Preparation of the bis(trimethylsilyl)amido lanthanide chlorides [{Ln[N(SiMe3)2]2(µ-Cl)(thf)}2](thf = tetrahydrofuran), and the crystal and molecular structures of the gadolinium and ytterbium complexes

Abstract

Reaction of LnCl₃ with 2 equivalents of LiL [L = N(SiMe₃)₂] in tetrahydrofuran (thf) at –5 °C yields [{LnL₂Cl(thf)}₂] for Ln = Eu, Gd, or Yb or [YL₂Cl(thf)₂] for Ln = Y. X-Ray crystal structure analysis of the compounds of Gd and Yb confirms the formation of halide-bridged dimers. In the M₂Cl₂ bridging unit the M–Cl bond lengths differ slightly and the angle at the metal (ca. 74°) is much smaller than at chlorine (ca. 106°). The metal co-ordination geometries are irregular but can be best described as distorted trigonal bipyramidal with the bridging chlorines spanning one axial and one equatorial site. The bond lengths M–Cl and M–N indicate a Gd–Yb radius difference of ca. 0.07 Å, but the M–O distances differ by 0.093 Å. Variable-temperature n.m.r. studies of [{EuL₂Cl(thf)}₂] and [{YbL₂Cl(thf)}₂] show that there is free rotation about Ln–N and Ln–O bonds at room temperature. These rotations are frozen out at low temperatures to give a solution structure having higher symmetry (C_2h) than that found in the crystal.