From Discrete Cluster to Chain of Rings: Ln-Radical Architectures Involving a Nitronyl Nitroxide with Two Imidazole Groups

The self-assembly of Ln(hfac)3 with NITPh-3,5-bMeIm radical (NITPh-3,5-bMeIm = 2-[3′,5′-bis(2″-methylimidazol-1″-yl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) results in two kinds of architectures depending on the rare earth element, namely, a tetranuclear cyclic molecular cluster {(NITPh-3,5-bMeIm-H)2[Ln(hfac)3]2[Ln(hfac)4]2} (LnIII = Pr, 1; Nd, 2) and a chain of rings {[(NITPh-3,5-bMeIm)2(Ln(hfac)3)3]·0.5CHCl3}n (LnIII = Gd, 3; Dy, 4). In all cases, NITPh-3,5-bMeIm acts as a three-connecting node, but distinct coordination schemes apply. For 1 and 2, one of the imidazoles of NITPh-3,5-bMeIm is protonated; consequently, the ligand connects three LnIII atoms by means of the two aminoxyl oxygen atoms (NO) and the second imidazole group. In the case of 3 and 4, one NO group and the two imidazole groups coordinate to Ln ions. Magnetic studies reveal ferromagnetic GdIII–ON interaction in 3 and show that Dy derivative displays field-induced slow magnetic relaxation behavior with the Ueff/kB value of 18.41 K.