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

• Published in: Chemistry : a European journal 2011-12, Vol.17 (50), p.14129-14138
• Main Authors: El Moll, Hani, Nohra, Brigitte, Mialane, Pierre, Marrot, Jérôme, Dupré, Nathalie, Riflade, Benoît, Malacria, Max, Thorimbert, Serge, Hasenknopf, Bernold, Lacôte, Emmanuel, Aparicio, Pablo A., López, Xavier, Poblet, Josep M., Dolbecq, Anne
• Format: Article
• Language: English
• Subjects: Affinity; catalysis; Catalysts; Chemistry; density functional calculations; Lanthanides; Lewis acid; Mathematical analysis; molybdenum; polyoxometalates; Rare earth metals; Spectroscopic analysis; Spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201101754

The [ε‐PMoV8MoVI4O36(OH)4{LnIII(H2O)}4]5+ (Ln=La, Ce, Nd, Sm) polyoxocations, called εLn4, have been synthesized at room temperature as chloride salts soluble in water, MeOH, EtOH, and DMF. Rare‐earth metals can be exchanged, and 31P NMR spectroscopic studies have allowed a comparison of the affinity of the reduced {ε‐PMo12} core, thus showing that the LaIII ions have the highest affinity and that rare earths heavier than EuIII do not react with the ε‐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 ε‐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. Integrated approach: A combined crystallographic, 31P NMR spectroscopic, and DFT calculation study gives a detailed description of cationic tetracapped lanthanide polyoxomolybdate species (see graphic). These species are efficient and highly chemoselective Lewis acid catalysts.