N-Pyridoxylidenehydrazine-N’, N’-diacetic Acid. III.1) Formation of Metal Chelates in Solution

Metal chelate formation of N-pyridoxylidenehydrazine-N1, N1-acid (1) and related hydrazines in solution was studied by means of absorption spectroscopy. Compound 1 and N-pyridoxylidene-N'-methylliydrazine (2) in methanol formed Cu(II) chelates of the same spectral character, which indicated the chelation of the phenolate oxygen and the hydrazine nitrogen atoms to Cu(II). The compositions of the chelates were 1:1 for 1 and 1:2 for 2, indicating that 1 acts as a tri- or tetradentate ligand. N-(3-Hydroxy-4-pyridylmethylene)hydrazine-N1,N'-diacetic acid formed a Cu(II) chelate similar to that of 1 but N-pyridoxylidene-N1,N1-dimethylhydrazine and N1,N1pyridoxylidene-N1.N1_diphenylhydrazine did not form chelates under similar conditions. Addition of an equimolar or excess amount of Co(II), Ni(II), Zn(II), Cd(II) or La(III) salt to 1 in methanol gave rise to absorption assignable to the chelate of 1, whereas 2 did not form metal chelates under the same conditions. It was concluded that the iminodiacetic acid moiety of 1 coordinated to the metal ions and enhanced the stability constant of the metal chelates.