Calcium acamprosate: a triclinic polymorph

The title compound, poly[bis(mu(3)-4-acetamidopropanesulfonato) calcium], [Ca(C5H10NO4S)(2)](n), is a triclinic polymorph of the previously reported monoclinic structure [Toffoli et al. (1988). Acta Cryst. C44, 1493-1494]. The triclinic modification was found to have an all-trans configuration of the acetamidopropane chain, in contrast with the monoclinic polymorph which shows an angle of 74.66 (8)degrees between the S-C-C-C chain plane and that of the amide group. The Ca2+ cation is situated on an inversion centre and is hexacoordinated by six O atoms belonging to different anions in a distorted octahedral geometry. This arrangement leads to a layered structure parallel to (011). The layers are held together by N-H center dot center dot center dot O hydrogen bonds and by short C-H center dot center dot center dot O interactions, both involving the sulfonate O atoms not coordinated to the Ca2+ cations. The structure was determined from a crystal twinned by non-merohedry [twin law ((1) over bar 00, 0 (1) over bar0, -0.335 -0.85 1), with a fractional contribution of the minor twin domain of 46.7 (1)%].