Thermodynamic studies of Y(III), La(III), Ce(III) and Sm(III) complexes of 5-hydroxy-2-methyl-1,4-naphthalenedione

The pH-metric and thermodynamic stability have been carried out for yttrium(III), lanthanum(III), cerium(III) and samarium(III). complexes of 5-hydroiy-2-methyl-1,4-naphthalenedione (plumbagin). Three molecules of plumbagin (5-hydroxy-2-methyl- 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(HI), lanthanum(III), cerium(III) and samarium(III) with plumbagin systems reveals a decrease in the value of log pk(H), log k(1), log k(2) and log k(3) 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.