Hydrogen-bonded helical self-assembly of sterically-hindered benzyl alcohols: Rare isostructurality and synthon equivalence between alcohols and acids

Article abstract of DOI:10.1021/cg3001619

Hydrogen-bonded aggregation has been examined in a series of sterically hindered benzyl alcohols with an objective to explore how sterics influence the otherwise inconsistent and variable synthons generally observed for alcohols. All the sterically hindered alcohols 8-15 were found to adopt a helical hydrogen-bonded synthon, and crystallize uniformly in the rare I4₁/a space group, for which the statistical prevalence in the CSD is abysmally small. Remarkably, the crystal packing in all of these alcohols is found to be isostructural to analogous sterically hindered carboxylic acids 1-4. The reason as to why all alcohols sustain the helical motif, despite being aggregated via rather weak hydrogen bonds as compared those in analogous acids 1-4 is traceable to unique molecular topology that permits close-packing as well as exploitation of intermolecular interactions comprehensively. It is shown that sterics permit a very rare packing as well as synthon equivalence between carboxylic acids and alcohols. It emerges from the present study that the hydrogen-bonded synthons of strongly interacting functional groups are not necessarily reproducible when sterics are brought into picture. By the same token, the synthons may sustain even when the interactions are weak when close packing is ensured.

Full text of DOI:10.1021/cg3001619

Article
pubs.acs.org/crystal
Hydrogen-Bonded Helical Self-Assembly of Sterically-Hindered
Benzyl Alcohols: Rare Isostructurality and Synthon Equivalence
Between Alcohols and Acids
Jarugu Narasimha Moorthy,*,† Susovan Mandal,† and Paloth Venugopalan‡
†Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
‡Department of Chemistry, Panjab University, Chandigarh 160014, India
S
* Supporting Information
ABSTRACT: Hydrogen-bonded aggregation has been examined in a series of
sterically hindered benzyl alcohols with an objective to explore how sterics
influence the otherwise inconsistent and variable synthons generally observed
for alcohols. All the sterically hindered alcohols 8−15 were found to adopt a
helical hydrogen-bonded synthon, and crystallize uniformly in the rare I41/a
space group, for which the statistical prevalence in the CSD is abysmally small.
Remarkably, the crystal packing in all of these alcohols is found to be
isostructural to analogous sterically hindered carboxylic acids 1−4. The reason
as to why all alcohols sustain the helical motif, despite being aggregated via
rather weak hydrogen bonds as compared those in analogous acids 1−4 is
traceable to unique molecular topology that permits close-packing as well as
exploitation of intermolecular interactions comprehensively. It is shown that
sterics permit a very rare packing as well as synthon equivalence between carboxylic acids and alcohols. It emerges from the
present study that the hydrogen-bonded synthons of strongly interacting functional groups are not necessarily reproducible when
sterics are brought into picture. By the same token, the synthons may sustain even when the interactions are weak when close
packing is ensured.
1−4,12 while the para-isomers as well as 2,3,4,5,6-pentam-
INTRODUCTION
■
ethylbenzoic acids (5−7) were found to exploit the dimer motif
in their crystal lattices, Chart 1.
Nature abhors vacuum. In general, the molecules in crystals
pack as efficiently as possible.1 Maximization of crystal density
and minimization of void volume is the enunciation of
Kitaigorodskii’s close packing.1a,b This tenet, however, is defied
in compounds containing functional groups that may exploit
strong hydrogen bonds.2 The relatively high energy of
hydrogen bonds as compared to van der Waals interactions
in conjunction with their directionality render them to be
structure-determining. Organization of rationally designed
molecular modules by strong and directional hydrogen bonds
in a predetermined fashion essentially constitutes crystal
engineering.3 Hydrogen bond-mediated aggregation is indeed
the basis for the phenomenon of lattice inclusion exhibited by a
variety of molecules such as urea,4 thiourea,5 dianin’s
compound,6 cholic acid,7 anthracene bis-resorcinol,8 diol
tubulands,9 tetrahedral tetraarylmethanes,10 etc.11 Insofar as
crystal engineering is concerned, identification of supra-
molecular synthons3b and the factors that affect their
manifestation reliably in crystals is very important. A decade
ago, we showed that simple sterically hindered benzene
carboxylic acids substituted at the meta position with a weakly
interacting halogen take a departure from conventional wisdom
as to the self-assembly of carboxylic acids in general into either
dimers or catemers; unprecedented helical assembly was
demonstrated in all sterically hindered meta-halobenzoic acids
After a long hiatus, we wondered as to how the sterics in
conjunction with halogens that may potentially involve in
weaker X···X13 and C−H···X14 interactions influence the self-
assembly of alcohols. The hydroxy compounds have long been
known to interact via a varied number of supramolecular
synthons, Figure 1.15 This propensity has been intimately
related to the shape and size of the compounds. Indeed, the
conflict between close packing and exploitation of hydrogen
bonds has been implicated for prevalence of unusually high Z′
(number of independent molecules in the asymmetric unit cell)
in the crystal structures of alcohols.15,16 Thus, we have
synthesized a series of sterically hindered benzyl alcohols 8−
15 (Chart 1) that are completely analogous to the set of acids
1−7 and examined their crystal packings to explore how sterics
built around the hydroxyl functional group manifest in specific
mode/s of hydrogen-bonded motifs/synthons. Herein, we
report heretofore unprecedented and unexpected packing
equivalence/isostructurality between acids and alcohols, and
some insights into the origin of this intriguing feature.
Received: February 3, 2012
Revised: May 7, 2012
Published: May 8, 2012
© 2012 American Chemical Society
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found to be isostructural crystallizing uniquely in the tetragonal
crystal system with the space group I41/a, see Table 1. The
differences in terms of the molecular structure as well as crystal
packing in all the compounds are unexceptional. In all of the
alcohols 8−15, the hydroxymethyl group is pointed almost
orthogonally from that of the aromatic plane. The angle
between the plane constituted by C−C−O atoms and the plane
of the aromatic ring is found to vary in the range of 74−88°;
the values in the region of 74° being specifically observed for
alcohols that contain halogens at meta positions. In Figure 2 are
shown the molecular structures of alcohols 8 and 12, and that
of the analogous benzoic acid 1, whose structure was reported
by us long ago.12 As can be seen, the O−H bond is oriented
almost orthogonally as that of the carboxylic acid group in 1.
As mentioned earlier, all alcohols 8−15 are isostructural.
Consequently, the crystal packings are similar with marginal
differences. In Figure 3 are shown the crystal packing diagrams
for 3 different alcohols, that is, 8, 12, and 13, together with that
for the dibromo acid 1 for comparison. In all cases, the alcohols
that are related by the 41-screw9 along c-axis are found to self-
assemble via strong O−H···O hydrogen bonds into a helix
(Figure 4); the geometrical parameters for hydrogen bonds in
all alcohols are given in Table 2. The repeat distance, that is, the
pitch of the helix that corresponds to 4 residues is typically the
dimension of the c-axis, which varies between 8.1 and 8.5 Å for
all alcohols. The helical strands along the c-direction are seen to
be close packed in the ab-plane. An incisive analysis shows that
C−H···π interactions that operate between the methylene
hydrogens and the aromatic rings of the adjacent helical strands
are uniformly present in all of the structures. Otherwise, one
observes C−H···Br and Br···Br interactions in the case of
dibromobenzyl alcohol 8, while no such interactions should be
expected for pentamethylbenzyl alcohol 12 (Figure 3). In view
of the isostructurality of all 8−15, the importance of these
weaker interactions in the overall crystal packing is ques-
tionable. Seemingly, they are a consequence of close packing,
but not of any serious consequence in crystal packing.
Chart 1
RESULTS AND DISCUSSION
■
Synthesis of Sterically-Hindered Benzyl Alcohols. The
benzyl alcohols 8, 9, 14, and 15 were readily prepared by
reduction of the corresponding aldehydes with NaBH4, see
Supporting Information. The other alcohols, that is, 10−13,
were prepared by hydrolysis of the corresponding benzyl
bromides with CaCO3 in H2O-1,4-dioxane (1:1) mixture at
reflux conditions Scheme 1.
Molecular Self-Assembly and Crystal Packing of
Helical Assembly (41-Screw) and Isostructurality of
Benzyl Alcohols 8−15. All the benzyl alcohols 8−15 were
Sterically-Hindered Benzyl Alcohols. Very incisive analysis
Figure 1. Typical O−H···O hydrogen bonded synthons by which alcohols in general aggregate.
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Scheme 1
Table 1. Crystal Data for Alcohols 8−15
8
9
10
C11H15Br1O1
11
C11H15Cl1O1
molecular formula
formula weight
solvent for crystallization
crystal system
space group
C10H12Br2O1
C10H12Cl2O1
308.02
219.10
243.14
198.68
Et2O
MeOH
MeOH
Et2O
tetragonal
tetragonal
tetragonal
tetragonal
I 41/a (No. 88)
21.960(2)
21.960(2)
8.121(1)
90.00
I 41/a (No. 88)
I 41/a (No. 88)
I 41/a (No. 88)
a (Å)
22.016(5)
21.877(2)
22.059(2)
b (Å)
22.016(5)
21.877(2)
22.059(2)
c (Å)
8.344(5)
8.118(1)
8.229(1)
α (deg)
90.00
90.00
90.00
β (deg)
90.00
90.00
90.00
90.00
γ (deg)
90.00
90.00
90.00
90.00
volume (Å3)
4044.0(3)
3885.4(6)
4004.7(8)
3916.7(6)
16
Z
16
16
16
calculated density (mg/m3)
absorption coefficient (mm−1
F (000)
2.023
1.498
1.613
1.348
)
7.974
0.622
4.063
0.346
2400
1824
1984
1696
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.039
1.038
1.048
1.066
R1 = 0.0364, R2 = 0.0821
R1 = 0.0469, R2 = 0.0858
12
R1 = 0.0396, R2 = 0.1035
R1 = 0.0448, R2 = 0.1070
13
R1 = 0.0461, R2 = 0.1159
R1 = 0.0586, R2 = 0.1225
14
R1 = 0.0395, R2 = 0.1007
R1 = 0.0416, R2 = 0.1024
15
molecular formula
formula weight
solvent for crystallization
crystal system
space group
C12H18O1
C11H15Br1O1
C11H15Cl1O1
C10H14O1
178.26
243.14
198.68
150.21
C6H6
Et2O
Et2O
Et2O + Pet ether
tetragonal
tetragonal
tetragonal
tetragonal
I41/a (No. 88)
I41/a (No. 88)
I41/a (No. 88)
I41/a (No. 88)
a (Å)
22.046(2)
22.035(2)
22.069(5)
20.924(2)
b (Å)
22.046(2)
22.035(2)
22.069(5)
20.924(2)
c (Å)
8.137(1)
8.494(1)
8.525(2)
8.102(1)
α (deg)
90.00
90.00
90.00
90.00
β (deg)
90.00
90.00
90.00
90.00
γ (deg)
volume (Å3)
90.00
90.00
90.00
90.00
3954.7(6)
4124.4(6)
4152.2(2)
3546.9(7)
Z
16
16
16
16
calculated density (mg/m3)
absorption coefficient (mm−1
F (000)
1.198
1.566
1.271
1.125
)
0.074
3.945
0.326
0.070
1568
1984
1696
1312
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.061
1.045
1.044
1.063
R1 = 0.0521, R2 = 0.1381
R1 = 0.0604, R2 = 0.1464
R1 = 0.0294, R2 = 0.0734
R1 = 0.0361, R2 = 0.0756
R1 = 0.0503, R2 = 0.1401
R1 = 0.0638, R2 = 0.1517
R1 = 0.0711, R2 = 0.1990
R1 = 0.0771, R2 = 0.2093
in 1994 by Brock and Duncan on the aggregation of alcohols15
in general are the following: (i) hydrogen-bonded aggregates of
alcohols are largely rings and chains, (ii) if the compounds are
relatively thin, they can be related by 21-screw, glide planes, and
translation rarely, and (iii) in sterically hindered molecules, the
difficulty in organizing molecules by 2-fold axes or inversion
symmetry may manifest in crystal structures with high Z′ or
aggregation of the molecules around screw or rotation inversion
axes of order 3, 4, or 6 in trigonal or tetragonal space groups.
Subsequent analyses by Taylor and Macrae in 200117 were
found to be in conformity with the inferences by Brock and
Duncan;15 the former observed that the helical chains are
common for secondary and tertiary monoalcohols suggesting
thereby that sterics could be very relevant in the helical self-
assembly. It was also observed that 3-fold helices are more
frequently observed than 4-fold helices. In 2003, Muir and co-
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Figure 2. X-ray determined molecular structures of benzyl alcohols 8 and 12 (left and center pairs), and dibromobenzoic acid 1 (right pair).
workers analyzed the aggregation with a particular emphasis on
tertiary alcohols and showed that trigonal and tetragonal space
groups are more prevalent for tertiary alcohols as compared to
all other structures in the database.18 In the backdrop of this
literature on hydrogen-bonded assembly of alcohols in general
and our own observation of dramatic influence of sterics on
benzene carboxylic acids,12 it was instructive to enquire into
̀
how sterically hindered benzyl alcohols aggregate vis-a-vis
unhindered parent benzyl alcohols. Further motivation for
comprehensive investigations into the steric effects on benzyl
alcohols was also the following. A quick perusal of the CSD
revealed that the synthons that are typically observed for simple
benzyl alcohols, for example, p-chloro/bromo/methyl benzyl
alcohols, are linear chains and 21-screw-related zigzag chains.19
Curiously, the X-ray crystal structures of sterically hindered
2,4,6-trimethylbenzyl alcohol and any of its derivatives are
unknown as revealed by the CSD search. From a thorough
CSD analysis, we recognized that 1,4-bis(hydroxymethyl)-
benzene crystallizes in P21/n space group,20 while its sterically
hindered 1,4-bis(hydroxymethyl)durene (OJEZUY) analog was
found to crystallize in I41/a space group.21
Clearly, the crystal structures of all benzyl alcohols 8−15
show that sterics divert the otherwise generally observed chain/
zigzag motif, and that minor substitutional changes do not
affect the aggregation via 41-helix. What is it that causes the 41-
screw helical synthon in sterically hindered benzyl alcohols to
be so robust as to be reliably observed in a series of derivatives?
Indeed, the crystallization of all of the benzyl alcohols 8−15 in
I41/a space group is quite intriguing when the fraction of total
number of alcohols as a whole that crystallize in this space
group is considered. Our analysis of CSD (as of 2012) reveal
that the number of structures in CSD that correspond to the
string “C−C−OH” is 35 689, of which only 73 are found to
crystallize in I41/a; this amounts to 0.20% of the total number
of alcohols (Table 3).
Figure 3. Comparison of the crystal packings of (a) 3,5-dibromo-2,4,6-
trimethylbenzyl alcohol 8, (b) 3,5-dibromo-2,4,6-trimethylbenzoic acid
1, (c) 2,3,4,5,6-pentamethylbenzyl alcohol 12, and (d) 4-bromo-
2,3,5,6-tetramethylbenzyl alcohol 13. Notice that in all the structures
O−H···O hydrogen bonds have been shown with broken green line,
while Br···Br and C−H···Br have been shown in blue and red color,
respectively.
The reason for helical aggregation around 41-axis appears to
be traceable to orthogonality of C−C−O bond with respect to
the aromatic bulky moiety; for all the alcohols, the angle
between C−C−O plane and the plane of the aryl ring varies
between 74° and 88° (Table 2), while the angle in sterically
unhindered alcohols that crystallize in P21 or P21/c or P21/a are
typically in the range of 34−51°.19 Seemingly, this orthogon-
ality of the aryl ring with respect to the C−C−O plane of C−
C−OH that self-assembles via O−H···O hydrogen bonding
permits best packing with each of the aryl ring stacked almost
perpendicular to the ab-plane along the c-axis. The aryl rings do
not tilt much into the ab-plane thereby allowing efficient
organization along the c-axis; the angles between the planes of
the aryl rings that are related by 41-screw axis varies between
81° and 90° for all alcohols (Table 2). As was prophetically
inferred by Brock and Duncan,15 the alcohols 8−15, which are
bulky, cannot presumably be linked up by C2-axis, inversion
Figure 4. Partial drawing of molecular packing in 3,5-dibromo-2,4,6-
trimethylbenzyl alcohol 8 (left) and the O−H···O hydrogen-bonded
self-assembly into 41-screw helix. Please note that the aromatic
hydrogens, bromines, and methyl groups have been removed in the
helix for clarity.
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Table 2. Geometrical Parameters for the Intermolecular Interactions Observed in the Crystals of Alcohols 8−15
a
a
a
b
b
c
d
e
f
compound
dO····O (Å)
θO−H····O (°)
dO−H····O (Å)
dX····X (Å)
θC−X····X (°)
dC−H ····X (Å)
dC−H····π (Å)
θaryl−CCO (°)
θ(tilting) (°)
8
2.75(1)
2.74(1)
2.74(1)
2.74(1)
2.76(1)
2.71(1)
2.74(1)
2.75(1)
173.4(2)
173.7(1)
175.8(2)
178.1(1)
176.6(1)
163.1(1)
167.0(1)
1.94(1)
1.93(1)
1.92(1)
1.92(1)
1.94(2)
1.91(1)
1.93(1)
1.94(1)
3.63(1)
3.60(1)
75.2(1)
75.3(1)
2.99(1)
2.87(1)
3.11(1)
3.08(1)
3.12(1)
3.10(1)
3.11(1)
3.16(1)
3.18(1)
2.88(1)
74.2(2)
74.6(1)
74.8(2)
74.4(1)
76.3(1)
87.4(1)
88.0(1)
85.6(1)
82.6(1)
82.1(1)
81.9(1)
81.7(1)
81.3(1)
84.7(1)
85.1(1)
9
10
11
12
13
14
15
2.93(1)
2.85(1)
169.7(1)
89.9(1)
a
b
c
d
e
For O−H···O hydrogen bond. For halogen···halogen interactions. Distance of C−H···X interaction. For closest C−H···π interaction. The angle
f
between the aryl ring and the plane constituted by the C−C−O(H) atoms. Angle between the planes of the aryl rings related by 41-screw axis.
Table 3. Statistical Analysis of Alcohols in the CSD as of
2012
actions, the packing appears to be unstable/inefficient such that
the helical synthon is readily compromised with any
perturbation that imparts little gain in terms of the lattice
energy. In contrast, the molecular organization in analogous
alcohols appears to be free from any stress and is seemingly
“relaxed” with best of close-packing and hydrogen bonding. In
spite of relatively weaker hydrogen-bonding interactions, the
packing is conserved for similar changes in the substitution
pattern. Evidently, the close-packing is not much affected. In
line with these considerations, the packing indexes, as revealed
by PLATON, for some of the alcohols 8−15 and acids 1−7
(Table 4) show that the helical organization of the molecules
search string
total hits hits with I41/a space group percentage
C−C−OH
35689
6843
73
26
0.20
0.38
0.13
0.20
0.23
C−CH2−OH
C−C(C)H−OH
C−C(C)2−OH
C−OH
14331
8174
19
16
46300
105
symmetry, translation and 21/31 screw axes. Thus, the fact that
sterics that impart a particular shape appears to be crucial for
the helical self-assembly based on O−H···O hydrogen bonding,
which is unaffected by the presence/absence of weakly
interacting groups that are remotely located from the hydroxyl
group.
Table 4. Packing Indexes for Some of the Benzoic Acids 1−7
a,b
and Benzyl Alcohols 8−15
compound
packing index (%)
compound
packing index (%)
Synthon (Packing) Equivalence of Sterically-Hindered
Benzyl Alcohols with Analogous Acids. As mentioned at
the outset, sterically hindered benzene carboxylic acids that
contain at least one halogen at the meta position were shown
by us to undergo helical assembly and crystallize in I41/a space
group.12 In fact, all of the alcohols 8−15 are isostructural to
those of acids 1−4. To the best of our knowledge, the observed
isostructurality between acids and alcohols is unprecedented.
The acids in general are strong hydrogen bond donors as well
as acceptors, while alcohols are relatively weaker donors and
acceptors; this is amply reflected in the significantly shorter
(2.4−2.55 Å) O···O distances in acids 1−4 than in alcohols 8−
15 (2.71−2.75 Å), cf. Table 2. What is the origin of packing
equivalence of acids 1−4 with those of all alcohols 8−15? Why
is it that replacement of halogens at 3,5-positions of the acids
with methyl groups as in 5 and location of a halogen at para
position as in 6 and 7 leads to dimeric motif, while similar
substitutional changes do not affect the helical assembly of
alcohols 8−15? It is ironic that the strongly hydrogen-bonded
helical motif in 1−4 is readily perturbed, while the rather less
strongly aggregated alcohols sustain the helical propagation!
The fact that the sterically hindered acids, despite being
strongly connected, are worst affected with weakly interacting
groups suggests that the crystal packing in 1−4 seemingly
corresponds to critical threshold at which there is a best trade-
off between close-packing and exploitation of strong as well as
weak interactions. This sensitive limit appears to be readily
perturbed with minute of changes, as reflected by the crystal
packings of 5−7 in which the dimer motif is observed. In other
words, the acids 1−4 appear to represent systems that are
“sensitive” from the point of view of crystal packing, although
carboxyl hydrogen in each case is involved in hydrogen
bonding. Despite maximization of hydrogen-bonding inter-
1
2
6
7
8
66.7
66.2
65.0
64.5
73.1
9
72.8
72.4
70.5
68.2
66.9
12
13
14
15
a
b
As calculated by the program PLATON. The packing indexes were
not calculated for the disordered structures.
with extra carbonyl oxygen in acids 1−4, when compared with
alcohols, renders the packing little poorer. In essence, the rare
packing equivalence for acids 1−4 and alcohols 8−15,
divergence for 5−7 point out subtle interplay between close-
packing and exploitation of hydrogen-bonded synthons in the
crystal packing. It emerges from the present study that the
hydrogen-bonded synthons of strongly interacting functional
groups are not necessarily reproducible when sterics are
brought into picture. By the same token, the synthons may
sustain even when the interactions are weak when close packing
is ensured.
CONCLUSIONS
■
We have investigated hydrogen-bonded self-assembly in a series
of sterically hindered benzyl alcohols with a view to inquire
about how sterics influence the hydrogen-bonded synthons of
hydroxyl groups. Contrary to the noted propensity of alcohols
to aggregate via different synthons, the sterically hindered
benzyl alcohols 8−15 were found to adopt helical hydrogen-
bonded synthon, and crystallize uniformly in the rare I41/a
space group, for which the statistical prevalence in the CSD is
abysmally small. The reason as to why all alcohols sustain the
helical motif, despite being aggregated via rather weak
hydrogen bonds as compared to those in analogous acid 1−
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packing as well as synthon equivalence between carboxylic acids
and alcohols.
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Craig, D. C.; Nguyen, V. T.; Scudder, M. L. Aust. J. Chem. 2001, 54,
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(11) (a) Hosseini, M. W. Acc. Chem. Res. 2005, 38, 313. (b) Moorthy,
J. N.; Natarajan, P.; Venugopalan, P. J. Org. Chem. 2009, 74, 7566.
(c) Moorthy, J. N.; Natarajan, P. Chem.Eur. J. 2010, 16, 7796.
(d) Moorthy, J. N.; Natarajan, P.; Bajpai, A.; Venugopalan, P. Cryst.
Growth Des. 2011, 11, 3406.
EXPERIMENTAL SECTION
■
Crystal Structure Determinations and Refinement. The
crystals suitable for X-ray analysis were grown in each case by slow
evaporation of their solutions in the solvents mentioned in Table 1. A
good quality crystal in each case was mounted in a glass capillary,
cooled to 100 K, and the intensity data were collected on a Bruker
Nonius SMART APEX CCD detector system with Mo-sealed Siemens
ceramic diffraction tube (λ = 0.71073 Å) and a highly oriented
graphite monochromator operating at 50 kV and 30 mA. The data
were collected on a hemisphere mode and processed with Bruker
SAINTPLUS. Empirical absorption correction was made using Bruker
SADABS. The structure was solved in each case by Direct Methods
using SHELXTL package and refined by full matrix least-squares
method based on F2 using SHELX97 program.22 For benzyl alcohols
10 and 11, the halogen and methyl groups at meta positions were
found to be statistically disordered. The refinement for these cases was
accomplished with associating partial occupancies for methyl carbon
and halogen atoms. All the non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were included in their ideal
positions with fixed isotropic U values and were allowed to ride with
their respective non-hydrogen atoms. The crystal data and details of
refinement are included in Table 1.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic information files (CIF), NMR spectral
data, and spectral reproductions. This information is available
free of charge via the Internet at http://pubs.acs.org/.
(12) Moorthy, J. N.; Natarajan, R.; Mal, P.; Venugopalan, P. J. Am.
Chem. Soc. 2002, 124, 6530.
(13) For a comprehensive account of the X···X interactions and their
application in crystal engineering, see: (a) Sharma, J. A. R. P.;
Desiraju, G. R. Acc. Chem. Res. 1986, 19, 222. (b) Desiraju, G. R.;
Parthasarathy., R. J. Am. Chem. Soc. 1989, 111, 8725. (c) Venkatesan,
K.; Ramamurthy, V. Photochemistry in Organized and Constrained
Media; Ramamurthy, V., Ed.; VCH: New York, 1991. (d) Thallapally,
P. K.; Nangia, A. CrystEngComm. 2001, 27, 1.
AUTHOR INFORMATION
Corresponding Author
*E-mail: moorthy@iitk.ac.in.
Notes
■
The authors declare no competing financial interest.
(14) van den Berg, J. A.; Seddon, K. R. Cryst. Growth Des. 2003, 3,
643.
ACKNOWLEDGMENTS
■
(15) Brock, C. P.; Duncan, L. L. Chem. Mater. 1994, 6, 1307.
(16) (a) Shieh, H. S.; Hoard, L. G.; Nordman, C. E. Acta Crystallogr.
1981, B37, 1538. (b) Lehmler, H. J.; Robertson, L. W.; Parkin, S.;
Brock, C. P. Acta Crystallogr. 2002, B58, 140.
J.N.M. is thankful to DST (Department of Science and
Technology), India for funding. S.M. is grateful to CSIR for a
senior research fellowship.
(17) Taylor, R.; Macrae, C. F. Acta Crystallogr. 2001, B57, 815.
(18) Fraile, A. G.; Morris, D. G.; Martinez, A. G.; Cerero, S. D. L. M.;
Muir, K. W.; Ryder, K. S.; Vilar, E. T. Org. Biomol. Chem. 2003, 1, 700.
(19) (a) Hashimoto, M.; Nakamura, Y.; Hamada, K. Acta Crystallogr.
1988, C44, 482. (b) Hashimoto, M.; Harada, M. Zeit. Natur., A: Phy.
Sci. 2003, 58, 63. (c) Braga, D.; Grepioni, F.; Maini, L.; Polito, M.;
Rubini, K.; Chierotti, M. R.; Gobetto, R. Chem.Eur. J. 2009, 15,
1508.
DEDICATION
■
Dedicated to Prof. T. N. Guru Row. IISc., Banaglore on the
occasion of his 60th Birthday
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