Magnetic clusters from polyoxometalate complexes

The present article highlights the increasing interest of polyoxometalates in molecular magnetism, providing at the same time a perspective of the state-of-the-art in this area. The main focus is the polyoxotungstates. The first aspect we discuss is that of the coordination chemistry of these metal-oxide ligands. We show that this chemistry leads to remarkable examples of well-insulated magnetic clusters of controlled nuclearity and topology. In these clusters detailed information on the nature of the magnetic exchange interactions can be extracted by using, in addition to the classical magnetic techniques (magnetic susceptibility, magnetization and EPR spectroscopy), other physical techniques as the inelastic neutron scattering (INS) spectroscopy, which provides more direct information on the lower lying energy levels of the magnetic cluster. The second aspect we discuss is that of the interplay between electron delocalization and exchange interactions in the mixed-valence polyoxometalates. We show that these high-nuclearity multielectronic clusters are model systems for the development of new theories in the mixed valence area. (C) 1999 Elsevier Science S.A. All rights reserved.