Synthesis and characterization of vanadyl(IV) complexes of Schiff bases derived from anthranilic acid and salicylaldehyde (or its derivatives) or acetylacetone. Single crystal X-ray structures of the oxidized products

Abstract

Anhydrous, dimeric vanadyl(IV) complexes of Schiff bases derived from [1+1] condensation of salicylaldehyde (or its derivatives) and anthranilic acid, have been synthesized from CH₃CN and were characterized by elemental analysis, FTIR, EPR, absorption, TGA, cyclic voltammetry and room temperature magnetic susceptibility measurements. These complexes were found to be oxidized by air in polar solvents like MeOH and DMF to V^V products. The E_½ values were found to be around 660 mV indicating that the car-ylate group favours vanadyl(IV) binding when compared to the alkoxo-bound vanadium complexes. Oxidative instability of these complexes are dependent on the substituent on the salicylaldehyde ring and follow an order, 5,6-benzo>H 3-OMe in MeOH and DMF. Attempted recrystallization of the dimeric vanadyl(IV) complex from pyridine led to products of oxidation, polymerization and loss of Schiff base ligand. Single crystal X-ray diffraction showed the oxidation product to be a decavanadate with the pyridinium counter cation, [C₅NH₆]₆ V₁₀O₂₈ · 2H₂O. When the dinuclear vanadyl(IV) complex was recrystallized from MeOH, it gave a product of mononuclear car-ylate bound octahedral VO³⁺ moiety along with the presence of both MeOH and OMe units in the coordination sphere with a formula, VO(L)(OMe)(MeOH), where L= 1 + 1 Schiff base derived from 5, 6-benzosalicylaldehyde and anthranilic acid, as studied through single crystal X-ray diffraction.