We have synthesized and structurally characterized the monolanthanide-containing polyanions [Ln(beta(2)-SiW11O39)(2)](13-) (Ln = La (1), Ce (2), Sm (3), Eu (4), Gd (5), Tb (6), Yb (7), Lu (8)). Synthesis was accomplished by reaction of the respective lanthanide ion with the monolacunary Keggin-type precursor [beta(2)-SiW11O39](8-) in a 1:2 molar ratio in 1 M KCl medium at pH 5. Polyanions 1-8 were isolated as potassium salts and then characterized by IR, single-crystal X-ray diffraction, and elemental as well as thermogravimetric analysis. The structures of 1-8 are composed of an eight-coordinated Ln(3+) center sandwiched by two chiral (beta(2)-SiW11O39) units. Large Ln(3+) ions appear to favor an (R,R) (or (S,S)) configuration (point group C-2) of the Keggin units, with an increasing amount of (R,S) (or (S,R)) configuration (point group C-1) found in the solid state as the Ln(3+) ion decreases in size. This trend is also supported by solution W-183 NMR results for the diamagnetic La3+ and Lu3+ derivatives.