The metal complexes of some azo and azomethine dyestuffs : Part I. Spectra in water, and in dioxan/water in the wavelength range 320-600 mμ

Abstract

The visible, spectra of the highly sensitive colorimetric reagent 4-(2-pyridylazo)-resorcinol (I), and of the coloured cpmplexes formed with copper(II), nickel(II), cobalt(II), lead(II), and uranium(VI) were obtained in water and in aqueous dioxan. The structures of these complexes were determined by spectrophotometric methods, and chelation by (I) established as essentially terdentate. Comparison is made with the visible spectra of salicylidene-2-aminopyridine (II), 2-(o-hydroxy-phenyl-imino-methyl)-pyridine (III), and benzeneazoresorcinol (IV), and of the metal complexes of (II) (III) and (IV). The red coloration obtained with 4-(2-pyridylazo)-resorcinol is explained by the presence of a pseudo-phenanthroline system and an o-o'-disubstituted azo system, the active groups in chelation being the pyridine nitrogen atom, the azo nitrogen farthest from the heterocycle, and the o-hydroxyl group.