Spectrophotometric study of complexation of Tri-Aza dibenzosulfide and dibenzosulfoxide macrocyclic compounds with heavy metal ions

Article abstract of DOI:10.1080/10426500701501441

The complexation reactions between 7,10,13-triaza-1-thia-4,16-dioxa-20,24- dimethyl-2,3;17,18-dibenzo-cyclooctadecane-6,14-dione (TTD) and 7,10,13-triaza-1-sulfoxo-4,16-dioxa-20,24-dimethyl-2,3;17,18-dibenzo- cyclooctadecane-6,14-dione (TSD) macrocycles w

Full text of DOI:10.1080/10426500701501441

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Spectrophotometric Study
of Complexation of Tri-
Aza Dibenzosulfide and
Dibenzosulfoxide Macrocyclic
Compounds with Heavy Metal
Ions
Shahla Mozaffari a , Marzieh Chaloosi a , Faten Divsar
a , Ebrahim Abouzari-Lotf a , Samad T Bavili a , Ali
Yousefi a & Abbas Shockravi a
a Faculty of Chemistry, Tarbiat Moallem University,
Tehran, Iran
Version of record first published: 23 Aug 2007.
To cite this article: Shahla Mozaffari , Marzieh Chaloosi , Faten Divsar ,
Ebrahim Abouzari-Lotf , Samad T Bavili , Ali Yousefi & Abbas Shockravi (2008):
Spectrophotometric Study of Complexation of Tri-Aza Dibenzosulfide and
Dibenzosulfoxide Macrocyclic Compounds with Heavy Metal Ions, Phosphorus, Sulfur,
and Silicon and the Related Elements, 182:10, 2439-2448
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Phosphorus, Sulfur, and Silicon, 182:2439–2448, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701501441
Spectrophotometric Study of Complexation of Tri-Aza
Dibenzosulfide and Dibenzosulfoxide Macrocyclic
Compounds with Heavy Metal Ions
Shahla Mozaffari
Marzieh Chaloosi
Faten Divsar
Ebrahim Abouzari-Lotf
Samad Bavili T
Ali Yousefi
Abbas Shockravi
Faculty of Chemistry, Tarbiat Moallem University, Tehran, Iran
The complexation reactions between 7,10,13-triaza-1-thia-4,16-dioxa-20,24-
dimethyl-2,3;17,18-dibenzo-cyclooctadecane-6,14-dione (TTD) and 7,10,13-triaza-
1-sulfoxo-4,16-dioxa-20,24-dimethyl-2,3;17,18-dibenzo-cyclooctadecane-6,14-dione
(TSD) macrocycles with Ag+, Cd2+, Cu2+, Pb2+, Sr2+, Tl+, and Zn2+ ions
have been studied in ethanol and methanol solutions at 25◦C. The complexes
formed between macrocycles (TTD) and (TSD) with these metals cations had a
stiochiometry of 1:1 and 1:2, respectively. The stability constants of the resulting
complexes were determined and found to decrease in the order Cu2+ > Zn2+
Ag+ > Tl+ > Cd2+ >Pb2+ > Sr2+ with macrocycle (TTD) and Tl+ > Zn2+
Cd2+ > Pb2+ > Cu2+ > Ag+ > Sr2+ with macrocycle (TSD).
>
>
Keywords Copper; formation constant; macrocycle; spectrophotometry; thallium; zinc
INTRODUCTION
Crown ethers, which were first discovered by Pederson in 1967,1 are
now important as a class of heteromacrocycles in the view of synthesis
and complexation properties for various cations and anions as well as
ionic and neutral molecules.2,3
Macrocyclic diamides and corresponding aza crown compounds have
gained a great deal of attention due to their wide applications in chem-
istry. This is generally due to their high capability in selective and
Received June 6, 2006; accepted August 29, 2006.
Address correspondence to Abbas Shockravi, Faculty of Chemistry, Teacher Train-
ing University, No. 49, Mofettah Avenue, Tehran 15614, Iran. E-mail: shock-
ravi@saba.tmu.ac.ir
2439

2440
S. Mozaffari et al.
effective complexation with variety of transition and heavy metals,
molecular ions, and neutral molecules, and there is an increasing inter-
est in the preparation of them.4 The use of thia-containing macrocycles
as building blocks in such systems yields the potential of binding soft
metals, this behavior is based on HSAB (hard-soft acid and base) con-
cept, sulfur is classified with soft base, some soft acids, such as Ag (I),
Pt (II), Hg (II), Cu (II), and Zn (II) can bind very strongly with ligands
containing sulfur atoms.5
Since most of heavy metal cations are toxic,6 their complexation stud-
ies are competitive area of research. The investigation of the reaction
conditions and the design of a highly selective ligand for removal of
these cations is of particular importance. Determination of formation
constants of complexes of these cations are performed by different meth-
1
ods such as: H NMR studies,7 spectrophotometric,8 conductometric,9
polarographically,10 square wave polarography,10 and potentiometric12
methods.
We have synthesized two triaza macrocycles TTD and TSD in our
previous works as are shown in Schemes 1 and 2.13 Herein, we wish to
report the complexation and stabilities of macrocycles TTD and TSD
with heavy metal cations Ag+, Cd2+, Cu2+, Pb2+, Sr2+, Tl+, and Zn2+
.
SCHEME 1 Synthesis of macrocycle TTD.

Sulfide and Sulfoxide Macrocyclic Compounds
2441
SCHEME 2 Synthesis of macrocycle TSD.
RESULTS AND DISCUSSION
The electronic absorption spectra of macrocycles with various concen-
trations are represented in Figures 1 and 2. Examination of Figures
1 and 2 indicate that the electronic spectra of these macrocycles are
largely depending on the concentration. Increasing the macrocycle TTD
and TSD concentrations result in increasing the absorbance of both
bands for both macrocycles at (248–254 and 278–286), and (230–246
and 280–284) nm, respectively. This behavior can be ascribed to the
association of the molecules through intermolecular hydrogen bonding.
The complexation behavior of these two macrocycles with Ag+, Cd2+
,

2442
S. Mozaffari et al.
TABLE I Maximum Wavelengths of Complextion of
Macrocycles-Mn+
λmax(nm)
Macrocycle Cu(II)
Zn(II)
Ag(I)
Tl(I) Cd(II) Pb(II) Sr(II)
TTD
TSD
216
212
216
212
218
212
216
214
214
212
212
212
212
212
Cu2+, Pb2+, Sr2+, Tl+, and Zn2+ are studied and the maximum absorp-
tion wavelengths are shown in Table 1. The electronic spectra of the
complextion of these two marocycles with above cations are shown in
Figures 3 and 4, respectively.
The formation constant of complexes are calculated by fitting the ob-
served absorptions of the ligands at various [Mn+] / [L] mole ratios by
using a nonlinear least-squares program KINFIT.14 Two of the typical
FIGURE 1 Electronic spectra of macrocycle TTD in different concentrations:
−(2 × 10−3 mol l−1); —·— (1.2 × 10−4 mol l−1), and . . . .. (3.59 × 10−5 mol l−1) in
ethanol.

Sulfide and Sulfoxide Macrocyclic Compounds
2443
TABLE II Formation Constants of Mn+with Macrocycle TTD (in
ethanol, at 25◦C) and Macrocycle TSD (in methanol, at 25◦C)
LogKf
Macrocycle
Cu(II)
Zn(II)
Ag(I)
Tl(I)
Cd(II)
Pb(II)
Sr(II)
TTD
TSD
4.28 0.09 1.99 0.08 1.56 0.06 0.79 0.15 0.73 0.04 0.45 0.11 0.64 0.02
0.74 0.15 1.29 0.14 0.68 0.02 2.28 0.05 0.90 0.15 0.87 0.02 0.67 0.02
fitting curves of macrocycles with cations using the above software
are illustrated in Figure 5 and 6. The fitting curves of complexation
process for both ligands are in very good agreement with calculated
and experimental data. The results of formation constants are shown in
Table 2.
As is evident from Table 2, the stability of the complexes of these
heavy metal ions with TTD decreases in the order of Cu2+ > Zn2+
>
Ag+ > Tl+ > Cd2+ > Pb2+ > Sr2+. This means that Cu2+ ion with the
least soft character and with a good fit condition for TTD cavity, forms
FIGURE 2 Electronic spectra of macrocycle TSD in different concentrations:
−(03 × 10−5 mol l−1); —- (5.03 × 10−4 mol l−1); (5.03 × 10−5 mol l−1); . . . . (3.09 ×
10−5 mol l−1); and . . . . (1.03 × 10−6 mol l−1) in methanol.

2444
S. Mozaffari et al.
FIGURE 3 Electronic spectra of complex of macrocycle TTD–Mn+: (a) Tl+; (b)
Sr2+; (c) Pb2+; (d) Cu2+; (e) Cd2+; (f) Ag+, and (g) Zn2+
.
FIGURE 4 Electronic spectra of complex of macrocycle TSD – Mn+: (a) Sr2+
(b) Pb2+; (c) Cu2+; (d) Cd2+; (e) Tl+; (f) Ag+; and (g) Zn2+
;
.

Sulfide and Sulfoxide Macrocyclic Compounds
2445
FIGURE 5 Fitting curve of macrocycle TTD–Cu2+ with ML (= presents fitting;
× presents experimental data; and 0 presents calculated data).
the most stable complex with TTD as a relatively hard donating lig-
and. It seems that the increased nature of covalent bonding character
of the Cu2+ ion could explain the larger value of the stability constant
of TTD-Cu2+ complex than the other six complxes in the protic sol-
vent. The stability order of complexes with TSD is changed to Tl+
>
Zn2+ > Cd2+ > Pb2+ >Cu2+ > Ag+ > Sr2+, in which Tl+ ion with a good
FIGURE 6 Fitting curve of macrocycle TSD–Tl+ with ML2 (= presents fitting;
× presents experimental data; and 0 presents calculated data).

2446
S. Mozaffari et al.
fit condition for TSD cavity, forms the most stable complex with this
ligand. As is seen from the Table 2, the Tl+ion forms a more stable
complex with TSD than other ions in protic solvent system. This obser-
vation seems reasonable, since the Tl+ion is bound in the complex by
an ion- dipole interaction with a covalent contribution.15
Based on the analytical data obtained in these experiments, it seems
the macrocycle TTD allows 1:1 complexation process with the cations in
its cavity. This process is apparently occurred in 1: 2 ratio by macrocycle
TSD. This may be because of formation of strong interamolecular hy-
drogen bonding in the cavity of macrocycle TSD between NH and S O
groups. Thus, this situation could provide a suitable conditions for 1:
2 ratio complexation in which the formation constants trends are gen-
erally lower than the macrocycle TTD. This could be because of more
rigidity of the macrocycle TSD due to S O group which is also found in
our previous studies.13c In this case, the macocycle may not be flexible
enough to keep the ions in its cavity. As a result, the formation of 1: 2
guest-host system will be more preferable.
EXPERIMENTAL
Apparatus
A Milton Roy Model 1201 photomultiplier tube spectrophotometer was
interfaced with an IBM PCS-486 microcomputer by the spectro program
that was developed to convert the absorption data acquire with the
spectrometer was used. The KINFIT software was used for fitting of
experimental and calculated data.
Reagents and Material
All experiments were performed with analytical reagent grade chemi-
cals and pure solvents. Doubly distilled water was used for preparation
of aqueous solutions.
Macrocycles were synthesized and reported previously.13 Macrocycle
TTD stock solution (3.59 × 10−3 mol l−1) was prepared in ethanol and
macrocycle TSD stock solution (3.09 × 10−3 mol l−1) was prepared in
methanol. Stock solutions of Ag+, Cd2+, Cu2+, Pb2+, Sr2+, Tl+, and Zn2+
were made by dissolving an appropriate of high purity nitrate salts of
these cations (Merck, Germany) in distilled water, respectively. Working
solutions were prepared by appropriate dilution of stock solution.
Procedure
Absorption spectra of macrocycles TTD and TSD are recorded in differ-
ent concentrations between 200 and 500 nm and the results are shown

Sulfide and Sulfoxide Macrocyclic Compounds
2447
in Figures 1 and 2. The absorption spectra of complexes of TTD and
TSD with Ag+, Cd2+, Cu2+, Pb2+, Sr2+, Tl+, and Zn2+are shown in Fig-
ures 3 and 4. The optimum concentrations of macrocycle TTD and TSD
were found in 3.59 × 10−5 mol l−1 and 3.09 × 10−5 mol l−1, respectively.
The stock solution concentrations of cations for complextion with macro-
cycles TTD and TSD were 8.95 × 10−4, 8.83 × 10−4, 7.07 × 10−4, 9.01 ×
10−4, 5.96 × 10−4, 5.26 × 10−4, and 8.59 × 10−4 mol l−1, respectively.
The absorption of each complex of macrocycles TTD and TSD with
cations in their maximum absorption wavelength are determined in
different [M+n] / [L] mole ratio for determination of formation constants.
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