Crystal structure of hepta­guanidinium nona­hydrogen bis­[α-hexa­molybdoplatinate(IV)] hepta­hydrate

The title compound, (CH(6)N(3))(7)H(9)[PtMo(6)O(24)](2)·7H(2)O, containing the well-known Anderson-type heteropolyoxomolybdate, was obtained by recrystallization of its powdered guanidinium salt. The protonated O atoms in the polyanion were confirmed by electron-density maps, inter­polyanion hydrogen bonds and bond-valance sums (BVS). The {[H(4.5)PtMo(6)O(24)](2)}(7−) polyanion is the same as that already characterized in K(7)[H(4.5)PtMo(6)O(24)](2)·11H(2)O [space group P-1; Lee & Joo (2010 ▸). Acta Cryst. E66, i8–i9]. The heteropolyanions form inversion-generated dimers, {[H(4.5)PtMo(6)O(24)](2)}(7−), held together by each of the four μ(3)-O—H⋯μ(1)-O, two μ(2)-O—H⋯μ(2)-O hydrogen bonds and one centrosymmetric μ(3)-O—H—μ(3)-O hydrogen bond. The H atom of the centrosymmetric hydrogen bond is located on an inversion centre. One guanidinium ion and one water mol­ecule are equally disordered about a twofold rotation axis.