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

Abstract

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 (VOL^1g) 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 (VOL^2g), 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 VOL^2g complex and dark brown VOL^1g 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 VOL^1,2 were reversible in DMF solution. The redox potentials of VOL^1,2 were determined to be 920 and 950 mV, respectively.

Keywords:

• Mechanochemical
• Thermal
• Oxovanadium(IV) complexes
• Electrochemical

Acknowledgements

We thank Dr S. Shahrokhian and his research group for their help in obtaining CV curves.