The novel polyanions [Ln(2)(H2O)(10)W22O71(OH)(2)](8-) (Ln = La (1), Ce (2), Tb (3), Dy (4), Ho (5), Er (6), Tm (7), Yb (8), Lu (9), Y (10)) have been synthesized by reaction Of WO42- and lanthanide ions in acidic aqueous medium. The low symmetry (C-i) polyanion family [Ln(2)(H2O)(10)W22O71(OH)(2)](8-) consists of the isopolyanion [H2W22O74](14-) and two {Ln(H2O)(5)}(3+) supporting units. The [H2W22O74](14-) cluster, which consists of two undecatungstate (Will fragments, acts as a tridentate ligand to two Ln(3+) ions. Polyanions 1-10 are isostructural, and the coordination number of the lanthanide ions correlates with their sizes. All compounds have been fully characterized in the solid state by Fourier transform infrared spectroscopy, single-crystal X-ray diffraction, thermogravimetric analysis, and elemental analysis. Single-crystal X-ray diffraction analyses show that 1-10 crystallize as sodium salts in the triclinic space group P (1) over bar.