Lanthanide complexes of anthraquinone-1,8-disulfonate: Syntheses, structures and catalytic studies

Two isostructural series of four lanthanide coordination complexes have been synthesized by hydrothermal method with anthraquinone-1,8-disulfonate as the anionic ligand. The complexes also comprise K⁺ ions that participate into coordination to form bimetallic complexes. The ligands in these complexes chelate to either lanthanide or K⁺ ions, and in some circumstance bridge the ions as well. Besides inter-/intra- molecular hydrogen bonding between the sulfonate groups and water molecules, π-π stacking interactions also contribute to the stabilization of the crystal packing. Investigation of the catalytic properties of the complexes indicated that they were able to promote the oxidation reaction of thioethers into sulfoxides, in which the Er³⁺ coordination complex exhibited the best catalytic efficiency over a wide range of substrates.