NMR and ab initio studies of Mg2+, Ca2+, Zn2+, Cu2+ alizarin complexes

Complexation of Mg2+, Ca2+, Zn2+ and Cu2+ with alizarin, characterized by NMR and theoretical studies (DFT, B3LYP/6-31G(d,p) PCM and NMR GIAO B3LYP/IGLOIII), indicated that the metal ion is attached to two hydroxyl groups in a bidentate mode. The alternative complexation in the bidentate mode, with only one hydroxyl group and a carbonyl oxygen, is less possible as it has a higher energy.

Graphical abstractAlizarin acts as a bidendate ligand on forming complexes with the metal ions Mg2+, Ca2+, Zn2+ and Cu2+. From the possible structures, the one with the metal attached to two hydroxyl oxygen atoms is of lower energy. A theoretical calculation of the structure of the complex, and NMR parameter analysis lead to the same conclusion.Figure optionsDownload full-size imageDownload as PowerPoint slide