Crystal structure and electrical properties of the mixed valent titanium oxysulfide Sm2Ti2S2O4.5

A new phase Sm₂Ti₂S₂O_4.5 was synthesized and its crystal structure was solved by single-crystal X-ray diffraction. This compound crystallizes in the monoclinic system (C2/m) with lattice constants a=17.9987(11) Å, b=3.71607(14) Å, c=12.6172(8) Å and β=133.645(4)°. The structure is built up from double chains of Ti-centered octahedra between which Sm-polyhedra develop. In spite of very close formulations, the structure of Sm₂Ti₂S₂O_4.5 differs completely from that of the defect Ruddelsden-Popper phase Sm₂Ti₂S₂O₅ previously reported. The title compound presents a mixed valence for titanium with Ti(III) (d¹) and Ti(IV) (d⁰) located in different crystallographic sites. However, conductivity measurements show that this compound is non-metallic.