CARBON-FREE FULLERENES - CONDENSED AND STUFFED ANIONIC EXAMPLES IN INDIUM SYSTEMS

Condensed, well-ordered analogs of the fullerenes occur in the hexagonal phases Na96In97Z2 (Z = nickel, palladium, or platinum). Large cages of In74 (D3h) and M60 (= In48Na12, D3d) share pentagonal faces to generate a double-hexagonal close-packed analog of NiAs. All these polyhedra are centered by partially disordered In10Z clusters within deltahedra of sodium atoms that cap all inner faces of the cages, namely, Z@In10@Na39@In74 and Z@In10@Na32@Na12In48 ''onions.'' The highest filled bands in these compounds apparently involve localized electron pairs on surface features on In74-based layers. Structural and electronic relations between diamond and NaIn (stuffed diamond structure) parallel those between certain fullerenes and Na96In97Z2 and, presumably, other valence-driven intermetallic phases.