Thermal and spectral studies of 5-(phenylazo)-2-thiohydantoin and 5-(2- hydroxyphenylazo)-2-thiohydantoin complexes of cobalt(II), nickel(II) and copper(II)

Article abstract of DOI:10.1016/j.tca.2003.11.021

Complexes of 5-(phenylazo)-2-thiohydantoin (L¹) and 5-(2-hydroxyphenylazo)-2-thiohydantoin (HL²) with Co(II), Ni(II) and Cu(II) salts have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The magnetic and spectral data suggested octahedral geometry for [L ¹M(OAc)₂(H₂O)₂]·xH ₂O {M=Ni^ll and Cu^ll} and [L ¹CuCl₂(H₂O)]·H₂O (dimeric form for the latter), trigonal bipyramidal geometry for [L²Co(OAc) (H₂O)]·2H₂O, square pyramidal geometry for [L ²Ni(OAc)(H₂O)]·H₂O and square planar geometry for [L²CuCl]·2H₂O. TG studies confirmed the chemical formulations of these complexes and showed that their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic parameters (n, E ^#, A, ΔH^#, ΔS^# and ΔG ^#) of the thermal decomposition stages were computed using the Coats-Redfern and other standard equations and are discussed.

Full text of DOI:10.1016/j.tca.2003.11.021

Thermochimica Acta 414 (2004) 105–113
Thermal and spectral studies of 5-(phenylazo)-2-thiohydantoin and
5-(2- hydroxyphenylazo)-2-thiohydantoin complexes of
cobalt(II), nickel(II) and copper(II)
Samir S. Kandil∗, Gad B. El-Hefnawy, Eman A. Baker
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
Received 25 March 2003; received in revised form 22 November 2003; accepted 22 November 2003
Abstract
Complexes of 5-(phenylazo)-2-thiohydantoin (L1) and 5-(2-hydroxyphenylazo)-2-thiohydantoin (HL2) with Co(II), Ni(II) and Cu(II) salts
have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The
magnetic and spectral data suggested octahedral geometry for [L1M(OAc)2(H2O)2]·xH2O {M = Nill and Cull} and [L1CuCl2(H2O)]·H2O
(dimeric form for the latter), trigonal bipyramidal geometry for [L2Co(OAc)(H2O)]·2H2O, square pyramidal geometry for [L2Ni(OAc)(H2O)]·
H2O and square planar geometry for [L2CuCl]·2H2O. TG studies confirmed the chemical formulations of these complexes and showed that
their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic
parameters (n, E#, A, ꢀH#, ꢀS# and ꢀG#) of the thermal decomposition stages were computed using the Coats–Redfern and other standard
equations and are discussed.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Complexes; Synthesis; Thermal degradation; Thermogravimetry; Kinetics
1. Introduction
2. Experimental
2.1. Synthesis of the ligands
2-Thiohydantoins have been reported to be of biological
importance as anticonvulsant, hypotonic and potential an-
titumor agents [1]. 2-Thiohydantions have been also used
in other purposes, including textile printing [2], as catalysts
for polymerization [3], in production of resins and plas-
tics [4] and as qualitative reagents for detection of some
metal ions upon complexation [5]. Transition metal ions
have proven advantageous in improving stability, clarity
and the brightness of the colour and effectiveness of the
organic ligands in their applications. The present paper re-
ports on the synthesis, spectral and thermal studies of some
cobalt(II), nickel(II) and copper(II) complexes derived from
5-(phenylazo)-2-thiohydantoin and 5-(2-hydroxyphenyl-
azo)-2-thiohydantoin, Scheme 1. The kinetic parameters
n, E# and A have been determined using Coats–Redfern
method [6,7]. The other kinetic parameters ꢀH#, ꢀS# and
ꢀG# have been computed using standard equations.
The ligands 5-(phenylazo)-2-thiohydantoin (L1) and
5-(2-hydroxyphenylazo)-2-thiohydantoin (HL2) were pre-
pared and purified according to the methods reported in the
literature [8,9].
2.2. Synthesis of metal complexes
Hot EtOH solution of L1 or HL2 (0.005 mol) and a
hot H2O-EtOH solution (50% (v/v)) of the metal(II) salts,
namely, NiCl2·6H2O, M(OAc)2·4H2O (M = CoII or NiII),
CuCl2·2H2O or Cu(OAc)2·H2O (0.005 mol) were mixed
and heated under reflux on water bath for 3 h with occa-
sional stirring. In case of the acetate complexes, two to
three drops of AcOH were added to the metal acetate solu-
tion. The reaction mixture was then concentrated by rotary
evaporation under reduced pressure until the onset of pre-
cipitation of the products. The products were separated and
washed successively with H2O, warm EtOH and Et2O, and
dried in vacuo over anhydrous CaCl2.
∗
Corresponding author.
E-mail address: kandilsamir@hotmail.com (S.S. Kandil).
0040-6031/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2003.11.021

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S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
OH
O
O
N
N
N
N
4
5
3
N
N
1
H
H
2
N
N
H
H
S
S
1
L
HL2
Scheme 1. Structures of ligands L1 and HL2.
The subnormal magnetic moment of [L1CuCl2(H2O)]·H2O
indicates copper−copper interaction and suggests dimeric
structure, presumably with chloride bridges [11].
2.3. Analytical methods
Infrared spectra in the 4000–200 cm−1 range were
recorded as KBr discs on a Perkin Elmer 683 spectropho-
tometer. Electronic spectra were recorded as nujol mulls
on a Shimadzu 240 spectrophotometer. Magnetic suscepti-
bilities were measured by the Gouy method. Diamagnetic
corrections were made using Pascal’s constants. Electron
spin resonanace (ESR) spectra of powdered samples of the
copper(II) complexes were recorded on a Jeol JEX-FE 2XG
spectrometer using diphenyl-1-picrylhydrazone (DPPH) as
standard (g = 2.0036). Thermogravimetric curves of the
complexes were recorded on a Shimadzu DT-50 at heating
rate of 10 ◦C min−1, using 10–14 mg of powdered samples
in nitrogen atmosphere. Microanalyses of C, H and N were
performed at the Microanalytical center at Cairo University.
The complexes were analyzed for their metal content by
EDTA titration. Molar conductances in DMF were mea-
sured at room temperature on a Hanna 8733 conductivity
meter.
3.1. Infrared spectra
The ligands L1 and HL2 show bands at 3290, 3180,
2890,1729/1715, 1424/1438 and 750 cm−1, assigned to
1
3
5
=
␯(N –H), ␯(N –H), ␯(C –H), ␯(C O) of 2-thiohydantoin
=
moiety, ␯(N N) and thioamide IV modes, respectively
[9,12]. The two strong bands at 1510 and 1330 cm−1 are
assigned to the thioamide I and II modes, respectively [12].
The spectrum of HL2 shows strong band at 1180 cm−1
assigned to the ␯(C–O) mode of the phenol group. The
absence of strong band at ∼2500 cm−1, assignable to the
␯(S–H) mode, indicate that both compounds exist in the
=
thiono(C S) form in the solid state. The IR spectra of the
metal(II) complexes of L1 and HL2 show shifts to lower
=
=
wavenumbers of the ␯(C O), ␯(N N) bands (by 34–46 and
13–22 cm−1, respectively) and to higher wavenumbers of
the ␯(C–O) band (by 34–50 cm−1 in case of HL2 com-
plexes), compared to the values of the free ligands. These
shifts suggest that the carbonyl–O of 2-thiohydantoin moi-
ety, an azo–N and phenolic–O (in case of HL2 complexes)
atoms are involved in coordination to metal ions [13,14].
However, the thioamide I, II and IV bands show no sig-
nificant wavenumber shifts in all complexes, indicating
non-participation of the sulphur atom in bonding to metal
ions. The acetate complexes show relatively broad bands
at ∼1595 cm−1 which may be considered as overlap of the
␦(N1–H) and ␦(N3–H) modes with ␯as(OCO) of the acetate
anions. On the other hand, the bands which appear in the
1361–1386 cm−1 region in the same complexes are assigned
3. Results and discussion
The metal complexes are microcrystalline, non-hygro-
scopic, partially soluble in most common organic solvents
but entirely soluble in DMF and DMSO. The analytical data
reveal 1:1 (metal:ligand) stoichiometry (Table 1). The molar
conductance values fall in the 8−14 ꢁ−1 mol−1 cm2 range,
indicating the non-electrolytic nature of these complexes
[10]. The magnetic moment values are in the range reported
for high-spin Co(II) and Ni(II) complexes and magnetically
dilute Cu(II) complexes containing an unpaired electron.
Table 1
Analytical, magnetic and conductivity data of Co(II), Ni(II) and Cu(II) complexes with L1 and HL2
Complex (formula wt.)
Elemental analysis (%)
Molar conductance
(ꢁ−1 mol−1 cm2)
Magnetic
moment (BM)
C
H
N
M
[L1CuCl2(H2O)]·H2O (390.5)
[L1Cu(OAc)2(H2O)2]·H2O (455.5)
[L1Ni(OAc)2(H2O)2]·2H2O (468.7)
[L2CuCl]·2H2O (370)
27.45 (27.65)
33.9 (34.2)
33.0 (33.3)
29.05 (29.3)
32.1 (32.4)
32.2 (32.45)
2.5 (3.1)
4.2 (4.4)
4.6 (4.7)
2.9 (3.0)
3.6 (3.9)
3.7 (3.9)
14.2 (14.3)
12.05 (12.3)
11.7 (11.9)
14.95 (15.1)
13.6 (13.8)
13.5 (13.8)
16.1 (16.3)
13.7 (13.9)
12.2 (12.5)
17.0 (17.2)
14.35 (14.5)
14.05 (14.4)
12
10
8
11
14
9
1.28
1.82
3.05
1.82
4.53
2.84
[L2Co(OAc)(H2O)]·2H2O (406.9)
[L2Ni(OAc)(H2O)]·2H2O (406.7)

S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
107
4
4
4
4
to the ␯s(OCO) mode of the acetate groups. This affords sep-
aration wavenumber values ꢀ, (ꢀ = νas(OCO)–νs(OCO)),
larger than 200 cm−1 for all the acetate complexes, char-
acteristic of unidentate acetate anion [15]. In the chloro
complexes, the bands that appear at 268 and 276 cm−1 in
[L1CuCl2(H2O)]·H2O and [L2CuCl]·2H2O, respectively,
are attributed to the ␯(Cu–Cl) mode of terminal chloride
ions and the shoulder at 238 cm−1 in the former one is due
to the ␯(Cu–Cl) mode of bridging chloride ions [16]. The
broad nature of the bands appearing in the 650–500 cm−1
region may be attributed to overlapping of differnt stretch-
ing modes of the M–O bonds of carbonyl–O, water–O and
acetate–O with the ligand bands.
assigned to A2 → A2(P) and A2 → E2(P) transitions,
respectively, similarly to trigonal bipyramidal cobalt(II)
complexes of D3h symmetry [17].
The visible spectrum of [L1Ni(OAc)2(H2O)2]·2H2O ex-
hibits two bands at 16333 and 25907 cm−1, attributable to
3A2g(F) → T1g(F) (␯2) and 3A2g(F) → T1g(P) (␯3) tran-
sitions, respectively, confirming octahedral geometry for this
complex [18]. The spectrum of [L2Ni(OAc)(H2O)]·2H2O
3
3
shows two absorption bands at 18,868 and 22,936 cm−1
,
characteristic of high-spin five coordinate nickel(II) com-
3
3
plexes [18] and could be assigned to B1g → A2g(P) and
3B1g → Eg(P), respectively, of square pyramidal environ-
3
ment with D4h microsymmetry.
The IR spectra of the complexes also show broad
band around 3400 cm−1, assignable to the two ␯(N–H)
modes overlapped with the stretching modes of water
molecules.
The electronic spectra of [L1CuCl2(H2O)]·H2O,
[L1Cu(OAc)2(H2O)2]·H2O exhibit a relatively broad band
of low intensity at 16103 and 15873 cm−1, respectively,
2
2
2
2
assigned to the superimposed B1g → B2g + Eg + A1g
transitions, suggesting distorted octahedral structure for
both complexes. The spectrum of [L2CuCl]·2H2O displays
3.2. UV-Vis spectra
a broad band at 15038 cm−1, assignable to B1g → A1g
transition in D4h microsymmetry, which is consistent with
square planar geometry [17].
2
2
The electronic spectrum of [L2Co(OAc)(H2O)]·2H2O
shows d–d bands at 15,267 and 19,157 cm−1 which could be
.
S
H
N
NH
OH2
Cl
O
Cl
N
N
Cu
.
Cu
N
OAc
M
2H2O
N
H
N
OH2
OH2
N
.xH2O
Cl
N
O
H2O
Cl
N
H
S
S
.
NH
N
H
O
OAc
[L1CuCl2(H2O)]2 2H2O
[L1M(OAc)2(H2O)2].xH2O
M = CuII, NiII
.
Cl
H
N
OAc
H
N
O
O
O
O
Cu
Co
.2H2O
.2H2O
S
S
H2O
N
N
N
N
N
H
N
H
[L2Co(OAc)(H2O)].2H2O
2
.
[
L CuCl] 2H2O
H
N
O
OH2
O
Ni
.2H2O
AcO
N
S
N
H
N
[L2Ni(OAc)(H2O)].2H2O
Scheme 2. Proposed structures of L1 and HL2 complexes.

108
S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
3.3. Electron spin resonance spectra
3.4. Thermal analysis
The ESR spectra of [L1Cu(OAc)2(H2O)2]·H2O and
[L1CuCl2(H2O)]·H2O exhibit axial signals with g values of
The stages of decomposition, temperature range, decom-
position product loss as well as the found and calculated
weight loss percentages of the complexes are given in
Table 2. The TG curve of [L1CuCl2(H2O)]·H2O, Fig. 1,
shows weight losses of 4.55 and 4.3% in temperature ranges
27–101 and 101–176 ◦C, corresponding to a loss of one
water lattice molecule and one coordinated water molecule,
respectively. [L2CuCl]·2H2O shows a weight loss of 10.0%
in the temperature range 27–112 ◦C which corresponds to
volatilisation of two lattice water molecules. The next de-
composition step of the two complexes, in the 176–392 ◦C
range, brings weight loss of about 38.54 and 40.25% which
correlate with elimination of 1/2Cl2 and decomposition of
the 2-thiohydantoin fragment. The remaining of ligand L1
(phenylazo moiety) is lost in the 382–637 ◦C range of the
two complexes with elimination of another 1/2Cl2 in case
of [L1CuCl2(H2O)]·H2O. The elimination of the chlorides
in two steps supports the presence of terminal and bridging
chloride ions in this complex. There is no further mass
loss beyond 637 and 607 ◦C for [L1CuCl2(H2O)]·H2O and
gll = 2.285 and 2.23, g = 2.07 and 2.065, respectively,
⊥
fitted using the procedure given by Hathaway and Billing
[19]. The fact that gll > g > 2.0 suggests an elongated
⊥
octahedral geometry for the two complexes and that the
unpaired electron is mainly in the dx2−y2 orbital, with pos-
sibly some dz2 character due to the low symmetry [20]. The
spectrum of [L1CuCl2(H2O)]·H2O shows an additional,
weak, half-field signal at 1587 G, due to ꢀMs = 2 transi-
tion, characteristic of magnetic interaction between copper
centers [21], which is further supported by the subnormal
magnetic moment (1.28 BM/Cu atom) of this complex.
The complex [L2CuCl]·2H2O gives an isotropic signal
at g = 2.12, in accordance with square-planar geometry
[17].
Based on the foregoing observations from elemental anal-
ysis, conductivity, magnetic moment and spectral studies,
the following tentative structures, Scheme 2, are proposed
for the present complexes.
Table 2
Thermal behaviour of metal complexes of 5-(phenylazo)-2-thiohydantoin, L1 and 5-(2-hydroxyphenylazo)-2-thiohydantoin HL2
Compound (molecular weight)
DTG peak
(◦C)
Temperature
range (◦C)
Decomposition product
lost (formula wt.)
Wt. (%) found (calculated)
[L1CuCl2(H2O)]·H2O (390.5)
72
139
352
557
27–101
1H2O (18)
1H2O (18)
1/2 Cl2 + C3H3N2OS (150.5)
1/2 Cl2 + C6H5N2 (140.5)
Residue; Cu metal (63.5)
4.3 (4.6)
4.3 (4.6)
38.45 (38.5)
35.5 (36.0)
17.2 (16.3)
101–176
176–382
382–632
632–800
[L1Cu(OAc)2(H2O)2]·H2O (455.5)
73
176
347, 450
588
725
25–100
1H2O (18)
2H2O (36)
4.0 (3.95)
7.7 (7.9)
37.8 (38.0)
22.8 (23.05)
9.6 (9.85)
100–236
236–481
481–640
640–760
760–800
(CH3)2CO + C3H3N2OS (173)
C6H5N2 (105)
CO2 (44)
Residue; CuO (79.5)
18.1 (17.45)
[L1Ni(OAc)2(H2O)2]·2H2O (468.7)
75.5
190
352
526
675.5
27–102
2H2O (36)
2H2O (36)
7.5 (7.7)
7.6 (7.7)
36.6 (36.9)
22.3 (22.4)
9.2 (9.4)
102–234
234–425
425–570
570–743
743–800
(CH3)2CO +C3H3N2OS (173)
C6H5N2 (105)
CO2 (44)
Residue; NiO (74.7)
16.1 (15.9)
[L2CuCl]·2H2O (370)
81
310
488
35–112
2H2O (18)
10.0 (9.7)
112–392
392–608
608–800
1/2 Cl2 + C3H3N2OS (150.5)
40.25 (40.7)
28.3 (28.1)
22.45 (21.5)
C6H4N2 (104)
Residue; CuO (79.5)
[L2Ni(OAc)(H2O)]·2H2O (406.7)
77
180
400
575
31–124
2H2O (36)
1H2O (18)
8.7 (8.85)
4.5 (4.4)
55.0 (53.6)
13.8 (14.5)
17.9 (18.4)
124–188
188–515
515–612
612–800
C3H3N2OS + C6H4N2 (218)
OAc (59)
Residue; NiO (74.7)
[L2Co(OAc)(H2O)]·2H2O (406.9)
80
200
320
519
36–129
2H2O (36)
1H2O (18)
C3H3N2OS (114)
C6H4N2 + OAc (163)
Residue; CoO (74.7)
8.7 (8.8)
4.85 (4.4)
28.8 (28.0)
38.8 (40.06)
19.0 (18.75)
129–225
225–385
385–625
625–800

S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
109
Fig. 1. TG and DTG curves of [L1CuCl2(H2O)]·H2O.
complex in the range 515–612 ◦C it represents loss of
acetate.
[L2CuCl]·2H2O; a plateau is obtained which corresponds
to the fomation of Cu and CuO, respectively.
The thermal decomposition curves of the [L1M(OAc)2
(H2O)2]·xH2O, M = Nill and Cull (Fig. 2 as a representative
example) show similar sequence of five decomposition steps
which could be correlated with elimination of the following
species:
In order to assess the influences of the structural prop-
erties of the ligand and the type of the metal on the ther-
mal behaviour of the complexes, the order, n, and the heat
of activation E# of the various decomposition stages were
determined from the TG and DTG themograms using the
Coats–Redfern equations in the following form:
(i) Lattice water molecules in the 25–120 ◦C range.
(ii) Coordinated water molecules in the100–236 ◦C range.
(iii) 2-Thiohydantoin moiety and acetone (resulting from
decomposition of the two acetate groups) in the
234–481 ◦C range.
ꢀ
ꢁ
1 − (1 − α)1−n
(1 − n)T2
M
T
ln
ln
=
+ B for n = 1
(1)
(2)
ꢀ
ꢁ
−ln (1 − α)
M
T
(iv) Phenylazo fragment (C6H4N2) in the 425–640 ◦C
range.
=
+ B for n = 1
T2
(v) Carbon dioxide in the 570–760 ◦C range.
where M = −E#/R and B = lnAR/ΦE#; E#, R, A and
Φ are the heat of activation, the universal gas constant,
pre-exponential factor and heating rate, respectively.
The correlation coefficient, r, was computed using the
least squares method for different values of n, by plotting
The TG curves of [L2M(OAc)(H2O)]·xH2O, {M = Coll
and Nill}, Fig. 3, show four steps. In the first step, loss
of lattice water occurs in the 31–129 ◦C range. The sec-
ond step, 124–225 ◦C, represents the loss of coordinated
water. In the case of the Coll complex, the decomposi-
tion of 2-thiohydantoin occurs in a separate third step
in the range 225–385 ◦C whereas in the case of the Nill
complex, this step is overlapped with decomposition of
phenylazo moiety in the temperature range 188–515 ◦C
on the TG curve. For the Coll complex the fourth step,
in the range 385–625 ◦C, represents decomposition of the
phenylazo moiety and the acetate group and for the Nill
the left-hand side of the Eqs. (1) and (2) versus 1000/T,
∼
Figs. 4–6. The n value which gave the best fit (r 1) was
=
chosen as the order parameter for the decomposition stage
of interest. From the intercept and linear slope of such stage,
the A and E# values were determined,. The other kinetic
parameters, ꢀH#, ꢀS# and ꢀG# were computed using the
relationships:ꢀH# = E#−RT, ꢀS# = R[ln(Ah/kT)−1] and
ꢀG# = ꢀH# −TꢀS#, where k is the Boltzmann’s constant

110
S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
Fig. 2. TG and DTG curves of [L1Cu(OAc)2(H2O)2]·H2O.
Fig. 3. TG and DTG curves of [L2Ni(OAc)(H2O)]·2H2O.

S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
111
Fig. 4. Coast–Redfern plots for [L1CuCl2(H2O)]·H2O: (a) first step; (b) second step; (c) third step; (d) fourth step; where Y = [1−(1−α)1−n/(1−n)T2]
for n = 1, or Y = [−ln(1 − α)/T2] for n = 1.
Table 3
Temperature of decomposition, order and activation parametersa of L1 and HL2 metal complexes
Complex
Step
T (K)
n
Aa
E#b
ꢀH#b
ꢀS#c
ꢀG#b
[L1CuCl2(H2O)]·H2O
1st
345
412
625
830
346
446
671.5
861
348.5
463
625
799
352
583
761.5
354
473
593
792
350
453
673
848
0
1
0.33
1
1
1
1
1
1
0.66
1
0
1
1
1
1
20529.13
73.7
10.3
44.16
36.70
42.67
35.30
36.12
47.32
53.11
142.95
37.05
57.90
63.49
109.54
72.97
39.98
96.30
39.03
77.50
45.97
114.445
27.34
68.79
35.83
86.41
41.27
33.27
37.45
28.38
33.23
43.59
47.51
135.78
34.15
57.9
63.49
109.54
70.03
35.11
89.94
36.07
73.56
41.02
107.83
25.02
65.01
30.21
79.33
−0.164
−0.212
−0.232
−0.242
−0.187
−0.192
−0.216
−0.128
−0.188
−0.157
−0.195
−0.165
−0.049
−0.229
−0.174
−0.181
−0.126
−0.229
−0.147
−0.212
−0.141
−0.253
−0.21
97.85
2nd
3rd
4th
1st
2nd
3rd
4th
1st
2nd
3rd
4th
1st
2nd
3rd
1st
2nd
3rd
4th
1st
2nd
3rd
4th
120.56
182.25
229.41
97.79
129.09
192.83
245.80
99.67
130.60
185.36
241.37
89.28
168.50
222.80
100.3
132.90
177.10
224.30
99.06
128.70
200.30
257.40
3.86
[L1Cu(Oac)2(H2O)2]·H2O
[L1Ni(OAc)2(H2O)2]·2H2O
1352.89
901.44
69.52
3.8 × 106
1106.55
60779
2986.96
139605
1.03 × 109
13.6
[L2CuCl]·2H2O
12222.1
2497.7
2.73 × 106
12.74
[L2Co(Oac)(H2O)]·2H2O
1
0
0.66
1
0.66
0.66
1
3.49 × 105
[L2Ni(OAc)(H2O)]·2H2O
65.12
4.3 × 105
0.88
212.7
a
Unit of A is s−1
.
b
c
Unit of E#, ꢀH# and ꢀG# is kJ mol−1
Unit of ꢀS# is kJ mol−1 K−1
.
.

112
S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
Fig. 5. Coats–Redfern plots for [L1Cu(OAc)2(H2O)2]·H2O.
Fig. 6. Coats–Redfern plots for [L2Ni(OAc)(H2O)]·2H2O.

S.S. Kandil et al. / Thermochimica Acta 414 (2004) 105–113
113
and h is the Planck’s constant. The kinetic parameters are
listed in Table 3. The following remarks can be pointed out:
(v) The reaction orders of the decomposition steps of the
complexes are 1, 0.66, 0.33 and zero. It was emphasized
that the reaction order of a solid-state decomposition
has no intrinsic meaning, but is rather a mathematical
smoothing device (parameter) [25].
(i) The negative values of the activation entropies ꢀS# in-
dicate a more ordered activated complex than the reac-
tants and/or the reactions are slow [22].
(ii) There are no obvious trends in the values of the heat of
activation E# or the activation enthalpies ꢀH#. How-
ever, the values of the activation energy ꢀG# increases
significantly for the subsequent decomposition stages
of a given complex. This is due to increasing the val-
ues of TꢀS# significantly from one step to another
which override the values of ꢀH#. Increasing the val-
ues of ꢀG# for the subsequent steps of a given com-
plex reflects that the rate of removal of the subsequent
ligand will be lower than that of the precedent ligand
[23,24]. This may be attributed to the structural rigidity
of the remaining complex after the explusion of one and
more ligands, as compared with the precedent complex,
which requires more energy, TꢀS#, for its rearrngement
before undergoing any compositional change.
References
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sition Met. Chem. 28 (2003) 168.
(iii) There is a conspicuous gap in the values of the
heat of activation E# and the enthalpy of activa-
tion ꢀH# of volatilisation of lattice water between
[L2CuCl]·2H2O (ꢀH# = 70.03 kJ mol−1) and the
two [L2M(OAc)(H2O)]·xH2O (ꢀH# = 36.07 and
25.02 kJ mol−1 for M = Co(II) and Ni(II), respec-
tively). This may be attributed to the packing structure
of [L2CuCl]·2H2O which may allow stronger interac-
tions of lattice water molecules in the crystal. However,
the values of the ꢀH# are compensated by the values
of the entropies of activation, leading to almost the
same values for the ꢀG# (89.28–100.30 kJ mol−1) for
this step of the three complexes.
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26A (1987) 698.
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Amsterdam, 1984.
[18] L. Sacconi, Transition Met. Chem. 4 (1968) 227.
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Pergmon Press, 1987, p. 663.
[21] K.K. Narang, V.P. Singh, Transition Met. Chem. 21 (1996) 507.
[22] A.A. Frost, R.G. Pearson, Kinetics and Mechanisms, Wiley, New
York, 1961.
[23] P.B. Maravalli, T.R. Goudar, Thermochim. Acta 325 (1999)
35.
(iv) The similar values of ꢀG# for the decomposition
steps involving the same decomposing species in the
octahedral complexes [L1M(OAc)2(H2O)2]·xH2O and
to some extent in the structurally similar complexes
[L2M(OAc)(H2O)]·xH2O, reveal that the mechanism
of decomposition is the same and the effect of the
ligands is more pronounced than that of the divalent
metals.
[24] K.K.M. Yusuff, R. Sreekala, Themochim. Acta 159 (1990)
357.
[25] D.B. Brown, E.G. Walton, J.C.S. Dalton (1980) 845.