Slow relaxation of magnetization in unprecedented Cu-Ln-Rad hetero-tri-spin chains constructed from multidentate nitronyl nitroxide

Reactions of the radical 3,5-bPy-Ph-Nit (2-[3,5-bis(3-pyridyl)-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) with Ln(hfac)(3) and Cu(hfac)(2) afforded four unprecedented radical-3d-4f chains with formula {[Ln(hfac)(3)][Cu(hfac)(2)](2)(3,5-bPy-Ph-Nit)(H2O)}(n)center dot nC(7)H(16) (Ln = Gd, 1; Tb, 2; Dy, 3; Ho, 4; hfac = hexafluoroacetylacetonate). In complexes 1-4, each 3,5-bPy-Ph-Nit radical serves as one mu(4)-bridge to bind one Ln(III) ion and three Cu-II ions via its two aminoxyl units and two pyridine-N atoms, giving rise to unique Cu-Ln-radical one-dimensional chains with a rare [Ln-NIT-Cu-NIT-Ln] structural motif. Magnetic investigation shows that ferromagnetic interactions are found between the aminoxyl unit and Cu(ii) or Ln(iii) ions. Interestingly, a Dy derivative displays two-step relaxations of magnetization, while a Tb complex exhibits field-induced slow magnetic relaxation, originating from the [Ln-NIT-Cu-NIT-Ln] ferromagnetic structural units.