Complexes of vanadium(IV) with 1,2-dihydroxybenzene and its substituted derivatives

Abstract

Complexes of two types have been prepared (a) Tl₂[V(RC₆H₃O₂)₃](R = H, 3-Me, 4-Me, 3-MeO) and (b) Tl₂[VO(RC₆H₃O₂)₂](R = CHO). The complexes have magnetic moments corresponding to one unpaired electron and so contain vanadium(IV). Their i.r. spectra show that in both types all ligand molecules are co-ordinated and that only the type (b) complex contains the VO²⁺ ion. Earlier formulation of the type (a) complexes as type (b) with ‘ligand of crystallisation’ is shown to be wrong. The electronic spectrum of the type (b) complex shows ‘d–d’ transitions characteristic of oxovanadium(IV) complexes, but the spectra of the type (a) complexes are different having charge-transfer transitions extending through the visible region. It is suggested that the type of complex formed depends on both the σ- and π-donating abilities of the ligands. Type (a) complexes are formed by good donors with electron-releasing substituents and type (b) by poorer donors with electron-withdrawing substituents.