Dilithium hexa­hydroxidostannate(IV) dihydrate, a second monoclinic modification with a layer structure

The title compound, Li₂[Sn(OH)₆]·2H₂O, is dimorphic. As for the previously described α-modification, the title β-modification crystallizes in the monoclinic system and contains the same primary building units, viz [Sn(OH)₆]²⁻ octa­hedra and [Li(μ₂-OH)₃(H₂O)] tetra­hedra. In contrast to the Sn—O bond lengths that are very similar in both modifications, the Li—O bond lengths differ significantly, in particular those involving the water mol­ecule. In the new β-modification, the primary building units are linked into layers parallel to (010). The [Sn(OH)₆]²⁻ octa­hedra (-1 symmetry) form hexa­gonal nets and the [Li(μ₂-OH)₃(H₂O)] tetra­hedra are situated in between, with their apices in an alternating fashion up and down. O—H...O hydrogen bonds between OH groups and water mol­ecules exist within the layers as well as between them.