Thermal, spectral and magnetic properties of 2-hydroxy-1,4-naphthoquinone monoximates of Ho(III), Er(III) and Yb(III)

Abstract

Ho(III), Er(III) and Yb(III) complexes of 2-hydroxy-1,4-naphthoquinone-1-oxime derivatives having [ML₃(H₂O)₂] are characterized using spectral and thermal decomposition studies. The thermolytic patterns suggested that they are decomposed in three distinct stages; 1^ststage is related to the loss of two coordinated water molecules while one of the coordinated ligands and remaining two ligands are lost during subsequent 2^nd and 3^rd stages of degradation. After the 2^nd stage, the structure of these complexes is reorganized reflecting that the structural associations through intermolecular hydrogen bonding network is essential for thermal stability. The kinetic parameters computed for 2^nd step using the non-isothermal procedures of Coats-Redfern are applied to the respective differential thermogravimetric plots to ascertain the thermal degradation mechanism in air. The order of thermal decomposition reaction is found to be between 1-2 indicating that more than one intermediate might have simultaneously been formed. It also reveals the intermixing of 1^st and 3^rd stages of decomposition with the predominant 2^nd stage leading to more gradual degradation. Energy of activation for 2^nd stage of decomposition for these complexes is comparatively lower than those observed earlier for similar types of complexes. Other spectral data indicate oximino nitrogen and phenolato oxygen as coordination sites of 2-hydroxy-1,4-naphthoquinone monoximates.