New 2p-4f and 2p-3d-4f compounds [Tb-(hfac)(3) (NIT-PhNO2)(2)]center dot 0.5C(7)H(16) (1) and [Ln(hfac)(3)(NIT-PhNO2)(2)](2)[Cu(hfac)(2)(NIT-PhNO2)(2)] (Ln(III) = Gd 2, Tb 3; hfac = hexafluoroacetylacetonate; NIT-PhNO2 = 2-(p-nitro-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been obtained. Complex 1 consists of mononuclear trispin [Tb(hfac)(3)(NIT-PhNO2)(2)] units in which two radical ligands are ligated to the Tb(III) ion as monodentate ligands through the NO groups, while complexes 2 and 3 contain two kinds of trispin moieties, namely, [Ln(hfac)(3)(NIT-PhNO2)(2)] and [Cu(hfac)(2)(NIT-PhNO2)(2)]. In the [Cu(hfac)(2)(NIT-PhNO2)(2)] moiety, the radicals are bonded to the copper(II) ion in the axial positions via the nitroxides. For three compounds, ID supramolecular chains are formed via the it pi-pi stacking interactions involving the radical ligands. Magnetic investigations show that both Tb complexes exhibit slow relaxation of magnetization at low temperature; strikingly, complex 3 displays a higher energy barrier than that of 1. It represents the first example to use the paramagnetic complex to tune magnetic relaxation of 4f-based compounds.