Composition and Crystal Structure of SmSb 2 O 4 Cl Revisited – and the Analogy of Sm 1.5 Sb 1.5 O 4 Br

The quaternary halide‐containing samarium(III) oxidoantimonates(III) Sm 1.3 Sb 1.7 O 4 Cl and Sm 1.5 Sb 1.5 O 4 Br were synthesized through solid‐state reactions from the binary components (Sm 2 O 3 , Sb 2 O 3 and Sm X 3 , X = Cl and Br) at 750 °C in evacuated fused silica ampoules. They crystallize tetragonally in the space group P 4/ mmm , like the basically isotypic bismuthate(III) compounds SmBi 2 O 4 Cl and SmBi 2 O 4 Br, but show larger molar volumes and therefore contradict an ideal composition of “SmSb 2 O 4 X ” ( X = Cl and Br). Both single‐crystal X‐ray diffraction and quantitative electron‐beam microprobe analysis revealed the actual compositions of the investigated antimony(III) compounds, which can be understood as heavily Sm 3+ ‐doped derivatives of “SmSb 2 O 4 X ” hosts at the Sb 3+ site. (Sm1) 3+ is coordinated eightfold by oxygen atoms in the shape of a cube. The mixed‐occupied (Sb/Sm2) 3+ cation has four oxygen atoms and four halide anions as neighbors forming a square antiprism. The oxygen atoms and anions establish alternating layers parallel to the ab ‐plane, which alternate when stacked along [001].