Conformation and structure of 1,3-bis(2-hydroxy-5-bromosalicylideneamine)propan-2-ol

The Schiff base, 1,3-bis(2-hydroxy-5-bromosalicylideneamine)propan-2-ol, has been studied by AM1 semiempirical quantum mechanical method and X-ray analysis. It crystallizes in the orthorhombic space group Pca2₁ with a = 8.458(3), b = 6.139(2), c = 32.957(4) Å, D_calc = 1.770 g cm^-3, V = 1711(1) ų, Z = 4 and (MoK) = 0.476. The structure was solved by direct methods and refined to R = 0.041 for 1715 independent reflections I > 2 (I)]. The title compound is not planar. Intramolecular hydrogen bonds are found between the hydroxyl and the amine nitrogen with O—H···N distances of 2.601(6) and 2.629(4) Å. There is also an intermolecular O—H···N hydrogen bond 3.176(6) Å] linking the neighbouring molecules. Minimum energy conformations from AM1 were calculated as a function of eight torsion angles varied every 5°. The optimized geometry of the crystal structure corresponding to the nonplanar conformation is the most stable conformation in all calculations. The results strongly indicate that the minimum energy conformation is primarily determined by nonbonded hydrogen—hydrogen repulsions.