A new indium phase with three stuffed and condensed fullerane-like cages: Na172In197Z2 (Z = Ni, Pd, Pt)

Abstract

Ternary compounds Na∼172In∼197Z2 with Z = Ni, Pd or Pt are obtained by slow cooling of the appropriate fused mixtures of the elements in welded Ta. They occur in the orthorhombic space group Pmmn, Z = 2 and, for Ni, a = 15.988 (5), b = 26.102 (7), c = 47.59 (6) Å and R(F), Rw = 6.0, 6.7% for the refined composition Na171.85(5)In197.1(2)Ni2. The structure contains puckered layers of condensed fullerane-type spheres or cages built of 70 and 78 indium atoms, each of which shares six of its twelve pentagonal faces with six other spheres, two of the same type and four of the other. These are joined into double layers via bonds to exo In11 and In14 polyhedra fused near one pole of the two fulleranes. The double layers are in turn separated by sodium cations and M60 = In48Na12 cages which share six of their pentagonal faces with two In70 cages and four In78 cages. All three cages have C2v symmetry but are close to those of the corresponding carbon fullerenes. The In70 and M60 cages are centered by isolated In∼10Z clusters, and the In78 spheres, by In16 clusters about a central Na that are tethered to the inside of the In78 fullerane via vertices of two icosahedra fused into the framework. In addition, all three cages contain endohedral sodium ion deltahedra that screen the encapsulated clusters from the fullerane. The partially disordered Ni-centered clusters of indium exhibit nearly spherical geometry and a diffuse distribution of the electron density on the surface that is excluded from positions below the 12 more inward-lying Na within the corresponding fulleranes. The cluster distributions were approximated by refining many closely positioned indium atoms, some partially occupied. In all three cases, the results could be reduced to geometries close to those of previously known In10Ni10- (within In70, M60) or In16 (within In78) species through removal of the disorder induced by mirror planes from the C2v symmetry imposed by the overall structure. The multiply endohedral descriptions Ni@In10@Na37@In70 and Ni@In10@ Na32O(In48Na12) are apt for the first two fullerane components. The suitability of large polyhedral constructs for the description of other condensed structures is also considered. © 1996 Academic Press, Inc.