MACROCYCLIC OXOVANADIUM(IV) COMPLEXES - STRUCTURE, MAGNETOCHEMISTRY AND ELECTROCHEMISTRY

The oxovanadium(IV) complexes, VO(L)!.H2O 1, VO(H2L)(SO4)!.3H2O 2,  (VO)2L(mu-SO4)!-MeOH.3H2O 3 and Zn(L)VO(SO4)!.4H2O 4 have been synthe sised from the dinucleating tetraaminodiphenol macrocyclic ligand H2L. The ESR and IR spectra of 1 have indicated stacking of the molecules due to ... V=O ... V=O ... interactions. In complexes 2 and 4 the unid entate sulfate is bound to the octahedral vanadium and two of the seco ndary amino groups in 2 are protonated. Both of these complexes underg o oxidation to produce oxovanadium(V) species with E1/2 = 0.40 V (2), 0.455 V (4) vs. saturated calomel electrode (SCE). Fairly strong antif erromagnetic exchange interaction has been found in 3 from variable-te mperature susceptibility measurements, J = -1 28 cm 1. The crystal str ucture of 3 has been determined; tetragonal, space group P4(1)22, a = b = 1 2.252(2), c = 40.819(5) angstrom and Z = 8; refinement led to R = 0.053 and R' = 0.055 using 1825 unique reflections with I > 3sigma(I ). The two octahedral vanadium centres in the complex, separated by 3. 077 angstrom, are bridged by sulfate and have syn oxo configuration.