Terbium(III) and Yttrium(III) Complexes with Pyridine-Substituted Nitronyl Nitroxide Radical and Different β-Diketonate Ligands. Crystal Structures and Magnetic and Luminescence Properties

A terbium(III) complex of nitronyl nitroxide free radical 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro1H-imidazolyl-1-oxy-3-oxide (NIT2Py), [Tb(acac)(3)NIT2Py]center dot 0.5H(2)O (3) (acac = acetylacetonate), was synthesized for comparison with the previously reported [Tb(hfac)(3)NIT2Py]center dot 0.5C(7)H(16) (1) (hfac = hexafluoroacetylacetonate), together with their yttrium analogues [Y(hfac)(3)NIT2Py]center dot 0.5C(7)H(16) (2) and [Y(acac)(3)NIT2Py]center dot 0.5H(2)O (4). The crystal structures show that in all complexes the nitronyl nitroxide radical acts as a chelating ligand. Magnetic studies show that 3 like 1 exhibits slow relaxation of magnetization at low temperature, suggesting single-molecule magnet behavior. The luminescence spectra show resolved vibronic structure with the main interval decreasing from 1600 cm-(1) to 1400 cm(-1) between 80 and 300 K. This effect is analyzed quantitatively using experimental Raman frequencies.