From Scheele and Berzelius to Müller Polyoxometalates ( POMs ) revisited and the “ missing link ” between the bottom up and top down approaches

This review provides a survey of polyoxometalate chemistry with special emphasis on its history, and special attention to Souchay’s and Müller’s contributions. Polyoxometalates are early transition metal oxygen cluster anions. Considering their structures, sizes and properties, polyoxometalates are intermediate between small molecules and oxides. They have been known for more than two centuries, but due to the lack of appropriate analytical methods, the field remained for long one of the most confused in inorganic chemistry. It was Pierre Souchay (Faculty of Sciences in Paris/University Pierre et Marie Curie) who brought clarity in the field. He started a school which is still active today and has provided a major contribution to polyoxometalate chemistry. In the last fifteen years, polyoxometalate chemistry has expanded tremendously, following fundamental discoveries by Achim Müller at the University of Bielefeld. Achim Müller and his group have shown that aqueous solutions of molybdates allow the generation of a huge variety of combinatorially linkable units and, consequently, the formation of a large variety of clusters, among them amazing wheels and spheres. Such wheel-shaped clusters exist in “molybdenum blue” solutions which were known by Scheele and Berzelius and of which many generations of chemists failed to uncover the mystery. Wheels can be considered as nanostructured landscapes mimicking oxide surfaces and allowing reactions to occur at a variety of well-defined sites. Capsules are not less remarkable as their synthesis was deliberately planned and because they can be considered as artificial cells mimicking fundamental biological processes. Among the perspectives offered by these discoveries, encapsulation chemistry seems to be one of the most attractive.