Structure and spectroscopic characteristics of Schiff bases of salicylaldehyde with 2,3-diaminopyridine

Abstract

The Schiff bases 2-amino-3-salicylideneaminopyridine ( 1) and 2,3-bis(salicylideneamino)pyridine (bimorphous, 2a and 2b) were prepared and characterized by X-ray crystallography and by IR and NMR spectrometry. ( 1) C 12H 11N 3O, M r = 213.240, monoclinic, space group P2 1/ c, a = 12.00(2), b = 6.594(3), c = 14.06(2) Å, β = 104.90(8)°, V = 1075(2) Å 3, Z = 4, D x = 1.317 g cm −3, λ(Mo Kα) = 0.71073 Å, μ = 0.82 cm −1, F(000) = 448, T = 295 K, R = 0.047, R w = 0.028 for 886 reflections with I –σ( I). ( 2a) C 19H 15N 3O 2, M r = 317.348 monoclinic, space group P2 1, a = 6.202(3), b = 17.622(7), c = 14.724(8) Å, β = 91.85(3)°, V = 1608(1) Å 3, Z = 4 (two crystallographically independent molecules A and B), D x = 1.311 g cm −3, λ(Mo Kα) = 0.71073 Å, μ = 0.816 cm −1, F(000) = 664, T = 295 K, R = 0.058, R w = 0.034 for 972 reflections with I > 3σ( I). The angle between the benzene and the pyridine ring is 51.5(2)° in 1, whereas in 2a the corresponding angles are 51.1(4)° in molecule A and 51.8(4)° in molecule B. Molecules of 1 are connected in pairs by two centrosymmetric hydrogen bonds NH⋯N Py of 3.024(5)Å. Intermolecular bonding of 1 does not take place in CHCl 3 solution. No evidence was found in the IR and NMR spectra for tautomeric interconversion of 1 and 2 into the ketoamine or for cyclization of 2 into the cyclic diamine.