Inorganic Chemistry Communications 22 (2012) 85–89
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, crystal structures and competitive binding property of a family of
functionalized calix[4]arene ionophores
Vallu Ramakrishna, Subrata Patra, E. Suresh, Anjani K. Bhatt, Pragnya A. Bhatt, Amjad Hussain, Parimal Paul ⁎
Analytical Science Division, Central Salt and Marine Chemicals Research Institute (constituents of CSIR, New Delhi), G. B. Marg, Bhavnagar 364002, India
a r t i c l e
i n f o
Article history:
Received 5 January 2012
Accepted 15 May 2012
Available online 23 May 2012
Keywords:
Calixarenes
Ion-selectivity
Crystal structure
Binding constant
Two-phase extraction
a b s t r a c t
A family of calix-crown hybrid molecules incorporating crown-4, crown-5 and crown-6 moieties as ionophore has been synthesized to evaluate their competitive complexing and extracting ability towards different
alkali and alkaline earth metal ions. Selectivity of these ionophores towards Li+, Na+, K+, Ca2+, Mg2+ and Sr2+
has been evaluated with aqueous solution containing equimolar mixture of these ions. The concentration of
metal ion in the extract (organic phase) has been estimated by ion chromatographic assay. Two of the ionophores show strong complexation with Na+ and K+, whereas the third ionophore exhibits no complexation
with any metal ions used in this study. Association constants (Ka) for the binding of Na+ and K+ with two of
these ionophores have been determined spectrophotometrically. Molecular structures of the Na+ and K+ complexes of these ionophores have been established by single crystal X-ray study. 1H NMR study of the ionophores
and their complexes has also been carried out to investigate conformational behavior of the ionophores and their
metal complexes in solution. Results have been discussed in light of various factors contribute to determine ionselectivity.
© 2012 Elsevier B.V. All rights reserved.
Calixarenes, which are macrocyclic oligomers made up of phenol
units linked by methylene bridge, are receiving increasing attention because of their ability to bind variety of ions [1–7]. In the calixarene family, calix[4]arenes are most popular because of their rigid structures,
which make them ideal candidates for the complexation with metal
ions [1–16]. This chemistry has become even more versatile because
of the ease with which calix[4]arene can be modified depending on the
requirement. These modified calixarenes provide a highly preorganized
architecture for the assembling of converging binding sites [17–22].
Among these calixarene derivatives, calix[4]arene-crown ethers have
attracted intense interest as alkali–metal-selective extractants [23–32].
The ion selectivity of this class of compounds is controlled mainly by
the conformation of the calixarene platform, the size of the crown
ether ring and substituents attached with the calix or crown moiety(ies).
Among various conformations of the calixarene, 1,3-alternate conformers have been studied extensively as complexing agent for alkali–
metal ions [26–39]. Other conformers have also been prepared but
metal ion complexation studies are rare. Among various crown ethers,
crown-5 and crown-6 containing calixarene derivatives are found more
suitable for complexation with alkali–metal ions [22–32]. We also
reported synthesis of a series of p-tert-butylcalix[4]arene-crown-5/6
with various substituents in lower rim and study on their competitive
complexation property with selected alkali and alkaline earth metal
ions [29–32].
⁎ Corresponding author. Tel.: + 91 278 2567760; fax: + 91 278 2567562.
E-mail address: ppaul@csmcri.org (P. Paul).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.05.028
In this communication, we report competitive complexation property of calix[4]arene-crown-n (n = 4, 5 and 6, Fig. 1) with the metal ions
Li+, Na+, K +, Mg 2+, Ca2+ and Sr2+. Selectivity of these ionophores towards the above mentioned metal ions has been evaluated by twophase extraction using aqueous solution containing equimolar mixture
of these ions. The concentration of metal ion in the extract (organic
phase) has been estimated by ion chromatographic assay. Association
constants for strongly interacting metal ions were also determined.
The molecular structures of the Na+ and K + complexes of the two ionophores were also determined by single crystal X-ray study.
The ionophores 1–3 were synthesized following the modified
published procedures [29,30,40], route followed for the synthesis
[Scheme S1, ESI] and details of the synthetic procedures [S2, ESI] are
available as ESI. These compounds were characterized on the basis
of elemental analysis, mass spectrometry, IR and 1H NMR data [S2,
ESI]. Elemental analysis and mass data are in excellent agreement
with the calculated values. It may be noted that the m/z values for 1
appeared as [1 + Na] +, whereas for 2 and 3, it appeared as both
Na + and K + salt, [2/3 + Na] + and [2/3 + K] +, with different intensity
of peaks. Association with different cations in ESI-MS depends on
complexation ability of the ligand with various metal ions, and the
variation in peak intensity depends on the stability of the complex
formed. Ion-binding property of 1–3 towards alkali and alkaline–
earth metal ions was evaluated by two-phase extraction method
using equimolar mixture of metal ions. The experiments were carried
out with an aqueous solution containing equimolar amounts of Li +,
Na +, K +, Mg 2+, Ca 2+ and Sr 2+ as their picrate salts and the respective ionophore dissolved in dichloromethane [29]. The metal ions
86
V. Ramakrishna et al. / Inorganic Chemistry Communications 22 (2012) 85–89
Table 1
Concentration of metal ions in the extract and selectivity ratio with respect to potassium ion.
Compound
2
Fig. 1. Structural drawings of the calix[4]arene-crown-n; n = 4 (1), 5 (2) and 6 (3).
added with stoichiometric amount and also with 25, 50, 75 and 100
times excess with respect to the concentration of ionophore used
[S3, ESI]. The organic phase containing the complex formed was separated and the metal ions in the extract were determined by ion chromatographic assay [S4, ESI]. It may be noted that the extract obtained
from ionophore 1 exhibited only trace amount of a few metal ions, indicating poor complexing ability of this ionophore towards the metal
ions tested. It was also examined with the aid of 1H NMR study, the
spectra of 1 and that in presence of metal ions were recorded in
CDCl3. The 1H NMR spectra recorded in presence of metal ions did not
show any significant change compared to that of 1, indicating that no
considerable amount of complex is formed with the metal ions used
for this study. This is probably due to cavity size of crown-4, which is
not large enough to allow the entry of the hydrated metal ion for complex formation. The organic extracts of 2 and 3 showed the presence of
Na+, K +, Mg2+ and Ca2+, and the distributions of metal ions in the extracts, together with values of the observed selectivity ratios, are shown
in Table 1. The plot of the mole fraction of the metal ions extracted
against concentration of metal ions used in the extraction process is
shown in Fig. 2 for ionophore 3, similar plot for 2 is given as ESI (S5).
The result clearly suggests that these two ionophores prefer to bind
Na+ and K + over the other metal ions; Mg2+ and Ca 2+ also form considerable amount of complexes but Li+ and Sr2+ do not form any complex with these ionophores. Small size and high hydration enthalpy
(−520 and −1443 kJ mol− 1 for Li+ and Sr2+, respectively) are likely
the factors, which prevented this metal ion to form complex. For Sr2+,
probably the large size of the hydrated metal ion also played important
role to prevent its entry into the cavity of the ionophore to form complex. The other notable observation is that the selectivity ratio (K+/
Na+) for 2 towards K + and Na+ ions is 0.84 (Table 1), whereas the
same for 3 is 1.08, indicating that the selectivity towards K + over Na +
is significantly high for 3, which is due to better size matching for K +
with the crown-6 cavity. For structural elucidation of these complexes,
we synthesized both Na+ and K + complexes of the ionophores 2 and 3.
These complexes were synthesized by stirring the solution of Na+/
K + picrate and the ionophore in chloroform–methanol (5:1) at room
temperature for 24 h and purified from dichloromethane [S6, ESI].
These complexes were characterized on the basis of elemental analysis,
3
Concentration (%) of metal ion in the extracta
Selectivity ratiob
Li+
K +/
Na+
K +/
Mg2+
K+/
Ca2+
10.93 Trace
0.84
amount
6.03 Trace
1.08
amount
8.59
5.41
33.87
15.85
Na+
K+
Mg2+ Ca2+
Trace
34.42 49.81 4.49
amount
Trace
32.09 59.57 2.16
amount
Sr2+
a
Concentration (%) of metal ion in the original solution (before extract), Li+ = 3.18,
Na+ = 10.4, K+ = 17.7, Mg2+ = 10.9, Ca2+ = 18.1 and Sr2+ = 39.5.
b
The ratio is calculated by [% of K+ in the extract][% of Mn+ in the original solution]/
[% of Mn+ in the extract][% of K+ in the original solution].
mass spectrometry, IR and 1H NMR data and finally molecular structures were determined by single crystal X-ray study. It is interesting
to note that the ESI-MS of all the four complexes exhibited m/z values
corresponding to both Na + and K + complexes; however the peak
with 100% intensity corresponds to the complex, which used is for measurement, i.e., for Na + complexes the 100% peak corresponds to [2/
3.Na+] and for K+ complexes the 100% peak corresponds to [2/3.K +]
[S6, ESI]. To check purity of the complexes, powder X-ray diffraction
patterns of all the four complexes were recorded and these patterns
were compared with those obtained by simulation from single crystal
X-ray data, good matching of both the patterns (S7 and S8, ESI) suggests
that the molecular structures determined from single crystal X-ray
analysis (described below) represent the bulk complexes. Suitable crystals for X-ray study of these complexes were grown from THF-toluene
(2:3), except K + complex of 3, which was grown from dichloromethane–toluene (1:1). The 1H NMR spectra of the ionophore 3
and that of its Na + and K + complexes (3.Na+.pic and 3.K +.pic) are
shown in Fig. 3. It may be noted that in the 1H NMR spectra of the ionophore, a typical AB pattern was observed for the methylene bridge
(ArCH2Ar) protons of the calix moiety, that is two widely separated
doublets at δ = 3.90–4.65 and 3.12–3.36 ppm (J = 12–13.8 Hz), which
suggests that these ionophores exist in cone conformation in solution
[29,41,42]. The low-field doublet is due to axial hydrogen atom, and
the high-field doublet is due to equatorial hydrogen atoms of the methylene bridge. These doublets are also observed in the Na + and K + complexes with slight change in chemical shifts, indicating that the cone
conformation of the calix moiety is retained in the complexes. The
chemical shifts of the signals due to crown moiety (δ = 3.71–4.15)
changed significantly upon complexation with metal ion (Fig. 3), indicating that the metal ion encapsulated in the crown cavity to form the
complex. A few changes in chemical shifts are also noted in the aromatic
c
b
a
8
Fig. 2. Bar diagram showing the fraction of metal ions extracted from equimolar solution of Li+, Na+, K+, Mg2+, Ca2+ and Sr2+ at different concentrations of metal ions
using the ionophore 3 (concentration of the ionophore was 0.002 M).
7
6
5
4
p pm
Fig. 3. 1H NMR spectra of the (a) ionophore 3, (b) complex 3.Na+Pic− and (c) complex
3.K+Pic− recorded in CDCl3.
V. Ramakrishna et al. / Inorganic Chemistry Communications 22 (2012) 85–89
87
Fig. 4. Mercury diagram for the crystal structures of (a) 2.Na+.pic and (b) 2.K+.pic
showing the labeling of coordinated atoms with the metal ions and the dimeric association in (b) (hydrogen atoms are omitted for clarity).
region (δ = 6.67–7.06), which is due to overall conformational change
of the molecule because of the complexation with metal ion. A new
peak appeared at δ = 8.85 in the complexes due to picrate counter
anion. The 1H NMR spectra of 2 and 3 are, therefore, consistent to the
formation of complexes encapsulating metal ion in the calix-crown
cavity.
Molecular structures of the Na + and K + complexes of 2 (2.Na +.pic
and 2.K +.pic) and 3 (3.Na +.pic and 3.K +.pic) were determined from
single crystal X-ray study, and details of unit cells are available as
ESI [S9]. Suitable crystals for X-ray study were grown from THF/
CH2Cl2-toluene, and the analysis of the data revealed the structures
shown in Figs. 4 and 5 (hydrogen atoms and lattice solvent molecules
are omitted for clarity). In all of these complexes, the metal ion is coordinated to one of the phenolic OH of the calix moiety and with oxygen atoms from picrate anion and crown moiety. The picrate anion is
coordinated in a bidentate fashion using the oxygen atom of the
deprotonated OH and one of the oxygen atoms of an adjacent nitro
group. The Na + ion is six coordinated in 2.Na +.pic and seven coordinated in 3.Na +.pic, whereas K + is seven coordinated in 2.K +.pic and
eight coordinated in the complex, 3.K +.pic. It is interesting to note
that for Na +, two of the oxygen atoms of the crown moiety and for
K +, one of the oxygen atoms of the crown ring do not participate in coordination. This is because of the size of the metal ions and this constrain,
which the crown ring is expected to experience for coordination of all of
the oxygen atoms to the same metal ion. The larger K+ ion is better fitted
in the cavity as evident from higher coordination number compared to
Na+ in the same crown ring. For 3, due to more flexibility of the larger
crown ring (crown-6), more oxygen atoms could come closer to metal
ion for coordination. It is noteworthy that the cone conformation of the
calixarene moiety, found in the ionophore, is retained even after complexation with metal ion. The Na+….O and K+….O distances in both
the complexes are found in the ranges 2.279(4) to 2.698(6) and
2.630(3) to 2.938(4) Å, respectively. In all of these complexes, there are
several intra- and intermolecular O―H…O and C―H…O interactions,
in which picrate anion is also involved. In an attempt to understand
the interaction between the 2.Na+.pic with lattice host p-xylene and
2.K+.pic with lattice host toluene, packing and hydrogen bonding interaction has been analyzed in detail (Table S1). Packing diagrams with hydrogen bonding between 2.Na+.pic and p-xylene viewed down b-axis,
Fig. 5. Mercury diagram for the crystal structures of (a) 3.Na+.pic and (b) 3.K+.pic
showing the labeling of coordinated atoms with the metal ions (hydrogen atoms are
omitted for clarity).
and the interaction between 2.K+.pic and toluene viewed down c-axis
are given in supplementary data (S10 and S11). In the case of 2.K+.pic,
the dimeric complex is involved in inter and intramolecular C-H…O
and O―H…O H-bonding generating a corrugated layer along ab plane.
Lattice toluene guest molecules are located in the clefts of the corrugated
layer and anchored by C―H…π interaction between the phenyl hydrogen H9 of the calix ring with the centroid of the toluene guest with
C1g…H9 distance 3.21 Å. For the Na+.pic complex, host moiety is
88
V. Ramakrishna et al. / Inorganic Chemistry Communications 22 (2012) 85–89
Table 2
Molar ratio of picrate to host in organic layer (R) and association constants (Ka) for 2
and 3 with Na+ and K+.
Compound
R
Na+
2
3
0.19
0.14
Ka
K+
0.34
0.37
Na+
Acknowledgements
K+
5
1.47 × 10
9.6 × 104
6
2.6 × 10
4.9 × 106
oriented diagonal to ac-plane involving inter and intra molecular C―H…
O and O―H…O interactions. Lattice p-xylene guest molecules are positioned between the diagonally oriented Na+.pic host and anchored by
C―H…O interaction. Thus, the methyl hydrogen H43A and phenyl hydrogen H46 of the symmetrically disposed host is involved in a bifurcated C―H…O interaction with the nitro oxygen O13 of the picrate
from the diagonally oriented Na+.pic host layers (C43–H43A…O13:
H43A ..O13 = 2.40; C43…O(13) = 3.233(13); bC43–H43A…O13 = 145
and C46–H46….O13:H46....O13 = 2.59; C46....O13 = 3.310(10); C46–
H46…O13 = 134). Details of the hydrogen bonding interaction for
both the complexes with symmetry code are given in supplementary
data (Table S1).
The association constants (Ka) for 2 and 3 with Na + and K + were
determined by two phase extraction method following the published
procedure [29,43–45]. The association constants were determined
using Eq. (1), where Ka is the association constant, Kd is the distribution constant, R is the molar ratio of picrate to host in the organic
layer, [Gi]H2O is the initial concentration of the guest (metal ion/
picrate), [Hi]CHCl3 is the initial concentration of the host (ionophore)
in chloroform,VCHCl3 the volume of the organic layer (chloroform)
and VH2Othe volume of the aqueous layer.
Ka ¼
K +. Molecular structures of the Na+ and K + complexes have been
determined by single crystal X-ray study. This study reveals that the
size-matching factor plays the predominant role in ion-selectivity.
R
n
o2
ð1−RÞK d ½Gi H2 o −R½H i CHCl3 V CHCl3 =V H2 o
ð1Þ
Details of the determination of different parameters of Eq. (1) are
given as ESI [S12] and the association constant thus determined are
given in Table 2. The data show that the association constant for K + is
significantly higher compared to that of Na+, which is due to strong
complexing ability of the larger K + because of the better sizematching fitting of the metal ion with the crown cavity, as evident
from the crystal structures. For Na+, two of the oxygen atoms of the
crown moiety are not involved in making interaction with metal ion,
whereas for K+ only one oxygen atom is left out for making coordination for both the ionophores. It is also interesting to note that between
two ionophores, Na + shows higher binding constant with crown-5
(2.Na+.pic) compared to that of crown-6 (3.Na +.pic), whereas K + exhibits reverse order. This suggests that Na+ being smaller fits better
with the smaller cavity size of the crown-5 of ionophore 2 to make
strong interaction and the larger K+ ion matched well with the cavity
size of the crown-6 of 3 and forms strong complex. The data are
consistent to the observation noted in the crystal structures of the
complexes.
In summary, a number of calix[4]arene crown ethers with hybrid
calix-crown cavity of different size as ionophore have been synthesized
in cone conformation to evaluate their performance as complexing
agent towards Li+, Na +, K +, Ca2+, Mg2+ and Sr2+. Competitive complexation study in aqueous media with the mixture of cations taken
shows preferential binding of K + and Na+ for the ionophores containing crown-5 and crown-6 as ion-binding cavity and the latter
shows significantly higher selectivity towards K +. Ca 2+ and Mg2+
also form complexes with 2 and 3 but with very poor selectivity, especially for 3. Li+ and Sr2+ do not exhibit any complex formation with
these ionophores. No metal ion used in this study shows complexation
with the ionophore 1. Association constants for 2 and 3 have been determined with Na + and K + and the values are significantly higher for
We are grateful to the Department of Science and Technology
(DST), Government of India, for financial support. S.P. gratefully acknowledges the CSIR for awarding Senior Research Fellowship
(SRF). We thank Dr. Babulal Rebary for assistance in recording ion
chromatography, Mr. H. Bhatt and Dr. V. Boricha for recording NMR
spectra, Mr. Arun K. Das for recording mass spectra and Mr. V. Vakani
for elemental analysis. We thank CSIR, New Delhi for generous
support towards infrastructures and core competency development.
Appendix B. Supplementary data
CCDC 834098, 834099, 834100 and 834101 contain the supplementary crystallographic data for 2.Na +.pic, 2.K +.pic, 3.Na +.pic and
3.K +. pic, respectively. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif. Other supplementary data associated
with this article can be found in the online version. Supplementary
data to this article can be found online at http://dx.doi.org/10.1016/
j.inoche.2012.05.028.
References
[1] C.D. Gutsche, Calixarenes, The Royal Society of Chemistry, Cambridge, UK, 1989.
[2] V. Boehmer, Calixarenes, macrocycles with (almost) unlimited possibilities,
Angew. Chem. 107 (1995) 785–818;
Angew. Chem. Int. Ed. Engl. 34 (1995) 713–745.
[3] A. Ikeda, S. Shinkai, Novel cavity design using calix[n]arene skeletons: toward
molecular recognition and metal binding, Chem. Rev. 97 (1997) 1713–1734.
[4] F. Arnaud-Neu, M.A. McKervey, M.J. Schwing-Weill, Calixarenes, in: Z. Asfari, V.
Bohmer, J. Harrowfield, J. Vicens (Eds.), Kluwer Academic Publishers, Dordrecht,
The Netherlands, 2001.
[5] P.D. Beer, E.J. Hayes, Transition metal and organometallic anion complexation
agents, Coord. Chem. Rev. 240 (2003) 167–189.
[6] J. Yoon, S.K. Kim, N.J. Sing, K.S. Kim, Imidazolium receptors for the recognition of
anions, Chem. Soc. Rev. 35 (2006) 355–360.
[7] J.S. Kim, D.T. Quang, Calixarene-derived fluorescent probes, Chem. Rev. 107
(2007) 3780–3799.
[8] A. Ikeda, S. Shinkai, On the origin of high ionophoricity of 1,3-alternate calix[4]
arenes: π-donor participation in complexation of cations and evidence for
metal-tunneling through the calix[4]arene cavity, J. Am. Chem. Soc. 116 (1994)
3102–3110.
[9] S. Leon, D.A. Leigh, F. Zerbetto, The effect of guest inclusion on the crystal packing
of p-tert-butylcalix[4]arenes, Chem. Eur. J. 8 (2002) 4854–4866.
[10] G. Guillemot, E. Solari, C. Rizzoli, C. Floriani, Alkali and alkaline–earth-metalated
forms of calix[4]arenes: synthons in the synthesis of transition metal complexes,
Chem. Eur. J. 8 (2002) 2072–2080.
[11] A. Shivanyuk, M. Saadioui, F. Broda, I. Thondorf, M.O. Vysotsky, K. Rissanen, E.
Kolehmainen, V. Boehmer, Sterically and guest-controlled self-assembly of calix
[4]arene derivatives, Chem. Eur. J. 10 (2004) 2138–2148.
[12] P.K. Lo, M.S. Wong, Extended calix[4]arene-based receptors for molecular recognition and sensing, Sensors 8 (2008) 5313–5335.
[13] B.S. Creaven, D.F. Donlon, J. Mcginley, Coordination chemistry of calix[4]arene
derivatives with lower rim functionalisation and their applications, Coord.
Chem. Rev. 253 (2009) 893–962.
[14] L.-L. Liu, H.-X. Li, L.-M. Wan, Z.-G. Ren, H.-F. Wang, J.-P. Lang, A Mn(III)-superoxo
complex of a zwitterionic calix[4]arene with an unprecedented linear end-on
Mn(III)–O2 arrangement and good catalytic performance for alkene epoxidation,
Chem. Commun. 47 (2011) 11146–11148.
[15] L.-L. Liu, Z.-G. Ren, L.-W. Zhu, H.-F. Wang, W.-Y. Yan, J.-P. Lang, Temperature driven
assembly of Ln(III) (Ln Nd, Eu, Yb) coordination polymers of a flexible azo calix[4]
arene polycarboxylate ligand, Cryst. Growth Des. 11 (2011) 3479–3488.
[16] L.-L. Liu, L.-M. Wan, Z.-G. Ren, J.-P. Lang, Construction of a unique 3D coordination
polymer from assembly of Cd(NO3)2 with a new tetrakis(m-carboxyphenyl) azo
calix[4]arene ligand, Inorg. Chem. Commun. 14 (2011) 1069–1072.
[17] P.L.H.M. Cobben, R.J.M. Egberink, J.G. Bomer, P. Bergveld, W. Verboom, D.N.
Reinhoudt, Transduction of selective recognition of heavy metal ions by chemically modified field effect transistors (CHEMFETs), J. Am. Chem. Soc. 114 (1992)
10573–10582.
[18] J. Rebek Jr., Host–guest chemistry of calixarene capsules, Chem. Commun.
8 (2000) 637–643.
[19] D. Diamond, K. Nolan, Calixarenes: designer ligands for chemical sensors, Anal.
Chem. 73 (2001) 23A–29A.
V. Ramakrishna et al. / Inorganic Chemistry Communications 22 (2012) 85–89
[20] S.E. Matthews, P. Schmitt, V. Felix, M.G.B. Drew, P.D. Beer, Calix[4]tubes: a new
class of potassium-selective ionophore, J. Am. Chem. Soc. 124 (2002) 1341–1353.
[21] P.R.A. Webber, A. Cowley, M.G.B. Drew, P.D. Beer, Potassium selective calix [4]
semi tubes, Chem. Eur. J. 9 (2003) 2439–2446.
[22] L.-L. Liu, Z.-G. Ren, L.-M. Wan, H.-Y. Ding, J.-P. Lang, Inclusion of unique four-clawed
crown like nitrate-water cluster [(NO3)6(H2O)6]6− anions into the inter-space of a
3D H-bonded cationic net formed by a cationic calyx[4]arene, CrystEngComm 13
(2011) 5718–5723.
[23] A. Casnati, A. Pochini, R. Ungaro, F. Ugozzoli, F. Arnaud, S. Fanni, M.-J. Schwing, R.J.M.
Egberink, F. de Jong, D.N. Reinhoudt, Synthesis, complexation, and membrane
transport studies of 1,3-alternate calix[4]arene-crown-6 conformers: a new class
of cesium selective ionophores, J. Am. Chem. Soc. 117 (1995) 2767–2777.
[24] J. Guillon, J.-M. Leger, P. Sonnet, C. Jarry, M. Robba, Synthesis of cone, partial-cone,
and1,3-alternate 25,27-bis[1-(2-ethyl)hexyl] and 25,27-bis[1-(2-tert-butoxy) ethyl]
calix [4]arene-crown-6 conformers as potential selective cesium extractants, J. Org.
Chem. 65 (2000) 8283–8289.
[25] K. Takahashi, A. Gunji, D. Guillaumont, F. Pichierri, S. Nakamura, Through-space
exciton coupling and multimodal Na+/K+ sensing properties of calix[4]
arenecrowns with the thienylene analogue of para-terphenoquinone as chromophore, Angew. Chem. Int. Ed. 3 (2000) 2925–2928.
[26] J.S. Kim, O.J. Shon, J.W. Ko, M.H. Cho, I.Y. Yu, J. Vicens, Synthesis and metal ion
complexation studies of proton-ionizable calix[4]azacrown ethers in the 1,3alternate conformation, J. Org. Chem. 65 (2000) 2386–2392.
[27] A. Casnati, N. Della Ca, F. Sansone, F. Ugozzoli, R. Ungaro, Enlarging the size of
calix[4]arene-crowns-6 to improve Cs+/K+ selectivity: a theoretical and experimental study, Tetrahedron 60 (2004) 7869–7876.
[28] J. Luo, Q.-Y. Zheng, C.-F. Chen, Z.-T. Huang, Synthesis and optical resolution of a
series of inherently chiral calix[4]crowns with cone and partial cone conformations, Chem. Eur. J. 11 (2005) 5917–5928.
[29] P. Agnihotri, E. Suresh, P. Paul, P.K. Ghosh, Synthesis, crystal structures, cationbinding properties and the influence of intramolecular C―H···O interactions
on the complexation behaviour of a family of cone p-tert-butylcalix[4]arenecrown-5 compounds, Eur. J. Inorg. Chem. 17 (2006) 3369–3381.
[30] S. Patra, E. Suresh, P. Paul, Functionalized calix[4]arene as an ionophore: synthesis,
crystal structures and complexation study with Na+ and K+ ions, Polyhedron 26
(2007) 4971–4980.
[31] S. Patra, P. Paul, Synthesis, characterization, electrochemistry and ion-binding
studies of ruthenium(II) bipyridine receptor molecules containing calix[4]
arene-azacrown as ionophore, Dalton Trans. 40 (2009) 8683–8695.
[32] S. Patra, D. Maity, A. Sen, E. Suresh, B. Ganguly, P. Paul, Effect of steric crowding on
ion selectivity for calix-crown hybrid ionophores: experimental, molecular
modeling and crystallographic studies, New J. Chem. 34 (2010) 2796–2805.
89
[33] R. Ungaro, A. Casnati, F. Ugozzoli, A. Pochini, J.-F. Dozoli, C. Hill, H. Rouquette,
1,3-Dialkoxycalix[4]arenecrowns-6 in 1,3-alternate conformation: cesium selective
ligands that exploit cation–arene interactions, Angew. Chem. Int. Ed. Engl. 33
(1994) 1506–1509.
[34] V. Lamare, J.F. Dozol, F. Ugozzoli, A. Casnati, R. Ungaro, X-ray crystal structures
and molecular modeling studies of calix[4]dibenzocrowns-6 and their alkali
metal cation complexes, Eur. J. Org. Chem. 8 (1998) 1559–1568.
[35] J.S. Kim, J.H. Pang, I.Y. Yu, W.K. Lee, I.H. Suh, J.K. Kim, M.H. Cho, E.T. Kim, D.Y. Ra,
Calix[4]arene dibenzocrown ethers as caesium selective extractants, J. Chem. Soc.
Perkin Trans. 2 (2) (1999) 837–846.
[36] A. Casnati, N.C. Della, F. Sansone, F. Ugozzoli, R. Ungaro, Enlarging the size of calix
[4]arene-crowns-6 to improve Cs+/K+ selectivity: a theoretical and experimental
study, Tetrahedron 60 (2004) 7869–7876.
[37] H. Zhou, K. Surowiec, D.W. Purkiss, R.A. Bartsch, Proton di-ionizable p-tertbutylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate
conformations: synthesis and alkaline earth metal cation extraction, Org. Biomol.
Chem. 3 (2005) 1676–1684.
[38] M. Yuan, W. Zhou, X. Liu, M. Zhu, J. Li, X. Yin, H. Zheng, Z. Zuo, C. Ouyang, H. Liu, Y.
Li, D. Zhu, A multianalyte chemosensor on a single molecule: promising structure
for an integrated logic gate, J. Org. Chem. 73 (2008) 5008–5014.
[39] X. Liu, K. Surowiec, R.A. Bartsch, Di-ionizable p-tert-butylcalix[4]arene-1,3crown-4 ligands: synthesis and alkaline earth metal cation extraction, Tetrahedron 65 (2009) 5893–5898.
[40] C.D. Gutsche, J.A. Levine, P.K. Sujeeth, Calixarenes.17. Functionalized calixarenes:
the Claisen rearrangement route, J. Org. Chem. 50 (1985) 5802–5806.
[41] P.J. Dijkstra, J.A.J. Bbrunink, K.E. Bugge, D.N. Reinhoudt, S. Harkema, R. Ungaro, F.
Ugozzoli, E. Ghidini, Kinetically stable complexes of alkali cations with rigidified
calix [4]arenes: synthesis, X-ray structures, and complexation of calixcrowns
and calix sphereands, J. Am. Chem. Soc. 111 (1989) 7567–7575.
[42] E. Ghidini, F. Ugozzoli, R. Ungaro, S. Harkema, A.A. El-Fadl, D.N. Reinhoudt, Complexation of alkali metal cations by conformationally rigid, stereoisomeric calix[4]
arene crown ethers: a quantitative evaluation of preorganization, J. Am. Chem.
Soc. 112 (1990) 6979–6985.
[43] S.S. Moore, T.L. Tarnowski, M. Newcomb, D.J. Cram, Host–guest complexation. 4.
Remote substituent effects on macrocyclic polyether binding to metal and ammonium ions, J. Am. Chem. Soc. 99 (1977) 6398–6405.
[44] K.E. Koeing, G.M. Lein, P. Stuckler, T. Kaneda, D.J. Cram, Host‐guest complexation. 16.
Synthesis and cation binding characteristics of macrocyclic polyethers containing
convergent methoxyaryl groups, J. Am. Chem. Soc. 101 (1979) 3553–3566.
[45] D.J. Cram, G.M. Lein, Host–guest complexation. 36. Spherand and lithium and sodium
ion complexation rates and equilibria, J. Am. Chem. Soc. 107 (1985) 3657–3668.