Synthesis and spectroscopic studies on oxovanadium(IV) tetraaza macrocyclic complexes derived from substituted β-diketones and 2,6-diaminopyridine

The in situ reactions of 1-phenyl-3-(4-chlorophenyl/4-nitrophenyl/4- methoxyphenyl)-diketone with 2,6-diaminopyridine in the presence of oxovanadium(IV) sulphate yield macrocyclic complexes of type [VO(mac)]SO ₄. Attempts to synthesize the corresponding metal free macrocyclic ligands did not prove successful. The magnetic moments of the complexes lie in the range 1.70-1.75 μg, suitable for complexes with one unpaired electron. The electronic spectra exhibit three bands. The infrared spectra indicate that the ligands coordinate through four azomethine nitrogen atoms. The fluid solution EPR spectra show an eight line pattern typical for a mononuclear VO^IV complexes. The spectral studies support square-pyramidal geometry for the vanadium(IV) complexes.