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.