Structural Variety in Solvated Lanthanoid(III ) Halide Complexes

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(dig-lyme)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 Ì(La–Clter), suggest that [LaCl3(dme)] is polymeric with six bridging chlorides per lanthanum. For [YbCl2(MeCN)5]2[YbCl3(MeCN)(-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.