Thermal stability of some new complex compounds with alylacetoacetate as ligand

Article abstract of DOI:10.1007/s10973-005-0713-7

This paper reports the investigation of the thermal stability of two new complexes with allylacetoacetate anion, Cu(C₇H₉O ₃)₂ (1) and Ni(C₇H₉O ₃)₂(OH₂)₂ (2), respectively. The bonding and stereochemistry of the complexes have been characterized by IR, electronic and EPR spectra. The main decomposition steps were evidenced. The two complexes exhibit a different thermal behaviour. Thus, the copper complex suffers an oxidative degradation of allylacetoacetate ligand leading to copper carbonate, which is decomposed to copper oxide. The Ni(II) complex lose the water molecules first and then the organic ligand decomposition occurs. An intermediary malonaldehyde complex seems to be obtained. Complex (1) presents in vitro antimicrobial activity.

Full text of DOI:10.1007/s10973-005-0713-7

Journal of Thermal Analysis and Calorimetry, Vol. 80 (2005) 679–682
THERMAL STABILITY OF SOME NEW COMPLEX COMPOUNDS WITH
ALLYLACETOACETATE AS LIGAND
M. Badea1*, R. Olar1, D. Marinescu1, G. Vasile2 and S. Stoleriu3
1University of Bucharest, Faculty of Chemistry, Department of Inorganic Chemistry, 90-92 Panduri St., 050663 Sector 5, Bucharest,
Romania
2University of Agronomical Sciences and Veterinary Medicine, Department of Agrochemistry, Bd. Marasti 59, Bucharest, Romania
3University ‘Politehnica’ Bucharest, Faculty of Industrial Chemistry, S.I.M.O. Department, P.O. Box 12-134, 011061 Bucharest,
Romania
This paper reports the investigation of the thermal stability of two new complexes with allylacetoacetate anion, Cu(C7H9O3)2 (1)
and Ni(C7H9O3)2(OH2)2 (2), respectively. The bonding and stereochemistry of the complexes have been characterised by IR, elec-
tronic and EPR spectra. The main decomposition steps were evidenced. The two complexes exhibit a different thermal behaviour.
Thus, the copper complex suffers an oxidative degradation of allylacetoacetate ligand leading to copper carbonate, which is decom-
posed to copper oxide. The Ni(II) complex lose the water molecules first and then the organic ligand decomposition occurs. An in-
termediary malonaldehyde complex seems to be obtained. Complex (1) presents in vitro antimicrobial activity.
Keywords: allylacetoacetate anion, Cu(II) complex, Ni(II) complex, thermal stability
Introduction
(C7H9O3) anion, that represent the products of a first
step in the synthesis of polymeric materials. The com-
pounds were formulated as Cu(C7H9O3)2 (1) and
Ni(C7H9O2)5(OH2)2 (2) respectively on the basis of
chemical analysis, IR and electronic spectra as well as
EPR study.
Allylacetoacetate (AAA) is a very interesting organic
derivative that acts as bidentate ligand in complexes
with many transition metal ions [1]. The complexes
with similar ligands could adopt extended supramo-
lecular structures induced by the presence of hydro-
gen bonds. The interest in using this ligand increased
recently because the obtained complexes have inter-
esting magnetic and catalytic properties. Moreover,
they can be used as monomers in order to include
some metallic ions in polymeric matrix [2, 3].
Considering their intended use as metal contain-
ing monomers their thermal stability and behaviour
are supposed to be clearly known. The thermal analy-
sis (TG, DTG, DTA) of these complexes was per-
formed in order to elucidate the composition and also
the number and nature of water molecules. In both
cases, the final residue was the metal oxide, indicated
by powder X-ray diffraction.
Complexes could be copolymerised with proper
organic monomers in order to obtain new materials with
predefined properties. Also, this process improves the
properties of monomers and leads to the development of
new ones. In the solid-state, when compounds contain
an unsaturated polymerisable ligand (as allylaceto-
acetate), reactions such as polymerisation induced by
thermal and/or radiation sources may lead to the forma-
tion of valuable compounds. On the other hand, the ob-
tained metal-containing copolymers could be used to
synthesize metal-polymer composites having unusual
physico-chemical and mechanical properties [4]. These
are widely used as optical and magnetic materials [5],
catalyst for various reactions, drugs and coatings [2].
There are less data reported concerning the thermal be-
haviour of polymers [6].
Experimental
All reagents were of commercial analytical quality
and have been used without further purification.
Chemical analysis of carbon, nitrogen and hydrogen
has been performed using an EA 1110 analyzer. Cop-
per and nickel were determined gravimetrically in the
laboratories of Inorganic Chemistry Department.
IR spectra were recorded in KBr pellets with a
Bio-Rad FTIR 135 spectrometer in the range
400–4000 cm–1. Electronic spectra by diffuse
reflectance technique, with MgO as standard, were re-
corded in the range 380–1100 nm, on a VSU 2P-Zeiss
Jena spectrometer. The EPR spectra were recorded on
We report here the thermal behaviour of two new
complexes of Cu(II) and Ni(II) with allylacetoacetate
*
Author for correspondence: e_m_badea@yahoo.com
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2005 Akadémiai Kiadó, Budapest

BADEA et al.
a JES-ME-3 spectrometer. The field was calibrated
plex (1) is very soluble in ethanol and in other common
organic solvents while (2) is sparingly soluble even in
organic solvents having coordinative properties.
using crystalline diphenylpicrylhydrazyl (g=2.0036).
The heating curves (TG, DTA and DTG) were re-
corded in a static air atmosphere using a Shimadzu
DTG-TA-51H thermogravimetric analyzer with a
sample mass of 4 and 8 mg over the temperature range
20–1000°C, using a heating rate of 10 K min–1.
In the IR spectra of the complexes the character-
istic patterns of the estheric groups are present as is
presented in the experimental part. These groups lead
to strong bands around 1600 cm–1, assigned to
ν(C=O) vibrations. The presence of these bands at
lower wavenumbers sustains their implication in in-
teractions with the metal ions. The allylic fragment
could be identified due to the band located at
1535 cm–1. The band at 1175 cm–1 assigned to ν(C–O)
vibration indicates the presence of the ligand in the
enolic form [7]. In the spectrum of complex (2) the
broad band at 3400 cm–1 could be associated with the
presence of water molecules [8].
Synthesis of the complexes
Complex Cu(C7H9O3)2, (1): to 25 mL of aqueous solu-
tion of 10 mmoles of Cu(CH3COO)2⋅H2O ammonia so-
lution was added dropwise, under continuous stirring
until the colour of the solution turned dark blue as a re-
sult of copper tetraammine formation. Under continu-
ous stirring, ethanolic solution of 20 mmoles allyl-
acetoacetate was added. The dark green solution was
left at room temperature for several days until needle
blue-green crystals were formed. The compound was
filtered off, washed with water and air-dried. Analysis,
found: Cu, 18.34; C, 47.79; H, 5.18%; calculated:
Cu, 18.38; C, 48.64; H, 5.20%; IR (KBr pellet), cm–1:
ν(C=O), 1602vs; δ(CH=CH), 1537s; ν(C–O), 1283s,
1175m; γ(CH), 928w, ρ(CH3), 776m.
The electronic spectra of complexes are shown in
Fig. 1. The diffuse-reflectance spectrum of Cu(II) com-
plex in the Vis-near-IR range shows a single broad band
at 18 020 cm–1, as is usually observed for this ion due to
the different nature of the ligands and also of the
Jahn–Teller effect [9, 10]. In the spectrum of com-
plex (2) the bands at 10 300, 16 666 and 24 390 cm–1
could be assigned to the spin allowed transitions
3
3
3A2g→3T2g, A2g→3T1g and A2g→3T1g [9]. The posi-
tions of the absorption maxima are in agreement with an
octahedral stereochemistry for a [NiO6] chromophore.
The EPR spectrum presented in Fig. 2 contains
an isotropic signal.
Complex Ni(C7H9O3)2(H2O)2, (2): to 25 mL of
aqueous solution of 10 mmoles of Ni(CH3COO)2⋅4H2O
an ethanolic solution of 20 mmoles allylacetoacetate
was added dropwise under continuous stirring. The light
green solution was stirred for 30 min and then the pH
was adjusted to 8 with ammonia solution. After several
days, at room temperature needle light green crystals
were obtained. The compound was filtered off, washed
with water and air-dried. Analysis, found: Ni, 15.53;
C, 44.58; H, 5.76%; calculated: Ni, 15.58; C, 44.62;
H, 5.84%; IR (KBr pellet), cm–1: ν(OH), 3400s,
ν(C=O), 1600vs; δ(CH=CH), 1535s; ν(C–O), 1280s,
1175m; γ(CH), 930w, ρ(CH3), 770m.
On the basis of the above data the coordination
proposed for the complexes are as it follows:
Results and discussion
Cu(C7H9O3)2
Physico-chemical and biological characterisation of
complexes
The major goal of this paper was to determine the ther-
mal behaviour of these complexes that could be used as
intermediates for obtaining some polymer metal con-
taining species. The complexes have been formulated
on the basis of chemical analysis, IR and electronic
spectra as well as EPR study at room temperature.
The new complexes were synthesized by direct re-
action between metal acetates and allylacetoacetate in
alkaline medium. The complexes have different chemi-
cal formulae and IR spectra; (1) does not contain water
or solvent molecules in spite of the fact that it was ob-
tained under similar condition as complex (2). Com-
Ni(C7H9O3)2(H2O)2
Biological activity
Antimicrobial activity of the complexes has been car-
ried out against strains of bacteria (Bacillus subtilis
and Escherichia coli), fungus (Aspergillus niger and
Aspergillus oryzae) and yeasts (Saccharomyces
cerevisiae and Hansemila anomala) using liquid me-
680
J. Therm. Anal. Cal., 80, 2005

NEW COMPLEX COMPOUNDS WITH ALLYLACETOACETATE AS LIGAND
Thermal behavior of complexes
dium dilution method. The values of minimum inhibi-
tory concentration (MIC) indicate that only the com-
plex (1) is active against the Escherichia coli with a
MIC of 75 ppm.
Thermal decomposition of Cu(C7H9O3)2
The TG, DTG and DTA curves corresponding to the
complex (1) are presented in Fig. 3.
The thermal analysis has confirmed the compound
formulation, the complex being stable until 112°C.
The thermal decomposition occurs in two basic,
exothermic steps. One step corresponds to the com-
plex transformation to CuCO3, while the second one
corresponds to decomposition of CuCO3 to CuO. Un-
like the first step that is a single one, the decomposi-
tion of CuCO3 seems to occur in three steps (accord-
ing to DTA curve). Considering the tendency of cop-
per to form basic salts, it could be supposed that the
intermediates are oxocarbonates with different mol
CuCO3:CuO ratio.
The copper oxide obtained at 412°C as final
product of decomposition is stable until 650°C.
Thermal decomposition of Ni(C7H9O3)2(H2O)2
Fig. 1 Diffuse reflectance spectra of complexes (1) and (2)
The TG and DTG curves (Fig. 4) indicate that the
thermal decomposition occurs in a different way.
As the IR spectrum indicates, the complex (2) con-
tains water, which is eliminated in two successive well-
separated steps [11]. The first decomposition step corre-
sponds to the elimination of 0.5 water molecules while
the second one could be associated with the elimination
of 1.5 water molecules per nickel atom. On the basis of
the thermal interval that corresponds to the decomposi-
tion one can conclude that the water molecules are in-
volved in interactions having different strength. Another
essential difference in the thermal behaviour of this
compound arises from the ligand decomposition mode.
Unlike complex (1), complex (2) gives as intermediate a
complex with an organic ligand resulted after the partial
oxidative degradation of allylacetoacetate. According to
the mass loss and IR spectrum, the remaining compound
seems to be [Ni(C3H3O2)2]. In the next step, the oxida-
tive degradation of this compound leads to NiO, stable
until 750°C.
Fig. 2 EPR spectrum of complex (1)
Table 1 Thermal behaviour data (in static air atmosphere) for the allylacetoacetate complexes
Temperature interval/
°C
∆mexp
/
∆mcalc/
Complex
Step Thermal effect
Residue used for calculation
%
%
1
2
3
4
exothermic
exothermic
exothermic
exothermic
112–225
225–295
295–346
346–412
64.34
4.14
4.28
4.18
64.26
4.24
4.24
4.24
CuCO3
1/3(2CuCO3⋅CuO)
1/3(CuCO3⋅2CuO)
CuO
Cu(C7H9O3)2
residue (CuO)
23.06
23.02
1
2
3
4
endothermic
endothermic
exothermic
exothermic
27–83
83–137
137–280
280–436
2.24
7.32
2.38
7.16
Ni(C7H9O3)2(H2O)1.5
Ni(C7H9O3)2
Ni(C3H3O2)2
NiO
37.21
33.28
37.17
33.45
Ni(C7H9O3)2(H2O)2
residue (NiO)
19.95
19.84
J. Therm. Anal. Cal., 80, 2005
681

BADEA et al.
The thermal analysis (TG, DTG and DTA) of the
complexes elucidated the composition, the number and
nature of water molecules. The presence of the water
molecules for Ni(II) complex generated two decompo-
sition steps which indicate a different bonding charac-
ter of water molecules as ligands. The following de-
composition step in the case of this compound could be
associated with formation of a stable intermediate with
malonaldehyde, coordinated to metal ion.
In both cases, the final residue is metal oxide, in-
dicated by powder X-ray diffraction.
Fig. 3 TG, DTG and DTA curves of Cu(C7H9O3)2
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682
J. Therm. Anal. Cal., 80, 2005