The solubilities of three ternary systems LaX_3-PIAP-H_2O (X~- = C1O_4~-, NO_3~-, Cl~-; PIAP =phthalimidoantipyrine, G_(19)H_(15) N_3O_3) were determined at 30℃. It is discovered that the systems La (NO_3)_3-PIAP-H_2O and LaCl_3-PIAPH_2O are simple eutonic type, while the system La(C1O_4)_3-PIAP-H_20 contains a new solid phase, the composition of which is La(PIAP)_3(C10_4)_3·4H_20 that is an incongruent compound. Based on the phase equilibrium of the system La (C10_4)_3-PIAP-H_20, the corresponding lanthanide complexes Ln(PIAP)_3 (C10_4)_3·4H_20 (Ln=La, Pr, Nd, Sm, Gd, Yb) were synthesized and characterized by chemical analysis, elemental analysis, TG-DTG, IR spectra and density.

Key words: lanthanum perchlorate, lanthanum chloride, lanthanum nitrate, ANTIPYRINU, SOLUBILITY, ELEMENTAL ANALYSIS, TG, IR, PHASE EQUILIBRIUM, PRASEODYMIUM COMPLEX