Synthesis,characterization, electrochemical and solvatochromic investigations of novel monomeric and polymeric vanadyl Schiff-base complexes

This article describes the synthesis and characterization of oxovanadium(IV) complexes containing tetradentate Schiff-base ligands derived from condensation of ethylenediamine, meso-1,2-diphenyl-1,2-ethylenediamine, 1,2-orthophenylenediamine and 1,2-cyclohexanediamine with 5-bromo-3-nitro-2-hydroxybenzaldehyde. The novel VOL¹:[VO(5-Br-3-NO₂salen)], VOL²:[VO(5-Br-3-NO₂saloph)] and VOL³:[VO(5-Br-3-NO₂salchxn)] complexes were obtained in orange polymeric form with (V=O) stretching bands at 878, 884 and 884?cm^?1, respectively, but the VOL⁴ complex was obtained as a green monomer with (V=O) stretching band at 978?cm^?1. The redox process in acetonitrile was reversible for VOL⁴ and E° was determined to be approximately 950?mV but for VOL^1–3 this process was irreversible or quasi-reversible. The VOL⁴ complex is considerably soluble in a wide variety of solvents and shows solvatochromic behavior. The ² B ₂?→²?E(I) transition wavenumber shows a linear correlation to the D.N. of the solvent.