Carboxylic acid and phenolic hydroxyl interactions in the crystal structures of co-crystals/clathrates of trimesic acid and pyromellitic acid with phenolic derivatives

Article abstract of DOI:10.1021/cg100862y

Crystallization of trimesic acid (H₃TMA) in the presence of phenol resulted in the single crystals of [(H₃TMA)?(phenol)], 1. The crystal structure consists of two-dimensional hydrogen bonding layers with herringbone geometry via an acid-phenol synthon in which the O-H group of phenol inserts into a conventional acid dimer in an unsymmetrical fashion. The consistency and robustness of this observed phenomenon were confirmed by reproducing a similar structure by treating H₃TMA with m-cresol [(H₃TMA)?(m-cresol)], 2. On the other hand, similar reactions with H₄PMA resulted in unprecedented clathrates of H₄PMA containing a square grid network via a conventional acid synthon. The square grids have dimensions of 8.3 × 8.3 A and clathrate phenolic guests. Our studies indicate that H₄PMA can act as a host only for the phenolic derivatives such as phenol [(H₄PMA)?(phenol)], 3, o-cresol [(H₄PMA)₂?(o-cresol)], 4, p-cresol [(H ₄PMA)₂?(p-cresol)], 5, and p-chlorophenol [(H ₄PMA)₂?(p-chlorophenol)], 6.

Full text of DOI:10.1021/cg100862y

DOI: 10.1021/cg100862y
Carboxylic Acid and Phenolic Hydroxyl Interactions in the Crystal
Structures of Co-Crystals/Clathrates of Trimesic Acid and Pyromellitic
Acid with Phenolic Derivatives
2010, Vol. 10
4565–4570
Lalit Rajput, Navendu Jana, and Kumar Biradha*
Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India
Received June 29, 2010; Revised Manuscript Received August 4, 2010
ABSTRACT: Crystallization of trimesic acid (H3TMA) in the presence of phenol resulted in the single crystals of [(H3TMA) (phenol)],
1. The crystal structure consists of two-dimensional hydrogen bonding layers with herringbone geometry via an acid-phenol synthon in
which the O-H group of phenol inserts into a conventional acid dimer in an unsymmetrical fashion. The consistency and robustness of
3
this observed phenomenon were confirmed by reproducing a similar structure by treating H3TMA with m-cresol [(H3TMA) (m-cresol)],
3
2. On the other hand, similar reactions with H4PMA resulted in unprecedented clathrates of H4PMA containing a square grid network
˚
via a conventional acid synthon. The square grids have dimensions of 8.3 ꢀ 8.3 A and clathrate phenolic guests. Our studies indicate that
H4PMA can act as a host only for the phenolic derivatives such as phenol [(H4PMA) (phenol)], 3, o-cresol [(H4PMA)2 (o-cresol)], 4,
p-cresol [(H4PMA)2 (p-cresol)], 5, and p-chlorophenol [(H4PMA)2 (p-chlorophenol)], 6.
3
3
3
3
Introduction
containing derivatives.10 Compared to H3TMA, H4PMA has
been less explored in organic crystal engineering. H4PMA crys-
tallizes as a dihydrate in which each water is hydrogen bonded
to two carbonyl groups of two different H4PMA molecules.11
However, in this structure the molecular symmetry is not trans-
ferred into the symmetry of network due to the inclusion of
water molecule. Therefore, the most expected square grid net-
work via conventional carboxylic acid dimer or clathrates with
H4PMA have not been realized yet. Therefore, herein we report
our results on crystallization reactions of H3TMA and H4PMA
inthepresencevariousphenolicderivatives. Wenoteherethatto
date no crystal structure of any carboxylic acid containing
phenol as solvate was reported. Interestingly, in the case of
H3TMA, the hexagonal cavities were found to transform into
rectangular cavities due to the formation of synthon-II, while in
the case of H4PMA the phenol derivatives template the square
grid networks and form clathrates.
Crystal engineering offers an excellent opportunity to synthe-
size self-assembled structures through a supramolecular synthon
approach via noncovalent synthesis.1 For such an exercise, the
precise knowledge of supramolecular synthons, the frequency of
synthon occurrence, and the exploration of synthon robustness in
the presence of other hydrogen bonding groups is essential.
Hydrogen bonded supramolecular synthons are commonly used
to build the co-crystals or organic-based self-assembly because of
their strength and directionality.1,2 Molecules containing multiple
carboxylic groups such as trimesic acid (H3TMA) and pyromel-
litic acid (H4PMA) are of particular interest as building blocks for
the synthesis of salts, co-crystals, and clathrates.3 The combina-
tion of 3-fold symmetry and robustness of the carboxylic acid
dimeric synthon makes H3TMA an ideal building block in crystal
engineering. H3TMA is known to form open and interpenetrated
honeycomb networks containing cavities of dimensions 14 ꢀ 14
4
˚
A. These hexagonal cavities were shown by us to be expanded up
˚
to 42 ꢀ 42 A in the co-crystals of H3TMA with the molecules con-
taining bis-pyridine units (spacers).5 Further, recently the honey-
comb networks of H3TMA were shown to be truncated in the
crystal structures of acetic acid and MeOH solvates of H3TMA.6
Although the synthon-I is a robust synthon, it was shown in
several cases that it can be expanded or disrupted by the inclusion
of water or alcohols to form synthons-II and -III. For example,
the crystal structure of the mono hydrate of H3TMA exhibits
synthon-II.7 Further, H3TMA was also shown to form co-crystal
with 1,3,5-trihydroxybenzene in which none of these synthons
(I-III) were observed.8 However, the crystal structures of H3-
TMA with p-hydroquinone or resorcinol exhibit a general hon-
eycomb network in which the O-H group does not show any
interference.9 These observations motivated us to investigate the
effect of phenolic derivatives in the crystallization of H3TMA and
H4PMA.
On the other hand, pyromellitic acid (H4PMA) has drawn
attention for its 4-fold symmetry and the presence of carboxylic
acid groups on the benzene ring, especially for the construction
of coordination polymers and preparation of salts with pyridine
Results and Discussion
The crystallization of H3TMA and H4PMA with phenolic
derivatives such as phenol, m-cresol, p-cresol, and p-chlorophenol
*Corresponding author. Fax: þ91-3222-282252. Tel: þ91-3222-283346.
E-mail: kbiradha@chem.iitkgp.ernet.in.
r
2010 American Chemical Society
Published on Web 08/18/2010
pubs.acs.org/crystal

4566 Crystal Growth & Design, Vol. 10, No. 10, 2010
Table 1. Crystallographic Parameters for Compounds 1-6
Rajput et al.
compound
1
2
3
4
5
6
formula
C15H12O7
304.25
293(2)
monoclinic
P21/c
9.9470(5)
15.7431(7)
9.9494(5)
90
114.942(1)
90
1412.7(1)
4
1.430
0.0422
0.1394
C16H14O7
318.27
293(2)
monoclinic
P21/n
9.179(2)
15.460(3)
10.645(2)
90
91.261(7)
90
1510.2(5)
4
1.400
C16H12O9
348.26
293(2)
monoclinic
C2/m
10.247(1)
15.757(1)
5.093(1)
90
115.816(1)
90
740.2(2)
2
1.643
C27H20O17
616.44
293(2)
triclinic
P1
8.342(5)
9.621(6)
9.665(6)
66.405(2)
71.27(2)
73.37(2)
662.0(7)
2
C27H20O17
616.44
293(2)
triclinic
P1
8.537(8)
9.584(8)
9.584(8)
66.297
70.363(2)
70.363(2)
657.7(1)
2
C26H17ClO17
636.86
293(2)
monoclinic
C2/c
16.075(9)
10.529(6)
8.551(5)
90
114.207(2)
90
1320.0(1)
4
1.926
0.0769
0.1920
mol. wt.
T (K)
system
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (°)
β (°)
γ (°)
3
˚
vol (A )
Z
D (Mg/m3)
R1 (I >2σ(I))
wR2 (on F2, all data)
1.817
0.0756
0.2213
1.829
0.0852
0.2265
0.0535
0.1374
0.0654
0.1855
Figure 1. Illustrations for the complex 1: (a) Part of 2D-layer constructed by synthon-I and -II; (b) space-fill representation of herringbone
layer of H3TMA units (phenol is shown in green color); (c) packing of adjacent layers; (d) interaction between H3TMA molecules of adjacent
layers; edge-to-edge aromatic interactions between phenols in the column: (e) top view; and (f) side view.
has been carried out by dissolving required amounts of acid
and phenol in the minimum amount of MeOH. In the case of
H3TMA, the crystals suitable for single crystal X-ray diffrac-
tion analysis were obtained with phenol and m-cresol to yield
complexes [(H3TMA) (phenol)], 1, and [(H3TMA) (m-cresol)],
molecule of phenol. The crystal structure analysis of 1 reveals
that the popular hexagonal arrangement of H3TMA has been
disrupted and phenol was inserted into two of the -COOH
dimers to form synthon-II. One -COOH group exhibits con-
ventional synthon-I, while two -COOH groups exhibit acid-
phenol synthon-II (Figure 1a). Para hydrogen of phenol is also
3
3
2, respectively, whereas in the case of H4PMA, the single crys-
tals were obtained with four phenolic derivatives, namely,
[(H4PMA) (phenol)], 3, [(H4PMA)2 (o-cresol)], 4, [(H4PMA)2
˚
˚
involved in a C-H O (2.466 A, 151.55°, 3.313 A) hydrogen
3 3 3
bond with the carbonyl of H3TMA. Because of the forma-
tion of unsymmetrical synthon-II, the honeycomb network of
H3TMA has been modulated into a herringbone arrangement
as shown in Figure 1b. The interpenetration observed in the
3
3
3
(p-cresol)], 5, and [(H4PMA)2 (p-chlorophenol)], 6. The crystal-
3
lographic parameters and hydrogen bonding parameters for all
the crystal structures are given in Tables 1 and 2, respectively.
The complex 1 crystallizes in P21/c space group and the
asymmetric unit contains one molecule of H3TMA and one
˚
crystal structures of H3TMA (cavity dimension 14 ꢀ 14 A) was
eschewed here by the inclusion of aromatic rings of two phenol

Article
Crystal Growth & Design, Vol. 10, No. 10, 2010 4567
˚
units inside the cavity. The herringbone network contains a
˚
(closest C C distance 4.016 A) and dipole-dipole interac-
3 3 3
rectangular cavity of dimension 21.9 ꢀ 11.5 A.
tions between the carbonyl groups of H3TMA (CdO C,
˚
3.420 A) as shown in Figure 1d. Phenyl groups of phenols
from adjacent layers also interact with each other via edge-to-
˚
edge aromatic interaction (closest C C distance 3.630 A)
(Figure 1e,f).
The crystal structure of 2 also exhibits similar herringbone
3 3 3
In 1, the adjacent layers packon toeach other in AB fashion
such that rectangular cavities of layers are nearly perpendi-
cular to each other. Such arrangement generates the channels
with a dimension of half of rectangular cavities across the
layers (Figure 1c). Thepacking of the layersgovernedbyedge-
to-edge aromatic interactions between H3TMA molecules
3 3 3
layers as those of 1 with some minor differences (Figure 2a,b).
˚
The cavities (21.5 ꢀ 12.0 A) of herringbone layer nicely adjust
Table 2. Geometrical Parameters of Hydrogen Bonds in Compounds 1-6
to accommodate additional methyl group of m-cresol. The
packing of the layers differs significantly from that of 1. In 2,
the layerspack in ABCtypepacking aseach layer repeats itself
after three layers (Figure 2c). Across the layer, rectangular
channels exist which are occupied by a column of m-cresol
molecules (Figure 2d-f). The phenol and m-cresol in 1 and 2
occupy 41% and 45% of crystal volumes, respectively.
The crystal structure of 3 exhibitsC2/m space group and the
asymmetric unit contains half a molecule of H4PMA and half
a molecule of phenol. Unlike in 1 and 2, the hydroxyl group of
˚
A (A)
˚
type
H
D
A (A) D-H A (deg)
3 3 3 3 3 3
3 3 3
1.84
1
2
O-H
O
hd-aa
ad-aa
ad-ha
Syn-I
2.703(2)
2.640(2)
2.657(2)
2.647(2)
3.314(3)
2.677(3)
2.695(3)
2.667(2)
2.648(2)
2.658(3)
2.694(4)
2.685(4)
2.696(4)
2.662(5)
2.682(5)
2.678(6)
2.671(6)
2.647(6)
2.673(5)
2.666(5)
177
165
175
179
152
169
169
178
170
168
3 3 3
1.67
1.71
1.59
2.47
1.86
1.78
1.78
1.60
1.94
C-H
O-H
O
O
3 3 3
3 3 3
hd-aa
ad-aa
ad-ha
Syn-I
Syn-I
Syn-I
3
4
O-H
O-H
O
O
phenol here does not insert into the conventional synthon-I;
˚
3 3 3
3 3 3
rather it glues to the synthon-I via weak O-H O (2.854 A,
3 3 3
˚
117.4°, 3.265 A) hydrogen bond with O-atom of -COOH. The
H4PMA units form an elusive 2D layer containing square grid
geometry via synthon-I (Figure 3a). Each H4PMA molecule
interacts with four of its neighbors (Figure 3b). These layers
pack on each other with a perfect overlap such that contin-
uous channels exist across the layers. In these channels, the
phenolic columns were included which accounts for 40% of
5
6
O-H
O-H
O
O
Syn-I
Syn-I
3 3 3
3 3 3
Figure 2. Illustrations for the complex 2: (a) Part of H3TMA 2D-layer and m-cresol constructed by synthon-I and -II; (b) space-fill
representation of herringbone layer of H3TMA molecules (phenol is shown in yellow color); (c) slipped packing of adjacent layers;
(d) rectangular channels generated across the layers; and column of m-cresols: (e) top view and (f) side view (space-fill mode).

4568 Crystal Growth & Design, Vol. 10, No. 10, 2010
Rajput et al.
Figure 3. Illustrations for the complex 3: (a) square grid networks of H4PMA; (b) one H4PMA is hydrogen bonded to four H4PMA via
synthon-I and weak O-H O hydrogen bonds between phenol and H4PMA; (c) enclathration of phenol (disordered) in between the adjacent
3 3 3
layers; (d) edge-to-edge aromatic interactions between phenol and H4PMA; (e) edge-to-edge aromatic interactions between phenols in the
column.
the crystal volume. In the column, the phenols interact with
each other via edge-to-edge aromatic interactions (closest
˚
and dipole-dipole interactions between -COOH groups of
˚
H4PMA (OdC OdC distance 3.2-3.5 A) govern the inter-
3 3 3
C
C distance 3.431 A) (Figure 3c).
Interestingly, somewhat bigger guest molecules such as
layer packing (Figure 3d-f). o-Cresol and m-cresol occupies
31% and 32% volume of the crystal lattice, respectively.
The crystal structure of 6 exhibits C2/c space group, and the
asymmetric unit is constituted by the half of H4PMA unit and
one-fourth of the guest which is highly disordered and could
not be located. The crystal structure has similar features as
those of 4 and 5 with the exception that the adjacent layers are
symmetry related. The guest p-chlorophenol occupies the
same volume (32%) as those in 4 and 5.
3 3 3
o-cresol, p-cresol, and p-chlorophenol were also found to
include in H4PMA square nets by reducing the amount of
guest to half in 4, 5, and 6, respectively.
Complexes 4 and 5 containing o-cresol and p-cresol, respec-
tively, crystallize in P1 space group. In both cases, the asym-
metric unit contains two half units of H4PMA and a half
molecule of cresols. The H4PMA moieties form similar 2D-
layers as observed in 3. The cresol molecules exhibited disorder
which could not be modeled. Although the 2D-layers in 4 and 5
have similar features as those of 3, the packing of the layers and
the geometry of guest inclusion with respect to the layer differ
significantly. In 3, the overlapped synthon-I of adjacent layers
are parallel to each other, while they are perpendicular to each
other in 4 and 5 (Figure 4). This change in orientation could be
partly attributed to the change in H4PMA geometry: in 3, all
the -COOH groups of H4PMA maintain nearly equal angles
(∼38°) with a central C6-ring, while in 4 or 5 the two -COOH
groups make different angles (∼22° and ∼66°) with central
C6-ring. Further, in both cases, the adjacent layers are sym-
metry independent layers. Because of this type of arrangement
of the layers the guest molecules have different orientations of
inclusion with respect to the layer. In 3, the guest molecule
phenol is almost parallel to the 2D layer, whereas in 4 or 5 the
disordered cresol molecules are inserted within the square unit
of H4PMA such that they are perpendicular to the 2D layers
We have carried out the CSD analysis for synthons-II and -III
to investigate their frequency of occurrence and geometrical
features.12 Further, it is interesting to note here that the synthon-
II is constituted by three types of O-H O hydrogen bonds:
3 3 3
acid donor to acid acceptor (ad-aa), hydroxyl donor to acid
acceptor (hd-aa), and acid donor to hydroxyl acceptor (ad-ha).
Generally, given acid and base strengths one would anticipate
the following order in their hydrogen bond strengths: ad-ha>
ad-aa>hd-aa. We have carried out the searches for alcohol and
water molecules separately. The results are tabulated in Table 3.
The synthon-II with water and alcohol was observed in 23 and
11 crystal structures, respectively. The mean values of O
˚
O
distances confirm the anticipated trend (ad-ha (2.559 A)>ad-aa
3 3 3
˚
˚
(2.619 A) > hd-aa (2.773 A)). Similar observations also are
found in the case of synthon-III where 51 crystal structures were
observed with water. Further, the asymmetric (II) and sym-
metric (III) nature of synthons was clearly reflected in their
O
both these synthons were found to exhibit by the molecules
O distances. Another interesting observation was that
3 3 3
(Figures 3c and 4c). The edge-to-edge aromatic interactions
˚
between H4PMA molecules (closest C C distance: 3.770 A)
3 3 3
containing multiple -COOH groups. In the case of synthon-II

Article
Crystal Growth & Design, Vol. 10, No. 10, 2010 4569
Figure 4. Illustrations for the complex 5: (a) square grid network of H4PMA; (b) packing of the H4PMA layers; notice the inclusion of
disordered p-cresol in the channels; (c) enclathration of p-cresol in between the adjacent layers (notice the orientation of p-cresol with respect to
H4PMA layer and compare with Figure 3c).
Table 3. CSD Analysis for Synthon-II and -III
The consistent formation of a square grid network through
synthon-Iis observed in all four complexes. Further, two packing
modes were observed for these square nets depending on the
host/guest ratios and the size of guest molecules. We note here
that the phenol disrupts synthon-IinthecaseofH3TMA, while it
induces square grid formation via synthon-I in the case of
H4PMA. The phenolic complexes with H3TMA could be
considered as co-crystals, as their hydroxyl groups are part of
a network, while those of H4PMA could be considered as
clathrates. The CSD studies of synthon-II and -III clearly
illustrates the relation of acid-base strength versus hydrogen
bond strength even within a synthon.
O
O
min
max
mean
no. of obs
11
3 3 3
RdC for II
RdH for II
RdC for III
ad-aa
hd-aa
ad-ha
ad-aa
hd-aa
ad-ha
hd-aa
ad-ha
hd-aa
ad-ha
hd-aa
ad-ha
hd-aa
ad-ha
2.594
2.650
2.476
2.548
2.577
2.489
2.626
2.533
2.626
2.505
2.646
2.493
2.646
2.509
2.647
2.814
2.604
2.755
2.931
2.793
2.796
2.771
2.796
2.771
2.80
2.619
2.773
2.559
2.634
2.829
2.613
2.738
2.625
2.739
2.626
2.761
2.591
2.764
2.592
23
85
RdH for III
51
2.80
2.80
2.80
Experimental Section
In a typical crystallization process, H3TMA (0.5 g) was taken in
excess phenol (2 mL) and while heating this solution a minimum
amount of methanol (∼1 mL) was added to dissolve the acid. The
solution was kept at room temperature for crystallization by slow
evaporation. Colorless prismatic crystals were formed after two days.
All the other crystallizations were carried out in a similar fashion.
in the crystal structures of 1 and 2, the differences in ad-ha,
ad-aa, and hd-aa are reduced as the acidity of phenol hydroxyl is
higher than that of alcohol or water.
Conclusion
[(H3TMA) (phenol)] (1): Elemental analysis: (Anal. calcd. For
C15H12O7: C, 59.21%; H, 3.98%. Observed: C, 59.39%; H, 3.58%.)
3
Crystallization of H3TMA has shown the tendency for the
formation of co-crystals in phenol or m-cresol solvents.
Hydroxyl group insertion is observed in carboxylic acid dimer
for the formation of synthon-II. Because of the change in
synthons, the usual honeycomb network of H3TMA has been
distorted to herringbone arrangement. The cavities generated
are filled by aromatic moieties of phenols.
However, such phenolic insertion into -COOH synthons is
not observed in the case of H4PMA. For the first time, H4PMA
was shown to form clathrate complexes given the phenolic
guests such as phenol, o-cresol, p-cresol, and p-chlorophenol.
[(H3TMA) (m-cresol)] (2): Elemental analysis: (Anal. calcd. For
3
C16H14O7:C, 60.38%; H, 4.43%. Observed C, 60.92%; H, 4.23%.
[(H4PMA) (phenol)] (3): Elemental analysis: (Anal. Calcd. For
3
C16H12O9: C, 55.18%; H, 3.47%. Observed: C, 54.46%; H, 3.02%.)
[(H4PMA)2 (o-cresol)] (4): Elemental analysis: (Anal. calcd. For
3
C27H20O17: C, 52.61%; H, 3.27%. Observed: C, 52.58%; H, 2.94%.)
[(H4PMA)2 (p-cresol)] (5): Elemental analysis: (Anal. calcd. For
3
C27H20O17: C, 52.61%; H, 3.27%. Observed: C, 52.22%; H, 3.12%.)
[(H4PMA)2 (p-chlorophenol)] (6): Elemental analysis: (Anal.
3
Calcd. For C26H17ClO17 Calculated: C, 49.03%; H, 2.69%. Ob-
served: C, 49.72%; H, 2.78%.)

4570 Crystal Growth & Design, Vol. 10, No. 10, 2010
Rajput et al.
Crystal Structure Determination. Single crystal data were col-
lected on a Bruker-APEX-II CCD X-ray diffractometer that uses
graphite monochromated Mo KR radiation (λ=0.71073 A) at room
(f) Biradha, K. CrystEngComm 2003, 5, 374. (g) Wuest, J. D. Chem.
Commun. 2005, 5830. (h) Desiraju, G. R. Angew. Chem., Int. Ed.
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Zaworotko, M. J. Mol. Pharm. 2007, 4, 401. (j) Biradha, K.; Mahata, G.
Cryst. Growth Des. 2005, 5, 49. (k) Rajput, L.; Biradha, K. Cryst.
Growth Des. 2009, 9, 40.
˚
temperature (293 K) by a hemisphere method. The structures were
solved by direct methods and refined by least-squares methods on
F2 using SHELX-97.13 Non-hydrogen atoms were refined aniso-
tropically and hydrogen atoms were fixed at calculated positions
and refined using a riding model. The H-atoms attached to O-atom
are located wherever possible and refined using the riding model.
Further the guest molecules were found to be highly disordered
in the crystal structures of 4-6. Therefore, final refinement was
done using PLATON squeeze option without guest molecules.14
PLATON was also used for the calculation of guest available
volumes.
(3) (a) Sharma, C. V. K.; Zaworotko, M. J. Chem. Commun. 1996,
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Acknowledgment. We gratefully acknowledge the DST for
the financial support and DST-FIST for the single-crystal
X-ray facility. L.R. thanks IIT (Kharagpur) for research
fellowship.
(10) (a) Felix, O.; Hosseini, M. W.; De Cian, A. Solid State Sci. 2001, 3,
Supporting Information Available: Crystallographic tables of
bond lengths, angles, and ORTEP drawings for 1-6. This material
is available free of charge via the Internet at http://pubs.acs.org.
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