Trigonal Planar Heteroleptic Lanthanide(III) Bis(silyl)amide\nComplexes Containing Aminoxyl Radicals and Anions

Modulation of the\ncrystal field (CF) in lanthanide (Ln) complexes\ncan enhance optical and magnetic properties, and large CF splitting\ncan be achieved with low coordination numbers in specific geometries.\nWe previously reported that the homoleptic near-linear Sm<sup>2+</sup> complex [Sm<sup>II</sup>{N(Si<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub>] (<b>1-Sm</b>) is oxidized by the 2,2,6,6-tetramethylpiperidinyl-1-oxy\n(TEMPO<sup>•</sup>) radical to give the heteroleptic, approximately\ntrigonal planar Sm<sup>3+</sup> complex, [Sm<sup>III</sup>{N(Si<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(TEMPO<sup>–</sup>)] (<b>2-Sm</b>). Here, we report the synthesis of homologous\n[Ln<sup>III</sup>{N(Si<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(TEMPO<sup>–</sup>)] (<b>2-Ln</b>; Ln = Tm, Yb)\ncomplexes by the oxidation of the parent [Ln{N(Si<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub>] (<b>1-Ln</b>; Ln = Tm, Yb)\nwith TEMPO<sup>•</sup>; complexes <b>2-Ln</b> all contain\nTEMPO<sup>–</sup> anions. The homoleptic bent Ln<sup>3+</sup> complexes [Ln<sup>III</sup>{N(Si<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]\n(<b>3-Ln</b>; Ln = Sm, Tm, Yb) were also treated with TEMPO<sup>•</sup> to yield the heteroleptic, approximately trigonal\nplanar Ln<sup>3+</sup> complexes [Ln<sup>III</sup>{N(Si<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(TEMPO<sup>•</sup>)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>4-Ln</b>;\nLn = Sm, Tm, Yb); the cations of <b>4-Ln</b> all contain TEMPO<sup>•</sup> radicals. We have compared the electronic structures\nof the two geometrically similar families of Ln<sup>3+</sup> complexes\nwith the TEMPO<sup>–</sup> anion (<b>2-Ln</b>) or TEMPO<sup>•</sup> radical (<b>4-Ln</b>) using a combination of\nUV–vis-NIR and EPR spectroscopy, magnetic measurements, and <i>ab initio</i> calculations. These studies revealed no single-molecule\nmagnet behavior for <b>2-Yb</b> despite evidence for sizable\nCF splitting and a high degree of purity of the ground stabilized <i>m</i><sub>J</sub> = |±7/2⟩ state, while the radical\nTEMPO<sup>•</sup> in <b>4-Yb</b> did not significantly\nimprove performance.