Tautomeric properties, conformations and structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine

The crystal structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine (C13H10NO2Cl) was determined by X-ray analysis. It crystallizes orthorhombic space group P2(1)2(1)2(1) with a = 12.967(2) Angstrom, b = 14.438(3) Angstrom, c = 6.231(3) Angstrom, V = 1166.5(6) Angstrom(3), Z = 4, D-c = 1.41 g cm(-3) and mu(MoKalpha) = 0.315 mm(-1). The title compound is thermochromic and the molecule is nearly planar. Both tautomeric forms (keto and enol forms in 68(3) and 32(3)%, respectively) are present in the solid state, The molecules contain strong intramolecular hydrogen bonds, N1-H1 ... O1/O2 (2.515(1) and 2.581(2) Angstrom) for the keto form and O1-H01 ... N1 for the enol one. There is also strong intermolecular O2-H ... O1 hydrogen bonding (2.599(2) Angstrom) between neighbouring molecules. Minimum energy conformations AM1 were calculated as a function of the three torsion angles, theta(1)(N1-C7-C6-C5), theta(2)(C8-N1-C7-C6) and theta(3)(C9-C8-N1-C7), varied every 10 degrees. Although the molecule is nearly planar, the AM1 optimized geometry of the title compound is not planar. The non-planar conformation of the title compound corresponding to the optimized X-ray structure is the most stable conformation in all calculations. (C) 1999 Elsevier Science B.V. All rights reserved.