[Open access]

Acta Cryst. (2013). E69, i30-i31
[ doi:10.1107/S1600536813010921 ]

Trilithium thioarsenate octahydrate

K. Mereiter

Abstract: 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 tetrahedral AsS43- 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 octahedral and two in tetrahedral coordination by water O atoms. An outstanding feature of this chain is a linear group of three edge-sharing LiO6 octahedra to both ends of which two LiO4 tetrahedra are attached by face-sharing. Such groups of composition Li5O16 are linked into branched chains by means of a further LiO4 tetrahedron sharing vertices with four adjacent LiO6 octahedra. The Li-O bonds range from 1.876 (5) to 2.054 (6) Å for the LiO4 tetrahedra and from 2.026 (5) to 2.319 (5) Å for the LiO6 octahedra. The two independent AsS43- anions have As-S bond lengths ranging from 2.1482 (6) to 2.1677 (6) Å [<As-S> = 2.161 (10) Å]. The eight independent water molecules of the structure donate 16 relatively straight O-H...S hydrogen bonds to all S atoms of the AsS4 tetrahedra [<O...S> = 3.295 (92) Å]. Seven water molecules are in distorted tetrahedral coordination by two Li and two S; one water molecule 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.

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