A NEW STRUCTURE TYPE FOR RARE-EARTH-METAL CLUSTER COMPOUNDS STABILIZED BY TRANSITION-METALS - KPR6I10OS, CSPR6I10FE, CSLA6I10FE, AND CSLA6I10MN

Reactions of KI, Pr, PrI3, and Os in niobium tubes at 800 degrees C yi elded black, air- and moisture-sensitive crystals of KPr6I10Os which w ere characterized by single crystal X-ray diffraction (orthorhombic, P nma, a = 15.362(3), b = 13.498(2), c = 14.128(3) Angstrom, Z = 4, R(F) /R(w) = 4.4/5.6%). Subsequent parallel experiments also gave, accordin g to Guinier powder pattern data, the isostructural compounds CsPr6I10 Fe (a = 15.312(2), b = 13.426(1), c = 14.154(1) Angstrom), CsLa6I10Fe (a = 15.523(2), b = 13.646(2), c = 14.334(1) Angstrom) and CsLa6I10Mn (a = 15.457(4), b = 13.737(2), c = 14.329(2) Angstrom). The important structural feature is the presence of octahedral rare-earth-metal clus ter units R(6) that are centered by a transition-metal atom Z and brid ged and interconnected by halide atoms. The new compounds exhibit the same general pattern of halide connectivity (R(6)Z)X(2)(i)X(4/2)(i-i)X (6/2)(i-a)X(6/2)(n-i) as do the triclinic compounds R(6)X(10)Z. Howeve r, the structural arrangement of the metal octahedra is significantly different; they are linked by I-i-i atoms into zigzag chains along [01 0] and these are interconnected into a three dimensional network by I- i-a atoms to form channels in which the alkali-metal atoms are located . The introduction of alkali-metal atoms into reactions leads to new q uaternary compounds with discrete rare-earth-metal clusters centered b y transition metals and more open structure frameworks. Measurements o f the temperature dependencies of the magnetic susceptibilities for Cs La6I10Fe and CsLa6I10Mn are consistent with expectations for 17- and 1 6-electron cluster systems, respectively.