engleski

Intramolecular N-H...O hydrogen bonding, quinoid effect, and partial π -electron delocalization in N-aryl Schiff bases of 2-hydroxy-1-naphthaldehyde : the crystal structures of planar N-(α -naphthyl)- and N-(β -naphthyl)-2-oxy-1-naphthaldimine

The structures of N-(α -naphthyl)-2-oxy-1-naphthaldimine 1 and N-(β -naphthyl)-2-oxy-1-naphthaldimine 2 have been investigated by X-ray analysis and by spectroscopic methods. Crystals of 1 are monoclinic, space group Pn, with cell dimensions a = 10.823(3), b = 5.826(2), c = 11.899 (3) Å , and β = 99.66(3)°. Compound 2 crystallizes in the orthorhombic space group Pca21 with a = 17.564(3), b = 6.314(2), and c = 13.663(4) Å . The IR spectra exhibited neither N-H nor O-H stretching frequencies. The existence of the intramolecular hydrogen bonding of N-H O type was predicted by spectroscopic experiment but unequivocally established by diffraction experiment in both cases 1 and 2. The molecules 1 and 2 are significantly planar with considerable quinoid effect at the 2-oxy-naphthaldimine moiety. Although essentially planar, both molecules 1 and 2 show the delocalization of π -electrons only in the central part of the molecules including C=N imino group with pendent ring carbon atoms. Intermolecular attractions in the crystals belong to weak van der Waals interactions between discrete planar molecules spatially arranged into the expected herringbone motif in the solid state.

planar Schiff base ligands; intramolecular N-H...O hydrogen bond; quinoid effect; X-ray crystal structure

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