Lanthanide-Containing 22-Tungsto-2-germanates [Ln(GeW₁₁O₃₉)₂]^13–: Synthesis, Structure, and Magnetic Properties

We report on the synthesis and structural characterization of two series of lanthanide-containing 22-tungsto-2-germanates. The first series corresponds to a family of polyanions with the formula [Ln­(β₂-GeW₁₁O₃₉)₂]^13– (Ln^III = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Gd (6), Dy (7)), and the second series corresponds to a family with the formula [Ln­(β₂-GeW₁₁O₃₉)­(α-GeW₁₁O₃₉)]^13– (Ln^III = Ho (8), Er (9), Tm (10)). All compounds were characterized in the solid state by single-crystal and powder XRD, IR, TGA, and SQUID magnetometry. The polyanions were synthesized in aqueous medium by direct reaction of the monolacunary [β₂-GeW₁₁O₃₉]^8– POM precursor with the corresponding lanthanide salts. The structure of the polyanions consists of an 8-coordinated lanthanide ion in a square-antiprismatic geometry, which is sandwiched either between two [β₂-GeW₁₁O₃₉]^8– units for 1–7 or between a [β₂-GeW₁₁O₃₉]^8– and a [α-GeW₁₁O₃₉]^8– unit for 8–10. Furthermore, the effect of the central paramagnetic lanthanide ion on the magnetic behavior of the polyanions was investigated, with the erbium-derivative [Er­(β₂-GeW₁₁O₃₉)­(α-GeW₁₁O₃₉)]^13– (9) showing single-molecule magnet (SMM) behavior.