Determination and comparison of the stability constants of some metal complexes of 8-hydroxyquinoline N-oxide and 8-hydroxyquinoline

Abstract

The stability constants of 8-hydroxyquinoline N-oxide (or "oxine N-oxide") complexes with Mn^II, Fe^ll, Co^II, Ki^ll, Cu^II, Zn^II, Cd^II, UO₂¹¹, Al^III, Fe^III, Y^III, La^III, Ce^III, Pr^III, Nd^III, Sm^III, Gd^III, Dy^III, Ho^III, Er^III, Tm^III, Yb^III, and Lu^III, and oxine complexes with Ln^III and Y^III have been determined using pH-metric titrations in 50% v/v aqueous dioxan in the presence of 0.30M sodium perchlorate as the constant ionic medium. With both the ligands, the "gadolinium break" is observed in the case of the lanthanon complexes, whereas the bivalent ion complexes follow the Irving-Williams order of stability constants in the case of the oxine complexes. The stability constants of the oxine complexes have been found to be larger than those of the N-oxide complexes, though the oxine anion is only five times as basic as the N-oxide anion. A possible explanation for the increased stability of the oxine complexes in comparison with the corresponding N-oxide derivative is proposed.