2p-4f Loop-chains {[Ln(hfac)3]2-radical}n achieved through multidentate nitronyl nitroxide radicals

Abstract

Reactions of the designed multidenate nitronyl nitroxide radical ligands Nit-pH-3,5-bPy or Nit-pH-3,5-btrz (Nit-pH-3,5-bPy = 2-[3,5-bis(4-pyridyl)-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; Nit-pH-3,5-btrz = 2-[3,5-bis(1H-1,2,4-triazol-1-yl)-phenyl]-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide) with Ln(hfac)3 obtained four rare Ln-radical loop-chains, namely, {[Ln(hfac)3]2(Nit-pH-3,5-bPy)}n (LnIII = Gd 1, Tb 2; hfac = hexafluoroacetylacetonate) and {[Ln(hfac)3]2(Nit-pH-3,5-btrz)}n (LnIII = Tb 3, Ho 4). In all complexes, each pyridyl- or triazolyl-functionalized radical ligand is binded to four Ln(hfac)3 centers with a μ4-η1:η1:η1:η1-coordination mode through its two NO units and two N atoms of pyridines/triazoles, giving rise to interesting radical-bridged loop-chains with the scarcely reported 4f-2p-4f structural motifs. Magnetic measurements indicate that there are ferromagnetic interactions between the Ln(III) ions and the coordinated NO groups in these compounds. Tb 2 exhibits clear frequency-dependent out-of-phase (χ′′) signals in a zero dc field indicating slow relaxation of magnetization, while no non-zero χ′′ signals are observed for Tb 3 without an external magnetic field, which could be ascribed to the slightly different heterocyclic ligands.