Isolation of an Asymmetric Lanthanide Polyoxometalate, Na12H[(W5O18)Tb(H2W11O39)]·42H2O, Containing Two Distinct Isopolyanions

Abstract

The structural characterization of a new, asymmetric polyoxoanion, Na12H[(W5O18)Tb(H2W11O39)]·42H2O, is reported herein. This new structure was isolated from a mixture of a number of compounds, including the symmetric Na9[Tb(W5O18)2] sandwich cluster, and the lanthanide-free cluster, Na10(H2W12O42). The major product of the reaction was Na9[Tb(W5O18)2], and the compound reported here is a minor product that is obtained reproducibly. The salts of these three clusters do not differ significantly in their crystal habit, size, and color. The crystal structure of Na12H[(W5O18)Tb(H2W11O39)]·42H2O was determined by single-crystal X-ray diffraction and shows that the cluster is composed of a lacunary Lindqvist (W5O18)6− building block and an unusual lacunary metatungstate (H2W11O39)10− polyanion connected through a central Ln3+ cation. The central Tb3+ cation has a square antiprismatic symmetry, the lacunary metatungstate has a square pyramidal symmetry, and the lacunary Lindqvist polyanion exhibits a cuboctahedral symmetry. This is the first example of a crystallographically characterized sandwich cluster possessing a lacunary metatungstate (H2W11O39)10− ligand.