A NEW INDIUM PHASE WITH 3 STUFFED AND CONDENSED FULLERANE-LIKE CAGES - NA(172)IN(197)Z(2) (Z=NI, PD, PT)

Ternary compounds Na-similar to 172 In-similar to 197 with Z(2) = Ni, Pd or Pt are obtained by slow cooling of the appropriate fused mixture s of the elements in welded Ta. They occur in the orthorhombic space g roup Pmmn, Z = 2 and, for Ni, a = 15.988 (5), b = 26.102 (7), c = 47.5 9 (6) Angstrom and R(F), R(w) = 6.0, 6.7% for the refined composition Na-171.85(5)In-197.1(2)Ni-2. The structure contains puckered layers of condensed fullerane-type spheres or cages built of 70 and 78 indium a toms, 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 In-11 and In-14 polyhedra f used near one pole of the two fulleranes. The double layers are in tur n separated by sodium cations and M(60) = In48Na12 cages which share s ix of their pentagonal faces with two In-70 cages and four In-78 cages . All three cages have C-2v symmetry but are close to those of the cor responding carbon fullerenes. The In-70 and M(60) cages are centered b y isolated In-similar to 10 clusters, and the In-78 spheres, by In-16 clusters about a central Na that are tethered to the inside of the In- 78 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 partiall y disordered Ni-centered clusters of indium exhibit nearly spherical g eometry and a diffuse distribution of the electron density on the surf ace that is excluded from positions below the 12 more inward-lying Na within the corresponding fulleranes. The cluster distributions were ap proximated by refining many closely positioned indium atoms, some part ially occupied. In all three cases, the results could be reduced to ge ometries close to those of previously known In10Ni10- (within In-70, M (60)) or In-16 (within In-78) species through removal of the disorder induced by mirror planes from the C-2v symmetry imposed by the overall structure. The multiply endohedral descriptions Ni@In-10@Na37In70 and Ni@In-10@Na-32@(In48Na12) are apt for the first two fullerane compone nts.