The metal complexes of some azo and azomethine dyestuffs : Determination of stability constants,and preparation of solid complexes

The stability constants of the complexes of 4-(2-pyridylazo)-resorcinol (I) with copper(II), cobalt-(II), zinc(Il), lead(ll), and uranium(VI) were determined by potentiometric titration in aqueous media, and were shown to have very high values, the stability constant of the copper(ll) complex approaching that of the copper(ll)-EDTA complex. The nickel(II) complex was shown to behave anomalously. The stability constants were also determined by this method in 1:1 dioxan/water, and the values obtained compared with those for the complexes of salicylidene-2-aminopyridine (II), 2-(o-hydroxy-phenyl-imino-methyl)-pyridine(III), and benzeneazoresorcino (IV). It is shown that chelation by (1) is terdentate, involving the pyridine nitrogen, the o-hydroxyl group and the azo nitrogen farthest from the heterocycle.The solid copper(II) complexes of these four ligands were prepared; in the solid complexes the azo nitrogen nearest the heterocycle plays a greater part than in the complexes in solution.