Syntheses of novel calix[4]arene hydrazone-based receptors and their cooperative complexation with soft and hard metal ions

Article abstract of DOI:10.1007/s10847-010-9851-z

Four novel calix[4]arene hydrazone-based receptors 3a-d were prepared in yields of 69-87% by condensating formylated calix[4]arene ester (2) with salicylyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarhazide, respectively. New compounds were characterized through elemental analysis, IR, ESI-MS, ¹H NMR studies. Compounds 3a-d containing two binding sites had the complexation abilities for hard and soft cations concurrently. The noncompetitive extracting experiments showed compounds 3a-d were excellent receptors for hard and soft metal cations. The competitive extracting experiments exhibited the cooperative complexation in binding hard and soft metal cations and compound 3a possessed outstanding selectivity for Na⁺ and Hg²⁺. The IR spectra of compound 3a before and after complexation revealed that the soft metal cation was binded in the cavity composed of hydrazone groups and azo groups at the upper rims of calix[4]arene units and hard metal cations was binded in cavity composed of ester groups and phenolic hydroxyl groups at the lower rims of calix[4]arene units.

Full text of DOI:10.1007/s10847-010-9851-z

J Incl Phenom Macrocycl Chem (2011) 70:11–18
DOI 10.1007/s10847-010-9851-z
ORIGINAL ARTICLE
Syntheses of novel calix[4]arene hydrazone-based receptors
and their cooperative complexation with soft and hard metal ions
•
Fafu Yang Zhisheng Huang Jianwei Xie
•
•
•
Xiaoyi Zhang Hongyu Guo
Received: 4 June 2010 / Accepted: 25 August 2010 / Published online: 5 September 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Four novel calix[4]arene hydrazone-based
receptors 3a–d were prepared in yields of 69–87% by con-
densating formylated calix[4]arene ester (2) with salicylyl
hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine
or phenyl thiosemicarhazide, respectively. New compounds
were characterized through elemental analysis, IR, ESI–MS,
1H NMR studies. Compounds 3a–d containing two binding
sites had the complexation abilities for hard and soft cations
concurrently. The noncompetitive extracting experiments
showed compounds 3a–d were excellent receptors for hard
and soft metal cations. The competitive extracting experi-
ments exhibited the cooperative complexation in binding
hard and soft metal cations and compound 3a possessed
outstanding selectivity for Na? and Hg2?. The IR spectra of
compound 3a before and after complexation revealed that
the soft metal cation was binded in the cavity composed of
hydrazone groups and azo groups at the upper rims of
calix[4]arene units and hard metal cations was binded in
cavity composed of ester groups and phenolic hydroxyl
groups at the lower rims of calix[4]arene units.
attention in supramolecular chemistry [1]. Calixarenes
were excellent building blocks to construct the polytoptic
systems combining two or more binding sites within the
same architecture, such as calixarene-based co-receptors
for hard and soft metal cations [2]. Up to now, two
methods were reported to prepare calixarene-based
co-receptors for hard and soft metal cations. One was the
calix-biscrowns in 1,3-alternate conformation with full-
oxygen crown and heteroatom crown at lower rims [3–5].
For examples, Vicens etc. reported series calix[4]biscr-
owns with complexation abilities for hard and soft metal
cations [6, 7]. The another method was calix[4]arene
derivatives or biscalixarene with oxygen and heteroatom
containing functional groups at lower rims, which could
bind hard and soft metal cations at different binding sites
[8–11]. For examples, the calix[4]arene derivatives with
EtS(CH2)nNHCOCH2O- or RCH=NNHCOCH2CO- groups
exhibited binding capabilities for hard and soft metal cat-
ions [10, 11]. Our groups also reported several calix[4]
arene derivatives or biscalix[4]arene with two binding sites
for hard and soft metal cations [11–14]. Lately, some
research concerned on the selectively formylated calixa-
rene ethers with special complexation abilities [15–18].
Moreover, from the view of molecular design, this kind of
compound was an excellent platform to construct the new
calixarene derivatives with binding abilities for hard and
soft cations, because the two separate binding sites and
cone conformation might be favorable for producing
excellent cooperative complexation abilities for different
cation concurrently, which were not studied by far,
however. In this paper, we wish to report the synthesis
of four novel calix[4]arene hydrazone-based receptors
derivatived from formylated calixarene ethers as well as
their cooperative complexation abilities for hard and soft
metal cations.
Keywords Calix[4]arene Á Hydrazone Á Synthesis Á
Complexation Á Cooperative
Introduction
The ability of multiple recognition and the mutual effects
of binding subunit occupation has been paid much
F. Yang (&) Á Z. Huang Á J. Xie Á X. Zhang Á H. Guo
College of Chemistry and Materials, Fujian Normal University,
Fuzhou 350007, People’s Republic of China
e-mail: yangfafu@fjnu.edu.cn
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J Incl Phenom Macrocycl Chem (2011) 70:11–18
Experimental
Compound 3a was obtained as maple powder in yield of
82%. m.p.: 189–191°C: IR(KBr, cm-1): 1748(C=O), 1634
(C=O), 1604 (C=N); 1HNMR(400, MHz, CDCl3) d: 1.04(s,
18H, C(CH3)3), 1.25(t, 6H, CH2CH3), 3.47(d, J = 12.0 Hz,
4H, ArCH2Ar), 4.32 (bs, 4H, CH2CH3), 4.43 (d,
J = 12.0 Hz, 4H, ArCH2Ar), 4.73 (s, 4H, ArOCH2),
6.84–7.62(m, 16H, ArH), 7.83, 8.09, 9.79, 11.94(s, each,
2H, each, CH, OH and NH); ESI–MS m/z (%): 1032.1
(M?, 100); Anal.calcd for C60H64N4O12: C, 69.75; H, 6.24;
N, 5.42; found C, 69.63; H, 6.36; N, 5.30.
1
Melting points were uncorrected. H NMR spectra were
recorded in CDCl3 on a Bruker-ARX 400 instrument,
using TMS as reference. ESI–MS spectra were obtained
from DECAX-30000 LCQ Deca XP mass spectrometer.
Elemental analyses were performed at Vario EL III
Elemental Analyzer. The UV–Vis measurements were per-
formed on Varian UV–Vis spectrometer. Cation concen-
trations in competitive extracting experiments were
measured with Thermo Intrepid XSP Radial ICP-OES. IR
spectra were recorded on a Thermo Nicollet AVATAR 5700
FTIR spectrometer using KBr pellets in spectral range
4000–400 cm-1. The picrate salts were prepared according
to literature [19, 20]. Compound 1 was prepared according
to literature [11]. The organic and inorganic reagents were
analytical grade or chemical grade without further
purification.
Synthesis of calix[4]arene hydrazone derivative 3b
Under N2 atmosphere, a mixture of compound 2 (0.22 g,
0.3 mmol) and 0.2 mL glacial acetic acid was stirred and
refluxed in 15 mL CHCl3 and 15 mL MeOH solution con-
taining 2,4-dinitrophenyl hydrazine (0.13 g, 0.64 mmol)
was added by dropwise in 1 h. The solution was stirred and
refluxed in 6 h and some precipitation appeared. TLC
analysis revealed that the starting materials were disap-
peared. After distilling off the solvent by reduced pressure,
10 mL methanol was added and the precipitation was sep-
arated, and then recrystallized in CHCl3/MeOH. Compound
3a was obtained as red powder in yield of 87%. m.p.:
274–276oC: IR(KBr, cm-1): 1744 (C=O), 1616 (C=N);
1HNMR(400, MHz, CDCl3) d: 1.25(s, 18H, C(CH3)3),
1.35(t, 6H, CH2CH3), 3.46(d, J = 12.4 Hz, 4H, ArCH2Ar),
4.35 (q, 4H, CH2CH3), 4.55 (d, J = 12.4 Hz, 4H,
ArCH2Ar), 4.82 (bs, 4H, ArOCH2), 6.94–8.38(m, 16H, ArH
and CH), 9.13, 11.20(s, each, 2H, each, OH and NH); ESI–
MS m/z (%): 1147.1 (MNa?, 100); Anal.calcd for
C58H60N8O16: C, 61.91; H, 5.38; N, 9.96; found C, 61.88; H,
5.47; N, 9.87.
Synthesis of calix[4]arene 1,3-diformyl derivative 2
With the method in literature [18], a mixture of compound 1
(0.5 g, 0.6 mmol) and hexamethylenetetramine (3.4 g,
24 mmol) was stirred in 16 mL TFA solution for 5 h at room
temperature. Then 40 g ice was added in the solution. After
the unfreeze of ice, the solution was extracted by 3 9 10 mL
CHCl3. The CHCl3 solution was washed by 10 mL distilled
water, dried by MgSO4, concentrated. The residue was
purified by chromatographic column (50 cm 9 3 cm, SiO2
100–200 mesh, acetone/CH2Cl2 (1:2, V/V) as eluant,
400 mL), then compound 2 was obtained as white powder
in yield of 68%. m.p.: 173–175 °C;IR(KBr, cm-1):
1
1746(C=O), 1700 (HC=O); HNMR(400, MHz, CDCl3) d:
1.03(s, 18H, C(CH3)3), 1.35(t, 6H, CH2CH3), 3.47(d,
J = 12.8 Hz, 4H, ArCH2Ar), 4.34 (q, 4H, CH2CH3), 4.47
(d, J = 12.8 Hz, 4H, ArCH2Ar), 4.75 (s, 4H, ArOCH2),
6.91(s, 4H, ArH), 7.60(s, 4H, ArH), 8.53(s, 2H, CHO),
9.77(s, 2H, OH); ESI–MS m/z (%): 763.4 (M?, 100); Ana-
l.calcd for C46H52O10: C, 72.23; H, 6.85; found C, 72.14; H,
6.94.
Synthesis of calix[4]arene hydrazone derivative 3c
Under N2 atmosphere, a mixture of compound 2 (0.22 g,
0.3 mmol), 0.2 mL glacial acetic acid was stirred and
refluxed in 15 mL CHCl3 and 10 mL MeOH solution
containing nicotinyl hydrazine (0.088 g, 0.64 mmol) was
added by dropwise in 1 h. TLC analysis revealed that the
starting materials were disappeared in 6 h. After distilling
off the solvent by reduced pressure, 10 mL methanol was
added and the precipitation was separated, and then re-
crystallized in CHCl3/MeOH. Compound 3c was obtained
as straw yellow powder in yield of 69%. m.p.: 159–162oC:
IR(KBr, cm-1): 1744 (C=O), 1666(C=O), 1633(C=N);
1HNMR(400, MHz, CDCl3) d: 1.23(s, 18H, C(CH3)3),
1.36(t, 6H, CH2CH3), 3.43(d, J = 12.8 Hz, 4H, ArCH2Ar),
4.34 (q, 4H, CH2CH3), 4.56 (d, J = 12.8 Hz, 4H,
ArCH2Ar), 4.79 (bs, 4H, ArOCH2), 6.96–7.88(m, 16H,
ArH and CH), 7.85, 9.04, 11.12(s, each, 2H, each, CH, OH
and NH); ESI–MS m/z (%): 1003.9 (M?, 100); Anal.calcd
Synthesis of calix[4]arene hydrazone derivative 3a
Under N2 atmosphere, a mixture of compound 2 (0.22 g,
0.3 mmol) and 0.5 mL glacial acetic acid was stirred and
refluxed in 15 mL CHCl3 and 10 mL MeOH solution
containing salicylyl hydrazine (0.097 g, 0.64 mmol) was
added by dropwise in 1 h. The solution was stirred and
refluxed in 10 h and some precipitation appeared. TLC
analysis revealed that the starting materials were disap-
peared. After distilling off the solvent by reduced pressure,
10 mL methanol was added and the precipitation was
separated, and then recrystallized in CHCl3/MeOH.
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J Incl Phenom Macrocycl Chem (2011) 70:11–18
13
Competitive extracting experiments of metallic cations
for C58H62N6O10: C, 69.39; H, 6.23; N, 8.37; found C,
69.26; H, 6.32; N, 8.25.
Competitive extraction experiments were performed with
equal volumes (10 mL) of an aqueous solution of an
equimolar mixture of picrate salts (Li?, Na?, K?, Cs?,
Synthesis of calix[4]arene hydrazone derivative 3d
Ag?, Hg2?, Ni2?, Co2?, Cu2?, and Zn2?, 2.0 9 10-5
M
Under N2 atmosphere, compound 2 (0.15 g, 0.2 mmol) was
stirred and refluxed in 40 mL CHCl3 and 10 mL EtOH
solution containing phenyl thiosemicarhazide (0.07 g,
0.42 mmol) was added by dropwise in 1 h. TLC analysis
revealed that the starting materials were disappeared in 5 h.
After distilling off the solvent by reduced pressure, 10 mL
methanol was added and the precipitation was separated,
and then recrystallized in CHCl3/MeOH. Compound 3d
was obtained as straw yellow powder in yield of 72%. m.p.:
218–219oC: IR(KBr, cm-1): 1743 (C=O), 1599(C=N);
1HNMR(400, MHz, CDCl3) d: 1.18(s, 18H, C(CH3)3),
1.34(t, 6H, CH2CH3), 3.42(d, J = 13.2 Hz, 4H, ArCH2Ar),
4.32 (q, 4H, CH2CH3), 4.48 (d, J = 13.2 Hz, 4H,
ArCH2Ar), 4.77 (s, 4H, ArOCH2), 6.93–7.66 (m, 18H,
ArH), 7.73, 8.11, 9.15, 9.45(bs, each, 2H, each, CH, OH
and NH); ESI–MS m/z (%): 1085.4 (MNa?, 50); Ana-
l.calcd for C60H66N6S2O8: C, 67.77; H, 6.20; N, 7.90;
found C, 67.66; H, 6.32; N, 7.79.
each) and a CHCl3 solution (10 mL) of the hosts
(2.0 9 10-5 M) were mixed in a stoppered flask and vig-
orously shaken for 15 min. The solution was stored for 2 h.
This was repeated three times. Then the solutions were left
standing for 24 h until phase separation was complete. The
relative concentrations of the cations in the aqueous phase
were determined by ICP-OES. Quantification was made by
using a standard solution containing a mixture of picrate
salts (Li?, Na?, K?, Cs?, Ag?, Hg2?, Ni2?, Co2?, Cu2?
,
and Zn2?,). Blank experiments without added hosts were
carried out under same experimental conditions.
Results and discussion
Synthesis and characterization of novel calix[4]arene
hydrazone derivatives 3a–d
The synthetic route was shown in Scheme 1. Compound 1
was prepared according to literature [11]. According to the
reference [18], compound 2 was obtained in low purity. We
improved this method with chromatographic column and
purified compound 2 was obtained in yield of 68%. It was
well known that the formacyl group could react with
hydrazino group easily. Thus, salicylyl hydrazine, 2,4-
dinitrophenyl hydrazine, nicotinyl hydrazine and phenyl
thiosemicarhazide was chosen to react with compound 2. In
order to avoid the reaction of hydrazino group and ester
groups in compound 2, the hydrazine derivatives were
added by dropwise and glacial acetic acid was used as
catalyst in preparing compounds 3a–d. Also, the optimized
mole ratio of compound 2 and hydrazine derivatives were
1:2 approximately. The excess hydrazine derivatives
resulted in complicated products although the react times
decreased greatly. The experimental results showed com-
pounds 3a–d were obtained conveniently by recrystalliza-
tion in ideal yields of 69%–87%.
Noncompetitive extracting experiment of metallic
picrates
According to the reported method [18], 3 mL of chloro-
form solution containing calixarene derivatives
(2.0 9 10-5M) and 3 mL of aqueous solution containing a
metallic picrate (2.0 9 10-5M) were placed in a flask. The
mixture was shaken for 5 min and stored for 2 h at room
temperature. The extraction ability was not affected by
further shaking, indicating that the equilibrium had been
attained within 2 h. The aqueous phase was separated and
subjected to the analysis by UV absorption spectrometry in
near 357 nm. The extracting percentage (E%) was deter-
mined by the decrease of the picrate concentration in the
aqueous phase: E% = {([Pic]blank–[Pic]water)/[Pic]blank} 9
100, where [Pic]blank denoted the picrate concentrations in
the aqueous phase after extraction with pure chloroform,
and [Pic]water denoted the picrate concentrations in the
aqueous phase after extraction with chloroform solution
containing calixarene derivatives as extractants. Average of
two independent experiments was carried out. Control
experiments showed that no picrate extraction occurred in
the absence of the calixarene derivatives. The relative
standard deviations from the mean were less than 5%. The
test showed that the pH value in each aqueous phase were
neutral (6.9–7.1) and the values made no change before and
after extraction, which indicated the metallic picrates were
extracted successfully.
The structures of new compounds 3a–d were confirmed
by IR spectra, ESI–MS spectra, elemental analyses, 1H
NMR spectra. In the IR spectra, the adsorption peaks
(1700 cm-1) of formacyl groups of compound 2 was
disappeared utterly and new adsorption peaks of C=N
groups were appeared. The ESI–MS spectra of compounds
3a–d showed clearly molecular base peaks (M? or MNa?)
at 1032.1, 1147.1, 1003.9, 1085.4, respectively, which
indicated the ‘‘1 ? 2’’ condensation were accomplished
completely. As compound 2 was confirmed to adopt cone
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J Incl Phenom Macrocycl Chem (2011) 70:11–18
Scheme 1 The synthetic routes
of title compounds
t-BuBu-t
Bu-t
t-Bu
t-BuBu-t
Bu-t
t-Bu
ClCH2COOC2H5
K2CO3, KI
OH
OH
O
O
OH
OH
OH
HO
EtO
OEt
O
O
1
R
R
NH HN
N
N
Bu-t
CHO
t-Bu
OHC
Bu-t
t-Bu
HC
HC
N
N
N
TFA
N
R NHNH2
OH
OH
1
O
O
OH
OH
O
O
O
OEt
O
EtO
O
OEt
O
EtO
2
3
NO2
OH
3a: R=
3b: R=
NO2
C
O
N
S
R=
3c:
3d
:
NHC
R=
C
O
Noncompetitive extracting experiments of metallic
cations
conformation [18], it was reasonable to deduce that
compounds 3a–d were also in cone conformations, which
were confirmed by 1H NMR spectra. The 1H NMR spectra
of compounds 3a–d showed one singlet for tert-butyl
groups, one pair of doublets (1:1) for the methylene
bridges of the calix[4]arene skeleton. All the spectral data
were in accordance with the assigned structures and
indicated that the calix[4]arene units adopt the cone con-
formation as showed in Scheme 1. As to the cis/trans
conformers about C(O)–N bond and E/Z geometrical
isomers respect to the C=N double bonds in these new
compounds, it could be deduced that the mixed con-
formers and isomers were existed by comparing with the
similar report[21]. However, in this paper, it was difficult
to determine the percentage of different isomers due to the
overlapped signal of NH and OH in IR spectra and the
absence of CH2 groups beside the C(O)–N bond and C=N
double bond which were crucial to study the percentages
of different isomers [21].
It could be seen that compounds 3a–d possessed two
binding sites for guests. One was the cavity composed of
ester groups and phenolic hydroxyl groups at the lower
rims of calix[4]arene units and the other was the cavity
composed of hydrazone groups and azo- or sulfur- groups
at the upper rims of calix[4]arene units. According to
principle of ‘‘hard and soft acids and bases’’, the two
cavities could bind hard and soft metal cations, respec-
tively. Also, the stable cone conformations of compounds
3a–d were favorable for producing complexation abilities.
Thus, the binding abilities of compounds 3a–d were stud-
ied for series of metal cations. There were two methods to
study the extracting abilities. One was by using metallic
picrates as extract directly in neutral solution and another
was metal picrate in buffered solution [19, 22]. Due to the
binding abilities of NH and OH were greatly influenced by
123

J Incl Phenom Macrocycl Chem (2011) 70:11–18
15
70
65
60
55
50
45
40
35
30
25
20
15
10
5
pH, the method of using metallic picrates as extract directly
in neutral was employed in our extracting experiments to
avoid the fall of complexation abilities in buffered solution.
Thus, in our extracting experiment, the pH value in each
aqueous phase were neutral (6.9–7.1) and the values made
no change before and after extraction, which indicated the
metallic picrate were extracted successfully.
2
3a
3b
3c
3d
Figure 1 showed the noncompetitive extraction results
of compounds 3a–d towards alkali metal cations. It could
be seen that compounds 3a–d exhibited good extraction
percentage. For example, the extraction percentages of
compound 3c for Li?, Na?, K?, Cs? were as high as
25.8%, 52.1%, 48.3%, and 44.9%, respectively. The low
extraction selectivity might be attributed to the open chain
structures of compounds 3a–d. Moreover, comparing with
the extraction abilities of precursor 2, the extraction abili-
ties of compounds 3a–d made little changes. These results
indicated that the binding sites for alkali metal cations were
the same cavity composed of ester groups and phenolic
hydroxyl groups at the lower rims of calix[4]arene units of
compounds 2 and 3a–d.
0
Ag+
Cu2+
Zn2+
Hg2+
Ni2+
Co2+
Fig. 2 The extraction percentages of receptors 3a–d for soft metal
cations
Competitive extracting experiments of metallic cations
Based on the noncompetitive extracting experiments, the
competitive extracting experiments were carried out to
investigate the cooperative complexation of two different
binding sites. The competitive extraction percentages were
summarized in Table 1. It can be seen that compounds 3a–
d showed good extraction abilities towards both hard and
soft metal cations, which were in accordance with non-
competitive extracting experiments. It was worthy of not-
ing that all of total extraction percentages (the addition of
each extraction percentage) of compounds 3a–d for metal
cations exceeded 100%. The biggest total extraction per-
centage of compound 3a was as high as 148.7%. These
results could be explained that the two different complex-
ing sites of compounds 3a–d binded soft and hard metal
cations concurrently. On the other hand, comparing with
noncompetitive extracting experiments, the extraction
selectivity was improved greatly in competitive extracting
experiments, especially for compound 3a. Compound 3a
exhibited high extraction selectivity for Na? among hard
metal cations and for Hg2? among soft metal cations,
respectively. For example, the extraction ratio Na?/Li? and
Hg2?/Ag? of compound 3a were up to 8.44 and 7.09 in
competitive extracting experiments, whereas it were only
1.52 and 1.45 in noncompetitive extracting experiments,
respectively. These results suggested that the cooperative
complexation exists between the two binding sites of
compounds 3a–d. The complexation in one cavity would
influence the complexing behavior of another cavity for
binding another guest, which improved or reduced the
extraction percentages. To the best of our knowledge, this
kind of cooperative complexation for hard and soft metal
cations was reported for the first time in calixarene
chemistry by far.
However, the extraction results of compounds
3a–d towards soft metal cations were utterly different from
that of compound 2. In Fig. 2, compound 2 showed very
low extraction percentage. But compounds 3a–d exhibited
very high extraction percentages for tested soft cations. For
example, the Hg2? extraction percentage increased from
0.8% of compound 2–50.9% of compound 3a. These results
indicated that it was the cavity composed of hydrazone
groups and azo- or sulfur- groups at the upper rims of
calix[4]arene units played the crucial roles in binding soft
metal cations. All these noncompetitive extracting experi-
ments suggested that compounds 3a–d were excellent
receptors for soft and hard metal cations in two different
binding sites as expected.
70
2
3a
3b
65
60
55
50
45
40
35
30
25
20
15
10
5
3c
3d
0
Li+
Na+
K+
Cs+
Fig. 1 The extraction percentages of receptors 3a–d for hard metal
cations
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J Incl Phenom Macrocycl Chem (2011) 70:11–18
Table 1 Competitive extracting percentages (%E) of receptors 3a–d for picrate salts
Cations
Li?
Na?
K?
Cs?
Ag?
Hg2?
Ni2?
Co2?
Cu2?
Zn2?
3a
3b
3c
3d
5.2
8.4
43.9
23.8
24.8
18.6
12.1
11.5
20.5
9.7
10.4
8.9
5.4
10.2
16.9
8.6
38.3
22.9
18.8
10.9
8.5
11.7
6.6
7.6
14.4
9.8
6.8
9.4
10.5
11.3
8.9
9.4
18.4
17.3
17.8
8.4
11.6
12.4
11.7
7.5
Fig. 3 IR studies of compound
3a (a) and its complex with
Hg2? (b) and Na?
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J Incl Phenom Macrocycl Chem (2011) 70:11–18
The IR spectra of complexation studies
17
lower rims of calix[4]arene units, which also suggested
that compounds 3a–d containing two binding sites had
the complexation abilities for hard and soft cations
concurrently.
The IR spectra of compound 3a before and after com-
plexation with Hg2? and Na? picrate were employed to
study the complexation behavior. The results were as
showed in Fig. 3. After complexation with Hg2?, the
adsorption peaks of C=O (1748 cm-1 for ester group and
1634 cm-1 for amido group) made little shift. However,
Acknowledgments Financial support from the National Natural
Science Foundation of China (No: 20402002), Fujian Natural Science
Foundation of China (No: 2009J01019) and Program for New Cen-
tury Excellent Talents in University of Fujian Province were greatly
acknowledged.
the peak at 3436 cm-1 moved to 3406 and 3086 cm-1
,
which was attributed to the N–H peak (3086 cm-1) split
from the mixture peak of N–H and O–H after complexa-
tion. Also, the shifting of C=N peak from 1604 to
1610 cm-1 suggested C=N groups participated in the
complexation. Thus, it could be concluded that the Hg2?
was binded in the cavity composed of hydrazone groups
and azo groups at the upper rims of calix[4]arene units.
However, the IR spectra of compound 3a before and after
complexation with Na? picrate showed little shift of
adsorption peaks of NH, NC=O and C=N groups except the
shift of adsorption peaks of C=O in ester groups(from 1748
to 1742 cm-1) and OH groups (from 3436 to 3448 cm-1).
This result indicated that the complexation mode of 3a for
Na? were occurred in cavity composed of ester groups and
phenolic hydroxyl groups at the lower rims of calix[4]arene
units. These complexation results of IR spectra also indi-
cated the hard and soft metal cations were binded in two
different cavities, respectively, which was in accordance
with the results of extracting experiments. These com-
plexation results revealed that receptors 3a–d with two
different binding sites might possess multiple complexa-
tion capabilities for other complicated guests, such as ion
pairs and amino acids, which will be studied in further
work.
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´
´
´
Conclusion
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