Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=gsch20 Download by: [CSMCRI Central Salt & Marine Chemicals Res. Inst.] Date: 02 November 2015, At: 02:53 Supramolecular Chemistry ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20 Synthesis, crystal structures and competitive complexation property of a family of calix- crown hybrid molecules and their application in extraction of potassium from bittern Vallu Ramakrishna, E. Suresh, Vinod P. Boricha, Anjani K. Bhatt & Parimal Paul To cite this article: Vallu Ramakrishna, E. Suresh, Vinod P. Boricha, Anjani K. Bhatt & Parimal Paul (2015) Synthesis, crystal structures and competitive complexation property of a family of 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 View supplementary material Published online: 15 Oct 2015. Submit your article to this journal Article views: 14 View related articles View Crossmark data
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Full Terms & Conditions of access and use can be found athttp://www.tandfonline.com/action/journalInformation?journalCode=gsch20
Download by: [CSMCRI Central Salt & Marine Chemicals Res. Inst.] Date: 02 November 2015, At: 02:53
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
View supplementary material Published online: 15 Oct 2015.
Submit your article to this journal Article views: 14
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.
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.
3708 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
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.
4 709Supramolecular 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
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
Figure 4. (Colour online) Ball and stick model of 2 depictingthe structure of the calix-crown ligand moiety with atomnumbering scheme.
6 711Supramolecular 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
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).
7712 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
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
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].
8 713Supramolecular 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
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
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
11716 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
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.