Mixed ligand complexes of 5-arylazo-8-hydroxyquinoline and α-amino acids with Co(II), Ni(II) and Cu(II)

Article abstract of DOI:10.1023/A:1026761007006

Ten mixed ligand complexes of the type [M(X-QA)(aa)] and [Ni(X-QA)₂(Haa)(H₂O)], where X-HQA=5-arylazo-8-hydroxyquinoline derivatives, M=Co(II) or Cu(II) and Haa=glycine (gly), alanine (ala) or methionine (met), have been prepared. The complexes have been characterized by elemental analysis, IR and electron spectra and thermal analysis. A tetrahedral structure has been proposed for the cobalt(II) and copper(II) complexes with bidentate coordination of amino acids. The nickel(II) complexes have been assigned an octahedral structure with the amino acids acting as monodentate ligands. The thermal behaviour of the complexes has been studied before and after γ-irradiation.

Full text of DOI:10.1023/A:1026761007006

Journal of Thermal Analysis and Calorimetry, Vol. 62 (2000) 665–679
MIXED LIGAND COMPLEXES OF
5-ARYLAZO-8-HYDROXYQUINOLINE AND α–AMINO
ACIDS WITH Co(II), Ni(II) AND Cu(II)
A. S. A. Zidan, A. I. El-Said, M. S. El-Meligy, A. A. M. Aly and
O. F. Mohammed
Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt
(Received April 17, 2000)
Abstract
Ten mixed ligand complexes of the type [M(X-QA)(aa)] and [Ni(X-QA)2(Haa)(H2O)], where X-HQA=
5-arylazo-8-hydroxyquinoline derivatives, M=Co(II) or Cu(II) and Haa=glycine (gly), alanine (ala) or
methionine (met), have been prepared. The complexes have been characterized by elemental analysis,
IR and electron spectra and thermal analysis. A tetrahedral structure has been proposed for the co-
balt(II) and copper(II) complexes with bidentate coordination of amino acids. The nickel(II) complexes
have been assigned an octahedral structure with the amino acids acting as monodentate ligands. The
thermal behaviour of the complexes has been studied before and after γ-irradiation.
Keywords: α-amino acids, 5-arylazo-8-hydroxyquinoline, characterization, mixed ligand com-
plexes, thermal analysis
Introduction
Azo compounds are known to be involved in a number of biological reactions such as in-
hibition of DNA, RNA and protein synthesis, carcinogenesis and nitrogen fixation [1–3].
Furthermore they are proved to have biological activity against bacteria and fungi [4–5].
Some of the 8-hydroxyquinoline derivatives and their complexes with transition metals
were reported to be active vs. bacteria [6]. In view of the above importance of azo and
8-hydroxyquinoline compounds and the biological significance of amino acids, a number
1418–2874/2000/ $ 5.00
Akadémiai Kiadó, Budapest
© 2000 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

666
ZIDAN et al.: MIXED LIGAND COMPLEXES
of mixed ligand complexes of Co(II), Ni(II) and Cu(II) with some α-amino acids and
substituted 5-arylazo-8-hydroxyquinoline were prepared and characterized.
Experimental
All reagents and solvents required for the preparation of the compounds were of AR
grade and used without purification. All metal chlorides were obtained from Merck
and α-amino acids were purchased from BDH. The substituted 5-arylazo-8-hydroxy-
quinolines were prepared by published procedure [7].
Preparation of the ternary complexes
The following general procedure was adopted for the synthesis of the ternary com-
plex. 5-Phenylazo-8-hydroxyquinoline or 5-(p-methyl-phenylazo)-8-hydroxyquino-
line (5 mmol) in 50 ml ethanol was added with stirring to 2.5 mmol of metal chloride
in 20 ml aqueous ethanolic solution, when a solution (20 ml) of 2.5 mmol of α-amino
acid was added an orange to brown precipitates formed were filtered, washed with
ethanol and dried over P4O10.
Physical measurements
The infrared spectra were recorded on a 470 Shimadzu infrared spectrophotometer.
The electron absorption spectral measurements were carried out on a UV-2101PC
Shimadzu spectrophotometer. The thermogravimetric analyses were determined by
using an electrobalance of the type Sartorius 200MP converted to a thermobalance by
the addition of a small furnace and sample holder. The temperature was measured by
using a Chromel-Alumel thermocouple attached to a digital multimeter type Soar
ME-550, the heating rate was adjusted to be 8°C min–1. The complexes were kept in
small glass containers and subjected to γ-irradiation for appropriate times at ambient
temperature by using a 60Co gamma cell having a dose rate of 1.1 Gy s–1.
Results and discussion
The complexes are partially soluble in ethanol and acetone; they have good solubility
in DMSO. Analytical data, decomposition points and colours of the complexes are
shown in Table 1.
Mixed ligand complexes are easily formed according to the following equations:
Haa+M2++X-HQA → [M(X-QA)(aa)]+2H+
Haa+Ni2++2(X-HQA) → [Ni(X-QA)2(Haa)(H2O)]+2H
H2 O
(1)
(2)
+
where M=Co(II) or Cu(II) X-HQA=5-phenylazo-8-hydroxyquinoline (HQA) or
5-p-methyl-phenylazo-8-hydroxyquinoline (p-Me-HQA) and Haa=glycine (gly),
alanine (ala) or methionine (met). As can be seen from Eqs 1 and 2, the Co(II) and
Cu(II) complexes are formed in the molar ratios 1:1:1 (metal ion:X-QA–:aa–), while
J. Therm. Anal. Cal., 62, 2000

Table 1 Colour, elemental analyses and decomposition temperature of the complexes
Elemental analysis/%
Decomp.
m.p./°C
Compound
Colour
C
H
N
M
found
54.71
55.70
59.35
59.71
58.17
60.55
60.97
59.42
calcd.
54.69
55.76
59.28
59.84
58.18
60.38
60.89
59.21
54.06
55.13
found
4.02
4.77
4.22
4.46
4.62
4.66
4.83
5.02
4.00
4.66
calcd.
4.08
4.43
4.20
4.41
4.60
4.62
4.82
4.97
4.03
4.38
found
14.22
13.68
14.89
14.79
13.61
14.51
14.20
13.12
14.09
13.59
calcd.
14.17
13.68
15.12
14.80
13.57
14.49
14.20
13.05
14.01
13.53
found
14.79
14.40
9.12
calcd.
14.91
14.39
9.06
[Co(p-Me-QA)(gly)]
[Co(p-Me-QA)(ala)]
[Ni(QA)2(Hgly)(H2O)]
[Ni(QA)2(Hala)(H2O)]
[Ni(QA)2(Hmet)(H2O)]
brown
309
303
337
332
327
327
322
319
269
255
brown
orange
pale orange
orange
8.90
8.86
8.14
8.13
[Ni(p-Me-QA)2(Hgly)(H2O)] pale orange
[Ni(p-Me-QA)2(Hala)(H2O)] pale orange
[Ni(p-Me-QA)2(Hmet(H2O)] orange
8.76
8.68
8.50
8.50
7.92
7.82
[Cu(p-Me-QA)(gly)]
[Cu(p-Me-QA)(ala)]
reddish brown 54.02
reddish brown 55.22
15.81
15.44
15.89
15.35

668
ZIDAN et al.: MIXED LIGAND COMPLEXES
the Ni(II) complexes possess the molar ratio 1:2:1. The complexes were obtained by
mixing the metal ion and the two ligands in the molar ratio 1:2:1.
IR spectra
The most important IR peaks of the complexes are reported in Table 2. Mixed ligand
complexes exhibit the characteristic bands of the involved ligands. Thus, the
5-arylazo-8-hydroxyquinoline moieties display three bands in the regions 1380–1410,
1550–1570 and 1130–1140 cm–1 corresponding to ν(N=N), ν(C=N) and ν(C–O), respec-
tively. The position of ν(C=N) and ν(C–O) indicates that the coordination occurs through
nitrogen and oxygen of the 8-hydroxyquinoline part [8, 9] for all the complexes.
The free amino acids exhibit νs(NH2) around 3120 cm–1 [10–13]. The band is
shifted to lower frequency region (∆ν=20–80 cm–1) in the spectra of the com-
plexes, indicating the involvement of the amino nitrogen in coordination. For the
complexes [Co(p-Me-QA)(gly)], [Co(p-Me-QA)(ala), [Cu(p-Me-QA)(gly)] and
[Cu(p-Me-QA)(ala)], the bands due to ν(COO–) of carboxylic group are observed
in the region 1570–1575 cm–1; a lowering of the frequency of this band suggests
the coordination of the carboxylic oxygen to the metal ions.
The IR spectra of [Ni(QA)2(Hgly)(H2O)], [Ni(QA)2(Hala)(H2O)],
[Ni(QA)2(Hmet)(H2O)], [Ni(p-Me-QA)2(Hgly)(H2O)], [Ni(p-Me-QA)2(Hala)(H2O)]
and [Ni(p-Me-QA)2(Hmet)(H2O)] display a band in the region 1590–1600 cm–1, this
band can be assigned to ν(COOH). Furthermore, the ν(OH) stretching vibrations of
coordinated water are located in the region 3300–3400 cm–1.
From the forgoing band positions of ν(NH2), ν(COO–) and comparison with
similar compounds [14], it may be concluded that the amino acids in the complexes
Co(II) and Cu(II) are bidentate coordinating through the NH2 and COO– groups and
monodentate through the NH2 group in the Ni(II) complexes. Monodentate coordi-
nate ion of amino acids is known in the literature [15, 16]. For all the complexes,
metal–nitrogen and metal–oxygen bonds are manifested by the appearance of two
bands in the ranges 415–428 and 460–480 cm–1, respectively. This is further evidence
for coordination of the metal ions through oxygen and nitrogen atoms of the ligands.
The electron spectra
The electron spectral data of the complexes in DMSO and Nujol mull are given in Ta-
ble 3. For the Co(II) and Cu(II) complexes, a relatively intense band is observed in
the region 450–480 nm, which can be attributed to the characteristic azo n→π
[9, 17]. The complexes further display a band in the range 388–417 nm; this band is
assigned to charge transfer transition (most probably LMCT). It seems that the d-d
transitions of both Co(II) and Cu(II) complexes are obscured by the azo group ab-
sorption in the expected d–d regions. The close similarity between the electron spec-
tra of the complexes and related compounds [18] indicates the tetrahedral structure
around Co(II) and Cu(II). For the Ni(II) complexes, however, a d–d band appears in
the range 500–601 nm, due to the transition 3A2g(F)→3Tlg(F) (ν2) typical of octahedral
J. Therm. Anal. Cal., 62, 2000

Table 2 IR absorption bands of the complexes
Compound
ν(N=N) ν(C=N) ν(C–O) ν(C–N) ν(COOH) ν(COO–) ν(NH2)
ν(OH)
–
ν(M–O) ν(Μ−Ν)
[Co(p-Me-QA)(gly)]
[Co(p-Me-QA)(ala)]
1390
1400
1400
1410
1400
1400
1405
1405
1380
1380
1570
1570
1560
1565
1550
1560
1555
1560
1570
1565
1135
1140
1135
1140
1130
1140
1135
1135
1130
1140
1490
1500
1498
1500
1495
1490
1490
1490
1495
1490
–
1575
3050
3050
3050
3100
3050
3040
3100
3050
3100
3050
465
470
460
465
460
480
460
460
460
465
420
420
420
425
428
420
420
415
425
425
–
1570
–
[Ni(QA)2(Hgly)(H2O)]
[Ni(QA)2(Hala)(H2O)]
[Ni(QA)2(Hmet)(H2O)]
[Ni(p-Me-QA)2(Hgly)(H2O)]
[Ni(p-Me-QA)2(Hala)(H2O)]
[Ni(p-Me-QA)2(Hmet)(H2O)]
[Cu(p-Me-QA)(gly)]
[Cu(p-Me-QA)(ala)]
1590
1590
1600
1595
1600
1600
–
–
3350
3400
3400
3300
3350
3380
–
–
–
–
–
–
1570
1575
–
–

670
ZIDAN et al.: MIXED LIGAND COMPLEXES
structure around Ni(II). The transition ν3 is obscured by the band of the azo group lo-
cated in the region 457–477 nm. The charge transfer transition of the nickel(II) com-
plexes occurs in the range 355–408 nm. For all the complexes, the bands at
258–279 nm are associated with intraligand transitions.
Table 3 Electron spectral bands for the complexes λmax (nm)
Complex
In DMSO
480, 410, 258
479, 411, 260
500, 359, 265
504, 370, 266
507, 375, 266
500, 355, 270
506, 356, 270
502, 360, 260
456, 266
In Nujol
453, 417, 279
[Co(p-Me-QA)(gly)]
[Co(p-Me-QA)(ala)]
[Ni(QA)2(Hgly)(H2O)]
[Ni(QA)2(Hala)(H2O)]
[Ni(QA)2(Hmet)(H2O)]
[Ni(p-Me-QA)2(Hgly)(H2O)]
[Ni(p-Me-QA)2(Hala)(H2O)]
[Ni(p-Me-QA)2(Hmet)(H2O)]
[Cu(p-Me-QA)(gly)]
[Cu(p-Me-QA)(ala)]
470, 410, 271
503, 462, 408, 258
510, 471, 403, 260
539, 477, 376
500, 453, 355, 279
560, 455, 358
601, 473, 373
460, 450, 388, 359, 276
451, 392, 360, 276
457, 267
From the forgoing data the following structures can be postulated.
Fig. 1 Suggested structure for the complexes
Thermal analysis
The thermogravimetric analysis of the complexes were recorded in the 50–600°C
range. The complexes [Co(p-Me-QA)(gly)] and [Co(p-Me-QA)(ala)] show the same
decomposition pattern. They decompose in two steps at 136, 135 and 382 and 375°C
(DTG curves), respectively. The first step is related to the evolution of a nitrogen
molecule (found 6.8 and 6.5%; calc. 7.0 and 6.7%) respectively leaving compound (I)
(Eq. (3) which decomposes in the second step. The final product is CoO. Elimination
J. Therm. Anal. Cal., 62, 2000

ZIDAN et al.: MIXED LIGAND COMPLEXES
671
(3)
of nitrogen molecule from metal complexes of 5-arylazo-8-hydroxyquinoline during
their thermal decomposition is known in the literature [8].
Table 4 Thermal data of the complexes
Ti/
Tm/
Tf/
Mass loss
(calcd.)/%
Complex
Step
°C
1st
2nd
130
300
136
382
151
451
6.8 (7.0)
74.7 (–)
[Co(p-Me-QA)(gly)]
1st
2nd
130
294
135
375
145
444
6.5 (6.7)
73.8 (–)
[Co(p-Me-QA)(ala)]
1st
2nd
122
331
140
398
169
456
7.3 (7.1)
80.9 (–)
[Ni(QA)2(Hgly)(H2O)]
[Ni(QA)2(Hala)(H2O)]
[Ni(QA)2(Hmet)(H2O)]
[Ni(p-Me-QA)2(Hgly)(H2O)]
[Ni(p-Me-QA)2(Hala)(H2O)]
[Ni(p-Me-QA)2(Hmet)(H2O)]
1st
2nd
119
325
138
390
166
450
7.1 (6.9)
81.8 (–)
1st
2nd
116
319
150
388
180
450
6.4 (6.2)
82.6 (–)
1st
2nd
120
319
140
405
177
505
6.5 (6.6)
81.7 (–)
1st
2nd
115
327
131
390
160
451
6.3 (6.5)
82.6 (–)
1st
2nd
105
350
124
428
160
500
6.1 (6.0)
83.8 (–)
1st
2nd
3rd
–
341
582
265
466
596
–
542
615
28.8
45.9
5.8
[Cu(p-Me-QA)(gly)]
[Cu(p-Me-QA)(ala)]
1st
2nd
3rd
–
338
572
261
452
589
–
536
610
27.3
47.6
5.4
The TG curves of the Ni(II) complexes, [Ni(QA)2(Hgly)(H2O)],
[Ni(QA)2(Hala)(H2O)], [Ni(QA)2(Hmet)(H2O)], [Ni(p-Me-QA)2(Hgly)(H2O)],
[Ni(p-Me-QA)2(Hala)(H2O)] and [Ni(p-MeQA)2(Hmet)(H2O)] consist of two stages
of mass loss. The first mass loss occurs in the range 124–150°C and can be attributed
to a loss of one water and one nitrogen molecules. The second step is a major step in
J. Therm. Anal. Cal., 62, 2000

672
ZIDAN et al.: MIXED LIGAND COMPLEXES
the TG curve of all the complexes and corresponds to unidentified decomposition
products. The final product for these complexes is the NiO.
Three decomposition steps are observed in the TG curves of [Cu(p-Me-QA(gly)]
and [Cu(p-Me-QA)(ala)]. It was difficult to correlate the first and the second decomposi-
tion steps of the two complexes with the proper decomposition products. However, the
third step in both complexes at 596 and 589°C respectively, is consistent with the forma-
tion of CuCO3, which decomposes to the final product CuO.
Kinetic parameters of the complexes
The Coast–Redfern [19] and Horowitz–Metzger [20] equations were used for evalu-
ating the kinetic parameters.
• Coats–Redfern equation
1−(1−α )1−n
(1−n)T 2
M
T
ln
=
+B for n≠1
(4)
(5)
−ln(1−α )
M
ln
=
+B for n=1
T 2
T
where M= –E/R and B=lnZR/φE where E, R, Z and φ are the activation energy, gas
constant, pre-exponential factor and heating rate, respectively.
• Horowitz–Metzger equation
ZRTs2
1−(1−α )1−n
1−n
E
Eθ
ln
=ln
−
+
for n≠1
(6)
(7)
RTs2
φE RTs
Eθ
RTs2
ln[−ln(1−α )]=
for n=1
where θ=T–Ts is the temperature at the DTG peak.
The correlation coefficient r was computed by using the least square method for
Eqs (4), (5), (6) and (7). Linear curves were drawn for different values of n ranging
from 0 to 2 in increments of 0.2. The value of n, which gave the best fit, was chosen as
the order parameter for the decomposition stage of interest. The kinetic parameters
were calculated from the plots of the L.H.S. of Eqs (4) and (5) vs. 1/T and vs. θ for
Eqs (6) and (7) (Figs 2 and 3).
For all the complexes studied, the activation energies of the first and second
steps are recorded in Table 5. The activation energies for the elimination of nitrogen
molecule from the cobalt(II) complexes are shown in the range 41.9–48 kJ mol–1. Re-
garding the nickel(II) complexes, the activation energy of the first step is shown in
the range 71.9–91.9 kJ mol–1. Moreover, the copper(II) complexes exhibit an activa-
tion energy of 94.4–104.1 kJ mol–1 for the first step.
J. Therm. Anal. Cal., 62, 2000

ZIDAN et al.: MIXED LIGAND COMPLEXES
673
Fig. 2 Coats–Redfern plots for the two decomposition steps of [Cu(p-Me-QA)(gly)];
a – first step; b – second step where Y=ln{[1–(1–α)1–n]/[(1–n)T 2]} for n≠1 or
Y=ln[–ln(1–α)] for n=1
Table 5 Kinetic parameters of the complexes
Coats–Redfern
Horowitz–Metzger
Complexes
Step
E/
kJ mol–1
E/
kJ mol–1
n
r
n
r
1st
2nd
0.00
2.00
1.000
0.998
48
280
0.00
2.00
0.998
50.00
[Co(p-Me-QA)(gly]
0.995 290.90
0.999 45.80
0.997 369.80
0.994 87.17
1.000 120.00
0.996 83.13
0.999 171.22
0.999 75.21
0.995 131.60
0.996 79.60
0.999 102.80
0.997
0.996 190.20
0.998 75.62
0.997 110.72
1st
2nd
0.00
2.00
0.989
0.990
41.9
380
0.00
2.00
[Co(p-Me-QA)(ala)]
1st
2nd
1.00
2.00
0.987
0.992
91.9
113
0.33
2.00
[Ni(QA)2(Hgly)(H2O)]
[Ni(QA)2(Hala)(H2O)]
[Ni(QA)2(Hmet)(H2O)]
[Ni(p-Me-QA)2(Hgly)(H2O)]
[Ni(p-Me-QA)2(Hala)(H2O)]
[Ni(p-Me-QA)2(Hmet)(H2O)]
1st
2nd
1.00
0.66
0.999
0.979
79.42
163
1.00
0.66
1st
2nd
1.00
2.00
1.000
0.992
72.15
–
1.00
2.00
1st
2nd
1.00
0.66
0.999
0.995
84.9
109.2
1.00
0.66
1st
2nd
0.66
0.66
1.000
0.989
71.9
188.1
2.00
0.66
–
1st
2nd
1.00
1.00
0.995
0.996
79.95
108.7
1.00
1.00
1st
2nd
3rd
–
2.00
0.00
–
–
–
2.00
0.00
–
–
[Cu(p-Me-QA)(gly)]
[Cu(p-Me-QA)(ala)]
0.994
0.996
104.1
196.1
0.999 107.78
0.977 202.72
1st
2nd
3rd
–
2.00
0.33
–
–
–
2.00
0.00
–
–
0.991
1.000
94.43
165.9
0.997
0.999
99.22
–
J. Therm. Anal. Cal., 62, 2000

674
ZIDAN et al.: MIXED LIGAND COMPLEXES
Fig. 3 Horowitz–Metzger plots for the two decomposition steps of
[Ni(p-Me-QA)2(Hmet)(H2O)]; a – first step; b – second step where
Y=ln[(1–(1–α)1–n)/(1–n)] for n≠1 or Y=ln[–ln(1–α)] for n=1
Thermal studies of irradiated samples
Four complexes were selected for irradiation with γ-rays at doses of 104 and 105 Gy.
These
complexes
are
[Co(p-Me-QA)(gly)],
[Ni(QA)2(Hmet)(H2O)],
[Ni(p-Me-QA)2(Hgly)(H2O)] and [Cu(p-Me-QA)(gly)]. The irradiated samples ex-
hibit essentially the same TG profile compared to those before irradiation (Fig. 4).
Table 6 includes the initial temperature (Ti), peak temperature (Tm) and final tempera-
ture (Tf) of decomposition after irradiation. The cobalt(II) and copper(II) complexes
are most affected by the two γ-ray doses among the studied complexes. Thus, irradia-
tion of the cobalt(II) complex lowers Tm by 9 and 21°C of the first step and by 15 and
26°C of the second step, upon irradiation with the 104 and 105 Gy doses, respectively.
For the copper(II) complex, irradiation with the 104 and 105 Gy doses lowers Tm of the
first step by 10 and 25°C, of the second step by 10 and 19°C and of the third step by
19 and 28°C. The Ni(II) complexes are practically unaffected by the two doses at 104
and 105 Gy.
Fig. 4 TG and DTG curves of unirradiated (—) and γ-irradiated (---)
[Cu(p-Me-QA)(gly)]. Irradiation dose=1 105 Gy
J. Therm. Anal. Cal., 62, 2000

ZIDAN et al.: MIXED LIGAND COMPLEXES
675
Table 6 Thermal data after γ-irradiation of 104 and 105 Gy
Irradiaton dose: 104 Gy
Irradiation dose: 105 Gy
Compound
Step
Ti/
Tm/
Tf/
Ti/
Tm/
Tf/
°C
1st
2nd
120
292
127
367
145
440
112
287
115
356
137
430
[Co(p-Me-QA)(gly)]
1st
nd
116
317
146
382
177
441
114
313
141
376
172
438
[Ni(QA)2(Hmet)(H2O]
[Ni(p-Me-QA)2(Hgly)(H2O)]
1st
2nd
117
313
135
387
164
447
114
323
132
380
161
445
1st
2nd
3rd
–
335
571
255
436
587
–
535
607
–
323
560
240
427
558
–
524
590
[Cu(p-Me-QA)(gly)]
The activation energy of the different decomposition steps was calculated by us-
ing the Coats–Redfern and Horowitz–Metzger equations. Table 7 shows that the acti-
vation energy of the irradiated complexes decreases compared with the unirradiated
ones. The two Co(II) and Cu(II) complexes display a greater decrease in activation
energy than those of the Ni(II) complexes. This may suggest their lower stability be-
sides the autocatalytic effect of Co(II) and Cu(II) on the decomposition of their com-
plexes. However, there are relatively small changes in activation energy for all the
studied complexes by increasing the radiation dose, suggesting that the same chemi-
cal processes govern the decomposition of the complexes for the two doses. The in-
fluence of γ-irradiation on the thermal decomposition of [Cu(p-Me-QA)(gly)] is de-
picted in Fig. 4.
The IR spectra of the irradiated [Co(p-Me-QA)(gly)] and [Cu(p-Me-QA)(gly)]
complexes (Figs 5 and 6) show that the intensity of most of the bands decreases and that
the metal oxygen (460–480 cm–1) or metal nitrogen (415–428 cm–1) bands are more af-
fected with irradiation. However, the position of all the bands did not change with irradia-
tion. As expected from the thermal decomposition data of Co(II), Ni(II) and Cu(II) com-
plexes, the effect of Co(II) and Cu(II) complexes are more pronounced, whereas those of
Ni(II) experience no change upon irradiation. The degradation mechanism of the M–O
and M–N bands is suggested as follows. The γ-ray ionizes the complex to produce posi-
tive ions and electrons. The excited unstable ions then decompose by bond scission to
give uncharged complex molecule and metal cations. These cations are then neutralized
through recombination with the slowed-down electrons to form metallic atoms [21]. In
conclusion, it is evident that γ-irradiation leads to the rupture of some metal oxygen and
metal nitrogen bonds and hence results in a decrease of the intensity of the IR band of the
M–O or M–N bonds.
Antibacterial activity
The data listed in Table 8 indicate that the Ni(II) complexes are inactive against the tested
bacteria (except against B. cereus G+ve), whereas the two complexes of Co(II) and
J. Therm. Anal. Cal., 62, 2000

Table 7 Kinetic parameters of the decomposition of complexes after irradiation with 104 and 105 Gy irradiation doses
Coats–Redfern
Horowitz–Metzger
Complex
Step
n
r
E1
E2
n
r
E1
E2
1st
2nd
0.00
2.00
1.000
0.998
41.2
266
33.52
251.5
0.00
2.00
0.998
0.995
44
275
36.0
252.5
[Co(p-Me-QA)(gly)]
1st
2nd
1.00
2.00
0.999
0.979
70.0
–
66.21
–
1.00
2.00
0.999
0.995
71
128
68.5
124.12
[Ni(QA)2(Hmet)(H2O)]
[Ni(p-Me-QA)2(Hgly)(H2O)]
1st
2nd
1.00
0.66
0.999
0.995
84
100
78.0
92.5
1.00
0.66
0.996
0.999
70.2
93.2
67.9
88.5
1st
2nd
3rd
–
2.00
0.00
–
–
90.8
182
–
–
2.00
0.00
–
–
–
[Cu(p-Me-QA)(gly)]
0.996
0.994
81.6
171
0.997
0.999
92.90
189.9
80.2
175.6
Activation energies, E1 at 104 Gy, E2 at 105 Gy, kJ mol–1

ZIDAN et al.: MIXED LIGAND COMPLEXES
677
Fig. 5 IR spectra of unirradiated (—) and γ-irradiated (----) [Co(p-Me-QA)(gly)]. Irra-
diation dose=1 105 Gy
Fig. 6 IR spectra of unirradiated (—) and γ-irradiated (----) [Cu(p-Me-QA)(gly)]. Irra-
diation dose=1 105 Gy
Cu(II) show some inhibiting activity against them. It is thought [22] that the increase in
the activity of the complexes may be due to the effect of metal ions on the cell.
Conclusions
The thermoanalytical results of the Co(II), Ni(II) and Cu(II) complexes conclusively
prove that the main feature of first step decomposition is the evolution of nitrogen and
that the metal oxides CoO, NiO and CuO are the final products. The TG curves as well as
the activation energies of decomposition for the Co(II) and Cu(II) complexes are more
J. Therm. Anal. Cal., 62, 2000

Table 8 Antibacterial activity of the complexes
Bacteria
E. Coli
G–ve
Fungi
A. niger
Complex
B. Cereus
G+ve
P. Aeruginosa
G–ve
P. oxaliaum
A. flavus T. roseun
[Co(p-Me-QA)(gly)]
+++
+
–
–
++
–
–
–
++
–
+
–
++
–
[Ni(QA)2(Hmet)(H2O)]
[Ni(p-Me-QA)2(Hmet)(H2O)]
[Cu(p-Me-QA)(ala)]
++
–
–
–
–
–
–
+++
++
+
++
+++
++
++++

ZIDAN et al.: MIXED LIGAND COMPLEXES
679
affected by γ-irradiation than those of Ni(II), indicating their lower stability and the
autocatalytic effect of Co(II) and Cu(II) on the decomposition of these complexes.
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