Single-chain magnet behavior in a 2p–3d–4f spin array with a nitronyl nitroxide biradical

Abstract

Three biradical-bridged heterometallic chains, [LnCu₂(hfac)₇(bisNITPhPy)]_n (Ln^III = Gd, 1; Tb, 2; Ho, 3), were synthesized by means of a nitronyl nitroxide biradical bisNITPhPy ([5-(4-pyridyl)-1,3-bis(1′-oxyl-3′-oxide-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene; hfac = hexafluoroacetylacetonate). In these structures, the bisNITPhPy biradical serves as a pentadentate ligand to hold one Ln^III ion through two neighboring aminoxyl (NO) moieties in chelating mode, while other two NO groups are coordinated to Cu(hfac)₂ units, leading to a 1D Cu–Ln-birad chain. An additional terminal Cu(hfac)₂ unit linked to a pyridine-N atom is found at the periphery. The magnetic susceptibility data of compound Gd have been analyzed with a closed ring model comprising three [Cu–Rad–Gd–Rad] units, which indicates ferromagnetic Gd(III)–nitroxide and Cu(II)–axial nitroxide interactions. The Tb derivative was found to behave as a single chain magnet with an energy barrier for magnetization reversal of 26 K.