Tuning Magnetic Relaxation in a Tb-Nitronyl Nitroxide Complex by Using Cocrystalline Paramagnetic Complex.

New 2p-4f and 2p-3d-4f compounds [Tb(hfac)3(NIT-PhNO2)2]· 0.5C7H16 (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-nitrophenyl)-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, 1D supramolecular chains are formed via the π-π 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.