Thermal and spectral studies of 3-N-methyl-morpholino-4-amino-5-mercapto-1,2,4-triazole and 3-N-methyl-piperidino-4-amino-5-mercapto-1,2,4-triazole complexes of cobalt(II), nickel(II) and copper(II)

Article abstract of DOI:10.1016/S0040-6031(98)00548-6

Novel complexes obtained by 3-N-methyl-morpholino-4-amino-5-mercapto-1,2,4-triazole and 3-N-methyl-piperidino-4-amino-5-mercapto-1,2,4-triazole with Co(II), Ni(II) and Cu(II) have been synthesized and characterized by elemental analysis, electronic, IR, E

Full text of DOI:10.1016/S0040-6031(98)00548-6

Thermochimica Acta 325 (1999) 35±41
Thermal and spectral studies of 3-N-methyl-morpholino-4-amino-5-mercapto-
1,2,4-triazole and 3-N-methyl-piperidino-4-amino-5-mercapto-1,2,4-triazole
complexes of cobalt(II), nickel(II) and copper(II)
*
P.B. Maravalli, T.R. Goudar
P.G. Department of studies in Chemistry, Karnatak University, Dharwad-580 003, India
Received 2 September 1998; received in revised form 11 September 1998; accepted 15 September 1998
Abstract
Novel complexes obtained by 3-N-methyl-morpholino-4-amino-5-mercapto-1,2,4-triazole and 3-N-methyl-piperidino-4-
amino-5-mercapto-1,2,4-triazole with Co(II), Ni(II) and Cu(II) have been synthesized and characterized by elemental analysis,
electronic, IR, ESR and TG studies. TG studies of these complexes showed that thermal degradation proceeds in two steps.
Kinetic and thermodynamic parameters were computed from the thermal decomposition data. The activation energy of both
�
1
the thermal degradation steps is in the 0.22±44.67 kJ mol range. Based on the spectral and TG studies, an octahedral
geometry can be proposed for the above complexes. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Complexes; Synthesis; Thermal degradation; Thermodynamic; Thermogravimetry
1
. Introduction
and thermal studies of new cobalt(II), nickel(II) and
copper(II) complexes derived from 3-N-methyl-mor-
pholino-4-amino-5-mercapto-1,2,4-triazole
In recent years, there has been considerable interest
in the complexes formed by oxadiazole, triazole and
related ligands as they are common components of
some important biological molecules [1,2]. Further-
more, triazoles have been reported to possess a wide
range of biological activities, including antibacterial,
antifungal, antitumour and antiviral [3±6].
(MMAMT) and 3-N-methyl-piperidino-4-amino-5-
mercapto-1,2,4-triazole(MPAMT). Kinetic and ther-
modynamic parameters have been calculated using
Broido's relation [14].
Thermal decomposition parameters, such as E, ln A,
#
2. Experimental
#
#
ÁH , ÁS and ÁG have been derived for transition-
metal complexes of various classes of organic ligands
[
All the chemical and solvents used were of AR
grade.
7±13]. However, very little work has been done on
triazole±metal complexes of transition elements.
Hence, the present paper reports the synthesis, spectral
2.1. Synthesis of ligands
The ligands 3-N-methylmorpholino-4-amino-5-
mercapto-1,2,4-triazole (MMAMT) and 3-N-methyl-
*
Corresponding author. Fax: +1-91-836 747884; e-mail:
Karuni@bom2.vsnl.net.in
0040-6031/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 4 0 - 6 0 3 1 ( 9 8 ) 0 0 5 4 8 - 6

3
6
P.B. Maravalli, T.R. Goudar / Thermochimica Acta 325 (1999) 35±41
percentage mass loss as a function of temperature. The
number of decomposition steps were identi®ed using
DTG. The activation energy (E ) and frequency factor
a
(ln A) of the degradation process were obtained by
Broido's method [14].
3
. Results and discussion
All the prepared complexes are crystalline, non-
hygroscopic, insoluble in non-polar solvents. How-
ever, they are soluble in polar solvents like DMF and
DMSO. The molar conductance values fall in the
Fig. 1. Structure of ligands MMAMT and MPAMT.
�
1
�1
2
piperidino-4-amino-5-mercapto-1,2,4-triazole
MPAMT) (Fig. 1) were prepared and puri®ed accord-
ing to the methods reported in the literature [15].
2.54±9.78 ꢀ mol cm range which suggests the
non-electrolytic nature of the complexes. The analy-
tical data reveals 1 : 1 stoichiometry between metal : -
ligand (Table 1). The magnetic moment data of
Co(II), Ni(II) and Cu(II) complexes shown in Table 1
reveals distorted octahedral geometry. However, the
subnormal magnetic moment in Cu(II) complex indi-
cates copper±copper interaction leading to polymeric
nature [17,18].
(
2
.2. Synthesis of complexes
Metal(II) chloride (0.01 mol) was treated with the
ligand (0.01 mol) in alcoholic medium. The reaction
mixture was re¯uxed for about one hour and then 2 g
of sodium acetate was added to the reaction mixture
and re¯uxed for ca. 3 h. The separated complex was
®
ltered, washed with aqueous alcohol followed by
3.1. Electronic spectra
absolute alcohol and ®nally dried in vacuum over
fused calcium chloride.
The electronic spectra of Co(II) complexes shows
two d-±d bands in the 19 600±20 830 and 7849±
�
1
2
.3. Analytical methods
8130 cm
4
ranges which could be assigned to
4
T (P) T1g(F) and T (F) T1g(F) transitions
4
4
1g
2g
Metal in the complexes were analysed according to
the standard procedures [16]. Magnetic moments were
measured using Gouy balance. Conductance measure-
con®rming octahedral geometry for these complexes
[19].
The visible spectrum of the nickel(II) complexes
�
3
�1
ments were made using 10 M solutions of the
complexes in DMF with the help of Elico conductivity
bridge type CM-82. IR spectra of the ligands and the
corresponding complexes were recorded in Nicolet
Impact 410 spectrophotometer using KBr pellets. A
Hitachi 150-20 spectrophotometer was used for
recording the electronic spectra. The ESR spectra
were recorded on a EPR-E-4 spectrometer, operating
in the x-band region with TCNE as the reference
material at 300 and 77 K. Thermal studies were
carried out with a Rigaku TAS-100 Model thermal
analyser. A 5±8 mg pure sample was subjected to
exhibits three bands at 8696±8969 cm , 14 368±
�
1
15 267 cm and 23 529±24 096 cm , attributed to
�1
3
the transitions T (F) A (F), T (F) A2g(F) and
3
3
3
2g
2g
1g
3
3
T (P) A2g(F), respectively. This reveals the octa-
1g
hedral geometry around nickel(II) ion [20]. The elec-
tronic spectra of copper(II) complexes show a very
broad band of low intensity in the 17 200±
�
1
17 391 cm region, which can be assigned to the
2
2
T2g E transition. In addition to this band, another
g
�
1
band is also seen in the 23 529±24 691 cm region.
This band is due to symmetry forbidden ligand!
�
1
metal charge transfer. The band above 27 000 cm
�
1
dynamic TG scans at a heating rate of 108C min
in an air atmosphere, in the temperature range from
is assigned as ligand band. Distorted octahedral
structures are proposed on the basis of electronic
spectra.
ambient to 9008C. The TG curves were analysed as

P.B. Maravalli, T.R. Goudar / Thermochimica Acta 325 (1999) 35±41
37
Table 1
Analytical, magnetic and conductivity data of Co(II), Ni(II) and Cu(II) complexes with MMAMT and MPAMT
S. No.
Complex
Elemental analysis %
Molar
conductance,lM
Magnetic
moment
(
mB)
� �1
1
2
C
H
N
S
Cl
10.25
M
ꢀ
mol cm
1
2
3
4
5
6
[Co(MMAMT)ClÁ2H
2
O]
24.46
3.62
20.28
9.18
16.94
2.54
7.74
2.17
8.76
6.41
9.78
4.30
3.10
1.32
4.27
2.93
0.86
(
24.38)
(3.48)
(20.33)
(9.28)
(10.39)
(17.12)
[Ni(MMAMT)ClÁ2H
2
O]
24.70
3.84
(3.48)
20.42
(20.34)
9.25
(9.39)
10.64
(10.36)
17.24
(17.05)
(
(
(
(
(
24.42)
[Cu(MMAMT)ClÁH
2
O]
25.46
3.42
(3.65)
20.42
(21.19)
9.60
(9.66)
10.55
(10.72)
19.12
(19.30)
25.36)
[Co(MPAMT)ClÁ2H
2
O]
28.12
3.90
27.98
9.38
10.24
17.16
28.09)
(4.09)
(20.46)
(9.40)
(10.37)
(17.22)
[Ni(MPAMT)ClÁ2H
2
O]
28.36
4.18
20.82
9.30
9.78
18.02
28.07)
(4.09)
(20.46)
(9.40)
(10.37)
(18.12)
[Cu(MPAMT)ClÁH
2
O]
28.92
4.12
20.65
9.65
10.56
20.24
29.19)
(4.00)
(21.27)
(9.72)
(10.79)
(19.46)
3
.2. Infrared spectra
The ligands MMAMT and MPAMT show resolved
methine groups to the metal atom through nitrogen
�
1
which results in a shift of the 1579 cm band due to
higher wave number. The band due to ꢀ(C=S) would
shift towards lower wave numbers on complexation.
Both these effects are actually observed since the
thioamide band which has a major contribution from
ꢀ(C=N) and a minor contribution from ꢀ(C±N), appear-
�
1
bands at 3271, 3141 and 2570 cm . These bands have
been assigned to ꢀ(NH) and ꢀ(SH) [15] modes, respec-
tively. The high intensity bands in the 1622±
1
assigned to >C=N stretching frequencies. The two
strong bands at 1510 and 1307 cm
respectively assigned to thioamide bands [21] I and
II. A medium-intensity band at 900 cm is assigned
to N±N stretching vibration. The thioamide band IV
which is mainly due to >C=S stretching vibration is
�
1
�1
604 cm
and 1579±1567 cm
regions can be
�
1
ing at 1307 cm , in the spectrum of the ligand, shifts
�1
�
1
have been
by 60 cm
complexes. The thioamide at 750 cm in the ligand,
towards higher wave numbers in the
�
1
�
1
�1
which is mostly due to ꢀ(C=S), shifts by 80±70 cm
towards lower wave numbers on complexation [22].
�
1
observed at 750 cm
.
3.3. Electron spin resonance spectra
The IR spectra of metal(II) complexes with the
above-mentioned ligands show a broad band around
3
water. The NH stretching frequencies observed at
In the ESR spectra, from the observed `g' values of
Cu(II) complexes at LNT (g ˆ2.289, g ˆ2.103), it is
�
1
430 cm which is due to ꢀ(OH) of coordinated
k
evident that the unpaired electron is predominantly in
?
�
1
271 cm in the ligand has shifted to 3221 cm
�1
3
in the complexes suggesting the coordination of amino
group to metal(II) ion. The ꢀ(C=N) vibration observed
d
being mixed with it because of low symmetry. The g
2
2
orbital with the possibility of some dz character
2
x �y
k
value (g ˆ2.289<2.3) indicates a larger percentage of
k
�
1
in the 1622±1604 and 1579±1567 cm regions in the
spectrum of the ligand show some changes in the
complexes. A broad band, with halfwidth ca.
70 cm is observed around 1630 cm . This obser-
vation indicates the coordination of one of the azo-
covalency. The G value (Gˆ2.8) of less than four
concludes interaction between copper centres, which
is further supported by the subnormal magnetic
moment. The relation g >g >2.0 in the present case
�
1
�1
k
?
suggests an elongated octahedral geometry [23].

3
8
P.B. Maravalli, T.R. Goudar / Thermochimica Acta 325 (1999) 35±41

P.B. Maravalli, T.R. Goudar / Thermochimica Acta 325 (1999) 35±41
39
Fig. 2. Plots of ln (ln 1/y) vs. 1/T for the first degradation process of: (A) [Co(MMAMT)ClÁ2H
2
O]; (B) [Ni(MMAMT)ClÁ2H
2
O]; (C)
[
Cu(MMAMT)ClÁH O]; (D) [Co(MPAMT)ClÁ2H O]; (E) [Ni(MPAMT)ClÁ2H O]; and (F) [Cu(MPAMT)ClÁH
2
2
2
2
O].
3
.4. Thermal analysis
The temperature of decomposition, the pyrolysed
1/T (where y is the fraction not yet decomposed) for
different stages of the thermal degradation process of
the complexes were identi®ed and are shown in Figs. 2
and 3. Fig. 2 represents the ®rst step of degradation
and Fig. 3 the second.
products, the percentage mass loss of the ligands, and
the percent ash are given in Table 2.
All the complexes decompose in two steps. The ®rst
step, 35±3108C, brings about a mass loss ranging
between 16.2 and 20.1%. This loss corresponds to a
loss of one coordinated water and chloride as HCl. In
the second step of decomposition the ligand is lost in
the 211±8508C range. There is no further mass loss
beyond 8508C and a plateau is obtained which corre-
sponds to the formation of a stable metal oxide. It
agrees well with analytical results within the experi-
mental errors.
In order to determine the thermal stability trend, the
parameters T , T , Tmax, the activation energy (Ea)
and the frequency factor (ln A), were evaluated and are
0
10
given in Table 3. The thermodynamic parameters,
#
#
enthalpy (ÁH ), entropy (ÁS ) and free energy
#
(ÁG ) of activation were calculated using standard
equations and the values are given in Table 4.
#
The ÁS values were found to be negative, which
indicates a more ordered activated state that may be
possible through the chemisorption of oxygen and
other decomposition products [24]. The values of
activation energy for the second stage of decomposi-
tion were found to be higher than that for the ®rst stage
which indicates that the rate of decomposition of the
second stage is lower than that of ®rst stage. This may
be attributed to the structural rigidity of the ligand, 3-
N-methyl-morpholino-4-amino-5-mercapto-1,2,4-tri-
azole and 3-N-methyl-piperidino-4-amino-5-mer-
The measured curves obtained during TG scans
were analysed to give the percentage mass loss as a
function of temperature. T (temperature of onset of
0
decomposition), T10 (temperature for 10% mass loss)
and Tmax (temperature of maximum mass loss) are the
main criteria to indicate the thermal stability of the
complexes. The higher the values of T , T and Tmax
0
,
10
the higher the thermal stability.
Broido's method was used to evaluate the kinetic
parameters from the TG curve. Plots of ln (ln 1/y) vs.
capto-1,2,4-triazole, as compared with H O and Cl,
2
which requires more energy for its rearrangement

4
0
P.B. Maravalli, T.R. Goudar / Thermochimica Acta 325 (1999) 35±41
Fig. 3. Plots of ln (ln 1/y) vs. 1/T for the second degradation process of: (A) [Co(MMAMT)ClÁ2H
2
O]; (B) [Ni(MMAMT)ClÁ2H
2
O]; (C)
[
Cu(MMAMT)ClÁH O]; (D) [Co(MPAMT)ClÁ2H O]; (E) [Ni(MPAMT)ClÁ2H O]; and (F) [Cu(MPAMT)ClÁH
2
2
2
2
O].
before undergoing any compositional change. Further,
it is generally observed that stepwise formation con-
stants decrease with an increase in the number of
ligands attached to the metal ion [25]. During the
decomposition reactions a reverse effect may occur.
Hence, the rate of removal of the remaining ligands
will be smaller after the expulsion of one or two
ligands [26].
Table 3
Data obtained from TGA analysis: temperature characteristics, activation energies and frequency factors of the decomposition process
�
1
�1
ln [A/min ]
Complex
T
0
/8C
T10/8C
T
max/8C
Process
E
a
/(kJ mol
)
[
[
[
[
[
[
Co(MMAMT)ClÁ2H
2
O]
40
35
40
40
50
70
210
125
220
98
640
580
688
850
580
720
I
0.95
4.34
9.17
II
12.44
Ni(MMAMT)ClÁ2H
2
O]
I
1.66
5.14
9.25
II
12.12
Cu(MMAMT)ClÁH
2
O]
I
1.53
14.67
5.02
9.90
II
Co(MPAMT)ClÁ2H
2
O]
I
2.17
27.52
5.60
13.02
II
Ni(MPAMT)ClÁ2H
2
O]
220
285
I
1.14
4.56
5.91
II
30.63
Cu(MPAMT)ClÁH
2
O]
I
0.22
2.60
II
44.67
16.94

P.B. Maravalli, T.R. Goudar / Thermochimica Acta 325 (1999) 35±41
41
Table 4
Thermogravimetric parameters for the thermal degradation of the process
#
ÁH /(kJ mol
�1
#
ÁS /(J K mol
�1
�1
#
ÁG /(kJ mol
�1
Complex
Process
)
)
)
[
Co(MMAMT)ClÁ2H
2
O]
I
�2.26
�150.90
�126.82
56.13
87.46
II
7.18
[
Ni(MMAMT)ClÁ2H
2
O]
I
�1.35
7.26
�149.41
�126.77
�149.69
�122.89
50.67
81.42
52.85
82.96
II
I
[
Cu(MMAMT)ClÁH
2
O]
�1.48
9.72
II
[
[
[
Co(MPAMT)ClÁ2H
2
O]
I
�0.76
�147.99
�100.63
51.47
84.85
II
22.36
Ni(MPAMT)ClÁ2H
2
O]
I
�1.75
�151.57
�87.73
51.47
80.11
II
25.45
Cu(MPAMT)ClÁH
2
O]
I
�3.50
�152.25
�73.85
64.70
84.06
II
39.67
[
[
11] N.S. Bhave, V.S. Iyer, J. Therm. Anal. 32 (1987) 1369.
12] N. Calu, L. Odochian, G.L. Brinzan, N. Bilba, J. Therm.
Anal. 30 (1985) 547.
The values of the entropy for all degradation steps
of all the complexes are negative. The enthalpies of
activation are negative for the ®rst step and positive for
the second. However, the negative values of the
entropies of activation are compensated by the values
of the enthalpies of activation, leading to almost the
[
13] H.S. Bhojya Naik, Siddaramaiah, P.G. Ramappa, Thermo-
chim. Acta, 2998 (1996).
[14] A. Broido, J. Polym. Sci., Part A-2 7 (1969) 1761.
[
[
[
[
15] M.C. Hosur, M.B. Talawar, S.C. Bennur, Indian J. Chem. 34B
(1995) 707.
�
1
same values (50.67±87.46 kJ mol ) for the free ener-
gies of activation.
16] A.I. Vogel, A Text Book of Quantitative Inorganic Analysis,
Longmans Green, London, 1968.
17] B.C. Bahl, B.L. Dubey, N. Nath, A. Tripathi, J.K. Srivastav, J.
Indian Chem. Soc. 59 (1982) 1127.
References
18] R.C. Varma, K. Varma, R.K. Varma, N.C. Bhattacharjee, J.
Indian Chem. Soc. 69 (1992) 577.
[
[
[
1] V. Dwivedi, R.K. Agarwal, Indian J. Pharm. Sci. 53 (1991)
2.
[19] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elserier,
New York, 1968, pp. 333.
8
2] L. Mishra, V.K. Singh, N.K. Dubey, A.K. Mishra, Biosci.
Biotech. Biochem. 57 (1993) 989.
[20] C.J. Ballhausen, Introduction to Ligand Field Theory,
McGraw Hill, New York, 1962.
3] P.H. Freeman, P.A. Worthington, W.G. Rathmell, Eur. Pat.
Appl. EP 0044, (1982) 407.
[21] B.M. Badiger, S.A. Patil, S.M. Kudari, V.H. Kulkarni, Revue
Roumaine de Chimie 31 (1986) 849.
[
[
[
[
4] J.L. Hilton, J. Agric. Food Chem. 17 (1969) 182.
5] C.K. Joshi, K. Dubey, Phamazie 34 (1979) 801.
6] L. Mishra, M. Kamil Said, Indian J. Chem. 35A (1996) 304.
7] R.K. Agrawal, S.C. Rastogi, Thermochim. Acta 63 (1983)
[22] B.K. Gupta, D.S. Gupta, S.K. Dikshit, U. Agarwala, Indian J.
Chem., 15A (1987) 1021.
[23] G. Wilkinson, Comprehensive Coordination Chemistry,
Pergmon press, 5 (1987) 663.
3
63.
[24] P.M. Madhusudanan, K.K.M. Yusuff, C.G.R. Nair, J. Therm.
Anal. 8 (1975) 31.
[
8] V.V. Savant, P. Ramamurthy, C.C. Patel, J. Less Common
Metals 22 (1970) 479.
[25] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry,
Wiley Interscience, New York, 1988.
[
9] A.K. Srivastava, S. Sharma, R.K. Agrawal, Inorg. Chim. Acta
1 (1982) 235.
6
[26] K.K.M. Yusuff, R. Sreekala, Thermochim. Acta 159 (1990)
357.
[
10] K. Arora, Asian J. Chem. 7 (1995) 508.