Four new rare-earth nitronyl nitroxide radical complexes: Magnetic and luminescent properties

Abstract

Four new rare-earth nitronyl nitroxide radical complexes, [Ln(hfac)3(NITPh-Pa)2][0.5CH3(CH2)5CH3] (Ln = Gd(1), Tb(2), Dy(3), Ho(4), hfac = hexafluoroacetylacetonate, NITPh-Pa = 2-(3′,4′-dioxylmethylene-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide), have been synthesized. The X-ray crystal structure analysis revealed that four compounds have similar mononuclear tri-spin structures, in which the Ln(III) ions are eight-coordinated by two nitronyl nitroxide radicals and three hexafluoroacetylacetonate ligands to form a slightly distorted dodecahedron. In complexes 1–4, isolated mononuclear molecules connect each other through intermolecular hydrogen bonds to form 3D supermolecular framework. Magnetic investigation indicates there are ferromagnetic interactions between Gd(III) ions and radicals in complex 1. Alternating current(ac) magnetic susceptibilities of complexes 2 and 3 show that there are no non-zero out-of-phase signal, which indicates the inexistence of slow magnetic relaxation. The luminescence properties of complex 2 exhibit the characteristic emission peaks of Tb3+ ions and the potential for recognition of Cr2O72− and Cr3+ ions. Furthermore, nearly linear at low concentration and the low detection limit (0.01 μM) indicate that complex 2 may potentially be acted as luminescence-based sensor for quantitative and highly sensitive detection of Cr2O72− ion.