Determination of the stability constants of trivalent iron, aluminium, and lanthanon complexes of some 8-hydroxyquinoline N-oxide derivatives

Abstract

The stability constants of iron(III), aluminium(III), yttrium(III), and the lanthanon(III) (excluding Pm(III), Eu(III) and Tb(III)) complexes with 5,7-dichloro- and 5,7-dinitro-8-hydroxyquinoline N-oxide in 50% v v aqueous dioxan, and with 5,7-dibromo-8-hydroxyquinoline N-oxide in 75% v v aqueous dioxan have been determined by pH titration. The stability constants (log K 1) of the lanthanon complexes with each of these ligands increase with increase in the atomic number of the lanthanon, the “gadolinium break” also being observed. The value of log K 1 for the yttrium(III) complexes is in the neighbourhood of that for the holmium(III) complexes. The stability constants of the complexes of a particular metal decrease with the decreasing basicity of the ligands.