Lanthanide halides dimers, structure

Structural studies by Baker, Brown, and Raymond (42) have shown the dimeric nature of lanthanide dicyclopentadienyl halides. They reported that the molecular structure of [Y (C H CH ) Cl] consists of two ytterbium atoms, each with two n -bound methyl-cyclopentadienyl rings, which are nearly symmetrically bridged by the two chlorine atoms. The crystal structure of Yb(C(.H Me was reported by Halton et al. (43). The complex actually nas a dimeric structure, Cp2YbMe2YbCp2, remarkably similar to Me2ALMe2 AlMe2 The overall molecular geometry is identical with that or the chloride analogue Yb(C H CH )2CI. 

All four scandium(III) halides are known, all but the fluoride (WO3 structure) having the FeCR structure. They can be obtained as white solids directly from the elements and in some cases by dehydration of the hydrated salts, as well as by thermal decomposition of (NH4)3ScXe (X = Cl, Br), a method also used for the lanthanides. Gas-phase studies have identified isolated planar Scp3 molecules at 1750 K ScCR molecules with a very slight pyramidal distortion and both monomers and dimers in Scis vapour at 1050 K. 

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