Pyrolytical characterization of transition metal complexes of cobalt, nickel, copper and zinc with ethylenediamine-N,N′-diacetate

A series of octahedral complexes, [M(EDDA) (H2O)(2)] center dot H2O (where, M+2 = Co(II), Cu(II), Ni(II) and Zn(II); EDDA, ethylenediamine-N,N'-diacetate), was prepared and studied by means of thermogravimetry (TG) and differential thermal analysis (DTA). Their compositions were investigated by elemental analysis in order to ensure their purity and structural elucidation was based on spectral and magnetic properties. Thermal decomposition of these distorted octahedral complexes, [Ni(EDDA)(H2O)(2)], [Co(EDDA)(H2O)(2)] center dot H2O, [Cu(EDDA)(H2O)(2)] center dot H2O and [Zn(EDDA)(H2O)(2)] center dot H2O came of in one, two, three and four steps, respectively, upon heating to 800 degrees C, with the loss of organic and inorganic fragments. Ligand decomposed in three steps. The thermal degradation of all the complexes in static air atmosphere started at temperatures lower than those observed for the free ligand degradation (Ni-complex being the only exception). The composition of intermediates formed during degradation was confirmed by microanalysis and IR spectroscopy. The residues corresponded to metal oxide except for Ni(II) and Zn(II) complexes. It was found that thermal stability of the complexes increased in the following sequence: Cu(II)similar to Co(II)<Zn(II)<Ni(II)