Characterization of molecular complexes of 1,4-naphthoquinone derivatives

Article abstract of DOI:10.1007/s10870-011-0024-8

The structures of sulphur atom tethered quinone containing flexible carboxylic acid (3-methyl-1,4-dioxo-1,4-dihydronaphthalen-2-ylsulfanyl)acetic acid (1) and its molecular complex with 4,4′-bipyridine (3) are determined. The compound 1 crystallizes in P-1 (triclinic, a = 7.5378(6) A, b = 7.6413(7) A, c = 10.3101(9) A; α = 89.779 (7)°, β = 81.042 (5)°, γ = 89.101(7)°) and the molecular complex 3 crystallises in P2(1)/n (monoclinic, a = 9.3383(7) A, b = 3.970(3) A, c = 42.130(3) A, β = 91.056(5)°) space groups, respectively. The R ₂ ² (8) type hydrogen bonding between dicarboxylic acid groups present in the parent compound 1 is lost on interaction with 4, 4′-bipyridine; in the molecular complex 3 R ₂ ² (7) type of O???H-C and O-H???N interactions are present between the pyridine rings and carboxylic acid groups. The molecular complex (4) derived from 3-carboxymethylsulfanyl-1,4- dihydroxynaphthalen-2-yl-sulfanyl) acetic acid (2) with triphenylphosphine oxide in 1:2 ratio, crystallises in C2/c space group have monoclinic, a = 26.0494(13) A, b = 10.5402(5) A, c = 17.1023(8) A, β = 108.719 (5)°). The triphenylphosphine oxide molecules are preferentially held by O-H???O interactions between carboxylic acid and P=O bond.

Full text of DOI:10.1007/s10870-011-0024-8

J Chem Crystallogr (2011) 41:952–958
DOI 10.1007/s10870-011-0024-8
ORIGINAL PAPER
Characterization of Molecular Complexes of 1,4-Naphthoquinone
Derivatives
W. Marjit Singh Jubaraj B. Baruah
•
Received: 28 June 2010 / Accepted: 3 February 2011 / Published online: 18 February 2011
Ó Springer Science+Business Media, LLC 2011
Abstract The structures of sulphur atom tethered quinone
containing flexible carboxylic acid (3-methyl-1,4-dioxo-1,
orientations [1–10] and varieties in coordination chemistry
[11–23]. The organic motifs possessing supramolecular
binding abilities have attracted extra attention to under-
stand their properties in confined medium [24–30]. In this
regard, quinone unit is one such motif and quinones con-
taining natural products are associated with anti-tumor,
antibacterial, anti-malarial, and anti-fungal activities [31].
Quinones accept electrons to form radical anion or dianions
which are useful in biological activity [32–38]. Among the
quinones, 1,4-naphthoquinone derivatives are studied in
details [38]. Oxygen atom tethered dicarboxylic acids are
common [21] in contrast to sulphur tethered carboxylic
acid [3, 22]. Thus, it is worthwhile to study the structural
features of sulphur atom tethered carboxylic acid deriva-
tives of 1,4-naphthoquinones and their molecular com-
plexes, to understand the role of sulphur atom in their self
assembling. In this article we describe synthesis and
characterization of molecular complexes of quinone con-
taining carboxylic acids shown in Fig. 1.
4
-dihydronaphthalen-2-ylsulfanyl)acetic acid (1) and its molec-
0
ular complex with 4,4 -bipyridine (3) are determined. The
˚
compound 1 crystallizes in P-1 (triclinic, a = 7.5378(6) A,
˚
˚
b = 7.6413(7) A, c = 10.3101(9) A; a = 89.779 (7)°, b =
1.042 (5)°, c = 89.101(7)°) and the molecular complex 3
8
˚
crystallises in P2(1)/n (monoclinic, a = 9.3383(7) A, b =
˚
˚
3
.970(3) A, c = 42.130(3) A, b = 91.056(5)°) space groups,
2
respectively. The R (8) type hydrogen bonding between
2
dicarboxylic acid groups present in the parent compound 1 is
0
lost on interaction with 4, 4 -bipyridine; in the molecular
2
complex 3 R (7) type of OꢀꢀꢀH–C and O–HꢀꢀꢀN interactions are
2
present between the pyridine rings and carboxylic acid groups.
The molecular complex (4) derived from 3-carboxymethylsulfa-
nyl-1,4-dihydroxynaphthalen-2-yl-sulfanyl) acetic acid (2) with
triphenylphosphine oxide in 1:2 ratio, crystallises in C2/c
˚
space group have monoclinic, a = 26.0494(13) A, b = 10.
˚
˚
5
402(5) A, c = 17.1023(8) A, b = 108.719 (5)°). The tri-
phenylphosphine oxide molecules are preferentially held
by O–HꢀꢀꢀO interactions between carboxylic acid and P=O bond.
Experimental
Keywords 1,4-Naphthoquinone derivatives ꢀ Molecular
complexes ꢀ Crystal structure ꢀ Electrochemistry
The X-ray data were collected at 296 K with Mo-Ka
radiation (k = 0.71073 A) using a Bruker Nonius SMART
˚
CCD diffractometer equipped with graphite monochroma-
tor. The SMART software was used for data collection and
also for indexing the reflections and determining the unit
cell parameters; the collected data were integrated using
SAINT software [40]. The structures were solved by direct
methods and refined by full matrix least-squares calcula-
tions using SHELXTL software [40]. All non-H atoms
Introduction
The host–guest chemistry of flexible carboxylic acids finds
importance due to enhancements in number of possible
W. Marjit Singh ꢀ J. B. Baruah (&)
2
were refined in the anisotropic approximation against F of
Department of Chemistry, Indian Institute of Technology
Guwahati, Guwahati 781 039, Assam, India
e-mail: juba@iitg.ernet.in
all reflections. The H-atoms, except those attached to O
were placed at their calculated positions and refined in the
1
23

J Chem Crystallogr (2011) 41:952–958
953
O
O
O
O
O
have CCDC numbers 743768–743770. The crystal data and
refinement parameters are listed in Table 1.
S
S
S
OH
OH
OH
O
O
Synthesis of (3-methyl-1,4-dioxo-1,
1
2
4-dohydronaphthalen-2-yl-sulfanyl)acetic acid (1)
N
N
O
O
O
O
O
O
To a solution of 2-methyl 1,4-naphthoquinone (0.86 g,
5 mmol) in methanol (15 ml), thioglycolic acid (0.46 g,
S
OH
S
S
P
OH
O
OH
5
mmol) was added and stirred for 2 h under ambient
O
condition. The reaction mixture was then left undisturbed
3
4
for 12 h. The desired product 1 crystallized out as yellow
needles and it was collected by filtration. Isolated yield:
-1
Fig. 1 1,4-Naphthoquinone derivatives and their molecular
complexes
7
1% (KBr, cm ): 3445 (bw), 2925 (w), 1716 (s), 1662 (s),
589 (m), 1551 (m), 1424 (m), 1375 (w), 1318 (s), 1287
1
(
s), 1212 (m), 1177 (m), 1113 (w), 1026 (w), 946 (m), 840
1
(w), 702 (s). H NMR (CDCl
isotropic approximation; those attached to a heteroatom
were located in the difference Fourier maps, and refined
with isotropic displacement coefficients. The compounds
, 400 MHz): 8.08 (dd,
3
J = 7.2, 3.2 Hz, 2H), 7.54 (dd, J = 7.2, 3.2 Hz, 2H), 3.98
1
(s, 2H), 2.37 (s, 3H). C NMR (CDCl
3
, 100 MHz):
3
Table 1 The crystallographic parameters of 1, 3, and 4
Compound no.
Formulae
1
3
4
C
13 10
H O
4
S
C
18
H14NOS
25 15 4
C H O PS
Mol. wt.
262.27
340.36
442.40
Crystal system
Space group
Triclinic
P-1
Monoclinic
P2(1)/n
9.3383(7)
3.970(3)
42.130(3)
90.00
Monoclinic
C2/c
˚
a (A)
7.5378(6)
7.6413(7)
26.0494(13)
10.5402(5)
17.1023(8)
90.00
˚
b (A)
˚
c (A)
10.3101(9)
89.779(7)
81.041(5)
89.101(7)
586.53(9)
2
a/°
b/°
c/°
91.056(5)
90.00
108.719(5)
90.00
3
˚
V (A )
1561.6(2)
4
4447.3(4)
8
Z
-3
Density/Mg m
1.485
1.448
1.321
-1
Abs. Coeff./mm
Abs. correction
F(000)
0.279
0.230
0.246
None
None
None
272
708
1824
Total no. of reflections
Reflections, I 2r(I)
Max. 2h/°
3559
13891
15860
1635
3549
3277
47.00
54.94
46.98
Ranges (h, k, l)
-5 B h B 8
-11 B h B 12
-5 B k B 3
-54 B l B 53
99.7
-28 B h B 29
-11 B k B 11
-19 B l B 19
99.6
-
-
8 B k B 8
11 B l B 11
Completeness to 2h (%)
Data/Restraints/Parameters
Goof (F2)
94.1
1635/0/164
1.047
3549/0/219
1.124
3277/0/281
1.048
R indices [I [ 2r(I)]
R indices (all data)
wR indices
0.0304
0.0337
0.0855
0.0819
0.0468
0.1495
0.0700
0.2186
0.1203
123

9
54
J Chem Crystallogr (2011) 41:952–958
1
1
82.05, 181.09, 170.96, 146.38, 145.26, 133.78, 133.49,
32.82, 131.97, 126.75, 126.52, 35.57, 15.09.
triphenylphosphineoxide (0.083 g, 3 mmol) was dissolved
in methanol (15 ml) and the solution was boiled for half an
hour. The resulting solution was left undisturbed for 24 h.
Red plates like crystals were formed. The crystals were
collected by filtration. Isolated yield: 61%, IR (KBr,
Synthesis of (3-carboxymethylsufanyl-1,
-dihydronaphthalen-2-yl-sulfanyl)acetic acid (2)
4
-
1
cm ): 3431 (bs), 2923 (w), 1732 (s), 1651 (s), 1588 (w),
1495 (w), 1436 (m), 1384 (s), 1315 (m), 1274 (m), 1149
To a well stirred solution of 1,4-naphthoquinone (1.26 g,
mmol) in ethanol (25 ml) a solution of thioglycolic acid
1.47 g, 16 mmol) was added and stirred for 6 h under
8
(s), 1138 (s), 1120 (s), 1089 (m), 801 (w), 752 (m), 725 (s),
1
690 (s), 542 (s). H NMR (DMSO-d , 400 MHz): 8.04
(
6
aerial condition. To this reaction mixture water (10 ml)
was added and then left undisturbed for 24 h. The com-
pound 2 was precipitated from the solution, isolated as red
(d, J = 3.2 Hz, 2H), 7.86 (d, J = 6.8 Hz, 2H), 7.65 (m,
1
12H), 7.56 (m, 6H), 7.48 (m, 12H), 4.06 (s, 4H). C NMR
3
(DMSO-d , 100 MHz): 170.9, 150.8, 144.3, 134.1, 133.8,
6
-
1
31
132.7, 126.9, 121.7, 35.7. PNMR (DMSO-d ): -25.69.
solid by filtration. Isolated yield: 61%, IR (KBr, cm ):
434 (bw), 2921 (w), 1714 (s), 1659 (s), 1590 (m), 1488
6
3
(
(
w), 1467 (s), 1346 (m), 1281 (s), 1176 (m), 1139 (s), 869
1
m), 811 (w), 702 (s). H NMR (DMSO-d , 400 MHz):
Results and Discussion
6
8
2
1
.03 (dd, J = 6.0, 2.4 Hz, 2H), 7.71 (dd, J = 5.6, 2.4 Hz,
1
H), 4.02 (s, 4H). C NMR (DMSO-d , 100 MHz): 178.9,
3
The compound (3-methyl-1,4-dioxo-1,4-dihydro-naphtha-
6
70.6, 145.9, 134.7, 133.0, 127.2, 36.3.
len-2-yl-sulfanyl)acetic acid (1) was prepared by reacting
2-methyl-1,4-naphthoquinone with thioglycolic acid in
Synthesis of Molecular Complex (3)
O
O
O
HO
A solution of (3-methyl 1,4-dioxo-1,4-dihydro-naphthalen-
S
O CH3OH
RT
OH
(1)
+
2
4
-yl-sulfanyl)acetic acid (1) (0.13 g, 0.5 mmol) and 4,
0
CH3
CH3
SH
-bipyridine (0.076 g, 0.5 mmol) in 10 ml of metha-
O
O
nol:chloroform (1:1) was kept undisturbed for 24 h. Red
1
crystals of 3 were formed, the crystals were collected by
-
filtration. Isolated yield: 84%, IR (KBr, cm ): 3444 (bw),
1
methanol as shown in Eq. 1. It crystallised from methanol
as yellow blocks in P-1 space group. The structure of the
complex is shown in Fig. 2a. In solid state the carboxylic
acid group of the molecule is non planar with respect to the
quinone ring (Fig. 2a) and the molecules of the acid 1 self-
2
1
922 (w), 1698 (s), 1661 (s), 1588 (s), 1564 (m), 1508 (m),
422 (m), 1384 (w), 1325 (w), 1283 (s), 1265 (m), 1180
(
1
w), 1140 (w), 1035 (w), 956 (w), 840 (s), 730 (m), 710 (s).
H NMR (DMSO-d , 400 MHz): 8.63 (d, J = 4.4 Hz, 4H),
6
assembles through O1–H1ꢀꢀꢀO2 interactions to form
7
.93 (dd, J = 7.2, 3.4 Hz, 2H), 7.65 (dd, J = 5.6, 2.4 Hz,
H). 7.54 (d, J = 4.4 Hz, 4H), 3.86 (s, 2H), 2.24 (s, 3H).
2
2
dimeric structures having [R (8)] type hydrogen bonds
2
1
3
[
39]. The oxygen atom O2 of the carboxylic acid group is
C NMR (DMSO-d , 100 MHz): 178.9, 170.6, 146.2,
6
involved in hydrogen bonding such as intermolecular
C–HꢀꢀꢀO interactions between hydrogen atoms of C8 and
intramolecular H-bond interaction with one of the oxygen
atom (O3) of 1,4-naphthoquinone. This leads to trifurcated
type of hydrogen bonding. Thus, the presence of relatively
strong O–HꢀꢀꢀO interactions and weak C–HꢀꢀꢀO interactions
between the carboxylic acids units assembles the molecules
1
33.9, 132.9, 132.2, 132.1, 128.9, 128.8, 127.0, 36.4, 16.8.
Synthesis of Molecular Complex (4)
The (3-carboxymethylsufanyl-1,4-dihydro-naphthalen-2-yl-
sulfanyl)acetic acid (2) (0.104 g, 0.3 mmol) together with
Fig. 2 a Crystal structure of
compound 1 (ORTEP drawn
with 50% thermal ellipsoid)
and b Self-assembly of 1
1
23

J Chem Crystallogr (2011) 41:952–958
955
to form an infinite one dimensional chain running parallel
to the crystallographic c-axis, as shown in Fig. 2b. The
carbonyl groups of quinones are not associated with
hydrogen bonds.
molecular complex 4 with triphenylphosphine oxide. The
1
composition is reflected in H NMR spectra. Further to this
the carbonyl frequency of dicarboxylic acid appearing at
-
1,714 cm shifts to higher frequency side and appears at
1
-
1
The (3-methyl-1,4-dioxo-1,4-dihydro-naphthalen-2-ylsul-
fanyl)-acetic acid 1 forms 1:1 molecular complex (3)
1,732 cm in 4. The molecular complex crystallizes in
centrosymmetric C2/c space group. Each end of the car-
boxylic acid binds to one molecule of triphenylphosphine
oxide. The two carboxylic acid groups are disposed at same
plane with respect to the 1,4-naphthoquinone rings and
these molecules adopt planar sheet like structure. Between
these planar sheets triphenylphosphine oxide molecules are
held. In this molecular complex two molecules of tri-
phenylphosphine oxide get anchored at the distal end of
two carboxylic acid by O1ꢀꢀꢀH3A–O3 interaction. The P=O
0
with 4,4 -bipyridine; the molecular complex crystallizes as
red crystals. In this molecular complex two molecules of (3-
methyl-1,4-dioxo-1,4-dihydro-naphthalen-2-ylsulfanyl)-acetic
0
acid 1 gets anchored to one 4,4 -bipyridine molecule. The
1
composition of the co-crystal is reflected in the H NMR
1
integration of 3. In H NMR presumably, the OH peak
exchanges with water present in deuterated solvent or may
occur above offset region (due to fast exchange) which we
could not show exactly. The parent carboxylic acid has car-
bond is involved in weak C24–HꢀꢀꢀO1 interaction. These
-
1
2
boxylic group stretching at 1,716 cm , it shifts towards
two interactions makes R (6) type of cyclic hydrogen
2
lower side in the molecular complex and appears at
bond. The crystal packing of the molecular complex 4 is
governed by weak C–HꢀꢀꢀO interactions (Table 3). It is
important to note that the O–HꢀꢀꢀO interactions observed in
the parent compound is lost upon molecular complex for-
mation. The orientation of the carboxylic acid is controlled
by the orientation of lone pairs of electrons on the sulphur
atom. The molecules in lattice opt for a thermodynamically
stable structure by accommodation of bulky triphenyl-
phosphine oxide molecules in the lattice. The packing
effect makes the orientation of C19–H and C24–H to
project in space such a way that they are in vicinity of the
oxygen atoms to have C–HꢀꢀꢀO interactions (Fig. 4b). Thus,
even the C–HꢀꢀꢀO interactions are of lower hierarchy in
terms of difference in bond strength with O–HꢀꢀꢀO inter-
actions, former type of interactions predominates in the
lattice (C19–H19ꢀꢀꢀO4, C24–H24BꢀꢀꢀO2, and C24–
H24AꢀꢀꢀO1) as shown in Fig. 4. In has two dimensional
infinitely extended hydrogen bonded networks in the
crystal lattice. The hydrogen atoms of quinone motif are
involved in C–HꢀꢀꢀO interactions but the hydrogen atoms of
the triphenylphosphine oxide are not involved in weak
-1
1,698 cm . The carbonyl frequency of the naphthoquinone
ring is not affected significantly. The molecular complex is
stabilized by O2ꢀꢀꢀH14–C14 and O1–H1ꢀꢀꢀN1 interactions
2
which has R (7) type hydrogen bond pattern [39]. Recently
2
different types of interaction schemes between aromatic
amine and carboxylic acid functional group are demonstrated
2
[9]. The R (7) type of interaction observed here is shown to
2
be a stable interaction over the other possible interactions.
The bipyridine molecules bridges two molecules of carbox-
ylic acids (1) via cyclic hydrogen bond interactions. These
synthons are interconnected by C–HꢀꢀꢀO interactions
(Table 2) of carbonyl oxygen of naphthoquinone with C18–H
bond of the bipyridine. The other carbonyl oxygen is also
weakly bound to C8–H of another 1,4-naphthoquinone unit.
Some important donor acceptor bond distances and bond
angles contributing to the H-bond interactions are O1ꢀꢀꢀN1,
˚
˚
2
.64 A and H14ꢀꢀꢀO2, 2.58 A; \O1–H1ꢀꢀꢀN1, 175.8° and
\
C14–H14ꢀꢀꢀO2, 128.5°, respectively (Fig. 3b). There are no
pꢀꢀꢀp interactions present in the crystal lattice; as well as
sulphur atoms do not participate in hydrogen bond
interactions.
3
1
interactions. P NMR spectrum of the 4 shows one singlet
at -25.69 ppm in DMSO-d6.
The (3-carboxymethylsulfanyl-1,4-dihydro-naphthalen-
2
1
-yl-sulfanyl)acetic acid 2 was prepared from reaction of
,4-naphthoquinone with thioglycolic acid as described
The 1,4-naphthoquinone has two one electron redox
couples [41] which arises from two stepwise one electron
redox processes to form anion radical and dianion. The
cyclic voltamogram of the compound 1 has also two one
electron redox couples. The reduction peak at -0.550 V is
associated with a sharp oxidation counterpart at -0.200 V
with i /i 1.08 and DEp 0.350 V which is attributed to the
earlier [21]. The (3-carboxymethylsulfanyl 1,4-dioxo-1,
-dihydro-naphthalen-2-yl-sulfanyl)-acetic acid forms 1:2
4
Table 2 The hydrogen bond parameters for 3
p
c
D - H (A) HꢀꢀꢀA ( A˚ ) DꢀꢀꢀA ( A˚ ) \D–HꢀꢀꢀA (°)
˚
D–HꢀꢀꢀA
formation of an anion radical. This process is followed by
another quasi-reversible redox couple, the reduction
peak at -0.852 V is also associated with sharp oxidation
counterpart (Fig. 5a) at -0.790 V with i /i 0.99 and DEp
O1–H1ꢀꢀꢀN1
0.819
1.821
2.581
2.419
2.713
2.423
2.639
3.243
3.313
3.630
3.371
175.75
124.53
161.55
169.5
C14–H14ꢀꢀꢀO2 0.930
C15–H15ꢀꢀꢀO2 0.929
p
c
0.062 V. The second couple is attributed to the formation
C8–H8ꢀꢀꢀO4
0.930
of dianion from the anion radical. The cyclic voltamogram
C2–H2BꢀꢀꢀO3 0.970
165.30
of the corresponding molecular complex 3 has similar
123

9
56
J Chem Crystallogr (2011) 41:952–958
Fig. 3 a Structure of molecular
complex 3 (ORTEP drawn with
N
O
O
O
5
0% thermal ellipsoids). b Two
dimensional network of
S
OH
molecular complex 3
CH3
N
3
Table 3 The hydrogen bond parameters for 4
D–HꢀꢀꢀA
˚
D–H (A)
HꢀꢀꢀA ( A˚ )
DꢀꢀꢀA ( A˚ )
\D–HꢀꢀꢀA (°)
O3–H3AꢀꢀꢀO1 [-x ? 1/2, -y ? 3/2, -z]
C24–H24AꢀꢀꢀO1
0.820
0.969
0.970
0.930
1.721
2.530
2.461
2.559
2.530
3.142
3.357
3.351
169.14
123.40
153.46
143.32
C24–H24BꢀꢀꢀO2
C19–H19ꢀꢀꢀO4
two one electron redox couples. The reduction peak at
0.507 V is associated with its oxidation counterpart at
.084 V to show a quasi-reversible couple is attributed to
reduction potential shifted towards the positive potential
over 0.043 V. This positive shift in reduction potential
[42, 43] is attributed decrease in acidity in the molecular
complex 3.
-
0
anion radical formation. This process is followed by a
reversible redox couple with reduction peak at -0.730 V
and its oxidation peak (Fig. 5b) at -0.660 V. It has ip/ic
In conclusion, structural features of molecular com-
plexes of 1,4-naphthoquinone derivatives with intervening
sulphur atom attached to flexible carboxylic acid reveal
that the sulphur atoms do not participate in weak
0.98 and DEp 0.070 V which is attributed to dianion for-
mation. In the case of the molecular complex 3, the
1
23

J Chem Crystallogr (2011) 41:952–958
957
Fig. 4 a Structure of molecular
complex 4 (ORTEP drawn with
O
O
5
0% thermal ellipsoids). b Two
O
O
OH
OH
dimensional network of
molecular complex 4 through
O–HꢀꢀꢀO and C–HꢀꢀꢀO
interactions
S
S
O P
4
123

9
58
J Chem Crystallogr (2011) 41:952–958
Fig. 5 a Cyclic voltamogram
of compound 1 at scan rate
5
of molecular complex 3 at scan
0 mV/s. b Cyclic voltamogram
-4
rate 50 mV/s (10 M in
acetonitrile with tetrabutyl
ammonium perchlorate as
supporting electrolyte)
interactions but provides the directional effect to the flex-
ible carbon atom to which carboxylic acid groups are
attached.
17. Delgado FS, Ruiz-Perez C, Sanchiz J, Lloret F, Julve M (2006)
Cryst Eng Comm 8:530
1
8. Pasan J, Sanchiz J, Ruiz-Perez C, Lloret F, Julve M (2005) Inorg
Chem 44:7794
9. Lightfoot P, Snedden A (1999) JCS Dalton Trans 3549
1
Acknowledgments The authors thank Council of Scientific and
Industrial Research, New-Delhi, India for financial assistance.
20. Rodriquez-Martin Y, Sanchiz J, Ruiz-Perez C, Lloret F, Julve M
(2002) Cryst Eng Comm 4:631
2
2
2
1. Mondal P, Karmakar A, Singh WM, Baruah JB (2008) Cryst Eng
Comm 10:1550
2. Karmakar A, Baruah JB, Shankar RB (2009) Cryst Eng Comm
References
1
1:832
3. Yaghi OM, O’keefe M, Ockwig NW, Chae HK, Eddaoudi M,
Kim J (2003) Nature 423:705
4. Heller A, Feldman B (2008) Chem Rev 108:2482
5. Aubart KM, Heathcock CH (1999) J Org Chem 64:16
6. Huang Y, Zhang J, Pettus TRR (2005) Org Lett 7:26
7. Liu JK (2006) Chem Rev 106:2209
8. Tandon VK, Maurya HK, Yadav DB, Tripathi A, Kumar M,
Shukla PK (2006) Bioorg Med Chem Lett 16:5883
9. Benites J, Rojo L, Valderrama JA, Taper H, Calderon PB (2008)
Eur J Med Chem 43:1813
0. Eyong KO, Kumar PS, Kuete V, Folefoc GN, Nkengfack EA,
Baskaran S (2008) Bioorg Med Chem Lett 18:5387
1. O’Brien PJ (1991) Chem Biol Interact 80:1
1
2
. Du M, Zhang Z-H, Zhao X-J, Cai H (2006) Cryst Growth Des
:114
. Beatty AM, Schneider CM, Simpson AE, Zaher JL (2002) Cryst
Eng Comm 4:282
6
2
2
2
2
2
3
4
. Du M, Zhang Z-H, Zhao X-J (2006) Cryst Growth Des 6:335
. Pedireddi VR, Chaterjee S, Ranganthan A, Rao CNR (1998)
Tetrahedron 54:9457
5
6
7
8
9
. Xiao J, Yang M, Lauher JW, Fowler FW (2000) Angew Chem Int
Ed 39:2132
. Aaker o¨ y CB, Beatty AM, Helfrich BA, Niuwenhuyzen M (2003)
Cryst Growth Des 3:159
. Vishweshwar P, Nangia A, Lynch VM (2003) Cryst Growth Des
2
3
3
3
3
3
:783
2. Tucker JHR, Collinson SR (2002) Chem Soc Rev 31:147
3. Lehn JM (1995) Supramolecular chemistry, concepts and per-
spectives. VCH, Weinheim
. Braga D, Maini L, Sanctis G, Rubini K, Grepioni F, Chierotti
MR, Gobetto R (2003) Chem Eur J 9:5538
. Singh D, Bhattacharyya P, Baruah JB (2010) Crystal Growth Des
3
3
4. Katz E, Baron R, Willner I (2005) J Am Chem Soc 127:4060
5. Hogan CF, Hutchison JA, Ghiggino KP, Langford SJ, Latter JM,
Lau VL, Murali V (2005) Supramol Chem 17:513
6. Lee J-Y, Park S-M (1998) J Phys Chem B 102:9940
7. Cooke G, Sindelar V, Rotello VM (2003) Chem Commun 752
8. Singh WM, Baruah JB (2009) J Mol Struct 931:82
9. Bernstein J, Davis RE, Shimoni L, Chang NL (1995) Angew
Chem Int Ed 34:1555
1
0:348
1
1
1
0. Barooah N, Sarma RJ, Baruah JB (2006) Cryst Eng Comm 8:608
1. Erxleben A (2003) Coord Chem Rev 246:203
2. Fletchera AJ, Thomasa KM, Rosseinsky MJ (2005) J Solid State
Chem 178:2491
3
3
3
3
1
1
1
3. Uemura K, Matsuda R, Kitagawa S (2005) J Solid State Chem
1
78:2420
4. Delgado FS, Sanchiz J, Ruiz-Perez C, Lloret F, Julve M (2004)
Crys Eng Comm 6:73
4
4
4
4
0. Sheldrick GM (2008) Acta Cryst A64:112
1. Bauscher M, Maentele W (1992) J Phys Chem 96:11101
2. Miller GY, Ouimet L, Smith TDK (2000) J Org Chem 65:8831
3. Amatore C, Capobianco G, Farnia G, Sandona G, Saveant J-M
5. Delgado FS, Hernandez-Molina M, Sanchiz J, Ruiz-Perez C,
Rodriguez-Martin Y, Lopez T, Lloret F, Julve M (2004) Cryst
Eng Comm 6:929
(
1985) J Am Chem Soc 107:1815
1
6. GildeMuro I, Lezama L, Insausti M, Rojo T (2004) Polyhedron
2
3:859
1
23