Study of the stability of violurate complexes of some d- and f-metals

The stability constants of 1: 1 and 1: 2 acidic copper(II) violurate complexes and the CuL complex, where L is the anion of violuric acid (H2L), were determined by pH-metry at ionic strength I = 0.1 at 20°C. The stability of the violurate complexes of triply charged cations [ML]+ and quadruply charged thorium [ThL]2+ increases in the sequence La3+, Gd3+, Y3+, Sc3+, Th4+, Fe3+. It was shown that violuric acid behaves as either mono- or dibasic, depending on the conditions, with respect to all of these cations.