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)(2)mac](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 1.65AB (91 K). The electronic spectra exhibit three bands at ca. 12 000-14 200, 18 200-19 500 and an intense band at ca. 30 000 cm(-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.