Calcium disodium hexathiodiphosphate(IV) octahydrate

Single crystals of the title compound, CaNa2(P2S6)·8H2O, were obtained by adding calcium hydroxide to an aqueous solution of Na4(P2S6)·6H2O. The structure is isotypic with that of its strontium analogue and consists of one Ca2+ cation, two Na+ cations, one-half of a centrosymmetric (P2S6)4− anion with staggered confirmation and four water molecules in the asymmetric unit. The crystal structure can be described as being built up from layers of cations and anions extending parallel to (101). Within a layer, each CaO8 polyhedron is connected via edge-sharing to two NaO4S2 octahedra and to one NaO2S4 octaedron. The NaO4S2 octahedra are, in turn, linked with two (P2S6)4− anions through common corners. Various O—H...S hydrogen-bonding interactions lead to cohesion of adjacent layers. The Ca2+ and one Na+ cation are situated on a twofold rotation axis and the second Na+ cation is situated on an inversion centre.