Heterospin 2p–4f and 2p–3d–4f complexes constructed by a nitronyl nitroxide ligand: syntheses, structures and magnetic properties

Abstract

Two novel 2p–4f complexes [Ln(hfac)₃(Nit-Ph-PyIm)]₂·CHCl₃ (Ln(III) = Gd^III (1), Tb^III (2)) have been obtained through reacting a nitronyl nitroxide radical ligand Nit-Ph-PyIm (2-[4-[2-(2-pyridinyl)-1H-imidazol-1-yl]-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) with Ln(hfac)₃·2H₂O (hfac = hexafluoroacetylacetonate). Interestingly, by introducing Cu(hfac)₂, one 2p–3d–4f complex {[Tb(hfac)₄]⁻[Cu(hfac)(Nit-Ph-PyIm)]⁺}_n (3) was synthesized. Compounds 1 and 2 possess the [Ln–radical]₂ cyclic dimer structure. In complex 3, two neighboring [Cu(hfac)]⁺ moieties are linked by a Nit-Ph-PyIm radical, generating a positively charged [Cu(hfac)–radical]⁺ chain containing [Tb(hfac)₄]⁻ as the counterion. In the cation chain, Cu(II)⋯O–N interactions were strongly antiferromagnetic due to the equatorially coordinated NO units. Magnetic studies reveal that compound 3 displays field-induced slow magnetization relaxation, caused by the [Tb(hfac)₄]⁻ unit which possess a distorted D_4d geometry.