Pyridine nitrosazones and their cobalt(III) chelates

Nitrosation of pyridine aldehyde p-tolylhydrazones 2 with amyl nitrite gives rise to p-tolueneazopyridine aldoximes 4 which form stable tris chelates with cobalt(III). Spectral data (ir, uv, and 1Hmr) indicate that the ligands exist mainly in the assigned azooxime structure 4, and that their chelates have five-membered ring structure 7. Also, the 1Hmr spectra imply mer-configuration 9 for the chelates examined. No evidence for the tautomeric nitrosohydrazone structure 3 for the ligands and the fac-configuration 8 for Co(III) chelates could be obtained. Using the HMO method, the azooxime form 4 for the ligand was shown to be more stable than the nitrosohydrazone structure 3. Also, good agreement was obtained between observed transition energies and those calculated by the HMO method. The acid dissociation constants of the ligands in 50 vol% ethanol–water at 25 °C and ionic strength of 0.1 were determined spectrophotometrically.