CS(3)ZR(6)BR(15)Z (Z=C, B) - A STUFFED RHOMBOHEDRAL PEROVSKITE STRUCTURE OF LINKED CLUSTERS

The isostructural title compounds are synthesized in good yields from reactions of Zr, ZrBr4, CsBr, and Z in sealed Ta tubing for similar to 3 weeks at 850 degrees C. Their single-crystal data refinements established the products as Cs-3.02(7)-(7)Zr6Br15C and Cs-3.39(5)Zr6Br15B (R (3) over bar c, Z = 6, a = 13.1031(6), 13,116(1) Angstrom, c = 35.800(3), 35.980(6) Angstrom, R(F)/R(w) = 5.4/5.9, 5.4/4.4%, respectively). The structure is derived from a three-dimensional [Zr-6(Z)Br-12]Br-6/2 network of four-rings (as in ReO6/2) twisted into a rhombohedral perovskite analogous to VF3. The three necessary Cs+ cations are fractionally distributed over five sites that are far from optimal or common, with either eight asymmetric or only three close bromide neighbors. Refinement of a third CS3.18(5)Zr6Br15C structure at -50 degrees C gave the same result with, somewhat smaller positional distributions of the atoms.