Macrocyclic oxovanadium(IV) complexes: structure, magnetochemistry and electrochemistry

Abstract

The oxovanadium(IV) complexes, [VO(L)]·H₂O 1, [VO(H₂L)(SO₄)]·3H₂O 2, [(VO)₂L(µ-SO₄)]·MeOH·3H₂O 3 and [Zn(L)VO(SO₄)]·4H₂O 4 have been synthesised from the dinucleating tetraaminodiphenol macrocyclic ligand H₂L. The ESR and IR spectra of 1 have indicated stacking of the molecules due to ··· VɕO ··· VɕO ··· interactions. In complexes 2 and 4 the unidentate sulfate is bound to the octahedral vanadium and two of the secondary amino groups in 2 are protonated. Both of these complexes undergo oxidation to produce oxovanadium(V) species with E_½= 0.40 V (2), 0.455 V (4)vs. saturated calomel electrode (SCE). Fairly strong antiferromagnetic exchange interaction has been found in 3 from variable-temperature susceptibility measurements, J=-128 cm^-1. The crystal structure of 3 has been determined; tetragonal, space group P4₁22, a=b= 12.252(2), c= 40.819(5)Å and Z= 8; refinement led to R= 0.053 and R'= 0.055 using 1825 unique reflections with I > 3σ(I). The two octahedral vanadium centres in the complex, separated by 3.077 Å, are bridged by sulfate and have syn oxo configuration.