Structure investigation, spectral, thermal, X-ray and mass characterization of piroxicam and its metal complexes

Article abstract of DOI:10.1016/j.saa.2003.12.051

[M(H₂L)₂](A)₂.yH₂O (where H₂L: neutral piroxicam (Pir), A: Cl^- in case of Ni(II) or acetate anion in case of Cu(II) and Zn(II) ions and y=0-2.5) and [M(H ₂L)₃](A)_z.yH₂O (A: SO ₄^2- in case of Fe(II) ion (z=1) or Cl^- in case of Fe(III) (z=3) and Co(II) ions (z=2) and y=1-4) chelates are prepared and characterized using elemental analyses, IR, magnetic and electronic reflectance measurements, mass spectra and thermal analyses. IR spectra reveal that Pir behaves a neutral bidentate ligand coordinated to the metal ions through the pyridyl-N and carbonyl-O of the amide moiety. The reflectance and magnetic moment measurements reveal that these chelates have tetrahedral, square planar and octahedral geometrical structures. Mass spectra and thermal analyses are also used to confirm the proposed formulae and the possible fragments resulted from fragmentation of Pir and its chelates. The thermal behaviour of the chelates (TGA and DTA) are discussed in detail and the thermal stability of the anhydrous chelates follow the order Ni(II)?Cu(II)a confirmatory tool to elucidate the crystallinity of the chelates.

Full text of DOI:10.1016/j.saa.2003.12.051

Spectrochimica Acta Part A 60 (2004) 2843–2852
Structure investigation, spectral, thermal, X-ray and mass
characterization of piroxicam and its metal complexes
M.A. Zayed, F.A. Nour El-Dien, Gehad G. Mohamed∗, Nadia E.A. El-Gamel
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
Received 19 August 2003; accepted 2 December 2003
Abstract
[M(H2L)2](A)2.yH2O (where H2L: neutral piroxicam (Pir), A: Cl− in case of Ni(II) or acetate anion in case of Cu(II) and Zn(II) ions
2−
and y = 0–2.5) and [M(H2L)3](A)z.yH2O (A: SO4 in case of Fe(II) ion (z = 1) or Cl− in case of Fe(III) (z = 3) and Co(II) ions
(z = 2) and y = 1–4) chelates are prepared and characterized using elemental analyses, IR, magnetic and electronic reflectance mea-
surements, mass spectra and thermal analyses. IR spectra reveal that Pir behaves a neutral bidentate ligand coordinated to the metal
ions through the pyridyl-N and carbonyl-O of the amide moiety. The reflectance and magnetic moment measurements reveal that these
chelates have tetrahedral, square planar and octahedral geometrical structures. Mass spectra and thermal analyses are also used to con-
firm the proposed formulae and the possible fragments resulted from fragmentation of Pir and its chelates. The thermal behaviour of the
∼
chelates (TGA and DTA) are discussed in detail and the thermal stability of the anhydrous chelates follow the order Ni(II)
Fe(II) < Zn(II) < Fe(III) < Co(II) chelates. The water molecules are removed in the first step while the Pir molecule is removed
Cu(II) <
=
in the second and subsequent steps. X-ray powder diffraction was also used as a confirmatory tool to elucidate the crystallinity of the
chelates.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Piroxicam; Chelates; IR; TGA and DTA; Magnetic; Solid reflectance spectra; XRD; Mass spectra
1. Introduction
junction with anti-inflammatory drugs exhibit synergistic ac-
tivity [3]. It had also been found that the Cu complexes
of some anti-arthritic drugs are themselves more active as
anti-inflammatory agents than their parent compounds [4,5].
However, inspite of that, the preparation of the transition
metal complexes of Pir had been reported earlier [6–8] and
by screening the literature survey, no studies concerning their
thermal and mass are reported. This led to give the main
idea of the studies.
In addition to being an important article of commerce as
a nonsteriodal anti-inflammatory agent [1], piroxicam (Pir)
(4-hydroxy-2-methyl-N-2-pyridyl-2H-1,2-benzothiazine-3-
carboxamide) was an intrinsically interesting chemical
compound by virtue of possessing four different heteroatom
sites for positioning the two substituents necessary to com-
plete its partial structure in Fig. 1.
Recently, it had been reported that the metabolic product
of Pir in the biological system showed highly photosen-
sitizing properties [2]. In order to investigate the possible
role of the metal ions in the photosensitizing effect of Pir
in biological system, the interaction of Cu(II) and other
first row transition-metal ions using different spectroscopic
methods had been studied. A variety of recent observations
indicated that copper complexes when administered in con-
Hence, one of the goals of this paper is to calculate the
stability constant values of Pir chelates with Fe(II), Fe(III),
Co(II), Ni(II), Cu(II) and Zn(II) ions. From the structural
data it is possible to discern how they are coordinated to the
metal ions, then to hypothesize how they can be coordinated
in biological systems. The study aims also to determine the
coordination capacity of Pir that incorporates served binding
sites via the IR, magnetic moment, conductance and solid
reflectance spectra measurements. Thermal analyses tech-
niques (TGA and DTA) were also used. The crystallinity of
the chelates are confirmed by using X-ray powder diffrac-
tion technique.
∗
Corresponding author. Fax: +202-572556.
E-mail address: ggenidy@hotmail.com (G.G. Mohamed).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2003.12.051

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M.A. Zayed et al. / Spectrochimica Acta Part A 60 (2004) 2843–2852
3. Results and discussion
Some physical properties of the synthesized complexes
are listed in Table 1. The complexes are less soluble than
the Pir ligand in solvents, such as alcohols, tetrahydrofuran,
dichloromethane, and acetone. The elemental analyses are
satisfactory in the acceptable range of 0.5% error and show
that the complexes have a ligand-to-metal ratio of 2:1 for
Ni(II), Cu(II) and Zn(II) ions and 3:1 for Fe(II), Fe(III) and
Co(II) ions, in accordance with the results obtained by molar
ratio method. Mass spectra of Pir show that the expected
molecular ion. The molecular ion in the mass spectra of
Cu(II) and Zn(II) chelates agree with 2:1 ligand-to-metal
stocichiometric ratio.
Fig. 1. Piroxicam system diagram and positional notation the planer
configuration shown is EZE, from left to right.
2. Experimental
3.1. Calculation of metal complexes stability constants
2.1. Materials and measurements
The stability constants of the metal chelate are evalu-
ated spectrophotometrically using recommended methods
[9]. The calculated log K values for the Fe(II)-, Fe(III)-,
Co(II)-, Ni(II)-, Cu(II)- and Zn(II)-chelates of Pir are given
All reagents and solvents were of the analytical grade.
Elemental analyses were carried out at the Microanalyt-
ical center at Cairo University. IR spectra were recorded
on a Perkin-Elmer FT-IR type 1650 spectrophotometer in
wavenumber region 4000–200 cm−1. The solid reflectance
spectra were measured on a Shimadzu 3101PC spectropho-
tometer. The molar magnetic susceptibilities were mea-
sured on powdered samples using the Faraday method.
The diamagnetic corrections were made by Pascal’s con-
stant and Hg[Co(ScN)4] was used as calibrant. The molar
conductance of solid complexes in DMF was measured
using Sybron–Barnstead conductometer (Meter-PM.6, E =
3406). The thermogravimetric analysis (TGA and DTGA)
and differential thermal analysis (DTA) were carried out in
dynamic nitrogen atmosphere (20 ml min−1) with a heat-
ing rate of 10 ◦C min−1 using Shimadzu TGA-50H and
DTA-50H thermal analyzer, respectively. The mass spectra
were recorded by the EI technique at 70 eV using MS-5988
GS–MS Hewlett-Packard instrument in the Microanalytical
Center, Cairo University. The X-ray powder diffraction anal-
yses were carried out by using Rigku Model ROTAFLEX
Ru-200. Radiation was provided by copper target (Cu an-
ode 2000 W) high intensity X-ray tube operated at 40 KV
and 35 MA. Divergence and the receiving slits were 1 and
0.1, respectively.
in Table 2. The stability of Pir–metal chelates follows the
∼
sequence: Cu(II) > Co(II) > Zn(II) Ni(II) > Fe(III) >
Fe(II).
=
3.2. IR spectra and mode of bonding
Detailed interpretation of IR spectra and the effect
of binding of Fe(II), Fe(III), Co(II), Cu(II) and Zn(II)
ions on the vibration frequencies of the free Pir is dis-
cussed. The IR spectrum of Pir shows well-defined peaks
at 3385 and 3336 cm−1 are assigned to the ␯(N–H) and
ν(O–H) vibrations, respectively. In the wave number range
1700–1000 cm−1, some of the most characteristic bands of
these groups are found. The so-called amide I band, which
=
represents mainly the ν(C O) stretching mode, is seen as
a very strong band at 1630 cm−1, with a weak shoulder at
1612 cm−1 in free Pir. In Pir complexes, this band is shifted
to higher or lower frequencies or disappear, supporting the
participation of the amide carbonyl group of Pir in the coor-
dination to metal ion. This band appears broadened in most
of the complexes by the simultaneous appearance of the
δ(H2O) vibration in the same range, a fact which obstructs
the clear visualization of the effective displacement of the
=
2.2. Synthesis of the complexes
ν(C O) band [7].
The band located at 1572 cm−1 is assigned to the ν(C N)
stretching vibration of pyridyl nitrogen. Coordination of the
pyridyl nitrogen is indicated by a 3–26 cm−1 shift to a higher
wavenumber or 55–50 cm−1 shift to a lower wavenumber
in all the chelates [10–12]. The participation of pyridine
in complex formation can be established from the shift of
the ring deformation found at 604 and 405 cm−1 in the
free pyridine to higher frequencies [13]. In the present case,
the in-plane ring deformation (604 cm−1 in free pyridine)
is probably overlapped by the 623 cm−1. After complexa-
tion, the band at 623 cm−1 disappears and a new band at
=
A hot ethanol solution (60 ◦C) of the respective metal
chlorides ((Fe(II), Fe(III), Co(II) and Ni(II)) or acetates
(Cu(II) and Zn(II)) (25 ml, 0.5 mM) was added to hot ethanol
solution (60 ◦C) of Pir (1 mM, 25 ml). The resulting mix-
ture was stirred under reflux for 30 min. The complexes
were precipitated as microcrystalline powders. They were
removed by filtration, washed with hot ethanol followed by
diethylether and dried in a vacuum desiccator over anhy-
drous calcium chloride. The m.p and analytical data are col-
lected in Table 1.

Table 1
Analytical and physical data of piroxicam and their metal chelates
Compound
Chemical formula
Colour
M.P. (◦C)
Found (Calcd.)%
C
Molecular wt.
found (Calcd.)
µeff (BM)
ΛmΩ−1 cm2
mol−1
H
N
S
M
Piroxicam [Pir]
Fe(II)–Pir
Fe(III)–Pir
Co(II)–Pir
Ni(II)–Pir
C
15H13N3O4S
White
198
115
174
206
219
193
236
54.50 (54.38)
46.41 (46.43)
43.50 (43.99)
47.45 (47.33)
44.35 (44.44)
48.00 (48.37)
47.59 (47.27)
3.70 (3.90)
3.60 (3.53)
3.62 (3.82)
3.36 (3.59)
3.25 (3.33)
3.62 (3.79)
4.05 (4.17)
12.34 (12.68)
11.20 (10.80)
10.50 (10.26)
11.20 (11.04)
10.25 (10.37)
10.10 (9.95)
9.50 (9.73)
9.55 (9.66)
11.42 (11.00)
7.71 (7.82)
8.62 (8.41)
7.81 (7.90)
7.75 (7.58)
7.65 (7.42)
–
331 (331)
–
–
–
(810)
842 (843.5)
863 (863)
–
–
83
[Fe(Pir)3]SO4·H2O
[Fe(Pir)3]Cl3·4H2O
[Co(Pir)3]Cl2·H2O
[Ni(Pir)2]Cl2·H2O
[Cu(Pir)2](Ac)2
Reddish brown
Reddish brown
Orange
Light green
Olive green
Lemon
4.81 (4.82)
4.60 (4.57)
5.38 (5.17)
7.22 (7.28)
7.38 (7.52)
8.09 (7.53)
4.98
5.30
4.95
Diam
1.81
Diam
320
153
165
140
117
Cu(II)–Pir
Zn(II)–Pir
[Zn(Pir)2](Ac)2·H2O

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M.A. Zayed et al. / Spectrochimica Acta Part A 60 (2004) 2843–2852
bands at 12.27 × 103, 15.04 × 103 and 17.59 × 103 cm−1
Table 2
Stability constants of di- and tri-valent metal–Pir chelates
wavenumber regions, respectively, which are assigned
4
4
to the transitions T1g(F) → T2g(F)(ν1), 4T1g(F) →
Metal
log K
Metal
log K
4A2g(F)(ν2) and 4T1g(F) → T2g(P)(ν3), respectively, sug-
4
FeII
FeIII
CoII
5.26
5.42
5.91
0.48
0.17
0.31
NiII
CuII
ZnII
5.49
6.96
5.50
0.78
0.47
0.27
gesting that there is an octahedral geometry around Co(II)
ion [25–27]. The magnetic susceptibility measurement
value is 4.95 BM is an indication of octahedral geometry
[28].
[Mn+–Pir] = 2.5 × 10−5 M; t = 25 ◦C.
Cu(II) complex exhibits two broad bands at 16.67 ×
672–656 cm−1 is found in the chelates, as previously re-
ported for pyridine complexes of divalent ions of the first
row transition metal series [14]. Detecting the shift of the
out-of-plane ρ(py) at 405 cm−1 is difficult because the spec-
tra are rich for the complexes.
2
103 cm−1 and 14.71 × 103 assigned to 2Eg → T2g
and2B1g → A1g transitions as well as a shoulder band in
2
the range 17.54 × 103 cm−1 characteristic of a square plan-
ner geometry for Cu(II) complexes with dx2−y2 ground state
[29,30]. The magnetic moment of the Cu(II)-complex is
1.81 BM, which support this geometry [31]. Zn(II) complex
is diamagnetic and is likely to be tetrahedral.
Two bands, located at 1351 and 1040 cm−1, are assigned
to the antisymmetric and symmetric stretching vibrations
of the SO2 group, respectively. These two SO2 bands are
shifted to lower or higher frequencies in complexes, in ac-
cordance to the assignment of Cini et al. [15]. As the SO2
group is not involved in metal binding, this shift to higher
frequencies must be related to important hydrogen bonding
effects. Similar effects are also known to occur in divalent
metal saccharinates (a molecule with a structure very simi-
lar to that of the benzothiazine part of Pir) [16,17]. Another
possible explanation for this shift may be due to the elec-
tronic density changes on the sulfur atom and in the ring
after complex formation.
The ν(M–N) bands for the pyridyl nitrogen appeared in the
wave number range 564–572 cm−1 for the di- and trivalent
metal ion chelates [14]. New peaks of weak or medium inten-
sity are observed in the wave number range 358–386 cm−1
which are attributed to ν(M–O) vibrations of binary chelates
[18]. The vibrations of the sulphate ion in Fe(II)-chelate ap-
pear at 1160 and 629 cm−1. This indicates the uncoordinated
nature of sulphate group [19].
3.4. Mass spectra
The mass spectrum of Pir shows a well-defined parent
peak at m/z = 331 (M+) with a relative intensity = 22%.
The C3H3NO+ ion, m/z = 69, RI = 100% is the base
peak in the spectrum of Pir. The parent ion and other frag-
ments obtained by cleavage in different positions in the
Pir molecule and the possible fragment ions are shown in
Scheme 1. It is found that, the molecular ion peaks agree
to a great extent with those previously published [32]. This
means that Pir drug is a pure substance and ready for the
use as a reagent in this study.
The mass histograms of Cu(II)- and Zn(II)-complexes
with Pir show parent peaks in their mass spectra at m/z =
845 (MH+1.5, RI = 46%) and 863 (M+, RI = 24%) for
the Cu(II)- and Zn(II)-complexes, respectively (as given in
Table 3). The mass spectra of both chelates show a molecu-
lar ion peak with m/z = 173 (RI = 59 and 26% for Cu(II)-
and Zn(II)-chelates, respectively) which can be assigned to
C10H7NO2+ ion. The different molecular ion peaks given in
Table 3 can be attributed to the loss of metal oxide, hydrated
water, anions and different ions resulted from Pir molecule
decomposition.
3.3. Magnetic susceptibility and electronic spectra
measurements
In the solid reflectance spectrum of Fe(III)-complex,
one band is observed at 21.93 × 103 cm−1, which may be
6
assigned to the A1g → T2g (G) transition in octahedral
3.5. Thermal analyses (TGA and DTA)
geometry of the complex [20]. The magnetic moment of the
Fe(III)-complex (µeff = 5.30 BM) is within the range of
values corresponding to octahedral geometry. The diffused
reflectance spectra of Fe(II) complex shows two absorption
bands at 12.20 × 103 and 22.22 × 103 cm−1 which are as-
The TGA curve of Pir refers to two stages of mass
losses at temperature ranges ∼170–360 and 360–650 ◦C.
These stages involved mass losses of 92.15% (f. 92.26%)
and 7.85% (f. 7.65%) for the first and second steps of
decomposition, respectively. These mass losses may be
due to the successive losses of C13H11N3O4S and C2H2
at the given temperature ranges, respectively. DTA curve
referes to five endothermic and three exothermic peaks.
The first two endo- and two exothermic peaks are strong
and centered at 200 (endo-), 212 (exo-), 243 (endo-), and
266 ◦C (exo-). The remaining peaks are weak and cen-
tered at 370 (endo-), 492 (exo-), 562 (endo-) and 620 ◦C
(endo-).
5
signed to 5T2g → Eg transition and charge transfer, respec-
tively [21,22].The magnetic moment of the Fe(II) complex
(µeff = 4.98 BM) is within the range of octahedral geome-
try. The d–d spectrum of the Ni(II) complex shows two bands
at 16.89 × 103 and 20.92 × 103 cm−1 which are assigned to
1A1g → A2g and A1g → B1g transitions, respectively,
in a square planar geometry [23,24]. The diamagnetic na-
ture of the complex lends support to the above geometry.
The electronic spectrum of the Co(II) complex gives three
1
1
1

M.A. Zayed et al. / Spectrochimica Acta Part A 60 (2004) 2843–2852
2847
Scheme 1. Mass fragmentation pattern of Pir.
The dehydration step in Fe(III)–Pir complex is found
in the temperature range 65–170 ◦C (wt. loss: calcd.
5.87%, f. 6.27%). While, in case of Ni(II)–Pir and
Fe(II)–Pir complexes, this step occurs in the temperature
range 25–80 ◦C (wt. loss: calcd. 2.22%, f. 2.35%) and
25–110 ◦C (wt. loss: calcd. 1.55%, f. 1.61%) for Ni(II) and
Fe(II)-complexes, respectively. In addition, the dehydration
step in Zn(II)-complex, the dehydration step is immedi-
ately accompanied by a loss of C2H6 molecule within the
temperature range 30–150 ◦C (wt. loss: calcd. 5.79%, f.
5.83%). The Co(II)-Complex losses water of hydration in
the temperature range 50–200 ◦C (wt. loss: calcd. 7.80%,
f. 7.63%) is accompanied by the loss of Cl2 gas. It is
obvious from the DTA curves (Table 4) that, the loss of
water molecules of hydration appears endothermic and/or
endothermic accompanied by exothermic peaks in the tem-
perature ranges mentioned above. For Co(II)-complex, the
loss of water of hydration and Cl2 gas molecules appear as

2848
M.A. Zayed et al. / Spectrochimica Acta Part A 60 (2004) 2843–2852
Table 3
at higher temperature range than those of water of hydra-
tion. It is recommended in literature [33] that the water of
coordination is usually eliminated in the temperature ranges
100–350 ◦C.
Mass spectral data of Cu(II)- and Zn(II)–Pir metal chelates
Compound
m/z Found
(calcd.)
RI (%) Fragments
[Cu(Pir)2](Ac)2
845 (843.5)
662 (661.5)
569.5 (570.5) 50
516.5 (515.5) 45
400 (401)
283 (282)
211 (210)
173 (173)
152.5 (153)
139 (138)
117 (117)
98 (97)
46
59
[C34H32CuN6O12S2]+
[C30
26CuN6O6S]+
The complexes of Pir with di- and tri-valent metal ions
undergo thermal decomposition in a series of overlapping
reactions with multiple products. The interpretation of the
TGA and DTA curves in terms of discrete stages with asso-
ciated weight losses requires a great deal of imagination and
certain amount of wishful thinking. The organic part (Pir)
together with the anions (Cl−, Ac− or SO42−) in the moi-
ety of complexes may decompose in more than two steps
with the possibility of the formation of more than one inter-
mediate. These intermediates may finally decompose to sta-
ble metal oxides or sulfides (see Table 4). It is shown from
these results that, the calculated and estimated mass losses
are comparable.
The DTA curves show a medium to strong exothermic
and endothermic peaks; the position of each peak is given in
Table 4, accompanying the decomposition of the anions and
Pir molecule to different gases like H2O, O2, CO2, CO, NO,
NO2, SO2, SO3, etc. The Fe(II)-, Fe(III)- and Zn(II)-chelates
show a medium to strong exo- or endothermic peaks in the
DTA curves which may be attributed to phase transitions.
The position and nature of the peaks (exo- or endo-) are
given in Table 4.
H
[C28H23CuN6O4]+
[C25H20CuN6O3]+
[C19H19N3O5S]+
[C10H8N3O5S]+
[C9H8NO3S]+
[C10H7NO2]+
[C7H5O2S]+
68
59
59
59
64
100
59
68
55
[C6H2O2S]+
[C8H5O]+
[C4H3NS]+
71 (69)
[C3H3NO]+
[Zn(Pir)2](Ac)2·H2O 863 (863)
741 (742)
24
30
20
29
29
39
26
25
31
100
[C34H34N6O13S2Zn]+
[C31H29N6O8S2Zn]+
[C19H21N3O9SZn]+
[C14H10N3O2SZn]+
[C10H8N2O4SZn]+
[C15H10N3O2]+
[C10H7NO2]+
532 (532)
351 (349)
316 (317)
263 (264)
175 (173)
144 (145)
106 (106)
81 (80)
[C9H5O2]+
[C7H6O]+
[C5H6N]+
endo- and exothermic peaks in the temperature range 50–
200 ◦C.
On the other hand, the coordinated water molecules are
directly bonded to the metal ion. Hence, they are eliminated
On the basis of the above observations, the ther-
mal decomposition of the metal chelates under inves-
tigation may be generally summarized in the proposed
Scheme 2.
Scheme 2. Thermal decomposition of Pir complexes.

Table 4
Thermal analyses (TGA and DTA) results of Pir-binary chelates
Complex
Temperature
range (◦C)
Peak temperature in DTA (◦C)
No. of
decomposed steps
Mass loss %
found (calcd.)
Total mass loss %
found (calcd.)
Assignment
Metallic
residue
Fe(II)–Pir
25–110
110–700
−100(+)
1.0
2.0
1.61 (1.55)
90.84 (90.88)
Loss of H2O
Loss of SO4 and Pir molecules
FeS
2−
−248(−), 279(+), 370(−), 390(+), 432(−),
500(+), 483(−), 548(+), 659(−)
−934(−), 1141(+)
92.45 (92.43)
94.09 (94.14)
93.17 (93.42)
Phase transition
Loss of 4H2O
Loss of 1.5 Cl2 and Pir molecules
Fe(III)–Pir
65–170
170–650
−120(+), 147(−)
1.0
2.0
6.27 (5.87)
87.82 (88.27)
FeO
−190(+), 206(−), 252(−), 270(+), 380(+),
468(−), 630(+), 659(+)
−805(+), 825(−)
Phase transition
Loss of H2O and Cl2
Loss of Pir molecules
Co(II)–Pir
Ni(II)–Pir
50–200
200–1200
−71(+), 85(−), 135(+), 150(−), 190(−)
−361(+), 540(−), 656(+), 766(+), 790(+),
935(+), 946(−), 1020(+), 1030 (−)
−40(+), 75(−)
1.0
2.0
7.63 (7.80)
85.54 (85.62)
CoO
NiO
25–80
80–1200
1.0
1.0
2.35 (2.22)
88.47 (88.52)
Loss of H2O
Loss of Cl2 and Pir molecules
−91(+), 113(−), 180(+), 195(−), 275(−),
330(−), 380(+), 405(−), 445(+), 516(+)
−237(−), 260(+), 470(−), 500(−), 891(+),
1050(−), 1090(−), 1150(−)
90.82 (90.74)
90.58 (90.76)
Cu(II)–Pir
Zn(II)–Pir
80–1200
3.0
90.58 (90.76)
Loss of acetate and Pir molecules
CuO
ZnS
30–150
150–750
−45(+), 75(+), 86(−), 130(+)
−170(+), 185(−), 276(+), 390(−), 405(−),
586(−), 680(+), 710(−), 730(+), 748(−),
755(−)
1.0
3.0
5.83 (5.79)
82.10 (82.97)
Loss of H2O and C2H6
Loss of 2CO2 and Pir molecules
87.93 (88.76)
−790(−), 849(−), 952(+), 1183(+)
Phase transition
(+): endothermic, (−): exothermic.

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3.6. Calculation of activation thermodynamic parameters
of pir chelates
The thermodynamic activation parameters of decomposi-
tion processes of dehydrated complexes namely activation
energy (E∗), enthalpy (ꢀH∗), entropy (ꢀS∗) and Gibbs free
energy change of the decomposition (ꢀG∗) were evaluated
graphically by employing the Coast–Redfern relation [34]:
ꢀ
ꢁ
ꢀ
ꢁ
log{Wf/(Wf − W)}
AR
∗ (1 −
2RT
E∗
log
= log
)
T2
θE
E∗
2.303RT
−
where Wf is the mass loss at the completion of the reac-
tion, W the mass loss up to temperature T; R the gas con-
stant, E∗ the activation energy in kJ mol−1, θ the heating
∗
∼
rate and (1−(2RT/E )) 1. A plot of the left-hand side of
=
equation 1 against 1/T gives a slope from which E∗ was cal-
culated and A (Arrhenius factor) was determined from the
intercept. The activation energy for the elimination of wa-
ter molecules of hydration from the Fe(II)-chelate is equal
138.3 kJ mol−1. Regarding the Fe(III)-chelate, the activa-
tion of the first step is equal 47.20 kJ mol−1. Meanwhile,
the data listed in Table 5 show that the Co(II)-, Ni(II)- and
Zn(II) chelates are found to have activation energy for the
elimination of water molecules of hydration are equal to 3,
17.4 and 34.69 kJ mol−1, respectively. From the activation
energy values, one can concluded that, the water and anion
molecules are easy to be eliminated from the chelates ac-
cording to the following order: Co(II) > Ni(II) > Zn(II) >
Fe(III) > Fe(II) chelates. According to the kinetic data ob-
tained fro DTG curves, all the complexes have −ve entropy,
which indicates that activated complexes have more ordered
systems than reactants.
3.7. X-ray powder diffraction
The corresponding spectrum of the X-ray powder diffrac-
tion pattern is presented in Fig. 2. By comparing the X-ray
chart of Pir with that previously published [27,28] and the
interplanar distances (d(Å)), it is concluded that Pir exists
in the cubic form and not in the needle form. XRD anal-
ysis for chelates shows that the coordination of Pir alone
or in the presence metal ions (Fe(II), Fe(III), Co(II), Ni(II),
Cu(II) and Zn(II)) changes the XRD pattern of the ligand.
This means that the metal ions are not fitted in the same
phase of Pir. Therefore, the non-similarity of XRD pat-
tern between the metal ions and complexes suggests that
these complexes have a different phase structure than the
Pir.
Fig. 2. X-ray diffraction pattern of (a) Pir, (b) Fe(II), (c) Fe(III), (d)
Co(II), (e) Ni(II), (f) Cu(II) and (g) Zn(II) chelates.
3.8. Structural interpretation
The structure of the complexes was confirmed by the IR,
magnetic, solid reflectance, conductance and XRD analysis.

M.A. Zayed et al. / Spectrochimica Acta Part A 60 (2004) 2843–2852
2851
Table 5
Thermodynamic data of the thermal decomposition of metal chelates with Pir
Complex
Decomposed range (◦C)
E* (kJ mol−1
)
A (S−1
)
ꢀS* (JK−1 mol−1
)
ꢀH* (kJ mol−1
)
ꢀG* (kJ mol−1
)
[Fe(II)(Pir)3]SO4·H2O
25–110
138.3
193.6
212.5
47.20
52.71
28.85
3.0
1.72 × 105
5.09 × 1017
1.55 × 1013
2.08 × 105
1.05 × 104
5.59 × 102
1.64 × 102
5.16 × 102
1.64
1.97 × 102
1.62 × 103
1.4 × 107
6.86 × 107
1.88 × 102
5.12 × 103
1.12 × 1010
6.42 × 104
2.5 × 102
−15.69
−11.40
−0.38
137.8
191.3
208.3
46.35
50.47
22.91
0.656
6.337
26.293
16.52
7.74
118.9
127.0
53.84
33.67
113
38.64
188.2
208.1
47.99
55.88
44.99
2.93
16.21
51.53
19.22
21.44
112.4
133.2
81.0
110–330
330–700
65–170
170–365
365–650
50–200
200–540
540–1200
25–80
80–1200
80–300
300–600
600–1200
30–150
150–333
333–531
531–750
[Fe(III)(Pir)3]SO4·4H2O
[Co(II)(Pir)3]Cl2·H2O
−16.15
−20.11
−30.92
−32.58
−30.22
−30.01
−25.46
−31.66
−12.86
−11.97
−27.72
−20.04
−6.30
9.05
33.30
17.40
11.34
121.1
131.3
62.00
34.69
115.4
79.3
[Ni(II)(Pir)2]Cl2·H2O
[Cu(II)(Pir)2](Ac)2
[Zn(II)(Pir)2](Ac)2·H2O
36.12
114.8
84.11
27.10
−18.82
−34.16
75.51
0.40
6.29
[6] R. Cini, G. Giorgi, A. Cinquantini, C. Rossi, M. Sabat, Inorg. Chem.
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The chelation is brought about by the pyridine nitrogen and
=
C O of amide group of Pir. From the reflectance spectra and
magnetic moment measurements, the geometrical structure
of the chelates were proposed and found to be octahedral,
tetrahedral or square planar.
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ligands in all the chelates. The structure of the chelates can
be given as follows:
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355.
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