CHELATION BEHAVIOR OF LANTHANIDES WITH SOME THIO-SCHIFF BASES

The stability constants of complexes of trivalent Y, La, Ce, Pr, Sm, G d, Dy, Ho, Er, and Yb ions with some thio-Schiff bases have been deter mined potentiometrically using the Calvin-Bjerrum titration technique as modified by Irving and Rossotti at 25 degrees C and an ionic streng th of 0.1 M (NaCl) in 70% (v/v) aqueous ethanol. 1:1 and 1:2 complexes are formed and evidenced by conductometric studies. The pK(a) values of the SH group were correlated with the Hammet constants of substitue nts. The values of the stability constants are correlated with the ato mic numbers of the lanthanides and with the sum of the ionization cons tants of the ligands.