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

The title compound, (CH₆N₃)₇H₉[PtMo₆O₂₄]₂·₇H₂O, 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_4.5PtMo₆O₂₄]₂} polyanion is the same as that already characterized in K7[H_4.5PtMo₆O₂₄]2₁₁H₂O [space group P1; Lee & Joo (2010). Acta Cryst. E66, i8-i9]. The heteropolyanions form inversion-generated dimers, {[H₄₅PtMo₆O₂₄]2}^7-, held together by each of the four μ₃-O - H⋯μ₁-O, two μ₂-O - H⋯μ₂-O hydrogen bonds and one centrosymmetric μ3-O - H - μ3-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.