Synthesis of new chromogenic calix[4]arene based molecular receptors for palladium and platinum

Article abstract of DOI:10.1007/s10847-012-0105-0

Four new chromogenic alkylthiophenylazocalix[4]arenes (3-6) have been synthesized. It has been observed that methylthioazocalix[4]arene (6) has a potential for developing into molecular diagnostics for Pd(II) and Pt(II). Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10847-012-0105-0

J Incl Phenom Macrocycl Chem (2012) 74:239–249
DOI 10.1007/s10847-012-0105-0
ORIGINAL ARTICLE
Synthesis of new chromogenic calix[4]arene based molecular
receptors for palladium and platinum
•
H. M. Chawla N. Venkatesan Satish Kumar
•
Received: 27 October 2011 / Accepted: 2 January 2012 / Published online: 15 February 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Four new chromogenic alkylthiophenylazo-
calix[4]arenes (3–6) have been synthesized. It has been
observed that methylthioazocalix[4]arene (6) has a poten-
tial for developing into molecular diagnostics for Pd(II)
and Pt(II).
sheets, encapsulation of bioactive molecules and binding of
calcium ions. Although calixarene derivatives have been
used for the development of receptors for heavy metal ions,
research on their use is limited [20, 21].
In recent years development of chromogenic receptors
have attracted considerable attention for use as analytical
reagents and chemical sensors [22]. Azo chromophore
(–N=N–) has been variously utilized in the development of
chromogenic compounds for applications in dyeing [23],
coloring and optical sensing [20, 24] as well as construc-
tion of molecular devices [20]. Coupling of azo group to
the unique architecture of calixarenes, introduces a desir-
able specificity and selectivity which in principle can result
in highly sensitive and selective receptors for metal ions
especially the development of sensors for monitoring toxic
metal ions in the environment and help keep the environ-
ment green and clean while attempting large scale organic
synthesis. During recent years many diazo-coupled calix-
arenes have been reported which have also been used for
selective extraction of metal ions [25–28]. For example,
Karakus et al. [29] have reported removal of heavy metal
Keywords Alkylthiaazocalixarenes ꢀ Molecular receptors ꢀ
Platinum ions ꢀ Palladium ions
Introduction
The presence of distinct hydrophobic and hydrophilic
domains and adjustable cavity dimensions in calixarene
molecular architecture has enhanced their potential use in
recognition of metal ions of biological [1, 2], medicinal [3,
4], radioactive [5, 6] and environmental significance [7].
Easy functionalization of hydrophobic region (upper rim)
or hydrophilic region (lower rim) further creates opportu-
nities for development of efficient and specific molecular
hosts for complexation of cations [8–11], anions [12–14]
and neutral species [15–17]. A large volume of research
work has been accomplished on the use of calixarenes for
developing receptor of alkali and alkaline earth metal ions.
For example, Chawla et al. [18] have reported calix[4]-
crowns which have shown considerable selectivity for
potassium over sodium. Similarly, Martin et al. [19] have
reported p-phosphonic acid substituted calix[n]arenes and
their O-alkylated lower rim analogues for selective stabil-
ization and protection of nano-particles and graphene
ions (Ag?, Hg?, Hg2?, Co2?, Ni2?, Cu2?, Cd2? and Cr3?
)
from aqueous solution by azocalix[4]arenes.
We believe that soft binding sites having large affinity
for the guest ions should be useful to achieve optical
transduction through azo groups even when they are
present in the calix[4]arene molecular architecture [30–33].
It has been well established by us [34–36] as well as by
others [37–40] that attachment of ionisable chromogenic
azo groups in positions adjacent to the polar cavity of
calixarenes yield useful materials that exhibit both coloring
and binding attributes. Working on this line, we have
recently reported the development of chromogenic calixa-
renes that exhibit selective interaction with mercury and
platinum ions [36]. Deligoz and coworkers [41] have
H. M. Chawla (&) ꢀ N. Venkatesan ꢀ S. Kumar
Department of Chemistry, Indian Institute of Technology, Delhi,
New Delhi 110016, India
e-mail: hmchawla@gmail.com; hmchawla@chemistry.iitd.ac.in
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utilized azocalixarene derivatives for extraction of transi-
tion metal ions (Ag?, Hg2? and Hg?) from aqueous solu-
tion. Similarly a calixarene carboxyphenylazo derivative
has been synthesized by Lu et al. [42] as a diagnostic for
lead. While a large number of azo calixarenes have been
reported in the literature [20, 22, 43], there is very little
information about azocalixarenes with additional sulphur
hetero atom that interact specifically with palladium and
platinum ion. There seems to be very less work on inter-
action of palladium and platinum ions by calixarene based
molecular receptors. In this paper we report the synthesis of
five new calixarene derivatives containing multi heteroat-
oms as potential diagnostics for heavy and precious metal
ions especially with special reference to their interaction
with Pd2? and Pt4? ions through use of NMR and UV-vis
spectroscopic measurements.
chlorides at 0–5 °C. All the products were further purified
by extensive chromatography (silica gel) to provide new
chromogenic calixarenes in good yields (Scheme 1). The
structures of synthesized molecular receptors were estab-
lished by analyzing their spectral and physical character-
istics as well as chemical derivatization. For instance,
while presence of azo group in the synthesized receptor
(R0=CH3) was confirmed from its UV spectrum (kmax
356 nm with a shoulder at 400 nm in methanol) and
characteristic IR absorption (1,593 cm-1), chemical
derivatization of 3–6 (reaction with benzoyl chloride,
methyl iodide, acetyl chloride) and spectral identification
of synthesized derivatives, (Scheme 2) confirmed the gross
structure assigned to it.
1H NMR spectrum of 6 showed two broad signals at d
4.30 and 3.65 (which became sharper at low temperatures
and on derivatization) to reveal that phenyl rings in 6 are in
a syn orientation and the compound could undergo tem-
perature dependent conformational isomerization. This
conclusion was confirmed by its HSQC spectrum (Fig. 1).
Cone (or near cone) conformation of 6 was confirmed by
the observation of 13C NMR signal for methylene carbons
Results and discussion
The new calix[n]arene dyes, 3–6 were synthesized by
coupling calix[4]arene and 2-alkylthiobenzenediazonium
N
N
3: X = Y =
4: X = Y =
5: X = Y =
X
Y
CH3S
Conc. HCl, NaNO2
+
N
N
N
CH2
CH2
SR
Pyridine, 0-5oC
4
2
C2H5S
OH
OH
NH2
OH
2
3-6
N
1
R= CH3, C2H5, C3H7, C16H33
C3H7S
6:
N
N
X = H; Y =
MeS
Scheme 1 Synthesis of chromoionophore 3–6
X
Y
N
N
a R' = CH3CO
3: X = Y =
CH2
CH3S
2
b = R' = C6H5CO
OH
OH
4: X = Y =
5: X = Y =
N
N
N
c
= R' = CH3
3-6
i or ii or iii
C2H5S
N
C3H7S
6:
X = H; Y =
N
N
X
Y
MeS
CH2
OR'
3a-6a
3b-6b
i = pyridine, (CH3CO)2O
ii = pyridine, C6H5COCl
2
OR'
3c-6c iii = pyridine, CH3
Scheme 2 Further chemical derivatization of chromoionophore 3–6
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241
Fig. 1 Aromatic (a) and
methylene (b) regions of
1H-13C-HSQC spectrum of 6
(CDCl3, 300 MHz, r.t.)
Fig. 2 a
Changes
in
the
absorbtion
spectrum
of
absorption spectrum of 4.6 9 10-7 mol dm-3 solution of 6 in
methanol (1) resulting from the addition of the following concentra-
tions (in mol dm-3) of K2PtCl4 in methanol, 2, 2.29 9 10-7; 3,
4.5 9 10-7; 4, 6.0 9 10-7; 5, 7.24 9 10-7; 6, 9.36 9 10-7; 7,
13.24 9 10-7
4.6 9 10-7 mol dm-3 solution of 6 in methanol (1) resulting from
the addition of the following concentrations (in mol dm-3) of
Na2PdCl4 in methanol, 2, 0.6 9 10-7
;
3, 1.2 9 10-7
;
4,
3.59 9 10-7; 5, 4.79 9 10-7; 6, 17.95 9 10-7.b Changes in the
of calix[4]arene at d 31.75 which is in consonance with
similar literature precedents as well as analysis of 1H, 13C-
HSQC-NMR spectra (Fig. 1) [36, 44].
could be followed spectrophotometrically when significant
bathochromic shifts were observed in kmax of 6 (350,
400 nm) on addition of K2PdCl4 (330, 430, 520 nm) and
K2PtCl4 (420, 470, 560(br) nm) respectively (Fig. 2).
However, A slight deviation has been observed for free
ligand in Fig. 2 and a clear isobestic point was not observed
presumably due to in situ conformational morphosis (this
point is being investigated) [45] in the synthetic receptor.
Evaluation of mole ratio plots provided [6]/[Pd] and [6]/[Pt]
ratio as 1:1 or 1: 2 respectively which was confirmed by
investigations through Jobs plots (Figs. 3, 4) [36].
The synthesized chromogenic calixarenes appended with
sulfur and nitrogen heteroatoms in addition to oxygen are
expected to coordinate with heavy or transition metal
atoms. Based upon this expectation, experiments were
carried out with 6 and transition metal ions such as Pt2?
,
Pd2?, Cu2?, Ni2?, Co2?, and Fe2?. To rule out binding with
soft metal ions, we have also examined interactions with
alkali metal ions (Na? and K?). It has been observed that 6
can interact with platinum and palladium ions but not with
aqueous methanolic solutions containing iron, copper,
nickel, cobalt, sodium and potassium ions. For example,
addition of palladium(II) and platinum(II) salts to a meth-
anolic solution of 6 gave an immediate color change from
yellow to red. Differential spectral response to these ions
obeyed Lambert–Beer relationship at 10-3 M concentration
of calix[4]arene derivative. The 6-metal ion interaction
The NMR titrations indicated that addition of Pd(II)
solution (Na2PdCl4) of 6 caused a down field shift of thio-
methyl (S–Me) protons from d 2.17 to 2.93 while addition
of Pt(II) solution (K2PtCl4) caused a similar shift from 2.17
to 2.50 ppm (Fig. 5). The aromatic region of the NMR
spectrum became quite complex in both the cases
and hydroxyl protons of the lower rim of the calixarene
r-framework in 6 remained unaltered.
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Fig. 3 a Mole ratio plot for the
formation of 6–Pd complex.
b Job’s continuous variation
plot for the formation of 7–Pd
complex
Fig. 4 a Mole ratio plot for the
formation of 6–Pt complex.
b Job’s continuos variation plot
for the formation of 7–Pt
complex
An equimolar solution of the metal ion and the synthe-
sized molecular receptor on slow evaporation in a desiccator
left a residue which was not found to be suitable for single
crystal X-ray but the residue showed a considerable reduc-
tion in the mN=N stretch frequency, e.g. to 1,550 cm-1 for 6-
palladium complex and to 1,565 cm-1 for 6-platinum
complex indicating the involvement of azo group in metal-
receptor interaction [36]. Strangely, metal–carbon and mS–C
absorptions were also observed at 759 and 720 cm-1 in the
case of 6-Pd(II) and 738 and 695 cm-1 in the case of 6-Pt(II)
compounds respectively. Preliminary observations on
selectivity of 6 for Pd(II) and Pt(II) were made on their
related compounds to obtain suitable sensor components
for precious metal ions is in progress.
Experimental
General procedure for coupling reaction
of tetrahydroxycalix(4)arene with diazotized
2-alkylthioaniline
A solution of 2-alkylthiobenzenediazonium chlorides
prepared from 2-alkylthioaniline (10 mmol) and concen-
trated HCl (2.5 ml) in water (15 ml), at 0–5 °C was added
drop wise to an ice-cold solution of calix(4)arene (1.0 g,
2.36 mmol) in pyridine (25 ml) with constant stirring to
give red suspension. After stirring the suspension for 5 min
at the same temperature range, it was gradually allowed to
attain the room temperature. The reaction mixture was kept
for 15 min at room temperature and then the suspension
mixture with diverse transition metal ions (Fe3?, Cu2?, Ni2?
,
Co2?, Fe2?) and alkali metal ions (K?, Na? and Cs?) by
following the methods described in the literature [46]. The
observed selectivity (as determined by measuring the shift in
the absorption maximum of 6) followed the sequence
Pd [ Pt [[[ Cu2? [ Ni2? [ Fe2?–Fe3? [[[ K? [
Na?. Further functionalization and evaluation of 6 and
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243
(vapour pressure osmometry): 1055 (Calculated 1025). UV
(kmax, DMSO): 412 nm. IR (KBr; mmax, cm-1): 3456(bs),
1584(s), 1567(m), 1482(m), 1436(w), 1372(w), 1276(w),
1
1212(w), 762(m), 620(w). H-NMR (DMSO–d6; d, ppm):
9.03 (4H, bs, exchangeable with D2O, OH), 7.60–6.80
(24H, m, ArH), 4.14 (8H, bs, ArCH2Ar), 2.44 (12H, s,
CH3).
25,26,27,28-Tetrahydroxy-5,11,17,23-tetra(2-
thioethylphenylazo)calix[4]arene
A solution of 2-ethylthioaniline (1.53 g, 10 mmol) (prepared
from 2.5 g of 2-aminothiophenol and iodoethane), sodium
nitrite (1.0 g, 15 mmol) and concentrated HCl (2.5 ml) in
water (15 ml) was slowly added (over a period of about
30 min) into an ice-cold solution of tetrahydroxyca-
lix(4)arene (1.0 g, 2.36 mmol) in 25 ml of pyridine at
0–5 °C to give red suspension. The reaction was worked out
as described in the general procedure. It was purified from
THF and methanol to give 4 (0.53 g, 21%) as a red solid.
m.p. [ 250 °C. (Calculated for C60H56N8O4S4: C, 66.64; H,
5.22; N, 10.36; S, 11.86). Found: C, 66.50; H, 5.02; N, 10.53;
S, 11.56. Mol. mass (vapor pressure osmometry): 1,108
(Calculated 1,081). UV (kmax, DMSO): 420 nm. IR (KBr;
m
max, cm-1): 3456(bs), 1578(m), 1567(m), 1492(m),
1436(w), 1372(w), 1256(w), 1210(w), 765(m), 635(w). 1H-
NMR (DMSO–d6; d, ppm): 8.70 (4H, bs, exchangeable with
D2O, OH), 7.61–6.83 (24H, m, ArH), 4.10 (8H, bs,
ArCH2Ar), 2.44 (8H, s, SCH2), 1.44 (12H, s, CH3).
Fig. 5 1H-NMR spectrum of 6 (a) and its change upon addition of
Pd(II) (b) Pt(II) (c) and Cu(II) (d) solutions
25,26,27,28-Tetrahydroxy-5,11,17,23-tetra(2-
thiopropylphenylazo)calix[4]arene: 5
was poured into 500 ml of water followed by acidification
with concentrated HCl. The mixture was warmed to 60 °C
for 30 min to produce azo calixarenes in moderate to poor
yields as red solids which were filtered and subsequently
washed with water and methanol. The compounds were
finally dried and used for further studies.
A solution of 2-propylthioaniline (1.68 g, 10 mmol) (pre-
pared from 3.0 g of 2-aminothiophenol and iodo propane),
sodium nitrite (1.0 g, 15 mmol) and concentrated HCl
(2.5 ml) in water (15 ml) was slowly added (over a period
of about 30 min) into an ice-cold solution of tetra-
hydroxycalix(4)arene (1.0 g, 2.36 mmol) in 25 ml of pyr-
idine at 0–5 °C to give red suspension. The reaction was
worked out as described in the general procedure. It was
purified by crystallization from THF and methanol to give
5 (1.52 g, 57%) as a red solid. m.p. 240 °C (decomp.).
(Calculated for C64H64N8O4S4: C, 67.58; H, 5.67; N, 9.85;
S, 11.28). Found: C, 67.90; H, 5.20; N, 10.12; S, 11.56.
Mol. mass (vapor pressure osmometry): 1,157 (Calculated
1,138). UV (kmax, CHCl3): 420 nm. IR (KBr; mmax, cm-1):
3430(bs), 2870(m), 1584(s), 1563(m), 1492(m), 1436(w),
1372(w), 1256(w), 1210(w), 765(m), 635(w). 1H-NMR
(CDCl3; d, ppm): 8.70 (4H, bs, exchangeable with D2O,
OH), 7.07–7.00 (24H, bm, ArH), 4.08 (8H, bm, ArCH2Ar),
2.48 (8H, s, SCH2), 1.73 (8H, m, SC-CH2), 1.00 (12H, t,
SC.C.CH3).
25,26,27,28-Tetrahydroxy-5,11,17,23-tetra(2-
thiomethylphenylazo)calix[4]arene: 3
A solution of 2-methylthioaniline (1.40 g, 10 mmol) (pre-
pared from 2.5 g of 2-aminothiophenol and iodo methane),
sodium nitrite (1.0 g, 15 mmol) and concentrated HCl
(2.5 ml) in water (15 ml) was slowly added (over a period
of about 30 min) into an ice-cold solution of tetra-
hydroxycalix(4)arene (1.0 g, 2.36 mmol) in 20 ml of pyr-
idine at 0–5 °C to give red suspension. The reaction was
worked out as described in the general procedure. It was
purified by crystallization from THF and methanol to give
3 (1.23 g, 51%) as a red solid. m.p. [ 300 °C. (Calculated
for C56H58N8O4S4: C, 65.60; H, 4.72; N, 10.93; S, 12.5.
Found: C, 66.50; H, 4.02; N, 11.53; S, 11.5. Mol. mass
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25,26,27,28-Tetrahydroxy-5, 17-di(2-
thiomethylphenylazo)calix[4]arene: (6)
osmometry): 1177 (Calcd. 1193). UV (kmax, CHCl3):
412 nm. IR (KBr; mmax
,
cm-1): 2908(sh), 1758(s),
1563(m), 1452(m), 1436(w), 1372(w), 1256(w), 1212(w),
762(m), 620(w). 1H-NMR (CDCl3; d, ppm): 7.60–6.80
(24H, m, ArH), 4.12 (8H, bs, ArCH2Ar), 2.44 (12H, s,
SCH3), 2.04 (12H, s, OCCH3).
An ice cold solution of 2-methylthiobenzenediazo-
niumchloride (0.75 g, 5.79 mmol), concentrated HCl
(1.4 ml) in water (1.5 ml) and NaNO2 (0.4 g, 10.86 mmol)
in water (1.9 ml) as added to an ice cold solution of tet-
rahydroxycalix[4]arene (1.06 g, 2.5 mmol) in pyridine
(10 ml) and THF (15 ml) at 0–5 °C with constant stirring.
The addition of diazonium salt was done slowly over a
period of about 20 min. After addition was complete, the
reaction mixture was stirred for additional 30 min at
10–15 °C and then it was gradually brought to room tem-
perature. The reaction mixture was poured into water and
stirred well to produce the diazocalix[4]arene as red solid
which was filtered, washed successively with water, dilute
HCl and ether. The solid obtained was purified by crys-
tallization from CHCl3 and hexane to give 6 as red solid.
The samples of analytical standard were prepared by
passing the crude compound through silica gel column
using ethyl acetate as eluent. Yield (0.9 g, 49%). m.p.
263–270 °C. Mol. Mass (vapor pressure osmometry): 742
(calcd. 724.9). Anal. calcd. for C42H36N4O4S2: C, 69.59; H,
5.01; N, 7.73; S, 8.85. Found: C, 68.50; H, 5.52; N, 7.53; S,
8.41. UV [CHCl3; kmax (e)]: 350 nm (24774), 400 nm
(18842) (appears as shoulder). IR (KBr; mmax, cm-1):
3178(bs), 1593(m), 1436(w), 1372(w), 1276(w), 1212(w),
753(m), 620(w). 1H-NMR (CDCl3; d, ppm): 10.21 (4H, bs,
exchangeable with D2O, OH), 7.72–6.71 (18H, m, ArH),
4.30, 3.65 (8H, s, ArCH2Ar), 2.17 (6H, s, SCH3). 13C-NMR
(CDCl3; d, ppm): 151.91, 148.65, 130.69, 129.19, 125.32,
124.78, 124.61, 122.45, 122.36, 115.67, 31.75, 31.64,
14.91.
25,26,27,28-Tetraacetyloxy-5,11,17,23-tetra(2-
thioethylphenylazo)calix[4]arene: 4a
(0.23 g, 25%) m.p. [ 250 °C, Calcd. for C68H64N8O8S4:
C, 65.36; H, 5.16; Found: C, 65.64; H,5.22. UV (kmax
,
CHCl3): 415 nm. IR (KBr; mmax, cm-1): 2898(sh), 1752(s),
1582(s), 1567(m), 1492(m), 1436(w), 1372(w), 1256(w),
1210(w), 765(m), 635(w). 1H-NMR (CDCl3; d, ppm):
7.61–6.83 (24H, m, ArH), 4.10 (8H, bs, ArCH2Ar), 2.44
(8H, s, SCH2), 2.13 (12H, s, OCCH3), 1.44 (12H, s, CH3).
25, 26, 27, 28-Tetraacetyloxy-5,11,17,23-tetra(2-
thiopropylphenylazo)calix[4]arene: 5a
(0.21 g, 21%), m.p. [ 223 °C (decomp.), Calcd. for
C72H72N8O8S4: C, 66.23; H, 5.56. Found: C, 67.64; H,
5.22. UV (kmax, CHCl3): 420 nm. IR (KBr; mmax, cm-1):
2898(sh), 1733(s), 1572(m), 1453(m), 1436(w), 1372(w),
1
1256(w), 1212(w), 762(m), 620(w). H-NMR (CDCl3; d,
ppm): 7.60–6.80 (24H, m, ArH), 4.14 (8H, bs, ArCH2Ar),
2.38 (8H, s, SCH2), 2.06 (12H, s, OCCH3), 1.68 (8H, m,
SCCH2), 1.18 (12H, t, SC.C.CH3).
25,26,27,28-Tetraacetyloxy-5,17-di(2-
thiomethylphenylazo)calix[4]arene: 6a
(0.15 g, 22%). m.p. [ 250 °C (decom.); Mol. Mass (vapor
pressure osmometry): 845 (calcd. 839). Anal. calcd. for
C50H44N4O8S2: C, 67.25; H, 4.97; N, 6.27; S, 7.18. Found:
C, 67.64; H, 4.02, N, 6.60; S, 7.86. UV (kmax, CHCl3):
412 nm. IR (KBr; mmax, cm-1): 2998 (sh), 1750 (s),
1560(m), 1452(m), 1436(w), 1372(w), 1256(w), 1212(w),
762(m), 620(w). 1H-NMR (CDCl3; d, ppm): 7.60–6.80
(18H, m, ArH), 4.30, 3.65 (8H, d, ArCH2Ar), 2.26 (12H, s,
OCOCH3), 2.18 (6H, s, SCH3).
General procedure for the reaction
of diazocalix(4)arenes 3–6 with acetic anhydride
A solution of diazocalix(4)arene 3–6 (0.75 mmol) in pyr-
idine (10 ml) was treated with acetic anhydride (5 ml) on
boiling water bath for 20 h. The reaction mixture was
cooled and poured into ice-cold dilute HCl (5%, 300 ml) to
yield a yellow precipitate, which was collected by suction
filtration and dissolved in CHCl3 (30 ml) and charcoalized
with active charcoal (2 g). Recrystallization of the product
from CHCl3–methanol (1:1) gave 3a–6a as yellow crys-
talline solids.
General procedure for the reaction
of diazocalix(4)arenes 3–6 with benzoyl chloride
and pyridine
25,26,27,28-Tetraacetyloxy-5,11,17,23-tetra(2-
thiomethylphenylazo)calix[4]arene: 3a
A solution of diazocalix(4)arene 3–6 (0.75 mmol) was
taken in pyridine (15 ml) and benzoyl chloride (0.60 g,
4.25 mmol) was added to it. After heating on boiling water
bath for 15 h, the reaction mixture was cooled and poured
into crushed ice (200 g) and the yellow precipitate obtained
was collected by suction filtration. It was dissolved in
(0.27 g, 30%) m.p. [ 250 °C, Calcd. for C64H56N8O8S4:
C, 64.41; H, 4.73; N, 9.39; S, 10.75. Found: C, 65.64; H,
5.02; N, 9.60; S, 11.26. Mol. Mass (vapor pressure
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245
CHCl3 (30 ml) and washed with dilute HCl, saturated
NaHCO3 solution and water. The residue obtained on
evaporation was recrystallized from CHCl3–methanol (1:1)
gave 3b–6b as pale yellow crystalline solids.
410 nm. IR (KBr; mmax, cm-1): 2998 (sh), 1720(s),
1543(m), 1470(m), 1426(w), 1372(w), 1256(w), 1212(w),
1
1120(s), 1090(w), 762(m), 635(w). H-NMR (CDCl3; d,
ppm): 8.01–7.81 (38H, m, ArH), 4.32, 3.67 (8H, d,
ArCH2Ar), 2.24 (6H, s, SCH3).
25,26,27,28-Tetrabenzoyloxy-5,11,17,23-tetra(2-
thiomethylphenylazo)calix[4]arene: 3b
General procedure for the reaction
of diazocalix(4)arenes 3–6 with methyl iodide
and sodium hydride
(0.32 g, 30%), m.p. [ 250 °C, Calcd. for C84H64N8O8S4:
C, 69.98; H, 4.47; N, 7.77. Found: C, 68.64; H, 4.22; N,
7.36. Mol. Mass (vapor pressure osmometry): 1450 (Calcd.
1442). UV (kmax, CHCl3): 410 nm. IR (KBr; mmax, cm-1):
2978(sh), 1740(s), 1684(m), 1560(m), 1452(m), 1436(w),
A mixture of diazocalix[4]arene 3–6 (0.7 mmol), NaH
(0.30 g, 12.5 mmol), methyl iodide (2.79 g, 19.65 mmol)
in dry dimethyl formamide (50 ml) was stirred at 60 °C for
20 h. The reaction mixture was cooled and poured into ice
cold water (200 ml) to yield yellow coloured precipitate
which was collected by suction filtration and dissolved in
chloroform (30 ml) and charcoalized with active charcoal
(2 g). Recrystallization of the product from chloroform to
methanol (1:1) gave 3c–6c as yellow crystalline solid.
1
1372(w), 1256(w), 1212(w), 1120(s), 762(m), 620(w). H-
NMR (CDCl3; d, ppm): 7.73–7.62 (20H, m, ArH),
7.60–6.80 (24H, m, ArH), 4.14 (8H, bs, ArCH2Ar), 2.44
(12H, s, SCH3).
25, 26, 27, 28-Tetrabenzoyloxy-5, 11, 17, 23-tetra(2-
thioethylphenylazo)calix[4]arene: 4b
25,26,27,28-Tetramethoxy-5,11,17,23-tetra(2-
thiomethylphenylazo)calix[4]arene: 3a
(0.25 g,
22%),
m.p. [ 245–247 °C,
Calcd.
for
C88H72N8O8S4: C, 70.58; H, 4.85; N, 7.48. Found: C, 70.64;
H, 4.22; N, 7.36. Mol. Mass (vapor pressure osmometry):
1500 (Calcd. 1498). UV (kmax, CHCl3): 410 nm. IR (KBr;
Compound 3c (0.24 g, 30%). m.p. 255 °C was obtained as
yellow crystalline solid from the reaction of diazoca-
lix[4]arene 3 (0.78 g, 0.76 mmol) with methyl iodide
(2.79 g, 19.6 mmol) and NaH (0.3 g, 12.5 mmol) by fol-
lowing the general procedure. Mol. Mass (vapor pressure
osmometry): 1087 (calcd. 1081). Anal. calcd. for
C60H56N4O4S4: C, 66.64; H, 5.22; N, 10.36. Found: C,
67.24; H, 4.98, N, 10.76. UV (kmax, CHCl3): 420 nm. IR
(KBr; mmax, cm-1): 2898(sh), 1560(m), 1452(m), 1436(w),
1372(w), 1256(w), 1212(w), 762(m), 620(w). 1H-NMR
(CDCl3; d, ppm): 7.60–6.80 (24H, m, ArH), 4.14 (8H, bs,
ArCH2Ar), 3.51 (12H, s, OCH3), 2.44 (12H, s, SCH3).
mmax
,
cm-1): 2889(sh), 1756(s), 1696(m), 1573(m),
1492(m), 1436(w), 1372(w), 1256(w), 1210(w), 1120(m),
765(m), 635(w). 1H-NMR (CDCl3; d, ppm): 7.73–7.52
(20H, m, ArH), 7.51–6.83 (24H, m, ArH), 4.10 (8H, bs,
ArCH2Ar), 2.42 (8H, q, SCH2), 1.44 (12H, t, CH3).
25,26,27,28-Tetrabenzoyloxy-5,11,17,23-tetra(2-
thiopropylphenylazo)calix[4]arene: 5b
(0.24 g, 21%), m.p. [ 243 °C (decomp.), Calcd. for
C92H80N8O8S4: C, 71.11; H, 5.19; N, 7.21. Found: C,
70.12; H, 5.96; N, 8.12. Mol. Mass (vapor pressure
osmometry): 1601 (Calcd. 1554). UV (kmax, CHCl3):
25,26,27,28-Tetramethoxy-5,11,17,23-tetra(2-
thioethylphenylazo)calix[4]arene: 4c
420 nm. IR (KBr; mmax
,
cm-1): 2898(sh), 1962(s),
1752(m), 1560(m), 1452(m), 1436(w), 1372(w), 1256(w),
1212(w), 762(m), 620(w). 1H-NMR (CDCl3; d, ppm):
7.73–7.52 (20H, m, ArH), 7.42–6.80 (24H, m, ArH), 4.14
(8H, bs, ArCH2Ar), 2.44 (8H, m, SCH2), 1.62 (8H, m,
SCCH2), 1.02 (12H, t, SC.C.CH3).
(0.23 g, 27%). m.p. 245–247 °C was obtained as yellow
crystalline solid from the reaction of diazocalix[4]arene 4
(0.81 g, 0.75 mmol) with methyl iodide (2.79 g,
19.6 mmol) and NaH (0.3 g, 12.5 mmol) by following the
general procedure. Mol. Mass (vapor pressure osmometry):
1147 (calcd. 1138). Anal. calcd. for C64H64N8O4S4: C,
66.64; H, 5.22; N, 10.36. Found: C, 67.58; H, 5.67, N, 9.85.
UV (kmax, CHCl3): 420 nm. IR (KBr; mmax, cm-1):
2898(sh), 1584(s), 1567(m), 1492(m), 1436(w), 1372(w),
25,26,27,28-Tetrabenzoyloxy-5,17-di(2-
thiomethylphenylazo)calix[4]arene: 6b
1
(0.22 g, 26%). m.p. [ 250 °C; Mol. Mass (vapor pressure
osmometry): 1131 (calcd. 1141). Anal. calcd. for
C70H52N4O8S2: C, 73.66; H, 4.59; N, 4.91; S, 5.62. Found:
C, 73.94; H, 4.22, N, 4.36; S, 5.16. UV (kmax, CHCl3):
1256(w), 1210(w), 765(m), 635(w). H-NMR (CDCl3; d,
ppm): 7.61–6.83 (24H, m, ArH), 4.10 (8H, bs, ArCH2Ar),
3.78 (12H, s, OCH3), 2.44 (8H, q, SCH2), 1.44 (12H, t,
CH3).
123

246
J Incl Phenom Macrocycl Chem (2012) 74:239–249
25,26,27,28-Tetramethoxy-5,11,17,23-tetra(2-
thiopropylphenylazo)calix[4]arene: 5c
General procedure for spectrophotometric analysis
of interaction between 6 and metal ions
(0.21 g, 24%). m.p. 223 °C (decom.) was obtained as
yellow crystalline solid from the reaction of diazoca-
lix[4]arene 5 (0.85 g, 0.75 mmol) with methyl iodide
(2.79 g, 19.6 mmol) and NaH (0.3 g, 12.5 mmol) by fol-
lowing the general procedure. Mol. Mass (vapor pressure
osmometry): 1201 (calcd. 1194). Anal. calcd. for
C68H72N8O4S4: C, 68.42; H, 6.08; N, 9.39. Found: C,
67.64; H, 6.22, N, 9.86. UV (kmax, CHCl3): 420 nm. IR
(KBr; mmax, cm-1): 2898(sh), 1560(m), 1452(m), 1436(w),
1372(w), 1256(w), 1212(w), 762(m), 620(w). 1H-NMR
(CDCl3; d, ppm): 7.60–6.80 (24H, m, ArH), 4.14 (8H, bs,
ArCH2Ar), 3.51 (12H, s, OCH3), 2.48 (8H, t, SCH2), 1.73
(8H, m, SCCH2); 1.06 (12H, t, SCCH3).
The stock solution L1 was diluted 2.5 times to get the
optical density (OD) within scale of the spectrophotome-
ter. This solution was divided into several 3 ml portions
and 0.5 ml of the solutions of the following metals
(in methanol) were added to them followed by a record of
UV-VIS spectrum of each solution. The metal ions taken
were Pd2? [Na2PdCl4] and Pt2? [K2PtCl4]. The spectral
changes upon addition of Pd(II) and Pt(II) are shown in
Fig. 2.
General procedure for quantitative examination
of the interaction between chromogenic calixarene (6)
with metal ions by spectrometry
25,26,27,28-Tetramethoxy-5,17-di(2-
thiomethylphenylazo)calix[4]arene: 6c
The metal to ligand ratio of the 6-metal complexation was
ascertained by mole-ratio plots and it was further con-
firmed by the Jobs continuous variation method.
(0.23 g, 27%). m.p. 245 °C (decom.) was obtained as
yellow crystalline solid from the reaction of diazoca-
lix[4]arene 6 (0.73 g, 1.0 mmol) with methyl iodide
(3.72 g, 26.2 mmol) and NaH (0.4 g, 16.6 mmol) by
following the general procedure. Mol. Mass (vapor pres-
sure osmometry): 792 (calcd. 781). Anal. calcd. for
C46H44N4O4S2: C, 70.74; H, 5.68; N, 7.17. Found: C,
71.20; H, 5.52, N, 7.03. UV (kmax, CHCl3): 360 nm. IR
(KBr; mmax, cm-1): 2823(m), 1593(m), 1482(m), 1436(w),
1372(w), 1276(w), 1212(w), 753(m), 620(w). 1H-NMR
(CDCl3; d, ppm): 7.72–6.71 (18H, m, ArH), 4.30, 3.65 (8H,
d, ArCH2Ar), 3.52 (12H, s, OCH3), 2.17 (6H, s, SCH3).
(a) Mole-ratio plots for stoichiometry of the platinum
and palladium complexes with synthesized calix[4]arene
derivatives. A series of solutions with fixed concentration
of ligand and gradually varied concentration of metal
ions were prepared. The mixed solutions were shaken
well and left for about 5–10 min so as to ensure equi-
librium between the ligand and metal ions. The optical
spectrum of each solution was recorded. The OD was
observed at a wavelength at which neither the metal nor
the ligand absorbed (470 nm in the case of Na2PdCl4 and
520 nm in the case of K2PtCl4). The metal to ligand ratio
(M/L) was calculated for each metal ion from the plots of
OD and CM/CL where CM is the concentration of the
metal ions and CL is the concentration of the ligand (CM/
CL).
UV-VIS spectrophotometric titrations
(b) Evaluation of interaction of metal ions with molec-
ular receptors by Jobs method of continuous variation. A
series of solutions with varied metal ion and ligand con-
centrations were prepared. The total ligand and metal ion
concentration was fixed which was kept the same for each
of them (i.e. C = CM ? CL, where CL, CM and C are
concentrations of the ligand, metal ion and total concen-
tration respectively). The solutions were allowed to stand
for about 10 min to attain equilibrium between the metal
and the ligand. The OD was measured at 470 and 520 nm
for Na2PdCl4 and K2PtCl4 respectively and was plotted
against the mole-fraction of the ligand, XL (=CL/C).
Assuming that only one complex is formed with a com-
position MLn, the value of n was calculated from the Xmax
(mole-fraction of the ligand (XL) at maximum absorption)
from the following relation.
Preparation of the stock solution of the ligands (6)
and metals
The chromogenic calix(4)arene (6) was weighed (16.62 mg)
accurately and dissolved in 2 ml of CHCl3 in 100 ml stan-
dard flask. The rest of the volume was made up to the mark by
adding methanol. The concentration of the solution was
calculated as 2.2927 9 10-4 M. This solution was labelled
as L1. Sodium tetrachloropalladate (II), (Na2PdCl4) was
weighed (17.6 mg) accurately and dissolved in methanol in a
5 ml standard flask. The concentration of this solution was
determined to be 1.1965 9 10-2 M. This solution was
labeled as Pd. Potassium tetrachloroplatinate (II), (K2PtCl4)
was weighed (12.5 mg) accurately and dissolved in metha-
nol containing 1 ml of water in a 25 ml standard flask. The
concentration of this solution was determined to be
1.2045 9 10-3 M. This solution was labeled as Pt.
n ¼ Xmax=1 ꢁ Xmax
123

J Incl Phenom Macrocycl Chem (2012) 74:239–249
247
Table 1 Solutions of different composition of 6 and Pd solutions
Table 2 Solutions of different composition of 6 and Pt solutions
No.
Volume of ligand
solution (ml)a
Volume of metal
solution (ml)b
XL
T. No. Volume of ligand Volume of metal XL
solution (ml)a
Absorbance
(OD) at
470 nm
solution (ml)b
1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.00
0.09
0.19
0.29
0.38
0.49
0.59
0.69
0.79
0.80
1.00
1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.00 0.00
2
2
0.10 0.22
0.20 0.42
0.30 0.66
0.40 0.60
0.50 0.48
0.60 0.38
0.70 0.26
0.80 0.18
0.90 0.05
1.00 0.00
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
11
a
10
11
a
Concentration of ligand (6) solution was 2.2327 9 10-4
M
Concentration of ligand (6) solution is 2.2927 9 10-4
M
b
Concentration of metal ion (Na2PdCl4) solution was
2.393 9 10-4
b
M
Concentration of metal (K2PtCl4) solution is 2.2653 9 10-4
M
Interaction between 6 and Na2PdCl4
plot, metal to ligand mole ratio was determined to be 2.2
that corresponded to approximately 1:2 ratio of ligand to
metal (platinum).
Application of mole-ratio method
A series of solutions containing 2 ml of ligand (6)
(2.2927 9 10-4 M) and 0.00, 0.05, 0.10, 0.30, 0.40 and
1.5 ml respectively of metal ion solution (1.196 9 10-3
M) were prepared. The spectrum of each solution was
recorded as mentioned in the general procedure to produce
(Fig. 2a). The OD at 470 nm was plotted against the metal
to ligand mole ratio (CM/CL) (Fig. 3a) which gave metal to
ligand mole ratio as 1.2. This corresponded to around 1.2
indicating the ratio of the ligand to metal (palladium) as 1:1.
Application of Jobs continuous variation method
A series of solutions of the compositions mentioned in
Table 2 were prepared and after treating them as described
in the general procedure, their OD at 470 nm was recorded.
From the plot of OD Vs XL (Fig. 4b), the value of ‘Xmax
was found to be 0.33 that gave the value of ‘n’ as
approximately 0.5 [0.33/(1 - 0.33)].
’
Acknowledgments The authors are thankful to the Department of
Science and Technology, for financial assistance and Indian Institute
of Technology, Delhi for a part of research fellowship to one of them
(NV).
Jobs continuous variation method
A series of solutions of the composition mentioned in the
Table 1 was prepared and after treating them as described
in the general procedure, their OD at 520 nm was recorded.
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