IR, UV-Vis, magnetic and thermal characterization of chelates of some catecholamines and 4-aminoantipyrine with Fe(III) and Cu(II).

Article abstract of DOI:10.1016/j.saa.2003.08.027

The dopamine derivatives participate in the regulation of wide variety of physiological functions in the human body and in medication life. Increase and/or decrease in the concentration of dopamine in human body reflect an indication for diseases such as Schizophrenia and/or Parkinson diseases. Alpha-methyldopa (alpha-MD) in tablets is used in medication of hypertension. The Fe(III) and Cu(II) chelates with coupled products of adrenaline hydrogen tartarate (AHT), levodopa (LD), alpha-MD and carbidopa (CD) with 4-aminoantipyrine (4-AAP) are prepared and characterized. Different physico-chemical methods like IR, magnetic and UV-Vis spectra are used to investigate the structure of these chelates. Fe(III) form 1:2 (M:catecholamines) chelates while Cu(II) form 1:1 chelates. Catecholamines behave as a bidentate mono- or dibasic ligands in binding to the metal ions. IR spectra show that the catecholamines are coordinated to the metal ions in a bidentate manner with O,O donor sites of the phenolic -OH. Magnetic moment measurements reveal the presence of Fe(III) chelates in octahedral geometry while the Cu(II) chelates are square planar. The thermal decomposition of Fe(III) and Cu(II) complexes is studied using thermogravimetric (TGA) and differential thermal analysis (DTA) techniques. The water molecules are removed in the first step followed immediately by decomposition of the ligand molecules. The activation thermodynamic parameters, such as, energy of activation, enthalpy, entropy and free energy change of the complexes are evaluated and the relative thermal stability of the complexes are discussed.

Full text of DOI:10.1016/j.saa.2003.08.027

Spectrochimica Acta Part A 60 (2004) 1775–1781
IR, UV-Vis, magnetic and thermal characterization of chelates of some
catecholamines and 4-aminoantipyrine with Fe(III) and Cu(II)
Gehad G. Mohamed∗, M.A. Zayed, F.A. Nour El-Dien, Reham G. El-Nahas
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
Received 12 June 2003; accepted 1 August 2003
Abstract
The dopamine derivatives participate in the regulation of wide variety of physiological functions in the human body and in medication
life. Increase and/or decrease in the concentration of dopamine in human body reflect an indication for diseases such as Schizophrenia and/or
Parkinson diseases. ␣-Methyldopa (␣-MD) in tablets is used in medication of hypertension. The Fe(III) and Cu(II) chelates with coupled
products of adrenaline hydrogen tartarate (AHT), levodopa (LD), ␣-MD and carbidopa (CD) with 4-aminoantipyrine (4-AAP) are prepared
and characterized. Different physico-chemical methods like IR, magnetic and UV-Vis spectra are used to investigate the structure of these
chelates. Fe(III) form 1:2 (M:catecholamines) chelates while Cu(II) form 1:1 chelates. Catecholamines behave as a bidentate mono- or dibasic
ligands in binding to the metal ions. IR spectra show that the catecholamines are coordinated to the metal ions in a bidentate manner with O,O
donor sites of the phenolic –OH. Magnetic moment measurements reveal the presence of Fe(III) chelates in octahedral geometry while the
Cu(II) chelates are square planar. The thermal decomposition of Fe(III) and Cu(II) complexes is studied using thermogravimetric (TGA) and
differential thermal analysis (DTA) techniques. The water molecules are removed in the first step followed immediately by decomposition of
the ligand molecules. The activation thermodynamic parameters, such as, energy of activation, enthalpy, entropy and free energy change of
the complexes are evaluated and the relative thermal stability of the complexes are discussed.
© 2003 Elsevier B.V. All rights reserved.
Keywords: AHT; LD; ␣-MD and CD complexes; IR; Magnetic moment; UV-Vis; TGA and DTA
1. Introduction
tients produced more dopamine, especially in the striatum
of the brain, than in normal brains [7]. In this case, the drug
used block dopamine receptors in the brain. The increase of
awareness of biological significance of dopamine derivatives
has promoted a great deal of research into their detection
and quantitative determination [8–10]. Several methods had
been described in the literature for dopamine determination
in biological samples and pharmaceutical formulations like
chromatography and amperometry [11,12]. Miceller liquid
chromatography with spectrophotometric procedures was
applied on detection of LD, 2-ethyldopa and isoproterenol
in their pharmaceutical preparations as well as other com-
pounds frequently associated with them [13]. Many hospi-
tal laboratories are now adopting HPLC method for mea-
suring catecholamines [14–17]. However, HPLC technique
consuming very time and restricted to highly specialized
laboratories, so many spectrophotometric procedures were
recommended for determination of dopamine using ninhy-
drin [18] and chloramine-T [19]. On screening literature, no
studies concerning metal chelates of catecholamines coupled
products with 4-AAP have been reported. Therefore, this
Hormones acted as chemical messengers controlling the
activity of living things. In humans, they were released in
small amounts in the blood stream from a number of vital
sites especially some brain regions. Dopamine was recog-
nized as neurotransmitter in its own right but the demonstra-
tion of its non-uniform distribution in the brain suggested
that it might had a specific functional role of dopamine
[1]. It had an important role in the pathogenesis of drug
treatment of certain brain diseases, e.g. Parkinson’s dis-
ease and Schizophrenia [2]. Parkinson’s disease was asso-
ciated with decrease of dopamine concentration in brain
[3,4]. So, it must be medicated with drugs contain LD com-
bined with certain amount of CD, which makes LD avail-
able for transport to the brain and converted to dopamine
in the basal ganglia [5,6]. The brain of Schizophrenic pa-
∗
Corresponding author. Fax: +20-2-5727556.
E-mail address: ggenidy@hotmail.com (G.G. Mohamed).
1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2003.08.027

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G.G. Mohamed et al. / Spectrochimica Acta Part A 60 (2004) 1775–1781
2.2. Preparation of solid complexes
2.2.1. Catecholamines–iron(III) complexes (Ia, Ib and Ic
complexes)
15 ml of 1 mmol hot water solution (60 ◦C) of cate-
cholamines (0.333 g AHT, 0.197 g LD or 0.211 g ␣-MD)
was mixed with 10 ml hot water solution (60 ◦C) of 4-AAP
(0.203 g, 1 mmol). The resulting mixture was mixed with
constant stirring with 25 ml of hot water solution (60 ◦C)
of PFC (0.120 g, 0.5 mmol). The mixtures were allowed
to stand at room temperature for 6 h to give a chance for
complete precipitation. The obtained crystals were filtered
off, washed several times with water then pentane, col-
lected, dried in vacuum over anhydrous calcium chloride
and stored in dark and in dry conditions.
Fig. 1. Structural formulae of catecholamines.
work was undertaken in order to study the preparation and
characterization of the solid chelates of dopamine deriva-
tives (AHT, LD, ␣-MD and CD) and 4-AAP with Fe(III) and
Cu(II) tetramine complex. Interested solid products are sep-
arated and different physicochemical studies are used to in-
fer the structure in order to give a clear idea about the role of
metal ions on biological activity of these drugs in the biolog-
ical systems. Thermal analyses (TGA and DTA) techniques
are also used to give a clear idea about the thermal behavior
and relative thermal stability of these chelates. The structures
of the catecholamines used in this study are shown in Fig. 1.
2.2.2. Catecholamines–copper(II) complexes (IIa, IIb, IIc
and IId complexes)
Copper tetramine complex was prepared by adding 3.5 M
ammonia solution dropwisely to 20 ml copper sulphate so-
lution (0.25 g, 0.5 mmol) with continuous stirring; till deep
blue color appeared. Fifteen milliliters of 0.5 mmol hot wa-
ter solution (60 ◦C) of catecholamines (0.333 g AHT, 0.197 g
LD, 0.211 g ␣-MD or 0.226 g CD) and 10 ml of 0.5 mmol
hot water solution (60 ◦C) of 4-AAP were added to copper
tetramine complex with continuous stirring. The excess sol-
vent was removed by evaporation and solutions were kept in
cupboard to get the precipitates. The obtained crystals were
treated as mentioned above.
2. Experimental
2.1. Materials and methods
All chemicals used were of analytical reagent grade. They
included AHT (Beohringer Ingelheim), LD, ␣-MD and CD,
ammonia solution (33%) and sulphuric acid (El-Nasr Phar.
Chem. Co.). 4-AAP (Fluka), potassium ferricyanide (PFC)
(BDH) and copper sulphate (Sigma) were used as received.
Elemental analyses (C, H and N) were carried out in the
Microanalytical Center at Cairo University. The spectropho-
tometric measurements in solution were carried out using
automated spectrophotometer UV-Vis Perkin-Elmer model
lambda 20 ranged from 200 to 900 nm. pH measurements
were carried out using 716 DMS Titrino Metrohm connected
with 728 Metrohm Stirrer. IR spectra were carried out using
FTIR-8210 PC in the range of 4000–400 cm−1. The molar
magnetic susceptibilities were measured on powdered sam-
ples using the Faraday method. The thermogravimetric anal-
ysis (TGA) and differential thermal analysis (DTA) were
3. Results and discussion
Different colorimetric methods described for phenol de-
termination [20–24] are based on the reaction between phe-
nols and 4-AAP to form antipyrine dyes where 4-AAP is
found to be the most sensitive, fastest and precise colorimet-
ric reagents. 4-AAP reacts with phenolic type compounds
according to the reaction shown in Fig. 2. The reaction prod-
uct may by any color from red to purple depending on the
phenolic type compounds involved.
The solid products resulted from the interaction of cou-
pled products of catecholamines and 4-AAP with PFC or
copper(II) complex are discussed. The complexes Ia, IIa, Ib,
IIb, Ic and IIc are formed as the result of interaction be-
tween AHT, LD and ␣-MD coupled products with PFC or
Cu(II) tetramine complex. The complex IId is resulted from
carried out in dynamic nitrogen atmosphere (20 ml min−1
)
with a heating rate of 10 ◦C min−1 using Shimadzo
TGA-50H and DTA-50H thermal analyzers, respectively.
The metal contents of the complexes were determined using
complexometric EDTA titration in a buffering medium of
pH 11.
Fig. 2. Coupling reaction between phenol and 4-AAP.

G.G. Mohamed et al. / Spectrochimica Acta Part A 60 (2004) 1775–1781
1777
Table 1
Analytical and physical data of Fe(III) and Cu(II) chelates
Complex
Color
mp
(◦C)
Found (%)
Calcd. (%)
µeff
(B.M.)
General molecular formulae
C
H
N
M
C
H
N
M
Ia
Ib
Ic
IIa
IIb
IIc
IId
Deep red
Deep red
Deep red
Deep violet
Deep violet
Deep violet
Deep violet
>300
>300
>300
>300
>300
>300
>300
51.00
55.60
56.50
44.50
48.20
43.40
42.25
4.45
4.80
4.8
5.48
4.54
5.45
5.67
11.10
14.50
13.50
8.85
11.22
9.45
5.02
6.00
6.35
50.60
55.28
56.21
44.34
48.44
43.34
42.45
4.28
4.49
4.79
5.23
4.84
5.85
5.87
10.84
14.16
13.73
8.62
11.30
9.63
4.82
6.29
6.10
5.83
5.92
5.96
1.83
1.85
1.82
1.85
[Fe(C24H27N4O10) (CN) (H2O)]
2
[Fe(C22H19N4O5)2 (CN) (H2O)]
[Fe(C21H21N4O5)2 (CN) (H2O)]
[Cu(C24H28N4O10) (H2O)2]·H2O
[Cu(C20H20N4O5) (H2O)2]
9.20
9.78
12.48
10.60
10.45
12.82
10.92
10.65
[Cu(C21H22N4O5) (H2O)2]·4H2O
11.54
11.74
[Cu(C21H23N5O5) (H2O)2]·4H2O
the interaction of coupled product of CD and 4-AAP with
Cu(II) tetramine complex. Applying the molar ratio method,
it is found that catecholamines form a dye coupled product
with 4-AAP in the ratio 1:1 then the coupled dye react in
the ratio 1:2 and 1:1 (M:dye) with Fe(III) and Cu(II) com-
plex, respectively. According to the elemental analyses data
(Table 1) the formed complexes are found to have the gen-
eral formula [Fe(L)2(CN)(H2O)] and [Cu(L)(H2O)2], where
L is the coupled product between AHT, LD, ␣-MD and CD
with 4-AAP. L behaves as a uninegatively bidentate ligand
in case of Fe(III) complexes or binegatively bidentate in case
of Cu(II) chelates. It coordinated to the Fe(III) and Cu(II)
ions via the –O of the catechol moiety. The coordination
number of Fe(III) ion is six in octahedral arrangement while
that of Cu(II) is four with square planer geometry. The com-
plexes are colored and have high melting points. The isolated
complexes are characterized and identified using different
spectroscopic (IR, magnetic moment and UV-Vis spectra
measurements) and thermal analyses (TGA and DTA) tech-
niques.
νasym(COO) of the tartaric acid, and ν(OH) of the aliphatic
chain, are still in the same position and not affected by com-
plex formation.
The IR spectra of all the complexes show bands at 871,
813, 869, 789, 856, 756 and 826 cm−1 for Ia, Ib, Ic, IIa, IIb,
IIc and IId complexes, respectively, characteristic of water
of coordination [26]. The bonding of oxygen to the Fe(III)
or Cu(II) ions is proved by the presence of bands at 504,
457, 458, 486, 471, 450 and 448 cm−1 for Ia, Ib, Ic, IIa, IIb,
IIc and IId complexes, respectively [25].
3.2. UV-Vis spectra
The absorption spectra of Ia, Ib and Ic complexes in
de-ionized water have an absorption bands centered around
λ = 480, 510 and 495 nm for Ia, Ib and Ic complexes, respec-
tively. Effect of pH on the reaction of catecholamines (AHT,
LD and ␣-MD) coupled products with 4-AAP and PFC was
studied using universal buffer of different pH values ranged
from 3 to 9. The absorption spectra of Ia complex show that,
when the pH ranged from 3 to 4, two bands are appeared.
The first is sharp band at 420 nm (ε = 2.45 × 103 to 2.18 ×
103 l mol−1 cm−1) and the second is a broad band which ap-
peared at λ = 500 to 520 nm (ε = 262–273 l mol−1 cm−1).
The sharp band at λ = 420 nm disappeared by increasing the
pH value to alkaline medium (pH 9), while the broad band
at λ = 500–520 nm starts to shift into shorter wavelength
with the increase of pH value. The gradual shift into shorter
wavelength region is attributed to the deprotonation of the
entity of AHT. The broad band is shifted to 480 nm in the pH
range of 6–9. The highest absorbance value at λ = 480 nm
was measured at pH 6 (ε = 2.4 × 103 l mol−1 cm−1). So,
the pH = 6 is selected as the most suitable pH value for
Ia complex for microdetermination of AHT using PFC as
complexing agent.
3.1. IR spectra and mode of bonding
A substantial part of the knowledge concerning the mode
of bonding in metal complexes can be gained by applying
IR spectroscopy. A verification of the structure of the com-
plexes of the organic ligands can be easily achieved com-
paring the IR spectra of the free ligands with those of the
complexes. The IR spectra of catecholamines (AHT, LD,
␣-MD and CD) reveal a sharp band at 3472, 3472, 3217 and
3210 cm−1, which attributed to OH group. This band is hid-
den and broaded upon complexation with Fe(III) or Cu(II)
complex in the region 3500–3000 cm−1 for the chelates
which make it difficult to indicate coordination through the
phenolic OH of catechol moiety. This is also attributed to
the presence of –OH group of the carboxylate, the amino
group, aliphatic OH group or even NH group, which may
appear in this range. The involvement of the phenolic cat-
echol in complex formation is confirmed by the red shift
of the frequency of the ν(C–O) from 1211, 1205, 1249 and
1211 cm−1 in the free ligands; AHT, LD, ␣-MD and CD; to
the extent of 30–50 cm−1 in the complexes [25]. The bands
The effect of pH on the absorption spectra of Ib complex
is similar to that observed with Ia complex. The spectra
reveal the presence of only one sharp band at pH = 3 (ε =
2.31 × 103 l mol−1 cm−1) at λ = 420 nm. A broad band
began to appear at λ = 500–550 nm (ε = 0.662 × 103
to 0.62 × 103 l mol−1 cm−1) with the increase of pH. The
intensity of this broad band increases with the increase of
pH up to 5 (ε = 1.48 × 103 l mol−1 cm−1). The sharp band
=
due to ν(C O) and ν(NH) of the 4-AAP; νsym(COO) and

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G.G. Mohamed et al. / Spectrochimica Acta Part A 60 (2004) 1775–1781
(λ = 420 nm) disappears by increasing the pH value to
alkaline medium (from 6 to 9) and the broad band is shifted
from λ = 500–550 nm to shorter wavelength at λ = 430 to
480 nm. High intensity band is observed at pH = 5 (ε =
1.48 × 103 l mol−1 cm−1) at λ = 510 nm. So the pH = 5
is selected as the most suitable pH value for further studies
concerning microdetermination of LD. Also in case of Ic
complex, the same behavior was observed and pH = 5 at
λ = 495 nm (ε = 0.75 × 103 l mol−1 cm−1) is selected for
further studies on ␣-MD.
Mixing of catecholamines (AHT, LD, ␣-MD or CD) with
copper tetramine complex allows the formation of com-
plexes that have a grey color of λmax = 460 nm in case
of AHT and 600 nm for dopamine derivatives (LD, ␣-MD
and CD). This complex does not stable for a long time.
By adding 4-AAP, the color changed to violet that lead to
change in λmax of dopamine derivatives only to be 525, 545
and 525 nm for LD, ␣-MD and CD, respectively. But those
of AHT, λmax still stable at 460 nm. To be sure that the
new λmax is not the result of an interaction between copper
tetramine and 4-AAP, they mixed together giving pale blue
color with λmax at 620 nm.
The study of the effect of pH on the color of the pos-
sible formed complex species in solution between copper
tetramine complex and catecholamines in the presence of
4-AAP helps us to choose the suitable pH for microdetermi-
nation of catecholamine derivatives (AHT, LD, ␣-MD and
CD). The obtained spectra of the formed complexes (IIa, IIb,
IIc and IId) in solution at various pH values ranged from 10.2
to 12 using ammonia solution indicate that the most suitable
pH for microdetermination is pH = 10.5 for AHT, LD and
␣-MD, and pH = 11.2 in case of CD. At the selected pH
values the absorbance still stable in a broad range for a long
time. Above pH 10.5 in case of AHT, LD and ␣-MD, the
absorbance is changed quickly as a result of volatilization
of ammonia solution.
complexes, respectively, where a dsp2 hybrid orbital being
involved [30].
3.4. Thermal analyses studies (TGA and DTA)
Thermal analyses techniques (TGA and DTA) are useful
in both quantitative and qualitative analyses. Samples can be
identified and characterized by investigation of their thermal
behavior. TGA measures weight changes, while DTA mea-
sures temperature of transitions and reactions. The TGA for
the Fe(III) and Cu(II) complexes under study is carried out
within the temperature range from room temperature up to
1000 ◦C. The estimated mass losses found from TGA curves
give a 1:1 and 1:2 metal-to-catecholamines coupled prod-
ucts ratio with Cu(II) and Fe(III) ions which confirm the
results of elemental analyses and molar ratio studies.
Table 2 shows the results of the thermal analyses (TGA
and DTA) of the Fe(III) complexes with the coupled prod-
ucts of AHT (Ia), LD (Ib) and ␣-MD (Ic) with 4-AAP. The
TGA curves show that Ia, Ib and Ic complexes decompose in
two steps within the temperature range of 25–760 ◦C. The
first step (within the temperature range of 25–150 ◦C) is
accompanied with weight loss of 4.51% (calcd. = 4.57%),
7.15% (calcd. = 6.98%) and 4.68% (calcd. = 4.80%) for
Ia, Ib and Ic complexes, respectively. This may be attributed
to the loss of CO2 and 1 H2O, H2O and CO2 and CO2
2
gases for Ia, Ib and Ic complexes, respectively. This step
appears in the DTA curves as endothermic peak at 57 and
70 ◦C (Table 2). The next step, which takes place within the
temperature range of 130–760 ◦C may involves the decom-
position of the two ligand molecules leaving metal oxide,
carbonate and oxycyanide as residues for Ia, Ib and Ic com-
plexes, respectively. The overall weight losses are amounted
to 93.14% (calcd. = 93.20%), 84.15% (calcd. = 83.67%)
and 89.59% (calcd. = 89.52%) for Ia, Ib and Ic complexes,
respectively. The latter step appears as endothermic peaks
in the temperature range of 255–595 ◦C as given in Table 2.
The results of the thermal analyses (TGA and DTA) of the
Cu(II) complexes with the coupled products of AHT (IIa),
LD (IIb), ␣-MD (IIc) and CD (IId) with 4-AAP are listed
in Table 2. The TGA thermograms of IIa, IIb, IIc and IId
complexes show three to four steps of decomposition within
the temperature range of 25–800 ◦C.
For IIa and IIc complexes, the first and second steps (from
30–265 ◦C) correspond to the loss of hydrated and coordi-
nated water and tartarate molecules (f. mass loss = 31.45%;
calcd. = 31.36%), and loss of hydrated and coordinated wa-
ter molecules (f. mass loss = 18.64%; calcd. = 18.58%)
for IIa and IIc complexes, respectively. The DTA curves
show two endothermic peaks at 47 and 195 ◦C for IIa com-
plex, while IIc complex show an endothermic peak at 63 ◦C
and an exothermic peak at 112 ◦C. The loss of the ligand
molecules takes place in the third and fourth steps within
the temperature range of 256–700 ◦C with a mass loss of
56.40% (calcd. = 56.42%) and 69.82% (calcd. = 69.30%)
for IIa and IIc complexes, respectively, leaving copper oxide
3.3. Magnetic moment and electronic spectra
As further structural tools, magnetic moment studies have
been used to confirm the geometry of the complexes. The
magnetic moments of the Fe(III) complexes have been found
to be 5.83, 5.92 and 5.96 B.M. for Ia, Ib and Ic complexes,
respectively, is within the range values corresponding to oc-
tahedral geometry. In the UV-Vis spectra of Fe(III) com-
plexes, one band is observed at 20.83 × 103, 19.61 × 103
and 20.20 × 103 cm−1, for Ia, Ib and Ic complexes, respec-
6
tively. This band may be assigned to the A1g → T2g(G)
transition in octahedral geometry of the complexes [27].
Cu(II) complexes exhibit one broad band at 21.74 × 103,
19.05×103, 18.35×103 and 19.05×103 cm−1 for IIa, IIb, IIc
and IId complexes, respectively, assigned to 2Eg → T2g and
2
2B1g → A1g transitions characteristic of a square planner
2
geometry for Cu(II) complexes with dx2 − y2 ground state
[28,29]. The magnetic moments of the Cu(II) complexes
are 1.83, 1.85, 1.82 and 1.85 B.M. for IIa, IIb, IIc and IId

Table 2
Thermoanalytical results (TGA, DTG and DTA) of Fe(III) and Cu(II) chelates
Compound
Ia
T (◦C)
DTGmax (◦C)
DTA (◦C)
Weight loss (%)
Total weight loss (%)
Assignment
Found
Calcd.
Found
Calcd.
25–140
140–750
50
281, 444
57(+)s
4.51
4.57
Loss of CO2 and 1 H2O.
Loss of H2O, CN and C47H53N8O16
leaving metal oxide residue.
2
257(−)s, 343(+)s, 403(−)s, 462(−)s,
88.63
88.71
93.14
93.20
577(−)b
Ib
25–130
130–760
62
70(−)s
7.15
77.00
6.98
76.69
Loss of H2O and CO2.
Loss of CN and C37.5H36N8O3.5 leaving
metal carbonate residue.
375, 434, 591
214(+)s, 349(−)b, 391(+)sh, 423(−)sh,
84.15
89.59
83.67
89.52
572(−)sh
–
Ic
25–150
150–650
41
311, 469
4.68
84.91
4.80
84.72
Loss of CO2.
Loss of H2O and C40H40N8O9 leaving
metal oxycyanide residue.
260(−)s, 350(+)b, 550(+)b, 594(−)b
IIa
IIb
30–145
145–265
265–660
53
255
47(−)s
8.46
22.99
56.40
8.30
23.06
56.42
Loss of 3H2O.
Loss of C4H6O6.
Loss of AHT leaving metal oxide residue.
196(−)s
300, 362, 451, 664
272(−)s, 348(−)s, 453(+)b, 588(−)b
87.94
79.22
87.85
79.03
25–150
150–410
410–800
58
44(−)s
13.41
25.50
40.12
3.28
25.68
40.26
Loss of CO2 and NH3.
Loss of C2H2, C6H5 and CH3.
Loss of C10H7N3O leaving metal oxide
residue.
196, 298, 373
465
210(−)b, 369(−)s
425(−)s, 453(+)b, 754(−)b, 869(−)b
IIc
IId
35–115
115–220
220–700
69
135
292, 419, 507
63(−)b, 112(+)b
9.23
9.41
69.82
9.29
9.29
69.30
Loss of 3H2O.
Loss of 3H2O.
Loss of C21H22N4O4.5 leaving metal oxide
residue.
–
252(−)s, 330(+)b, 446(+)b, 486(−)b
88.45
87.78
87.88
88.01
25–150
150–650
76
59(−)s, 115(+)b
13.09
74.69
13.58
74.43
Loss of 4.5H2O.
Loss of 1.5H2O and C21H23N5O4.5 leaving
metal oxide residue.
209, 338, 384, 505
328(+)b, 373(−)b, 451(−)s, 556 (−)s
s: small; sh: sharp; and b: broad.

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G.G. Mohamed et al. / Spectrochimica Acta Part A 60 (2004) 1775–1781
as a residue. The DTA curves show an endothermic peak
at 453 ◦C and exothermic peaks at 272, 348 and 588 ◦C for
IIa complex, and endothermic peaks at 252, 297 and 486 ◦C
and exothermic peaks at 330 and 466 ◦C for IIc complex.
This may corresponds to the pyrolysis of the ligand in the
form of lot of gases such as CO2, H2O, CO, NO, NO2, etc.
For IIb and IId complexes, the first step of decomposi-
tion within the temperature range of 25–150 ◦C corresponds
to the loss of CO2 and NH3 molecules (f. mass loss =
13.41%; calcd. = 13.28%) and 4.5 H2O molecules (f. mass
loss = 13.09%; calcd. = 13.58%) for IIb and IId com-
plexes, respectively. The loss of coordinated water and lig-
and molecules takes place in the remaining steps within
the temperature range of 150–800 ◦C leaving metal oxide
residue. The overall weight losses are amounted to 79.03%
(calcd. = 79.22%) and 87.78% (calcd. = 88.01%) for IIb
and IId complexes, respectively. The presence of endother-
mic and exothermic peaks in the DTA curves (Table 2) may
be resulted from the pyrolysis of the ligand and water into
gases.
where Wf is the mass loss at the completion of the reaction,
W the mass loss up to temperature T, R the gas constant,
E the activati∗on energy in kJ mol−1, θ the heating rate, and
against 1/T gives a slope from which E∗ was calculated
and A (Arrhenius constant) was determined from the inter-
cept. The entropy of activation (ꢀS∗), enthalpy of activation
(ꢀH∗) and the free energy change of activation (ꢀG∗) were
calculated using the following equations
∼
(1 − (2RT/E )) 1. A plot of the left-hand side of Eq. (1)
=
log(Ah/kT)
ꢀS∗ = 2.303
(2)
R
ꢀH∗ = E∗ − RT
ꢀG∗ = H∗ − TS∗
(3)
(4)
where k and h are the Boltzman and Blank constants, respec-
tively. The calculated values of E∗, A, ꢀS∗, ꢀH∗ and ꢀG∗
for the decomposition steps are given in Table 3. Accord-
ing to the kinetic data obtained from DTG curves, all the
complexes have −ve entropy, which indicates that activated
complexes have more ordered systems than reactants.
3.5. Kinetic studies
3.6. Structural interpretation
The kinetic parameters such as activation energy (ꢀE∗),
enthalpy (ꢀH∗), entropy (ꢀS∗) and free energy change of
the decomposition (ꢀG∗) were evaluated graphically by em-
ploying the Coats–Redfern relation [31]
The structure of the complexes (Ia, Ib, Ic, IIa, IIb, IIc and
IId) was confirmed by the IR, magnetic, UV-Vis spectra and
thermal analyses data. The chelation is brought by the phe-
nolic –OH groups of catecholamines (AHT, LD, ␣-MD and
CD). The catecholamine ligands behaves as a binegatively
bidentate in coordination to the metal ions. IR and ther-
mal anaslyses confirmed the existence of water molecules
of hydration and/or coordination. From the magnetic mo-
ment measurements, the geometrical structure of the chelates
ꢀ
ꢁ
log{Wf/Wf − W}
log
T2
ꢀ
ꢂ
ꢃꢁ
AR
θE∗
2RT
E∗
E∗
= log
1 −
−
(1)
2.303RT
Table 3
Thermodynamic data of the thermal decomposition of Fe(III) and Cu(II) chelates
Complex
Ia
Decomposition range (◦C)
E∗ (kJ mol−1
)
A (s−1
)
ꢀS∗ (J K−1 mol−1
)
ꢀH∗ (kJ mol−1
)
ꢀG∗ (kJ mol−1
)
25–140
140–750
50.15
140.2
1.24 × 104
−25.46
−34.81
52.28
80.03
53.12
140.1
3.1 × 106
Ib
25–130
130–760
40.27
105.44
2.7 × 108
−28.04
33.75
98.26
33.50
119.5
11.6 × 105
−47.17
Ic
25–150
150–650
44.65
165.4
2.37 × 106
−20.29
−32.81
−16.40
−22.40
−17.52
−13.98
−30.69
−29.75
−13.50
−14.75
−29.35
44.14
165.6
71.95
185.5
5.41 × 108
IIa
30–145
145–265
265–660
39.40
79.71
187.0
3.4 × 108
2.71 × 107
3.21 × 1010
38.95
87.85
182.3
59.40
60.60
195.6
IIa
IIc
IId
25–150
150–410
410–800
50.63
88.32
170.4
2.42 × 107
3.48 × 106
6.45 × 108
56.32
60.75
102.3
54.56
89.46
173.0
35–115
115–220
220–700
50.10
67.40
153.0
2.33 × 106
4.94 × 107
1.5 × 1011
59.37
86.60
188.1
50.38
90.10
172.2
25–150
150–650
49.21
85.63
1.85 × 104
−9.68
66.53
101.8
26.46
95.37
4.44 × 106
−16.73

G.G. Mohamed et al. / Spectrochimica Acta Part A 60 (2004) 1775–1781
1781
Fig. 3. Proposed structures of Fe(III) and Cu(II) complexes with AHT, LD, ␣-MD and CD.
[13] C.R.M. Villanueva, M.J.M. Sanchis, L.J.R. Torres, R.G. Ramis, An-
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were proposed and found to be octahedral in case of Ia, Ib
and Ic complexes or square planar in case of IIa, IIb, IIc
and IId complexes. The structure of the chelates is shown
in Fig. 3.
[17] A.H. Gowenlock, J.R. McMurray, D.M. McLauchlan, Varely’s Prac-
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London, 1982.
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