Thermodynamic Studies of Y(III), La(III), Ce(III) and Sm(III) Complexes of 5-Hydroxy-2-methyl-1,4-naphthalenedione

Abstract

The pH-metric and thermodynamic stability have been carried out for yttrium(III), lanthanum(Ill), cerium(III) and samarium(llI). complexes of 5-hydroxy-2-methyl-1,4-naphthalenedione (plumbagin). Three molecules of plumbagin (5-hydroxy-2-methyI-1,4-naphthalenedione) react with these metal ions in solution phase (50% aqueous EtOH, 0.1 M KNO₃ ionic strength) at varied temperatures. The data for yttrium(llI), lanthanum(III), cerium(III) and samariurn(III) with plumbagin systems reveals a decrease in the value of log pk^H, log k_1, log k₂ and log k₃ with the increase in temperature; this indicates that the lower temperature is favourable for complexation due to the decrease in the number of collisions and kinetic energy of the molecules and hence their stabilities are lowered.