Trigonal Planar Heteroleptic Lanthanide(III) Bis(silyl)amide Complexes Containing Aminoxyl Radicals and Anions.

Modulation of the crystal field (CF) in lanthanide (Ln) complexes can enhance optical and magnetic properties, and large CF splitting can be achieved with low coordination numbers in specific geometries. We previously reported that the homoleptic near-linear Sm complex [Sm{N(SiPr)}] () is oxidized by the 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical to give the heteroleptic, approximately trigonal planar Sm complex, [Sm{N(SiPr)}(TEMPO)] (). Here, we report the synthesis of homologous [Ln{N(SiPr)}(TEMPO)] (; Ln = Tm, Yb) complexes by the oxidation of the parent [Ln{N(SiPr)}] (; Ln = Tm, Yb) with TEMPO; complexes all contain TEMPO anions. The homoleptic bent Ln complexes [Ln{N(SiPr)}][B(CF)] (; Ln = Sm, Tm, Yb) were also treated with TEMPO to yield the heteroleptic, approximately trigonal planar Ln complexes [Ln{N(SiPr)}(TEMPO)][B(CF)] (; Ln = Sm, Tm, Yb); the cations of all contain TEMPO radicals. We have compared the electronic structures of the two geometrically similar families of Ln complexes with the TEMPO anion () or TEMPO radical () using a combination of UV-vis-NIR and EPR spectroscopy, magnetic measurements, and calculations. These studies revealed no single-molecule magnet behavior for despite evidence for sizable CF splitting and a high degree of purity of the ground stabilized = |±7/2⟩ state, while the radical TEMPO in did not significantly improve performance.