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Catalytically induced polymorphism and partial pi-electron delocalization in some N-aryl 2-hydroxy-1-naphthaldimines

The salicylaldimines have been studied comprehensively more than any other kind of Schiff bases. In comparison to that, the structural data on the Schiff bases derived from 2-OH-naphthaldehide are quite scarce. The type of N-substituent on the azomethine nitrogen of naphthaldimines can affect remarkably their physical and chemical properties. Two main features of these class of compounds are: (i) the type of intramolecular hydrogen bond (keto/enol tautomerism) and (ii) spatial orientation of an aryl N-substituent compared to the plane of naphthalene moiety. Conversely to the salicylaldimines, naphthaldimines contain, with just a few exceptions, N-HˇˇˇO intramolecular hydrogen bond and in the case of aromatic N-substituent often exhibit planar configuration. The type of the tautomer the most probably depends on the symmetry of aromatic aldehyde used. Crystal data. (I) C25H17NO, Mr = 347.42, orthorhombic, space group P ca21, a = 11.090(2), b = 6.066(1), c = 26.249(4) A, V = 1765.9(2) A3, Z = 4, Dx = 1.307 gcm-3, F(000) = 728, lambda(MoKa) = 0.7107 A, mi(MoKa) = 0.07mm-1, R = 0.052, wR = 0.111 for 2674 reflections (Inet gt 2s Inet). (II) C18H12N2O, Mr = 272.31, orthorhombic, space group P 212121, a = 7.7260(6), b = 12.577(1), c = 14.123(2) A, V = 1372.3(3) A3, Z = 4, Dx = 1.318 gcm-3, F(000) = 568, lambda(MoKa) = 0.7107 A, mi(MoKa) = 0.08 mm-1, R = 0.067, wR = 0.112 for 1514 reflections (Inet gt 2s Inet). (III) C18H12N2O, Mr = 272.31, monoclinic, space group P 21/n, a = 13.458(1), b = 7.444(1), c = 15.239(2) A, ß = 115.406(9)o, V = 1379.0(3) A3, Z = 4, Dx = 1.312 gcm-3, F(000) = 568, lambda(MoKa) = 0.7107 A, mi(MoKa) = 0.08 mm-1, R = 0.099, wR = 0.131 for 1684 reflections (Inet gt 2s Inet).Although N-(1-antracyl)- (I) and N-(2-cyanophenyl)-2-oxy-1-naphthaldimine (III) show significant non-planarity [two aryl moieties dihedral angles amount 10.35(5) and 8.9(1)o, respectively] partial pi-electron delocalization is for sure quite possible as there was established in the corresponding alpha- and beta-naphthyl derivatives [M. Gavranić et al., J. Chem. Crystallogr. 26 (1996) 23-28] Yellow and red polymorphs (II) and (III) were prepared using catalytic amounts of different metal cations [Co(II) for (II) and Fe(II) for (III)]. The color depends on the N-aryl substituent orientation to the plane of naphthalene fused rings [naphthalene to benzene plane dihedral angle in (II) is 34.6(1)o]. Electron-withdrawing group on the N-phenyl core does not effect the H-atom position in the intramolecular hydrogen bond. All three compounds crystallize as keto tautomers. The refinement procedure for (II) and (III) are in progress. We are thankful to the Austrian Academic Exchange Service (ÖAD) for a scholarship to M. Gavranić-Đaković during which a part of this study was carried out.

N-arylnaphthaldimines; polymorphism; pi-electron delocalization

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