Magnetic relaxation in [Ln(hfac)4]− anions with [Cu(hfac)-radical]nn+ cation chains as counterions

Abstract

Using a new nitronyl nitroxide radical Nit-Ph-PyIm, two novel 3d–4f complexes with the formula {[Ln(hfac)₄]⁻[Cu(hfac)(Nit-Ph-PyIm)]⁺}_n (Ln^III = Gd 1, Dy 2) have been isolated (Nit-Ph-PyIm = 2-[4-[2-(2-pyridinyl)-1H-imidazol-1-yl]-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate). Interestingly, for both compounds, there are discrete [Ln(hfac)₄]⁻ anions while [Cu(hfac)-radical]_nⁿ⁺ chains serve as counter-ions in which the Nit-Ph-PyIm radicals link [Cu(hfac)]⁺ units through their NO groups and imidazolyl pyridine moieties. The [Cu(hfac)(Nit-Ph-PyIm)]⁺ unit is diamagnetic owing to the strong antiferromagnetic coupling between the Cu(II) ion and the equatorially coordinated NO group. Complex 2 shows field-induced slow magnetization relaxation, arising from [Dy(hfac)₄]⁻ anions that exhibit distorted square-antiprism (D_4d) geometries.