Homobinuclear oxovanadium(IV) complexes with octaaza macrocyclic ligands derived from primary diamines and 3,6-dimethyl/diphenyl-4,5-diazaocta-3,5-diene-2,7-dione

The in situ reactions of 3,6-dimethyl/diphenyl-4,5-diazaocta-3,5-diene-2,7-dione with diamines (ethylenediamine, o-phenylenediamine) in the presence of vanadyl salt yielded binuclear macrocyclic complexes of type [(VO)₂mac](SO₄)₂. Attempts to synthesize the corresponding metal-free macrocyclic ligands did not prove successful. The magnetic moment of the complexes decreases from ca. 1.73 (295K) to 1.65 μ_B (91 K). The electronic spectra exhibit three bands at ca. 12 000-14 200, 18 200-19 500 and an intense band at ca. 30 000cm^-1. The third band is probably due to a oxo → V(IV) charge-transfer transition. The infrared spectra indicate that the ligands coordinate through four aza nitrogen atoms to each V(IV). The fluid solution EPR spectra show an eight line pattern typical of a mononuclear VO(IV) compound and indicating the absence of VO...VO electron spin interaction. The electrochemical behavior of one complex with regards to oxidation has been studied by cyclic voltammetry in MeCN-MeOH solution.