Synthesis and thermal decomposition of new complexes of bipyridine isomers with zinc(II) and cadmium(II) oxalates

Article abstract of DOI:10.1023/A:1010145223514

The new mixed ligand complexes with the formulae Zn(2-bipy)(ox), Zn(4-bipy)_1.5(ox)·H₂O, Zn(2,4′-bipy)₂(ox)·2H₂O, Cd(2-bipy)(ox)·2H₂O, Cd(4-bipy)2(ox) and Cd(2,4′-bipy)(ox)·2H₂O (2-bipy, 4-b

Full text of DOI:10.1023/A:1010145223514

Journal of Thermal Analysis and Calorimetry, Vol. 60 (2000) 151–156
SYNTHESIS AND THERMAL DECOMPOSITION
OF NEW COMPLEXES OF BIPYRIDINE ISOMERS WITH
ZINC(II) AND CADMIUM(II) OXALATES
D. Czakis-Sulikowska, A. Malinowska and M. Markiewicz
Institute of General and Ecological Chemistry, Technical University of £ódŸ, 90-924 £ódŸ, Poland
Abstract
The new mixed ligand complexes with the formulae Zn(2-bipy)(ox), Zn(4-bipy)1.5(ox)H2O,
Zn(2,4’-bipy)2(ox)2H2O, Cd(2-bipy)(ox)2H2O, Cd(4-bipy)2(ox) and Cd(2,4’-bipy)(ox)2H2O
(2-bipy, 4-bipy, 2,4’-bipy=2,2’-, 4,4’- and 2,4’bipyridine, ox=oxalate) were prepared. The thermal
decompositions of these compounds were studied by means of TG, DTG and DTA in air. During
heating the complexes decompose via different intermediate products to ZnO and CdO. The Zn(II)
complexes are thermally more stable than the corresponding Cd(II) complexes. The influence of
nitrogen atom position in the bipyridine isomers and nature of central atom on the thermal behav-
iour of these complexes was discussed.
Keywords: bipyridine-oxalato complexes, cadmium(II), thermal decomposition, zinc(II)
Introduction
This paper is a continuation of the research on Zn(II), Cd(II) complexes with the
bipyridine isomers [1]. The mixed bipyridine-oxalato complexes with Zn(II) and
Cd(II) are unknown. Recently only several studies of synthesis and characterization
of mixed 2,2’-bipyridine-oxalato complexes with Mn(II), Fe(II), Fe(III) and Cu(II)
have been published [2–5].
The object of the present investigation was to obtain in pure form of the solid state
of the mixed bipyridine-oxalato complexes of zinc(II) and cadmium(II) (bipyri-
dine(bipy)=2,2’-bipyridine(2-bipy), 4,4’-bipyridine(4-bipy) or 2,4’-bipyridine-
(2,4’-bipy)) and to study their thermal decomposition in air atmosphere. It was interesting
to examine the influence of the position of the nitrogen atoms in the bipyridine isomers
and the nature of the central atom on thermal behaviour of the isolated complexes.
Experimental
Solutions for synthesis
Water solutions of oxalate complexes of Zn(II) and Cd(II): 4.3 mmol of Zn(ox)2H2O
(ox=C2O24– ) in 70 cm3 of 0.4 M K2(ox) solution with 0.1 cm3 of 0.5 M H2(ox) solution;
1418–2874/2000/ $ 5.00
Akadémiai Kiadó, Budapest
© 2000 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

152
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE ISOMERS
4.3 mmol Cd(ox) in 100 cm3 of 1.0 M K2(ox) solution with 0.1 cm3 of 0.5 M H2(ox) solu-
tion. Solutions of bipyridine: 8.6 mmol of 2-bipy or 4-bipy in 10 cm3 of 96% v/v ethanol;
8.6 mmol of 2,4’-bipy in 10 cm3 water with 0.2 cm3 of 96% v/v ethanol. 2-Bipy, 4-bipy
and 2,4’-bipy were obtained from Aldrich; other chemicals were p.a. products from
POCh-Gliwice.
The mixed bipyridine-oxalato complexes of Zn(II) and Cd(II) were prepared by re-
acting solutions of oxalate complexes of these metals (M) with suitable isomers of
bipyridine dissolved in ethanol or water. The resulting mixtures were heated to 80°C for
ca 10 min. The precipitates were formed immediately. They were filtered off, washed
with 40% v/v ethanol, then with ethanol and diethyl ether mixture (1:1). The products
were dried in room temperature.
The apparatus, measuring conditions and analyses were the same as described in
our previous papers [1, 6].
Results and discussion
The new mixed bipyridine-oxalato complexes of Zn(II) and Cd(II) with the empirical
formulae Zn(2-bipy)(ox), Zn(4-bipy)1.5(ox)H2O, Zn(2,4’-bipy)2(ox)2H2O,
Cd(2-bipy)(ox) 2H2O, Cd(4-bipy)2(ox) and Cd(2,4’-bipy)(ox)2H2O in the solid state
were obtained. Chemical analysis confirmed the theoretical composition with 0.0÷0.3%.
All complexes are stable air in room temperature. The data for the TG, DTG and DTA
curves of these compounds are given in Table 1. The decomposition products obtained
during heating were established from thermoanalytical curves and confirmed by chemi-
cal analysis together with the X-ray diffraction pattern investigations. The thermal curves
of bipyridine-oxalato complexes with Cd(II) are presented, as an example, in Fig. 1.
Fig. 1 Thermoanalytical curves of a – Cd(2-bipy)(ox)2H2O; b – Cd(4-bipy)2(ox);
c – Cd(2,4’-bipy)(ox)2H2O
J. Therm. Anal. Cal., 60, 2000

CZAKIS-SULIKOWSKA et al.: BIPYRIDINE ISOMERS
153
Table 1 Thermal decomposition data for the mixed bipyridine-oxalato complexes with zinc(II)
and cadmium(II) in air
Mass loss/%
Trange
°C
/
DTApeak
°C
/
Intermediate and
residue
Complex
found calcd.
ZnO with
ca 2% Zn(ox)
Zn(2-bipy)(ox)
310–410
380 endo
71.5
73.72
>590
2.0
23.0
57.0
7.0
ZnO
Zn(4-bipy)1.5(ox)H2O
218–280
310–410
55–108
120–270
268 endo
360 endo
90 endo
23.69 Zn(4-bipy)(ox)
56.25 ZnO
Zn(2,4’-bipy)2(ox)2H2O
7.18 Zn(2,4’-bipy)2(ox)
31.12 Zn(2,4’-bipy)(ox)
210 endo
30.5
Zn(ox) with
31.12
270–340
320 endo
37.5
ca 6% ZnO
340–590
155–240
560 exo
8.5
9.5
14.35 ZnO
Cd(2-bipy)(ox)2H2O
Cd(4-bipy)2(ox)
218 endo
9.18 Cd(2-bipy)(ox)
CdO with
58.12
280–380
365 exo
58.5
traces of CdCO3
600
CdO
140–215
215–295
205 endo
285 endo
14.5
15.5
15.23 Cd(4-bipy)1.5(ox)
15.23 Cd(4-bipy)(ox)
CdO with
44.50
295–360
342 exo
43.5
traces of CdCO3
600
CdO
Cd(2,4’-bipy)(ox)2H2O
65–125
130–170
170–242
118 endo
165 endo
238 endo
5.0
4.5
4.59 Cd(2,4’-bipy)(ox)H2O
4.59 Cd(2,4’-bipy)(ox)
19.89 Cd(2,4’-bipy)0.5(ox)
17.0
mixture of Cd(ox)
with CdCO3 and
traces of CdO
242–345
330 exo
370 exo
27.0
345–400
600
5.5
7.0
32.62 CdCO3CdO
5.61 CdO
In the first stage of thermal decomposition of the hydrated bipyridine-oxalato com-
plexes liberation of water takes place. The Zn(2,4’-bipy)2(ox)2H2O and Cd(2-bipy)(ox)
2H2O lose all water in one step. The Zn(4-bipy)1.5(ox)H2O is very stable, in temperature
range 218–280°C 1 mol of H2O and 0.5 mol of 4-bipy are eliminated. The complex
Cd(2,4’-bipy)(ox)2H2O undergoes dehydration in two stages. The hydrated 2,4’-bipyri-
dine-oxalato complexes with Zn(II) and Cd(II) are very unstable and begin to lose water
at 55–65°C. The endothermic effects connected with dehydration are observed for all hy-
drated bipyridine complexes.
J. Therm. Anal. Cal., 60, 2000

154
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE ISOMERS
The anhydrous transient bipyridine-oxalato complexes and prepared complex
Cd(4-bipy)2(ox) decompose to give intermediate compounds of type M(bipy)(ox). The
complexes Zn(2-bipy)(ox) and Zn(4-bipy)(ox) transformed endothermically to ZnO
(DTA peak at 380 and 360°C, respectively). The complexes Cd(2-bipy)(ox) and
Cd(4-bipy)(ox) undergo decomposition to CdO via mixture of CdO with traces of
CdCO3 and the exothermic peaks are observed at 365 and 342°C. The pure CdO level be-
gins at ca 600°C. The X-ray diffraction patterns indicate CdO in the decomposition prod-
uct of Cd(4-bipy)2(ox) heated up to 600°C [7]. The intermediate compound
Zn(2,4’-bipy)(ox) eliminated 1 mol of 2,4’-bipy and gives ZnO with ca 6% ZnO. A con-
stant mass for pure ZnO begins at 590°C (small exothermic peak at 560°C). However,
complex Cd(2,4’-bipy)(ox) deaminates in two stages. In the temperature range
242–345°C, the last portion of diamine is split off and decomposition of cadmium oxa-
late begins. During this decomposition a mixture of cadmium oxalate and carbonate with
traces of oxide is formed. Then, latter mixture is converted into CdO CdCO3 at 400°C.
The DTA curve exhibits exothermic peaks at 330 and 370°C, associated with these pro-
cesses. A plateau in the TG curve begins at 600°C, corresponding to the formation of
pure CdO.
The thermal stabilities of hydrated bipyridine-oxalato complexes are as follows:
Zn(4-bipy)1.5(ox)H2O>Zn(2,4’-bipy)2(ox)2H2O and Cd(2-bipy)(ox)2H2O
>Cd(2,4’-bipy)(ox)2H2O. These sequences result from the temperature relating to the
first decomposition process.
The influence of central atom and nature of bipyridine isomers on thermal de-
composition of the studied complexes can be illustrated by scheme for the complexes
of Zn(II)
a)with ca 2% Zn(ox), b)with ca 6% ZnO; and scheme for complexes of Cd(II)
c)with traces of CdCO3, d)with CdCO3 and traces of CdO
J. Therm. Anal. Cal., 60, 2000

CZAKIS-SULIKOWSKA et al.: BIPYRIDINE ISOMERS
155
DTA curves show that the decompositions of Zn(2-bipy)(ox) and Zn(4-bipy)(ox) to
ZnO are endothermic, whereas the decomposition of Zn(ox) (formed as intermediate of
Zn(2,4’-bipy)(ox)) exhibits an exothermic peak. The exothermic effects also are pre-
sented on DTA curve for the step of total decomposition of all intermediate complexes of
Cd(II).
On the basis of the literature data the change in character of the decomposition
from endothermic to exothermic for oxalates is due to the autocatalytic oxidation of
pyrolysis products in air [8]. Thus, endothermic effect connected with the decompo-
sition of intermediate Zn(2,4’-bipy)(ox) or intermediate compounds of Cd(II) is
probably masked by the exothermic nature of the reaction conversion of carbon mon-
oxide to carbon dioxide catalysed by surface of solid decomposition products in air.
The isolated complexes Cd(2-bipy)(ox)2H2O, Cd(2,4’-bipy)(ox)2H2O and the
intermediate compounds M(2-bipy)(ox), M(4-bipy)(ox), M(2,4’-bipy)(ox) (where:
M(II)=Zn or Cd) are new example of complexes with ligand isomerism.
Conclusions
Generally, the Zn(II) complexes are thermally more stable than the corresponding
Cd(II) complexes.
The temperature of decomposition of mixed bipyridine-oxalato complexes of
these metals increases according to the type of bipyridine isomers in order:
2-bipy > 4-bipy > 2,4’-bipy
This trend can be attributed to the molecular structure of these isomers. The
bipyridine isomers favour mainly following types of coordination: 2-bipy is potential
bidentate chelating ligand; 4-bipy act as bidentate bridging ligand; 2,4’-bipy can co-
ordinate as monodentate ligand via the least hindered (4’)N atom [9, 10]. The higher
stability of 2-bipy and 4-bipy complexes than that of 2,4’-bipy complexes may be due
to the strong ability of the five-ring forming and polymeric structures, respectively.
References
1 D. Czakis-Sulikowska, J. Radwañska-Doczekalska, M. Markiewicz, N. Pustelnik and B.
KuŸnik, Polish J. Chem., 71 (1997) 513.
2 D. Degueon, G. Bernardinelli, J. P. Tuchagues and P. Castan, Inorg. Chem., 29 (1990) 3031.
3 S. Ducurtins, H. W. Smalle, P. Schneuwly, J. Ensling and P. Gutlich, J. Am. Chem. Soc., 116
(1994) 9521.
4 A. Gleizes, M. Julve, M. Verdaguer, J. A. Real, J. Faus and X. Solans, J. Chem. Soc. Dalton
Trans., (1992) 3209.
5 P. Roman, C. Guzman-Miralles and A. Lugue, ibid, (1996) 3985.
6 D. Czakis-Sulikowska and A. Malinowska, J. Thermal Anal. Cal., 51 (1998) 575.
7 Powder Diffraction File. International Center of Diffraction. ICPDS-ICDD, 1990.
J. Therm. Anal. Cal., 60, 2000

156
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE ISOMERS
8 D. Dollimore, J. Thermal Anal., 11 (1977) 185; Thermochim. Acta, 117 (1987) 331 and refer-
ences therein.
9 D. Czakis-Sulikowska, J. Radwañska-Doczekalska, B. KuŸnik and A. Malinowska, Transition
Met. Chem., 20 (1995) 203.
10 I. S. Ahuja, Raghuvier Singh and C. L. Yadava, J. Mol. Struct., 74 (1981) 43.
J. Therm. Anal. Cal., 60, 2000