Slow magnetic relaxation in two-dimensional 3d-4f complexes based on phenyl pyrimidyl substituted nitronyl nitroxide radicals

Three isostructural two-dimensional 2p-3d-4f complexes, namely, {Tb(hfac)(3)[Cu(hfac)(2)](3)(NITPhPyrim) 2}center dot 2CH(2)Cl(2) 1 and {Ln(hfac)(3)[Cu(hfac)(2)](3)(NITPhPyrim)(2)} (Ln(III) = Ho 2, Yb 3; hfac = hexafluoroacetylacetonate; NITPhPyrim = 2-[4-(5-pyrimidyl) phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were characterized in terms of structure and magnetism. These heterospin compounds possess a two-dimensional sheet structure involving Cu-II and Ln(III) ions bridged by NITPhPyrim radicals through their NO groups and pyrimidine rings. DC magnetic studies show that these complexes exhibit ferromagnetic exchange coupling between radical ligands and metal atoms. AC measurements of the Tb complex reveal slow relaxation of the magnetization. Interestingly, the Tb complex displays two field-induced relaxation processes.