Lanthanide Polyoxocationic Complexes: Experimental and Theoretical Stability Studies and Lewis Acid Catalysis

The [epsilon-(PMo8Mo4O36)-Mo-V-O-VI(OH)(4){Ln(III)(H2O)}(4)](5+) (Ln=La, Ce, Nd, Sm) polyoxocations, called epsilon Ln(4), have been synthesized at room temperature as chloride salts soluble in water, MeOH, EtOH, and DMF. Rare-earth metals can be exchanged, and P-31 NMR spectroscopic studies have allowed a comparison of the affinity of the reduced {epsilon-PMo12} core, thus showing that the La-III ions have the highest affinity and that rare earths heavier than Eu-III do not react with the epsilon-Keggin polyoxometalate. DFT calculations provide a deeper insight into the geometries of the systems studied, thereby giving more accurate information on those compounds that suffer from disorder in crystalline form. It has also been confirmed by the hypothetical La -> Gd substitution reaction energy that Ln ions beyond Eu cannot compete with La in coordinating the surface of the epsilon-Keggin molybdate. Two of these clusters (Ln=La, Ce) have been tested to evidence that such systems are representative of a new efficient Lewis acid catalyst family. This is the first time that the catalytic activity of polyoxocations has been evaluated.