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

Three series of nitronyl nitroxide radical 3d-4f compounds, namely, [Ln(hfac)(3)Cu(hfac)(2)NIT-5Br-3Py](n) (Ln(III) = La (1), Pr (2)), [Ln(hfac)(3)Cu(hfac)(2)NIT-5Br-3Py] (Ln(III) = Gd (3), Tb (4), Dy (5)) and [Ln(hfac)(3)Cu(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 LnIII 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.