New binuclear iron–vanadium complexes of arylazo oximates. Crystal structure of [Fe(PhN⁼NCPh⁼NO)3VO(bipy)]PF₆(bipy = 2,2′-bipyridine)

Abstract

Binuclear iron(II)–vanadium(IV) complexes of types [FeL₃VO(acac)]1 and [FeL₃VO(diam)]PF₆² 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.