Structure and Properties of Mixed‐valence Compound Eu 5 Zr 3 S 12

Needle‐shaped crystals of Eu 5 Zr 3 S 12 and Eu 3.67 Sr 1.33 Zr 3 S 12 were synthesized by solid‐state reactions of the elements and ZrS 2 at 673–1273 K in alumina crucibles, and their crystal structures were determined by single‐crystal methods. They are isotypic with hexagonal symmetry (space group P $\bar{6}$ 2 m , Z = 1, Eu 5 Zr 3 S 12 : a = 1170.7(2), c = 394.27(8) pm, wR 2 = 0.0636 for 552 F 2 and 27 parameters; Eu 3.67 Sr 1.33 Zr 3 S 12 : a = 1167.0(2), c = 395.71(8) pm, wR 2 = 0.0887 for 484 F 2 and 29 parameters) and contain one‐dimensional chains of edge‐sharing ZrS 2 S 4/2 octahedra running parallel to [001]. Two europium sites are seven‐ or ninefold‐coordinated by sulfur. Eu 5 Zr 3 S 12 is a Curie paramagnet with an effective magnetic moment of μ eff = 13.37(1) μ B per formula unit (fu), in agreement with three Eu 2+ /fu. 151 Eu Mössbauer spectra show two absorption lines suggesting a static mixture of Eu 2+ and Eu 3+ in accordance with Eu 3 2+ Eu 2 3+ Zr 3 4+ S 12 2– .This assignment is not in line with the observed Eu–S distances. To resolve this, we suggest pure Eu 2+ at the 2 c site and inhomogeneous mixed valence at the 3 f site according to (Eu 2 2+ ) 2 c (Eu 2+ Eu 2 3+ ) 3 f Zr 3 4+ S 12 2– . This is supported by the site preference of Sr 2+ in Eu 3.67 Sr 1.33 Zr 3 S 12 .