Spectral, thermal, electrochemical and analytical studies on Cd(II) and Hg(II) thiosemicarbazone complexes

Article abstract of DOI:10.1016/j.saa.2007.11.018

The coordination characteristic of the investigated thiosemicarbazones towards hazard pollutants, Cd(II) and Hg(II), becomes the first goal. Their complexes have been studied by microanalysis, thermal, electrochemical and spectral (electronic, IR and MS) studies. The substitutent (salicylaldehyde, acetophenone, benzophenone, o-hydroxy-p-methoxybenzophenone or diacetylmonoxime) plays an important role in the complex formation. The coordination sites were the S for thiosemicarbazide (HTS); NN for benzophenone thiosemicarbazone (HBTS); NS for acetophenone thiosemicarbazone (HATS) and salicylaldehyde thiosemicarbazone (H₂STS); NNS or NSO for diacetylmonoxime thiosemicarbazone (H₂DMTS). The stability constants of Hg(II) complexes were higher than Cd(II). The kinetic and thermodynamic parameters for the different thermal decomposition steps in the complexes have been evaluated. The activation energy values of the first step ordered the complexes as: [Cd(H₂STS)Cl₂]H₂O > [Cd(H₂DAMTS)Cl₂] > [Cd(HBTS)₂Cl₂]2H₂O > [Cd(HATS)₂Cl₂]. The CV of [Cd(H₂STS)Cl₂]H₂O and [Hg(HBTS)Cl₂] were recorded. The use of H₂DMTS as a new reagent for the separation and determination of Cd(II) ions from water and some synthetic samples using flotation technique is aimed to be discussed.

Full text of DOI:10.1016/j.saa.2007.11.018

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 71 (2008) 39–44
Spectral, thermal, electrochemical and analytical studies on Cd(II)
and Hg(II) thiosemicarbazone complexes
∗
A.A. El-Asmy , O.A. El-Gammal, H.S. Saleh
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
Received 2 June 2007; received in revised form 11 November 2007; accepted 15 November 2007
Abstract
The coordination characteristic of the investigated thiosemicarbazones towards hazard pollutants, Cd(II) and Hg(II), becomes the first goal.
Their complexes have been studied by microanalysis, thermal, electrochemical and spectral (electronic, IR and MS) studies. The substitutent (sal-
icylaldehyde, acetophenone, benzophenone, o-hydroxy-p-methoxybenzophenone or diacetylmonoxime) plays an important role in the complex
formation. The coordination sites were the S for thiosemicarbazide (HTS); NN for benzophenone thiosemicarbazone (HBTS); NS for ace-
tophenone thiosemicarbazone (HATS) and salicylaldehyde thiosemicarbazone (H
DMTS). The stability constants of Hg(II) complexes were higher than Cd(II). The kinetic and thermodynamic parameters for the different
thermal decomposition steps in the complexes have been evaluated. The activation energy values of the first step ordered the complexes as:
Cd(H STS)Cl ]H O > [Cd(H DAMTS)Cl ] > [Cd(HBTS) Cl ]2H O > [Cd(HATS) Cl ]. The CV of [Cd(H STS)Cl ]H O and [Hg(HBTS)Cl
were recorded. The use of H DMTS as a new reagent for the separation and determination of Cd(II) ions from water and some synthetic samples
using flotation technique is aimed to be discussed.
2007 Elsevier B.V. All rights reserved.
2
STS); NNS or NSO for diacetylmonoxime thiosemicarbazone
(H
2
[
2
2
2
2
2
2
2
2
2
2
2
2
2
2
]
2
©
Keywords: Thiosemicarbazone complexes; Cyclic voltammetry; Thermogravimetric analysis
1
. Introduction
and thiosemicarbazide (9.1 g, 0.1 mol) were mixed in EtOH
30 ml) with few drops of glacial CH3COOH and heated under
(
Sulfur compounds have very promising in coordination
reflux on a water bath for 3 h. The formed precipitate was
removed by filtration, recrystallized from absolute EtOH and
dried. The yields are 65–80%. Identification of the ligands was
confirmed by IR spectra and the purity was checked by TLC.
The proposed formulae of the ligands are in good agreement
chemistry due to their pharmaceutical properties [1–3]. They
have a remarkable interest due to their ability to form sta-
ble chelates with the essential metal ions in which the fungus
needs in its metabolism [4]. Transition metal complexes of some
thiosemicarbazones possess some degree of cytotoxic activity
with the stoichiometry concluded from their elemental analy-
1
[
5]. The structure of many Cd(II) and Hg(II) complexes was
ses. The H NMR spectrum of H2DMTS in d -DMSO shows
6
suggested and confirmed by single crystal X-ray analysis [6–12].
signals at δ 12.08 ppm (s, 1H) and 9.92 ppm (s, 1H) assigned to
the OH and NH protons, respectively; the relatively high value of
the OH signal may be due to intra-molecular hydrogen bonding.
The spectra of HATS and H2STS show signals at δ = 10.29 ppm
(s, 1H), 8.09 ppm (s, 2H) and 10.07 ppm (s, 1H), 8.03 ppm (s,
2
. Experimental
2
.1. Synthesis of ligands
2H) assigned to the NH and NH2 protons, respectively. More-
Thiosemicarbazones (Scheme 1) were prepared by the
over, the spectrum of H2STS showed the OH proton signal at
10.17 ppm (s, 1H).
same method reported earlier [13]. The synthesis of diacetyl-
monoxime thiosemicarbazone (H2DMTS) was explained as a
representative example. Diacetylmonoxime (10.1 g, 0.1 mol)
2.2. Synthesis of complexes
∗
The complexes were prepared by heating under reflux a mix-
Corresponding author. Tel.: +20 101645966.
E-mail address: aelasmy@yahoo.com (A.A. El-Asmy).
ture of each ligand (2 mmol) and CdCl2 or HgCl2 (1 mmol) on
1
386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.11.018

4
0
A.A. El-Asmy et al. / Spectrochimica Acta Part A 71 (2008) 39–44
2.4. pH metric method
All pH titrations were carried out at room tempera-
ture. The following solutions were titrated against NaOH
−
3
−1
(
(
3.4 × 10 mol l ) in 50% EtOH-H2O at ionic strength
−
1
0.1 mol l KCl):
−
3
−1
−1
(
(
a) 1 ml of KCl + 5 ml ligand (2.5 × 10 mol l );
−
3
b) 1 ml of KCl + 5 ml ligand (2.5 × 10 mol l ) + 1 ml Cd or
Scheme 1.
−
3
−1
Hg (2.5 × 10 mol l ).
a water bath for 4–6 h. All the formed precipitates were filtered
off, washed with EtOH and Et2O and finally dried. The yields
are 60–75%. As an example, [Cd(H2DAMTS)Cl2] is described
in detail. To 50 ml reaction flask, 0.34 g (2 mmol) of diacetyl-
monoxime thiosemicarbazone, dissolved in 20 ml ethanol, and
The total volume was completed to 50 ml with bidistilled
H2O. The solution was stirred and the pH was recorded.
The number of protons attached to the ligand is calculated
according to the following equation [14]:
0
.44 g (2 mmol) of CdCl2·2H2O, dissolved in 20 ml distilled
V1No
n¯ A = Y −
VoTL
water, were added and heated on a water bath for 2 h. The pre-
cipitate thus formed was removed by filtration, washed withH2O
and EtOH then dried at 80 C.
◦
where Y is the number of ionized protons, V the volume of
1
alkali required to reach the same pH in the titration curves, Vo
3
the initial volume of the titrated solution (50 cm ), TL the lig-
2
.3. Chemical and physical measurements
−
3
−1
and concentration (×10 mol l ), and No is the concentration
of NaOH. The stability constants of the complexes have been
evaluated from the n¯ –pL plots, where n¯ is the average number
of ligand molecules attached per M(II) ion and pL is the free
ligand exponent. The n¯ values can be calculated as [15]
Carbon and hydrogen analyses of Cd(II) complexes were per-
formed at the Microanalytical Unit of Cairo University. Cd(II)
and Hg(II) were determined complexometrically using xylenol
orange as an indicator and the chloride gravimetrically as AgCl.
1
The infrared, electronic, H NMR in d -DMSO (200 MHz) and
6
(V − V )N
2
1
o
n¯ =
mass spectra were recorded on a Mattson 5000 FTIR Spec-
trophotometer, provided with CsI beam splitter, UV2 Unicam
UV/Vis, Varian Gemini and Varian MAT 311 Spectrometers,
respectively. The pH values were measured using a calibrated
pH-meter (Hanna-Instruments, 8519, Italy). The cyclic voltam-
metry measurements were carried out with a Potentiostat Wave
Generator (Oxford Press) equipped with a Phillips PM 8043 X-Y
recorder. The electrochemical cell assembly consists of platinum
wires of 0.5 mm diameter as working and counter electrodes and
Ag/AgCl as a reference electrode.
n¯ ATM(Vo − V1)
where V2 is the volume of alkali required to reach the desired pH
in the complex titration curve, and TM is the initial concentration
of Cu(II). The pL can be calculated as
ꢀ
ꢃ
ꢁ
ꢂ
+
1 + k1 H
V2 + Vo
pL = log
×
T − n¯ T
L
M
V
o
where k1 is the protonation constant of the ligand.
Table 1
Physical, analytical data, and formula weight (FW) of the prepared Cd(II) complexes
a
◦
Complex
Color
Λ
m.p. ( C)
Found (calcd.) (%)
C
H
M
Cl
[
[
[
[
[
[
[
[
Cd(H2DAMTS)Cl2], 357.5
Hg(HTS)Cl2]3H2O, 453.8
Cd(H2STS)Cl2]H2O, 396.6 (392)
Hg(H2STS)2Cl2], 662
Cd(HATS)2Cl2], 569.9
Hg(HATS)Cl2], 482.8
Yellow
White
Yellowish white
Pale yellow
White
White
Yellowish white
White
Yellow
White
13.6
9.5
15.3
8.50
8.6
8.3
15.6
11.8
15.4
2.46
9.5
>300
224
>300
16.6 (16.8)
3.0 (2.8)
2.6 (2.8)
4.0 (3.9)
3.9 (4.1)
1.0 (1.5)
2.3 (2.3)
31.6 (31.4)
44.2 (44.2)
28.6 (28.3)
29.7 (30.3)
20.0 (19.7)
41.2 (41.5)
15.5 (15.4)
25.1 (25.6)
36.9 (36.7)
51.3 (50.9)
33.7 (33.6)
35.0 (35.0)
19.7 (19.8)
15.2 (15.6)
18.3 (17.9)
10.9 (10.7)
12.8 (12.4)
14.7 (14.7)
9.0 (9.7)
9.5 (9.1)
23.7 (23.2)
9.3 (9.0)
24.5 (24.2)
37.9 (37.9)
47.0 (46.1)
28.0 (27.5)
26.3 (27.0)
223
242
183
212
>300
194
191
219
b
Cd(HBTS)2(H2O)2Cl2], 730.1 (730)
Hg (HBTS)2Cl2], 782.3
Cd(S)Cl2, 305.5
[
[
[
Hg(HS)Cl]2H2O, 394.2
Cd2(H2oHpMBTS)Cl4], 668.2
Hg(H2oHpMBTS)Cl2], 573
Yellowish white
White
21.6 (21.3)
12.8 (12.4)
11.7
a
−1
2
−1
Molar conductance in ohm cm mol .
b
Molecular weight obtained from mass spectra.

A.A. El-Asmy et al. / Spectrochimica Acta Part A 71 (2008) 39–44
41
2
.5. Flotation method
The free energy (Table 1S, supplemental information) was
*
calculated applying the relation: −ꢀG = 2.303 log β . It is well
−
−1
5
−1
Cd(II) was
A 3 ml aliquot containing 0.5 × 10 mol l
known that stable complexes have larger negative ꢀG. The sta-
bility of Hg(II) complexes is higher than Cd(II) and the most
stable is Cd–H2DMTS.
−
4
mixed with H2DMTS (1 × 10 mol l ) and 3 ml bidistilled
water. The pH was adjusted at ≈7. The solution was then trans-
ferred quantitatively to the flotation cell and completed to 10 ml
with bidistilled water. The cell was shaken well for few sec-
onds to ensure complete complexation. To this solution, 3 ml of
3.2. Characterization of the solid complexes
−3
−1
1
× 10 mol l HOL were added and the cell was then inverted
Cd(II) and Hg(II) complexes of H2DMTS, HATS, H2STS,
HBTS and H2oHpMBTS have been isolated in the pure state.
They are white, yellowish white or yellow; quite stable in atmo-
spheric conditions; insoluble in water, ethanol and diethylether
but are completely soluble in DMSO and DMF. The complexes
upside down many times by hand. After complete separation,
the scum containing Cd(II)–H2DMTS complex was separated,
eluted with 4 ml of 4 M HCl, diluted to 10 ml in a volumetric
flask and subjected to AAS determination.
◦
have melting points less than 300 C except [Cd(H2DMTS)Cl2]
◦
3
. Results and discussion
and [Cd(H2STS)Cl2] which have values >300 C. The molar
conductivity values of the complexes, in DMF, indicate non-
electrolytes. The analytical data and some physical properties
of the complexes are listed in Table 1.
3
.1. pH-metric studies
The proton ligand formation constants and the stability con-
1
stants of their Cd(II) and Hg(II) complexes were evaluated
3.2.1. IR, H NMR and mass spectra
◦
at 25 ± 1 C in 50% ethanol–water solution. The shift of the
The IR spectra of the investigated thiosemicarbazones show
bands at 3254–3409, 3231–3367, 3146–3223, 1538–1647,
1550, 1485–1532, 1261–1288, 930–1001 and 763–800 cm
attributed to νas(NH2), νs(NH2), ν(N H), ν(C N)thio, ν(C N)ox
[12], [δ(C H) + δ(N H)], [ν(C S) + ν(C N) + δ(C H)],
[ν(C N) + ν(C S)] and ν(C S) [16], respectively. The spectra
of H2DMTS, H2STS, H2oHpMBTS and HS show a band at
3188–3442 cm due to ν(OH), while the ν(C O) of HS is
observed at 1666 cm . The data suggest the binding of ligands
to Cd(II) and Hg(II) in different coordination modes:
ligand titration curve from that of HCl is undetectable when
applying Irving and Rossotti technique due to the weak basic-
ity of ligands and the presence of NH2 group. It is suitable
to do the titration in absence of HCl [14]. The average num-
ber of protons associated per ligand molecule ( n¯ A) at different
pH values was graphically plotted against pH. The ligand con-
stants log k1 and log k2 have been determined by interpolation
at n¯ A = 0.5 or 1.5 (Table 3S, supplemental information). It is
found an agreement between the data of half and least square
−1
2
−
1
−
1
[
15] methods.
In [Cd(H2DMTS)Cl2], the shifts of ν(OH), ν(C N)
and
thio
−
1
HATS or HBTS dissociates its thioamidic proton,
ν(C S) by 18, 80 and 31 cm indicate the tridentate behav-
ior of H2DMTS. In [Cd(HATS)2Cl2], [Cd(HBTS)2Cl2]2H2O
and [Hg(HBTS)2Cl2], the ligands act as monodentate through
while H2DMTS, H2STS and H2oHpMBTS have two
thioamidic and phenolic and/or oxime). The effect of
substitution on C N group ordered the pk1 values as:
H2DMTS < H2oHpMBTS < H2STS < HATS < HBTS. The
(
−
1
C N by its shift by 47 cm , while the remarkable shift of
ν(NH) to higher wavenumber may due to neighboring effect.
−
1
presence of two phenyl groups (electron withdrawal) of HBTS
decreases the electron density on the azomethine group and
facilitates the proton withdrawal.
The new band at ca. 465 cm is assignable to ν(M–N) [16]. In
[Cd2(H2oHpMBTS)Cl4], the ligand behaves as a neutral biden-
tate coordinating via C SH and C N groups proving by: the
−
1
The formation constants of the complexes have been deter-
negativeshiftofν(C N)by14 cm , theabsenceof ν(C S)con-
−
1
−1
mined at constant ionic strength (0.1 mol l KCl) and at
2
jugated with the appearance of ν(SH) at 2364 cm and ν(C S)
at 684 cm [17] and the band at 436 cm due to ν(Cd N)
◦
−1
−1
5 ± 1 C in ethanol–water solution (v/v). The metal–ligand
−1
curves are below and well separated from that of the free ligand
indicating that the complexation process accompained by evolu-
tion of hydrogen ions. In all cases, the curves of Hg(II) systems
are well defined than Cd(II) indicating that Hg(II) ions easily
react with sulfur compounds more than Cd(II).
[16]. The ν(OH) is shifted to higher frequency by 32 cm due
to the dissociation of its hydrogen bonding. The spectral data
of [Cd(H2STS)Cl2]H2O support a mononegative bidentate (NO
2
donors) by the negative shifts of ν(OH) and ν(N H) by 44 and
−
1
20 cm , respectively, and the appearance of new bands at 504
−
1
The n¯ –pL plots are drawn for solutions containing 1:5
and 400 cm assigned to ν(Cd O) [18] and ν(Cd N), respec-
tively. The band at 274 cm is due to ν(Cd Cl) [19] proving the
presence of Cl inside the coordination. Theband due to ν(C N)
is shifted to higher frequency by 22 cm where the dissociation
of the hydrogen bonding between OH and C N occurred. The
−
1
(metal:ligand) ratio to ensure the formation of the most sta-
−
ble species. The stability constants of the investigated systems
have been evaluated by half and least square methods [15].
The data (Table 1S) show clearly that log k1 are higher than
log k2 for the same complex. The stability of Cd(II) com-
plexes (log k1) gives the following order with respect to the
ligands: H2DMTS ≈ H2STS > H2oHpMBTS > HATS > HBTS:
o-hydroxy-p-methoxybenzophenone hinders the stability of its
complex than salicylaldehyde.
−
1
1
H NMR spectrum of [Cd(H2STS)Cl2]H2O shows no difference
comparing with the spectrum of its ligand due to coordination
with C N. The NH and NH2 signals are shifted downfield by
1.15 and 0.64 ppm in the spectrum of [Hg(HBTS)2Cl2] due to
the effect of neighboring groups to C N.

4
2
A.A. El-Asmy et al. / Spectrochimica Acta Part A 71 (2008) 39–44
Table 2
Electronic spectral data of the free ligands and their Cd(II) and Hg(II) complexes
Intra-ligand band (cm 1)
−
−1
Charge transfer band (cm )
Compound
[
[
[
[
[
[
[
[
Cd(H2DMTS)Cl2]
Cd(HATS)2Cl2]
Cd(H2STS)Cl2]
Cd(HBTS)2Cl2]H2O
Hg(HTS)Cl2]3H2O
Hg(HATS)Cl2]
(42,920); 40,490 (40,485); 37,880 (38,168); 33,000 (33,003)
43,670 (42,194); 40,980 (40,000); 38,910; 32,260 (32,573)
41,490 (40,984); 39,370 (38,314); 32,360 (30,864); 29,670 (29,070)
42,550 (43,480); 39,220 (37,170); 31,550 (32,680); 29,670 (29,940)
36,230; 40,650; 43,103
40,000; 43,290; 41,840; 38,610; 32,051
41,840; 38,610; 32,470; 30,120; 29,100
42,920; 40,000; 37,170; 32,680; 30,860; 29,410
26,460; 25,840; 24,700
26,670; 25,840
26,740; 25,770; 23,870; 24,450
24,750
–
–
–
Hg(H2STS)2Cl2]
Hg(HBTS)2Cl2]
24,450
The values within parentheses for the ligands.
and 25,770 cm 1 are attributed O → M charge transfer. Also,
−
H2STS behaves as a neutral monodentate when coordinating
−
1
to Hg(II) through the OH supporting by the shift of ν(OH) by
the bands located at 24,750–24,450 cm in some complexes
may be attributed Cl → M charge transfer [22].
−1
2
8 cm . The shift of ν(C N) is due to the dissociation of the
hydrogen bond. In [Hg(HATS)Cl2], HATS behaves as a neutral
bidentate coordinating via C N and NH2 concluded by the shifts
3
.2.3. Redox behavior
The CV of [Cd(H2STS)Cl2]H2O and [Hg(HBTS)Cl2] dis-
−
1
of δ(NH2) and ν(C N) to lower frequency by 65 and 42 cm
.
In [Hg(H2oHpMBTS)Cl2] and [Hg(HTS)Cl2]·3H2O, the lig-
played one well defined electrode couple (Fig. 1) with E1/2 of
.29; 0.23 V and ꢀEp of 0.58; 0.54 V assigned to irreversible
ands are bidentate coordinating via C N and C S groups. The
0
−
1
bands due to ν(C N) and ν(C S) are shifted by 37 and 14 cm
,
0
2+
couple M /M . The linear relation between the cathodic peak
current and the square root of the sweep rate indicates a
diffusion-controlled irreversible electrochemical process. The
ratio ip,c/ip,a > 1 at the sweep rate 20–200 mV confirms the irre-
versible nature of the electrode couple. The increased values
of ꢀEp with the scan rate confirming the occurrence of a slow
chemical reaction following the electrode process.
−1
respectively. New band appearing at 412 cm is assigned to
ν(Hg N). The ν(OH) and δ(NH2) bands in the spectrum of
[
3
Hg(H2oHpMBTS)Cl2] shift to higher frequency by 29 and
5 cm , due to the dissociation of the hydrogen bonding.
The mass spectra of [Cd(H2STS)Cl2]H2O and [Cd(HBTS)
−1
2
Cl2]2H2O were recorded and their molecular ion peak
confirmed their empirical formulae. The spectrum of
Cd(HBTS)2Cl2]2H2Oshowsapeakatm/e = 730corresponding
[
3
.2.4. Thermal studies
The kinetic and thermodynamic parameters for the
to its molecular weight (730.09). The base peak at 180 represents
the stable species CHN2SCd.
different thermal decomposition steps in the complexes
employing the Coats–Redfern equation [23] have been
evaluated (Table 4S, supplemental information). The acti-
3
.2.2. Electronic spectra
#
The electronic absorption bands of ligands and their Cd(II)
vation enthalpy (ꢀH = E − RT); the activation entropy
*
and Hg(II) complexes are recorded in DMF. The ligands have
(ꢀS = 2.303[log(Zh/KT)]R) and the free energy of activation
−
1
#
#
#
␲
→ ␲* bands in the region 44,444–37,040 cm and n → ␲*
(ꢀG = ꢀH − TꢀS ) are calculated. The high values of E
for [Cd(H2STS)Cl2]H2O indicates that the ligand is strongly
bonded to Cd(II) ion. The E value observed for the fourth
decomposition stage of [Cd(HATS)2Cl2] was found the higher
than that of the first indicating low rate of decomposition.
In [Cd(H2DAMTS)Cl2] and [Cd(H2STS)Cl2]H2O, the E val-
−
1
bands at 33,000–29,940 cm [20] and little change in their
energies are recorded on their complexes. The band located at
6,740–23,870 cm in the spectra of the complexes may be
−
1
2
due to LMCT (Table 2) [21]. Previous studies on thiosemicar-
bazone complexes indicated that the observed bands at 25,840
+
−
Fig. 1. Cyclic voltammograms of (A) [Hg(HBTS)2Cl2] and (B) [Cd(HBTS)2Cl2]2H2O in DMSO/TBA BF4 vs. Ag/AgCl electrode.

A.A. El-Asmy et al. / Spectrochimica Acta Part A 71 (2008) 39–44
43
results. The floatability of series of solutions containing
−
4
−1
2+
−3
−1
0
.5 × 10 mol l Cd , 1 × 10 mol l HOL and various
amounts of H2DMTS at pH ∼7 was performed. The results
show a maximum efficiency (ca. 100%) at 1:2 (Cd:H2DMTS)
ratio. Moreover, excess ligand has no effect, so the procedure
find application for real samples containing Cd(II). Accord-
ingly, a concentration of H2DMTS equals two-fold of Cd(II)
or more was used.
•
•
Surfactant concentration. Cd(II) was separated using various
concentrations of (HOL). The results show maximum floata-
−
5
−2
−1
bility at 1 × 10 to 1 × 10 mol l of HOL, above which
−3
−1
the flotation decreases. Accordingly, 1 × 10 mol l HOL
was the desired concentration.
Cd(II) concentration. Trials were carried out to float vari-
ous amounts of Cd2 in the presence of 1 × 10 mol l
+
−4
−1
Fig. 2. Thermogravimetric analysis (TGA and DrTGA) of [Cd(H2
DAMTS)Cl2].
−
3
−1
H2DMTS using 1 × 10 mol l
HOL at pH ∼7. The
−4
−1
floatability reaches 100% at 0.5 × 10 mol l
of Cd(II)
corresponding to Cd:2H2DMTS. At higher concentration of
Cd(II), the efficiency decreases and needs excess H2DMTS.
Temperature. Solutions of Cd(II), H2DMTS and HOL were
either heated or cooled, then the HOL quickly poured into
the mixture and introduced into the flotation cell jacketed
with 1 cm thick fiberglass. The floatability does not affected
ues are higher than those of the other complexes explaining
why their rates of decomposition are low. Most complexes
•
•
#
have negative ꢀS values indicating that the complexes are
more ordered. The values of E of the first step ordered the
complexes as: [Cd(H2STS)Cl2]H2O > [Cd(H2DAMTS)Cl2] >
[
Cd(HBTS)2Cl2]2H2O > [Cd(HATS)2Cl2].
In the thermograms (30–800 C) of some complexes, the first
◦
by temperature (5–80 C). Since the industrial wastewaters
◦
are usually hot, the present procedure find successful appli-
cation in the direct analysis of Cd(II) ions in this type of
influents. The subsequent measurements were carried out at
◦
step begins at higher temperature over than 190 C indicating
that the coordination waters are inside the sphere. The final
stage corresponds to Cd or CdS. The thermogram (Fig. 2) of
◦
room temperature ∼25 C.
[
Cd(H2DAMTS)Cl2] is taken as a representative example for
−4
−1
)
Foreign ions. Separation of Cd(II) (0.5 × 10 mol l
the decomposition of these complexes. It is characterized by
five degradation steps in the range 198–252, 253–347, 348–514,
−4
−1
)
using H2DMTS (1 × 10 mol l
and oleic acid
−3
−1
(
1 × 10 mol l ) was carried out at high concentra-
◦
◦
5
15–637 and 638–787 C. The complex is stable till 198 C after
which two chlorine atoms (calcd. 19.9%, found 19.5%) is elim-
inated in the first step. The second step consumed C4H radical
tions of various cations and anions usually found in some
water samples (Table 5S, supplemental information). Toler-
able amount (presented as ion:Cd ratio) giving a maximum
error of ± 2% in the flotation efficiency. All investigated
ions do not interfere. Thus the presented procedure is fairly
selective and can be safely employed for the separation and
determination of Cd(II) in various materials.
6
(
calcd. 15.1%, found 13.1%). The radical N2H3 is assumed to
be evolved in the third step (calcd. 8.7%, found 9.3%). More-
over, the fourth and fifth steps consumed CHN2OS radical up
◦
to 787 C after which a constant weight was observed and Cd
(
calcd. 31.4%, found 33.1%) was apparently the final residue.
•
•
Ionic strength. The effect of some salts on the flotation effi-
−
4
−1
ciency of 0.5 × 0 mol l Cd(II) is studied. The salts used
may be resembled those in natural water samples. The ionic
strength of the medium has no effect on the flotation process.
Flotation mechanism. The flotation mechanism of Cd(II) has
been suggested based on careful comparison of the IR spectra
of the complexes isolated in absence and presence of HOL.
The ligand functions as a bidentate molecule coordinating
through the C N and C S groups. The infrared spectrum of
the scum complex has no absorption bands corresponding to
oleic acid. The surfactant binds with [Cd(H2DAMTS)Cl2]
giving hydrophobic aggregates that float to the solution sur-
face with aid of air bubbles (created inside the flotation cell
by slight shaking).
3
.3. Separation of Cd(II) using diacetylmonoxime
thiosemicarbazone
Different factors affecting the flotation of Cd(II) using
H2DMTS have been studied to maximize its separation effi-
ciency. The most important are:
•
•
pH. Series of experiments were carried out to show the effect
−
4
−1
of HCl and/or NaOH on the separation of 0.5 × 10 mol l
−
3
−1
Cd(II), in the presence of 1 × 10 mol l oleic acid (HOL)
−
4
−1
and 1 × 10 mol l H2DMTS. The results show that the
floatability of Cd–H2DMTS increases with increasing the
pH, reaching a maximum at pH 5.5–8.5. Therefore, all work
experiments were carried out at pH ∼7.
• Application. To apply the recommended procedure for water
−1
samples taken from different sources, add 0.5 or 1.5 mg l
Ligand concentration. Trials were performed to float Cd(II)
with oleic acid individually; the efficiency does not exceed
of Cd(II) to 10 ml of clear water and adjust the pH to ∼7.
After flotation, the concentration of Cd(II) was determined
by AAS in both the surfactant layer and the mother liquor.
2
5%. H2DMTS was the reagent added to give good

4
4
A.A. El-Asmy et al. / Spectrochimica Acta Part A 71 (2008) 39–44
From the data obtained, Cd(II) can be determined by AAS
after flotation with satisfactory results.
[10] R.M. El-Shazly, G.A.A. Al-Hazmi, S.E. Ghazy, M.S. El-Shahawi, A.A.
El-Asmy, Spectrochim. Acta 61A (2005) 243.
[
[
11] G.A.A. Al-Hazmi, M.S. El-Shahawi, I.M. Gabr, A.A. El-Asmy, J. Coord.
Chem. 58 (8) (2005) 713.
12] G.A.A. Al-Hazmi, M.S. El-Shahawi, A.A. El-Asmy, TransitionMet. Chem.
Appendix A. Supplementary data
3
0 (2005) 464.
[13] M. Saad, M.S. El-Shahwai, H. Saleh, A.A. El-Asmy, Transition Met. Chem.
2 (2007) 155.
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.saa.2007.11.018.
3
[
14] J. Bejerrum, Metal Amine Formation Aqueous Solutions, P. Hasse and
Sons, Copenhagen, 1941.
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1