Atomic radii lanthanoids

Fig. 9.54 The variation of atomic radius through the periodic table. Note the contraction of radius following the lanthanoids in Period 6 (following lutetimn, Z=71).

The a-structure exhibits void positions with seven N atoms as nearest neighbours (Sect. 2). These positions can be partially occupied by ions with an ionic radius of about 0.1 nm, causing a stabilisation of the metastable a-modification (Fig. 11). The cations M which can be incorporated in the a-structure are Li+, Mg2+, Ca2+, Y3+ and lanthanoides with 2 > 60 [123, 169, 187]. Additionally Si4+ and N3- must be replaced by Al3+ and O2- to obtain electroneutrality. The formula for the resulting a-solid solutions is... 

The thermal stability and reactivity of Cp2LnR type complexes significantly depends on the coordination saturation of the metal atom, its size and bulkiness of ligands, i.e. the factors, which determine strain of the complexes and steric shielding of the Ln-R bond. Due to the increase of molecule strain the thermal stability of the complexes as a rule decreases from early to heavier lanthanoids, which have smaller ionic radius. 

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