Double salt crystal structure of nona­sodium dihydrogen nona­vanadoplatinate(IV) tri­hydrogen nona­vanadoplatinate(IV) tetra­contahydrate: stepwise-protonated nona­vanadoplatinate(IV)

Nonavanadoplatinate [Pt(IV)V(9)O(28)](7−), which is the first heteropolyoxovanadate in the deca­vanadate framework, [V(10)O(28)](6−), has been investigated crystallographically. The title compound, Na(9)[H(2)Pt(IV)V(9)O(28)][H(3)Pt(IV)V(9)O(28)]·40H(2)O, was obtained by a hydro­thermal reaction at pH = 2. This compound contains two different protonated heteropolyoxovanadates, [H(2)Pt(IV)V(9)O(28)](5−) [polyanion (A)] and [H(3)Pt(IV)V(9)O(28)](7−) [polyanion (B)]. The locations of the H atoms on the protonated O atoms were observed in difference Fourier maps and confirmed by the inter­polyanion hydrogen bonds, bond-length elongation and bond-valence-sum (VBS) analysis. The two (Pt and V)-bound μ(2)-O atoms are protonated in both polyanions. The position of the third protonated O atom in polyanion (B) is an inter­esting feature of the structure, being located on one (V(2))-bound μ(2)-O atom. The discrete heteropolyanions form a dimer, {H(5)[PtV(9)O(28)](2)}(9−), through five inter­polyanion hydrogen bonds. Additional O—H⋯O hydrogen bonds and interactions between Na(+) cations and water molecules as well as terminal O atoms of one of the polyanions consolidate the crystal packing.