Tetrad effect in mixed-ligand lanthanide chelates. Part II: Lanthanide. CDTA/DTPA. orcinol/resorcinol/phloroglucinol ternary systems

The variation profiles of certain properties of the lanthanide Ln(III)] series show discontinuities at or around Gd(III) (4f⁷ stage), Nd (IH)-Pm(III) (4f³−4f⁴ stage) and Ho (III)-Er (III) (4f¹⁰−4f¹¹ stage) due to the presence of a tetrad effect. In the present work the occurrence of the tetradic phenomenon has been studied for the formation constants, log K _MAL ^MA of the mixed-ligand Ln (III) chelates of the type Ln(III).A.L], where Ln(III) = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb (III) or Dy(III); A = CDTA or DTPA; L = orcinol, resorcinol or phloroglucinol. The presence of the tetrad effect in log K _MAL ^MA values has been tested with the help of the straight line approximation method, differential plot method and inclined-W hypothesis. The magnitude of the effect has been found to lie in the sequence f⁷ > f³ −f⁴.