New binuclear iron-vanadium complexes of arylazo oximates. Crystal structure of [Fe(PhN=NCPh=NO) < inf > 3 < /inf > VO(bipy)]PF < inf > 6 < /inf > (bipy = 2,2′-bipyridine)

Abstract

Binuclear iron(II)-vanadium(IV) complexes of types [FeL3VO(acac)] 1 and [FeL3VO(diam)]PF6 2 have been prepared where HL is PhN=NC(R)=NOH with R = Ph(HL1) or Me(HL2), Hacac is acetylacetone and diam is 2,2′-bipyridine (bipy), 1,10-phenanthroline or 3,5-dimethyl-1-(2-pyridyl)pyrazole. Complexes of type 1 are obtained from Na[FeL3]·H2O and [VO(acac)2] and 2 by adding diam to acidified 1. The crystal structure of [FeL13VO(bipy)] PF6 has been determined. The low-spin iron(II) atom is facially tris chelated in the Fe(N,N)3 fashion and the three pendant oximato oxygen atoms engage the vanadium atom which is also bonded to an oxo oxygen and bipy nitrogen atoms. The VO4N2 co-ordination sphere is distorted octahedral. The trans influence of the oxo oxygen lengthens a V-O(oximate) bond by 0.2 Å. The complexes behave as one-electron paramagnets due to the VO2+ centre. Their ESR spectra are axial with g∥ < g⊥. The 51V hyperfine interaction follows the trend 1 > 2.