Abstract: Twelve rare earth metal mono-substituted polyoxometalates, K₁₃[Ln(γ-SiW₁₀O₃₆)₂]·nH₂O(Ln=La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Yb³⁺), were synthesized by vacant sites-filling method by using γ- [SiW₁₀O₃₆]^8- as the ligand. The compounds were characterized by elemental analysis, UV-Vis absorption spectra, IR spectra, CV, paramagnetic measurement, fluorescence spectra and ¹⁸³W NMR. These results indicate that the rare earth metal ion is coordinated with eight terminal oxygen atoms of two γ- [SiW₁₀O₃₆]^8- ligands with D_2d symmetry and the title compounds have 1;2 sandwich structure.

Key words: Rare earth metal, Di-vacant γ-Keggin type ligand, Sandwich structure