A thermal analysis study of 1,2-dipiperidinoethane complexes of cobalt, nickel, copper, zinc and cadmium by TG-DTG-DTA techniques

Article abstract of DOI:10.1016/S0040-6031(00)00640-7

A number of complexes of the general formula ML(NO₃)₂, (M=Co(II), Ni(II), Cu(II), Zn(II) and Cd(II); L = 1,2-dipiperidinoethane (DPE)) were prepared and studied by means of TG-DTG-DTA techniques. Their compositions were investigated by elemental analysis in order to ensure their purity and structural elucidations were based on conductivity measurements, room temperature magnetic measurement, proton NMR, and IR spectra. Thermal decomposition of these distorted tetrahedral complexes and their ligand took place in two distinct steps upon heating up to 720 °C with the loss of inorganic and organic fragments and show almost the same mode of decomposition. The thermal degradation of all the complexes in static air atmosphere starts at temperature lower than observed for free ligand degradation. The composition of intermediates formed during degradation was confirmed by microanalysis and IR spectroscopy. The residues after heating above 600 °C correspond to metal oxide. It follows from the results that thermal stability of the complexes increases in the following sequence: Ni(II) < Co(II) < Cu(II) < Zn(II) < Cd(II). (C) 2000 Elsevier Science B.V.

Full text of DOI:10.1016/S0040-6031(00)00640-7

Thermochimica Acta 364 (2000) 143±153
A thermal analysis study of 1,2-dipiperidinoethane complexes
of cobalt, nickel, copper, zinc and cadmium
by TG±DTG±DTA techniques
a,*
Muhammad Arshad , Saeed-ur-Rehman , Shad Ali Khan ,
b
b
c
Khalid Masud , Nasima Arshad , Abdul Ghani
d
e
a
APD, PINSTECH, PO Nilore, Islamabad, Pakistan
b
Department of Chemistry, University of Peshawar, Peshawar, N.W.F.P., Pakistan
c
Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
d
Department of Chemistry, Allama Iqbal Open University, Islamabad, Pakistan
e
Miras International University, Shymkent, Kazakhstan
Received 25 February 2000; received in revised form 25 July 2000; accepted 29 July 2000
Abstract
A number of complexes of the general formula ML(NO
3
)
2
, (M ˆ CoꢀII†, Ni(II), Cu(II), Zn(II) and Cd(II);
L ˆ 1; 2-dipiperidinoethane (DPE)) were prepared and studied by means of TG±DTG±DTA techniques. Their compositions
were investigated by elemental analysis in order to ensure their purity and structural elucidations were based on conductivity
measurements. room temperature magnetic measurement, proton NMR, and IR spectra. Thermal decomposition of
these distorted tetrahedral complexes and their ligand took place in two distinct steps upon heating up to 7208C with the
loss of inorganic and organic fragments and show almost the same mode of decomposition. The thermal degradation of
all the complexes in static air atmosphere starts at temperature lower than observed for free ligand degradation. The
composition of intermediates formed during degradation was con®rmed by microanalysis and IR spectroscopy. The residues
after heating above 6008C correspond to metal oxide. It follows from the results that thermal stability of the complexes
increases in the following sequence: NiꢀII† < CoꢀII† < CuꢀII† < ZnꢀII† < CdꢀII†. # 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Thermoanalytical techniques; Nitrate complexes; 1,2-Dipiperidinoethane
1
. Introduction
and Cd(II), X ˆ Cl, Br and L ˆ 1; 3-dipiperidino-
propane (DPP) or 1,2-dipiperidinoethane (DPE)
[1,2]. We have also investigated their thermal proper-
ties [3±5] to understand the mechanisms of decom-
position and the nature of decomposition products. In
a previous paper, we have already described the pre-
paration, characterisation and thermal properties of
the complexes with the composition ML(NO ) ,
Much work is currently being carried out on the
preparation and characterisation of [M(L)X ] and
2
[
M(L)(NO ) ], where M ˆ CoꢀII†, Ni(II), Zn(II)
3
2
3
2
*
Corresponding author.
where M ˆ CoꢀII†, Ni(II), Cu(II), Zn(II) and Cd(II);
0040-6031/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 0 0 ) 0 0 6 4 0 - 7

1
44
M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
L ˆ CH ꢀCH NC H † (1,3-dipiperidinoproprane)
was left overnight to get dipiperidinoethane dihydro-
bromide crystals with a yield of 80%.
2
2
5
10 2
[
5].
2
.3. Preparation of ligand solution
The ligand 1,2-dipiperidinoethane dihydrobromide
was dissolved in minimum amount of methanol, to
which a calculated amount of alcoholic potassium
hydroxide was added. Potassium bromide, which pre-
cipitated immediately, was removed by ®ltration. The
®ltrate was used as ligand solution.
Thermogravimetry (TG) and differential thermal
2
.4. Synthesis of solid complexes
analysis (DTA) are valuable techniques for studying
the thermal properties of various compounds. How-
ever, no systematic study has been made of the thermal
behaviour for the metal complexes of 1,2-dipiperidi-
noethane. The preparation and characterisation of
these metal complexes by elemental analysis, IR
spectroscopy, UV visible spectroscopy, conductance
and magnetic susceptibility studies were reported ear-
lier [1]. This work is a continuation of the studies [3,5]
on the thermal decomposition of complexes formed
between transition metals and DPP. In the present
work, we describe the preparation, characterisation
and thermal properties of metal complexes of the type
M(DPE)(NO ) , where M ˆ CoꢀII†, Ni(II), Cu(II),
All the complexes reported were prepared using
similar general procedure. Approximately 10 mmol of
partially dehydrated salt was dissolved in minimum
amount of anhydrous solvent. Ethanol was used as
solvent for the synthesis of all the metal complexes.
The ligand (suf®cient to exceed a 1:2 ligand to metal
ratio) was also dissolved in minimum amount of the
same solvent and slowly added to the hot metal salt
solution with constant stirring. The mixture was stir-
red and kept at 508C for half an hour, then cooled for
about 20 min. The metal complexes precipitated either
immediately or on cooling. They were washed thrice
with ether and dried under vacuum at 508C.
3
2
Zn(II), Cd(II), and DPE ˆ 1; 2-dipiperidinoethane.
2
2
.5. Analysis procedures and instrumentation
2
. Experimental
.5.1. Elemental analysis
The metal contents were determined by reported
2
.1. Reagents
procedures [7,28], whereas nitrate ion are determined
by phenoldisulfonic acid method [8]. Carbon, hydro-
gen and nitrogen were determined with CHN analyser,
Carloerba Mod. 1106.
Salts of transition metals and other chemicals
obtained from standard source suppliers were of ana-
lytical grade and used without further puri®cation.
Solvents were distilled before use. The partial dehy-
dration of metal salts was carried out in vacuum oven
for several hours at 80±1008C.
2
.5.2. Infrared spectra
The infrared spectra of the complexes and those of
intermediates of their thermal decomposition were
recorded with PYE UNICAM infrared spectrophot-
ometer in the range 4000±400 cm using the KBr
discs.
2
.2. Synthesis of 1,2-dipiperidinoethane
�
1
The ligand was synthesised by the reported method
6]. Brie¯y, piperidine (0.25 mol) in absolute ethanol
40 ml) was added drop wise to 0.1 mol of 1,2-dibro-
[
(
2.5.3. UV and visible absorption spectra
Ultra violet and visible absorption spectra
of complexes were obtained on Jasco DEC-1
moethane in ethanol (20 ml). The contents were
re¯uxed for about 8 h at 808C. The reaction mixture

Table 1
Analytical data for 1,2-dipiperidinoethane and its metal complexes
Compound
Composition
Appearance
Decomposition
%C Found
%H Found
%N Found
Metal (%)
Anion (%)
point (8C)
a
±
DPE(HBr)
Co(DPE)(NO
2
White
340
207
179
210
241
266
40.33 (40.24)
38.22 (38.00)
38.27 (38.02)
37.09 (37.54)
37.15 (37.56)
33.13 (33.30)
7.75 (7.26)
6.21 (6.33)
6.55 (6.33)
6.49 (6.25)
6.97 (6.26)
5.67 (5.55)
7.56 (7.82)
±
±
I
3
)
2
Bluish green
Green
Green
15.09 (14.77)
15.13 (14.78)
14.85 (14.60)
14.31 (14.60)
13.23 (12.95)
15.37 (15.55)
15.27 (15.50)
16.26 (16.56)
16.37 (16.52)
25.72 (25.99)
32.49 (32.72)
32.41 (32.74)
32.06 (32.33)
32.39 (32.34)
28.13 (28.67)
II
III
IV
V
Ni(DPE)(NO
Cu(DPE)(NO
3
)
2
3
)
2
Zn(DPE)(NO
Cd(DPE)(NO
3
)
2
White
3
)
2
White
a
Figures in parentheses are the calculated values.

1
46
M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
Table 2
spectrophotometer with 1 cm matched quartz cells in
the range 200±900 nm using various solvents.
Values of molar conductance, magnetic moment for complexes,
M(DPE)(NO
3 2
)
2
.5.4. Mass and NMR spectra
Mass spectra of the ligand was measured on MAT
12 mass spectrometer, whereas proton NMR spectra
Complex
Solvent
Molar conductance
�
m
eff
(BM)
1
(
mS mol
)
a
3
I
DMSO
12.16
12.32
12.71
9.63
4.34
3.15
2.22
±
were recorded with Bruker (AM-300) instrument
using tetramethylsilane (TMS) as an internal standard.
Chemical shifts are reported as d (ppm) values.
II
DMSO
III
IV
V
Nitromethane
Acetone
Acetone
9.88
±
a
Dimethyl sulphoxide.
2
.5.5. Molar conductance
The molar conductance of the solution of com-
plexes was measured on a conductivity meter type
HI 8333. All the measurements were taken at room
temperature on freshly prepared solutions.
3. Results and discussion
The results of the elemental analysis (Table 1)
proved the expected composition of the complexes.
The proton NMR of 1,2-dipiperidinoethane in D O
2
.5.6. Magnetic susceptibilities
The magnetic susceptibilities data on the complexes
2
were determined by Guoy method at room tempera-
ture using Hg[Co(SCN) ] as standard. The magnetic
moments were calculated using Pascal's constants [9].
with TMS as internal standard showed a singlet at
1.55 ppm for terminal hydrogen, a singlet at 1.75 ppm
for eight hydrogens attached to the ring carbons, a
singlet at 3.20 ppm for eight hydrogens attached to the
ring carbons adjacent to nitrogen atoms and a singlet
for four ethyl hydrogens at 3.70 ppm. The IR spectrum
of DPE showed vibrations in the range 2990±
4
2
.5.7. Thermal measurement
The thermoanalytical measurements were carried
out with Netzsch simultaneous thermal analyser STA
29. Samples were contained in an aluminium cruci-
�
1
� 1
4
2880 cm
and 1228±1070 cm , which indicate
ble Al 203 (8 mm dia  10 mm depth) with central
base recess. The crucible was then adjusted on palla-
dium ruthenium crucible support platform, which
gave a proportional signal to the recorder and com-
puter interface to plot the weight loss of sample
against temperature.
the presence of C±H and C±N bonds in the molecule,
respectively [10,11]. A mass peak of moderate inten-
sity at m/z 196 corresponding to molecular ion
‡
(C H N ) was observed in the spectrum of DPE.
The base peak at m/z 98 is probably due to the
formation of N-methyl piperidine cation radical, while
12 24 2
Table 3
Maxima of absorption bands in electronic and IR spectra for DPE complex (m: medium, s: sharp, w: wide, vw: very wide, sh: shoulder)
Complex
Maxima of absorption bands
Electronic spectra
�
1
IR spectra (cm
)
�
1
)
� 1
� 1
l
max (nm)
n (cm
e
max (M cm
)
n (C±N)
I
655
05
645
15,270
24,690
15,500
19,610
15,040
14,600
22,470
±
367
57
1175m, 1165w, 1130vw, 1105s
4
II
158
243
177
52
1172m, 1165vw, 1135sh, 1112s
1175m, 1165vw, 1135sh, 1112vs
5
6
10
65
III
685
4
±
±
45
165
±
IV
V
1175w, 1165vw, 1135vw, 1110vs
1175m, 1165vw, 1138vw, 1110s
±
±

M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
147
�
1
the signals at m/z 112 could be assigned to N-ethyl
piperidine fragment due to loss of piperidine moiety,
which appeared at m/z 84. The ligand 1,2-dipiperidi-
noethane behaves as a bidentate ligand and bears
resemblance to 1,2-dimorpholinoethane (DME) [12±
and 1135 cm which are assigned to C±N stretching
vibrations, appear to have been split into four distinct
bands. The strong one moves to lower side and is
�
1
observed at about 1110 cm , whereas the other two
weak bands shift toward higher side and appear at
�
1
1
4]. The data shown in Table 1 indicate that only one
1175 and 1165 cm (Table 3). The shifts are almost
to the same extent with minor variation in position and
intensities. This is caused by the withdrawal of elec-
tron density from C to N bond, where nitrogen atom
becomes coordinated to the metal ion. Thus, DPE
behaves as bidentate ligand like substituted ethylene-
diamine coordinating through nitrogen atoms. The
molar conductance (Table 2) values, ranging from
9.63 to 12.32 mS mol , show that complexes are
non-electrolytic in these media and clearly indicate
that anions are coordinated with the metal atoms. The
magnetic moment of Co(II) complexes is 4.34 BM,
DPE molecule like DME is found to coordinate with
metal ion and form complexes of the general formula
M(DPE)(NO ) , where M ˆ CoꢀII†, Ni(II), Cu(II),
3
2
Zn(II), Cd(II), and DPE ˆ 1; 2-dipiperidinoethane.
The complexes are soluble in DMSO, CoL(NO ) ,
3
2
NiL(NO ) in acetone ZnL(NO ) , CdL(NO ) and
3 2
3
2
3 2
CuL(NO ) is soluble in nitromethane (Table 2). Infra-
3
2
�
1
red spectra of metal complexes clearly indicate that C±
N stretchings are shifted to lower and in some cases to
higher frequencies with changes in sharpness and
intensities. In these complexes the bands at 1150
2 5 10 2
Fig. 1. Thermal curves of (CH NC H ) in air atmosphere.

1
48
M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
which is characteristic value for the presence of three
unpaired electrons, while that for Ni(II) complex it is
electronic transition are consistent with C symmetry
2n
�
1
and are in the range 12,000±22,000 cm . Four transi-
tion are to be expected but only two were observed.
Similar spectra is observed for other copper(II) com-
plexes having CuN X chromophore vibrations [15].
3
.15 BM, indicating the presence of two unpaired
electrons. The value 2.22 is for Cu(II) complex, which
is characteristic for the presence of a single unpaired
electron. The solution spectra of Co(II) complex
exhibited two bands, which could be assigned to
2
2
The thermal curves (TG, DTG and DTA) of 1, 2-
dipiperidinoethane and its complexes were recorded in
static air atmosphere (Figs. 1±6) from ambient to
7208C. The characteristic data and stages of pyrolysis
regarding the thermal behaviour of ligand and its
complexes are given in Table 4. The TG and DTA
curves reveal that the ligand 1,2-dipiperidinoethane
decomposes in two steps in the temperature range
320±7208C (Fig. 1). In the ®rst step the ligand loses
piperidine and N-methylenepiperidine by the break-
age of C±N and C±C bonds around 320±4608C with an
accompanying endothermic effect and the intermedi-
ate is then decomposed exothermally in the tempera-
4
4
transition A ꢀF† ! T ꢀP†, for n in Td symmetry.
2
1
3
4
4
The low energy transition, A ꢀF† ! T ꢀP†, n was
2
2
2
not observed. The intensities and band widths are in
accordance with the Td symmetry [15]. The non-
electrolytic behaviour and high spin type magnetic
moments of 3.15 BM for Ni(II) complexes are clearly
indicative of Td coordination geometry with nitrate
ion as unidentate ligand and the strong bands observed
3
3
can be assigned to transition. A ꢀF† ! T ꢀP†, n in
1
1
3
tetrahedral symmetry [16]. The solution spectra of
copper nitrate complex exhibit only two bands. The
2 5 10 2 3 2
Fig. 2. Thermal curves of Co(CH NC H ) (NO ) in air atmosphere.

M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
149
2 5 10 2 3 2
Fig. 3. Thermal curves of Ni(CH NC H ) (NO ) in air atmosphere.
Table 4
Thermoanalytical results for the complexes, M(DPE)(NO
3
)
2
((� ), endothermic (‡), exothermic)
Compound
DTA peak temperature (8C)
TG, temperature range (8C)
Weight loss (%)
Phenomena
Calculated
Found
DPE
I
330(� ), 390(� )
320±460
460±720
200±330
330±600
>600
92.85
7.14
91.84
8.00
5 6 12
C H11N, C H N
4
68(‡)
±CH
2
±
310(� )
28.50
51.74
19.77
28.51
51.76
19.74
28.16
51.10
20.74
28.02
50.86
21.12
24.97
45.34
29.71
28.77
50.88
20.33
29.00
51.00
20.12
29.67
50.23
21.31
27.00
51.32
22.56
25.00
46.11
30.23
N
2C
CoO
2
O
5
5
±
70(‡)
6
H
12
N
N
N
N
N
II
372(� )
170±390
390±590
>590
200±380
380±580
>580
230±380
380±650
>650
260±390
390±600
>600
N
2C
2
O
5
5
70(‡)
6
H
12
12
12
12
±
NiO
III
IV
V
362(� )
N
2C
2
O
5
5
67(‡)
6
H
±
CuO
370(� )
N
2C
2
O
5
6
39(‡)
6
H
±
ZnO
370(� )
N
2C
2
O
5
5
77(‡)
6
H
±
CdO

1
50
M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
2 5 10 2 3 2
Fig. 4. Thermal curves of Cu(CH NC H ) (NO ) in air atmosphere.
ture range 460±7208C (second step) liberating methy-
lene group. The ®rst endothermic peak at about 3308C
may be attributed to the phase changes during the
melting and second sharp endothermic peak at 3908C
corresponds to the loss of two species. The second step
is slower one and corresponds to the oxidation and
vaporisation of methylene indicating that pyrolysis is
exothermic in nature. Heating of sample above 7008C
leaves no ®nal residue. The sequence of loss is com-
parable with mass spectrum [1,17]. The TG and DTA
curves reveal that the complexes decompose in two
stages. The TG curves show that ®rst stage involves
the loss of two nitrate radicals in the form of N O
3.1. Characteristic features of the thermal
decomposition of the complexes
(1) Co(DPE)(NO ) . The thermal decomposition of
3
2
this complex takes places in the temperature range
200±6008C (Fig. 2). The ®rst step involves decom-
position (200±3308C) in which the complex loses two
nitrate radicals in the form of N O . In the second
2
5
stage, the intermediate decomposes further with the
evolution of 1,2-dipiperidinoethane and leaves CoO as
®nal residue.
(2) Ni(DPE)(NO ) . The complex loses its nitrate
3
2
radicals in the temperature range 170±3908C and for
this decomposition the DTA curve shows one
endothermic peak at 3728C (Fig. 3). The intermediate
is not stable at this temperature, subsequently as the
temperature is raised, the complex decomposes further
and ®nally yields a residue of NiO.
2
5
[
5,18±21] for all the complexes. The second decom-
position stage involves one step, which appear as
exothermic peaks in the DTA curves. The residue left
in the crucible consists of corresponding metal oxide
[
22±24].

M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
151
2 5 10 2 3 2
Fig. 5. Thermal curves of Zn(CH NC H ) (NO ) in air atmosphere.
(
3) Cu(DPE)(NO ) . The nitrate radicals begin to
3
begins to decompose in two steps in the temperature
range 260±6008C (Fig. 6). Endothermic and exother-
mic peaks accompany the decomposition processes at
370 and 5778C, respectively. Heating the sample
above 6008C leaves the respective metal oxide as
residue.
On the basis of the observed thermal decomposition
studies, it can be inferred that all the complexes
undergo thermal decomposition in two steps accord-
ing to the following general equations:
2
come off in the temperature range 200±3808C (®rst
step). Further decomposition of the complex occurs in
second step in the range 380±5808C (Fig. 4). The
residue of the foregoing decomposition is CuO. The
DTA curve shows endothermic and exothermic peaks
at 362 and 5678C, respectively, corresponding to the
®
rst and the second step of the TG curve.
(
4) Zn(DPE)(NO ) . This complex loses two nitrate
3
2
radicals in the temperature range 230±3808C (Fig. 5)
and for this step of decomposition the DTA curve
shows a strong endothermic peak (3708C). In the
second stage of decomposition (380±6508C), another
peak at 6398C in the DTA curve indicates that this
decomposition stage is exothermic in nature. The end
product is ZnO.
MꢀCH2NC5H10† ꢀNO3†
2
2
! N O ‡ ‰MꢀCH NC H † Š
2
5
2
5
10 2
�
1
2
ꢀ
2NO3 ! N2O5 ‡ O2†
1
‰MꢀCH NC H † Š ‡ O ! MO ‡ 2CH NC H
2
5
10 2
2
2
5
10
2
(
5) Cd(DPE)(NO ) . When heated in a dynamic air
3 2
atmosphere, this complex is stable up to 2608C and
where M ˆ CoꢀII†; Ni(II), Cu(II), Zn(II) and Cd(II).

1
52
M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
2 5 10 2 3 2
Fig. 6. Thermal curves of Cd(CH NC H ) (NO ) in air atmosphere.
While comparing the thermal stabilities of com-
show almost a similar decomposition pattern with the
evolution of inorganic and organic fragments when
heated above 6008C leave corresponding metal oxides
as residue except for ligand, which behaves differ-
ently. Ligand appears to be more stable than the
complexes as it exhibits higher initial decomposition
temperature. The coordination of metal ion to ligand is
responsible for weakening of the system, that is why
complexes start losing weight at lower temperature
and at a faster rate and consequently, decomposition of
complexes is completed earlier than that of pure
ligand. The intermediate products are not stable over
a long range of temperature and decompose soon after
their formation. The source of oxygen in the formation
of residue (metal oxide) appears to have arisen from
the decomposition product and not from the atmo-
sphere [18,19]. Zinc and cadmium complexes show
greater thermal stability, probably owing to the lower
plexes on the basis of initial temperature of decom-
position [25,26], the following sequence of increasing
thermal stability was observed.
II < I < III < IV < V
The highest thermal stability is displayed by the
complex V. The solid residue comprised of 19±30% of
the initial mass and elemental analysis indicated that
these were pure metal oxides.
4
. Conclusion
The available experimental data allow us to suggest
that the prepared complexes of different metals as well
as ligand decompose in two step process. All the
complexes possessing distorted tetrahedral geometry

M. Arshad et al. / Thermochimica Acta 364 (2000) 143±153
153
[
10] R.M. Silverstein, G.C. Basler, T.C. Morrill, Spectroscopic
Identi®cation of Organic Compounds, 4th Edition, Wiley,
New York, 1981, p. 95.
distortion of the tetrahedral structure and the smaller
size of zinc and cadmium ions [27].
[
[
[
[
11] The Sadtler Standard Spectra, Vol. 5, Sadtler Research
Laboratories, Philadelphia, PA, 1974, p. 5991.
Acknowledgements
12] J. Steinhardt, S. Beychok, The Proteins, Vol. 2, 2nd Edition,
Academic Press, New York, 1964, p. 261.
The authors are indebted to Pakistan Atomic Energy
Commission for providing the facility of thermoana-
lytical techniques. Thanks are due to Nadeem Ahamd,
Irfan Waheed and Shahid Mahmood for extending
technical assistance.
13] M.S. Hussain, T. Ali, S.M. Ali, Pak. J. Sci. Ind. Res. 16 (3±4)
(
1973) 96.
14] M.S. Hussain, T. Ali, S.M. Ali, Pro. Pak. Acad. Sci. B 1
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[15] D.L. Wood, J.P. Pemeika, J. Chem. Phys. 46 (9) (1967) 3595.
(
[
[
16] A.D. Liehr, C.J. Ballhausen, Ann. Phys. 2 (1959) 134.
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