Ferromagnetic versus antiferromagnetic exchange in oximato-bridged nickel(ii) complexes

Abstract

Four Ni(II) complexes [Ni₂(Br-pao)₃(Me₃tacn)]ClO₄ (1), [Ni₂(Br-pao)₃(Me₃tacn)]BF₄ (2), [Ni₂(Hpyaox)₃(Me₃tacn)]BPh₄·3MeOH (3) and [Ni₅(Hpyaox)₄(pyaox)₂L₂](ClO₄)₂·4CH₃CN·2H₂O (4) have been synthesized and characterized (Br-Hpao = 6-Br-2-pyridinealdoxime, Me₃tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, H₂pyaox = pyridine-2-amidoxime, L = 2-(2-aminoethylamino)ethanol). Complexes 1–3 have a similar triply oximato-bridged dinuclear structure, and complex 4 has a novel pentanuclear structure with three octahedral and two square planar Ni(II) ions. The variable temperature magnetic susceptibility measurement data show the antiferromagnetic (AFM) coupling for 1–3 and uncommon ferromagnetic (FM) coupling for 4. Furthermore, the oxime N–O bond lengths are a crucial factor affecting the magnetic coupling between two adjacent ions.