Tautomeric polymorphism in salicylideneamine derivatives: an X-ray diffraction and solid-state NMR study

The crystal structure of the N-(3-hydroxysalicylidene)-4-methoxyaniline has been studied by single-crystal X-ray diffraction and solid-state NMR spectroscopy. This is the first example of a Schiff base derived from 3-hydroxysalicylaldehyde which displays in the asymmetric unit, four distinct molecules linked together in the crystal lattice by two types of intermolecular O-H ... O hydrogen bonds and formed by two independent tetramers. The C-13 CPMAS NMR study corroborates the above results; the presence of different tautomeric equilibria in the same crystal structure is demonstrated and a qualitative estimation of the equilibrium mixture composition is given. (C) 2000 Elsevier Science B.V. All rights reserved.