Charge-assisted complexation of anions of different dimensionality by benzimidazole-based receptors bearing -OH functionality

Article abstract of DOI:10.1021/cg300496t

Two benzimidazole-based receptors (L¹ and L²) bearing -OH functionality form crystalline salts with different organic and inorganic acids viz. [L¹H⁺][Cl^-] (1), [L ¹H⁺][NO₃^-] (2), [L¹H ⁺][OAc^-] (3), [L¹H⁺][DNB ^-]DMF (4), [L¹H⁺][H₂PO ₄^-] (5), [L²H⁺][OAc^-]AcOH (6), [L²H⁺][DNB^-] (7), and [L ²H⁺][HSO₄^-]H₂O (8) where the shape of the counteranion drives the solid structure from a one-dimensional polymeric chain to a three-dimensional structure. Structural analyses show that the anion binding in all eight complexes is attributable entirely to NH ⁺anion, NHanion, OHanion, and multiple CHanion hydrogen bonding interactions. In the solid structure the planar nitrate anion forms a cyclic structure with receptor L¹, whereas the acetate anion with the same receptor leads to a molecular barrel type structure. Again the tetrahedral dihydrogen phosphate anion forms a polymeric interanionic chain structure with L¹, and the other tetrahedral hydrogen sulfate anion forms hydrogen sulfate-(water)₂-hydrogen sulfate adducts with charged L².

Full text of DOI:10.1021/cg300496t

Article
pubs.acs.org/crystal
Charge-Assisted Complexation of Anions of Different Dimensionality
by Benzimidazole-Based Receptors Bearing -OH Functionality
Abhijit Gogoi and Gopal Das*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India
S
* Supporting Information
ABSTRACT: Two benzimidazole-based receptors (L1 and
L2) bearing -OH functionality form crystalline salts with
different organic and inorganic acids viz. [L1H+][Cl−] (1),
[L1H+][NO3 ] (2), [L1H+][OAc−] (3), [L1H+][DNB−]·DMF
−
−
(4), [L1H+][H2PO4 ] (5), [L2H+][OAc−]·AcOH (6), [L2H+]-
−
[DNB−] (7), and [L2H+][HSO4 ]·H2O (8) where the shape
of the counteranion drives the solid structure from a one-
dimensional polymeric chain to a three-dimensional structure.
Structural analyses show that the anion binding in all eight
complexes is attributable entirely to NH+···anion, NH···anion,
OH···anion, and multiple CH···anion hydrogen bonding
interactions. In the solid structure the planar nitrate anion
forms a cyclic structure with receptor L1, whereas the acetate anion with the same receptor leads to a molecular barrel type
structure. Again the tetrahedral dihydrogen phosphate anion forms a polymeric interanionic chain structure with L1, and the
other tetrahedral hydrogen sulfate anion forms hydrogen sulfate−(water)2−hydrogen sulfate adducts with charged L2.
With respect to the above, we have synthesized two
benzimidazole-based receptors (Scheme 1) with hydroxyl
INTRODUCTION
■
Benzimidazole is typical nitrogen-containing fluorescent
heterocyclic molecule having biological importance, and due
to the amphoteric nature of the imidazole core it can function
as a selective and effective anion and/or cation and even neutral
organic molecules receptor. The imidazole functionality plays a
crucial role in many structures within the human body, notably
as histamine and histidine. The imidazole-containing amino
acid histidine is one of the most common functional groups
present at the active site of metalloprotein.1−4 It has also the
ability to hydrogen bond with drugs and proteins which
promote it to an important bioagent. In recent years many
benzimidazoles, imidazole, and related compounds have been
employed in colorimetric, fluorescent, and electrochemically
active anion sensors.5,6 Anions are ubiquitous and play a vital
role in many biological systems7−10 for the maintenance of life
and also affect the environment as anionic pollutants.
Consequently, synthetic receptors that bind anions are
increasingly being pursued for applications in waste remedia-
tion, sensing, and the treatment of disease.11 Compared to the
imidazole-containing receptors benzimidazole-containing re-
ceptors have the extra advantage of having a fluorogenic
antenna, and in order to get electrostatic assistance
benzimidazole nitrogen can be protonated which can then
interact more strongly with anions because of reinforced
interactions of hydrogen bonding and electrostatic interaction.
This is the easiest way to target and strongly bind the larger and
variably shaped, relatively diffuse weakly basic anions and to
tackle multiple solvation effects in protic media.12−14
Scheme 1. Molecular Structure of the Receptors (L1, L2)
functionality keeping in mind the significance of the -OH
group in nature and wish to study the effect of variable anion
dimensionality on their crystallization. Nature has already
shown the importance of phenolic -OH and -NH functionality
and constructed highly efficient and selective anion receptors
by using surprisingly few building blocks, the most important of
which are the amino acids serine, tryptophan, and arginine.15 In
nature orthophosphate in the active site of phosphate binding
protein (PBP) contains 11 hydrogen bonds comprising five
hydrogen bonds to backbone NH groups, four to serine or
threonine OH groups (Thr10, Ser38, Ser139, Thr141) and two
to the guanidinium group of Arg135.16 Similarly, a tryptophan
NH and a serine OH group are involved in sulfate binding
protein (SBP) along with five peptide NH groups (Ala173,
Asp11, Gly131, Gly132, Ser45).17−19 Again in the chloride
Received: April 12, 2012
Revised: June 7, 2012
Published: June 14, 2012
© 2012 American Chemical Society
4012
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
Table 1. Crystallographic Parameters of L1 and Complexes 1−4
L1
1
2
3
4
empirical formula
FW
C14H13N3O
239.27
C14H14ClN3O
275.73
C14H14N4O4
302.29
C16H17N3O3
299.33
C24H24N6O8
525.50
crystal system
space group
a (Å)
monoclinic
P21/c
triclinic
monoclinic
C2/c
monoclinic
P21/c
triclinic
P1
̅
P1
̅
10.9851(5)
9.1493(4)
12.1930(5)
90.00
7.6301(8)
8.0885(8)
10.9791(11)
83.499(6)
84.620(6)
85.996(5)
669.06(12)
2
35.231(4)
7.2754(8)
24.078(2)
90.00
12.7458(13)
8.4450(8)
15.3489(16)
90.00
9.7632(8)
11.2290(10)
12.5870(10)
84.504(6)
73.247(6)
71.892(6)
1255.88(19)
2
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
95.467(2)
90.00
111.710(5)
90.00
105.319(7)
90.00
1219.90(9)
4
5733.9(10)
16
1593.4(3)
4
Z
ρ(cal) (g/cm)
μ(Mo Kα) (mm−1
1.303
1.369
1.401
1.248
1.387
)
0.085
0.281
0.106
0.088
0.107
R1; wR2 (I > 2σ(I))
R1; wR2 (all)
0.0611; 0.179
0.0872; 0.193
0.354/−0.260
0.961
0.0393; 0.1584
0.0443; 0.1690
0.252/−0.352
0.961
0.0446; 0.0998
0.0955; 0.1203
0.172/−0.216
0.955
0.0460; 0.1178
0.1027; 0.1436
0.136/−0.136
0.942
0.0434; 0.1278
0.0551; 0.1456
0.188/−0.282
0.978
residual electron density (e/Å3)
goodness-of-fit
reflection collected
independent reflection
4892
2086
4907
3643
5788
2853
1806
4825
1940
5745
Table 2. Crystallographic Parameters Complexes 5−8
5
6
7
8
empirical formula
FW
C15H20N3O6P
369.31
C22H23N3O5
409.43
C25H19N5O7
501.45
C18H19N3O6S
405.43
crystal system
space group
a (Å)
monoclinic
P21/c
orthorhombic
Pbcn
triclinic
monoclinic
P21/c
P1
̅
11.1440(11)
19.3775(19)
8.1560(8)
90.00
20.5488(8)
8.7943(4)
22.5893(9)
90.00
7.5534(7)
12.6592(11)
24.360(2)
83.284(5)
86.424(6)
84.813(6)
2300.7(4)
4
11.9549(13)
12.3956(15)
16.3123(19)
90.00
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
94.871(5)
90.00
90.00
121.255(7)
90.00
90.00
1754.9(3)
4
4082.2(3)
8
2066.5(4)
4
Z
ρ(cal) (g/cm)
μ(Mo Kα) (mm−1
1.398
1.332
1.448
1.303
)
0.193
0.096
0.109
0.194
R1; wR2 (I > 2 σ(I))
R1; wR2 (all)
residual electron density (e/Å3)
goodness-of-fit
0.0482; 0.1699
0.0643; 0.1935
0.643/−0.369
0.906
0.0496; 0.1284
0.1046; 0.1505
0.216/−0.188
0.953
0.0550; 0.1188
0.1619; 0.1662
0.185/−0.203
0.960
0.0799; 0.1880
0.0991; 0.2149
0.850/−0.746
0.981
reflection collected
independent reflection
3902
5046
11692
5186
2864
2865
9031
4257
and ortho phosphoric acids were purchased from Merck and used as
received. Solvents were purified freshly following standard procedures
prior to use.
channel proteins of Escherichia coli and Salmonella Typhimu-
rium, chloride is held by four hydrogen bonds, two from main-
chain amide groups (Phe357 and Ile 3356) and two from side-
chain hydroxyl groups (Ser107 and Tyr 445).20 Our main
concerns have been to ascertain the complexation of anions in
the solid state and the consequences of weak hydrogen bonding
in the intermolecular network structure. Along with this one of
our focuses would be to explore the anion···π and C−H/anion
hydrogen bonds as they play a crucial role in nature.21
1
Physical Measurements. H NMR spectra were recorded on a
Varian FT-400 MHz instrument. The chemical shifts were recorded in
parts per million (ppm) on the scale using tetramethylsilane
[Si(CH3)4] as a reference, and 13C spectra were obtained at 100
MHz. The electrospray ionization mass spectrometry (ESI-MS)
spectra of all the complexes were recorded in a Waters Q-Tof
Premier liquid chromatography (LC)-MS system in acetonitrile. The
IR spectra were recorded on a Perkin-Elmer-Spectrum One FT-IR
spectrometer with KBr disks in the range 4000−450 cm−1. Powder X-
ray diffraction (PXRD) was recorded with a Bruker D2 phaser with
CuKα source (λ = 154 Å) on a glass surface of air-dried sample.
X-ray Structure Determination. The intensity data were
collected using a Bruker SMART APEXII CCD diffractometer,
equipped with a fine focus 1.75 kW sealed tube Mo−Kα radiation
EXPERIMENTAL SECTION
■
Materials and Methods. All reagents were obtained from
commercial sources and used as received. 2-Amino benzimidazole,
salicylaldehyde, 2-hydroxy naphthaldehyde, and 3,5-dinitrobenzoic
acid was purchased from Sigma-Aldrich and used as received. 37%
hydrochloric acid, acetic acid, nitric acid, concentrated sulfuric acid,
4013
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
(λ = 0.71073 Å) at 298(2) K, with increasing ω (width of 0.3° per
frame) at a scan speed of 3 s per frame. The SMART software was
used for data acquisition. Data integration and reduction were
undertaken with SAINT and XPREP22 software. Multiscan empirical
absorption corrections were applied to the data using the program
SADABS.23 Structures were solved by direct methods using SHELXS-
9724a and were refined by full-matrix least-squares on F2 using
SHELXL-9724b program package. In all the nine complexes, non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
attached to all carbon atoms are geometrically fixed. Structural
illustrations have been generated using ORTEP-325a and MERCURY
1.325b for Windows. Crystal data, as well as details of data collection
and refinement for the complexes, are summarized in Tables 1 and 2.
Selected bond distances and angles of the complexes are listed in
Table S1 of Supporting Information. Purity of the crystallographic
phases of the bulk sample was proven by the PXRD technique. PXRD
patterns of all the crystals match with the simulated one (see
Supporting Information).
Synthesis and Characterization. Both receptors have been
prepared by slight modification of a known literature procedure. The
2-[(2′-hydroxybenzyl) amino] benzimidazole (L1) and 2-[(2′-hydrox-
ynaphthylmethylene) amino] benzimidazole (L2) were synthesized by
the condensation of 2-aminobenzimidazole with corresponding
aromatic aldehyde in ethanol solution and in situ reduction with
sodium borohydride. It was finally recrystallized from ethanol.
L1: 1H NMR (DMSO-d6, 400 MHz) δ (ppm) 11.130(bs,1H),
7.371(s,1H), 7.243(d,1H), 7.169(dd,2H), 7.103(t,1H), 6.924(dd,2H),
6.804(d,1H), 6.765(d,1H), 4.390 (s,2H). 13C NMR (DMSO-d6)
155.622, 154.829, 133.566, 129.386, 128.410, 128.303, 126.389,
122.774, 122.599, 121.180, 117.848, 37.708. m.p. = 130 °C. m/z =
240.0710 (calcd. m/z = 240.11 in positive mode).
room temperature, which yielded light yellow crystals suitable for X-
ray crystallography analysis within 7−10 days. Yield 65%; H NMR
1
(DMSO-d6, 400 MHz; ppm): δ (ppm) 8.922(s, 1H), 8.644(bs, 1H),
7.951(s, 1H), 7.291−7.244(m, 3H), 7.125(t, 1H), 7.086 (m, 2H),
6.842−6.766(m, 2H), 4.457(s, 2H), 2.910(s, 3H), 2.710(s, 3H). m.p.
= 207°.
−
Synthesis of complex [L1H+][H2PO4 ] (5): The neutral host L1 (25
mg) was suspended in MeOH (10 mL), and a few drops of ortho
phosphoric acid were added in the mixture. After being stirred for 30
min, the clear solution was kept at room temperature. Block-shaped
crystals suitable for X-ray analysis were grown from this solution by
slow evaporation after one week. Yield 82%; 1H NMR (DMSO-d6, 400
MHz) δ 8.931(s, 1H), 7.269−7.220(m, 3H), 7.127−7.050 (m, 3H),
6.835(d, 1H), 6.762(t, 1H), 4.451(s, 2H), 3.164 (s, 3H). m.p. = 219°.
Synthesis of complex [L2H+][OAc−]·AcOH(6): It was obtained by
adding 0.4 mL of 37% acetic acid (AcOH) to 5 mL of methanol
solution of L2 (25 mg). After the addition of acid, the solution was
stirred at room temperature for 30 min and filtered in a test tube. The
filtrate was allowed to evaporate at room temperature, which yielded
colorless crystals suitable for X-ray crystallography analysis within 6−7
1
days. Yield 72%; H NMR (DMSO-d6, 400 MHz) δ (ppm) 8.142(d,
1H), 7.869(s, 1H), 7.800(d, 1H), 7.739(d, 1H), 7.518(t, 1H), 7.319(t,
1H), 7.186(m, 2H), 7.126(d, 1H), 6.942(m, 2H), 4.760(s, 2H),
1.906(s, 3H). m.p. = 215°.
Synthesis of complex [L2H+]·[DNB−] (7): It was obtained by
adding 0.5 mL of saturated solution of 3,5-dinitroacetic acid (DNB) to
5 mL of methanol solution of L2 (25 mg). The solution was stirred at
room temperature for 30 min and filtered in a test tube. The filtrate
was allowed to evaporate at room temperature, which yielded light
yellow crystals suitable for X-ray crystallography analysis within 7−10
1
days. Yield 74%; H NMR (DMSO-d6, 400 MHz) δ (ppm) 8.943(s,
L2: 1H NMR (DMSO-d6, 400 MHz) δ (ppm) 13.351(bs, 1H),
11.096(bs, 1H), 8.171(d, 1H), 7.884(s, 1H), 7.798(d, 1H), 7.743(d,
1H), 7.523(t, 1H), 7.319(t, 1H), 7.212(bs, 2H), 7.142(d, 1H),
6.960(bs, 2H), 4.790(s, 2H). 13C NMR (DMSO-d6) 156.095, 154.562,
154.119, 130.447, 128.914, 128.639, 127.106, 126.832, 125.291,
119.792, 119.075, 118.290, 117.542, 117.237, 115.704, 41.834. m.p.
= 233 °C. m/z = 290.0638 (calcd. m/z = 290.12 in positive mode).
Synthesis of complex [L1H+][Cl−] (1): It was obtained by adding
0.4 mL of 37% hydrochloric acid (HCl) to 5 mL of methanol solution
of L1 (25 mg). After the addition of acid, the solution was stirred at
room temperature for 30 min and filtered in a test tube. The filtrate
was allowed to evaporate at room temperature, which yielded colorless
crystals suitable for X-ray crystallography analysis within 6−7 days.
1H), 8.893(s, 1H), 8.435(s, 1H), 8.197(d, 1H), 7.948(s, 1H), 7.796(s,
1H), 7.515(t, 1H), 7.342(t, 1H), 7.252(m, 2H), 7.177(d, 1H),
7.039(m, 2H), 4.824(d, 2H), 2.932(s, 3H), 2.78(s, 3H). m.p. = 233°.
−
Synthesis of complex [L2H+][HSO4 ]·H2O (8) was obtained by
adding 0.4 mL of 37% of sulphuric acid (H2SO4) to 5 mL of methanol
solution of L2 (25 mg). After the addition of acid, the solution was
stirred at room temperature for 30 min and filtered in a test tube. The
filtrate was allowed to evaporate at room temperature, which yielded
colorless crystals suitable for X-ray crystallography analysis within 6−7
1
days. Yield 73%; H NMR (DMSO-d6, 400 MHz) δ (ppm) 12.471(s,
1H), 10.308(s, 1H), 9.178(s, 1H), 7.985(d, 1H), 7.879(d, 1H),
7.527(t, 1H),7.439(dd, 1H), 7.360(t, 1H), 7.274(dd, 1H), 4.931(s,
2H). m.p. = 245°.
1
Yield: 82%; H NMR (DMSO-d6, 400 MHz): δ (ppm) 9.238(t, 1H),
7.410(m, 1H), 7.264(d, 1H), 7.225(m, 1H), 7.160(t, 2H), 6.904(d,
RESULTS AND DISCUSSION
■
1H), 6.797(t, 2H), 4.547(d,2H). m.p. = 233°.
−
Synthesis of complex [L1H+][NO3 ] (2): It was obtained by adding
Anion Binding Studies in Solid State. For a receptor to
bind with the anionic guests, it should possess preorganized
anion binding elements decorated on the suitable platform/
framework. Here benzimidazole NH is a strong hydrogen bond
donor and in order to achieve electrostatic assistance the other
nitrogen can be protonated which can then strongly interact
with anions through (N−H)+···X− type ionic hydrogen
bonding because the charge−charge electrostatic interaction
dominates to bind the anions. Again OH functionality already
proved its importance in nature. Both aromatic and aliphatic
CH can also interact with anions through C−H···π interaction.
The crystallization of the complexes was achieved by slow
evaporation of methanolic or a binary solution of methanolic
and DMF solutions containing the receptor and appropriate
quantities of the acids. Attempts were made to synthesize
complexes of L1and L2 from various acids such as HCl, HBr,
HI, HNO3, H2SO4, H3PO4, CH3COOH, and 3,5-dinitrobenzoic
acid (DNB). However, we successfully isolated crystalline
complexes 1, 2, 3, 4, and 5 using respectively HCl, HNO3,
CH3COOH, DNB, and H3PO4 with L1 and complexes 6, 7, and
8 using CH3COOH, DNB, and H2SO4 with L2.
0.4 mL of 37% nitric acid (HNO3) to 5 mL of methanol solution of L1
(0.5 mmol). After the addition of acid, the solution was stirred at room
temperature for 30 min and filtered in a test tube. The filtrate was
allowed to evaporate at room temperature, which yield colorless
crystals suitable for X-ray crystallography analysis within 6−7 days.
Yield 82%; 1H NMR (DMSO-d6, 400 MHz) δ 7.989 (s, 1H),
7.235(dd, 1H), 7.138 (t, 2H), 7.109(t, 1H), 7.025 (dd, 2H), 6.832−
6.764 (m, 2H), 4.431(d, 2H), 1.910(s, 3H); m.p. = 125°.
Synthesis of complex [L1H+][OAc−] (3): The neutral host L1 (25
mg) was suspended in MeOH (10 mL), and a few (approximately
five) drops of acetic acid were added in the mixture. After being stirred
for 30 min, the clear solution was kept at room temperature. Block-
shaped crystals suitable for X-ray analysis were grown from this
1
solution by slow evaporation after one week. Yield 72%; H NMR
(DMSO-d6, 400 MHz) δ (ppm) 7.363(t, 1H), 7.223(d, 1H), 7.145(m,
2H), 7.109(t, 1H), 6.907(m, 2H), 6.765(m, 2H), 4.365(d, 2H),
1.910(s, 3H). M.pt. = 118°.
Synthesis of complex [L1H+][DNB]·DMF (4): It was obtained by
adding 0.4 mL of methanolic solution of 3,5-dinitro acetic acid (DNB)
to 5 mL of methanol−DMF binary solution of L1 (25 mg). After the
addition of acid, the solution was stirred at room temperature for 30
min and filtered in a test tube. The filtrate was allowed to evaporate at
4014
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
Structural information obtained from single-crystal X-ray
analysis of anion complexes 1−8 can provide insight into the
proper binding topology of anions having variable dimension-
ality with the protonated receptor molecule and anion template
supramolecular assembly formation. Complexation of anions is
primarily governed by N−H···anion, (N−H)+···anion, and C−
H···anion interactions involving cationic receptors. In addition,
the complexes are further stabilized by multiple weak
intermolecular C−H···O hydrogen bonds, π···π, C−H···π
interactions. The detailed structural analyses of these complexes
are described as follows.
The receptor L1 crystallizes through two N−H···O, one O−
H···N, and two C−H···π interactions involving both aromatic
and aliphatic C−H in triclinic space group (Figure 1). H1N and
Figure 2. (a) Illustration of various nonbonding interactions (dotted
lines) between spherical chloride anion and receptor L1 in salt 1 and
(b) the one-dimensional polymeric chain structure along the a axis.
Figure 1. Solid state structure of L1 showing both aromatic and
aliphatic C−H···π interactions along with normal hydrogen bonding
interactions.
Csalicylaldehyde (C8−N1−C7−C1 = 79.88°, C22−N4−C21−
C15 = 76.56°) resulting in two different coordination modes
for the nitrate ions. In one structure the nitrate ion and the
interacting portions from three receptor unit are almost in one
plane, and the fourth receptor interacts from top of this plane
through aromatic C−H···O interaction. But in the second
nitrate bonded structure N−H···O interactions from two π
stacked receptors and active participation of OH groups from
other two receptor lead to a capsular type assembly as shown in
Figure 3a. But both nitrate anions decorate an eight point
attachment with four receptor molecules engaging all three
nitrate oxygens with a number of NH and both aliphatic and
aromatic CH.
In the planar type nitrate bonded structure, nitrate oxygens
interact with five NH and three CH hydrogens, both aromatic
and aliphatic from four receptors through average N···O and
C···O bond distances of 2.9974 Å and 3.360 Å respectively. But
in the other structure, nitrate oxygens interact with two NH,
three OH, and three aromatic CH of four receptors through
average N···O, O···O, and C···O bond distances of 3.185 Å,
2.919 Å, and 3.276 Å respectively. Both structures are also
stabilized by strong C−H···π interactions. The nitrate oxygen
O6 is a bifurcated hydrogen bond acceptor and interacts also
with H3N and H13 of the same receptor (C13−H13···O6 =
2.684(2) Å). O7 and O8 are trifurcated hydrogen bond
acceptors; O7 interacts with H5N and H24 of the same
receptor and with H2O with an average bond distance of 3.260
Å ranging from 3.170(3) to 3.432(2) Å. Again O8 engaged with
H2O, H1O, and aryl hydrogen H3 with an average bond
distance of 2.878 Å ranging from 2.665(2) to 3.310(3) Å. Aryl
H3N from one receptor are engaged with O1 of another
receptor (N1···O1 = 3.407(1) Å, ∠N1H1N···O1 = 137(1)°;
N3···O1 = 2.799(1) Å, ∠N3H3N···O1 = 165(1)°) and N2
involves in intermolecular hydrogen bonding with phenolic
hydrogen H1O (N2···O1 = 2.614(1) Å, ∠O1H1O···N2 =
169.83(6)°). Again aromatic hydrogen H11 and aliphatic
hydrogen H7A are also engaged with each other through weak
C−H···π interactions (C7A···Cg1 = 4.285 Å, H11···Cg1 =
3.816 Å) and thereby extends the three-dimensional structure.
But on introducing the spherical chloride anion (complex 1)
both the NHs (both protonated and neutral) and OHs interacts
with it and there are no C−H···π interactions, Figure 2a.
However the intermolecular N−H···O bonding is still there
with the N···O distance 2.980(2)Å weaker than that in L1. The
binding of chloride ion demonstrates that each chloride ion is
engaged with three receptor molecules through three strong
hydrogen bonds, two with NH of average N···Cl distance
3.0865 Å and one with -OH groups from 3.043(2) Å (O···Cl)
of the receptor and thereby decorates an one-dimensional
polymeric chain structure, Figure 2b. In Figure 2a the chloride
anion is interacts with H2N, H3N of two receptors and H1O of
the third receptor with N3H3N···Cl1 = 2.2256(5) Å, N2
H2N···Cl1 = 2.236(6) Å, and H1O···Cl1 = 2.2479(7) Å.
To stabilize the planar nitrate anion, eight coordination
bonds from four receptors are required which comprise various
N−H···O and C−H···O bonding. The receptor exhibits
conformational isomorphorism26 with Z′ = 2, and they differ
in their torsions involving the Cbenzimidazole−NH−CH−
4015
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
Figure 3. (a) Coordination mode of NO3− anion in the salt 2; (b) 2D structure of the salt 2 with the same nitrate in space fill and the other nitrate in
ball and stick and (c) the cyclic aggregate of four receptor molecules with four nitrate anions.
Figure 4. (a) Crystal structure of [L1H+][OAc−] showing one acetate anion with three N−H···O, two C−H···O, and one O−H···O as a perspective
view. (b) The acetate anion induced molecular barrel with spacefill guest molecules along the c axis. (c) The three-dimensional crystal packing
diagram of the acetate anion with C−H···π interactions in red-colored broken lines extending the molecular barrels.
hydrogen H24 also decorates a C−H···π (C24−H24···Cg2)
interaction of distance 3.011 Å. The crystal packing motif of the
nitrate ion along the b axis with space fill second type of nitrate
is shown in Figure 3b. Again on extending the hydrogen
bonding interactions a nitrate directed cyclic assembly is found,
Figure 3c.
With planar organic anion acetate having two strong donors,
L1 crystallizes in the monoclinic space group P21/c and contains
one protonated receptor along with one acetate anion in the
asymmetric unit. Acetate anion is stabilized through six point
interactions with five receptors comprised of three N−H···O,
two C−H···O, and one O−H···O interactions with average
N···O, C···O, and O···O distances of 2.634 Å, 3.431 Å, and
2.692 Å, respectively. Again four from five interacting receptors
also interacts with second acetate which is anti to the first
acetate and interacts with one more receptor leading to a
molecular barrel type structure as shown in Figure 4b. It is
interesting to note that all the six receptors in this barrel
structure are placed alternatively in an up and down fashion
with all the possible interacting groups in the middle engaged
with two encapsulated acetate anions with a short acetate−
acetate distance of 3.490 Å (C16···C16). The average width of
the barrel is 10.242 Å as measured from Schiff base nitrogen to
nitrogen of two completely opposite Schiff base nitrogens of
the receptors, Figure S1 (Supporting Information). Very
recently Wu et al. reported a similar molecular barrel with
4016
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
Figure 5. (a) Coordination mode of 3,5-dinitro benzoate anion in the salt 4; (b) the solvent DMF molecules forming a bridge between two dimeric
protonated receptor and DNB anion assembly; and (c) the different types of C−H···π and π···π interactions leading to the ultimate three-
dimensional structure.
−
Figure 6. (a) Crystal structure of [L1H+][H2PO4 ] showing the coordination of H2PO4− through NH···O and CH···O interactions in a perspective
view. (b) The ladder type H-bond interactions along with the polymeric dihydrogen phosphate chain. (c) One-dimensional interanionic polymeric
2
dihydrgen phosphate chain along the c axis with R2 (8) type cyclic hydrogen bonding.
encapsulated tetraalkylammonium cations based on a bis−
trisurea stave.26
along the c axis extending the molecular barrels two
dimensionally as shown in Figure 4c.
The electron demanding aromatic acid 3,5-dinitrobenzoic
acid (DNB) stabilized in the solid state through a number of
N−H···O, C−H···O, O−H···O, C−H···π, and π···π interactions
to give molecular salt 4. In the asymmetric unit of this
molecular salt 4, there is one protonated receptor neutralized
by DNB anion and one cocrystallizes DMF. The benzoate
anion of DNB interacts with two receptors through a four point
attachment with two NH, one aromatic CH, and one OH
group with average N···O, C···O and O···O distances of 2.779
In the complex, the acetate oxygen O3 is bifurcated hydrogen
bond acceptor and interacts with H1N and H2N of N···O
distances 2.783(2) Å and 2.743(2) Å, respectively. O2 engaged
with H3, H1O,and H3N with D···A distances 3.292(2) Å,
2.692(2) Å, and 2.678(2) Å respectively. Aromatic hydrogen
H15B interacts with O1 of the fifth receptor with C···O
distances 3.570 Å. In addition to this there are weak C−H···π
(C4H4···Cg = 3.934 Å) interactions between the receptors
4017
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
Å, 3.282 Å, and 2.709 Å respectively, Figure 5a. The benzoate
oxygens O2 and O3 interact with H2N and H1N from the
same receptor through R2 (8) type cyclic hydrogen bonding.
plane. It crystallizes as [L2H+][OAc−]·AcOH (complex 6)
where the acetate anion neutralized the monoprotonated
benzimidazole receptor L2, and one acetic acid also
cocrystallizes in the solid structure. Compared to the six
point attachment of the acetate anion in earlier complex 3, now
the acetate anion is involved in a seven point attachment with
two receptors and an acetic acid through two N−H···O, one
O−H···O, and three C−H···O interactions including both
aliphatic and aromatic hydrogen. Whereas in complex 3, all NH
protons were engaged with the acetate anion, in this complex
because of intermolecular O1···H3N hydrogen bonding H3N is
not available to interact with guest anions. As a consequence,
the receptor is locked and bent in such a way that its
benzimidazole π cloud is suitably positioned to interact with the
guest π cloud and its aromatic CH interacts with the naphthyl π
cloud.
2
Again aromatic hydrogen H3 and H1O from a second receptor
1
also interacts with O3 through R2 (6) type cyclic hydrogen
bond. Both the receptors are also engaged in C−H···π
interaction of distance 2.920 Å (C7H7B···Cg2). Again
H3N and H7A of the receptor engaged with O8 of solvent
1
DMF through R2 (7) type cyclic hydrogen bond and its
aliphatic hydrogen H23C is engaged with O4 of one of the
nitro group from same DNB molecule. A careful observation
reveals that two DMF molecules linked the two dimeric DNB-
receptor assemblies and thereby forms a cyclic structure as
shown in Figure 5b. Again the other nitro group oxygen O6
and O7 interact with aryl hydrogen H11 and aliphatic hydrogen
H22A respectively. Aryl hydrogen H5 interacts with the highly
electron deficient DNB through a C−H···π interaction
(H5···Cg1 = 2.817 Å). In addition to this, there is very weak
π···π interaction of 4.696 Å between the DNB molecules and
different C−H···π (C7−H7B···Cg2 = 2.920 Å, C12
H12···Cg2 = 3.150 Å, C5H5···Cg1 = 2.817 Å) interactions
leading to the ultimate three-dimensional solid structure as
shown in Figure 5c.
The acetate anions decorate a few very strong hydrogen
bond interactions ranging from 2.569(2) to 2.713(2) Å with
both receptors and cocrystallized acetic acid. O5 interacts with
2
H1O and H3 through R1 (6) type cyclic hydrogen bonding
with corresponding D···A distances 2.571(2) Å and 3.207(2) Å.
Again H14 and H2N interact with O5 and O4 of the second
2
receptor through R2 (8) type cyclic hydrogen bonding, Figure
With tetrahedral dihydrogen phosphate anion, L1 crystallizes
in monoclinic space group where dihydrogen phosphate anion
neutralizes the protonated receptor and one methanol also
cocrystallized in the asymmetric unit. Both the NH and the
N+H group of the benzimidazole ring act as H-bond donors
and interact very strongly with dihydrogen phosphate anions.
The cocrystallized methanol oxygens, NH and OH groups of
the receptors also interact with dihydrogen phosphate anions to
give a ladder type H-bonding structure as shown in Figure 6b.
Again the H2PO4− anions with their very usual ability to donate
and accept hydrogen bonds in between themselves forms a
polymeric inter anionic chain structure along the c axis with
7a. The acetate oxygen O4 interacts with H2O from one acetic
2
R2 (8) type cyclic hydrogen bonding as shown in Figure 6c.
Each H2PO4− anion interacts with other two H2PO4− anions
through four O−H···O interactions. O2 interacts with H2N
and H4O, whereas the trifurcated hydrogen bond acceptor O3
−
interacts with H3N and H5O of the H2PO4 and H6O of the
methanol with D···A distances ranging from 2.590(3) to
2.696(2) Å. Thus these O···O and N···O bonds are much
shorter and stronger than normal hydrogen-bond distances
(OH···O ≥ 2.8 Å).27 The hydrogen bond between O2 and O4
with O···O distance 2.590(3) Å is comparable to the low barrier
hydrogen bonds (LBHB) which are observed in biology within
protein interiors and are thought to play roles in protein
functions, enzymatic catalysis, and the stabilization of specific
reaction intermediates in enzymes.28,29 Again aromatic hydro-
gen H13 also interacts with O4 of the anionic guest. In addition
to this the solid state structure also accounts for the presence of
aryl C−H···π interactions between the receptor molecules
(C5···Cg1 = 3.790 Å, C12···Cg2 = 3.946 Å). Previously Steed
et al. reported a dimeric hydrogen phosphate and phosphate−
water chain with triprotonated tris-N-(2-aminoethyl)-1,3-
propanediamine,30 Hossain et al. reported a cyclic dihydrogen
phosphate anion octamer with triprotonated tris-[2-(2-
thienylmethylamino)ethyl] amine31 and Ghosh et al. also
reported dihydrogen phosphate dimer with a pentafluorophenyl
substituted tripodal urea-based receptor.32
Figure 7. (a) Coordination mode of acetate anion in salt 6 and (b) the
guest induced dimeric assembly of the receptors along the b axis along
with weak interactions. The guest molecules, noninteracting hydro-
gens, and all other types of short interactions are deleted for clarity.
acid and its other oxygen O3 interacts with H1N forming a
3
R2 (10) type cyclic hydrogen bonding. Again as a consequence
of locking induced by intermolecular N3H3N···O1 interaction
aromatic H15 interacts with the aromatic π cloud (C15···Cg2 =
3.652 Å) of the receptor leading to a dimeric receptor assembly,
Figure 7b. The figure also describes other C−H···π interactions
(C4···Cg1 = 3.789 Å) along the b axis.
Under the same crystallization condition, acetate anion
shows different coordination chemistry with receptor L2 and
found to face toward two interlocked receptors in the same
4018
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
Similar to earlier DNB molecular salt 4, L2 also crystallizes in
triclinic space group with two protonated receptor molecules
and their charge is neutralized by two deprotonated DNB
molecules with Z′ = 2. The isomorphs (C1 and C2) differ in
their torsions involving the Cbenzimidazole−NH−CH−
Cnaphthaldehyde (C37−N6−C36−C26 = −92.30° for C2, C12−
N1−C11−C1 = −96.91° for C1). This also leads two different
coordination modes for DNB anions. As expected two of the
receptor NHs, namely. H6N and H7N interact with O6 and O7
2
of the benzoate group of one DNB anion through R2 (8) type
cyclic hydrogen bonding from one side and H8N interacts with
O3 of the nitro group DNB from the opposite side with an
average N···O distance of 2.825 Å ranging from 2.708(3) to
3.004(3) Å. Again the benzoate oxygen O7 also interacts with
hydroxyl group of the receptor with D···A distance of 2.682(3)
Å (O7···O1). This strong hydrogen bonding forced the acidic
aromatic hydrogen H20 from DNB anion to interact with the π
cloud of the same receptor from a distance 4.291 Å
(C20···Cg3) and the π cloud of the DNB to interact with the
same receptor’s π cloud (Cg1···Cg2) from a distance 3.607 Å.
Thus these two interactions wipe out any possibility of π···π
interactions between the DNB anions which were very
prominent in earlier DNB complex, complex 4. Again the
other two nitro group oxygens O4 and O5 interact with three
aromatic hydrogens, O4 interacts with H32 and H29; and O5
interact with H15 (C32···O4 = 3.330(4) Å, C29···O4=3.555(5)
Å, C15···O5 = 3.282(5) Å).
A close up view in the crystal structure also reveals that when
the nitro group oxygen interacts with the other isomorphs with
O8···O13 bond distance of 2.684 Å as a consequence of the
torsion about C37−N6−C36−C26 the second nitro group
interacts only with one aromatic hydrogen H40 (C40−
H40···O9 = 2.435(3) Å) making its nature different from the
earlier one. Both types of isomorphs with the two different
DNB anions are shown in Figure 8b.
Figure 8. (a) Coordination mode of 3,5-dinitrobenzoate (DNB) anion
in the molecular salt 7 and (b) the crystal packing diagram for both the
isomorphs (C1 and C2) in green and red with DNB anions in yellow
and blue. Few important C−H···π and π···π are shown in black and all
other sort interactions are deleted for clarity.
Tetrahedral hydrogen sulfate anion with L2 crystallizes in
triclinic space group along with one water molecule. The
−
interactions of the HSO4 with the receptor and water
hydrogen bonding. The receptor molecule interacts with two
hydrogen sulphates which are further tied up through two water
molecule in face to face fashion resulting in a dimeric bisulphate
water adduct. The hydrogen sulfate oxygen O2 interacts with
O6 and O3 interacts with H1N through hydrogen bond
distances of 2.645 Å and 2.737 Å respectively. Again O4
interacts with H2N and one O6 from one symmetric water
molecule (O4···N2 = 2.726(5) Å, ∠N2H2N···O4 = 155.6(3)
°; O4···O6 = 2.978(1) Å).
molecules are shown in Figure 9a. Each hydrogen sulfate
anion interacts with two receptor molecules and two water
molecules through a four point attachment involving two
NH···O and two OH···O interactions. The water molecules
display bridge hydrogen bonding between the hydrogen sulfate
anions and thereby a molecular bowl is formed, Figure 9b. Das
et al. had previously reported a sulfate−(H2O)3−sulfate adduct
with a tren based tris(urea) receptor where the sulfate anion
interacts through 12 hydrogen bonds with three water
molecules and one receptor molecule.33a A similar type of
result is also reported by Huang et al., with pyrazine derived
mixed valence AgI/AgII coordination polymer and they were
Solution State Anion Binding Studies. Analysis of the
1
1H NMR Spectra. The H NMR spectrum of complex 1−8
(DMSO-d6) showed appreciable downfield shift of the NH
proton except the two acetate complexes 3 and 6. For complex
1, NH resonance with a Δδ shift of 1.867 ppm indicates strong
solution state binding of Cl− with the NH functions. But with
acetate anion NH is shifted to upfield with a Δδ value of 0.008
ppm and with 3,5-dinitrobenzoate in complex 4 NH resonance
with a downfield Δδ shift of 1.273 ppm with broadening of the
signal. This could be because of strong binding of the benzoate
anion of DNB compared to the acetate anion in the solution
state because of the higher acidity of the former. In addition,
spectral changes have also been observed for the aliphatic CH2
and aromatic protons (Ar−CH) of the receptor, which undergo
a notable downfield shift (Δδ CH2 = 0.076 ppm; Δδ ArH =
0.013−0.037) and get broadened upon recognition of the 3,5-
dinitro benzoate anion. This also suggests the solution state
−
able to crystallize both the 1D (HSO4 −H2O)n chain and 2D
(SO42−−H2O)n anionic sheet in the solid state, where the key
role was played by the lattice water molecules and silver ions.33b
−
Here the HSO4 anions linearly interact with water molecules
and the other two sides interact with the silver ions to give the
1D chain structure. But in our case because of the geometry of
the receptor it forms the molecular bowl like structure.
Compared to six point coordination of the tetrahedral
dihydrogen phosphate anion in complex 5, tetrahedral
bisulphate anion is stabilized through a four point attachment
with receptor L2 and cocrystallized water molecule. Again
similar to the acetate complex 6, here also the receptor
molecules are locked because of intramolecular N−H···O
4019
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
dinitrobenzoate anion complexes (complexes 4 and 7)
hydrogen bonds are stronger than the corresponding acetate
complexes (complexes 3 and 6) both in solid as well as in
solution state because of electron withdrawing nitro groups.
Both receptors also exhibit conformational isomorphs (Z′ = 2),
L1 with the nitrate anion and L2 with the DNB anion.
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic files in CIF format, additional crystallographic
data, characterization data, 1H NMR spectra, 13C NMR spectra,
and IR spectra, PXRD pattern of all the complexes. This
information is available free of charge via the Internet at http://
pubs.acs.org/.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: gdas@iitg.ernet.in. Tel.: +91 361 258231. Fax: +91
0361 2582349.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Figure 9. (a) Perspective view of bonding of hydrogen sulfate in the
complex 8; (b) hydrogen sulfate-(H2O)2-hydrogen sulfate adduct in
spacefill model and (c) crystal packing view along the c axis showing
the hydrogen sulfate and water layer between the hydrophilic layer of
the receptors. The hydrogen bonds and all other interactions are
deleted for clarity.
G.D. gratefully acknowledges Department of Science and
Technology (DST), New Delhi, India, for financial support and
DST-FIST for its single-crystal XRD facility and Central
Instrument Facility at IIT Guwahati. A.G. acknowledges IIT
Guwahati, India, for a junior research fellowship.
binding of both aliphatic and aromatic proton with the guest
anion. In complex 2 with the nitrate anion and in complex 5
with the dihydrogen phosphate anion NH resonance has a
downfield Δδ shift of 0.589 and 0.56 ppm. With receptor L2
also NH proton shifted to downfield with a Δδ value of 0.551
ppm with DNB anion (complex 7) but no significant change
for acetate complex (complex 6). Both are evidence of weak
binding of the acetate anion in the solution phase. In complex
8, NH proton shifted to a maximum Δδ shift of 1.289 ppm with
hydrogen sulfate anion in complex 8.
REFERENCES
■
(1) Bertini, I.; Sigel, A.; Sigel, H. Handbook on Metalloproteins; Marcel
and Dekker, New York, 2001.
(2) Molina, P.; Tar
1711−1724.
́ ́
raga, A.; Oton, F. Org. Biomol. Chem. 2012, 10,
(3) Gale, P. A.; Hiscock, J. R.; Lalaoui, N.; Light, M. E.; Wells, N. J.;
Wenzel, M. Org. Biomol. Chem. 2011, DOI: 10.1039/C1OB06800H.
(4) Yoon, J.; Sook, K. K.; Singh, N. J.; Kim, K. S. Chem. Soc. Rev.
2006, 35, 355−360.
(5) (a) Zapata, F.; Caballero, A.; Arraga, A. T.; Molina, P. J. Org.
Chem. 2010, 75, 162−169. (b) Singh, N.; Jang, D. K. Org. Lett. 2007,
9, 1991. (c) Saha, D.; Das, S.; Bhaumik, C.; Dutta, S.; Baitalik, S. Inorg.
Chem. 2010, 49, 2334−2348. (d) Saha, D.; Das, S.; Maity, D.; Dutta,
S.; Baitalik, S. Inorg. Chem. 2011, 50, 46−61. (e) Watanabe, S.;
Onogawa, O.; Komatsu, Y.; Yoshida, K. J. Am. Chem. Soc. 1998, 120,
229−230. (f) Joo, T. Y.; Singh, N.; Lee, W.; Jang, D. O. Tetrahedron
Lett. 2007, 48, 8846−8850. (g) Lee, D. Y.; Singh, N.; Kim, M. J.; Jang,
D. O. Org. Lett. 2011, 13, 3024. (h) Kang, J.; Kima, H. S.; Janga, D. O.
Tetrahedron Lett. 2005, 46, 6079−6082.
CONCLUSION
■
In conclusion, we have first reported a hydrogen sulfate−
(H2O)2−hydrogen sulfate adduct with a charged benzimidazole
receptor, where two water molecules display bridge hydrogen
bonding with the two hydrogen sulfate anions. To the best of
our knowledge, it is the first example of a hydrogen sulfate−
(H2O)2−hydrogen sulfate adduct with a charged receptor. In
detail, we have shown the effect of variable anion dimension-
ality and variable hydrophobicity of the receptor on the
crystallization of charged benzimidazole type receptors.
Receptor L1 crystallizes from a one-dimensional polymeric
chain structure with spherical chloride anion to a one-
dimensional interanionic polymeric dihydrogen phosphate
chain with tetrahedral dihydrogen phosphate anion through
planar nitrate anion directed cyclic assembly. Especially in the
phosphate complex, there are a few very strong hydrogen bonds
which are comparable to the low barrier hydrogen bonds
(LBHB) encountered in biology within protein interiors. Again
the acetate anion induces a molecular barrel formation with
charged benzimidazole receptor L1 but shows different
coordination chemistry with the other receptor L2 because of
different hydrophobicity of the second receptor. For both
(6) (a) Yu, M.; Zhao, G.; Lin, H. J. Mol. Recognit. 2007, 20, 69−73.
(b) Saha, D.; Das, S.; Bhaumik, C.; Dutta, S.; Baitalik, S. Inorg. Chem.
2010, 49, 2334−2348. (c) Cui, Y.; Mo, H. J.; Chen, J. C.; Niu, Y. L.;
Zhong, Y. R.; Zheng, K. C.; Ye, B. H. Inorg. Chem. 2007, 46, 6427−
6436. (d) Shao, J.; Qiao, Y.; Lin, H. J. Fluoresc. 2009, 19, 183−188.
́
(e) Zapata, F.; Caballero, A.; Espinosa, A.; Tarraga, A.; Molina, P. J.
Org. Chem. 2008, 73, 4034−4044. (f) Zapata, F.; Caballero, A.;
́
Tarraga, A.; Molina, P. J. Org. Chem. 2010, 75, 162−169.
(7) Burkhard, P.; Tai, C. H.; Jansonius, J. N.; Cook, P. F. J. Mol. Biol.
2000, 303, 279−286.
(8) Tai, C. H.; Burkhard, P.; Gani, D.; Jenn, T.; Johnson, C.; Cook, P.
F. Biochemistry 2001, 40, 7446−7452.
(9) Burlington, B. T.; Widlanski, T. S. J. Org. Chem. 2001, 66, 7561−
7567.
(10) He, J. J.; Quiocho, F. A. Science 1991, 251, 1479−1481.
(11) Courtemanche, R. J. M.; Pinter, T.; Hof, F. Chem. Commun.
2011, 47, 12688−12690.
4020
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021

Crystal Growth & Design
Article
(12) (a) Bianchi, A.; James, K. B.; Espana, E. G. Supramolecular
Chemistry of Anions; Wiley-VCH: New York, 1997. (b) Beer, P. D.;
Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486. (c) Sessler, J. L.; Gale,
P. A.; Cho, W. S. Anion Receptor Chemistry; The Royal Society of
Chemistry: Cambridge, UK, 2006.
(13) (a) Schneider, H. J.; Yatsimirsky, A. K. Chem. Soc. Rev. 2008, 37,
263. (b) Espana, E. G.; Diaz, P. J.; Llinares, M.; Bianchi, A. Coord.
Chem. Rev. 2006, 250, 2952. (c) Kang, S. O.; Hossain, A.; James, K. B.
Coord. Chem. Rev. 2006, 250, 3038. (d) Llinares, J. M.; Powell, D.;
James, K. B. Coord. Chem. Rev. 2003, 240, 57.
(14) (a) Lakshminarayanan, P. S.; Ravikumar, I.; Suresh, E.; Ghosh,
P. Chem. Commun. 2007, 46, 5214. (b) Lakshminarayanan, P. S.;
Suresh, E.; Ghosh, P. Inorg. Chem. 2006, 45, 4372.
(15) Kubik, S. Chem. Soc. Rev. 2009, 38, 585−605.
(16) Luecke, H.; Quiocho, F. A. Nature 1990, 347, 402−406.
(17) He, J. J.; Quiocho, F. A. Science 1991, 251, 1479−1481.
(18) Pflugrath, J. W.; Quiocho, F. A. Nature 1985, 314, 257−260.
(19) Pflugrath, J. W.; Quiocho, F. A. J. Mol. Biol. 1988, 200, 163−180.
(20) Dutzler, R.; Campbell, E. B.; Cadene, M.; Chait, B. T.;
MacKinnon, R. Nature 2002, 415, 287−294.
(21) (a) Auffinger, P.; May, S. L.; Westhof, E. J. Am. Chem. Soc. 1996,
118, 1181−1189. (b) Metzger, S.; Lippert, B. J. Am. Chem. Soc. 1996,
118, 12467−12468. (c) Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290.
(d) Steiner, T.; Saenger, W. J. Am. Chem. Soc. 1992, 114, 10146.
(e) Sharma, C. V. K.; Desiraju, G. R. J. Chem. Soc., Perkin Trans. 1994,
2, 2345. (f) Steiner, T. J. Chem. Soc., Perkin Trans. 1995, 2, 1315.
(g) Chaney, J. D.; Goss, C. R.; Folting, K.; Santarsiero, B. D.;
Hollingworth, M. D. J. Am. Chem. Soc. 1996, 118, 9432.
(22) Saint, Smart XPREP; Siemens Analytical X-ray Instruments Inc.:
Madison, Wisconsin, USA, 1995.
(23) Sheldrick, G. M. SADABS: Software for Empirical Absorption
Correction; University of Gottingen, Institute fur Anorganische
Chemieder Universitat: Gottingen, Germany, 1999−2003.
̈
(24) (a) Sheldrick, G. M. SHELXS-97; University of Gottingen:
Germany, 1997; (b) Sheldrick, G. M. SHELXL-97, Program for Crystal
Structure Refinement; University of Gottingen: Germany, 1997.
(25) (a) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (b) Mercury
1.3 Supplied with Cambridge Structural Database; CCDC: Cambridge,
U.K., 2003−2004.
(26) Li, S.; Wei, M.; Huang, X.; Yanga, X. J.; Wu, B. Chem. Commun.
2012, 48, 3097−3099.
(27) Day, V. W.; Hossain, M. A.; Kang, S, O.; Powell, D.; Lushington,
G.; Bowman-James, K. J. Am. Chem. Soc. 2007, 129, 8692−8693.
(28) Cleland, W. W.; Kreevoy, M. M. Science 1994, 264, 1887−1890.
(29) Frey, P. A.; Whitt, S. A.; Tobin, J. B. Science 1994, 264, 1927−
1930.
(30) Ilioudis, C. A.; Georganopoulou, D. G.; Steed, J. W. J. Mater.
Chem. 2002, 4, 26−36.
(31) Hossain, M. A.; Isıklan, M.; Pramanik, A.; Saeed, M. A.;
Fronczek, F. R. Cryst. Growth Des. 2012, 12, 567−571.
(32) Lakshminarayanan, P. S.; Ravikumar, I.; Suresh, E.; Ghosh, P.
Chem. Commun. 2007, 5214−5216.
(33) (a) Jose, D. A.; Kumar, D. K.; Ganguly, B.; Das, A. Inorg. Chem.
2007, 46, 5817−5819. (b) Sun, D.; Yang, C. F.; Xu, H. R.; Zhao, H.
X.; Wei, Z. H.; Zhang, N.; Yu, L. J.; Huang, R. B.; Zhengab, L. S. Chem.
Commun. 2010, 46, 8168−8170.
4021
dx.doi.org/10.1021/cg300496t | Cryst. Growth Des. 2012, 12, 4012−4021