Synthesis and structure of two 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 °C and 1000 °C followed by a final firing at 1350 °C for 12 h under a H2Ar 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 %, Rwp = 9.32 %, Rbragg = 8.95 %; Ba2HfS4, R = 9.45 %, Rwp = 11.06 %, Rbragg = 6.53 %. Both compounds possess the tetragonal K2NiF4 structure type with space group I4mmm; a = 4.7154 (2) Å, c = 16.023 (2) Å, V = 356.30 (5) Å3, Z = 2 [M = Zr]; and a = 4.8344 (4) Å, c = 15.842 (3) Å, V = 370.2 (1) Å3, Z = 2 [M = Hf]. The transition metal atoms are in unusually distorted octahedral geometries with normal axial MS distances [2.52 (1) Å (Zr), 2.53 (3) Å (Hf)] and short equatorial distances [2.357 (1) Å (Zr), 2.417 (1) Å (Hf)] relative to the octahedral MS distances in the MS2 binaries [MS = 2.56 Å for Zr and Hf].