A density functional study of alizarin two of its isomers and its transition metals and rare-earth complexes

Electronic structure of Alizarin, two of its isomers, 11 different transition metal complexes and five rare-earth complexes are studied using density functional theory (DFT). Complexation energies are evaluated and it is found that chelation has a negligible influence on the structure of the anthraquinone backbone; the molecule keeps a planar conformation except for some metals such as Cr, Al, and Zn where the metal atom M and the oxygen atoms are slightly out of the plane by few degrees. The M–O bonds involve p or d metal orbitals depending on whether the d shell is full or empty. The complexation effect leads to a red shift and hence to a colour change of the solutions of the complexes.

The calculated complexation energies are of the same order for metal transition and for rare-earth elements.