An unusual example of packing among molecular layers: the structures of two crystalline forms of 2,2-aziridinedicarboxamide, C4H7N3O2

Abstract

The structures of two crystalline forms of 2,2-aziridinedicarboxamide have been determined by X-ray diffraction. Form A, obtained from a solution in methanol, is tetragonal, space group P41212, with a = 12.382 (2), c = 30.211 (3)A, V = 4632 (1)/~ 3, Z ---- 32; form B, obtained from a solution in N,N-dimethylformamide, is triclinic, space group P1, with a = 15.829 (2), b = 12.381(2), c = 12.391(2)A, a = 90.0(1), fl = 74.3 (1), y= 83.1 (1) °, V= 2312 (1)/~3, Z = 16. The former has been refined to a final R of 0.051 for 1074 significant reflections while the latter has been refined to a final R of 0.070 for 2534 significant reflections. The pyramidal geometry of the ring nitrogen is discussed. In both cases crystal packing may be described in terms of layers, all having the same internal structure. The two crystalline forms are characterized by a different stacking of layers. The symmetry present within each layer is not extended to the whole packing, thus giving rise in both cases to an unusually high number of independent molecules, while a high non-crystallographic symmetry strongly affects the intensity statistics.