Cu–Ln compounds based on nitronyl nitroxide radicals: synthesis, structure, and magnetic and fluorescence properties

Abstract

Three series of nitronyl nitroxide radical 3d–4f compounds, namely, [Ln(hfac)₃Cu(hfac)₂NIT-5Br-3Py]_n (Ln^III = La (1), Pr (2)), [Ln(hfac)₃Cu(hfac)₂NIT-5Br-3Py] (Ln^III = Gd (3), Tb (4), Dy (5)) and [Ln(hfac)₃Cu(hfac)₂(NIT-5Br-3Py)₂]_n (Ln^III = Gd (6), Tb (7), Dy (8); NIT-5Br-3Py = 2-(5-bromo-3-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been successfully obtained. Single crystal X-ray crystallographic analysis reveals that complexes 1 and 2 consist of 1D chains built up by Ln(hfac)₃ units bridged by the radical ligands through their NO moieties and the additional Cu ions are coordinated to the nitrogen atoms of the radicals. Complexes 3–5 are rare hetero-binuclear Cu–Ln compounds bridged by the nitronyl nitroxide radicals while complexes 6–8 possess one-dimensional chain structures with a repeating [Cu–Rad–Ln–Rad] sequence. DC magnetic studies show ferromagnetic interaction between the Ln^III ion and the coordinated NO group in compounds 3–8. Tb–Cu derivatives (complexes 4 and 7) display frequency dependent ac magnetic susceptibilities, indicating slow magnetic relaxation behavior. The room-temperature photoluminescence spectra of complexes 4 and 7 exhibit strong characteristic emissions in the visible region.