Deacon, Glen B., Feng, Tiecheng, Junk, Peter C., Meyer, Gerd, Scott, Natalie M., Skelton, Brian W., and White, Allan H. (2000) Structural variety in solvated lanthanoid(III) halide complexes. Australian Journal of Chemistry, 53 (10). pp. 853-865.

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Abstract

Treatment of lanthanum metal with CH₂Br₂ or CH₂I₂ in tetrahydrofuran (thf) under ultrasound conditions yields the corresponding [LaX₃(thf)₄] (X = Br, I) complexes in good yield. Recrystallization of [LaBr₃(thf)₄] from 1,2-dimethoxyethane (dme) or bis(2-methoxyethyl) ether (diglyme) generates [LaBr₂(μ-Br)(dme)₂]₂ and [LaBr₂(diglyme)₂][LaBr₄(diglyme)]. Treatment of lanthanoid metals with hexachloroethane in dme yields [LnCl₃(dme)₂] (Ln = La, Nd, Er or Yb) and in acetonitrile [YbCl₂(MeCN)₅]₂[YbCl₃(MeCN)(-Cl)₂YbCl₃(MeCN)]. The reaction of Yb metal pieces with 1,2-dibromoethane in thf and dme gave single crystals of [YbBr₃(thf)₃] and [YbBr₃(dme)₂], respectively. The X-ray determined structure of [LaBr₃(thf)₄] shows a seven-coordinate monomer with pentagonal-bipyramidal stereochemistry and apical bromide ligands. For [YbBr₃(thf)₃], a monomeric structure with mer-octa-hedral stereochemistry is observed. In [LaBr₂(μ-Br)(dme)₂]₂, two eight-coordinate La centres are linked by two bridging bromides. The dme ligands have a trans relationship to each other, and cis terminal bromides are transoid to the bridging bromides with dodecahedral stereochemistry for La. By contrast, the 1: 1.5 diglyme adduct is found to be ionic [LaBr₂(diglyme)₂][LaBr₄(diglyme)], with an eight-coordinate bicapped trigonal-prismatic lanthanum cation and a seven-coordinate pentagonal-bipyramidal lanthanum anion. In the cation, the bromide ligands are cis to each other, and in the anion, two bromides are equatorial and two are axial. In [YbBr₃(dme)₂], [YbCl₃(dme)₂] and [ErCl₃(dme)₂], a seven-coordinate pentagonal-bipyramidal arrangement exists with apical halogen ligands. Far-infrared data, and in particular the absence of absorptions attributable to υ(La–Clter), suggest that [LaCl₃(dme)] is polymeric with six bridging chlorides per lanthanum. For [YbCl₂(MeCN)₅]₂[YbCl₃(MeCN)(μ-Cl)₂YbCl₃-(MeCN)], a remarkable ionic structure, with pentagonal-bipyramidal [YbCl₂(MeCN)₅]⁺ cations and octahedral di-nuclear [YbCl₃(MeCN)(-Cl)₂YbCl₃(MeCN)]²⁻ counter ions, is observed. In the former, chloride ligands are apical, while the MeCN ligands of the latter are transoid.

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