Heteroleptic samarium(iii) halide complexes probed by fluorescence-detected L(3)-edge X-ray absorption spectroscopy

The addition of various oxidants to the near-linear Sm(ii) complex [Sm(N(††))(2)] (1), where N(††) is the bulky bis(triisopropylsilyl)amide ligand {N(Si(i)Pr(3))(2)}, afforded a family of heteroleptic three-coordinate Sm(iii) halide complexes, [Sm(N(††))(2)(X)] (X = F, 2-F; Cl, 2-Cl; Br, 2-Br; I, 2-I). In addition, the trinuclear cluster [{Sm(N(††))}(3)(μ(2)-I)(3)(μ(3)-I)(2)] (3), which formally contains one Sm(ii) and two Sm(iii) centres, was isolated during the synthesis of 2-I. Complexes 2-X are remarkably stable towards ligand redistribution, which is often a facile process for heteroleptic complexes of smaller monodentate ligands in lanthanide chemistry, including the related bis(trimethylsilyl)amide {N(SiMe(3))(2)} (N′′). Complexes 2-X and 3 have been characterised by single crystal X-ray diffraction, elemental analysis, multinuclear NMR, FTIR and electronic spectroscopy. The Lα(1) fluorescence-detected X-ray absorption spectra recorded at the Sm L(3)-edge for 2-X exhibited a resolved pre-edge peak defined as an envelope of quadrupole-allowed 2p → 4f transitions. The X-ray absorption spectral features were successfully reproduced using time-dependent density functional theoretical (TD-DFT) calculations that synergistically support the experimental observations as well as the theoretical model upon which the electronic structure and bonding in these lanthanide complexes is derived.