Molecular packing modes. Part VII. Crystal and molecular structures of anhydrous acetylenedicarboxylic acid

Abstract

The crystal structure of anhydrous acetylenedicarboxylic acid has been solved from 1031 independent three-dimensional counter data and refined by least-squares methods to R 0·045. Crystals are monoclinic, space group P2₁/n, Z= 4, unit cell dimensions: a= 14·894, b= 6·420, c= 4·862 Å, β= 90·90°. σ For bond lengths involving heavy atoms only is estimated as 0·002 Å.

The molecule is non-planar: the dihedral angle between the carboxy-groups is 57·8°. The four C–O bond lengths are nearly equal (1·254 ± 0·01 Å). The mean C–C bond length is 1·458 ± 0·001 Å; the experimental value of the –CC– bond is short (1·68 Å). The molecular dimensions and packing arrangement are discussed.