Synthesis, characterization and studies of mechanochemical, electrochemical, and thermal behavior of electronegative oxovanadium(IV) Schiff-base complexes

This article describes the synthesis and characterization of electronegative oxovanadium(IV) complexes containing tetradentate Schiff-base ligands derived from condensation of 1,3-propanediamine and 1,8-naphthylamine with 5-bromo-3-nitro-2-hydroxybenzaldehyde. New VOL1: [VO(5-Br-3-NO2salnaph)] and VOL2: [VO(5-Br-3-NO2salpn)] complexes were obtained in orange polymeric form with (V=O) stretching bands at 884 and 876 cm-1, respectively. The orange VOL1 and VOL2 complexes turn dark brown and green, respectively, when ground thoroughly in mortars. X-ray powder diffraction patterns of the ground VOL1 complex (VOL1g) scarcely show diffraction peaks. The data suggest that the linear chain polymeric structure in VOL1 is destroyed on grinding to yield fragments of the polymeric chains. The color of VOL2 changed from orange to dark green (VOL2g), and the intensity of the V=O stretching bands of the polymeric form decreased with a complementary increase of those of the monomeric forms on grinding. The ground product of VOL2 showed the V=O stretching band at 984 cm-1, in addition to the original 860 cm-1 absorption. The dark green VOL2g complex and dark brown VOL1g complex turned to orange complexes after being suspended in absolute ethanol (99.8%, UV-IR spectroscopic grade), as a mechanochemical behavior. The redox processes of VOL1,2 were reversible in DMF solution. The redox potentials of VOL1,2 were determined to be 920 and 950 mV, respectively.