The structures of some ortho-hydroxy Schiff base ligands

Nine ortho-hydroxy Schiff base ligands, (1)-(9). were synthesized and characterized by chemical analysis, mass spectrometry, H-1 and C-13 NMR spectroscopy. The crystal and molecular structures of compounds (1), (3), (5), (7). (8) and (9) were determined. The solid state X-ray diffraction studies show that compounds (5) and (8) are in the keto-amine tautomeric form, while (1). (3), (7) and (9) are found as phenol-imine tautomers. Moreover, studies in the solution phase by H-1 and C-13 NMR spectroscopy indicate that compounds (2), (5) and (8) are found as keto-amine tautomers, while (1), (3), (4), (6), (7) and (9) are found as phenol-imine tautomers. Furthermore, ab initio calculations at the HF/6-31G* level with full optimization of geometry, performed for both tautomers of (1) and (5), agree with the observed behavior in solution and solid state of these compounds. (C) 2001 Elsevier Science B.V. All rights reserved.