Molecular packing modes. Part V. Crystal and molecular structures of fumaramic acid

Abstract

The crystal structure of the title compound has ben solved from X-ray diffractometer data by direct methods and refined by least-squares to R 0·038 for 1182 independent reflections. Crystals are monoclinic, space group P2₁, with Z= 2 in a unit cell of dimensions: a= 7·367(1), b= 9·041(1), c= 3·742(1)Å, β= 99·39(1)°. The mean σ for bond lengths not involving hydrogen is 0·002 Å.

The hydrogen-bond network is two-dimensional. The amide and carboxy-groups of molecules related by translation form cyclic hydrogen-bonded (asymmetric) pairs (OH ⋯ O, 2·660; NH ⋯ O, 2·838 Å) generating chains which are interlinked, along the 2₁ axis, by NH ⋯ O (2·935 Å) bonds. The conformations of the groups C:C·C(NH₂):O and C:C·C(OH):O are syn-planar, in contrast to the antiplanar C:C·C:O arrangements in the α- and β-forms of fumaric acid.

The bond lengths are: CC 1·320, C(OH)–C 1·497, C(NH₂)–C 1·486, C(OH)O 1·209, C(NH₂)O 1·247, C–OH 1·310, and C–NH₂ 1·323 Å.