Synthesis, characterization, and photochemical studies of some copper complexes of schiff bases derived from 3-hydrazino-6-methyl[1,2,4]triazin-5(4H) one

Article abstract of DOI:10.1081/SIM-120039258

Cu(II) complexes of new bidentate and tridentate Schiff bases derived from the condensation of 3-hydrazino-6-methyl[1,2,4]triazin-5(4H)one and aromatic aldehyde derivatives were synthesized and characterized. The structure of the complexes proposed according to elemental analyses, molar conductance, IR UV-Visible absorption spectra is square-planar. The thermodecomposition kinetics of the complexes were investigated under non-isothermal condition. TG and DTG curves indicated that the complexes decompose in three to six steps. The photochemical behavior of the complexes depends on the substituted group on the aromatic aldehyde. A mechanism has been suggested to account for the recorded results.

Full text of DOI:10.1081/SIM-120039258

SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 6, pp. 1069–1085, 2004
Synthesis, Characterization, and
Photochemical Studies of Some
Copper Complexes of Schiff Bases
Derived from 3-Hydrazino-6-
methyl[1,2,4]triazin-5(4H)one
*
Ahmed H. Osman, Magda S. Saleh, and
Sanaa M. Mahmoud
Chemistry Department, Faculty of Science, Assiut University,
Assiut, Egypt
ABSTRACT
Cu(II) complexes of new bidentate and tridentate Schiff bases derived from
the condensation of 3-hydrazino-6-methyl[1,2,4]triazin-5(4H)one and
aromatic aldehyde derivatives were synthesized and characterized. The
structure of the complexes proposed according to elemental analyses,
molar conductance, IR UV-Visible absorption spectra is square-planar.
The thermodecomposition kinetics of the complexes were investigated
under non-isothermal condition. TG and DTG curves indicated that the
complexes decompose in three to six steps. The photochemical behavior
*
Correspondence: Ahmed H. Osman, Chemistry Department, Faculty of Science,
Assiut University, Assiut, 71516, Egypt; E-mail: ahosman@acc.aun.eun.eg.
1069
DOI: 10.1081/SIM-120039258
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Osman, Saleh, and Mahmoud
of the complexes depends on the substituted group on the aromatic alde-
hyde. A mechanism has been suggested to account for the recorded results.
Key Words: Schiff bases; Copper(II) complexes; 3-Hydrazino-6-
methyl[1,2,4]triazin-5(4H)one; Photochemical and thermal behavior.
INTRODUCTION
Schiff bases continue to occupy an important position as ligands in
coordination chemistry even after almost a century since their discovery.
This is manifested by the huge number of publications ranging from the purely
synthetic[1,2] to modern physical and biochemical relevant studies of Schiff
base complexes.[3–6] To the best of our knowledge, no work has been done
on the metal complexes of Schiff bases derived from 3-hydrazino-6-methyl
[1,2,4]triazin-5(4H) one, and as a continuation of our previous studies on
photochemical and thermal behavior of transition metal complexes,[7,8] the
present investigation reports synthesis, photolysis, and thermogravimetrical
studies on some new copper(II) complexes of the above-mentioned Schiff
bases; their structures are given in Fig. 1.
EXPERIMENTAL
All chemicals used in the present work are of analytical grade.
3-Hydrazino-6-methyl[1,2,4]triazin-5(4H)one was prepared according to
published procedures.[9]
Figure 1. Structures of Schiff base ligands.

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Synthesis of Schiff Base Ligands
A mixture of 10 mL of an ethanolic solution of 3-hyrazino-6-methyl
[1,2,4]triazin-5(4H)one (10 mL, 1.41 g) and 10 mL of an ethanolic solution
of the appropriate aromatic aldehyde (10 mmol of benzaldehyde, 1.06 g;
p-dimethylaminobenzaldehyde 1.21 g; p-methoxybenzaldehyde, 1.36 g;
o-nitrobenzaldehyde, 1.51 g or o-hydroxybenzaldehyde, 1.22 g) was refluxed
for 4 hr. The reaction mixture was cooled to 5 8C, and yellow products preci-
pitated immediately. The precipitates were filtered, washed with ethanol,
diethyl ether, and finally dried in vacuo. The 1H NMR solution spectra of the
ligands in DMSO-d6 were recorded on a Jeol LA 400 spectrometer with TMS
as reference and are given in Table 1.
Synthesis of Cu(II) Schiff Base Complexes
The complexes were prepared by adding a DMF solution (20 mL) of
Cu(II) acetate (1 mmol, 0.19 g) to a DMF solution (20 mL) of the Schiff
base (2 mmol for the ligands HBe, HDBe, HMBe, and HNBe, or 1 mmol for
H2Sal). The mixture was heated on a water bath at 80 8C for 1 hr. On cooling,
a green to brown precipitate was separated immediately for HBe. HDBe, and
HMBe. For HNBe or H2Sal, the green product was precipitated after addition
of a 1 : 1 acetone/diethyl ether mixture (30 mL). The solid complexes were
filtered, washed with acetone and diethyl ether, and finally dried in vacuo.
The carbon, hydrogen, and nitrogen contents of the ligands and their Cu(II)
complexes were determined by an Elementar-Analysensystem GmbH Vario
El analyzer.
Physical Measurements
The infrared spectra were recorded as KBr pellets on a 470 Shimadzu
infrared spectrophotometer. The electronic spectra were measured in DMF
solution on a Perkin Elmer, Lambda, 35 UV/Vis spectrophotometer. Electri-
cal conductivities of 1024 M DMF solutions of the complexes were measured
at 25 8C by a Jenway 4330 conductivity-pH meter. The thermal studies were
carried out on a TGA V5 1A Dupont 2000 thermal analyzer at a heating rate
10 8C/min. The photolyses were achieved using an Osram HBO 200 w/2
lamp as a light source. Monochromatic light was obtained using the Scholt
IL interference filter 298 nm. Irradiations were carried out in solutions of
DMF in 1-cm spectrophotometer cells at room temperature. Progress of the
photolysis was monitored by the above-mentioned spectrophotometer.

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RESULTS AND DISCUSSION
The reactions of the Schiff base ligands (HL or H2L) with Cu(II) acetate
can be represented by Eq. (1) for 1 : 2 (M : HL ratio) and Eq. (2) for 1 : 1
(M : H2L) ratio. The ligands HBe, HDBe, HMBe, and HNBe form 1 : 2 com-
plexes, while H2Sal forms 1 : 1 complex.
CuðCH3COOÞ2 þ 2HL ꢀ! ½CuL2ꢁ þ 2CH3COOH
ð1Þ
ð2Þ
H2O
CuðCH3COOÞ2 þ H2L ꢀꢀ! ½CuLðH2OÞꢁ þ 2CH3COOH
For 1 : 2 complexes, the chelation is brought about by proton displacement
from the –CO–NH group in each ligand. On the other hand, the 1 : 1 complex
may be formed through two protons displacement from the phenolic OH
and –CO–NH groups to satisfy the divalency of the metal ions. A survey
of the published results shows that N-salicylidenes react with Cu(II) acetate
yielding bis(N-salicylidenaniline)Cu(II) complexes by deprotonation of the
OH group, the liberated protons are continuously removed from the reaction
medium via the formation of weakly ionized acetic acid and the decrease in
acetate concentration.[10]
The Cu(II) complexes are fairly soluble in DMF and DMSO and are not
suitable in alcohol, acetone, chloroform, and diethyl ether. All complexes
under investigation are amorphous solids. The colors, yields, analytical
data, and decomposition points of the free Schiff bases and their Cu(II) com-
plexes are collected in Table 2.
Conductance Measurements
The molar conductance of the Cu(II) complexes measured in 1024
M
dimethyl formamide are in the range 1.5–3.6 ohm21 cm2 mol21 thereby indi-
cating their non-electrolytic nature.[11]
Infrared Spectra
The important IR bands of the free ligands and their Cu(II) complexes
together with their assignments are listed in Table 3. Relevant IR bands provide
structural evidence for the mode of attachment of the ligands to the metal ion.
All spectra of the free ligands exhibit a strong band at 1580–1615cm21, which
is characteristic of the azomethine (–HC55N) group. It is to be expected that
coordination of the nitrogen to metal atom would reduce the electron density
in the azomethine link and thus lower the –HC55N absorption. In the IR spectra

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Osman, Saleh, and Mahmoud

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Table 3. IR spectral bands of the Schiff base ligands and their Cu(II)
complexes (cm21).
Compound
n(C55N)
n(CONH)
n(M–N)
HBe
[Cu(Be)2] 3H2O
1,615 s
1,590 s
1,590 s
1,580 s
1,600 s
1,545 s
1,590 s
1,560 s
1,580 s
1,540 s
1,640 s
1,680 s
—
565 w
—
.
HDBe
[Cu(DBe)2]
HMBe
1,670 m
1,690 m
1,620 sh
1,640 sh
1,670 m
1,690 m
1,660 m
1,680 m
560 w
—
[Cu(MBe)2]
HNBe
570 w
—
[Cu(NBe)2]
H2Sal
[Cu(Sal)(H2O)]
580 w
—
540 w
Note: s, strong; m, medium; w, weak; sh, shoulder.
of the complexes, this band is shifted to the 1540–1580cm21 region, indicating
coordination of the Schiff base through the azomethine nitrogen.[12,13] Due to
the presence of more than one-N–H group in the complexes, the deprotonation
of this group could not be confirmed. However, bands at 1620–1970cm21
assigned to the amido group (–CONH) in the Schiff base were shifted to
lower frequencies by 20–40cm21 in the complexes, indicating coordination
of the amido nitrogen to the metal. This is also supported by the appearance
of a new band around 540–580 cm21 attributable to the M–N bond.[14]
For the [Cu(Sal)(H2O)] complex, the strong OH stretching band at
3329 cm21 of the free ligand is absent in the spectra of the complexes,which
suggests that the phenolic oxygen atom is coordinated to the metal atom in the
ionized form. The coordination of the phenolic oxygen is further supported by
the fact that the strong band observed at 1260 cm21 in the spectrum of the
ligand, which was attributed to the phenolic C–O stretching vibration, under-
goes a shift to a higher wave number at 1280 cm21 in the spectrum of the com-
plex. In addition, a new band was observed at 470 cm21, which is assigned to
the M–O bond.[15]
Electronic Spectra
The electronic spectra of the complexes are recorded in DMF and the
relevant data are presented in Table 4. The spectra are characterized by a
2
2
broad band at 16,583 cm21, which is assigned to the transition B1g ! A1g.
Besides to the d–d transition, two bands are observed in the regions 25,542–

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Osman, Saleh, and Mahmoud
p
p
p
p
p
p
p
p
p
p

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32,711 and 30,581–37,105 cm21, respectively, which are attributed to intrali-
gand charge transfer p–pꢂ transitions. The nature of the electronic spectra of
all complexes indicates a square-planar geometry around the Cu(II).[16]
Thermal Behavior
The TG thermograms for example were carried out within the temperature
range from room temperature up to 700 8C. The observed mass losses are based
on the TG results, and the calculated mass losses are based on the molecular
weight of the proposed formulas. The initial, maximum, and final temperature
of the different decomposition step are listed in Table 4. Non-isothermal kinetic
analysis of the decomposition of Cu(II) complexes was carried out by the
application of two different procedures: the Coats–Redfern[17] and Horowitz–
Metzger[18] methods. Table 5 includes the following kinetic parameters:
reaction order (n), activation energy (E), pre-exponential factor (Z), together
with the correlation coefficient (r). These parameters were evaluated only for
clear-cut and non-overlapping steps. Kinetic studies were not attempted for
decomposition stages which occur within a very narrow temperature range. In
general, the calculated activation energies of the complexes are relatively low
indicating the autocatalytic effect of copper on the thermal decomposition of
the complexes. The catalytic activity of many catalysts containing Cu(II) has
been reported.[19] The following are the detailed thermal decomposition of the
.
complexes. The TG curve of [Cu(Be)2] 3H2O shows four steps of decom-
position within the temperature range 55–340 8C (Fig. 2). The first step at
55–200 8C corresponds to the loss of three water molecules of hydration
(calcd 9.30%, found 9.45%) with an activation energy of 42.60 kcalmol21
.
The small value of the activation energy indicates a rather fast dehydration of
crystal water molecules which are loosely bonded.[20] The anhydrous complex
decomposes in a major stage consisting of three overlapping steps.
The [Cu(DBe)2] complex was found to decompose in four steps within
the temperature range 275–460 8C. The first step occurs in the temperature
range 275–325 8C with a mass loss of 11.48% and an activation energy of
228.22 kcal mol21. This step cannot be correlated with any proper decompo-
sition product. The major step of decomposition consists of three overlapping
steps in the range 350–460 8C. The TG curve of [Cu(MBe)2] exhibits three
stages starting at 275 8C with an activation energy of 69.31 kcal mol21. The
latter two complexes did not show any loss of mass up to their decomposition
indicating their anhydrous nature. The pyrolysis of [Cu(NBe)2] shows a step-
wise decomposition in six stages, which are well discernible in the TG curve.
The first stage (50–100 8C) is commensurate with the release of some moist-
ure in the complex (2.24%). The complex then decomposes in a major step

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Osman, Saleh, and Mahmoud

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.
Figure 2. TG and DTG thermograms of [Cu(Be)2] 3H2O.
consisting of five overlapping steps in the temperature range 240–525 8C. In
its TG curve, [Cu(Sal)H2O)] shows a mass loss within the temperature range
211–260 8C, corresponding to evolution of one coordinated water molecule
(found 5.64%, calcd 5.5%) with an activation energy of 165.43 kcal mol21
.
Another three overlapping steps occurring in the temperature range 262–
430 8C are also observed as a major stage.
The decomposition of all complexes ended with oxide formation. An
almost horizontal thermal curve is observed above 525 8C. The percentage
weight of the residue in this horizontal region agrees well with CuO for-
mation (calcd 24.88%, found 24.83% for the [Cu(Sal)(H2O)] complex as
an example).
Based on the above studies, the suggested structures of the two types of
Cu(II) complexes are represented in Fig. 3. For the 1 : 2 complexes, structures
(a) and (b) are proposed, but structure (a) is more favorable through hydrogen
bond formation. Structure (c) is suggested for the 1 : 1 complex.
Photochemical Behavior
All studied Cu(II) Schiff base complexes, as mentioned above, exhibit,
in addition to d–d transition, two bands which have been assigned to

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Osman, Saleh, and Mahmoud
Figure 3. Proposed structures of Cu(II) Schiff base complexes; (a) and (b) are
two isomers of the 1 : 2 complexes and (c) is the 1 : 1 complex; R ¼ H, p-N(CH3)2,
p-OCH3 or o-NO2.
intraligand and p–pꢂ transitions (Table 4). Upon irradiating a DMF solution
of the complexes with monochromatic light of l ¼ 298 nm and recording the
spectral changes at different time intervals, the complexes behave differently.
For [Cu(Be)2], [Cu(MBe)2], and [Cu(NBe)2], within the first 2 min of
irradiation, the absorbance of the intraligand band increases, while the
absorption of the p–pꢂ band decreases, followed by a general decrease in
the intensity (Fig. 4). For [Cu(DBe)2] and [Cu(Sal)H2O], the most prominent
features in the absorption spectra is a decrease in intensity upon irradiation.
To explain these different behaviors, one assumes that the photochemical
reactions, which are rather clean as indicated by the observed isosbestic
points, occur in two steps for the [Cu(Be)2], [Cu(MBe)2], and [Cu(NBe)2]
complexes. In the first step, absorption of light leads to a weakening of

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.
Figure 4. Spectral changes during the photolysis of [Cu(Be)2] 3H2O in DMF at
various irradiation times: 1 ¼ 0 sec, 2 ¼ 5 sec, 3 ¼ 15 sec, 4 ¼ 30 sec, 5 ¼ 45 sec,
6 ¼ 120 sec and 7 ¼ 15 min, 8 ¼ 30 min, 9 ¼ 45 min, 10 ¼ 60 min (lex ¼ 298 nm;
1 cm cell).
Cu–N ionic bond in the complexes which facilitates the charge transfer from
the N-atom to the rest of the organic molecule. This is indicated by the
increase of the IL-charge transfer band. It is well known that light absorption
leads to charge separation which attracts much interest owing to its important
applications such as artificial photosynthesis and non-linear optical
properties.[21] This assumption is confirmed by the observation that this
first step is only recorded for Schiff base complexes containing a powerfull
electron withdrawing group such as the NO2 group in [Cu(NBe)2] or H
in [Cu(Be)2] or a weakly electron donating group such as OCH3 in
[Cu(MBe)2]. However, in case of strongly electron donating groups such
as N(CH3)2 in [Cu(DBe)2] or OH in [Cu(Sal)H2O], the first step was not
detected. As a result of the weakening of the Cu–N bond, the complexes
decompose in the second step as indicated by the general decrease of the
absorption.
For the [Cu(Sal)H2O] and [Cu(DBe)2] complexes, the photodecomposi-
tion occurs directly upon irradiation as indicated by their spectral changes
during photolysis (Fig. 5 as an example). From the above discussion, a reac-
tion scheme given by Eqs. 3–5 is suggested to account for our results.

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Osman, Saleh, and Mahmoud
Figure 5. Spectral changes during the photolysis of [Cu(Be)2] in DMF at various
irradiation times: 1 ¼ 0 min, 2 ¼ 1 min, 3 ¼ 2 min, 4 ¼ 4 min, 5 ¼ 8 min, 6 ¼ 16 min
(lex ¼ 298 nm; 1-cm cell).

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(where
represents a bidentate Schiff base ligand). The IL-excited
state generated by light absorption [Eq. (3)] transfers an electron to the
N-atom [Eq. (4)]. This step has been detected by the increase of the absorption
intensity of the IL-ligand band of [Cu(Be)2], [Cu(MBe)2], and [Cu(NBe)2].
The resulting complex seems to be unstable and decomposes to unidentified
products in a secondary thermal reaction [Eq. (5)]. A similar mechanism
has been proposed for the photolysis of the (acetylacetonato)bis(benzo-
hydroxomato)iron(III) complex.[22]
As an alternative to the above suggested assumption, one may attri-
bute the observed spectral changes of [Cu(Be)2], [Cu(MBe)2], and
[Cu(NBe)2] within the first step to a photoisomerization reaction. As a
result of an electron-transfer reaction represented by Eq. (4), another isomer
may be formed due to rotation of one ligand with respect to the another. The
structure of this isomer may be represented by Fig. 3(b). This isomer seems to
be unstable and decomposes to unidentified products. This assumption is
based on the following considerations: (i) only the [Cu(Be)2], [Cu(MeBe)2],
and [Cu(NBe)2] complexes show this photorearrangement, i.e., those having
bidentate ligands. (ii) For [Cu(Sal)H2O] which contains a tridentate ligand,
such isomerization is impossible. (iii) In addition, the rotation in
[Cu(DBe)], which have a bulky group, such as N(CH3)2, is unfavorable,
i.e., for [Cu(Sal)H2O] and [Cu(DBe)2], such isomerization does not occur
and the complexes decompose directly.
REFERENCES
1. El-Ansary, A.L.; Soliman, A.A.; Scherif, O.E.; Ezzat, J.A. Preparation
and thermal study of new complexes of salicylidene-2-aminothiophenol
Schiff bases. Synth. React. Inorg. Met.-Org. Chem. 2002, 32 (7),
1301–1318.
2. Dholakiya, P.P.; Pated, M.N. Synthesis, spectroscopic studies, and anti-
microbial activity of Mn(II), Co(II), Ni(II), Cu(II), and Cd(II) complexes
with bidentate Schiff bases and 2,20-bipyridylamine. Synth. React. Inorg.
Met.-Org. Chem. 2002, 32 (4), 753–762.
3. Mishra, A.P.; Mahima, K.; Gautam, S.K. Synthesis, physico-chemical
characterization and antibacterial studies of some bioactive Schiff bases

ORDER
REPRINTS
1084
Osman, Saleh, and Mahmoud
and their metal chelates. Synth. React. Inorg. Met.-Org. Chem. 2002,
32 (8), 1485–1500.
4. Raman, N.; Kulandaisamy, A.; Thangaraja, C. Redox and antimicrobial
studies of transition metal(II) tetradentate Schiff base complexes. Transit.
Met. Chem. 2003, 28, 29–36.
5. Bermejo, M.R.; Sanmartin, J.; Garcia-Deibe, A.M.; Fondo, M.; Novio, F.;
Novarro, D. Metallo-helicates with an N4-Schiff base containing a flexible
alkyl spacer. Inorg. Chim. Acta 2003, 347, 53–60.
6. Patel, M.N.; Patel, N.H.; Patel, K.N.; Dholokiya, P.P.; Patel, D.H.
Synthesis, characterization and biocidal studies of some transition metal
complex containing bidentate monobasic hydroxyaldehydes and a neutral
bidentate Schiff base. Synth. React. Inorg. Met.-Org. Chem. 2003, 33 (1),
51–62.
7. Osman, A.H.; Zidan, A.S.A.; El-Said, A.I.; Aly, A.A.M. Synthesis and
photochemistry of binary and mixed ligand complexes of copper(II)
containing 5-arylazo-8-hydroxyquinoline derivatives and alkyl xanthates.
Transit. Met. Chem. 1993, 18, 34–36.
8. Osman, A.H.; Aly, A.A.M.; Abo El-Maali, N.; Al-Hazmi, G.A.A. An
investigation on the Cu(II) complexes of certain cephalosporin anti-
biotics: spectral, thermal and photochemical studies. Synth. React.
Inorg. Met.-Org. Chem. 2002, 32 (7), 1289–1300.
9. Geies, A.A.; Abdel-Hafez, A.A.; Kamal El-Dean, A.M.; Hozien, Z.A.
Bromonitriles in heterocyclic synthesis (II): synthesis and reactions of
thiazolo[2,3-c]triazines and triazolo[3,4-c]triazines. Bull. Fac. Sci. Assiut
Univ. 1993, 22 (2-B), 37–47.
10. Shallaby, A.M.; Mostafa, M.M.; Bekheit, M.M. Coordination compounds
of N-salicylideneaniline and its derivatives with Cu(II), Cd(II), Zn(II),
and Hg(II). Ind. J. Chem. 1979, 17A, 516–518.
11. Geary, W.J. The use of conductivity measurements in organic solvents
for characterization of coordination compounds. Coord. Chem. Rev. 1971,
7, 81–122.
12. Ramesh, R.; Suganthy, P.K.; Natarajan, K. Synthesis, spectra and electro-
chemistry of Ru(II) complexes with tetradentate Schiff base. Synth.
React. Inorg. Met.-Org. Chem. 1996, 26 (1), 47–60.
13. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordi-
nation Compounds, 4th Ed.; Wiley: New York, 1986; 313–316.
14. Radhakrishnan, T.; Kolawole, G.A.; Revaprasadu, N.; Nair, P.S.;
Sreekala, N.B. Studies of microenvironmental effects on complexation
of polymer-bound Schiff bases with transition metal ions. Synth. React.
Inorg. Met.-Org. Chem. 2002, 32 (7), 1153–1175.
15. Mostafa, M.M.; El-Asmy, A.A. Transition metal complexes of 1-isova-
leryl-4-phenyl-3-thiosemicarbazide. J. Coord. Chem. 1983, 12, 197–202.

ORDER
REPRINTS
Copper Complexes
1085
16. Greenwood, N.N.; Earnshaw, A. Chemistry of the Elements, 1st Ed.;
Pergamon Press: UK, 1983; 1379–1386.
17. Coats, A.W.; Redfern, J.P. Kinetic parameters from thermogravimetric
data. Nature 1964, 20, 68–70.
18. Horowitz, H.H.; Metzger, G. New analysis of thermogravimetric traces.
Anal. Chem. 1963, 25, 1464–1467.
19. El-Awad, A.M. Catalytic effect of some chromites on the thermal
decomposition of KClO4, mechanistic and non-isothermal kinetic studies.
J. Therm. Anal. Cal. 2000, 61, 197–208.
20. Icbudak, H.; Yilmaz, V.T.; Olmer, H. Thermal studies on solid complexes
of saccharin with divalent transition metal ions. J. Therm. Anal. 1998, 53,
843–854.
21. Kunkely, H.; Vogler, A. Electronic spectra of p-cyclopentadienyl-
(triethylphosphine)copper(II): ligand-to-ligand charge transfer. Inorg.
Chem. Comm. 2002, 55, 112–114.
22. Aly, A.M.A.; El-Said, A.I.; Osman, A.H. Mixed benzohydroxamato-
acetylacetonato metal complexes: spectral, thermal, and photochemical
behaviour. Transit. Met. Chem. 1990, 15, 403–406.
Received June 3, 2003
Accepted December 22, 2003
Referee I: D. Ratsinovich
Referee II: K. Moedritzer

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