Actinoids metals

A = Alkali metal AE = Alkaline-earth metal a-P = Amorphous phosphorus CN = Mean coordination number (i(M-P) = Distance between M and P atom Distances between P atoms E = Element = Band gap M = Metal PBO = Pauling bond order (P) = Formal charge of a P atom (M) = Formal charge of a M atom R = Zr, Ftf, rare earth metal or actinoid metal RE = Rare earth element / cov = Covalent radius ... 

The field of transition metal-rich phosphides in the ternary systems R T P (R = Zr, Hf, rare earth metal, actinoid metal) has intensively been investigated in the last 10 years by the groups of Franzen and Kleinke, Guerin, Jeitschko, Kuz ma, and Mewis. From a geometrical point of view, the main building motifs of these stmctures are mono-, di-, or tricapped... 

Figure 20 Crystal structures of various ternary and quaternary phosphide oxides of the alkaline earth, rare earth, and actinoid metals. Alkaline earth (rare earth, actinoid), transition metal, phosphorus, and oxygen atoms are drawn as large light grey, medium grey, filled, and open circles, respectively. Some relevant coordination polyhedra around the oxygen atoms and the transition metal-phosphorus bonds are emphasized...

Among the actinoid metals, Am, Cf, and Es have properties sufficiently similar to the volatile lanthanoids that they can be prepared according to reaction (d) . Substitution of less volatile Th for La allows this method to be used for the reduction of Ac, Pu, and Cm. 

The actinoid can thus be reduced with hydrogen to form an alloy. In a subsequent step the actinoid metal is purified from the alloy by fractional sublimation ... 

All the actinoid metals can be prepared by reducing their carbides with Ta Carbides are prepared from oxides [reaction (a)] at 2000°C with graphite in vacuum, and the actinoid metals (except for Th and Pa) are purified from Ta and TaC by distillation. 

When a metal contains impurities more volatile than the metal, such as a volatile reductant metal or its halide, heating the metal well above its melting point in vacuum serves as a useful purification step. The lighter rare earth and actinoid metals, especially those prepared by the iodine vapor process, are efficiently refined by vacuum melting . Vacuum melting is not often employed industrially because of the expenses associated with heating and corrosion of crucibles. 

Table 6.8 gives stability constants for the complexes [FeX] and [HgX] for different halide ions while the stabilities of the Fe complexes decrease in the order F > CP > Br, those of the Hg complexes increase in the order F < CP < Br < P. More generally, in examinations of stability constants by Ahrland, Chatt and Davies, and by Schwarzenbach, the same sequence as for Fe + was observed for the lighter s- and /i-block cations, other early J-block metal cations, and lanthanoid and actinoid metal cations. These cations were collectively termed class (a) cations. The same sequence as for Hg complexes was observed for halide complexes of the later J-block metal ions, tellurium, polonium and thallium. These ions were collectively called class (b) cations. Similar patterns were found for other donor atoms ligands with O- and iV-donors form more stable complexes with class (a) cations, while those with S- and F-donors form more stable complexes with class (b) cations. 

In Section 19.7, we looked at coordination numbers up to 9. The large size of the lanthanoid and actinoid metals means that in their complexes, high coordination numbers (>6) are common. The splitting of the degenerate set of/ orbitals in crystal fields in small (A gt 1 kJmoH ) and crystal field stabilization considerations are of minor importance in lanthanoid and actinoid chemistry. Preferences between different coordination numbers and geometries tend to be controlled by steric effects. 

Alkyl derivatives are more stable if the actinoid metal is also bound to cyclopentadienyl ligands and reactions 24.44-24.46 show general methods of synthesis where M = Th or U. 

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