Spectroscopic studies of some heterocyclic hydrazones and their metal complexes
The PMR spectra of the two isomers of pyridine-2-aldehyde=2'-pyridyl hydrazone in carbon tetrachloride, dimethyl sulphoxide, and benzene solutions have been studied. Specific associations between PAPHY molecules and solvent molecules have been proposed to account for the observed solvent shifts. Dilution studies have shown that there are PAPHY-PAPHY molecular associations in solution. In the E-isomer these are of the n-donor type involving the lone pair electrons of the ring nitrogen atoms, whereas the Z-isomer association is a dipole-dipole interaction involving the aldehyde ring of different PAPHY molecules. Evidence from long range coupling shows that the uncomplexed E and Z-PAPHY molecules possess a different configuration to the complexed molecules. The chemical shift changes on isomerisation of the E to Z-isomer have been measured and those for the aldehyde ring are consistent with the withdrawal of charge from this ring via the nitrogen atom. Metal complexes of the two isomers of PAPHY have been prepared and their PMR spectra studied. The chemical shifts changes on complex formation have been interpreted in terms of the variation in magnetic anistropy of the ring nitrogen atoms in the ligand molecule and the degree of back donation of d-electrons from the metal atom.
PMR spectroscopy, Metal complexes, PAPHY molecules, Isomers
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