The heavy lanthanides

In the description of fhe sfandard model. Section 2.2, it is assumed that the electrons distribute themselves among the available f-states according to Hund s rules. However, Hund s rules are essentially based on experiment. A good first-principles theory of elecfronic sfrucfure is one where Hrmd s rules drop out of the theory rather than having to be included empirically. 

Now we go on to discuss the results of the calculation of the heavy lanthanide magnetic moments. These calculations were performed on a hexagonal close packed lattice at the experimental lattice constant, so these numbers should be 

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The classical methods used to separate the lanthanides from aqueous solutions depended on (i) differences in basicity, the less-basic hydroxides of the heavy lanthanides precipitating before those of the lighter ones on gradual addition of alkali (ii) differences in solubility of salts such as oxalates, double sulfates, and double nitrates and (iii) conversion, if possible, to an oxidation state other than -1-3, e g. Ce(IV), Eu(II). This latter process provided the cleanest method but was only occasionally applicable. Methods (i) and (ii) required much repetition to be effective, and fractional recrystallizations were sometimes repeated thousands of times. (In 1911 the American C. James performed 15 000 recrystallizations in order to obtain pure thulium bromate). 

The bulk of both monazite and bastnaesite is made up of Ce, La, Nd and Pr (in that order) but, whereas monazite typically contains around 5-10% Th02 and 3% yttrium earths, these and the heavy lanthanides are virtually absent in bastnaesite. Although thorium is only weakly radioactive it is contaminated with daughter elements such as Ra which are more active and therefore require careful handling during the processing of monazite. This is a complication not encountered in the processing of bastnaesite. 

Novel, mixed alkyl cyclopentadienides have also been prepared for the heavy lanthanides ... 

Figure 4.16. Rare earth-magnesium binary systems. A few selected diagrams of trivalent lanthanides are shown. Notice the progressive regular changes on passing from the light to the heavy lanthanides. Notice also the similarity of the Y-Mg diagram with those of the heavy lanthanides.

Within the lanthanides the first ones from La to Eu are the so-called light lanthanides, the other are the heavy ones. Together with the heavy lanthanides it may be useful to consider also yttrium the atomic dimensions of this element and some general characteristics of its alloying behaviour are indeed very similar to those of typical heavy lanthanides, such as Dy or Ho. An important subdivision within the lanthanides, or more generally within the rare earth metals, is that between the divalent ones (europium and ytterbium which have been described together with other divalent metals in 5.4) and the trivalent ones (all the others, scandium and yttrium included). 

The leach liquor is first treated with a DEHPA solution to extract the heavy lanthanides, leaving the light elements in the raffinate. The loaded reagent is then stripped first with l.Smoldm nitric acid to remove the elements from neodymium to terbium, followed by 6moldm acid to separate yttrium and remaining heavy elements. Ytterbium and lutetium are only partially removed hence, a final strip with stronger acid, as mentioned earlier, or with 10% alkali is required before organic phase recycle. The main product from this flow sheet was yttrium, and the yttrium nitrate product was further extracted with a quaternary amine to produce a 99.999% product. 

Other coordination polyhedra based on bicapped dodecahedra, but having Dz symmetry, have been found for orthorhombic Phcn, Z =4) crystals of M(dip)2 (N03)3 (M=La, Tb and dip = 2,2 -dipyridyl) complexes (27(5, 277). Both La(III) and Tb(III) complexes have the same structure and this might be taken as evidence for the maintenance of the structure at least until Tb in the series. Sinha 218) have prepared the heavy lanthanide-bis-dipyridyl-trisnitrate complexes and the infrared studies 218, 219) showed no difference in the infrared spectra within the series, both ligands (dipyridyl and nitrate) being coordinated. 

The principal sources of ytterbium are euxenite, gadolinite, monazite, and xenotime. the latter being the most important. Ytterbium is separated from a mixture of yttrium and the heavy Lanthanides by using the sodium amalgam reduction technique. Ytterbium metal is obtained by heating a mixture of lanthanum metal and ytterbium oxide under high vacuum. The ytterbium sublimes and is collected on condenser plates whereas the lanthanum is oxidized to the sesquioxide. 

It has been reported that ScBi2 has a tetragonal modification of the UBi2-type structure with lattice parameters of a = 5.22 A and c = 7.35 A with the space group of I4/mmm (Hamada et al., 1993 Paderno and Shitsevalova, 1995). Due to the small size of scandium as compared to the other rare earth atoms, scandium phases have been observed to form anomalous higher boride structures compared to the heavy lanthanides and yttrium, as will be discussed later in Sections 9 and 11. Small amounts of metal replacement for Sc in Sci xMxBi2 (x as small as 0.1, M = Y, Tm, Lu) have been reported to stabilize the structure in the normal cubic UBi2-type. 

Atomic parameters involving 5d electrons The trends for atomic parameters representing effects involving the 5d electron are markedly different from the trends for 4f 1 core parameters, as can be seen from table 1. Whereas the / (ff) and f (ff) parameters show a dramatic increase across the lanthanide series from Pr3"1" to Lu3+, due to the contraction of the 4f orbitals for the heavy lanthanides, the ( (dd) parameter increases much more slowly. This is due to the fact that the 5d orbitals contract much less across the lanthanide series than do the 4f orbitals. Also, the Fk(f ) and CF (fd) parameters decrease gradually, due to the reduced overlap between the 4f and 5d orbitals as the 4f orbitals contract. These calculations are useful for estimating the trends in the parameters across the lanthanide series, once they have been determined for a few ions. 

Elution of the heavy lanthanide ferns from cation exchange corumn using ammonium 3-hydroxyisobutyratc as the eluent Note that the higher atomic number lanthanides elute first because they have smaller radii and are more strongly complied by the ammonium 2-hydroxyiso butyrate. 

Assuming lighter lanthanides have coordination number 8, the heavy lanthanides have a coordination number of 9 and the intermediate lanthanides with a coordination number... 

In general, lighter lanthanide complexes are thermally more stable than the heavy lanthanide complexes. 

A series of investigations (32-35, 101) on the extraction of these elements with carboxylic acids has been carried out by workers in the Soviet Union. Miller and associates (86) extracted lanthanides with 2,5-dimethyl-2-hydroxyhexanoic acid in chloroform. The heavy lanthanides after samarium were not extracted. In the extraction of neodymium the extracted species such as NdA3(HA)5 and Nd2A6(HA) were found together with small amounts of Nd2A6 and still smaller amounts of further aggregates (NdA3) - (86). 

The thin films of those obtained RPO4 NPs of 2-5 ran in size could be fabricated via spin coating. Therefore, the NEXAFS studies could be carried out (Suljoti et al., 2008). The results show that the light lanthanides tend to form monoclinic monazite phase of 3-5 nm in size and the heavy lanthanides tend to form the tetragonal zircon phase of 3-5 nm in size, while the medium lanthanides tend to form a mixture of the two phases with 2 nm in sizes. 

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