Crystal structure of the thalidomide analog (3aR*,7aS*)-2-(2,6-dioxopiperidin-3-yl)hexa-hydro-1H-iso-indole-1,3(2H)-dione.

The title compound, C13H16N2O4, crystallizes in the monoclinic centrosymmetric space group, P21/c, with four mol-ecules in the asymmetric unit, thus there is no crystallographically imposed symmetry and it is a racemic mixture. The structure consists of a six-membered unsaturated ring bound to a five-membered pyrrolidine-2,5-dione ring N-bound to a six-membered piperidine-2,6-dione ring and thus has the same basic skeleton as thalidomide, except for the six-membered unsaturated ring substituted for the aromatic ring. In the crystal, the mol-ecules are linked into inversion dimers by R 2 2(8) hydrogen bonding involving the N-H group. In addition, there are bifurcated C-H⋯O inter-actions involving one of the O atoms on the pyrrolidine-2,5-dione with graph-set notation R 1 2(5). These inter-actions along with C-H⋯O inter-actions involving one of the O atoms on the piperidine-2,6-dione ring link the mol-ecules into a complex three-dimensional array. There is pseudomerohedral twinning present which results from a 180° rotation about the [100] reciprocal lattice direction and with a twin law of 1 0 0 0 0 0 0 [BASF 0.044 (1)].