The structure of dipotassium strontium hexaniobium octadecachloride is based on [Nb(6)Cl(i)(12)Cl(a)(6)](4-) units (i and a denote 'inner' and 'outer' ligands, respectively), which have crystallographically imposed -3 symmetry, linked together by K(+) and Sr(2+) cations. The K(+) cation occupies a tetrahedral site in the face-centered cubic lattice of cluster units, and is bonded to 12 Cl ligands. The Sr atom is located in an octahedral site and is bonded to six outer Cl ligands.