SYNTHESIS, CHARACTERIZATION, AND BONDING OF HETEROATOMIC CLUSTERS - NA13CD20E7 (E=PB, SN), A FURTHER EXAMPLE OF A STRUCTURE CONTAINING EMPTY ICOSAHEDRA WITHOUT AN ELEMENT OF GROUP-13

The compounds Na13Cd20E7 (E = Pb, Sn) were made in nearly 100% yield b y quenching the melts of appropriate mixtures of elements sealed in ni obium containers. They crystallize in the cubic space group Im (3) ove r bar, Z=4, with a=15.992(2) and 15.790(4) Angstrom for E=Pb and Sn, r espectively. The Cd/E part of the structure is a framework of heavily fused monocapped truncated trigonal prisms. Twelve-bonded icosahedra a re nested in cavities of the framework, This is the second example of a structure containing empty icosahedra made without the participation of an element of the boron group. The sodium cations occupy the space between the clusters and inside the 13-atom polyhedra.