Investigation into the Effects of a Trigonal-Planar Ligand Field on the Electronic Properties of Lanthanide(II) Tris(silylamide) Complexes (Ln = Sm, Eu, Tm, Yb)

• Published in: Inorganic chemistry 2017-05, Vol.56 (10), p.5959-5970
• Main Authors: Goodwin, Conrad A. P, Chilton, Nicholas F, Natrajan, Louise S, Boulon, Marie-Emmanuelle, Ziller, Joseph W, Evans, William J, Mills, David P
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b00664

In recent work we have reported the synthesis and physical properties of near-linear Ln­(II) (Ln = lanthanide) complexes utilizing the bulky bis­(silylamide) {N­(Si i Pr3)2}. Herein, we synthesize trigonal-planar Ln­(II) complexes by employing a smaller bis­(silylamide), {N­(Si t BuMe2)2} (N**), to study the effects of this relatively rare Ln geometry/oxidation state combination on the magnetic and optical properties of complexes. We show that the charge-separated trigonal-planar Ln­(II) complexes [K­(2.2.2-cryptand)]­[Ln­(N**)3] (Ln = Sm (1), Eu (2), Tm (3), Yb (4)) can be prepared by the reaction of 1.5 equiv of [{K­(N**)}2] with LnI2THF2 (Ln = Sm, Yb) or LnI2 (Ln = Eu, Tm) and 1 equiv of 2.2.2-cryptand in Et2O. Complex 3 is the first structurally characterized trigonal-planar Tm­(II) complex. In the absence of 2.2.2-cryptand, [K­(DME)3]­[Sm­(N**)3] (5) and [Ln­(N**)2(μ-N**)­K­(toluene)2] (Ln = Sm (6), Eu (7)) were isolated in the presence of DME (dimethoxyethane) or toluene, respectively. The 1:1 reaction of [{K­(N**)}2] with LnI2THF2 (Ln = Sm, Yb) in THF gave the four-coordinate pseudo-tetrahedral Lewis base adducts [Ln­(N**)2(THF)2] (Ln = Sm (8), Yb (9)) and the cyclometalated complex [Yb­(N**)­{N­(Si t BuMe2)­(Si t BuMeCH2)}­(THF)] (10). Complexes 1–10 have been characterized as appropriate by single-crystal XRD, magnetic measurements, multinuclear NMR, EPR, and electronic spectroscopy, together with CASSCF-SO and DFT calculations. The physical properties of 1–4 are compared and contrasted with those of closely related near-linear Ln­(II) bis­(silylamide) complexes.