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-dihydro1<i>H</i>-imidazolyl-1-oxy-3-oxide (NIT2Py), [Tb­(acac)­3NIT2Py]·0.5H<sub>2</sub>O (<b>3</b>) (acac = acetylacetonate), was synthesized for comparison with the previously reported [Tb­(hfac)<sub>3</sub>NIT2Py]·0.5C<sub>7</sub>H<sub>16</sub> (<b>1</b>) (hfac = hexafluoroacetylacetonate), together with their yttrium analogues [Y­(hfac)<sub>3</sub>NIT2Py]·0.5C<sub>7</sub>H<sub>16</sub> (<b>2</b>) and [Y­(acac)<sub>3</sub>NIT2Py]·0.5H<sub>2</sub>O (<b>4</b>). The crystal structures show that in all complexes the nitronyl nitroxide radical acts as a chelating ligand. Magnetic studies show that <b>3</b> like <b>1</b> 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<sup>–1</sup> to 1400 cm<sup>–1</sup> between 80 and 300 K. This effect is analyzed quantitatively using experimental Raman frequencies.