An imidazole-based bisphenol 2-((2-hydroxy-3,5-dimethylphenyl)(imidazol-4- yl)methyl)-4,6-dimethylphenol: A versatile host for anions

Article abstract of DOI:10.1021/cg2017215

Imidazole containing bisphenol 2-((2-hydroxy-3,5-dimethylphenyl)(imidazol- 4-yl)methyl)-4,6-dimethylphenol (1), (abbreviated as Imbp) and its salts with dicarboxylic acids and mineral acids, namely, maleic acid (H2mal), fumeric acid (H2fum), adipic acid (H2adpt), perchloric acid, sulphuric acid (sulfate and bisulphate), tetrafluoroboric acid, and nitric acid are structurally characterized. The crystal packing in the solid state structures of the salts are assisted by electrostatic N⁺-H???O and related weak interactions. The bisphenol 1 and its methanol solvate have extensive hydrogen bonded structures; in the later case the methanol molecule acts as a bridge through N-H???O and O-H???O interactions and strong π???π interactions between the two imidazole rings. Both the structures have strong intramolecular O-H^...O hydrogen bonds among the hydroxyl groups of the Imbp molecule. The mono-deprotonated salts of 1 with maleic acid, adipic acid, have layered structure, whereas anion encapsulation takes place in the case of dideprotonated salts of fumeric acid. In the case of perchlorate, bisulphate, tetrafluoroborate, and nitrate salts of 1 the intramolecular O-H???O is retained. The sulfate anchors trimeric self-assemblies formed through R₃³ (6) type of hydrogen bond in the protonated 1 and finally they form circular structures with a diameter of 15.193 A, in which anion is embedded. A bisulphate salt of 1 is prepared by the reaction of magnesium sulfate with sulphuric acid in methanol in the presence of 1; in this structure bisulphate occurs in pairs through intermolecular hydrogen bonds and it assists in the formation of an assembled structure of the protonated bisphenol 1.

Full text of DOI:10.1021/cg2017215

Article
pubs.acs.org/crystal
An Imidazole-Based Bisphenol 2-((2-Hydroxy-3,5-
dimethylphenyl)(imidazol-4-yl)methyl)-4,6-dimethylphenol: A
Versatile Host for Anions
Bhaskar Nath and Jubaraj B. Baruah*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati − 781039, Assam, India
S
* Supporting Information
ABSTRACT: Imidazole containing bisphenol 2-((2-hydroxy-3,5-dimethylphenyl)(imidazol-4-yl)-
methyl)-4,6-dimethylphenol (1), (abbreviated as Imbp) and its salts with dicarboxylic acids and
mineral acids, namely, maleic acid (H2mal), fumeric acid (H2fum), adipic acid (H2adpt), perchloric
acid, sulphuric acid (sulfate and bisulphate), tetrafluoroboric acid, and nitric acid are structurally
characterized. The crystal packing in the solid state structures of the salts are assisted by electrostatic
N+−H···O and related weak interactions. The bisphenol 1 and its methanol solvate have extensive
hydrogen bonded structures; in the later case the methanol molecule acts as a bridge through N−
H···O and O−H···O interactions and strong π···π interactions between the two imidazole rings. Both
the structures have strong intramolecular O−H...O hydrogen bonds among the hydroxyl groups of the
Imbp molecule. The mono-deprotonated salts of 1 with maleic acid, adipic acid, have layered structure, whereas anion
encapsulation takes place in the case of dideprotonated salts of fumeric acid. In the case of perchlorate, bisulphate,
tetrafluoroborate, and nitrate salts of 1 the intramolecular O−H···O is retained. The sulfate anchors trimeric self-assemblies
formed through R33 (6) type of hydrogen bond in the protonated 1 and finally they form circular structures with a diameter of
15.193 Å, in which anion is embedded. A bisulphate salt of 1 is prepared by the reaction of magnesium sulfate with sulphuric acid
in methanol in the presence of 1; in this structure bisulphate occurs in pairs through intermolecular hydrogen bonds and it assists
in the formation of an assembled structure of the protonated bisphenol 1.
of one or multiple electronegative heteroatom(s) such as
nitrogen in any of the ring of bisphenols would introduce
additional interactions leading to new supramolecular archi-
tectures. Furthermore, such heteroatoms may interact with
various anions to give rise to new charge assisted assembly of
bisphenols. Pyridine containing bisphenols are used to stabilize
methyl and ethyl sulfate salts of pyridinium bisphenols.13
Heterocycles such as imidazole derivatives are attractive due to
their ability to form supramolecular isomers and solvatopoly-
morphs.14 Thus, it would be interesting to attach an imidazole
unit to bisphenol to make interesting self-assembled structures.
Various imidazolium cations that are readily formed on acid
treatment of imidazole derivatives generally self-assemble
through N−H···N interactions.15 With these anticipations to
construct new charge-assisted assemblies of imidazole contain-
ing bisphenols, such as the few possibilities among many as
illustrated in Scheme 1, we have taken up a study on the
structural aspects of bisphenols by attaching an imidazole ring
to it. It is also anticipated that such new imidazole containing
bisphenols would bind to different anions depending on the
availability of binding sites and the nature of the anion
providing directional characteristics to self-assemblies. The
number of such possible ways of interactions would increase
when a bisphenol group is anchored to the imidazole part.
INTRODUCTION
■
Host−guest compounds, also known as inclusion compounds,
are a class of compounds where the host framework provides
apposite geometry to accommodate guest molecule(s), which
include cations, anions, and neutral molecules.1,2 The rational
design of such molecular solids has received significant
attention of the crystal engineers because of their potential
applications in molecular recognition, separation technology,
and heterogeneous catalysis.3,4 Phenolic compounds such as
bisphenols and related compounds are well-known for their
ability to form inclusion compounds, and they have found
potential applications in molecular recognition.5−7 Bisphenols
are organic compounds having propeller-like geometry, in
which the phenolic hydroxyl groups play a critical role to build
diverse supramolecular networks such as rings, linear chains,
ladders, etc.8 Two phenolic hydroxy groups provide directional
H-bonding sites for the formation of these types of structures.9
Different types of bisphenol molecules have been reported
where the two phenol rings were attached by various spacers. In
the majority of the cases, the methylene group is used to
connect the two phenol rings.10 Recently, some bisphenols
have been reported, where the two phenol rings are connected
by an adamentane spacer.11 Although there are many literature
reports available on the self-assembly and host−guest chemistry
of bisphenols, there are only a few references found on
heteroatom containing bisphenols. Generally, bisphenols and
their related phenolic compounds possess O−H···O and O−
H···π (aromatic) interactions in the solid state.12 The presence
Received: December 30, 2011
Revised: January 30, 2012
Published: February 6, 2012
© 2012 American Chemical Society
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Scheme 1. A Representative Case Showing Some Possible Ways through Which an Imidazolinium Salt Bearing Bisphenol May
Self-Assemble
Scheme 2. Some Possible Assemblies Arising from N−H···O¯ and N+−H···O¯ Interactions of Imidazolium Cation with
Carboxylate/Carboxylic Acid Functionality
Thus, imidazolium cation bearing bisphenols would have
diverse ways to interact with anions to form different types
of supramolecular assemblies. Some of the ways of N−H···O
and charge assisted N+−H···O¯ interactions of an imidazolium
cation with a carboxylate anion or with a combination of
carboxylate anion and neutral carboxylic acid are illustrated in
Scheme 2.
We have thus studied structural aspects of a series of salts of
an imidazole containing bisphenol. The advantage of using salts
rather than a neutral organic molecule for the designing of a
supramolecular network is that the hydrogen bonding between
ions is stronger than neutral organic molecules. Again, the role
of the hydroxyl group would be interesting in guiding the
interactions in the bisphenol molecule.
RESULTS AND DISCUSSION
■
The imidazole containing bisphenol 2-((2-hydroxy-3,5-
dimethylphenyl)(imidazol-4-yl)methyl)-4,6-dimethylphenol
(1, abbreviated as Imbp) was prepared by a procedure reported
for related bisphenols,16 and it was crystallized as solvent free
Imbp from dimethylsulfoxide and as methanol solvate
Imbp·MeOH (2) from methanol. Here, we present the
structural aspects of a series of imidazolium bisphenol salts
that are derived from 1 on interaction with three different
carboxylic acids, viz., maleic, fumeric, and adipic, and that bears
inorganic anions, viz., perchlorate, sulfate, bisulphate, tetra-
fluoroborate, and nitrate anions (Scheme 3).
The bisphenol 1 (abbreviated as Imbp) crystallizes in
monoclinic space group P21/n and has moderately strong
hydrogen bonded structure in the form of self-assembly. There
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stability of the system. A few prominent interactions are shown
in Figure 1b and bond parameters are listed in Table 1.
The methanol solvate of 1 Imbp·MeOH (2) crystallizes in
Scheme 3. Structure of the Imidazole Containing Bisphenol
(1) and the Anions Used in This Study
triclinic space group P1 and its asymmetric unit contains a
̅
methanol molecule along with the Imbp molecule. Each
methanol molecule in this solvate bridges two host molecules
through O(2)−H(2)···O(3) (dD···A, 2.664 Å; ∠D−H···A, 155°)
and O(3)−H(3A)···N(1) (dD···A, 2.748 Å; ∠D−H···A, 177°)
interactions. Such bridges lead to the formation of an infinite
chainlike structure as illustrated in Figure 2. The NH group of
the imidazole ring are involved in bifurcated hydrogen bonds
with two hydroxy groups present in another neighboring
bisphenol molecule via N−H···O interactions (N(2)−H-
(2A)···O(1) (dD···A, 3.123 Å; ∠D−H···A, 126°) and N(2)−
H(2A)···O(2) (dD···A, 3.071 Å; ∠D−H···A, 144°)). Moreover,
one of the hydroxy groups of the bisphenol molecule also are
involved in bifurcated hydrogen bonding with the NH group
and OH group of the solvent molecule through N−H···O and
O−H···O interactions (Figure 2). Over and above these, the
imidazole rings are placed parallel in the lattice with a plane-to-
plane sepation of 3.302 Å, and this distance of separation
suggests π−π interaction among the imidazole rings.
are two moderate H-bonds, viz., N(1)−H(1A)···N(2) and
O(2)−H(2)···N(2) (∠D−H···A; 164° and 145° and dD···A
,
2.991(3), 2.816(3)Å respectively). The two hydroxy groups of
each bisphenol molecule form strong intramolecular H-bonds
with ∠D−H···A as 174°; dD···A, 2.720(3)Å. The combination of
these H-bonds leads to the formation of two different types of
cyclic H-bonding motifs as shown in Figure 1a. Apart from
these H-bonds, there are some other interactions such as C−
H···O and C−H···π interactions which also contribute to the
When the bisphenol 1 is treated with maleic acid (H2mal) it
forms hydrated salt, namely, HImbp·Hmal·H2O (3). The salt 3
crystallizes in a monoclinic space group P21/c. The crystallo-
Figure 1. (a) Different types of cyclic H-bonding motifs in 1. (b) Selected C−H···O and C−H···π interactions in 1.
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Table 1. Selected H-Bond Parameters of 1−5
compd. nos.
D−H···A
dD‑H(Å)
dH···A(Å)
dD···A(Å)
∠D−H···A(°)
1
O(1)−H(1) ···O(2)
0.82
1.90
2.720(3)
2.991(3)
2.816(3)
2.905(3)
3.1352(18)
2.664(2)
3.123(2)
3.071(2)
2.748(2)
2.669(2)
2.750(2)
2.789(2)
2.772(2)
2.425(2)
2.893(2)
2.812(2)
2.6950(17)
2.6712(18)
2.7953(18)
2.6721(17)
2.6540(18)
2.7000(18)
2.759(2)
2.7268(19)
2.651(2)
174
164(3)
145
N(1)−H(1A) ···N(2) [−1/2 − x, 1/2 + y, 1/2 − z]
O(2)−H(2) ···N(2) [1/2 + x , 1/2− y, 1/2 + z]
C(9)−H(9) ···O(1)
0.85(3)
0.82
2.17(3)
2.11
0.98
2.48
106
2
3
O(1)−H(1) ···O(2)
0.82
2.32
174
O(2)−H(2) ···O(3) [1 − x, 1 − y, −z]
N(2)−H(2A) ···O(1) [−1 + x, y, z]
N(2)−H(2A) ···O(2) [−x, 1 − y, −z]
O(3)−H(3A) ···N(1)
O(1)−H(1) ···O(7) [x, 3/2 − y, −1/2 + z]
N(1)−H(1A) ···O(3) [−x, 1 − y, −z]
O(2)−H(2) ···O(1)
N(2)−H(2A) ···O(4) [x, 3/2 − y, 1/2 + z]
O(5)−H(5A) ···O(3)
O(7)−H(7E) ···O(5) [−x, 1/2 + y, 1/2 − z]
O(7)−H(7F) ···O(6)
O(1)−H(1) ···O(3) [1 − x, 1 − y, 1 − z]
N(1)−H(1A) ···O(4) [−x, 1 − y, 1 − z]
O(2)−H(2) ···O(1)
N(2)−H(2A) ···O(3) [−x, −y, 1 − z]
O(1)−H(1) ···O(3) [1 + x, 1/2 − y, 1/2 + z]
N(1)−H(1A) ···O(4) [x, 1/2 − y, 1/2 + z]
O(2)−H(2) ···O(1)
0.82
1.90
155
0.86
2.53
126
0.86
2.33
144
0.82
1.93
177
0.89(3)
0.86
1.78(3)
1.91
172(3)
166
0.82
1.98
167
0.86
1.95
158
0.82
1.61
170
0.86(3)
0.89(3)
0.82
2.07(3)
1.93(3)
1.95
160(3)
170(3)
150
4
5
0.96(3)
0.82
1.75(3)
1.98
159(2)
173
0.90(3)
0.82
1.78(3)
1.91
169(2)
151
0.86
1.92
150
0.82
1.95
169
N(2)−H(2A) ···O(3) [x, 1/2 − y, −1/2 + z]
O(5)−H(5A) ···O(4) [1 + x, 1/2 − y, 1/2 + z]
0.86
1.89
165
0.82
1.83
175
Figure 2. Different types of hydrogen bonding and π−π interactions in Imbp·MeOH (2).
graphic asymmetric unit consists of the HImbp cation, a
maleate anion, and a water molecule of crystallization. Strong
intramolecular H-bonding (O−H···O) is observed within the
maleate ion. The maleate anion generally forms an intra-
molecular hydrogen bonded structure17 and such anions
participate in hydrogen bond formation with host molecules.
In this case also this is not an exception but the water of
interest in the structure is the unconventionality obtained in
holding the anions by simultaneous hydrogen bonds with the
water molecule acting as a bridge on one side and a direct
hydrogen bond to the host cation (Figure 3a). Moreover, the
two hydroxy groups of the host cation (HImbp) also are
involved in intramolecular O(2)−H(2)···O(1) (dD···A, 2.789 Å;
∠D−H···A, 167°) hydrogen bonding. The water molecule is
coordinated to one hydroxy group of the host molecule and
two Hmal anions through O−H···O interactions and the Hmal
anion forms water bridged zigzag polymeric chain. The Hmal
anion interacts with the bisphenol through charge-assisted N−
H (imidazole)···O− interactions (Figure 3).
It is shown that the maleic acid on reaction with 1 forms salt
with mono-deprotonated acid, whereas its trans counterpart,
namely, fumeric acid, formed a di-deprotonated salt with the
cation of the bisphenol 1. For charge balance, two molecules of
imidazolinium bisphenol cation accept one fumerate anion to
give HImbp·0.5 fum (4). The pKa2 of these two acids is 6.62 for
maleic acid and 4.44 for fumeric acid; the difference is due to
geometry of the acids. The former acid adopts a strong
intramolecular hydrogen bonded structure upon first deproto-
nation. The salt 4 crystallizes in triclinic space group P1 and the
̅
crystallographic asymmetric unit contains one host cation,
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Figure 3. (a) The C−H···O, N−H···O, and O−H···O interactions in 3. (b) Formation of zigzag 1D chain of maleate mono anion and water through
H-bonding in 3. (c) Spacefill model of 3, green = host cation, blue = maleate anion, red = water molecule.
Figure 4. (a) Formation of the assembly of host with two fumerate ions in 4. (b) Encapsulation of fumerate ions in the hexameric assembly of the
host cations in 4. (c) Spacefill model of the complex (blue is fumerate anion and green is host cation). (d) Packing diagram showing the layered
structure when viewed along the crystallographic a-axis.
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Figure 5. (a) One-dimensional zigzag H-bonding chain of adipate ion showing all the H-bonding interactions in HImbp·Hadpt (5). (b) Packing of
the molecules in 5 when viewed along the crystallographic c-axis. (c) Spacefill model of the complex 5 (blue for Hadpt and green for HImbp).
Figure 6. (a) N+−H···O−, N−H···O, and O−H···O interactions in HImbp·ClO4 (6) to form a H-bonded ladder. (b) Interaction of the perchlorate
anion through N+−H···O¯, N−H···O and O−H···O and C−H···O interaction. (c) Formation of a layered structure which incorporates perchlorate
anions.
HImbp, and the half of the fumerate anion. The host molecules
form dimers with two fumerate ions through N−H
(imidazole)···O− and O−H···O interactions (Figure 4a). The
intramolecular O2−H···O1 interaction in the host molecule is
also observed as in the earlier case. Each fumerate ion interacts
with six host molecules through N−H (imidazole)···O− and
O−H···O interactions, resulting in the encapsulation of the
anion in the hexameric cavity formed by the host cation (Figure
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3
2−
Figure 7. (a) Formation of trimeric assembly of HImbp through R3 (6) type cyclic H-bonding in HImbp·0.5SO4 (7). (b) Interaction of two
trimeric assemblies through sulfate anion leading to a bowl like structure. (c) Packing of the crystal in spacefill model. (d) Packing of the molecules
in the crystal lattice viewed along the crystallographic c-axis.
4b). Here N−H (imidazole) acts as H-bond donor and the
oxygen (carboxylate) acts as a H-bond acceptor and finally the
salt forms a layered structure (Figure 4d). The salt of imidazole
and fumeric acid have a layered structure.15 In our system, the
complexity provided by the weak interactions of the phenolic
units forces the system to self-assemble to bind to the fumerate
anion.
formed by the host cations as shown in Figure 5b,c. The
formation of salt in the cases of 3−5 were also confirmed by
infrared spectroscopy in the solid state. The carbonyl stretching
frequency of the carboxylate groups are shifted toward lower
frequency compared to the free carboxylic acid upon salt
formation. In the case of HImbp·Hadpt and HImbp·Hmal·-
H2O, it is seen that two different CO stretching frequencies
appear around 1536−1574 cm−1 and 1711−1717 cm−1 for
carboxylate and carboxylic acid.
The perchlorate salt of 1, HImbp·ClO4 (6) crystallizes in a
monoclinic space group P21/c, and its asymmetric unit contains
one protonated host molecule and a perchlorate anion. Both
the N−H and the N+−H group of the imidazole ring act as a H-
bond donor and engage in hydrogen bonding with the
perchlorate ion forming a ladder like H-bonded network
when viewed along the a-axis. These types of supramolecular
features were found in the crystal structure of theophylline-
perchlorate salt.20 As in the earlier cases, the hydroxy groups of
the host cation are involved in intramolecular H-bonds (Figure
6a). Over and above these, one of the hydroxy groups
participating in the intramolecular hydrogen bond has a
hydrogen atom free, which acts as H-bond donor to the
oxygen atom of the perchlorate anion. Each perchlorate ion
interacts with four guest cations through N−H···O, O−H···O,
and C−H···O interactions (Figure 6b). Finally, the salt forms
two discrete layered sheets in two different crystallographic
The bisphenol 1 also forms salt of mono-deprotonated adipic
acid (Hadpt) HImbp·Hadpt (5). The salt formation by the
mono-deprotonation of this acid is rational as it has a pKa1
value of 4.42, which is comparable to the pKa2 value of the
fumeric acid. The salt 5 crystallizes in monoclinic space group
P21/c and the crystallographic asymmetric unit contains the
host cation and mono-deprotonated adipate ion. The adipate
monoanions form a 1D zigzag chain through O−H···O
interactions between the hydroxyl group of the carboxylic
acid (H-bond donor) and the O− carboxylate (H-bond
acceptor) (Figure 5a). Each oxygen atom of the carboxylate
group of the adipate ion is involved in a bifurcated H-bond
(O−H···O and N−H···O interactions). The hydrogen bond
parameters are listed in Table 1. The adipate anion adopts a
bent conformation different from the parent adipic acid
structure in the unsolvated form.18 The bent structure of
adipic acid is also observed in the cocrystal of adipic acid with
cytosine.19 Finally the salt forms a sheetlike structure in which
the Hadpt anions are incorporated between the two layers
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2
Figure 8. (a) Formation of R2 (6) types of cyclic H-bonding by the bisulphate anion. HImbp·HSO4. (b) Two discrete parallel sheets in
HImbp·HSO4, viewed along the crystallographic a-axis.
Figure 9. (a) Dimer of host cations through N−H···O interactions in HImbpBF4. (b) The C−H···π interactions between the sheetlike structures of
HImbp·BF4.
directions and each sheet is stabilized by perchlorate anions
(Figure 6c).
HImbp·HSO4 (8). The formation of the bisulphate salt is
attributed to hydrolytic
The sulfate salt of 1, HImbp·0.5SO42− (7), is in a 1: 0.5 ratio
of cation and anion; it crystallizes in the space group R32 and
the crystallographic asymmetric contains one HImbp molecule
and the half of the sulfate ion. The two cations are mainly held
together by electrostatic interaction and H-bonding. The O3 of
the sulfate anion is involved in bifurcated H-bonding with the
host cation through N−H···O and O−H···O, and the O4 of the
sulfate anion are involved in trifurcated H-bonding with the
host cation through N−H···O and C−H···O interaction. One
of the hydroxyl groups of the host molecule is involved in
intermolecular H-bonding (both as donor and acceptor) with
the same hydroxyl group of another two similar host molecules
2−
−
SO
+ H SO → 2HSO
2 4 4
(1)
4
disproportionation of magnesium sulfate in methanol as shown
in eq 1. The 1:1 salt 8 crystallizes in the P1 space group and the
crystallographic asymmetric unit contains one HImbp cation
and bisulphate anion. The two molecules are mainly held
together by electrostatic and H-bonding interactions. The
̅
2
HSO4 anions form a dimeric structure through R2 (6) types of
cyclic H-bonds, and these dimers are held in the assembly of
the protonated host molecules of Imbp through O−H···O and
N−H···O interactions involving the hydroxyl and the N−H
groups of Imbp (Figure 8a). The N+−H of the protonated
imidazole also serves as a H-bond donor to the guest anion.
There are no strong intermolecular interactions among the host
cations, but the two hydroxy groups of the host cation are
involved in intramolecular H-bond interactions. When we
viewed the packing pattern from the crystallographic a-axis, it is
seen that the molecules form two discrete sheets and each sheet
incorporates the HSO4 anion. Hydrogen sulfate salts have
found applications in various devices such as H2 and H2O
sensors, fuel and stream cells, and high-energy-density
batteries.21 Braga et al. have reported the crystal structure of
the stabilized hydrogen sulfate adducts of crown ethers.22
Hydrogen sulfate salts are of interest in supramolecular aspects
and crystal engineering because of its analogy to biologically
relevant biphosphate anion and the presence of H-bonding
between the ions for self-association.23 In a recent study, the
stabilization of the bisulphate anion along with the sulfate anion
by 3,5-diphenylpyrazole has been reported.24 In our earlier
studies, the stabilization of methyl and ethyl sulfate salts by
various bisphenol hosts has been reported.13,25
3
forming a trimeric assembly through R3 (6) types of cyclic
hydrogen bonding (Figure 7a). The other hydroxy groups and
the imidazole rings of this trimeric assembly projects upward
and gives rise to a cyclic type of structure that has a
resemblance to calix arene. Two such trimeric assemblies are
further connected to the O3 of three sulfate anions through N−
H···O and O−H···O interactions. These interactions lead to
formation of circular assemblies when viewed along the c-axis
(Figure 7b). These circular assemblies are connected to each
other by O4 of sulfate through N2−H···O4 interactions
completing the three-dimensional structure. Three such
assemblies are found to be in contact with each other in the
crystal lattice (Figure 7c,d).
A bisulphate salt of bisphenol 1 was formed serendipitously.
When magnesium sulfate hetahydrate was treated with bis-
phenol 1 in aqueous methanol, it led to formation of
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Table 2. Selected H-Bond Parameters of 6−10
compd. nos.
D−H···A
O(1)−H(1) ···O(6)
N(1)−H(1A) ···O(3) [x, 3/2 − y, −1/2 + z]
O(2) −H(2)···O(1)
N(2)−H(2A) ···O(6) [x, 1/2 − y, −1/2 + z]
O(1)−H(1)···O(1) [−y, x − y, z]
N(1)−H(1A)···O(3) [−y, x − y, z]
O(2)−H(2)···O(3)
N(2)−H(2A)···O(4) [1 − x, 1 − x + y, −z]
O(1)−H(1)···O(2)
N(1)−H(1A)···O(4) [x, −1 + y, 1 + z]
O(2)−H(2)···O(6) [−x, 1 − y, 1 − z]
N(2)−H(2A)···O(3) [1 + x, −1 + y, 1 + z]
O(5)−H(5A)···O(4) [1 − x, 1 − y, −z]
O(1)−H(1)···F(2) [1 + x, 1 + y, z]
N(1)−H(1A) ···O(3) [1 − x, 1 − y, 1 − z]
O(2)−H(2)···O(1)
dD‑H(Å)
dH···A(Å)
dD···A(Å)
∠D−H···A(°)
6
0.74(6)
0.79(6)
0.82
2.07(6)
2.14(6)
2.01
2.719(7)
2.895(6)
2.817(5)
2.988(6)
2.864(8)
2.759(8)
2.826(7)
2.719(8)
2.800(2)
2.869(2)
2.818(2)
2.888(2)
2.738(2)
2.832(3)
2.729(5)
2.853(3)
2.886(5)
2.939(3)
2.997(5)
2.762(7)
2.999(8)
2.765(6)
2.791(6)
2.803(6)
3.249(8)
146(5)
161(5)
170
0.93(7)
0.82
2.23(7)
2.15
138(6)
146
7
8
0.86
1.91
171
0.82
2.15
140
0.86
1.86
176
0.82
1.99
169
0.83(2)
0.82
2.07(2)
2.07
162.1(18)
151
0.86(3)
0.82
2.05(2)
1.93
165.6(18)
169
9
0.82
2.11
146
0.86(4)
0.82
1.89(4)
2.05
166(3)
166
131(3)
140(3)
140(8)
167(12)
133(9)
152
N(2)−H(2A)···F(4)
0.91(3)
0.91(3)
0.82(9)
0.85(13)
0.85(13)
0.86
2.21(3)
2.18(4)
2.32(10)
1.93(12)
2.36(14)
1.98
N(2)−H(2A) ···O(2) [1 − x, 1 − y, 1 − z]
O(3)−H(3N)···F(1) [1 − x, −y, 1 − z]
O(1)−H(1)···O(3)
O(1)−H(1)···O(5)
N(1)−H(1A)···O(5) [−1 + x, y, z]
O(2)−H(2)··· O(1)
10
0.82
1.98
170
N(2)−H(2A) ···O(3) [x, y, 1 + z]
N(2)−H(2A) ···O(4) [x, y, 1 + z]
1.00(7)
1.00(7)
1.84(8)
2.46(8)
162(7)
135(8)
Figure 10. (a) N+−H···O−, N−H···O, and O−H···O interactions in HImbp·NO3 to form the sheetlike structures. (b) Packing of the molecules in
HImbp·NO3 viewed along the crystallographic c-axis.
The reaction of sodium tetrafluoroborate in wet methanol
forms 1:1 salt of 1, HImbp·BF4·H2O (9) which crystallizes in a
N(2)−H(2A)···O(2) hydrogen bonding interactions (Figure
9a). These dimers are connected to each other via two water
molecules and two tetrafluoroborate anions through N−H···O,
O−H···F, and N−H···F interactions (Table 2). Such
interactions lead to the formation of sheetlike structures
parallel to the bc-plane (Figure 9b). These sheetlike structures
intercalate tetrafluoroborate anions and are held together by
C−H···π interactions as shown in Figure 9b.
Finally, we have prepared the salt of 1 with a planar anion,
namely, nitrate anion. The nitrate salt HImbp·NO3 (10) is a
1:1 electrolyte and crystallizes in a monoclinic space group P21/
c. The crystallographic asymmetric unit of 10 contains one host
cation and a nitrate anion. Both the N+−H and N−H bonds of
the imidazole act as H-bond donor toward the nitrate anion
(Figure 10a). In this case also, two hydroxy groups of the host
cation are involved in intramolecular H-bonding. The hydrogen
atom not participating in the cyclic structure of intramolecular
hydrogen bond acts as H-bond donor to the nitrate anion. This
assembly forms a sheet parallel to the ac-plane which
triclinic space group P1. The crystallographic asymmetric unit
̅
contains the host cation HImbp, tetrafluoroborate anion, and
water molecule of crystallization. Formation of such salts from
sodium tetrafluoroborate may be considered as unique as it is
formed through a hydrolytic reaction between sodium
tetrafluoroborate with water leading to the corresponding
acid tetrrafluoroboric acid and in such process the counter base
has to be sodium hydroxide. We had an earlier observation on
stabilization of tetrafluoroborate anion in a quinoline based
receptor, in which we obtained protonated quinoline derivative
by similar hydrolytic reaction of sodium tetrafluoroborate in
wet DMF.26 In the salt 9, the water of crystallization molecule
acts as a donor toward the tetrafluoroborate anion and acceptor
toward N−H of the imidazole ring. The protonated N+−H of
the imidazole ring is involved in bifurcated H-bonding with one
of the hydroxyl groups of the host cation and to the
tetrafluoroborate anion. The host cation forms a dimer through
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Article
incorporates the nitrate anions as shown in the Figure 10b. The
parameters of the H-bond interactions in the assembly of 10 are
listed in Table 2.
EXPERIMENTAL SECTION
■
Synthesis of 2-((2-Hydroxy-3,5-dimethylphenyl)(imidazol-4-
yl)methyl)-4,6-dimethylphenol (1). 4(5)-Imidazole carboxalde-
hyde (0.48 g, 5 mmol) and 2,4-dimethylphenol (1.22 g, 10 mmol)
were dissolved in acetic acid (20 mL) and the solution was stirred for
half an hour in an ice bath. A mixture of concentrated sulphuric acid
and glacial acetic acid in a 1:2 ratio (10 mL, v/v) was added dropwise
to the reaction mixture. After half an hour of stirring, the mixture was
kept in a deep freeze for one week. After one week, ice cold water (10
mL) was added to the reaction mixture; a white precipitate appeared.
The reaction mixture was filtered and the precipitate was washed with
aqueous sodium bicarbonate solution (20%, 25 mL). The product was
then dried in air. Yield, 87%. 1HNMR (400 MHz, DMS0-d6): 2.09 (s,
6H), 2.11 (s, 6H), 5.74 (s, 1H), 6.71 (s, 2H), 6.85 (s, 2H), 7.73 (s,
1H). ESI mass: [M + 1]: 323.0767. IR (cm−1): 3840 (w), 3439 (s),
3148 (m), 2912(w), 1615 (s), 1550 (s), 1486 (s), 1440 (m), 1325
(m), 1226 (s), 1185 (m), 1094 (w), 1012 (w), 935 (w), 856 (w), 751
(w), 658 (w). 2-((2-hydroxy-3,5-dimethylphenyl)(imidazol-4-yl)-
methyl)-4,6-dimethylphenol was crystallized in the solvent free form
1, from dimethylsulfoxide and solvated form as Imbp·MeOH (2) from
methanol.
HImbp·Hmal·H2O (3). Equimolar amounts (0.5 mmol) of Imbp
(0.161 g) and maleic acid (0.058 g) were dissolved in methanol (10
mL) and kept for crystallization. After one week, colorless crystals
appeared. Yield, 96%. IR (cm−1): 3461 (s), 3135 (m), 2920 (m), 1620
(s), 1578 (s), 1489 (s), 1443 (m), 1387 (m), 1363 (s), 1298 (w), 1212
(s), 1149 (w), 1089 (w), 993 (w), 863 (s), 788 (w), 751 (s), 661 (w),
625 (w), 568 (w).
HImbp·0.5fum (4). Imbp (0.322 g, 1 mmol) and fumeric acid
(0.058 g, 0.5 mmol) were dissolved in methanol (15 mL) and kept for
crystallization. After one week colorless crystals appeared. Yield,
∼94%. IR (cm−1): 3324 (s), 3140 (m), 2916 (s), 2569 (m), 1538 (s),
1489 (s), 1443 (s), 1352 (m), 1325 (m), 1304 (m), 1289 (m), 1228
(s), 1166 (s), 1101 (m), 988 (s), 920 (w), 874 (w), 846 (m), 790 (m),
750 (m), 674 (s), 641 (w), 620 (w), 574 (w).
HImbp·Hadpt (5). Equimolar amounts (0.5 mmol) of Imbp (0.161
g) and adipic acid (0.146 g) were dissolved in methanol (10 mL) and
allowed to stand for a week; colorless crystals were formed. Yield, 96%.
IR (cm−1): 3439 (s), 3313 (s), 3159 (s), 2923 (s), 2862 (m), 2626
(w), 1711 (s), 1610 (s), 1536 (s), 1481 (s), 1443(m), 1426 (m), 1327
(s), 1300 (m), 1262 (s), 1229 (s), 1166 (m), 1094 (w), 982 (w), 919
(w), 853 (m).
HImbp·ClO4 (6). Equimolar amounts of Imbp (0.161 g, 0.5 mmol)
and HClO4 were dissolved in methanol (10 mL) and solution was left
for crystallization. Colorless crystals were formed after one week. Yield,
93%. IR (cm−1): 3391 (s), 3159 (s), 3010 (m), 2917 (m), 1613 (s),
1487 (s), 1378 (w), 1337 (w), 1298(m), 1229(m), 1182 (m), 1142
(s), 1120 (s), 1087 (s), 1031(m), 984 (w), 929 (w), 866 (w), 806 (w),
789 (w), 624 (s).
HImbp·0.5SO4 (7). Imbp (0.322 g, 1 mmol) and H2SO4 in a 2:1
molar ratio were dissolved in methanol (15 mL) and kept for
crystallization. Colorless crystals were formed after one week. Yield
96%. IR (cm−1): 3391 (s), 3136 (s), 2856 (s), 1617 (s), 1490 (s), 1377
(w), 1340 (w), 1191 (s), 1154 (s), 1093 (m), 1060 (s), 931 (w), 864
(s), 817 (m), 787 (w), 750 (w), 590 (s).
HImbp·HSO4 (8). Imbp (0.322 g, 1 mmol) and magnesium sulfate
heptahydrate (0.124 g, 0.5 mmol) were dissolved in methanol and
then a few drops of sulphuric acid was added to it and the clear
solution thus obtained was kept undisturbed. After 3 days pink colored
crystals appeared. Yield, 91%. IR (cm−1): 3397 (s), 3131 (w), 3025
(w), 2918 (w), 1617 (s), 1483 (s), 1376 (w), 1340 (w), 1192 (w),
1154 (w), 1093 (m), 1060 (m), 931 (w), 864 (s), 589 (s), 493 (w).
HImbp·BF4·H2O (9). Equimolar amounts (0.5 mmol) of Imbp
(0.161 g) and NaBF4 (0.055 g) were dissolved in methanol (15 mL)
and kept for crystallization. After one week, colorless crystals formed
were filtered. Yield, 94%. IR (cm−1): 3344 (s), 3151 (m), 3016 (s),
2915 (m), 2851 (w), 1614 (m), 1551 (s), 1489 (s), 1439 (m), 1329
(w), 1303 (w), 1229 (s), 1185 (m), 1084 (w), 856 (w), 788 (w), 751
(w), 660 (w), 631 (w).
The powder X-ray diffraction (PXRD) of the samples was
recorded (please refer to Supporting Information) to see if
there are any other types of structural units in the salts. We
have found a good agreement on experimental and simulated
PXRD data for all the salts, and it suggests the uniformity of the
structural features of the bulk materials. The formation of salts
1
in case of 6−10 is also confirmed by HNMR spectra, as the
N−H protons on the imidazole ring shifted to a higher δ-value
on interaction with anions (please refer to Supporting
Information). We have studied the preferential crystallization
process of these salts by adding the salts to another acid
solution. We have observed that weak perchlorate anion or
nitrate anion can be successfully replaced by sulfate anion from
their respective salt. However, the reverse process, namely, the
sulfate salt, does not lead to formation of perchlorate or nitrate
salt on treatment with perchloric acid and nitric acid,
respectively. Because of the lack of distinguishable and
characteristic absorption maxima in the UV region of the
carboxylate salts that we have presented here, we have not
carried out the competitive binding of carboxylate anions.
The DSC of the crystalline solids of 3−5 show a flat baseline
with sharp peaks, which is also consistent of the high purity of
the bulk materials. The HImbp·Hmal·H2O, HImbp.fum, and
HImbp·Hadpt show endothermic peaks at 274, 247, and 216
°C, whereas the melting point of Imbp is 240 °C. From the TG
analysis of HImbp·Hmal·H2O (3), it is seen that the water of
crystallization is lost at around 134 °C from the hydrated form
of the salt, which indicates that the water molecule is strongly
bound in the assembly. Whereas in the case HImbp·BF4·H2O
(9), the water of crystallization is lost at around 85 °C, in this
case water molecules are attached to two dimeric assemblies of
the cations and are relatively weakly bound compared to water
molecules in 3.
CONCLUSIONS
■
A large number of structural variations by directional hydrogen
bonds in anion assisted assemblies of an imidazole containing
bisphenol are shown. The structural versatilities in terms of the
deprotonation process, structure, and charge on anions as well
as compositions of guest host assemblies are illustrated. Among
the two isomeric cis and trans dicarboxylic acids, maleic acid
(cis) led to the monodeprotonated salt, whereas fumeric acid
(trans) led to the dideprotonated salt; in the former case a
water-assisted sheetlike layered structure is observed. In the
latter case anion encapsulated assembly is formed through
assembling of cations. Among the tetrahedral anions sulfate led
to trimeric subassemblies of the cationic bisphenol part which is
held together by sulfate ions forming assemblies with circular
shapes. The intramolecular H-bonding between the phenolic
hydroxy groups of the bisphenol molecules is observed in all
the cases except in the case of the sulfate salt (7). It is attributed
to large electrostatic interactions offered by the sulfate dianion.
The formation of the tetrafluoroborate salt of 1 from sodium
tetrafluoroborate in methanol is a very rare phenomenon.
Finally, bisulphate anion is trapped from the acidolysis of
magnesium sulfate and sulphuric acid in methanol, and
stabilization of bisulphate anion by bisphenol guest from this
reaction is unprecedented to best of our knowledge.
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Crystal Growth & Design
Article
Table 3. Crystallographic Parameter of 1−10
compound no.
formulas
1
2
3
4
5
C20H22N2O2
859874
322.14
C21H26N2O3
859875
C24H28N2O7
859878
456.48
C22H24N2O4
859877
C26H32N2O6
859876
468.54
CCDC no.
mol wt
354.14
380.43
space group
a /Å
P21/n
P1
P21/c
P1
P21/c
̅
̅
13.7298(6)
9.1144(4)
14.9435(6)
90.00
8.7555(8)
10.3506(10)
11.3880(12)
79.478(7)
70.873(6)
79.682(6)
950.73(16)
1.238
15.7164(10)
9.2068(5)
16.0795(10)
90.00
8.0009(3)
9.2227(3)
13.6691(5)
90.928(2)
102.486(2)
103.478(2)
955.31(6)
1.323
8.0566(5)
33.229(2)
9.1803(7)
90.00
b /Å
c /Å
α/°
β/°
γ/°
V/ Å3
density/Mg m−3
abs coeff/mm−1
F(000)
90.00
90.744(4)
90.00
101.130(5)
90.00
90.00
1747.40(13)
1.225
2326.5(2)
1.303
2411.5(3)
1.291
0.080
0.083
0.096
0.092
0.092
688
380
968
404
1000
total no. of reflections
reflections, I > 2σ(I)
max θ/°
2910
3416
4484
3424
5997
2407
2790
2945
2943
3655
24.99
25.50
26.00
25.50
28.47
ranges (h, k, l)
−15 ≤ h ≤ 15
−10 ≤ k ≤ 10
−16 ≤ l ≤ 16
95.0
−10 ≤ h ≤ 10
−12 ≤ k ≤ 12
−13 ≤ l ≤ 13
96.3
−18 ≤ h ≤ 19
−11 ≤ k ≤ 8
−19 ≤ l ≤ 18
98.0
−9 ≤ h ≤ 9
−11 ≤ k ≤ 11
−16 ≤ l ≤ 16
96.2
−9 ≤ h ≤ 9
−11 ≤ k ≤ 11
−16 ≤ l ≤ 16
98.5
complete to 2θ (%)
data/restraints/parameters
GOF (F2)
2910/0/227
0.993
3416/0/247
1.053
4484/0/316
0.706
3424/0/267
0.926
5997/0/314
0.806
R indices [I > 2σ(I)]
R indices (all data)
compound no.
0.0577
0.0518
0.0505
0.0420
0.0526
0.0678
0.0621
0.0723
0.0490
0.0885
6
7
8
9
10
formulas
C20H23ClN2O6
859879
C40H46N4O8S
859883
742.87
C20H24N2O6S
859881
C20H25BF4N2O3
859880
C20H23N3O5
859882
CCDC no.
mol wt
422.85
420.47
428.23
385.41
space group
a /Å
P21/c
R32
P1
P1
P21/c
̅
̅
15.309(3)
8.9162(19)
15.951(4)
90.00
15.094(8)
15.094(8)
48.91(5)
90.00
8.0024(6)
10.0959(8)
13.6380(10)
81.435(4)
77.635(4)
70.938(4)
1013.53(13)
1.378
8.1285(5)
10.9801(7)
11.9948(7)
96.789(4)
95.608(4)
99.124(4)
1042.17(11)
1.365
8.0447(12)
26.422(5)
11.2878(18)
90.00
b /Å
c /Å
α/°
β/°
γ/°
V/ Å3
density/Mg m−3
abs coeff/mm−1
F(000)
110.878(13)
90.00
90.00
126.488(10)
90.00
120.00
2034.4(7)
1.381
9650(12)
1.150
1929.0(6)
1.327
0.227
0.127
0.200
0.114
0.097
888
3546
3546
448
816
total no. of reflections
reflections, I > 2σ(I)
max θ/°
3675
4002
3546
3700
3215
1838
3309
2974
2552
1694
25.50
25.48
25.25
25.49
25.25
ranges (h, k, l)
−18 ≤ h ≤ 17
−10 ≤ k ≤ 10
−19 ≤ l ≤ 18
97.1
−15 ≤ h ≤ 18
−18 ≤ k ≤ 18
−50 ≤ l ≤ 59
99.5
−9 ≤ h ≤ 9
−12 ≤ k ≤ 12
−16 ≤ l ≤ 14
96.6
−9 ≤ h ≤ 9
−13 ≤ k ≤ 11
−14 ≤ l ≤ 14
95.0
−9 ≤ h ≤ 8
−31 ≤ k ≤ 31
−13 ≤ l ≤ 11
92.0
complete to 2θ (%)
data/restraints/parameters
GOF (F2)
3675/0/279
0.983
4002/0/246
1.055
3546/0/277
1.050
3546/0/277
0.928
3215/0/266
1.083
R indices [I > 2σ(I)],
R indices (all data)
0.0730
0.0863
0.0457
0.0895
0.1774
0.1557
0.0741
0.0373
0.0635
0.1063
HImbp·NO3 (10). A solution prepared from an equimolar amount
(0.5 mmol) of Imbp (0.161 g) and HNO3 was allowed to crystallize.
After one week, colorless crystals were obtained. Yield, 95%. IR
(cm−1): 3352 (s), 3125 (s), 3024 (s), 2914 (s), 1744 (w), 1615 (s),
1491 (s), 1439 (m), 1419 (m), 1384 (s), 1330 (s), 1300 (s), 1260 (s),
1226 (s), 1188 (s), 1096 (m), 1041 (m), 987 (w), 934 (w), 834 (m),
626 (w), 565 (w).
spectrophotometer in the spectral region 4000−400 cm−1. Thermog-
ravimetric analysis (TGA) and differential scanning calorimetry (DSC)
analyses were performed on a TA Instruments, SDT Q600
thermogravimetric analyzer, and Q20 differential scanning calorimeter
respectively under an atmosphere of dry nitrogen from 25 to 500 °C
with a heating rate of 5 °C.
X-ray Crystallographic Studies. Diffraction data for compounds
́
Physical Measurements. Infrared spectra (KBr pellets) of the
solids were recorded on a Perkin-Elmer Spectrum One FT-IR
1−10 were collected at 296 K with MoKα radiation (λ = 0.71073 Å)
using a Bruker Nonius SMART APEX CCD diffractometer equipped
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Crystal Growth & Design
Article
with graphite monochromator and Apex CD camera. The SMART
software was used for data collection and also for indexing the
reflections and determining the unit cell parameters. Data reduction
and cell refinement were performed using SAINT software and the
space groups of these crystals were determined from systematic
absences by XPREP and further justified by the refinement results. The
structures were solved by direct methods and refined by full-matrix
least-squares calculations using SHELXTL software. All the non-H
atoms were refined in the anisotropic approximation against F2 of all
reflections. The H-atoms attached to heteroatoms in these crystals
were located in the difference Fourier synthesis maps and refined with
isotropic displacement coefficients. Negligible absorption was found in
each crystal. Crystal structure and details of the final refinement
parameters of 1−10 are summarized in Table 3.
Des. 2009, 9, 3692. (c) Tominaga, M.; Masu, H.; Azumaya, I. Cryst.
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(14) (a) Willans, C. E.; French, S.; Anderson, K. M.; Barbour, L. J.;
Gertenbach, J.-A.; Lloyd, G. O.; Dyer, R. J.; Junk, P. C.; Steed, J. W.
Dalton Trans. 2011, 40, 573. (b) du Plessis, M.; Barbour, L. J. Dalton
Trans. 2012, DOI: 10.1039/C1DT11564B.
(15) (a) Gandour, R. D.; Nabulsi, N. A. R.; Fronczek, F. R. J. Am.
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̈
ASSOCIATED CONTENT
■
P. Cryst. Growth Des. 2006, 6, 2699. (c) Sethuraman, V.; Stanley, N.;
Muthiah, P. T.; Sheldrick, W. S.; Winter, M.; Luger, P.; Weber, M.
Cryst. Growth Des. 2003, 3, 823. (d) Wichmann, K. A.; Boyd, P. D. W.;
S
* Supporting Information
CIF of all the 10 structures 1−10; the powder XRD, TG
analysis, FT-IR of all the salts, 1HNMR spectra of the salts. The
materials are available free of charge via the Internet at http://
pubs.acs.org.
Sohnel, T.; Allen, G. R.; Phillips, A. R. J.; Cooper, G. J. S. Cryst. Growth
̈
Des. 2007, 7, 1844.
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G. Z. Chem. Commun. 2007, 525.
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(20) Biradha, K.; Samai, S.; Maity, A. C.; Goswami, S. Cryst. Growth
Des. 2010, 10, 937.
AUTHOR INFORMATION
■
Corresponding Author
(21) (a) Haile, S. M.; Boyens, D. A.; Chisholm, C. R. I.; Merie, R. B.
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*E-mail: juba@iitg.ernet.in.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are thankful to the Department of Science and
Technology New-Delhi for XRD facility and financial
assistance.
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(Berlin) 2004, 111, 1. (b) Braga, D.; D’Oria, E.; Grepioni, F.; Mota, F.;
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