Probing through-space and through-bond magnetic exchange couplings in a new benzotriazinyl radical and its metal complexes

Abstract

The synthesis and characterization of a new chelating benzotriazinyl radical (Rad₂) are described. Crystallographic studies coupled with SQUID magnetometry on Rad₂ reveal the presence of discrete radical pairs which are antiferromagnetically coupled. The reaction of Rad₂ with the 3d transition metal complexes M(hfac)₂·xH₂O (hfac⁻ = hexafluoroacetylacetonate) led to mononuclear metal complexes of general formula M(hfac)₂(Rad₂) [M = Zn(II) (1); Ni(II) (2) and Co(II) (3)] whose structures have been determined by single crystal X-ray diffraction. Compounds 1–3 are isostructural and crystallize in the monoclinic space group P2₁/n with two molecules in the asymmetric unit. In the case of the Zn(II) complex (1) through-space intermolecular radical⋯radical antiferromagnetic exchange interactions via π*⋯π* contacts are observed, whereas strong intramolecular through-bond metal–radical ferromagnetic interactions [J = +59.3(9) cm⁻¹] are observed for the Ni(II) complex (2). For the Co(II) complex (3), computational and magnetic studies reveal substantial zero field splitting and ferromagnetic metal–radical interactions.