NOVEL CHAIN AND OLIGOMERIC CONDENSED CLUSTER PHASES FOR GADOLINIUM IODIDES WITH MANGANESE INTERSTITIALS

Reactions in the Gd-I-Mn system near 800-degrees-C in sealed Nb containers provide good yields of Gd3I3Mn and Gd5I7Mn. The first is isostructural with the Pr3I3Ru family (P2(1)/m, Z = 2, a = 8.928(3) angstrom, b = 4.127(1) angstrom, c = 12.266(4) angstrom, beta = 95.51(2)-degrees; R, R(w) = 4.1, 4.8%). The Gd5I7Mn phase has a new cubic structure (P43mBAR, Z = 4, a = 12.1765(1) angstrom; R, R(w) = 3.5, 3.4%). Both structures exhibit substantially shorter Mn-Mn interactions than seen before with electron-richer interstitials. Distorted double chains of edge-sharing Gd6Mn octahedra in Gd3I3Mn resemble those in Y3I3(Ru,Ir), but with 2.66-angstrom separations in a distinct zigzag Mn chain within. The new Gd5I7Mn contains two types of clusters: (a) Gd16I20Mn4 units that closely resemble the Ru4-centered tetracapped truncated tetrahedron Y16 in Y16I20Ru4 but with strong Mn displacements to dBAR(Mn-Mn) = 2.825 angstrom in the centered tetrahedra; (b) Gd4I8 capped tetrahedra interbonded with those of type a which have approximately 25% of each metal vertex displaced outward in a disordered manner. The small type b clusters appear to be oxidized to give a (Gd4I8)4+[Gd16(Mn)4I20]4-formulation. Calculations suggest this arrangement does not give a closed configuration with these elements, perhaps because of the stoichiometry limitations with a single type of interstitial.