A COMPARISON OF CARBOXYLATE COMPLEXES OF LANTHANUM(III) - FORMATE, ACETATE AND PROPIONATE

The stability constants of La(III)-formate and La(III)-propionate comp lexes in aqueous medium were determined by a potentiometric method usi ng a glass electrode. The temperature was kept at 25 degrees C and an ionic strength of 1.00 M (NaClO4) was used. Four mononuclear complexes were detected for both systems. The pK(a) values for the carboxylic a cids (formic and propionic) were determined at the same conditions. Th e final values of the overall stability constants determined by a matr ix solution of weighted simultaneous equations were: beta(1) = (13.2 /- 0.6) L mol(-1), beta(2) = (48 +/- 4) L(2) mol(-2),beta(3) = (118 +/ - 15) L(3) mol(-3), beta(4) = (85 +/- 15) L(4) mol(4) for La(III)-form ate system and beta(1) = (42 +/- 3) L mol(-1), beta(2) = (299 +/- 25) L(2) mol(-2), beta(3) = (1201 +/- 138) L(3) mol(-3), beta(4) = (2527 /- 174) L(4) mol(-4) for La(III)-propionate system. These data and tho se for La(III)/acetate from the literature were used to compare the te ndency to complex.