Lanthanide elements oxide fluorides

Americium may be separated from other elements, particularly from the lanthanides or other actinide elements, by techniques involving oxidation, ion exchange and solvent extraction. One oxidation method involves precipitation of the metal in its trivalent state as oxalate (controlled precipitation). Alternatively, it may be separated by precipitating out lanthanide elements as fluorosilicates leaving americium in the solution. Americium may also he oxidized from trivalent to pentavalent state by hypochlorite in potassium carbonate solution. The product potassium americium (V) carbonate precipitates out. Curium and rare earth metals remain in the solution. An alternative approach is to oxidize Am3+ to Am022+ in dilute acid using peroxydisulfate. Am02 is soluble in fluoride solution, while trivalent curium and lanthanides are insoluble. 

S.A. Kinkead, K.D. Abney and T.A. O Donnell, f-element speciation in strongly acidic media lanthanide and mid-actinide metals, oxides, fluorides and oxide fluorides in superacids 507... 

In the f-block the lanthanide elements show quite different behaviour, and oxidation state +3 dominates the binary oxides and fluorides formed... 

Recent Advances in the Chemistry of the Less-Common Oxidation States of the Lanthanide Elements D. A. Johnson Ferrimagnetic Fluorides... 

Neodymium oxide was first isolated from a mixture of oxides called didymia. The elemeut ueodymium is the secoud most abuudaut lanthanide element in the igneous rocks of Earth s crust. Hydrated neodymium(lll) salts are reddish and anhydrous neodymium compounds are blue. The compoxmds neodymium(III) chloride, bromide, iodide, nitrate, perchlorate, and acetate are very soluble neodymium sulfate is somewhat soluble the fluoride, hydroxide, oxide, carbonate, oxalate, and phosphate compounds are insoluble. 

Few lanthanide elements may be oxidized to the tetravalent state and stabilized, almost exclusively, in fluorides and oxides. These are the elements cerium, terbium, praseodymium, dysprosium, neodymium, holmium, for example all in the ternary fluorides CS3RF7 (Hoppe and Roedder 1961). There are also hints at pentavalent praseodymium, CsPrFe would be the example (Hoppe 1980). 

O Table 18.10 shows ionic radii of actinide elements together with those of lanthanide elements (Seaborg and Loveland 1990). The usefiil data on the ionic radii and coordination number are given by Shannon and Prewitt (1969). They carried out comprehensive study of crystal, or ionic, radii by analyzing the crystal structures of many fluoride, oxide, chloride, and sulfide compounds. Marcus published a data book on the properties of ions (Marcus 1997). The book covers a wide range of information on ionic radii of the actinide elements and other ions. Ionic radii of actinide elements decrease with increasing atomic number. This behavior is called actinide contraction and is one of the important examples of the actinide concept. 

AH of reaction (17) is an estimate since PuCl4(s) has not been synthesized AfH° [PuCl4(s)] = — 964 kJ is an estimate (Fuger et al. 1983). The dramatic difference in these enthalpies [Pu(IV) is more stable than Pu(III) in this complex chloride by -95-( —4) = - 91 kJ or almost 1.0 V, in comparison with the binary chloride] shows how acid-base effects influence oxidation-reduction properties. As noted above, there are few known lanthanide (IV) complex halides and no thermodynamic data on even these few halides, so no quantitative comparison can be made. Nevertheless it does show how complexation effects by basic complexants make high f-element oxidation states attainable. Perhaps the most dramatic evidence of the enhancement of high oxidation state by a basic fluoride is the existence of the Nd(IV) and Dy (IV) compounds such as Cs2(Cs, Rb, K) (Nd, Dy)Cl2 these AjRF, double fluorides are the only known Nd (IV) and Dy(IV) compounds. 

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