Hafnium nuclear charge

These are listed in Table 2.3 and shown in Figure 2.4. It will be seen that the atomic radii exhibit a smooth trend across the series with the exception of the elements europium and ytterbium. Otherwise the lanthanides have atomic radii intermediate between those of barium in Group 2A and hafnium in Group 4A, as expected if they are represented as Ln + (e )3. Because the screening ability of the f electrons is poor, the effective nuclear charge experienced by the outer electrons increases with increasing atomic number, so that the atomic radius would be expected to decrease, as is observed. Eu and Yb are exceptions to this because of the tendency of these elements to adopt the (+2) state, they have the structure [Ln +(e )2] with consequently greater radii, rather similar to barium. In contrast, the ionic radii of the Ln + ions exhibit a smooth decrease as the series is crossed. 

High-coordination-number complexes of 0-keto-enolates continue to be obtained with the metals such as zirconium(IV),8 hafnium(IV),8 cerium(IV),9 and the lanthanons(III),10 the last being tetrakis anionic species. At least one example of a volatile tetrakis 0-keto-enolate salt has been reported,11 Cs[Y(CF3-COCHCOCF3)4]. The ionic charge on the 0-keto-enolate complex has been shown to produce12 a high field nuclear magnetic resonance for anions and low field shifts for cations, relative to the positions observed for the neutral species. 

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