2 NEW EXAMPLES FOR THE UNUSUAL R(12)I(17)Z(2)-STRUCTURE TYPE - LA12I17FE2 AND CE12I17MN2

Reactions of KI, La, LaI3, and Fe in niobium tubes at 900 degrees C yi eld black crystals of La12I17Fe2 which were characterized by single-cr ystal X-ray diffraction (triclinic, <P(1)over bar>, Z = 1, a = 11.967( 8), b = 11.851(6), c = 9.918(7) Angstrom, alpha = 114.59(5)degrees, be ta = 104.83(6)degrees, gamma = 93.05(5)degrees, R(F)/R(w) = 3.8/4.3%). Similar experiments also gave the isostructural Ce12I17Mn2 according to the Guinier powder pattern (a = 11.863(6), b = 11.840(6), c = 9.857 (5) Angstrom, alpha = 14.90(4)degrees, beta = 104.47(4)degrees, gamma = 93.28(4)degrees). The Pr12I17Fe2-type structure contains octahedral rare-earth-metal cluster units R(6) centered by a transition-metal ato m Z and sheathed by iodine atoms. These are closely linked by seven I- i-i and one I-i-a-a bridges that lead to the unusually low I:Pr ratio for phases with isolated clusters. The compounds reported here togethe r with Pr(12)I(17)Z(2), Z = Fe, Re are the only phases known to adopt this structure type. The La12I17Fe2 phase formally has 17.5 e per clus ter, and its magnetic susceptibility data are consistent with equal nu mbers of 17-e and 18-e (closed shell) clusters, with mu = 1.11 BM for the former. (C) 1996 Academic Press, Inc.