Calcium disodium hexa-thio-diphosphate(IV) octa-hydrate.

Single crystals of the title compound, CaNa(2)(P(2)S(6))·8H(2)O, were obtained by adding calcium hydroxide to an aqueous solution of Na(4)(P(2)S(6))·6H(2)O. The structure is isotypic with that of its strontium analogue and consists of one Ca(2+) cation, two Na(+) cations, one-half of a centrosymmetric (P(2)S(6))(4-) anion with staggered confirmation and four water mol-ecules 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 CaO(8) polyhedron is connected via edge-sharing to two NaO(4)S(2) octa-hedra and to one NaO(2)S(4) octa-edron. The NaO(4)S(2) octa-hedra are, in turn, linked with two (P(2)S(6))(4-) anions through common corners. Various O-H⋯S hydrogen-bonding inter-actions lead to cohesion of adjacent layers. The Ca(2+) and one Na(+) cation are situated on a twofold rotation axis and the second Na(+) cation is situated on an inversion centre.