Trilithium thio­arsenate octa­hydrate

The title compound, Li3AsS4·8H2O, is built up from infinite cationic [Li3(H2O)8](3+) chains which extend along [001] and are cross-linked by isolated tetra-hedral AsS4 (3-) anions via O-H⋯S hydrogen bonds. Two Li and two As atoms lie on special positions with site symmetries -1 (1 × Li) and 2 (1 × Li and 2 × As). The [Li3(H2O)8](3+) chain contains four independent Li atoms of which two are in octa-hedral and two in tetra-hedral coordination by water O atoms. An outstanding feature of this chain is a linear group of three edge-sharing LiO6 octa-hedra to both ends of which two LiO4 tetra-hedra are attached by face-sharing. Such groups of composition Li5O16 are linked into branched chains by means of a further LiO4 tetra-hedron sharing vertices with four adjacent LiO6 octa-hedra. The Li-O bonds range from 1.876 (5) to 2.054 (6) Å for the LiO4 tetra-hedra and from 2.026 (5) to 2.319 (5) Å for the LiO6 octa-hedra. The two independent AsS4 (3-) anions have As-S bond lengths ranging from 2.1482 (6) to 2.1677 (6) Å [ = 2.161 (10) Å]. The eight independent water mol-ecules of the structure donate 16 relatively straight O-H⋯S hydrogen bonds to all S atoms of the AsS4 tetra-hedra [ = 3.295 (92) Å]. Seven water mol-ecules are in distorted tetra-hedral coordination by two Li and two S; one water mol-ecule has a flat pyramidal coordination by one Li and two S. At variance with related compounds like Schlippe's salt, Na3SbS4·9H2O, there are neither alkali-sulfur bonds nor O-H⋯O hydrogen bonds in the structure.