Lanthanum and praseodymium bromide pnictides. A convergence of interstitial chemistry in cluster halides and intermetallic pnictides

Reactions of metal R, RBr3 (R = La, Pr), and pnictogen Pn (P, As, Sb, Ri) at 900-1000 degrees C provide a new series of condensed cluster products, either cubic R(3)Br(3)Pn or hexagonal R(5)Pn(3)Br, but not both for the same Pit. Syntheses and lattice dimensions for all eight examples are reported. Cubic R(3)Br(3)Pn results with interstitial P or As (Ca3I3P type, 14(1)32 (No. 214), Z = 8), whereas hexagonal P(5)Pn(3)Br is formed for Pn = Sb, Ri with interstitial Pr (stuffed Mn5Si3 type), a new range of composition for these compounds. The latter structure for La5Sb3Br was refined by single-crystal X-ray diffraction data (P6(3)/mcm (No. 193), Z = 2, a = 9.602(2) Angstrom, c = 6.7331(3) Angstrom, R (F)/R-w = 1.7/2.0%), Features that determine the formation of a particular set of compounds in each structure type are discussed, (C) 1999 Academic Press.