STRUCTURAL CHARACTERISTICS OF N,N'-BIS(SALICYLIDENE)-2,6-PYRIDINEDIAMINE

The Schiff base N,N'-bis(salicylidene)-2,6-pyridinediamine has been sy nthesized and characterized in the solid state and in solution using X -ray analysis, IR, UV/Vis and NMR spectroscopy. Crystal data: C19H15N3 O2, M-r = 317.34, monoclinic, space group P2(1)/c, a = 19.313(5), b = 5.854(2), c = 14.957(6) Angstrom, beta = 110.45(2)degrees, V = 1584.4( 9) Angstrom(3), Z = 4, R = 0.049, R-w = 0.095 for 3323 independent ref lections with I > 2 sigma(I). There are two intramolecular hydrogen bo nds O-H...N between the hydroxyl and imino groups of 2.564(3) and 2.63 3(3) Angstrom. The enolimino form is found in the solid state and is a lso the predominant tautomeric form in solution. A tendency of interco nversion to ketoamine has been observed only in rather polar solvents, such as methanol and methanol/water mixtures and has been found to be very low: tautomeric constants K-t = [ketoamine]/[enolimine] amount t o 0.02 and 0.03 in methanol and methanol/water 4/1, respectively. (C) 1997 Elsevier Science B.V.