Chain versus Discrete Assembly of Nitronyl Nitroxide Radical-Lanthanide Complexes: Regulating Magnetization Dynamics by Modifying Coordination Symmetry

The self-assembly of nitronyl nitroxide radical NIT-4trz-2Py (NIT-4trz-2Py = 2-(4-(1-triazole)-2-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) with Ln(hfac)(3)center dot 2H(2)O (hfac = hexafluoroacetylacetonate) has successfully afforded two 1D chains [Ln(hfac)(3)NIT-4trz-2Py] (Ln(III) = Tb-III 1, Dy-III 2) and four discrete trinuclear species [Ln(3)(hfac)(9)(NIT-4trz-2Py)(2)] (Ln(III) = Gd-III 3, Tb-III 4, Dy-III 5, Ho-III 6). The nine-coordinated Ln(III) ions with C-4v symmetry in 1 and 2 are linked by the NIT-4trz-2Py ligand through a "head-to-tail" mode, leading to a 1D structure. Compounds 3-6 possess a linear trinuclear structure which contains two {Ln(III)-radical} chelating units and one Dy(hfac)(3) (ligated by two triazole groups). All Ln(III) centers in 3-6 are in eight-coordinate D-4d geometry. Magnetic studies reveal that slow magnetization relaxation occurs in the two Dy-III-containing compounds. No maxima of chi '' are observed for complex 2 while compound 5 presents visible maxima in frequency-/temperature-dependent chi '' signals, which is due to the optimization of symmetries around Dy-III ions from C-4v in 2 to D-4d in 5. For luminescent spectra, two Tb-III-based derivatives display characteristic emissions of Tb-III ions at room temperature.