IronIII and aluminiumIII complexes with substituted salicyl-aldehydes and salicylic acids

• Coordination properties of salicyl-aldheydes and salicylic acids were determined.
• The effect of substituents was discussed according Swain-Lupton treatment.
• Formation equilibria were studied by potentiometry, spectrophometry and 1H NMR.
• The 1:2 iron complex with p-nitro-salicylic acid was structurally characterized.

The chelating properties toward ironIII and aluminiumIII of variously substituted salicyl-aldehydes and salicylic acids have been evaluated, together with the effect of methoxy and nitro substituents in ortho and para position with respect to the phenolic group. The protonation and iron and aluminium complex formation equilibria have been studied by potentiometry, UV–visible spectrophotometry and 1H NMR spectroscopy. The overall results highlight that salicyl-aldehydes present good chelating properties toward ironIII, with pFe ranging from 14.2 with nitro to 15.7 with methoxy substituent, being ineffective toward aluminium; the pFe values for salicylic acids are generally lower than those for salicyl-aldehydes, and about 4 units higher than the corresponding pAl values. The effect of the two substituents on the chelating properties of the ligands can be rationalized in terms of the Swain–Lupton treatment which accounts for the field and resonance effects. The structural characterization of the 1:2 iron complex with p-nitro salicylic acid shows that ironIII ion exhibits an octahedral surrounding where two salicylate chelating ligands supply two O-phenolate and two O-carboxylate donor atoms in a roughly equatorial plane. The trans-apical sites are occupied by two aqua ligands.

The chelating properties toward ironIII and aluminiumIII of salicyl-aldehydes and salicylic acids and the effect of methoxy and nitro substituents have been evaluated. The protonation and complex formation equilibria have been studied by potentiometry, UV–visible spectrophotometry and 1H NMR spectroscopy. The 1:2 iron complex with p-nitro salicylic acid has been structurally characterized.Figure optionsDownload as PowerPoint slide