The stability constants of Lu[Lu=La(Ⅲ), Ce(Ⅲ), Pr(Ⅲ), Nd(Ⅲ), Sm( Ⅲ), Eu(Ⅲ),Gd(Ⅲ), Tb(Ⅲ), Dy(Ⅲ), Ho(Ⅲ),L=N,N'- dialkyl- 1,10- phenanthroline -2,9- dimethanamine, in which alkyl group denotes --- CH~3, CH~2CH~3, -----(CH~2)~2CH~3, ----(CH~2)~3CH~3,----CH(CH~3)~2,---- C(CH~3)~3]binary complexes hace been determined by pH potentiometric titration method at (25±0.1)℃, Ⅰ＝0.1mol· dm^-3NaClO~4. The probable structures of the corresponding complexes were proposed. The influence of the metal ions and the substituents on the stability of binary complexes is reported in detail. The stability difference between the complexes of rare earth ion and the corresponding complexes of Cu(Ⅱ) ion is also discussed. The stability constants of the corresponding binary complex of radioactive Pm(Ⅲ) ion are estimated by linear regression.

Key words: PHENANTHROLINE P, RARE EARTH METAL COMPLEX, STABILITY, POLYAMINE