Identification of a new supramolecular synthon in o-anisaldehydes: Molecular self-assembly into tapes and staircases

Article abstract of DOI:10.1016/j.molstruc.2005.01.072

We have shown through a rational design, synthesis and X-ray structural analyses of a set of aldehydes that o-methoxybenzaldehydes tend to associate in a centrosymmetric fashion, akin to the carboxylic acids, to give rise to a dimer motif II, which derives stabilization from four C-H?O hydrogen bonds in addition to a dipole-dipole interaction. That the synthon II is credible to be structure determining is revealed from the crystal structures of aldehydes 1-4 that are devoid of any other competing weak interactions. The aldehydes 1-4 are found to undergo self-assembly into 1-dimensional molecular tapes and staircases. We have shown that the steric factors as in aldehyde 5 and the presence of a functional group such as Br in 6 perturb the expected crystal packing based on synthon II.

Full text of DOI:10.1016/j.molstruc.2005.01.072

Journal of Molecular Structure 741 (2005) 107–114
www.elsevier.com/locate/molstruc
Identification of a new supramolecular synthon
in o-anisaldehydes: molecular self-assembly into tapes
and staircases
a,
a
J. Narasimha Moorthy , R. Natarajan , P. Venugopalan
b,
*
*
aDepartment of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
bDepartment of Chemistry, Punjab University, Chandigarh 160 014, India
Received 30 December 2004; revised 30 January 2005; accepted 31 January 2005
Available online 8 March 2005
Abstract
We have shown through
a
rational design, synthesis and X-ray structural analyses of a set of aldehydes that o-
methoxybenzaldehydes tend to associate in a centrosymmetric fashion, akin to the carboxylic acids, to give rise to a dimer
motif II, which derives stabilization from four C–H/O hydrogen bonds in addition to a dipole–dipole interaction. That the synthon
II is credible to be structure determining is revealed from the crystal structures of aldehydes 1–4 that are devoid of any other
competing weak interactions. The aldehydes 1–4 are found to undergo self-assembly into 1-dimensional molecular tapes and
staircases. We have shown that the steric factors as in aldehyde 5 and the presence of a functional group such as Br in 6 perturb
the expected crystal packing based on synthon II.
q 2005 Elsevier B.V. All rights reserved.
Keywords: X-ray crystallography; Supramolecular synthon; Molecular tapes and staircases; o-Methoxybenzaldehydes; Weak hydrogen bonds
1. Introduction
crystal packing. In this direction, a variety of supramo-
lecular synthons based on O/N–H/O/N hydrogen bonds
have been identified [3,4]. Although the importance of
weak but directional C–H/O/N hydrogen bonds has
been amply exemplified [5], the quest for identification
of new and novel synthons continues unabated, as it
constitutes one of the fundamental objectives of crystal
engineering.
The control of molecular organization based on
specific molecular attributes is a challenge in crystal
engineering [1]. Strong and directional properties associ-
ated with O/N–H/O/N hydrogen bonds [2] have been
reliably exploited in the construction of pre-designed
supramolecular architectures [1]. An advantageous
approach to the crystal structure prediction and engin-
eering relies on the identification and exploitation of
certain patterns of association (i.e. supramolecular
synthons [3]) that are robust and recur decisively in the
The aldehydes represent an important class of functional
group of organic compounds. Despite their widespread
utility in fragrances and pharmaceuticals as excellent
intermediates, the supramolecular interactions associated
with the formyl group have been explored only little, if any
[6]. Based on a CSD database search analysis, Koppen-
hoefer showed that the formyl oxygen orients itself away
from the o-halogen in o-haloaromatic aldehydes [7]. In the
course of our recent studies on the solid-state photochem-
istry of aldehydes based on this conformational preference
[8a], we uncovered a unique halogen bond-mediated
*
Corresponding authors. Tel.: C91 172 2597438; fax: C91 172
2597436.
E-mail addresses: moorthy@iitk.ac.in (J. Narasimha Moorthy),
venu@pu.ac.in (P. Venugopalan).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.01.072

108
J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
supramolecular dimeric synthon I [8b].
H
H
CH2
O
O
O
O
O
O
X
H
H
H
H
H
H
X
O
O
O
O
H2C
Synthon 'I'
CH3
CH3
Synthon 'II'
In analogy to o-haloaromatic aldehydes, we anticipated a
similar conformational preference in the case of o-anisalde-
hydes as well. Indeed, the crystal structure database (CSD)
search revealed the conformational preference for formyl
oxygen to orient away from the methoxy oxygen [9].
Presumably, the reason for such a preferential orientation is
due to subtle interplay of the following factors:
(i) minimization of repulsive interaction between the formyl
and methoxy oxygen atoms, (ii) intramolecular hydrogen
bond between the formyl hydrogen and the methoxy oxygen
atoms, and (iii) avoidance of steric hindrance.
synthon II is realizable.
CHO
OCH3
H3CO
OHC
CHO
H3CO
OCH3
OHC
1
2
CH3
H3CO
OHC
CHO
n
OCH3
H3CO
OCH3
CHO
CHO
Given that the contributing resonance structures lend a
strong dipole to such molecular systems and that the
Achiral polar molecules generally (although not necess-
arily) tend to pack in a centrosymmetric manner in the
solid state, the synthon II was readily conceived between
centrosymmetrically related molecules to stabilize the
crystal packing of o-anisaldehydes. In this arrangement,
the crystal lattice would energetically benefit from four
weak but directional C–H/O hydrogen bonds, in addition
to a dipole–dipole interaction arising from the pair of
aldehydes. Thus, the combination of a dipole–dipole
interaction (worth ca. 5–50 KJ/mol [10]) and the four
C–H/O hydrogen bonds, which may contribute as much,
may cause the centrosymmetric dimer motif to be decisive
in the crystal packing. This premise would be verified if
an ensemble of o-methoxybenzaldehyde structures reveals
the anticipated dimer synthon. Indeed, CSD analysis
showed that the synthon II is observed in at least one
of the crystal structures that contain o-methoxybenzalde-
hyde moiety (code: GOYZAV [9]). However, the absence
of synthon II in five other molecules containing
o-methoxy formyl moiety was contrary to our expectation.
A careful packing analysis to trace the reasons for the
observations against our expectations revealed the strong
influence of other functional groups that potentially
control the crystal packing. Consequently, we envisaged
that o-methoxybenzaldehyde derivatives that are not
endowed with other functional groups would exhibit the
dimer Synthon II in their crystal packing. Thus, we
designed, synthesized and examined the X-ray crystal
structures of aldehydes 1–4 that are entirely devoid of
other competing interactions to test whether or not the
CH3
3: n = 1
4: n = 2
5
CH3
Br
CHO
H3C
OCH3
H
6
We also examined the crystal structures of analogous
aldehydes 5 and 6 to probe the credibility of synthon II in
mediating the crystal packing when steric factors and other
interacting groups (such as Br atom) are present. Herein, we
report the results of our structural studies.
2. Experimental
2.1. Synthesis of aldehydes
All investigations were carried out using analytical grade
chemicals from Lancaster (UK) and S.D. Fine Chemicals
(India). Anisaldehydes 1 and 5 were prepared by following
the reported procedures [12]. The dimethoxy precursors of
aldehydes 2–4 and 6, viz. 7–9 and 10, were prepared
according to the literature-reported procedures (Scheme 1)
[13]. These dimethoxy-derivatives were subjected to bis-
formylation using TiCl4/Cl2CHOCH3 in CH2Cl2 at K78 8C
to obtain the aldehydes 2–4 and 6.

J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
109
CHO
OCH3
TiCl4/CHCl2OCH3
H3CO
OHC
H3CO
OCH3
˚
CH2Cl2, -78 C, 1h
7
2
n
TiCl4/CHCl2OCH3
n
OCH3
H3CO
˚
CH2Cl2, -78 C, 1h
H3CO
OCH3
CHO
CHO
3: n = 1
4: n = 2
8: (n = 1)
9: (n = 2)
CH3
OCH3
Br
CHO
TiCl4/CHCl2OCH3
H3C
OCH3
Me
Me
˚
CH2Cl2, -78 C, 1h
H
Br
10
6
Scheme 1.
Below is described the typical procedure for bis-
formylation to obtain the dianisaldehyde 2. The same
procedure was followed for 3 and 4 as well. A similar
procedure was employed for the preparation of aldehyde 5.
2.1.3. 1,2-Bis(3-formyl-p-anisyl)ethane 4
Yield 95%; mp 232 8C; IR (KBr) cmK1 1026, 1286, 1676,
2852, 2937; 1H NMR (CDCl3, 400 MHz) d 2.85 (s, 4H), 3.90
(s, 6H), 6.89(d, 2H, JZ8.56 MHz), 7.28(m, 2H), 7.62(s, 2H),
10.44 (s, 2H); 13C NMR (CDCl3, 100 MHz) d 36.6, 55.7,
111.7, 124.6, 128.1, 133.6, 136.1, 160.4, 189.9.
2.1.1. 4,40-Dimethoxy-3,30-biphenyldicarboxaldehyde 2
A 3 mL solution of 7 (0.12 g, 0.714 mmol) in dichlor-
omethane taken in a two-necked round bottom flask under a
N2 gas atmosphere was cooled to K30 8C. Subsequently,
TiCl4 (0.37 mL, 3.85 mmol) was added. After stirring for
10 min, the reaction mixture was further cooled to K80 8C
over a period of 1 h. At this stage, dichloromethyl methyl
ether (0.32 mL, 3.57 mmol) was slowly introduced. The
resultant dark-grey solution turned into pink color. The
reaction mixture was allowed to attain the room temperature
over a period of 1 h and quenched with 10% HCl.
The product was extracted with dichloromethane, dried
over Na2SO4 and concentrated. Filtration of the organic
residue over a short-pad silica gel afforded the pure
dialdehyde 2 in 81% yield (0.13 g), mp 180 8C; IR (KBr)
cmK1 1057, 1255, 1679, 2853, 2922; 1H NMR (400 MHz) d
3.97 (s, 6H), 7.07 (d, 2H, JZ8.56 Hz), 7.80 (dd, 2H, J1Z
8.56 Hz, J2Z2.68 Hz), 8.04 (d, 2H, JZ2.4 Hz), 10.51
(s, 2H); 13C NMR (100 MHz, CDCl3) d 55.9, 112.3, 124.9,
126.3, 132.2, 133.9, 161.3, 189.7.
2.1.4. 5-Bromo-4,6-dimethyl-o-anisaldehyde 6
Yield 87%, mp 128–130 8C; IR (KBr) cmK1 2920, 1681;
1H NMR (CDCl3, 400 MHz) d 2.47 (s, 3H), 2.69 (s, 3H),
3.88 (s, 3H), 6.77 (s, 1H), 10.51 (s, 1H), 10.51 (s, 1H); 13
NMR (CDCl3, 100 MHz) d 20.3, 25.6, 55.9, 111.4, 121.3,
122.9, 140.9, 145.4, 161.5, 191.6.
C
2.2. X-ray crystallography
The compounds were crystallized from appropriate
solvents as mentioned in Table 1 by a slow evaporation
method over a period of 2–3 days. The X-ray diffraction
data for all of the aldehydes 1–6 were collected on a
Siemens P4 single crystal diffractometer equipped with
˚
molybdenum sealed tube (lZ0.71073 A) and highly
oriented graphite monochromator. A detailed description
of the structure solution and refinement are given below
for compound 1 as a representative case. The structure
determinations of 2–6 were performed in similar manner
and the details are recorded in Table 1.
2.1.2. Bis(3-formyl-p-anisyl)methane 3
Good single crystals of 1 were grown by slow
evaporation of the solution of 1 in dichloromethane:
ethanol mixture (1.7:1, v/v). A single crystal with
dimension 0.30!0.29!0.19 mm3 was mounted along
the largest dimension and used for data collection. The
lattice parameters and standard deviations were obtained
Yield 81%; mp. 224 8C; IR (KBr) cmK1 1027, 1264,
1682, 2847, 2946; 1H NMR (CDCl3, 400 MHz) d 3.90 (s, 6
H), 6.91 (d, 2H, JZ8.0 Hz), 6.92 (s, 2H), 7.35 (d, 2H,
JZ7.08), 7.63 (s, 2H); 13C NMR (CDCl3, 100 MHz) d 34.9,
55.7, 110.6, 124.7, 128.3, 131.2,136.3, 160.5, 188.9.

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J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
Table 1
Crystallographic data for compounds 1–6
Properties
1
2
3
4
5
6
Chemical formula
Formula weight
Crystal system
Space group
C10H10O4
194.18
C16H14O4
270.28
Monoclinic
P21/c
C17H16O4
284.30
Monoclinic
P2/n
C18H18O4
253.05
Monoclinic
P21/n
C12H12O4
222
C10H11BrO2
243.10
Monoclinic
C2/c
Triclinic
ꢀ
P1
Monoclinic
P21/n
˚
a (A)
˚
b (A)
˚
c (A)
7.289(1)
8.063(1)
8.520(2)
99.780(1)
112.14(1)
93.679(1)
452.55(1)
2
4.793(1)
15.513(2)
8.670(1)
90.0
17.700(2)
4.796(1)
18.034(2)
90.0
4.801(1)
11.031(1)
14.425(2)
90.0
10.498(1)
4.201(1)
12.540(1)
90.0
14.561(3)
10.040(2)
13.821(3)
90.0
a (8)
b (8)
g (8)
94.54(1)
90.0
109.82(5)
90.0
98.33(1)
90.0
96.99(1)
90.0
105.74(2)
90.0
3
˚
V (A)
642.62(3)
2
1440.20(4)
4
755.89(2)
2
548.93(2)
2
1944.8(7)
8
Z
T (K)
Dc (Mg mK3
293(2)
293(2)
1.397
293(2)
1.311
293(2)
1.311
293(2)
1.345
293(2)
1.661
)
1.425
m (mmK1
)
0.098
0.100
0.093
0.092
0.101
4.190
F(000)
204
284
600
316
236
976
Reflections collected
Unique reflections
Reflections with IO2s(I)
Rint
1545
1107
2382
1345
897
1580
1409
983
2263
1190
847
1517
1198
713
1725
1013
680
1196
0.0152
0.0376
0.1040
CH2Cl2/CH3OH
0.0184
0.0851
0.1101
CH2Cl2/hexanes
0.0163
0.0527
0.0681
EtOAc/hexanes
0.0224
0.0337
0.0421
CH2Cl2
0.0152
0.0525
0.1443
CH2Cl2/hexanes
0.0377
0.0408
0.0569
CH2Cl2/hexanes
Final R1[IO2s(I)]
Final wR2
Solvent of crystallization
by least squares fit to 40 reflections (10.368!2q!
34.878). The data were collected by 2qKq scan mode
with a variable scan speed ranging from 2.08 to a
maximum of 60.08 minK1. Three reflections were
used to monitor the stability and orientation of the
crystal and were re-measured after every 97 reflections.
Their intensities did not change significantly during
17.85 h X-ray exposure time. The data were corrected
for Lorentz and polarization factors. All other relevant
information about the data collection is presented in
Table 1. The structure was solved by Direct Methods
using SHELX-97 package and also refined using the same
one [11]. All the non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were included in
the ideal positions with fixed isotropic U values and
were riding. Methyl hydrogen atom coordinates were
generated with the SHELXL AFIX 137 command and
that they were correctly positioned was verified from
difference Fourier maps. A weighting scheme of the
form wZ1/[s2(Fo2)C(aP)2CbP] with aZ0.0575 and
bZ0.10 was used. The refinement converged to a final
R value of 0.0376 (wR2 0.1040 for 1198 reflections,
[IO2s(I)]. The final difference map was featureless. All
other information regarding the refinement is also
recorded in Table 1.
3. Results and discussion
For X-ray crystallographic analyses, the crystals of all of
the aldehydes were grown by a slow evaporation method
(Table 1). The details of crystal structure determination
Fig. 1. The crystal packing of aldehyde 1. Notice that the tapes are constructed by synthon II.

J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
111
Fig. 2. The crystal packing of biphenyl-dialdehyde 2. The two phenyl rings are coplanar and the synthon II mediates the formation of tapes.
and refinement are given in Table 1. The crystal packing
diagrams of all of the aldehydes 1–6 are shown in Figs. 1–6,
respectively. A feature that is common to all of the
aldehydes 1–6 is that the formyl group orients itself away
from the o-methoxy group. As mentioned at the outset, this
preference may also be due to a subtle interplay of various
factors. Be this as it may, the six new structures, in addition
to those already reported in the literature [9], clearly
demonstrate the fact that the conformation in which the
formyl and methoxy oxygen atoms are far apart is the
preferred one in o-anisaldehydes.
The terephthalaldehyde 1 and the biphenyl derivative 2
yield tapes, which are sustained by the motif II. These tapes
are stacked in the bc plane in 1 (Fig. 1), and a similar
stacking with ca. 458 inclination to the ac plane is observed
in 2 (Fig. 2). This way of building-up the lattice from
linear tapes derives the stabilization from attractive p/p
inter-stack interactions (nearest mean aromatic ring separ-
˚
ation in 1 and 2 are 3.39 and 3.38 A, respectively). Due to
the intervening methylene/s in 3 and 4, the molecules
assume a twist, which results in an interesting alteration in
the molecular packing. Both of the structures preserve the
synthon II, and propagate in a zigzag manner to make up a
supramolecular staircase [14]. There are two additional
As can be seen, the aldehydes 1–4 exploit the
synthon/dimeric motif II effectively in the crystal packing.
Fig. 3. The crystal packing of diarylmethane 3. Notice that the tetrahedral angle between the two aryl rings leads to staircase structures mediated by synthon II.

112
J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
Fig. 4. The crystal packing diagram of diarylethane 4. The ‘steps’ are much longer than the ‘heights’.
Fig. 5. The molecular structure and crystal packing of dialdehyde 5. Notice that formyl groups assemble in a helical manner via C–H/O hydrogen bonds
involving the formyl groups.

J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
113
Fig. 6. The crystal packing of aldehyde 6. Notice that the halogen bonds involving C–Br/OaC mediates the crystal packing into 2-dimensional sheets.
points of interest here. As there is only one –CH2 group that
intervenes between the two o-anisaldehydes in 3, the
aromatic rings adopt a near orthogonal orientation with
respect to each other (angle between the least squares planes
of the two rings is 90.78). When such units assemble through
synthon II to make up staircase, the ‘step’ and the ‘height’
of the staircase are exactly equal; as the methylene group is
placed at the meeting points of step and height (see Fig. 3).
In 4 however, the two aromatic moieties are placed far apart
due to the ethylene group, and are exactly parallel to each
other (angle between the least squares planes of the two
rings is 0.18). When these molecules undergo self-assembly,
the ‘height’ is generated from the ethylene part, while the
step is generated from the synthon part; expectedly, the
height is shorter and the ‘step’ is longer (Fig. 4).
O/N–H/O/N hydrogen bonds, are not robust to structural
changes. The fact that the synthon II does not reproduce itself
faithfully is reflected from the crystal structures of 5 and 6. In
aldehyde 5, the introduction of two methyl groups causes a
conformational change about the methoxy group. The
molecule sits on the inversion center and the methoxy
methyl groups are almost orthogonal to the molecular plane
(C1–C2–O2–C5Z92.88). However, the molecule does not
lose one of its characteristic structural features, i.e. the
orientation of the formyl oxygen being away from the
methoxy oxygen as observed in all of the aldehydes 1–4. The
crystal packing is dominated by O–H/O hydrogen bonds
(Fig. 5) involving the formyl oxygen and the formyl
hydrogen atoms related by 21-screw relationship (symmetry:
1.5Kx, K0.5Cy, 0.5Kz); the geometrical parameters for
We shall now analyze the forces that are responsible for
the construction of arrays of linear tapes (1 and 2) and
zigzag staircases (3 and 4). Two sets of weak C–H/O
hydrogen bonds about the inversion center operate to
manifest in the synthon II, while an additional dipole–
dipole interaction, as mentioned earlier, might also
contribute to the stabilization. While the extent of dipolar
character due to the resonance structures of o-anisaldehydes
cannot be easily gauzed, it is certain that a definite dipolar
nature of the molecule aids in the centrosymmetric
arrangement of the molecules. As two dissimilar C–H/O
hydrogen bonds contribute to the synthon II, an analysis of
their nature and strength is pertinent. In Table 2 are provided
the geometrical parameters for C–H/O hydrogen bonds.
A perusal of these parameters shows that the hydrogen
bonding interactions between methoxy methyl hydrogen
and the carbonyl oxygen are stronger, while those involving
the formyl hydrogen and the methoxy oxygen are weaker.
This is presumably due to the weaker propensity of the
formyl hydrogen atoms to involve in hydrogen bonding.
Nonetheless, the reliability of the synthon II in decisively
controlling the molecular packing in a predetermined
manner is amply evident.
˚
˚
this hydrogen bond are: dC–H/OZ2.61 A, DC/OZ3.29 A
and qC–H/OZ130.38. In a similar manner, the bromo group
is also found to preclude the existence of synthon II in
aldehyde 6. Indeed, the C–Br/OaC interaction (dC–Br/O
Z
˚
3.21 A and qC–Br/OZ163.48) now controls the crystal
packing in aldehyde 6 in spite of the fact that o-methoxy
formyl moiety is entirely planar with the formyl oxygen
oriented away from the methoxy oxygen (Fig. 6). The
halogen bond together with one C–H/O hydrogen bond
involving the methoxy oxygen and one of the methyl
˚
˚
hydrogen atoms (dC–H/OZ2.81 A, dC/OZ3.62 A
Table 2
Geometrical parameters for C–H/O hydrogen bonds of the dimeric motif
II in aldehydes 1–4
Aldehyde O–CH2–H/OaC
OaC–H/OCH3
˚
d (A)
˚
d (A)
q (8)
q (8)
1a
2
3a
4
2.63 (2.71)
2.59
163.1 (146.7) 2.84 (2.96)
152.1 (133.3)
141.9
152.9
158.2 (152.4) 2.79 (2.93)
154.8 2.95
2.79
2.56 (2.69)
2.72
145.6 (139.8)
142.0
a
The crystal packing based on motifs constituted
by weaker intermolecular interactions, unlike the strong
The values in parentheses refer to second independent molecule in the
unit cell.

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J. Narasimha Moorthy et al. / Journal of Molecular Structure 741 (2005) 107–114
(b) J.-M. Lehn, Supramolecular Chemistry. Concepts and Perspec-
tives, VCH, Weinheim, 1995.
and qC–H/OZ143.28) bring about the molecular ordering in
a 2-dimensional sheet form. Thus, it is evident that the
formation of synthon II based on the dimeric motif is feasible
only in the absence of other competitive interactions arising
out of strongly interacting functional groups.
[2] (a) M.C. Etter, Acc. Chem. Res., 23(1990)120;
(b) G.A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford
University Press, Oxford, 1997;
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(e) L.J. Prins, D.N. Reinhoudt, P. Timmerman, Angew. Chem. Int.
Ed., 402382;
4. Summary
(f) F. Hof, S.L. Craig, C. Nuckolls, J. Rebek Jr., Angew. Chem. Int.
Ed., 41(2002)1488.
In summary, we have shown through a rational design,
synthesis and X-ray structural analyses of a set of aldehydes
that o-methoxybenzaldehydes associate in a centrosymmetric
fashion, akin to the carboxylic acids, to give rise to a dimer
synthon II, which derives stabilization from four C–H/O
hydrogen bonds in addition to a dipole–dipole interaction.
That the synthon II is credible to be structure determining is
revealed from the crystal structures of aldehydes 1–4, which
undergo self-assembly into 1-dimensional molecular tapes
and staircases. We have shown that the steric factors as in
aldehyde5 and the presence ofa functional group suchBras in
6 may perturb the expected crystal packing based on synthon
II. While a variety of ring motifs based on strong O/N–
H/O/N interactions have been identified in the realm of
supramolecular chemistry for application in crystal engineer-
ing [2a,c], the synthons based on weaker interactions are only
scant [4]. We believe that this knowledge is important in
crystalengineering inspite of the lackof robustnessassociated
with such motifs, for it is weaker interactions that, at times,
dictate altogether distinct modes of molecular association
even when strong O–H/O hydrogen bonds are involved in
the overall crystal packing [15].
[3] (a) G.R. Desiraju, Angew. Chem. Int. Ed. 34 (1995) 2311;
(b) A. Nangia, G.R. Desiraju, Top. Curr. Chem. 198 (1998) 57.
[4] F.H. Allen, W.D.S. Motherwell, P.R. Raithby, G.P. Shields, R. Taylor,
New J. Chem. (1999) 25.
[5] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural
Chemistry and Biology, Oxford University Press, Oxford, UK, 1999.
[6] E.J. Corey, T.W. Lee, Chem. Commun. (2001) 1321.
[7] B. Koppenhoefer, J.W. Bats, Acta Crystallogr. Sect. C 42 (1986)
1612.
[8] (a) J.N. Moorthy, P. Venkatakrishnan, P. Mal, P. Venugopalan,
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on molecules that contain o-methoxyaromatic aldehyde moiety. In all
the cases (GOYZAV, MELXAT, SODSIN, TOSJUG, WEBBOU,
WOVXEK), the formyl oxygen was found to orient away from o-
methoxy oxygen.
[10] J.W. Steed, J.L. Atwood, Supramolecular Chemistry, Wiley, Cheche-
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[11] G.M. Sheldrick, Programs SHELXS 97 and SHELXL 97, University of
¨
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(b) T. Shintou, W. Kikuchi, Chem. Lett. 32 (2003) 676;
(c) T. Nishino, Y. Nishiyama, N. Sonoda, Bull. Chem. Soc. Jpn 76
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5. Supplementary data
(d) A. Pelter, R. Drake, Tetrahedron 50 (1994) 13775.
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R.E. Melendez, A.D. Hamilton, Top. Curr. Chem. 198 (1998) 97;
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Crystallographic data for the structural analysis of 1–6
have been deposited at the Cambridge Crystallographic
Data Center, 12 Union Road, Cambridge, CB2 1EZ, UK,
and are available free of charge from the Director on request
quoting the deposition number CCDC 240156-60 and
CCDC 225295 (Fax: C44 1223 336033, e-mail: deposit@
ccdc.cam.ac.uk).
(c) I.L. Karle, D. Ranganathan, V. Haridas, J. Am. Chem. Soc. 119
(1997) 2777;
(d) V.R. Thalladi, T. Smolka, A. Gehrke, R. Boese, R. Sustmann,
New J. Chem. 24 (2000) 143;
(e) M.B. Zaman, M. Tomura, Y. Yamashita, Acta Crystallogr. Sect. C
57 (2001) 621;
(f) T.-J.M. Luo, T.R. Palmore, Cryst. Growth Des. 2 (2002) 337;
(g) K.A. Lyssenko, D.A. Lenev, A.G. Kostyanovsky, Tetrahedron 58
(2002) 8525;
Acknowledgements
We thank the Department of Science and Technology
(DST), India for financial support. R.N. is grateful to IIT
Kanpur for a senior research fellowship.
(h) I. Bensemann, M. Gdaniec, T. Polonski, New J. Chem. 26 (2002)
448;
(i) B. Jagadish, M.D. Carducci, C. Bosshard, P. Gunter, J.I. Margolis,
L.J. Williams, E.A. Mash, Cryst. Growth Des. 3 (2003) 811;
(j) P. Vishweshwar, A. Nangia, V.M. Lynch, Cryst. Eng. Commun. 5
(2003) 164;
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