[SnF(bipy)(H2O)]2[SnF6], a mixed-valent inorganic tin(II)–tin(IV) compound

The title compound represents a ionic mixed-valent tin(II)–tin(IV) compound with the bivalent tin atom as central atom of the cation and the tetra­valent tin atom as central atom of the anion. Regarding the first and second coordination sphere, the bivalent tin atom is fourfold, seesaw and fivefold, trapezoid–pyramidal coordinated while the tetra­valent tin atom exhibits an octa­hedral coordination.

In the title compound, bis­[aqua­(2,2′-bi­pyridine)­fluorido­tin(II)] hexa­fluorido­tin(IV), [SnF(C₁₀H₈N₂)(H₂O)]₂[SnF₆], an ionic mixed-valent tin(II)–tin(IV) compound, the bivalent tin atom is the center atom of the cation and the tetra­valent tin atom is the center atom of the anion. With respect to the first coordination sphere, the cation is monomeric, with the tin(II) atom having a fourfold seesaw coordination with a fluorine atom in an equatorial position, a water mol­ecule in an axial position and the two nitro­gen atoms of the chelating 2,2′-bi­pyridine ligand in the remaining axial and equatorial positions. The bond lengths and angles of this hypervalent first coordination sphere are described by 2c–2e and 3c–4e bonds, respectively, all of which are based on the orthogonal 5p orbitals of the tin atom. In the second coordination sphere, which is based on an additional, very long tin–fluorine bond that leads to dimerization of the cation, the tin atom is trapezoidal–pyramidally coordinated. The tetra­valent tin atom of the centrosymmetric anion has an octa­hedral coordination. The differences in its tin–fluorine bond lengths are attributed to hydrogen bonding, as the two of the four fluorine atoms are each involved in two hydrogen bonds, linking anions and cations together to form strands.