Synthesis and thermal studies on iron(III) complexes of 4-N-(4′-antipyrylmethylidene)aminoantipyrine with varying counter ions

Iron(III) complexes of the Schiff base 4-N-(4′-antipyrylmethylidene)aminoantipyrine (AA) with counter ions, such as, perchlorate, nitrate, thiocyanate, chloride and bromide have been prepared and characterized by elemental analyses, electrical conductance in non-aqueous solvents, IR and electronic spectra, magnetic susceptibility measurements as well as by thermogravimetric analysis. The complexes have the general formulae [Fe(AA)2(ClO4)](ClO4)2, [Fe(AA)2X2]X (X=NO3− or Br−) and [Fe(AA)X3] (X=SCN− or Cl−). In complexes, AA acts as a neutral bidentate ligand, coordinating through one of the carbonyl oxygens and azomethine nitrogen in perchlorate, nitrate and bromide complexes while the coordination of AA occurs in a neutral tridentate fashion through both carbonyl oxygens and azomethine nitrogen in thiocyanate and chloride complexes. In the perchlorate complex, one of the perchlorate ions is coordinated bidentately while in the nitrate complex two of the nitrate ions are coordinated monodentately to the metal ion. In the thiocyanate and chloride complexes all the anions are coordinated while in the bromide complex two of the bromide ions are coordinated. A high spin octahedral geometry is assigned to the iron(III) ion in all these complexes. The phenomenological, kinetic and mechanistic aspects of the nitrate, thiocyanate, chloride and bromide complexes were studied by TG and DTG techniques. The kinetic parameters like activation energy, pre-exponential factor and entropy of activation were also computed. The rate controlling process in all stages of decomposition is random nucleation with one on each particle (Mampel model) [Thermochim. Acta 2 (1971) 423].