Formation of the complexes between lanthanum(III) ion and 5-sulfosalicylate, 5-nitrosalicylate

The complexed species between lanthanum(III) ion and some salicylic acid (SA) derivatives: 5-sulfosalicylic acid (5-SSA:H3L) and 5-nitrosalicylic acid (5-NSA:H2L) were defined in ionic strength of 0.1 M NaClO4 and at 25 +/- 0.1 degrees C. The formation constants of complexes were determined by potentiometry and their stoichiometries were investigated by means of spectroscopy. The coordination of La(III) ion to 5-SSA and 5-NSA occurs; the analysis of potentiometric indicated the formation of LaL and LaL23- type complexes with 5-SSA; LaL+ and LaL2- type complexes with 5-NSA, respectively. 5-SSA and 5-NSA act as bidentate ligands towards La(III) ion; their coordinations are via salicylate sites, while SA forms only LaHL type complex. The stabilities of La(III) complexes between La(III) ion and SA and SA derivatives change in the following order: 5-SSA > 5-NSA > SA