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Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Synthesis, crystal structures and competitivecomplexation property of a family of calix-crown hybrid molecules and their application inextraction of potassium from bittern
Vallu Ramakrishna, E. Suresh, Vinod P. Boricha, Anjani K. Bhatt & ParimalPaul
To cite this article: Vallu Ramakrishna, E. Suresh, Vinod P. Boricha, Anjani K. Bhatt & ParimalPaul (2015) Synthesis, crystal structures and competitive complexation property of a familyof calix-crown hybrid molecules and their application in extraction of potassium from bittern,Supramolecular Chemistry, 27:10, 706-718, DOI: 10.1080/10610278.2015.1080367
To link to this article: http://dx.doi.org/10.1080/10610278.2015.1080367
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Synthesis, crystal structures and competitive complexation property of a family of calix-crownhybrid molecules and their application in extraction of potassium from bittern
Vallu Ramakrishnaa, E. Suresha,b, Vinod P. Borichaa, Anjani K. Bhatta and Parimal Paula,b*aAnalytical Division and Centralized Instrument Facility, CSIR-Central Salt and Marine Chemicals Research Institute,
G. B. Marg, Bhavnagar 364002, India; bAcademy of Scientific and Innovative Research (AcSIR), CSIR-CSMCRI, G. B. Marg, Bhavnagar364002, India
(Received 1 April 2015; accepted 2 August 2015)
A family of calix-crown hybrid molecules containing calix[4]arene and crown-5/6, either at lower rim or at both upper and
lower rims, have been synthesised, characterised and their competitive complexation property towards alkali and alkaline
earth metal ions in aqueous media have been investigated. The competitive metal ion extraction study, carried out with
equimolar mixture of Liþ, Naþ, Kþ, Mg2þ, Ca2þ and Sr2þ in aqueous media, revealed that the amount of Kþ extracted is
remarkably high compared to other metal ions. Complexation with Kþ has been investigated by 1H NMR, association
constants and thermodynamic parameters have been determined by isothermal calorimetric study. The molecular structures
of one of the receptors and two of the Kþ complexes have been established by single crystal X-ray study. One of the
receptors formed bimetallic complex and it exhibited interesting polymeric network structure with bridged picrate anion.
These receptors have been applied for extraction of metal ions from bittern.
Keywords: Calixarene; crystal structures; two-phase extraction; isothermal calorimetric study; alkali and alkaline earthmetal ions
Introduction
Calixarenes are receiving increasing attention because of
their applications in various areas such as supramolecular
chemistry, coordination chemistry, molecular sensor etc.
(1–15). The chemistry of calixarene has become more
versatile because they can be easily modified according to
the requirement and these modified calixarenes provide a
highly organised architecture for the assembling of
converging binding sites (16–20). Among various sizes
of calixarenes, calix[4]arenes have been mainly used for
the application in supramolecular chemistry and molecular
sensing because of their rigid structure and binding ability
towards various ions and molecules (21–26). Calix[4]
arenes exist in four conformations such as cone, partial
cone, 1,2 alternate and 1,3-alternate cone, among which
cone and 1,3 alternate cone conformations have been
extensively used for the study related to interaction with
metal ions (27–31). Another class of calixarene
derivatives has been developed incorporating crown ethers
as ionophore and these calix-crown hybrid molecules are
suitable to use as molecular sensor, particularly for the
interaction with alkali and alkaline earth metal ions (32–
38). This class of compounds has been extended to calix[4]
arene bis-crown ethers, in which two crown rings
incorporated at both sides of the calix moiety in its 1,3-
alternate conformation and it can accommodate two metal
ions in the two crown moieties (33, 34, 39–42).
The aim of the present study is to design and develop
calix-crown hybrid molecules, which can be used for
extraction of alkali metal ions, preferably potassium, from
aqueous solution/natural sources such as sea bittern.
Bittern is a solution, which left out after separation of
common salt (NaCl) from sea water by solar evaporation,
it mainly contains Naþ, Kþ, Mg2þ and Ca2þ and small
amount of Sr2þ and Liþ(43). If an extractant can be
developed, which can extract Kþ selectively in presence of
other metal ions mentioned above, then it may find
potential application in recovery of Kþ from the most
abundant natural source. It is commercially important as
India imports its entire requirement of potash.
In this paper we report synthesis, characterisation and
competitive complexation property of a family of calix-
crown hybrid receptors, in which crown-6 is incorporated
and the calixarene moiety is in cone and 1,3-alternate
conformations. In addition to the crown-6 moiety at the
lower rim, another crown-5/6 ring has also been
incorporated at the upper rim forming calix[4]arene
biscrown-5/6 receptors, which have the possibility of
complex formation with two metal ions. All of these
molecules have been characterised on the basis of
analytical and spectroscopic data and molecular structure
of one of the compound was established by single crystal
X-ray study. Competitive complexation property of all of
these molecules has been investigated using equimolar
q 2015 Taylor & Francis
*Corresponding author. Email: ppaul@csmcri.org
Supramolecular Chemistry, 2015
http://dx.doi.org/10.1080/10610278.2015.1080367Vol. 27, No. 10, 706–718,
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mixture of Liþ, Naþ, Kþ, Mg2þ, Ca2þ and Sr2þ in aqueous
media by two-phase extraction method followed by
analysis of metal ions in the extract by ICP. Kþ complexes
were also characterised in solid state and molecular
structures of two of the complexes were established by
single crystal X-ray study. Binding constant and other
thermodynamic parameters for the formation of two of the
Kþ complexes were evaluated by isothermal calorimetric
titration. These receptor molecules were applied for
extraction of metal ion(s) from bittern.
Results and discussion
Synthesis of compounds 1–4
The route followed for the synthesis of the compounds
1–4 is shown in Scheme 1 and details of the
experimental procedures are given in the ‘Experimental’
section. The starting compounds (A–D) were syn-
thesised following the literature procedure (44). The
compounds 1–4 were synthesised from the starting
compounds A–D, respectively by the reaction with one
equivalent amount of 1,2-catechol modified pentaethy-
lene glycol ditosylate in presence of two equivalent of
K2CO3/CsCO3 (for 2–4) as a base in refluxing
acetonitrile. The compounds were purified by column
chromatography using 1:2 ethyl acetate-hexane as eluent.
The C, H and N analysis of these compounds
(‘Experimental’ section) are in excellent agreement
with the proposed composition of the compounds. The
ES-MS spectra of all the four compounds are given as
supporting information (ESI, Figures S1–S4), the m/z
values are matched well with that of calculated values;
713.42 for 1 (calculated for [1 þ Kþ]þ ¼ 713.83),
797.56 (calculated for [2 þ Kþ]þ ¼ 797.99), 855.67
(calculated for [3 þ Naþ]þ ¼ 855.90) and 871.66
(calculated for [3 þ Kþ]þ ¼ 872.01), 1009.49 (calcu-
lated for [4 þ Csþ]þ ¼ 1009.86). The m/z values for all
of these compounds are in excellent agreement with the
metal containing cation (Mþ) instead of Hþ, indicatingthat these receptors can readily form complexes with
alkali metal ions. These compounds were further
characterised with the aid of 1H NMR spectroscopy.
The 1H NMR spectra of 1–4 have been submitted as ESI
(Figures S5–S8) and the data with assignment of peaks
are given in the ‘Experimental’ section. For compound 1,
the appearance of two doublets at d 3.41 and 4.34 for
Ar-CH2-Ar methylene protons confirmed its cone
conformation and the singlet appeared at d 7.73 is due
Scheme 1. Synthetic route for the synthesis of compounds (1–4); reagents/solvents: (i) iodo propane/K2CO3/acetonitrile, reflux, (ii)Tetra/pentaethyleneglycol ditosylate/K2CO3/acetonitrile, reflux, (iii) 1,2-catechol modified pentaethyleneglycol ditosylate /Cs2CO3/acetonitrile, reflux, (iv) 1,2-catechol modified pentaethyleneglycol ditosylate/K2CO3/acetonitrile, reflux and (v) 1,2-catechol modifiedpentaethyleneglycol ditosylate /Cs2CO3/acetonitrile, reflux.
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to OH protons (37). For the compounds 2–4, the signals
at d 3.86, 3.76 and 3.85, respectively are due to
ArCH2Ar methylene protons, suggesting 1,3-alternate
cone conformation for these compounds (33, 45). The
aromatic protons for the calix moiety, as expected,
appeared as two triplets and two doublets in the region d6.6–7.2 and the protons due to catechol moiety appeared
as multiplet at d 7.1. The methylene protons due to
crown moieties appeared in the region d 3.3–4.2. On the
basis of elemental analysis, ES-MS and 1H NMR data
the molecular structure assigned for 1–4 are shown in
Scheme 1. The molecular structure of 2 has been
established from single-crystal X-ray study (discussed
later).
Competitive complexation study of the compounds 1–4
The compounds 1–4 were used to investigate their
competitive complexation ability towards Liþ, Naþ, Kþ,Ca2þ, Mg2þ and Sr2þ (constituents of bittern) in aqueous
media containing equimolar amount of these metal ions
and picrate as counter anion. This study was carried out by
two-phase extraction in water-dichloromethane using
mixture of the metal ions and picrate, which facilitates
transport of metal complex formed from aqueous to non-
aqueous media by strong ion-pair interaction. The
concentrations of the metal ions in the extract were
determined by inductively coupled plasma (ICP) spec-
trometer, detail of the procedure has given in the
‘Experimental’ section and the data are given in Table 1.
The data indicate that the amount of metal ions extracted is
in the order Kþ . Naþ q Mg2þ, Ca2þ and no Liþ and
Sr2þ was detected in the extract. As far as the receptors are
concerned, the amount of Kþ in the extract increases in the
order 1 , 2 , 3 , 4, the maximum Kþ/Naþ ratio
observed for 4 is 4.31 (80.7 molar percentage). A bar
diagram showing the fraction of metal ions extracted using
all the four receptors is shown in Figure 1. Significantly
high amount of Kþ extracted for 3 and 4 is due to
incorporation of two crown rings at the opposite sides of
the calix moiety, the second crown ring incorporated is
without benzene ring and is flexible and can adjust for
making effective interaction with metal ion. Presence of
two rings can also encapsulate two metal ions enhancing
capability for extraction of metal ions. Lower extracting
capability of 1 and 2 for Kþ compared to 3 and 4 is due to
presence of one crown rings compared to two rings in 3
and 4, rigid nature of the 1,2-catechol containing crown-6
ring and the cavity size of the crown ring which is such that
it can accommodate Kþ as well as Naþ. For 1, probablyintramolecular H-bonding played important role for the
extraction of lowest amount of Kþ (discussed later).
Crystal structure of the Kþ complex of 2 (discussed in the
‘Crystal structures’ section) exhibited that the metal ion
bounded with four oxygen atoms of the crown ring and the
two oxygen atoms of the catechol moiety remained
uncoordinated, though Kþ in this case is co-ordinately
unsaturated and a water molecule occupied the fifth
coordination site. This observation clearly suggests the
rigid nature of the catechol containing crown-6 moiety and
the cavity size is such that it is difficult to discriminate Naþ
in the solution containing mixture of metal ions. For detail
solution study, we were interested to investigate
interaction of these receptors with Kþ with the aid of 1H
NMR spectroscopy, isothermal calorimetric titration and
solid state characterisation including structure determi-
nation by X-ray study.
1H NMR study
The interaction of Kþ ion with the receptors 1–4 were
investigated in acetonitrile by 1H NMR study using
Kþpic2. The 1H NMR spectral changes upon addition of
incremental amount of Kþpic2 were recorded, details of
the experimental procedure is given in the ‘Experimental’
Table 1. Ratio of the amount of metal ions extracted fromequimolar mixture of ions by two-phase extraction.a
Ratio of metal ions extractedb
Compounds Kþ/Naþ Kþ/Mg2þ Kþ/Ca2þ
1 1.15 10.97 2.752 1.66 16.79 6.753 4.19 9.53 23.554 4.31 11.97 35.94
a Concentration (%) of metal ion in the original solution (beforeextraction), Liþ ¼ 3.18, Naþ ¼ 10.4, Kþ ¼ 17.7, Mg2þ ¼ 10.9,Ca2þ ¼ 18.1 and Sr2þ ¼ 39.5.b The ratio is calculated by [% of Kþ in the extract][% of Mþ in theoriginal solution]/ [% of Mþ in the extract][% of Kþ in the originalsolution].
Figure 1. (Colour online) Bar diagram showing fraction ofmetalions extracted from equimolar mixture of metal ions using 1–4.
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section and the spectral changes for receptors 2 and 3 are
shown in Figures 2 and 3, respectively and that of 1 and 4
are submitted as ESI (Figures S9 and S10). It may be noted
that spectral changes upon incremental addition of Kþ ion
are two types, for 1 and 2 some of the peaks have shifted;
(Figures 2 and S9) on the other hand, for 3 and 4 new peaks
generated at the expense of some of the original peaks
(Figures 3 and S10). The continuous shift of peaks and
formation of new peaks with the progress of complex
formation is related to stability of complexes formed in
solution. If the donor atoms in the complexation unit can’t
make strong interaction due to improper size matching of
Figure 2. 1H NMR spectra for compound 2 upon addition of 0.24 (a), 0.48 (b), 1.20 (c), 3.61 (d) and 4.40 (e) molar equivalent amountsof Kþpic; shifting of some of the signals were noted upon addition of K-picrate.
Figure 3. 1H NMR spectra for compound 3 upon addition of 0.24 (a), 0.48 (b), 1.20 (c), 4.40 (d) and 6.62 (e), molar equivalent amountsof Kpic; new peaks are growing with the disappearance of the peaks of the original complex.
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the metal ion and the cavity size or for any other reason(s),
then simultaneous bond formation and dissociation
between metal ion and donors goes on in solution and in
such a situation the chemical shifts of the signals of the
complex formed and that of free receptor averaged out
resulting in a single peak for both the species showing
continuous shift of the signal with the progress of the
reaction (33, 34, 46). On the other hand, if the size of the
metal ion fits well in the calix-crown cavity, then it can
make stable complex with strong interaction with the
donor atoms and in such a situation new peaks grow due to
formation of the stable complex and the original signals of
the receptor disappear with the progress of complex
formation (33, 34). In the present case, the NMR data
indicate that for 1 and 2, the Kþ ion did not coordinate with
all the oxygen atoms of the crown moiety and the co-
ordinately unsaturated metal ion is involved in bond
formation and dissociation in solution involving all the
donor oxygen atoms of the crown moiety. For 3 and 4, the
NMR data indicates formation of stable complex, the
second crown ether moiety, which is more flexible, and
also involvement of picrate anion in coordination might
have played a major role in the formation of strong
complexes with Kþ. The crystal structures of 2 and 3 have
provided more information about it (discussed in the
crystallography section).
Isolated K1 complexes of the compounds 1–4
For solid state characterisation, Kþ complexes of 1–4
were synthesised. These complexes were obtained by the
reaction of the receptors with Kþ-pic2 in chloroform at
room temperature, as described in the ‘Experimental’
section. These complexes were characterised on the basis
of elemental analysis, ES-MS, IR and 1H NMR spectral
data, detail data of which are given in the ‘Experimental’
section. The C, H and N analysis data suggested 1:1
stoichiometry for the complexes derived from 1–3 and
1:2 stoichiometry for the complex of 4 with picrate as
counter anion. The ES-MS spectra of the Kþ complexes
of 1, 2, 3 and 4 have submitted as ESI (Figures S11–
S14). The m/z values of these complexes are in excellent
agreement with the calculated values. The values are
713.75 for [1 þ Kþ]þ (calculated 713.25), 797.72 for [2þ Kþ]þ (calculated 797.38), 871.57 for [3 þ Kþ]þ
(calculated 871.36), 915.83 and 477.38 for [4 þ Kþ]þ
and [4 þ K2þ]2þ, respectively (calculated 915.38 and
477.16). 1H NMR data with assignment of peaks are
given in the ‘Experimental’ section. The IR bands for
picrate anion are also given in the ‘Experimental’
section. Molecular structures of the Kþ-complexes of 2
and 4 have been established by single crystal X-ray study
and described below.
Table 2. Crystal data and refinement parameters for the compound 2 and the Kþ complexes, [2·Kþ·H2O]pic2 and [4·Kþ
2 ·1.5pic2]
0.5pic2·C6H5CH3.
Identification code cbc6prxm cb6prkm kcbc6prf
Chemical formula C48H54O8 C54H58KN3O16 C71H72K2N6O26
Formula weight 758.91 1044.13 1503.55Crystal Colour Colourless Yellow YellowCrystal Size (mm) 0.58 £ 0.14 £ 0.09 0.34 £ 0.29 £ 0.25 0.43 £ 0.20 £ 0.09Temperature (K) 150(2) 293(2) 150(2)Crystal System Monoclinic Monoclinic OrthorhombicSpace group P21 P21/n Pna21a(A) 11.6016(15) 19.0640(2) 15.760(2)b(A) 10.4070(13) 15.3264(16) 13.2369(17)c(A) 17.2280(2) 20.2810(2) 33.381(4)a (8) 90 90 90b (8) 107.377(2) 117.417(2) 90g (8) 90 90 90Z 2 4 4V(A3) 1985.1(4) 5260.3(10) 6963.8(15)Density (Mg/m3) 1.270 1.318 1.434m (mm21) 0.085 0.174 0.225F(000) 812 2200 3144Reflections collected 11,384 25,963 33,066Independent reflections 7204 9251 6255Rint 0.0221 0.0332 0.0521Number of parameters 507 759 947GOF on F 2 1.125 1.022 0.947Final R1/wR2 (I) $ 2s(I) 0.0451/ 0.1033 0.0625/0.1536 0.0697/0.2007Weighted R1/wR2 (all data) 0.0481/0.1050 0.1003/0.1775 0.0783/0.2118CCDC number CCDC 1043882 CCDC 1043883 CCDC 1043884
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Crystal structures
Single crystal X-ray structures of the compound 2 and that
of the Kþ complexes, [2·K1·H2O]pic2 and [4·K12 -
K12 ·1.5pic
2]0.5pic2·C6H5CH3 were determined and
details of crystallographic parameters are given in
Table 2. Compound 2 was crystallised in monoclinic
system with P21 space group and the calix moiety adopted
1,3-alternate conformation as depicted in Figure 4. The
packing diagram viewed down a-axis (Figure S15) shows
the layered orientation of the molecules along bc-plane.
Details of the intermolecular CZH· · ·O contacts with
symmetry codes are given in Table 3.
The Kþ complex of 2, [2 þ Kþ·H2O]þ, was
crystallised in monoclinic system with P21/n space
group. The crystal structure of this complex is shown in
Figure 5, it may be noted that Kþ in this complex is
penta-coordinated with four oxygen atoms from crown
moiety and one from coordinated water molecule
encapsulating the metal ion in the calix-crown cavity.
The K-O distances ranges from 2.804(2) to 3.344(3) A
and the K1-O16 distance is 2.604(4) A, respectively. The
packing diagram viewed down a-axis (Figure S16) shows
pairs of [2 þ Kþ·H2O]þ cations are tuned with opposite
orientations in which the coordinated water molecules
are positioned up and down fashion with the picrate
anions oriented between the pairs of the cations. Details
of pertinent H-bonding interactions with symmetry codes
are given in Table. 3.
Crystal structure analysis of the Kþ-complex of 4
revealed that it consists of two independent Kþ, two
picrate anions and a molecule of toluene as solvent of
Table 3. H-bonding parameters for the compounds 2 and the Kþ complexes, [2·Kþ·H2O] pic2 and [4·K2·1.5pic]0.5pic·C6H5CH3.
Compound DZH· · ·A d(H· · ·A)(A) d(D· · ·A)(A) ,DZH· · ·A(8)
Ionophore 2 C(7)ZH(7A)· · ·O(5)1 2.49(1) 3.435(3) 165.5(2)C(34)ZH(34)· · ·O(4)2 2.57 (2) 3.432(3) 153.6(3)
Symmetry code: (1) x, 2 1 þ y,z; (2) 2 2 x, 2 1/2 þ y,1 2 z[2·Kþ·H2O]pic
2 O(16)ZH(16C)· · ·O(9)1 1.84(2) 2.714(4) 157.2(3)O(16)ZH(16D)· · ·O(3) 1 2.40(2) 3.128(4) 135.3 (2)C(31)ZH(31A)· · ·O(14)2 2.54(3) 3.340(5) 139.7(3)C(41)ZH(41B)· · ·O(13)3 2.54(2) 3.293(3) 134.1(4)C(42)ZH(42B)· · ·O(13)3 2.55(2) 3.317(5) 136.2(3)C(10)ZH(10)· · ·O(9)1 2.56(4) 3.430(7) 158.2(3)
Symmetry code: (1) x,y,z; (2) 1/2 þ x,1/2 2 y, 2 1/2 þ z; (3) 1 2 x, 2 y,1 2 z[4·K2·1.5pic]0.5 pic·C6H5CH3 C(11)ZH(11)· · ·O(20)1 2.43(3) 3.312(8) 158.9(2)
C(30)ZH(30B)· · ·O(23)2 2.43(4) 3.324(7) 152.8(4)C(31)ZH(31B)· · ·O(17)3 2.54(5) 3.310(6) 136.6(6)C(32)ZH(32B)· · ·O(23)2 2.58(6) 3.480(8) 154.7(4)C(35)ZH(35)· · ·O(19)4 2.50(6) 3.390(5) 160.6(3)C(39)ZH(39B)· · ·O(19)3 2.53(4) 3.225(6) 128.7(3)C(44)ZH(44B)· · ·O(18)5 2.55(6) 3.288(7) 132.7(4)C(65)ZH(65A)· · ·O(15)5 2.49(5) 3.280(8) 139.7(3)C(65)ZH(65B)· · ·O(18)6 2.51(6) 3.448(8) 166.2(3)C(65)ZH(65B)· · ·N(3)6 2.48(4) 3.411(7) 164.4(4)
Symmetry code: (1)21/2 þ x,3/2 2 y,z; (2) 1/2 þ x,3/2 2 y,z; (3) 1 2 x,1 2 y, 2 1/2 þ z; (4) 3/2 2 x, 2 1/2 þ y, 2 1/2 þ z; (5) x,y,z;(6) 1/2 þ x,1/2 2 y,z
Figure 4. (Colour online) Ball and stick model of 2 depictingthe structure of the calix-crown ligand moiety with atomnumbering scheme.
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crystallisation. This complex was crystallised in orthor-
hombic system with Pna21 space group. The crystal
structure, shown in Figure 6, exhibits those two
independent potassium ions K1 and K2, which are
encapsulated in the crown cavity by coordinating with
the oxygen atoms of the crown moieties and picrate
anions. The K1–O distances involving oxygen atoms of
the crown moiety are in the range 2.828(5) to 3.307(6) A.
The other metal ion (K2) is hexa-coordinated with four
oxygen atoms from crown ether moiety with K2-O
distances ranging from 2.876(8) to 3.119(10) A and the
phenolate and nitro oxygen atoms of the picrate anion.
Packing and various hydrogen bonding interactions
between the K2-calix-crown monocationic strands with
the uncoordinated picrate and lattice toluene molecule
viewed down b-axis is shown in Figure S17. The zigzag
monocationic strands are oriented along c-axis and the
uncoordinated picrate anions and toluene molecules are
aligned and oriented along a-axis. Details of all these
hydrogen bonding interactions and the relevant symmetry
code are given in Table 3.
Powder XRD study
To confirm that the crystal structures of the Kþ-complexes are truly represent the bulk materials, the
powder XRD pattern of the bulk materials of the Kþ-complexes of 1 and 3 were recorded and the same were
simulated from the single crystal X-ray data. The
simulation was carried out following the method of Spek
(47). Excellent matching between the experimental and
simulated diffractograms (Figures S18 and S19) con-
firmed that the crystal structures actually represent the
bulk material.
Isothermal calorimetric titration
Isothermal calorimetric titration (ITC) for the reaction of
the ionophores 1, 3 and 4 with potassium picrate was
carried out in dry acetonitrile at 298 K for the
determination of association constant (Ka), stoichiometry
of the complexes formed and other thermodynamic
parameters. Detail experimental procedure has given in
the ‘Experimental’ section. The ITC titration profiles for
the receptors 1 and 3 are presented in Figure 7 and the
data such as association constant (Ka), entropy change
(TDS), enthalpy change (DH) and free energy change
(DG) are summarised in Table 4. The ITC titration
profiles indicate that the binding process is exothermic
and the curves for 1 and 3 exhibited complex formation
with a typical 1:1 stoichiometry. The ITC titration profile
for 4 didn’t fit well either for 2:1 or for 1:1 metal-ligand
stoichiometry, which probably due to the formation of
the polymeric complex and therefore the data for this
compound has not reported here. The log values of the
association constants (logKa) for 1 and 3 are 3.43 and
Figure 5. (Colour online) Ball and stick representation of[2·Kþ
. H2O]þ with atom numbering scheme (picrate anion is
omitted for clarity).
Figure 6. (Colour online) Ball and stick model for the complex [4·K12 ·1.5pic
2]0.5pic2 depicting the coordination of Kþ and formationof 1D coordination network (hydrogen atoms and lattice toluene molecule are omitted for clarity).
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5.67, respectively, which indicate that binding of Kþ
with 3 is much stronger than that of 1. For 1, the
catechol containing crown moiety is the only site for the
metal ion to interact; however, for 3 another crown ring
at the opposite side of the catechol containing crown
moiety is available for complex formation. Though the
cavity size of the crown-5 moiety does not fit well for
Kþ, yet the metal ion can interact strongly from above of
the plane of the crown moiety and also can interact with
the oxygen atom of the picrate anion to satisfy its
coordination number. The low association constant for 1
compared to 3 is probably due to strong intramolecular
H-bonding interaction between OH proton and adjacent
oxygen atom (OZH· · ·O) of the crown moiety, which
might have prevented easy entry of the metal ion into the
crown cavity to form complex. Similar situation was also
noted earlier for complexation of a calix-crown receptor
with Kþ and in that case the H-bonding interaction,
which prevented entry of metal ion into the cavity, has
been demonstrated with the help of crystallographic
study (32). The thermodynamic parameters obtained
from ITC study (Table 4) indicate that it is an enthalpy
driven process, which partially compensated by
unfavourable entropy change. The values of free energy
change (DG) are in agreement with the observed
association constants.
Application
All of these receptors were applied to extract metal ions
from a natural source such as sea bittern (the solution
obtained after removal of common salt from sea water by
solar evaporation). This sea bittern mainly contains
Naþ ¼ 6.8%, Kþ ¼ 1.4%, Mg2þ ¼ 3.6%, Ca2þ ¼ 0.02%
and trace amount of other metal ions such as Liþ, Sr2þ etc.,
however concentration of these metal ions may vary
slightly depending on the conditions under which bittern is
collected. The metal ions were extracted following the
0.0 0.5 1.0 1.5
–6.0
–4.0
–2.0
0.0
–15.00
–10.00
–5.00
0.00
0 10 20 30 40 50 60
Time (min)
µcal
/sec
Molar Ratio
kcal
mol
–1 o
f inj
ecta
nt
0.0 0.5 1.0 1.5 2.0
–35.0
–30.0
–25.0
–20.0
–15.0
–10.0
–5.0
0.0
–25.00
–20.00
–15.00
–10.00
–5.00
0.00
0 10 20 30 40 50 60
Time (min)
µcal
/sec
Molar Ratio
kcal
mol
–1 o
f inj
ecta
ntFigure 7. Isothermal calorimetric titration profiles of 1 and 3 with Kþ·pic2 in acetonitrile at 298K.
Table 4. Association constant (Ka), entropy change (TDS),enthalpy change (DH) and free energy change (DG) obtainedfrom isothermal calorimetric titration.
Isothermal calorimetric titrations’ data for Kþ ion
Ionophore logKa
DH(kcalmol21)
TDS(kcalmol21)
DG(kcalmol21)
1 3.43 28.95 24.26 24.693 5.67 233.40 225.63 27.77
Table 5. Ratio of the amount of metal ions extracted frombittern by two-phase extraction using all the four receptors.a
Ratio of metal ions extractedb
Compounds Kþ/Naþ Kþ/Mg2þ Kþ/Ca2þ
1 8.18 30.59 0.022 18.11 140.61 0.103 27.59 131.52 0.114 32.65 205.69 0.16
aConcentration (%) of metal ions in the bittern (before extraction)Naþ ¼ 57.65, Kþ ¼ 11.56, Mg2þ ¼ 30.64, and Ca2þ ¼ 0.13 %.b The ration is calculated by [% of Kþ in the extract] [% of Mnþ inbittern]/[% of Mnþ in the extract][% of Kþ in bittern].
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procedure similar to that used for extraction of metal ions
from their equimolar mixture (two-phase extraction). The
only difference is that bittern is used instead of solution
containing equimolar mixture of metal ions. The data are
presented in Table 5 and the bar diagram showing the
fraction of metal ions in bittern and that in the extract using
all the receptors is shown in Figure S20. It may be noted
that the amount of Kþ extracted is increased in the order
1 , 2 , 3 , 4, however considerable amount of Ca2þ
was also extracted.
Conclusion
A family of calix[4]arene derivatives incorporating crown-
6 moiety at the lower rim and crown-5/6 at the upper rim
for two of them have been synthesised, characterised and
their competitive complexation property towards alkali
and alkaline earth metal ions in aqueous media has been
investigated. The competitive complexation ability has
been studied by two-phase extraction method with
equimolar mixture of Liþ, Naþ, Kþ, Mg2þ, Ca2þ and
Sr2þ in aqueous media using picrate as counter anion. The
metal ions in the extract (organic phase) were analysed by
inductively coupled plasma (ICP) spectrometer and the
data suggests that the amount of Kþ extracted increases in
the order 1 , 2 , 3 , 4 and the maximum value noted
for 4 is 80.7 molar percentage. It also showed small
amount of Naþ, Ca2þ and Mg2þ, however no Liþ and Sr2þ
was detected in the extract. Binding constants, stoichi-
ometry of the complexes formed and thermodynamic
parameters such as entropy change, enthalpy change and
free energy change for two of the complexes have been
evaluated by isothermal calorimetric titration. The
complex formation in solution was investigated by 1H
NMR study. Molecular structures of one of the receptors
(1) and two of the Kþ complexes with 3 and 4 have been
established by single crystal X-ray study. These molecules
were applied to extract metal ions from the sea bittern,
where similar trend as observed for equimolar mixture of
metal ions, was noted. The larger ring size of the crown
moiety at upper rim, which fits well with the ionic size of
Kþ, and formation of bimetallic complexes, probably
helped to achieve high molar percentage of Kþ recovery
with the receptor 4.
Experimental
Materials
The materials catechol, 2-(2-chloroethoxy) ethanol,
tetraethylene glycol and pentaethlene glycol were
purchased from S.D Fine chemicals. All the solvents
were of analytical grade and purified by standard
procedures before use (48). Milli-Q (Millipore Corpor-
ation) water was used for two-phase extraction exper-
iments and ICP analysis. Metal picrate salts were prepared
by the reaction of picric acid and metal hydroxide in
aqueous media. All the reagents 2-(2-chloroethoxy)ethyl,
4-methylbezene sulfonate and pentaethyleneglycol dito-
sylate were prepared following the published procedure
(49). The starting materials p-tert-butylcalix[4]arene (50),
dealkylated calix[4]arene (51) were synthesised from the
literature procedure.
Measurements
Elemental analyses (C, H and N) were performed on a
model Vario Micro CUBE elemental analyser. Mass
spectra were recorded on a Q-TOF MicroTM LC-MS
instrument. Infrared spectra were recorded on a Perkin-
Elmer spectrum GXFT-system as KBr pellets. NMR
spectra were recorded on models DPX 200 and Avance II
500 Brucker FT-NMR instruments. The cation concen-
tration was measured with inductively coupled plasma
(ICP) spectrometer, model optima 2000DV, provided by
Perkin Elmer instrument. Single crystal X-ray structures
were determined using a Bruker SMART 1000 (CCD)
diffractometer. Thermodynamic parameters were deter-
mined using isothermal calorimeter (ITC200) provided by
Microcal Company.
Synthesis
Dihydroxycalix[4]arene benzocrown-6 (1)
This compound was prepared from calix[4]arene, in a
typical procedure 3.0 g (7mmol) of calix[4]arene, 0.976 g
(7mmol) K2CO3 were taken in dry acetonitrile (150mL)
and the content was stirred udder reflux for 2 h under
nitrogen atmosphere. After that 4.20 g (7mmol) of 1,2-
catechol modified pentaethyleneglycol ditosylate, dis-
solved in 20mL dry acetonitrile was added drop wise with
duration of 2 h and then the reaction mixture was refluxed
for 48 h. The solvent of the reaction mixture was then
evaporated under reduced pressure and the solid mass thus
obtained was dissolved in dichloromethane (100mL). The
solution was then treated with 100mL of 1N HCl, the
organic phase was separated and dried with anhydrous
MgSO4. After removal of solvent, the crude product
obtained was purified by column chromatography using
silica gel and 1:2 mixture of ethylacetate and hexane as
eluents. Yield: 2.8 g (60%). 1H NMR (CD3CN) d: 7.74 (s,
2H, ArOH-calix), 7.11 (d, J ¼ 7.5Hz, 4H, ArH, calix),
6.97–6.94 (overlapped doublet and multiplet, 6H, ArH,
calix and catechol), 6.92 (dd, 2H, ArH, catechol), 6.77 (t,
J ¼ 7.5Hz, 2H, ArH, calix), 6.65 (t, J ¼ 7.5Hz, 2H, ArH,
calix), 4.34 (d, J ¼ 13Hz, 4H, ArCH2Ar), 4.25 (t,
J ¼ 4.5Hz, 4H, Ar-OCH2), 4.11 (t, J ¼ 4.5Hz, 4H,
ArOCH2), 4.07 (t, J ¼ 4.5Hz, 4H, ArOCH2), 4.05 (t,
J ¼ 4.5 Hz, 4H, ArOCH2), 3.41 (d, J ¼ 13Hz, 4H,
ArCH2Ar). Selected IR band (KBr pellet, cm21) 3363 n
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(OH). ES-MS:m/z ¼ 713.42 (100%), calcd for [1þ Kþ]þ,713.83; Anal. Calcd for C42H42O8: C, 74.76; H, 6.27;
found: C, 74.32; H, 6.52;
1,3-Alternate dipropylcalix[4]arene-2,4-benzocrown-6
(2)
This compound was synthesised following the similar
procedure as described for 1 with the exception that 1,3-
dipropylcalix[4]arene was used instead of calix[4]arene
and Cs2CO3 was used as base instead of K2CO3. This
compound was purified by recrystallisation from chloro-
form and acetonitrile (1:1), which gave colourless crystals.
Yield: 3.0 g (62%). 1H NMR CD3CN d: 7.05 (overlapped,
dd, 6H, ArH, calix and catechol), 7.03 (d, J ¼ 4Hz, 2H,
ArH, calix), 6.95 (dd, J ¼ 6Hz, 2H, catechol), 6.75
(t, J ¼ 7.5Hz, 2H, ArH, calix), 6.68 (t, J ¼ 7.5Hz, 2H,
ArH, calix), 4.23 (t, J ¼ 3.75Hz, 4H, ArOCH2), 3.86
(t, J ¼ 3.5Hz, 4H, ArCH2Ar), 3.73 (t, J ¼ 4Hz, 4H,
ArOCH2), 3.67 (s, 4H, ArCH2Ar), 3.65 (s, 4H, ArOCH2),
3.63 (t, J ¼ 3.75Hz, 4H, ArOCH2), 3.49 (t, J ¼ 7.5Hz,
4H, ArOCH2), 1.57 (quartet, J ¼ 7.5Hz, 4H, -CH2-), 0.84
(t, J ¼ 7.5Hz, 6H, -CH3). ES-MS: m/z ¼ 797.56 (100%),
calcd for [2 þ Kþ]þ, 797.99; Anal. calcd for C48H54O8 C,
75.96; H, 7.17; Found: C, 75.46; H, 7.38.
1,3-Alternate calix[4]arenecrown-5-2,4-benzocrown-6 (3)
This compound was synthesised following the similar
procedure as described for 1, the only differences are calix
[4]arene-crown-5 was used instead of calix[4]arene and
Cs2CO3 was used as base instead of K2CO3. The
compound obtained was purified by column chromatog-
raphy using silica gel and 1:2 mixture of ethylacetate and
hexane. Yield: 60%. 1H NMR (CD3CN) d: 7.12 (d,
J ¼ 7.5Hz, 4H, ArH, calix), 7.01 (overlapped signals, 6H,
ArH, calix and catechol), 6.95 (dd, J ¼ 5.75Hz, 2H,
ArH, catechol), 6.84 (t, J ¼ 7.5Hz, 2H, ArH, calix),
6.63 (t, J ¼ 7.5Hz, 2H, ArH, calix), 4.16 (t, J ¼ 3.75Hz,
4H, -OCH2, crown), 3.76 (t, J ¼ 3.75Hz, 4H, ArOCH2,
crown), 3.75 (s, 8H, ArCH2Ar), 3.66 (t, J ¼ 4.5Hz, 4H,
OCH2CH2O, crown), 3.56 (s, 8H, -OCH2CH2O, crown),
3.50 (t, J ¼ 4.5Hz, 4H, -OCH2CH2O, crown), 3.45
(t, J ¼ 6.0 Hz, 4H, -OCH2CH2O, crown), 3.29
(t, J ¼ 6.25 Hz, 4H, -OCH2CH2O, crown). ES-MS:
m/z ¼ 872.42 for [3 þ Kþ]þ (calculated 872.01), 855.67
(50%), calculated for [3 þ Naþ]þ, 855.90. Anal. calcd for
C50H56O11: C, 72.10; H, 6.77; found: C, 71.71; H, 6.64;
1,3-Alternate calix[4]arenecrown-6-2,4-benzocrown-6 (4)
This compound was prepared following the similar
procedure as described for 3 using calix[4]arene-crown-6
as starting material. Yield 2.2 g (63%). 1H NMR (CD3CN)
d: 7.14 (d, J ¼ 7.5Hz, 4H, ArH, calix), 7.08 (m, 6H, ArH,
calix and catechol), 7.03 (dd, J ¼ 6.0Hz, 2H, catechol),
6.96-6.91 (m, 2H, ArH, calix), 6.76-6.69 (m, 2H, ArH,
calix), 4.22 (t, J ¼ 3.75Hz, 4H, –ArOCH2, crown), 3.85
(t, J ¼ 3.75Hz, 4H, –ArOCH2, crown), 3.73-3.69 (m, 4H,
-OCH2CH2O, crown), 3.66 (m, 12H, -OCH2CH2O,
crown; 8H, ArCH2Ar,), 3.64 (m, 4H, -OCH2CH2O,
crown), 3.60-3.59 (m, 4H, -OCH2CH2O, crown), 3.53
(m, 4H, -OCH2CH2O, crown). ES-MS: m/z ¼ 1009.49,
(100%) calcd for [4 þ Csþ]þ, 1009.86; Anal. calcd for
C52H60O12: C, 71.21; H, 6.89; Found: C, 71.59; H, 6.47.
Selectivity determination
Competitive complexation property of the receptors 1–4
towards Liþ, Naþ, Kþ, Mg2þ, Ca2þ and Sr2þ were
determined by two-phase extraction method using
aqueous solution containing equimolar mixture of these
metal ions with picrate as counter anion. In a typical
procedure, equimolar mixture (10mL) of alkali metal
picrate (Liþ, Naþ, Kþ, Mg2þ, Ca2þ and Sr2þ, 0.1M each)
in aqueous media and CH2Cl2 solution (10mL) of the
required receptor (0.002 M) were mixed and vigorously
shaken in a vortex mixture for 30min. The solution was
then transferred to a separating funnel and allowed to
stand for 4 h. After settling down, the dichloromethane
layer was separated and transferred to a crucible, the
solvent was evaporated by gentle heating on a water bath,
and then heated in a furnace at 5508C for 5 h. The residue
was dissolved in deionised water (, 5mL) and filtered
through filter paper (0.2mm). The concentrations of the
metal ions in the filtrate were estimated by ICP
spectrometer using a standard solution containing a
mixture of LiCl, NaCl, KCl, MgCl2,CaCl2 and SrCl2(10 ppm each) and the selectivity ratios of metal ions in
the extract are given in Table 1.
Synthesis of metal complexes
The Kþ complexes were synthesised following a general
procedure. In a typical experiment, a mixture of 0.05mmol
of the receptors (1/2/3/4) and Kþ picrate (0.5mmol, ten-
fold excess) was stirred in chloroform at room temperature
for 24 h. The unreacted picrate salt was then removed by
filtration and the complex was obtained by removing the
solvent from the filtrate under reduced pressure. The
yellow complex was then purified by dissolving the mass
in minimum volume (ca. 4mL) of dichloromethane (in
which Kþ picrate is almost insoluble) followed by
filtration to remove trace amount of unreacted Kþ picrate.
The solution was then removed, which gave yellow
product. The 1H NMR spectra of the complexes did not
show any signal corresponding to free ionophore or excess
picrate anion, which confirmed the complete complexa-
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tion. Yield: 85–90%. Crystals suitable for the single
crystal X-ray study were grown by diffusion of toluene
into the dichloromethane solution of the complexes.
Characterisation data of the complexes
[1·K1]pic2: 1H NMR (CD3CN) d: 8.61 (s, 4H, picrate
anion) 7.40 (s, 2H, Ar-OH-calix), 7.13 (d, J ¼ 7.5Hz, 4H,
phenylene), 6.91-6.85 (m, 6H, ArHm2calix, 2H over-
lapped ArHp2calix), 6.76 (t, J ¼ 7.5Hz, 2H, ArHm2calix),
6.70 (t, J ¼ 7.5Hz, 2H, ArHp2calix), 4.23 (t, J ¼ 4.25Hz,
4H, ArOCH2), 4.20 (d, J ¼ 4.5Hz, 4H, OCH2CH2O-
benzocrown-6), 4.17 (d, J ¼ 9.0Hz, 4H, ArCH2Ar), 4.07
(t, J ¼ 4.25Hz, 4H, OCH2CH2O-benzocrown-6), 4.02(t,
J ¼ 4.0Hz, 4H, OCH2CH2O-benzocrown-6), 3.47 (d,
J ¼ 13.5 Hz, 4H, ArCH2Ar). Selected IR band (KBr
pellet, cm21) 1592, 1502 cm21 for NO2 and 1333 cm-1 for
picrate; ES-MS: m/z ¼ 713.75 (100%), calcd for
[2 þ Kþ]þ713.83. Anal. calcd For C48H44O15N3K; C,
61.21; H, 4.71; N, 4.46; Found: C, 62.05; H, 4.51; N, 4.32;
[2·K1. H2O]Pic2: 1H NMR CD3CN d: 8.62(s, 2H,
picrate anion), 7.16 (d, J ¼ 7.5Hz, 4H, phenylene),7.04
(d, J ¼ 7.5Hz, 4H, ArHm2calix), 6.93 (d, J ¼ 4Hz, 2H,
ArHm2calix), 6.85 (t, J ¼ 7.5Hz, 2H, ArHp2calix), 6.73
(t, J ¼ 7.5Hz, 2H, ArHp2calix), 4.23 (broad, s, 4H,
ArOCH2), 4.05 (broad, s, 4H, ArCH2Ar), 3.93 (broad, s,
4H, -OCH2CH2O-crown-6), 3.85 (broad, s, 4H, ArCH2Ar),
3.72 (q, J ¼ 15.5Hz, 8H, -OCH2CH2O-crown-6), 3.56 (t,
J ¼ 7.5 Hz, 4H, -OCH2CH2O-crown-6), 1.57 (q,
J ¼ 7.5Hz, 4H, –CH2–), 0.85 (t, J ¼ 7.5Hz, 6H, -CH3).
Selected IR band (KBr pellet, cm21) 1591, 1500 cm21 for
NO2 and 1382 cm21 for picrate; ES-MS: m/z ¼ 797.72
(100%), calcd for [2 þ Kþ]þ797.99; Anal. calcd for C54
H58 O16 N3 K, C, 62.12; H, 5.59; N, 4.02; Found: C, 62.54;
H, 5.86; N, 4.11;
[3·K1]Pic2: 1H NMR (CD3CN) d: 8.60 (s, 2H, picrateanion), 7.30 (d, J ¼ 7.5Hz, 4H, phenylene), 7.18 (d,
J ¼ 7.5Hz, 4H, ArHm2calix), 7.04 (dd, J ¼ 3.16Hz, 2H,
ArHm2calix), 6.94 (dd, J ¼ 2Hz, 2H, ArHp2calix, 2H,
ArHm2calix), 6.84 (t, J ¼ 7.5Hz, 2H, ArHp2calix), 4.24
(t, J ¼ 5.5 Hz, 4H, Ar-OCH2-crown-5-), 3.88 (t,
J ¼ 2.25Hz, 4H, Ar-OCH2-benzocrown-6), 3.86 (t, 4H, -
OCH2CH2O-crown-5), 3.79 (broad, s, 4H, -OCH2CH2O-
crown-5), 3.74 (overlapped, s, 8H, ArCH2Ar, 2H, -
OCH2CH2O-benzocrown-6), 3.68 (t, 4H, J ¼ 1.5Hz -
OCH2CH2O-crown-5, 2H, -OCH2CH2O-benzocrown-6),
3.66 (s, 8H, –OCH2CH2O-benzocrown-6). Selected IR
band (KBr pellet, cm21) 1552, 1503 cm21 for NO2 and
1307 cm21 for picrate; ES-MS: m/z ¼ 871.42 (100%),
872.54 (85%) calcd for [3 þ Kþ]þ872.00; Anal. calcd for
C56 H58 O18 N3 K, C, 61.14; H, 5.31; N, 3.81; Found: C,
60.27; H, 5.24; N, 4.06;
[4·K12 ·1.5pic
2]0.5pic2·C6H5CH3:1H NMR (CD3CN)
d: 8.61 (s, 4H, picrate anion), 7.32 (d, J ¼ 7.5Hz, 4H,
phenylene), 7.23 (d, J ¼ 7.5Hz, 4H, ArHm2calix), 7.11 (t,
J ¼ 3.5Hz, 2H, ArHm2calix), 7.01 (dd, J ¼ 4.62Hz, 2H,
ArHp2calix, 2H, ArHm2calix), 6.74 (t, 2H, ArHp2calix),
4.26 (t, J ¼ 4.0Hz, 4H, Ar-OCH2-benzocrown-6), 3.96
(broad, s, 4H, ArOCH2-crown-6), 3.85 (t, J ¼ 4.25Hz, 8H,
OCH2CH2O-crown-6), 3.77 (s, 4H, OCH2CH2O-crown-6,
8H, ArCH2Ar), 3.73 (d, J ¼ 6.5Hz, 12H, OCH2CH2O-
benzocrown-6, overlapped, 2H, OCH2CH2O-crown-6).
Selected IR band (KBr pellet, cm21) 1594, 1505 cm21 for
NO2 and 1357 cm21 for picrate; ES-MS: m/z ¼ [4
þ K1þ]þ916.30, (100%) [4 þ K2
þ]þ477.65 (30%) calcd
for, [4 þ Kþ]þ916.05, [4 þ K2þ]þ477.57; Anal. calcd For
C71 H71 O26 N6 K2, C, 56.75; H, 4.76; N, 5.59; Found: C,
55.86; H, 4.97; N, 5.63.
Single crystal X-Ray study
Crystals of suitable size of the ionophore 1, and
the complexes [2·Kþ]pic2 and [4·K12 ·1.5pic
2]·0.5pic2·
C6H5CH3 were selected, immersed in partone oil and then
mounted on the tip of a glass fibre using epoxy resin.
Intensity data for all three crystals were collected at 100K
using graphite monochromatised MoKa (l ¼ 0.71073 A)
radiation on a Bruker SMART APEX diffractometer
equipped with CCD area detector. The data integration and
reduction were processed with SAINT software (52).
An empirical absorption correction was applied to the
collected reflections with SADABS (53). The structures
were solved by direct methods using SHELXTL (54) and
refined on F 2 by the full-matrix least-squares technique
using the SHELXL-97 (55) package. Graphics are
generated using PLATON (56) and MERCURY 1.3.
(57). For all the compounds, non-hydrogen atoms were
refined anisotropically till convergence is reached and the
hydrogen atoms attached to the ligand moieties were
stereochemically fixed. Crystallographic parameters for
both the compounds are given in Table 2.
Isothermal calorimetric titration
The stoichiometry of the complexes formed, binding
constant, and other thermodynamic parameters for the
reaction of the receptors with KþPic2 in acetonitrile were
determined by isothermal calorimetric titration (ITC).
In this experiment, first a blank experiment was carried out
using solute and solvent (without taking receptor) and this
data was subtracted from the titration data for complex
formation. For complexation study, the solution of the
ionophore (2mM for 1 and 0.67mM for 3) in dry
acetonitrile was taken in the cell and the solution of Kpic
in the same solvent (16mM for 1 and 6mM for 3) was
taken in the syringe. The solution of the Kpic was then
added maintaining the successive additions of 2mL,spacing 180 s intervals. The calorimetric study was
performed at 298K. The blank data was then subtracted
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from the ITC data for complex formation and the resultant
data was fitted with the aid of Origin 7 provided by
MicroCal by using (1:1) curve fitting model. This plot gave
the values of stoichiometry, binding constant (Ks),
enthalpy change (DH), entropy change (DS) and free
energy change (DG) was calculated using the equation
DG ¼ DH–TDS.
Application for extraction of metal ions from bittern
The receptors molecules were applied for extraction of
metal ions from sea bittern using the similar procedure
as described for competitive complexation study by two-
phase extraction method, except sea bittern and picric
acid were used instead of mixture of metal-picrate salts.
The concentration of metal ions in the organic phase was
estimated by ICP spectrometer, as described above.
Acknowledgements
CSIR-CSMCRI Registration No.: 041/2015.We gratefully thankone of the reviewers for valuable suggestions for ITCmeasurement. Financial assistance received in the form ofNetwork Project (CSC 0105) from CSIR, New Delhi is gratefullyacknowledged. V. R gratefully acknowledges CSIR for awardingSenior Research Fellowship (SRF). We thank Rajesh Patidar,Arun. K. Das, and V. Vakani for ICP analysis, mass and FT-IRspectra, respectively.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
(1) Beer, P.D.; Hayes, E.J. Coord. Chem. Rev. 2003, 240,167–189. doi:10.1016/S0010-8545(02)00303-X.
(2) Sliwa, W. J. Inclusion Phenom. Macrocycl. Chem. 2005,52, 13–37. doi:10.1007/s10847-005-0083-6.
(3) Yoon, J.; Kim, S.K.; Singh, N.J.; Kim, K.S. Chem. Soc. Rev.2006, 35, 355–360. doi:10.1039/b513733k.
(4) Kim, J.S.; Quang, D.T. Chem. Rev. 2007, 107, 3780–3799.doi:10.1021/cr068046j.
(5) Lo, L.P.; Wong, M.S. Sensors 2008, 8, 5313–5335. doi:10.3390/s8095313.
(6) Steed, J.W.; Atwood, J.L. Supramolecular Chemistry;Wiley: Chichester, 2009; pp 286–306.
(7) Creaven, B.S.; Donlon, D.F.; McGinley, J. Coord. Chem.Rev. 2009, 253, 893–962. doi:10.1016/j.ccr.2008.06.008.
(8) Ohto, K.; Matsufuji, T.; Yoneyama, T.; Tanaka, M.;Kawakita, H.; Oshima, T.J. Inclusion Phenom. MacrocyclicChem. 2011, 71, 489–497. doi:10.1007/s10847-011-9998-2.
(9) Kim, H.J.; Lee, M.H.; Mutihac, L.; Vicens, J.; Kim, J.S.Chem. Soc. Rev. 2012, 41, 1173–1190. doi:10.1039/C1CS15169J.
(10) Dube, H.; Rebek, J. Jr. Angew. Chem., Int. Ed. 2012, 51,3207–3210. doi:10.1002/anie.201108074.
(11) Slovak, S.; Cohen, Y. Chem. Eur. J. 2012, 18, 8515–8520.doi:10.1002/chem.201102809.
(12) Tang, H.; de Oliveira, C.S.; Sonntag, G.; Gibb, C.L.D.;Gibb, B.C.; Bohne, C. J. Am. Chem. Soc. 2012, 134,5544–5547. doi:10.1021/ja301278p.
(13) Chinta, J.P.; Ramanujam, B.; Rao, C.P. Coord. Chem. Rev.2012, 256, 2762–2794. doi:10.1016/j.ccr.2012.09.001.
(14) Harrowfield, J. Chem. Commun. 2013, 49, 1578–1580.doi:10.1039/c3cc38667h.
(15) Pathak, R.K.; Dessingou, J.; Hinge, V.K.; Thawari, A.G.;Basu, S.K.; Rao, C.P. Anal. Chem. 2013, 85, 3707–3714.doi:10.1021/ac400059w.
(16) Yuan, M.; Zhou, W.; Liu, X.; Zhu, M.; Li, J.; Yin, X.;Zheng, H.; Zuo, Z.; Ouyang, C.; Liu, H.; Li, Y.; Zhu, D.J. Org. Chem. 2008, 73, 5008–5014. doi:10.1021/jo8005683.
(17) Adhikari, B.B.; Gurung, M.; Kawakita, H.; Ohto, K.Analyst 2011, 136, 4570–4579. doi:10.1039/c1an15398f.
(18) Teresa Albelda, M.; Frıas, J.C.; Garcıa-Espana, E.;Schneider, H-J. Chem. Soc. Rev. 2012, 41, 3859–3877.doi:10.1039/c2cs35008d.
(19) Su, D.S.; Perathoner, S.; Centi, G. Chem. Rev. 2013, 113,5782–5816. doi:10.1021/cr300367d.
(20) Nimse, S.B.; Kim, T. Chem. Soc. Rev. 2013, 42, 366–386.doi:10.1039/C2CS35233H.
(21) Matthews, S.E.; Schmitt, P.; Felix, V.; Drew, M.G.B.; Beer,P.D. J. Am. Chem. Soc. 2002, 124, 1341–1353. doi:10.1021/ja011856m.
(22) Patra, S.; Suresh, E.; Paul, P. Polyhedron. 2007, 26,4971–4980. doi:10.1016/j.poly.2007.07.012.
(23) Maity, D.; Chakraborty, A.; Gunupuru, R.; Paul, P. Inorg.Chim. Acta 2011, 372, 126–135. doi:10.1016/j.ica.2011.01.053.
(24) Liu, L.-L.; Li, H.-X.; Wan, L.-M.; Ren, Z.-G.; Wang, H.-F.;Lang, J.-P. Chem. Commun. 2011, 47, 11146–11148.doi:10.1039/c1cc14262c.
(25) Horvat, G.; Stilinovic, V.; Hrenar, T.; Kaitner, B.; Frkanec,L.; Tomisic, V. Inorg. Chem. 2012, 51, 6264–6278. doi:10.1021/ic300474s.
(26) Yoneyama, T.; Sadamatsu, H.; Kuwata, S.; Kawakita, H.;Ohto, K. Talanta. 2012, 88, 121–128. doi:10.1016/j.talanta.2011.10.018.
(27) Lee, J.Y.; Kim, H.J.; Jung, J.H.; Sim, W.; Lee, S.S. J. Am.Chem. Soc. 2008, 130, 13838–13839. doi:10.1021/ja805337n.
(28) Liu, X.; Surowiec, K.; Bartsch, R.A. Tetrahedron. 2009, 65,5893–5898. doi:10.1016/j.tet.2009.06.004.
(29) Patra, S.; Gunupuru, R.; Lo, R.; Suresh, E.; Ganguly, B.;Paul, P. New. J. Chem. 2012, 36, 988–1002. doi:10.1039/c2nj20904g.
(30) Patra, S.; Lo, R.; Chakraborty, A.; Gunupuru, R.; Maity, D.;Ganguly, B.; Paul, P. Polyhedron 2013, 50, 592–601.doi:10.1016/j.poly.2012.12.002.
(31) Maity, D.; Vyas, G.; Bhatt, M.; Paul, P. RSC Adv. 2015, 5,6151–6159. doi:10.1039/C4RA12075B.
(32) Agnihotri, P.; Suresh, E.; Paul, P.; Ghosh, P.K. Eur. J. Inorg.Chem. 2006, 2006, 3369–3381. doi:10.1002/ejic.200600354.
(33) Patra, S.; Paul, P. Dalton Trans. 2009, 40, 8683–8695.doi:10.1039/b905695e.
(34) Patra, S.; Maity, D.; Sen, A.; Suresh, E.; Ganguly, B.; Paul,P. New J. Chem. 2010, 34, 2796–2805. doi:10.1039/b9nj00587k.
(35) Liu, L.-L.; Ren, Z.-G.; Zhu, L.-W.; Wang, H.-F.; Yan, W.Y.; Lang, J.-P. Cryst. Growth Des. 2011, 11, 3479–3488.doi:10.1021/cg200308k.
12 717Supramolecular Chemistry
Dow
nloa
ded
by [
CSM
CR
I C
entr
al S
alt &
Mar
ine
Che
mic
als
Res
. Ins
t.] a
t 02:
53 0
2 N
ovem
ber
2015
(36) Cacciapaglia, R.; Casnati, A.; Mandolini, L.; Peracchi, A.;Reinhoudt, D.N.; Salvio, R.; Sartori, A.; Ungaro, R. J. Am.Chem. Soc. 2007, 129, 12512–12520. doi:10.1021/ja0737366.
(37) Ramakrishna, V.; Patra, S.; Suresh, E.; Bhatt, A.K.; Bhatt,P.A.; Hussain, A.; Paul, P. Inorg. Chem. Commun. 2012, 22,85–89. doi:10.1016/j.inoche.2012.05.028.
(38) Patra, S.; Maity, D.; Gunupuru, R.; Agnihotri, P.; Paul, P.J. Chem, Sci. 2012, 124, 1287–1299. doi:10.1007/s12039-012-0329-y.
(39) Takahashi, K.; Gunji, A.; Guillaumont, D.; Pichierri, F.;Nakamura, S. Angew. Chem. Int. Ed. 2000, 39, 2925–2928.DOI: 10.1002/1521-3773(20000818)39:16,2925:AID-ANIE2925.3.0.CO;2-A
(40) Kim, J.S.; Shon, O.J.; Ko, J.W.; Cho, M.H.; Yu, I.Y.;Vicens, J. J. Org. Chem. 2000, 65, 2386–2392. doi:10.1021/jo9912754.
(41) Casnati, A.; Ca’, N.; Sansone, F.; Ugozzoli, F.; Ungaro, R.Tetrahedron. 2004, 60, 7869–7876. doi:10.1016/j.tet.2004.06.058.
(42) Luo, J.; Zheng, Q.Y.; Chen, C.F.; Huang, Z.-T. Chem. Eur.J. 2005, 11, 5917–5928. doi:10.1002/chem.200500272.
(43) Bardi, U. Sustainability 2010, 2, 980–992. doi:10.3390/su2040980.
(44) Asfari, Z.; Bressot, C.; Vicens, J.; Hill, C.; Dozol, J.-F.;Rouquette, H.; Eymard, S.; Lamare, V.; Tournois, B. Anal.Chem. 1995, 67, 3133–3139. doi:10.1021/ac00114a006.
(45) Rudzevich, V.; Kasyan, O.; Drapailo, A.; Bolte, M.;Schollmeyer, D.; Bohmer, V. Chem. Asian J. 2010, 5,1347–1355.
(46) Lee, J.Y.; Lee, S.Y.; Park, S.; Kwon, J.; Sim, W.; Lee, S.S.Inorg. Chem. 2009, 48, 8934–8939. doi:10.1021/ic901314b.
(47) Spek, A.L. Acta Cryst. 2009, D65, 148–155.(48) Perrin, D.D.; Armarego, W.L.F.; Perri, D.R. Purification of
Laboratory Chemicals; 2nd ed. Pergamon Press: Oxford,1980.
(49) Ouchi,M.; Inoue, Y.; Kanzaki, T.; Hakushi, T. J. Org. Chem.1984, 49, 1408–1412. doi:10.1021/jo00182a017.
(50) Gutsche, C.D.; Iqbal, M. Org. Syntheses 1990, 68,234–237. doi:10.15227/orgsyn.068.0234.
(51) Gutsche, C.D.; Levine, J.A.; Sujeeth, P.K. J. Org. Chem.1985, 50, 5802–5806. doi:10.1021/jo00350a072.
(52) Sheldrick, G.M. SAINT 5.1 ed; Siemens IndustrialAutomation, Inc.: Madison, WI, 1995.
(53) SADABS, Empirical Absorption Correction Program;University of Gottingen: Gottingen, 1997.
(54) Sheldrick, G.M. SHELXTL Reference Manual, Version 5.1;Bruker AXS: Madison, WI, 1997.
(55) Sheldrick, G.M. SHELXL-97, Program for Crystal Struc-ture Refinement; University of Gottingen: Gottingen, 1997.
(56) Spek, A.L. PLATON-97; University of Utrecht: Utrecht,1997.
(57) Mercury 1.3, Supplied with Cambridge Structural Data-base; CCDC: Cambridge, 2003.
13718 V. Ramakrishna et al.
Dow
nloa
ded
by [
CSM
CR
I C
entr
al S
alt &
Mar
ine
Che
mic
als
Res
. Ins
t.] a
t 02:
53 0
2 N
ovem
ber
2015
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