Laws of complex formation in a series of azo-substituted pyrocatechol derivatives and their tin(II) complexes

Physicochemical properties of new reagents, azo-substituted pyrocatechol derivatives and their tin(II) complexes, are studied. The acid-base properties of the hydroxy groups (pK′i, pK″i), parameters of complex formation reactions (pH, temperature, time), and instability constants of the complexes formed (pKi) are determined. Quantitative correlations between the dissociation constants (pK′a) of the functional analytical group, and the electronic Hammett constant σ for a substituent (pK′a-pH50 of the complex formation reaction), as well as between pK′a and instability constants of the complexes (pKa), are established. The quantitative correlations established allow the prediction of the physicochemical properties of the reagents and tin(II) complexes with new reagents of this class with the same functional analytical group (FAG) but other substituents.