Vanadium(III) complexes with VN3O3 co-ordination by sexidentate Schiff-base ligands: synthesis, spectra and redox activity

Abstract

A group of non-electrolytic red crystalline vanadium(III) complexes (µ_eff 2.78–2.89 in solution, 298 K) has been synthesized using sexidentate Schiff-base ligands. The complexes have a rare VN₃O₃ co-ordination sphere. From the paramagnetically shifted ¹H NMR spectra it is revealed that the metal co-ordination environment is distorted (≈C₁) due to the spatial arrangement of the ligand chelate rings. In N,N-dimethylformamide (dmf) solution charge-transfer band(s) together with crystal-field transitions are observed in the region ca. 340–600 nm. Cyclic voltammetric experiments in dmf solution at a platinum electrode reveal a quasi-reversible V^III–V^II couple [E_f–1.34 to –1.52 V vs. saturated calomel electrode (SCE)] and a reversible V^IV–V^III couple (E_f+0.21 to +0.54 V vs. SCE).