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)­3NIT2Py]·0.5H2O (3) (acac = acetylacetonate), was synthesized
for comparison with the previously reported [Tb­(hfac)3NIT2Py]·0.5C7H16 (1) (hfac = hexafluoroacetylacetonate),
together with their yttrium analogues [Y­(hfac)3NIT2Py]·0.5C7H16 (2) and [Y­(acac)3NIT2Py]·0.5H2O (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.