942(10) Å, c = 26.3653(17)
Å, α = 94.309(2)◦ , β = 91.765(2)◦ , γ = 93.892(2)◦ , Dcalc = 1.298 g/m3 for Z = 1. Within
the unit cell, six methanol molecules of crystallization plus one molecule of pyrazine were
found to accompany the pyrogallol macrocycle. In the solid state, the macrocycle is found
to adopt the chair conformation.
KEY WORDS: Pyrogallol[4]arene; chair conformation; crystal structure; naphthyl.
resorcenarenes and pyrogallolarenes can also
adopt crown structures that can act as hosts
for a variety of substrate species.1 While the
synthesis and chemistry of calixarenes and
resorcenarenes has become a subject of extensive
investigation in the past decade, studies involving
pyrogallolarenes are not as common.5b The
pyrogallolarenes are considered useful in the
synthesis of a wide array of novel materials such
as metal complexing agents,6 sensors,7 water
soluble macrocycles,8 phase transfer extraction of
heavy metals,9 for complexation of fullerenes10
and related molecules,11,12 for new bioorganic and
biomimetic chemistries,13 for self-assembled systems,14 for pyrogallolarene-based crown ethers,15
as stationary phases,16 and as novel pyrogallolarene polymers.5,17 In our group we have focused
our attention to the exploration of the chemistry
of these molecules. Herein we report the first
solid state structure, to the best of our knowlege,
of an aromatic-substituted pyrogallo[4]arene.
Introduction
During the past two decades numerous
investigations of organic compounds that can
adopt specific geometries have been conducted.1
These unique molecular architectures can be used
as templates to generate chemical entities with
applications in important fields. Among these
compounds the calixarenes have generated much
interest owing to their calix-like geometry, and
they can be employed as molecular platforms
for metal-ligand exchange complexes,2–4
polymeric materials,5 self-assembled systems,2d ,
and as prospective reaction sites for catalytic
processes.2b,d Similar to the calixarenes, the
(1)
Department of Chemistry, Eastern Kentucky University, Richmond, Kentucky.
(2) Department of Chemistry and Biochemistry, Miami University,
Oxford.
∗ To
whom correspondence should be addressed; e-mail:
eric.dueno@eku.edu.
67
C 2006 Springer Science+Business Media, Inc.
1074-1542/06/0100-0067/0 68
Experimental
Synthesis of 2,8,14,20-tetranaphthylpyrogallol[4]arene
A 200 mL round bottom flask was charged
with 10.0 g (79.4 mmol) of pyrogallol and 55 mL
of 95% ethanol. The reaction vessel was cooled
in an ice bath to 0◦ C and 16 mL of 5 M HCl was
added in one portion. 2-naphthaldehyde (12.32 g,
79 mmol) was then added dropwise over a period of 30 min with an addition funnel. The reaction vessel was allowed to warm slowly to
room temperature and then maintained at 80◦ C
for 12 h, the yellow needles that separated were
collected by filtration and washed with cold 1:1
ethanol-water until the material was pale yellow,
and neutral to pH paper. Drying under vacuum
at 40◦ C for 12 h afforded 66.5 g (63 mmol) of
2,8,14,20-tetranaphthylpyrogallol[4]arene, Yield,
79.8% mp >350◦ C.
Measurement of crystal structure
A single crystal of the titled compound with
dimensions 0.42 × 0.45 × 0.16 mm was mounted
on a Bruker APEX Single Crystal X-Ray Diffractometer with a 4K CCD Detector. Graphite momochromated Mo-Kα radiation (λ = 0.71073 Å)
was used. The data were corrected for Lorentz and
polarization effects during data reduction using
the BRUKER SAINT package.18 The calculated
absorption coefficient, µ, for Mo-Kα radiation
was 0.091 m−1 . The structure was solved by direct
methods. All non-hydrogen atoms were refined
anisotropically on F2 by full-matrix least squares
using SHELXL-97,19 while all hydrogen atoms
were placed in calculated position and refined as
riding atoms. Crystallographic information can be
found in Table 1.
Zambrano, Kass, Dueno, Ke, and Zhou
Table 1. Crystal Data and Refinement Parameters
CCDC deposit no.
Color/shape
Chemical formula sum
Chemical formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α ( ◦)
β ( ◦)
γ ( ◦)
Volume (Å3 )
Z
Density (calculated, g/m3 )
F(0 0 0)
µ (cm−1 )
No of collected reflections
No of unique reflections (Rint )
Data/restraints/parameters
Final R indices [I ≥ 2σ (I)]
R indices (all data)
Goodness of fit on F2
235410
violet/rod
C224 H200 N4 O48
3715.88
293(2)
Triclinic
P1bar (No. 2)
11.3396(7)
15.9942(10)
26.3653(17)
94.309(2)
91.765(2)
93.892(2)
4754.2(5)
1
1.298
1956
9.1
28549
17399 (0.0330)
8611/0/1305
R1 = 0.0809, wR2 = 0.2295
R1 = 0.1420, wR2 = 0.2629
0.95
containing pyrazine.20 Due to the difficulty in obtaining good quality crystals for analysis, four
equivalents of pyrazine were added to a solution of
1 with the expectation that the nitrogen contaning
molecule would form a self-assembled structure
with the macrocycle and help it precipitate out of
solution. However, as it was revealed through the
Results and discussion
Suitable crystals for X-ray analysis of
the 2,8,14,20-tetranaphthylpyrogallol[4]arene, 1
(Fig. 1) were obtained from a methanol solution
Fig. 1.
Drawing of 2,8,14,20-tetranaphthylpyrogallol[4]arene, (1), showing the substituted carbon atoms
and their numbering.20
Crystal structure of 2,8,14,20-tetranaphthylpyrogallol[4]arene
Fig. 2. Ortep representation of 1. Oxygen atoms are
shown with 50% probability ellipsoids, and carbon atoms
are spheres. Hydrogen atoms have been removed for clarity.
Selected atoms have been numbered.
X-ray study, only a single molecule of pyrazine
is present in the unit cell. This suggests that the
hydrogen-bonded interactions between the nitrogen heterocycle and the pyrogallol-OH groups did
lead to the formation of a three-dimensional network where the O–H···N bonding is important in
defining the periodicity of the system. Likewise,
the six methanol molecules of crystallization occupy random positions about the macrocycle and
do not appear to participate in any important structure forming properties.
It has been reported that resorc[4]arenes
and pyrogallol[4]arenas can adopt a variety of
conformations depending on the reaction conditions and the steric hindrance of the aldehyde
used in the condensation.2d Among these possible conformations, the most common ones are
the crown (rccc) structure and the chair (rctt)
structure.2d The X-ray analysis of 2,8,14,20tetranaphthylpyrogallol[4]arene shows that its geometry is consistent with the chair (rctt) structure
(Fig. 2). In this chair (rctt) structure, two opposite pyrogallol rings occupy the equatorial plane
with their OH groups pointing away from each
other. The remaining two pyrogallol fragments
69
are perpendicular to the plane generated by the
aforementioned rings, and the OH groups on each
ring also point in opposite directions.
An unusual feature of this structure is that
the naphthyl substituents are arranged (in the rctt
structure) as expected in pairs, but in one case,
both naphthalene rings are eclipsed to each other,
while the other pair exhibits a staggered geometry. Moreover, in both cases, the naphthalene
rings are not coplanar, but show a substantial deviation from a horizontal (parallel) arrangement.
This feature suggests that the conformation of 1
as it crystallized corresponds to a kinetic product. This observation is consistent with those of
other investigators, who state that in practice, only
one product is obtained from the condensation
reaction and a kinetic product possessing the rctt
(chair) configuration is the one that is most rapidly
formed.2d In order to determine the stability of 1,
a molecular modeling study was carried out using
MOE (MMFF94).21 This computational calculation indicated that the most stable conformation
was quite similar to the one obtained by recrystallization of 1. In the ground state configuration,
the naphthyl rings approach each other (they are
bound to the methylene sp3 centers which are in
turn attached to sp2 aromatic carbons from the
pyrogallol ring); however the inter-ring distance
is not close enough (4.5 Å) to implicate a π −π
interaction. In the crystal structure of 1, both pairs
of naphthyl substituents are juxtaposed at 27◦ of
the horizontal plane; but in addition, there is significant rotation (15◦ ) around a bridging methylene carbon of one of the aromatic rings of the
staggered naphthalene pair. This structural feature
appears to be a crystallization artifact because the
rotation of the naphthyl moiety does not allow
for proper π -orbital interaction between aromatic
rings even though the inter-ring distance decreases
to 3.4 Å.
Conclusion and outlook
The synthesis of an aromatic pyrogallolarene
was accomplished in good yield from pyrogallol
and 2-naphthaldehyde. X-ray analysis revealed
70
the compound adopted the chair form under kinetic conditions. The pyrogallolarene displayed
no affinity toward pyrazine in the chair conformation. Current studies are underway to isolate the
thermodynamic conformer derived from pyrogallol and 2-naphthaldehyde.
Supplementary materials CCDC 235410 contains the supplementary crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data request/cif, by emailing data request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2
1EZ, UK; Fax: +44 1223 336033.
Acknowledgments
The authors wish to thank Dr. Debra Bautista
from Eastern Kentucky University for her help
with the MOE calculations. Financial support for
this work was obtained through the University Research Committee at Eastern Kentucky University
(Grant No. 401062).
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