The crystal chemistry of phases in the BaFeS and Se systems

Abstract

The crystal structures of a number of new phases synthesized in the BaFeS and Se systems were investigated by X-ray diffraction techniques. Ba 2FeS 3 is orthorhombic, Pnma, a = 12.087(5)Å, b = 4.246(2)Å, c = 12.359(5)Å, ϱ meas = 4.0 g/cm 3, ϱ calc = 4.47 g/cm 3, Z = 4, mp >1300°C. The compound is isostructural with Ba 2ZnS 3 and the structure consists of FeS 4 tetrahedrons sharing corners to form an infinite linear chain. Ba 2FeSe 3 is isostructural with the sulfide and its parameters are a = 12.350(7)Å, b = 4.439(2)Å, c = 12.921(5)Å. BaFe 2S 3 is orthorhombic, Cmcm, a = 8.7835(9)Å, b = 11.219Å, c = 5.2860Å, ϱ meas = 4.0 g/cm 3, ϱ calc = 4.40 g/cm 3, Z = 4, mp 765 ± 10°C. Three-dimensional X-ray diffraction data were used to refine the structure which consists of two FeS 4 tetrahedrons sharing edges and this binuclear unit in turn shares edges with others to form an infinite chain. The structure of BaFe 2Se 3 is essentially the same as that of the sulfide but they are not isostructural. The selenide is orthorhombic, Pnma, a = 11.878(3)Å, b = 5.447(2)Å, c = 9.160(2)Å, ϱ calc = 5.44 g/cm 3, Z = 4; decomposes above 750°C. Ba 6Fe 8S 15 is tetragonal, I4 m , a = 11.408(2) Å, c = 10.256(2)Å, ϱ meas = 4.30 g/cm 3, ϱ calc = 4.36 g/cm 3, Z = 2, mp 880 ± 10°C. The structure was determined from three-dimensional X-ray diffraction data and consists of a tetranuclear unit formed by 4 FeS 4 tetrahedrons sharing corners and these units then share edges to form an infinite column. Ba 3Fe 3Se 7 is hexagonal, P6 3 mc, a = 10.843(3)Å, c = 7.384(2)Å, ϱ calc = 5.00 g/cm 3, Z = 2. The structure was determined using three-dimensional single crystal X-ray diffraction data and consists of isolated trinuclear units formed by edge sharing of three FeSe 4 tetrahedrons. In the several compounds the FeFe distances between chains are 6 Å, and vary from 2.6 to 4.2 Å within the chains. The FeS distances are 2.3 – 2.4 Å, the SFeS angles are tetrahedral and the BaS distances are essentially equal to the sum of the ionic radii. The corresponding distances in the selenides reflect the larger size of the anion.