The largest tungstogermanate and third-largest polytungstate (see picture) was obtained by K+-directed self-assembly of three unprecedented types of [GeW10O38]12- fragments stabilized by coordination of Ce ions on the vacancies. In its Ce6O42 central ring, which displays antiferromagnetic interactions, a K+ cation is captured by internal water molecules. Gray octahedra WO6, green tetrahedra GeO4; Ce orange, K purple, O red.
![Giant crown-shaped polytungstate formed by self-assembly of CeIIIstabilized dilacunary Keggin fragments](https://www.iciq.org/wp-content/uploads/2014/03/Giant-crown-shaped_8384.gif)