Lanthanum and Praseodymium Bromide Pnictides. A Convergence of Interstitial Chemistry in Cluster Halides and Intermetallic Pnictides

Reactions of metalR,RBr3(R=La, Pr), and pnictogenPn(P, As, Sb, Bi) at 900–1000°C provide a new series of condensed cluster products, either cubicR3Br3Pnor hexagonalR5Pn3Br, but not both for the samePn. Syntheses and lattice dimensions for all eight examples are reported. CubicR3Br3Pnresults with interstitial P or As (Ca3I3P type,I4132 (No. 214),Z=8), whereas hexagonal P5Pn3Br is formed forPn=Sb, Bi with interstitial Br (stuffed Mn5Si3type), a new range of composition for these compounds. The latter structure for La5Sb3Br was refined by single-crystal X-ray diffraction data (P63/mcm(No. 193),Z=2,a= 9.602(2) ?,c=6.7331(3) ?,R(F)/Rw=1.7/2.0%). Features that determine the formation of a particular set of compounds in each structure type are discussed.