In most magnetic molecular clusters studied so far, localized moments of metal ions are coupled bysuperexchange interactions via ligand atoms to yield the total moment of the cluster, which is basicallya piece of a magnetic insulator. Here we present an experimental and theoretical study of another formof molecular magnetism, arising from unfilled molecular orbitals delocalized over the entire metal coresof molecular metal clusters. These cores thus act as nanosize quantum dots, in which the metal valenceelectrons are confined. [S0031-9007(98)07157-9]