Tautomerism of metal complexes with carminic acid

The diversity of the absorption spectra of complexes with carminic acid was shown to be due to the shift of tautomeric equilibria that takes place upon the change in the medium pH, the nature of the metal, and the composition of the complex. A classification of known carminic acid complexes based on the results of correlation analysis of the positions of experimental π l ,π*absorption bands with those calculated by PPP quantum chemical methods is proposed. © 2008 MAIK Nauka.