Ba₂F₂Fe²⁺_0.5Fe³⁺S₃: A Two-Dimensional Inhomogeneous Mixed Valence Iron Compound

The structure of the new mixed valence compound Ba2F2Fe1.5S3 was solved by means of single crystal X-ray analysis. It crystallizes in an orthorhombic cell, in the Pnma space group with the cell parameters a = 12.528(3) Å, b = 18.852(4) Å, and c = 6.0896(12) Å. The structure is formed by the alternated stacking of fluorite type [Ba2F2]2+ blocks and the newly discovered [Fe1.5S3]2− blocks. This [Fe1.5S3]2− block exhibits a mixed valence of iron with Fe(+II) located in octahedrons and Fe(+III) in tetrahedrons. Preliminary susceptibility measurements suggest a low dimensional antiferromagnetic behavior.