Calcium hexa­kis(dihydrogen­phosphito)­stannate(IV), Ca[Sn(H₂PO₂)₆], with some remarks on the so-called Ge₂(H₂PO₂)₆ structure type

The title compound, Ca[Sn(H₂PO₂)₆], was formed after a few days when tin(II) fluoride was allowed to react with phosphinic acid at ambient conditions. The structure consists of chains of Ca²⁺ and Sn⁴⁺ cations in octa­hedral sites with -3 symmetry bridged by bidentate hypophosphite anions. The chains are hexa­gonally close packed along [001]. The discovery of the compound and the successful structure refinement provides strong evidence that an isostructural compound, originally described as the mixed-valence compound, Ge₂[H₂PO₂]₆ [Weakley (1983). J. Chem. Soc. Pak. 5, 279-281], must be reformulated as Ca[Ge(H₂PO₂)₆].