Abstract
The thermal decomposition of Ni(II) complexes of 3-(phenyl)-1-(2’-
hydroxy-naphthyl)-2-propen-1-one (PHPO), 3-(4-chlorophenyl)-1-(2’-hydroxynaphthyl)-2-propen-1-one(CPHPO), 3-(4-methoxyphenyl)-1-(2’-hydroxynapthyl)-2-propen-1-one (MPHPO), 3-(3,4-dimethoxyphenyl)-1-(2’-hydroxynaphthyl)-2-propen-1-one(DMPHPO) was studied by thermogravimetry. Mathematical analysis of the data has allowed us to determine various parameters using Freeman-Carroll equation, the integral method using the coats-Redfern equation and the approximation method using the Horowitz-Metzger equation. The trend of the kinetic parameters was found to be different from that of the thermal stability order. The low values of Z suggest the slow nature of the reaction.
Keywords: Thermogravimetry, Chalcones, Nickel Compounds, Frequency factor,
Introduction
Very few systems have been reported1 showing the relationship between thermal stability of metal
chelates and structure of the chelating agents. Wendlandt and co-workers2-5 and Hill and co-workers6,7
studied the thermal properties of metal chelates with different types of complexing ligands. Structural
studies on several metal chelates of _-diketones and 2-hydroxycarbonyl compounds have been
reviewed by Holm and O’ Connor.8 The metal chelates of divalent transition metals with some
o-hydroxychalcones standout as a distinct class of o-hydroxycarbonyl compounds with low spin
square-planar configuration, which do not easily form adduct. Extensive conjugation was found to be
responsible for the strong field nature of the ligand.9 Chalcones usually exhibit germicidal10
bactericidal,11 fungicidal12 and carcinogenic activities.13
In continuation of our earlier work14-19 on thermal decomposition kinetics of metal chelates, the
present investigation deals the thermal stability of the Nickel chelates of 3 - (phenyl) -1 - ( 2’-
hydroxynaphthyl ) – 2 – propen -1 –one (PHPO) , 3 - ( 4 – chlorophenyl ) - 1- (2’- hydroxynaphthyl ) -
2 – propen -1 –one (CPHPO), 3 - ( 4 – methoxyphenyl ) – 1 - (2’- hydroxynapthyl ) - 2-propen -1- one
(MPHPO), 3-(3,4-dimethoxyphenyl)-1-(2’-hydroxynaphthyl)-2-propen-1-one (DMPHPO) and
evaluation of kinetic parameters employing the differential Freeman-Carroll equation20 the integral
method using the Coats-Redfern equation21 and the approximation method using the Horowitz-
Metzger equation.
Experimental
The chalcones were prepared by the condensation of 2-hydroxy-1-acetonaphthone with benzaldehyde,
chlorobenzaldehyde, methoxybenzaldehyde and dimethoxybenzaldehyde employing the Claisen-
Schmidt condensation reported earlier.23 The copper complexes of chalcones were prepared by
refluxing a toluene solution of nickel acetate and the ligand in 1:2 molar ratios, in the presence of
dilute ammonia (pH 8.5-9.0) for 1h. The precipitates were filtered, washed with toluene and dried in a
vacuum desiccator over fused calcium chloride. The purity of the sample was checked by elemental
analysis. The thermograms were recorded using a Perkin-Elmer TGS-2 thermo balance in ambient air
and at a heating rate of 6K min-1


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