CRYSTAL AND MOLECULAR STRUCTURE OF SALICYLALDEHYDE AZINE

The crystal and molecular structure of salicylaldehyde azine has been determined by Patterson and Fourier methods from three-dimensional X-ray data, and refined by anisotropic least-squares methods to a final R value of 0.087. The crystals are monoclinic, space group P21/c, with two molecules in the unit cell of dimensions a = 8.467, b = 6.318, c = 12.432 Å, β = 112°22′. The molecules are centrosymmetric and nearly planar; the small deviations from planarity are indicative of intramolecular overcrowding between the two ortho-substituents in the benzene ring. The distribution of bond distances within the benzene ring is consistent with a significant contribution to the structure from a resonance quinonoid form. A strong internal hydrogen bond of 2.645 Å binds the phenolic hydroxy-group to the nearest nitrogen atom in the azine chain. The molecules are packed in plane-to-plane stacks within the crystal, with a perpendicular spacing between adjacent molecules of about 3.4 Å, which in part accounts for its thermochromic properties.