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 Sm2+ complex [Sm{N(SiiPr3)2}2] (1-Sm) is oxidized by 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO•) radical to give the heteroleptic, approximately trigonal planar Sm3+ complex, [Sm{N(SiiPr3)2}2(TEMPO)] (2-Sm). Here we report the synthesis of homologous [Ln{N(SiiPr3)2}2(TEMPO)] (2-Ln; Ln = Tm, Yb) complexes by the oxidation of the parent [Ln{N(SiiPr3)2}2] (1-Ln; Ln = Tm, Yb) with TEMPO•; complexes 2-Ln all contain TEMPO– anions. The homoleptic bent Ln3+ complexes [Ln{N(SiiPr3)2}2][B(C6F5)4] (3-Ln; Ln = Sm, Tm, Yb) were also treated with TEMPO• to yield the heteroleptic, approximately trigonal planar Ln3+ complexes [Ln{N(SiiPr3)2}2(TEMPO)][B(C6F5)4] (4-Ln; Ln = Sm, Tm, Yb); the cations of 4-Ln all contain TEMPO• radicals. We have used a combination of UV-vis-NIR and EPR spectroscopy, magnetic measurements and ab initio calculations to compare the electronic structures of geometrically similar 2-Ln and 4-Ln cations. These studies revealed no single-molecule magnet behavior for 2-Yb despite evidence for sizable CF-splitting and high degree of purity of the ground stabilized mJ = |±├ 7/2⟩┤ state, while the radical TEMPO• in 4-Yb did not significantly improve performance.