Magnetic slow relaxation of pseudo-binuclear Ln(III)-nitronyl nitroxide radical complexes involving non-covalent O⋯O interactions

Abstract

Five new nitronyl-nitroxide radical-Ln(III) complexes, [Ln(hfac)3(NITPh-2-OCH2Ph)(IMHPh-2–OCH2Ph)] (Ln = Tb(1), Dy(2)) and [Ln(hfac)3(NITPh-2-OCH2Ph)2] (Ln = Ho(3), Er(4), Yb(5)) (hfac = hexafluoroacetylacetonate, NITPh-2-OCH2Ph = 2-(2-benzyloxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, IMHPh-2-O-CH2Ph = the reduced derivative of NITPh-2-OCH2Ph), have been synthesized and characterized. The single-crystal X-ray diffraction analysis shows that all these complexes crystallize in triclinic P1−space group, and are composed of mononuclear molecules. The central Ln(III) ion is eight-coordinated by three bidentate chelating hfac anions and two monodentate NITR (or IMHR) molecules, with a dodecahedron environment. There arise a common interesting structural feature for these complexes that the mononuclear molecules form pseudo-binuclear structures through intermolecular non-covalent N–O⋯O–N contacts of nitroxide groups. All of them show intramolecular weak antiferromagnetic interactions between Ln(III) ion and radicals. Alternating current (ac) magnetic susceptibilities display a frequency-dependent characteristic for both Tb(1) and Dy(2), typical of magnetic slow relaxation of single-molecule magnet (SMM) behavior.