SYNTHESIS AND STRUCTURE OF 2 NEW BA2MS4 PHASES WHERE M = ZR, HF - A NEW SERIES OF K2NIF4 SOLIDS

The compounds Ba2MS4 where M = Zr, Hf were prepared from BaS, S, and the corresponding metal by several firings at temperatures between 500-degrees-C and 1000-degrees-C followed by a final firing at 1350-degrees-C for 12 h under a H2/Ar atmosphere. The structures of both phases were determined by Rietveld refinements of the powder X-ray diffraction data yielding the following residuals: for Ba2ZrS4, R = 9.65 %, R(wp) = 9.32 %, R(bragg) = 8.95 %; Ba2HfS4, R = 9.45 %, R(wp) = 11.06 %, R(bragg) = 6.53 %. Both compounds possess the tetragonal K2NiF4 structure type with space group I4/mmm; a = 4.7154 (2) angstrom, c = 16.023 (2) angstrom, V = 356.30 (5) angstrom 3, Z = 2 [M = Zr]; and a = 4.8344 (4) angstrom, c = 15.842 (3) angstrom, V = 370.2 (1) angstrom 3, Z = 2 [M = Hf]. The transition metal atoms are in unusually distorted octahedral geometries with normal axial M-S distances [2.52 (1) angstrom (Zr), 2.53 (3) angstrom (Hf)] and short equatorial distances [2.357 (1) angstrom (Zr), 2.417 (1) angstrom (Hf)] relative to the octahedral M-S distances in the MS2 binaries [M-S = 2.56 angstrom for Zr and Hf].