Crystal structure, spectroscopic properties, and magnetic behavior of the fluoride-derivatized lanthanoid(III) ortho-oxomolybdates(VI) LnF[MoO4] (Ln=Sm-Tm)

The fluoride-derivatized lanthanoid(III) ortho-oxomolybdates(VI) LnFMoO₄] (Ln=Sm-Tm) crystallize in the monoclinic space group P2₁/c with four formula units per unit cell (a=516-528 pm, b=1220-1248 pm, c=659-678 pm, β=112.5-113.1°). The structure contains one crystallographically unique Ln³⁺ cation surrounded by two fluoride and six oxide anions in a square antiprism (CN=8). The square antiprisms LnF₂O₆] are interconnected via three edges to form layers parallel (010), which are cross-linked along 010] by Mo⁶⁺ in tetrahedral oxygen coordination to form the three-dimensional crystal structure. The fluoride anions within this arrangement exhibit a twofold coordination of Ln³⁺ cations in the shape of a boomerang, which is connected to another F⁻ anion to form planar F₂Ln₂]⁴⁺ rhombuses. Magnetic measurements for GdFMoO₄], TbFMoO₄], and DyFMoO₄] show Curie-Weiss behavior, despite the peculiar arrangement of the lanthanoid(III) cations in layers comparable with those of gray arsenic. Furthermore, Raman, infrared, and diffuse reflectance spectroscopy data for these compounds were recorded and interpreted.