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(mu -Br)(dme)(2)](2) and [LaBr2(diglyme) (2)][LaBr4(diglyme)]. Treatment of lanthanoid metals with hexachloroethane in dme yields [LnCl(3)(dme)(2)] (Ln = La, Nd, Er or Yb) and in acetonitrile [YbCl2(MeCN)(5)](2)[YbCl3(MeCN)(mu -Cl)(2)YbCl3(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-octahedral stereochemistry is observed. In [LaBr2(mu -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 v( La-Cl-ter), suggest that [LaCl3(dme)] is polymeric with six bridging chlorides per lanthanum. For [YbCl2(MeCN)(5)](2)[YbCl3(MeCN)(mu -Cl)(2)YbCl3-( MeCN)], a remarkable ionic structure, with pentagonal-bipyramidal [YbCl2(MeCN)(5)](+) cations and octahedral dinuclear [YbCl3(MeCN)(mu -Cl)(2)YbCl3(MeCN)](2-) counter ions, is observed. In the former, chloride ligands are apical, while the MeCN ligands of the latter are transoid.