CsSc3F6[SeO3]2: A New Rare-Earth Metal(III) Fluoride Oxoselenate(IV) With Sections Of The ReO3-Type Structure

A new representative of rare-earth metal(III) fluoride oxoselenates(IV) derivatized with alkali metals could be synthesized via solid-state reactions. Colorless single crystals of CsSc3F6[SeO3](2) were obtained through the reaction of Sc2O3, ScF3, and SeO2 (molar ratio 1:1:3) with CsBr as reactant and fluxing agent. For this purpose, corundum crucibles embedded as liners into evacuated silica ampoules were applied as containers for these reactions at 700 degrees C for seven days. The new quintenary compound crystallizes in the trigonal space group P3m1 with a = 565.34(4) and c = 1069.87(8) pm (c/a = 1.892) for Z = 1. The crystal structure of CsSc3F6[SeO3](2) contains two crystallographically different Sc3+ cations. Each (Sc1)(3+) is surrounded by six fluoride anions as octahedron, while the octahedra about (Sc2)(3+) are formed by three fluoride anions and three oxygen atoms from three terminal [SeO3](2-) anions. The [(Sc1)F-6](3-) octahedra link via common F- vertices to six fac-[(Sc2)F3O3](6-) octahedra forming (2){[Sc3F6O6](9-)} layers parallel to (001). These layers are separated by oxygen-coordinated Cs+ cations (C.N. = 12), arranging for the charge compensation, while Se4+ cations within the layers surrounded by three oxygen atoms as (1)-tetrahedral [SeO3](2-) units complete the structure. EDX measurements confirmed the composition of the title compound and single-crystal Raman studies showed the typical vibrational modes of isolated [SeO3](2-) anions with ideal C-3v symmetry.