Molecular structure and conformation of N-2-[3 '-(methoxysalicylideneimino)benzyl]-3 ''-methoxysalicylideneimine

The Schiff base, N-2-[3 '-(methoxysalicylideneimino)benzyl]-3 " -methoxysal icylidene-imine 1,2-C6H4[N=CHC6H3(OMe-3 ' )OH-2 ' ]CH2N=CHC6H3(OMe-3 " )OH- 2 ", has been prepared by the reaction of 2-amino-1-benzylamine and 3-metho xysalicylaldehyde (o-vanillin) in ethanol. The molecular structure has been confirmed by single crystal X-ray crystallography. The crystal is in the m onoclinic space group P2(1)/n with a=16.179(5), b=6.715(5), c=18.780(6)Angs trom, beta = 100.56(3)degrees, D-calc = 1.293 mg cm(-3), V= 2006(2) Angstro m (3) and R = 0.0357 for 3929 independent reflections. The H-1 and C-13 NMR spectra in CDCl3 solution indicate the retention of solid state structure in solution. The title compound is not planar. Intramolecular hydrogen bond s occur between O(1) and N(1) [2.614(2) Angstrom] and between O(2) and N(2) [2.585(2) Angstrom] atoms, the hydrogen atom essentially being bonded to t he oxygen atom. Minimum energy conformations from AM1 were calculated as a function of five torsion angles theta (1) (C6-C7-N1-C8), theta (2) (C14-N2- C15-C16), theta (3) (C9-C8-N1-C7), theta (4) (C13-C14-N2-C15) and theta (5) (C10-C9-C8-N1), varied every 5 degrees. The optimized geometry of the crys tal structure corresponding to the non-planar conformation is the most stab le conformation in all calculations. The results strongly indicate that the minimum energy conformation is primarily determined by non-bonded hydrogen -hydrogen repulsions. (C) 2001 Elsevier Science B.V. All rights reserved.