Twisted aromatics, 9-anthryl and 1-pyrenyl terpyridines organize into novel multi-directional 'ladder-like' motifs in the solid state

Article abstract of DOI:10.1016/S0022-2860(02)00280-6

9-Anthryl and 1-pyrenyl terpyridines (1 and 2, respectively), key precursors for the design of novel fluorescent sensors have been synthesized and characterized by ¹H NMR, mass spectroscopy and X-ray crystallography. Twisted molecular conformat

Full text of DOI:10.1016/S0022-2860(02)00280-6

Journal of Molecular Structure 616 (2002) 103–112
www.elsevier.com/locate/molstruc
Twisted aromatics, 9-anthryl and 1-pyrenyl terpyridines
organize into novel multi-directional ‘ladder-like’ motifs
in the solid state
A. Gulyania, R. Srinivasa Gopalanb, G.U. Kulkarnib, S. Bhattacharyaa,
*
aDepartment of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
bChemistry and Physics of Materials Unit, Jawaharlal Nehru Centre For Advanced Scientific Research, Jakkur, Bangalore 560 064, India
Received 22 February 2002; accepted 8 May 2002
Abstract
9-Anthryl and 1-pyrenyl terpyridines (1 and 2, respectively), key precursors for the design of novel fluorescent sensors have
been synthesized and characterized by 1H NMR, mass spectroscopy and X-ray crystallography. Twisted molecular
conformations for each 1 and 2 were observed in their single crystal structures. Energy minimization calculations for the 1 and 2
using the semi-empirical AM1 method show that the ‘twisted’ conformation is intrinsic to these systems. We observe
interconnected networks of edge-to-face CH· · ·p interactions, which appear to be cooperative in nature, in each of the crystal
structures. The two twisted molecules, although having differently shaped polyaromatic hydrocarbon substituents, show similar
patterns of edge-to-face CH· · ·p interactions.
The presently described systems comprise of two aromatic surfaces that are almost orthogonal to each other. This twisted or
orthogonal nature of the molecules leads to the formation of interesting multi-directional ladder like supramolecular
organizations. A combination of edge-to-face and face-to-face packing modes helps to stabilize these motifs. The ladder like
architecture in 1 is helical in nature. q 2002 Published by Elsevier Science B.V.
Keywords: X-ray crystallography; Twisted conformations; Polyaromatic systems; CH· · ·p and p· · ·p interactions
1. Introduction
dicular) orientation. Edge-to-face interactions express
themselves, for instance, in determining the arrange-
ment of aromatic molecules both in the gas phase [1,2]
and in the solid state [3]. These interactions have
biological relevance as they are thought to signifi-
cantly influence the packing of aromatic side-chain
residues in proteins [4]. Moreover, the inclusion of
certain edge-to-face interactions in the category of
weak hydrogen bonds of the type CH· · ·p type has
generated considerable recent interest [5–14].
Stable aromatic–aromatic interactions have been
classified into two basic types, motifs having either
‘face-to-face’ (co-facial) or ‘edge-to-face’ (perpen-
*
Corresponding author. Address: Chemical Biology Unit of
JNCASR, Bangalore 560 012, India. Tel.: þ91-80-344-3529; fax:
þ91-80-360-0529.
E-mail address: sb@orgchem.iisc.ernet.in (S. Bhattacharya).
For some recent examples of development of new structural
1
In the synthesis of organic solids with controllable
packing in their crystalline states,1 we have earlier
motifs from organic templates using various structure directing
forces see: Refs. [15–18].
0022-2860/02/$ - see front matter q 2002 Published by Elsevier Science B.V.
PII: S0022-2860(02)00280-6

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A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
Table 1
The Crystal data and structure refinement for 1 and 2
Identification code
Empirical formula
Formula weight
Temperature
1
2
C
29H19N3
C31 H19 N3
433.49
298(2) K
409.47
298(2) K
˚
˚
0.71073 A
Wavelength
0.71073 A
Monoclinic
P21
Crystal system
Space group
Triclinic
P 2 1
Unit cell dimensions
˚
a/A, a/8
˚
b/A, b/8
6.0474(8)
9.0421(11), 78.971(2)
9.9857(12), 89.93
13.390(2), 66.857(2)
1087.5(2)
6.181(2), 102.443(2)
˚
10.940(2)A
˚
c/A, g/8
3
˚
Volume/A
1045.4(2)
Z
2
2
Density (calculated)/Mg/m3
Absorption coefficient/mm21
F(000)
1.301
1.324
0.077
0.079
428
452
u range/8
1.91–23.29
1.55–23.28
Limiting indices
26 # h # 6, 211 # k # 17, 212 # l # 12
210 # h # 10, 29 # k # 11, 211 # l # 14
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I . 2s(I)]
Absolute structure parameter
4314
4551
2125 [R(int) ¼ 0.0722]
Full-matrix least-squares on F 2
2123/1/289
3051 [R(int) ¼ 0.0577]
Full-matrix least-squares on F 2
3046/0/383
1.225
1.304
R1 ¼ 0:0722; wR2 ¼ 0:1475
210(10)
R1 ¼ 0:0761; wR2 ¼ 0:1853
23
˚
Largest diff. peak and hole/e A
0.212 and 20.247
0.268 and 20.266
exploited hydrogen bonding [19,20] or metal-to-
ligand bonds [21]. We now turn our attention to
exploit inter-aromatic stabilizing forces as elements in
the structural design [22]. To this end we have chosen
two systems, 40-(9-anthryl)-2,20:60,200-terpyridine (1)
and 40-(1-pyrenyl)-2,20:60,200-terpyridine (2), wherein
a polyaromatic moiety is directly linked to a
terpyridine unit via a C–C single bond. It may be
noted that 1 and 2 have a significant degree of
conformational flexibility along with considerable
aromatic/hetero-aromatic surfaces. Thus they offered
interesting possibilities for creating new structures. It
also provides an opportunity to explore the link
between the shape of the molecular component and
the resulting architectures. Also, in view of the
increasing demand for the design of ligands and
their metal complexes with luminescence properties
[23,24], the structural information obtained from 1
and 2 should provide original insights to prepare new
family of materials.
2. Experimental
2.1. General
The NMR spectra were recorded on a Bruker
AMX 400 MHz and Bruker DRX 500 MHz NMR

A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
105
Fig. 1. The ORTEP diagrams for (a) 1 and (b) 2 showing the twisted molecular conformations in each of the two cases.
spectrometers. The chemical shifts are reported in
parts per million (ppm) downfield relative to
standard tetra methyl silane (TMS). The Mass
Spectra were recorded on a Jeol Model JMS-DX
303 spectrometer equipped with Jeol JMA-DA
Mass Data Station. The mass spectra of the
compounds were recorded by a direct inlet system,
70 eV. IR spectra were recorded on a JASCO
FT/IR 410 spectrophotometer. 9-Anthryl aldehyde
and 1-pyrenyl aldehyde were obtained from Aldrich
Chemical Co., and used as received.
2.2. Synthesis
The compounds 1 and 2 were synthesised by a
modification of the reported procedure adopted after
Krohnke methodology in one step [23–25].
40-(1-Pyrenyl)-2,20:60,200-terpyridine (2): 1-Pyrenyl
aldehyde (1.33 g, 5.8 mmol), 2-acetyl pyridine
(1.38 g, 11.4 mmol), acetamide (8.15 g, 138 mmol)
and ammonium acetate (6 g, 78 mmol) were taken in
an R.B. flask and heated at 180 8C for three hours with
stirring. Subsequently, An aqueous solution of 4.8 g

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A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
Table 2
CH· · ·p Interactions for 1 and 2
b
d /A
c
Dpi /A
Descriptiona
ad/deg.
˚
˚
Interaction
a
b
c
d
C14H14· · ·ring 5
C20H20· · ·ring 1
C21H21· · ·ring 3
C13H13· · ·ring 4
2.7
2.7
2.8
3.2
2.6
2.5
2.8
2.9
140.5
173.4
145.4
135.2
e
f
C23H23· · ·ring 3B
C15H15· · ·ring 5B
C19H19· · ·ring 2B
2.7
2.8
3.0
2.6
2.7
2.8
145.6
144.0
161.3
g
a
Ring (5), C20.C21.C22.C23.28.C29; ring (1), N1.C1.C2.
C3.C4.C5; ring (3), N3.C11.C12.C13.C14.C15; ring (4),
C16.C17.C18.C19.C27.C26; ring (3B), N3.C11.C12.C13.C14.
C15; ring (2B), N2.C6.C7.C8.C9.C10. ring (5B), C19.C20.C.28.
C31.C30.C27.
Fig. 2. The interconnected C–H· · ·p interactions in the crystal
structure of 1 are shown. See Table 2 for details. The interaction ‘d’
is not shown for the sake of clarity.
b
H· · ·i (centroid) distance. The C–H bond lengths normalized to
˚
average neutron diffraction value of 1.083 A.
c
H· · ·p perpendicular distance.
CH· · ·i (centroid) angle.
d
2.3. X-ray diffraction studies
of NaOH in 9.6 ml water was added to the contents of
the R.B. flask and the reaction mixture was heated at
120 8C for a further 2 h without stirring. The reaction
mixture was then extracted with CHCl3 and the crude
product chromatographed repeatedly over silica using
Petroleum ether–Ethyl acetate. 2 was isolated
(Rf ¼ 0:4 in 7% ethyl acetate in Petroleum ether)
and further purified by recrystallization using 2:1
CHCl3–Ethyl acetate. The crystals obtained by this
method were analytically pure and were used for X-
Ray Crystallography and spectroscopic investi-
X-ray diffraction intensities were measured at room
temperature by 4 scans using a Siemens three-circle
diffractometer attached to a CCD area detector and a
graphite monochromator for the Mo Ka radiation
(50 kV, 40 mA). Initially, the unit cell parameters and
the orientation matrix of the crystal were determined
using ,45 reflections from 25 frames collected over a
small4scan of 7.58, sliced at3.58interval. A hemisphere
of reciprocal space was then collected using the SMART
software [26] with the 2u setting of the detector at 288.
The data reduction was performed using SAINT program
[26] and the orientation matrix along with the detector
and the cell parameters were refined for every 40 frames
on all the measured reflections. The crystal structures
were solved by direct methods using the SHELXTL
program [27] and refined by full matrix least squares
on F 2. All non-hydrogen atoms were refined anisotro-
pically. Hydrogen atoms in 2 were located by the
difference Fourier synthesis and refined isotropically,
and in 1 were fixed geometrically and treated as riding.
The hydrogen atom positions were then normalized to
the average neutron diffraction values [28].
1
gations. H NMR (500 MHz, CDCl3): d 7.35–7.39,
2H, m; 7.9–7.94, 2H, m; 8.02–8.28, 9H, m; 8.68–8.7,
2H, m; and 8.74–8.78, 4H, m. LR-MS (EI): Mþ
(C31H19N3)þ: 433; elemental analysis for C31H19N3:
calcd: C 85.91, H 4.38, N 9.69; found: C 86.08, H
4.54, N 9.68.
40-(9-Anthryl)-2,20:60,200-terpyridine (1): a similar
procedure was used except that 9-anthryl aldehyde
1
was used instead of 1-pyrenyl aldehyde. H NMR
(400 MHz, CDCl3): d 7.3–7.36, 4H, m; 7.44–7.48,
2H, m; 7.69–7.2, 2H, m; 7.89–7.93, 2H, m; 8.05–
8.07, 2H, m; 8.54, 1H, s; 8.6–8.62, 4H, m; and 8.77–
8.79, 2H, m. LR Mass Spectrum: Mþ (C29H19N3)þ:
409; elemental analysis for C29H19N3·0.4 H2O: calcd:
C 83.59, H 4.78, N 10.08; found: C 83.86, H 4.54, N
9.63.
2.4. Energy minimization calculations
GAUSSIAN94 [29] package using the AM1 Hamil-
tonian [30] was used to perform the semi-empirical

A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
107
Fig. 3. Orthographic depiction of the C–H· · ·p interaction ‘a’ in
crystal structure of 1 with (a) showing the side view and (b) showing
˚
the top view. Also provided are distances (in A) between the
approaching H and the carbons closest to it.
calculations to optimize the molecular geometry of (1)
and (2).
3. Results and discussion
Crystallization of 1 and 2 from their respective
solutions in CHCl3–EtOAc (2:1) yielded solids that
could be examined by single crystal X-ray diffraction.
The crystal structure data for the two compounds are
given in Table 1. In monoclinic crystals of 1, there are
two molecules in the unit cell in the chiral space group
P21. The ORTEP diagram for 1 is shown in Fig. 1a. A
noteworthy feature of this molecule is its highly
twisted conformation. The angle between the anthryl
ring in 1 and the plane of the central pyridyl ring of the
terpyridine moiety about the inter-annular C–C bond
is 74.58 (Fig. 1a). The triclinic crystals of 2 crystallize
in the Centro symmetric space group P 2 1 with two
molecules in the unit cell. In 2, the angle between the
plane of the pyrenyl ring and that of the central
pyridyl ring of the terpyridine moiety is 51.68 (Fig. 1b
shows the ORTEP diagram). Thus the twisted
molecular conformation is a common feature in both
these molecules.
Fig. 4. Orthographic depiction of the C–H· · ·p interaction ‘b’ in
crystal structure of 1 with (a) showing the side view and (b) showing
˚
the top view. Also provided are distances (in A) between the
approaching H and the carbons closest to it.
deviation from coplanarity about the polyaromatic-
pyridyl interannular C–C bond observed with 1 and 2
arises largely from the tendency of either molecule to
minimize the energetically demanding non-bonded
contacts between the 1,8-H’s of the anthryl ring in 1 or
10-H of the pyrenyl ring in 2 and those of the central
pyridyl ring (30,50-H’s) respectively. There are two
contacts that need to be minimized in 1 while there is
one such contact in case of 2. This explains the fact
that the twist angle is greater in case of 1.
Semi-empirical AM1 calculations were also per-
formed on each of these systems to ascertain their
energy-minimized ‘gas phase’ conformations. As in
their crystal structures, the molecules 1 and 2 show
twisted conformations in each case. In 1, the angle
Constable et al. [31] examined the crystal structure
of 1-phenyl terpyridine and found that the angle
between the phenyl ring and the central pyridyl ring
about the interannular C–C bond to be 10.98. Large

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A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
Fig. 6. The interconnected C–H· · ·p interactions in the crystal
structure of 2. See Table 2 for details.
and determine the nature of interactions that occur?
Detailed crystal structure analysis shows the presence
of interesting CH· · ·p interactions in 1 as listed in
Table 2. In two of the contacts a pyridyl H approaches
a ring of the anthracene p face while in the other two
contacts, an anthryl H approaches a pyridyl ring (Fig.
2). The distances between aromatic H and the
‘interacting’ p surface observed here are all in the
accepted range [5–14] for such type of contact. Two
of the contacts can be considered as ‘short’, viz.
˚
˚
interaction ‘a’, 2.64 A and interaction ‘b’, 2.52 A
(Table 2).
Fig. 5. Orthographic depiction of the C–H· · ·p interaction ‘c’ in
crystal structure of 1 with (a) showing the side view and (b) showing
˚
the top view. Also provided are distances (in A) between the
The CH· · ·p interactions observed fall into a
pattern of interconnected networks. In the interaction
‘a’ (Fig. 2), a pyridyl H approaches a p ring belonging
to the anthryl moiety of 1. The p ring that is the
acceptor in the CH· · ·p interaction ‘a’ happens to be
an H donor in the CH· · ·p interactions ‘c’ and ‘b’ (Fig.
2). A consideration of Fig. 2 and Table 2 also shows
that the pyridyl ring labeled ‘Ring 3’ (Table 2) that
acts an H donor in interactions ‘a’ and ‘d’ acts an H
acceptor in the CH· · ·p interaction ‘c’. If one assumes
the ‘soft’ CH· · ·p interactions can exhibit cooperativ-
ity, then interaction ‘a’ should augment the inter-
actions ‘b’ and ‘c’ (Fig. 4a and b).
approaching H and the carbons closest to it.
between the plane of the anthryl ring and the central
pyridyl ring is shown to be 67.58 while in 2, the plane
of the pyrenyl ring makes an angle of 55.48 with
central pyridyl ring of the terpyridine unit. Thus, the
twist angles obtained in the energy minimized
conformations are quite comparable to the twist
angles revealed from the crystal structure determi-
nation of the individual systems. This clearly
demonstrates that the presently described systems
comprise of two aromatic surfaces that are almost
orthogonal to each other and that the twisted
conformation is intrinsic to the two molecules.
It was important to ascertain the geometry of these
interconnected edge-to-face interactions, and the
results have been shown through orthographic depic-
tion of the individual CH· · ·p interactions. Fig. 3a and
b show the side and top view, respectively, of the
How do the twisted molecules comprising of two
essentially planar components pack in the solid state

A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
109
Fig. 8. Orthographic depiction of the C–H· · ·p interaction ‘f’ in
crystal structure of 2 with (a) showing the side view and (b) showing
˚
the top view. Also provided are distances (in A) between the
approaching H and the carbons closest to it.
geometry of interaction is such that H21 makes
close contacts with carbons C14 and C15. The angles
involved in the interaction C21H21· · ·C14, 143.68 and
C21H21· · ·C15, 169.38 again provide evidence that
the contacts are directional. The p carbon C14 in turn
acts as a donor in interaction ‘a’. Taken together, the
orthographic views of the CH· · ·p interactions clearly
bring forth a common feature of the geometry of the
interactions. These interactions are such that H makes
close contacts with one or two of the ring carbons and
Fig. 7. Orthographic depiction of the C–H· · ·p interaction ‘e’ in
crystal structure of 2 with (a) showing the side view and (b) showing
˚
the top view. Also provided are distances (in A) between the
approaching H and the carbons closest to it.
CH· · ·p interaction ‘a’. The figure also shows the
distance of the interacting H from the p carbons with
which it makes the closest contacts. Fig. 3a and b
clearly show that the H in the CH· · ·p interaction ‘a’ is
close to one edge of the p face. It is positioned closest
to p carbons C21 and C22, with the angle
C14H14· · ·C22 being 169.58. In turn, C21 acts as a
C H· · ·p donor in interaction ‘c’. Also, a proximal p
carbon C20 also acts as a C H· · ·p donor. Thus, there
appears to be directionality in this interaction that
suggests that these interconnected interactions are
cooperative in nature. This apparent cooperativity is
also in evidence in Fig. 5 that shows the side (Fig. 5a)
and top (Fig. 5b) view of interaction ‘c’. The
Fig. 9. Orthographic depiction of the C–H· · ·p interaction ‘g’ in
crystal structure of 2 with (a) showing the side view and (b) showing
˚
the top view. Also provided are distances (in A) between the
approaching H and the carbons closest to it.

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A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
Fig. 10. The ladder-like arrangements shown for 2 involving two
face-to-face interacting pyrene moieties. The ‘pyrene sandwich
dimer’ like unit forms the rung of the ladder.
Fig. 11. Another ladder-like arrangement in the crystal structure of
2. Here, face-to-face interacting pyridyl units constitute the rung of
the ladder.
is generally directed towards the edge of the p face
that is involved in propagating other CH· · ·p inter-
actions, suggesting cooperativity.
MultipleinterconnectedCH· · ·pinteractionsare also
seen in the crystalline state of 2 (Table 2, Fig. 6). The
as a donor in interaction ‘f’ (Fig. 9 provides the
orthographic depiction for interaction ‘f’).
˚
two short contacts ‘e’ and ‘f’ are in the range of ,2.6 A.
Thus, a common feature of the CH· · ·p interactions
in the two crystal structures is that interactions are
directional in nature so as to exemplify the apparent
cooperativity. The CH units are close to and directed
towards p carbons that are involved as donors in other
edge-to-face interactions. Cooperativity [10,11] in an
interconnected network of CH· · ·p interactions has
been earlier noted for acetylenic systems [11] and it is
believed that if a unit behaves both as donor and
acceptor in the CH· · ·p interaction, the net stabiliz-
ation is more than the sum of the isolated interactions.
In the context of the observations regarding
multiple CH· · ·p interactions, it is noteworthy that
anthracene and pyrene show different packing beha-
vior in their crystal structures. Anthracene shows a
‘herringbone-structure’ while pyrene packs in the
‘sandwich–herringbone’ arrangement with strong co-
facial interaction [3]. The molecules 1 and 2 having
twisted geometries, although having differently
Fig. 6 clearly shows p units involved as both as donor
and acceptor in the interconnected edge-to-face inter-
actions. The pyridyl ring that is an acceptor in the
interaction ‘e’ is a donor in interaction ‘f’. Similarly, the
ring unit ‘Ring 5B’ (See Table 2) that is the acceptor in
interaction ‘f’ is a donor in interaction ‘g’.
The orthographic projections (top and side views)
again shed light on the geometry of the interactions.
Fig. 7a and b shows C23H23 making close contacts
with one side of the p surface (C15 and C14) of the
proximal pyridyl ring (interaction ‘e’). The CH bond
is directed towards C15 (The angle C23H23· · ·C15 is
172.48). In turn, C15H15 interacts with pyrenyl p
carbons in interaction ‘g’ (Fig. 8a and b). Thus C15 is
strongly involved as a donor and acceptor of the
CH· · ·p interaction. Fig. 8 provides further evidence
in this regard. C15H15 makes close contact with C27
and is directed towards the adjacent C19 in interaction
‘g’ (the angle C15H15· · ·C19 being 170.9). C19 acts

A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
111
architecture together. Thus, the crystal structure of
2 can be said to have a ‘bi-directional twin ladder’
arrangement. Geometrical considerations would
necessitate the presence of bi-directional ladders
if an orthogonal system comprising two essentially
planar components packs itself. The periodicity of
the ‘ladder-like’ arrangement is determined by the
‘twist’ angle between the two planes and the
nature of interactions between the planes.
A multi-directional ladder arrangement is observed
with 1 as well. However, as the shape and nature of
the polyaromatic substituent differs, significant differ-
ences from 2 are indeed observed. Fig. 12 shows the
‘step-ladder’ arrangement where the pyridyl–pyridyl
˚
overlap (contact distance of 3.9 A) forms the rung of
the ladder. Also seen in the figure are interactions
where a part of the anthracene moiety overlaps with a
different part of another anthracene unit (contact
˚
distance of 3.6 A) giving a step-ladder of a different
directionality. This is unlike the ‘sandwich dimer’
type arrangement for overlap involving two pyrene
units that is observed in 2. The ladder like arrange-
ment in 1 is helical in nature.
Fig. 12. Multi-directional ladder-like architecture for 1. A partial
overlap of two anthracene units is shown leading to a ‘step-ladder
arrangement’. Also illustrated is the overlap of two pyridyl rings
leading to a ladder of a different directionality.
shaped polyaromatic hydrocarbon moieties, show
similar patterns of edge-to-face CH· · ·p interactions.
The crystal structures show interesting supra-
molecular architectures. Fig. 10a shows a ladder
type arrangement in the crystal structure of 2,
where each rung of the ladder happens to be a
‘pyrene sandwich dimer’! The twisted molecular
conformation leads to such an arrangement. Face-
to-face (p· · ·p) interaction between two pyrene
4. Concluding remarks
We have shown the crystal structures of two
‘twisted’ or ‘orthogonal’ molecular systems, 1 and 2.
Semi-empirical AM1 calculations have shown the
twisted molecular conformation is intrinsic to the
systems. Interconnected networks of cooperative
CH· · ·p interactions exist in the crystal structures of
these molecules. Simple-minded geometrical con-
straints can be used to rationalize the presence of
ladder-like arrangements in each of the crystal
structure of the two twisted molecules. Thus such
orthogonal or twisted aromatic molecules may lead to
the development of novel ladder like motifs with
varying periodicity. A combination of edge-to-face
and face-to-face interactions in each of the two cases
helps stabilize the multi-directional ladder-like supra-
molecular [32,33] scaffolds. Efforts are now under-
way to utilize these orthogonal systems for the
preparation of metal-mediated crystalline coordi-
nation polymers.
˚
moieties (face to face distance, ,3.9 A) is the
‘glue’ that helps make the ‘sandwich’ rung while
the edge-to-face CH· · ·p interactions hold the
architecture together. Interestingly, there is not
just one type of ladder, but two. Fig. 11 reveals
another ladder like arrangement in 2, where two
pairs of pyridyl rings overlapping each other
constitute the rung of the ladder (distance between
˚
the ring centroids, 3.7 A). In each of these
overlaps, a central pyridyl ring of the terpyridine
unit interacts with a peripheral pyridyl ring of
another terpyridine unit. Here, again it may be
emphasized that the CH· · ·p interactions hold the

112
A. Gulyani et al. / Journal of Molecular Structure 616 (2002) 103–112
[18] G.R. Desiraju, Angew. Chem., Int. Ed. 34 (1995) 2311.
Acknowledgments
[19] S.S. Mandal, R. Kadirvelraj, T.N. Guru Rao, S. Bhattacharya,
J. Chem. Soc., Chem. Commun. (1996) 2725.
We would like to acknowledge Professor C.N.R.
Rao and Professor K. Venkatesan for helpful
discussions.
[20] S. Bhattacharya, P. Dastidar, T.N. Guru Rao, Chem. Mater. 6
(1994) 531.
[21] S.N.G. Acharya, R.S. Gopalan, G.U. Kulkarni, K. Venkatesan,
S. Bhattacharya, J. Chem. Soc., Chem. Commun. (2000) 1351.
[22] For a recent example where orthogonal anthracene based
templates have been used for structural design and host-guest
adducts using hydrogen bonding, see:Y. Aoyama, K. Endo, T.
Anzai, Y. Yamaguchi, T. Sawaki, K. Kobayashi, N. Kanehisa,
H. Hashimoto, Y. Kai, H. Masuda, J. Am. Chem. Soc. 118
(1996) 5562 and references therein.
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