Intramolecular hydrogen bonding and tautomerism in Schiff bases. Part II. Structures of 1-[N-(2-pyridyl)aminomethylidene}-2(1H)-naphtalenone (1) and bis[2-hydroxy-kappa O-N-(2-pyridyl)-1-naphthaldiminato-kappa N]zinc(II) (2)

The Schiff base ligand (1) and its Zn(II) complex (2) have been synthesized and their crystal structures have been determined. Compound (1) crystalliz es in the monoclinic space group C2/c with a = 26.993(2), b = 5.891(1), c = 16.000(2) W, P = 103.29(1)degrees, V = 2476.0(6) Angstrom(3), Z = 8 and D- x = 1.332 g cm(-3) Compound (2) crystallizes in the orthorhombic space grou p Pbca with a = 19.580(3), b = 9.416(2), c = 27.801(2) Angstrom, V = 5125.5 (6) Angstrom(3), Z = 8 and D-x = 1.451g cm(-3) In the crystal structure of the free Schiff base ligand (1), the existence of a strong intramolecular N -H...O hydrogen bond INO = 2.572(4), N-H = 0.90(4), H...O = 1.759(4) Angstr om, N-H...O = 149.6(3)degrees] is observed. The C-N amine bond and C-N-C bo nd angle are 1.345(4)Angstrom and 124.4(3)degrees, respectively. The C3 = O 1 and C4 = C5 bond lengths [1.274(4) and 1.351(5) Angstrom] are shortened b y the pronounced quinoidal effect. In solution, compound (1) is in tautomer ic equilibria (phenol-imine, O-H ... N keto-amine, O ... H-N forms), as sup ported by H-1 NMR and UV-visible data. In the crystal structure of the Zn(I I) complex (2), zinc atom has a distorted tetrahedral coordination. One of the pyridine N atom of the ligands is in close contact with the Zn(II) atom [Zn1 ... N4 = 2.864(5) Angstrom].It is interesting that the C-N amine bond [1.345(4) Angstrom] in compound (1) changes to the imine bond [1.27(5) Ang strom] in the Zn(TI) complex (2). (C) 2000 Elsevier Science B.V. All rights reserved.