Intramolecular hydrogen bonding and tautomerism in Schiff bases: Part VI. Syntheses and structural investigation of salicylaldimine and naphthaldimine derivatives

Abstract

Salicyclaldimines (5-9) and naphthaldimines (10-13) derived from condensation reactions of N2O2 donor type bifunctional aminopodands (1-4), [(H2NPhO)2R, where R = CH 2CH2, CH2CH2CH2 and CH2PhCH2], and hydrazine monohydrate with salicylaldehyde and 2-hydroxy-1-naphthaldehyde, respectively, have been prepared (scheme 1) and characterized by elemental analyses, UV-vis, FTIR, NMR and MS. NMR assignments were made using 1H, 13C NMR, DEPT and aided by 2D HETCOR and HMBC heteronuclear correlation techniques. The UV-vis spectra of the Schiff bases have been systematically studied in organic solvents of different polarity, acidic and basic media and found useful in understanding of tautomeric equilibria (phenol-imine, O-H.N and keto-amine, O.H-N forms) in this series. The molecular structure of 8 has been determined crystallographically, and observed that the compound is in the form of phenol-imine, defined by the strong intramolecular [O-H.N = 1.72(3), 1.81(2) Å] hydrogen bonds. Compound 8 crystallizes in the monoclinic space group P21/a with a = 8.4675(7), b = 38.448(3), c = 9.3875(7) Å, β = 103.0780(10)°, V = 2976.9(4) Å3, Z = 4 and Dx = 1·271 Mg m-3, and contains acetonitrile molecule in the crystal lattice. © Indian Academy of Sciences.