Yttrium, Lanthanum and the Lanthanides

4 Yttrium, Lanthanum and the Lanthanides. P NMR spectroscopy has been used to study complexation of La by (4-02NC6H40)2P02H and (MeO)(4-02NC6H40)P02H. C and N NMR spectroscopy has been used to study complex formation between [SCN] andPr + and Nd. P chemical shifts of di(chlorophenyl)dithiophosphinic acid correlate quantitatively with the extrac-tability of Am and Eu .  

The complexation of calixarene derivatives and lanthanide cations has been studied by H NMR spectroscopy. Both 1 1 and 1 2 complexes between lanthanides and cyclohexanetriols have been demonstrated by H NMR spectroscopy. Pr +-serine complexation has been monitored by H NMR spectroscopy in aqueous solution. NMR titrations have been used to investigate 

Berger, M. Hartmamr, P. Pyykko. D. Sundholm and H. Schmidbaur, Inorg. Chem., 200t, 

Batbaro, F. Cecconi, D. Daktemieks, S. Dominguez, A. Duthie, CA. Ghilardi, S. Midolirni, A. 

Capron, P. Florian, F. Fayon, D. Trumeau, L. Hennet, M. Gaihlanou, D. Thiaudiete, C. Landron, A. Douy and D. Massiot, J. Non-Cryst. Solids, 2001,293,496. 

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Table 30.5 Stoichiometries and structures of reduced halides (X/M < 2) of scandium, yttrium, lanthanum and the lanthanides...

IV. Chalcogenocyanate Complexes of the Transition Elements A. Scandium, Yttrium, Lanthanum, and the Lanthanides i. Cyanates... 

Thermodynamic properties of yttrium, lanthanum and the lanthanide elements and ions. L. R. Morss, Chem. Rev., 1976,76,827-841 (149). 

This chapter centers on the determination of enthalpies of formation of pure rare earth binary oxides at 298.15 K. Inasmuch as possible, the other properties and the properties at temperatures other than 298.15 K are also presented. In this chapter the rare earths are considered to be yttrium, lanthanum, and the lanthanide elements Ce-Lu. The thermochemistry of scandium oxides is not treated in this chapter. 

Morss, L.R., 1985, Yttrium, lanthanum and the lanthanide elements, in Standard Potentials in Aqueous Solution, eds A.J. Bard, R. Parsons and J. Jordan (Marcel Dekker, New York) pp. 587-629. 

In this article the term organometallic compound includes alkyl and aryl derivatives of the rare earths—the transition metals of group III, scandium, yttrium, lanthanum and the lanthanides cerium to liitetium with covalent metal-to-carbon a-bonds, as well as the so-called 77-complexes with more than monohapto metal-to-carbon bonds, for example cyclopentadienyl and olefin complexes, metal acetylides, but not carbonyls, cyanides and isocyanide complexes. Derivatives of scandium, yttrium and lanthanum are included and discussed together with the compounds of the lanthanides, because of many similarities in the synthesis and the chemistry of these organometallic derivatives of the rare earths. 

Horss, L. R. Thermochemical Properties of Yttrium, Lanthanum, and the Lanthanide Elements and Ions... 

The yttrium, lanthanum and other lanthanide salts exploded after dehydration during heating to above 300°C. 

Scandium, Yttrium, Lanthanum and the 14 Lanthanides -Rare Earth Metals (REMs)... 

The rare earths (REs) are a group of chemically similar elements in the entire periodic table, consisting of scandium (Sc), yttrium (Y), and the lanthanides. The lanthanides are the series of elements with atomic numbers from 57 to 71, including lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). 

The 3rd group of the Periodic Table (the 1st column within the block of the transition elements) contains the metals scandium, yttrium, lanthanum, and actinium. Lanthanum (atomic number 57) may be considered the earliest member of the family of metals, called lanthanides (general symbol Ln), forming, inside the principal transition series, an inner transition series (up to atomic number 71). Scandium and yttrium together with the lanthanides are also called rare earth metals (general symbol R). 

Tricyclopentadienyl rare earth compounds form stable 1 1 adducts with many bases. THF adducts have been described for yttrium, lanthanum and nearly all lanthanides (Manastyrskyj and Dubeck, 1964 Calderazzo et al., 1966 E.O. Fischer and H. Fischer, 1966 R.D. Fischer and H. Fischer, 1967 Pappalardo, 1969 Raymond and Eigenbrodt, 1980 Rogers et al., 1981 Deacon et al., 1982). Tetrahydrofuran can be removed in high vacuum from all the complexes except for... 

The lanthanide elements comprise lanthanum and the 14 elements (cerium to lutetium) that follow lanthanum in the periodic table. Frequently, the terms lanthanides and lanthanons are used as synonyms for the rare earth elements (REEs), although strictly the REEs comprise the lanthanides and also yttrium, which together with gadolinium, the subject of Chap. 29, is omitted from this chapter. As in many accounts of the chemistry of the lanthanides, will be used as the collective chemical symbol for the trivalent cations. 

The elements in the group III B scandium, yttrium, lanthanum and actinium that have an incompletely filled d subshell in their atomic state (n - l)d ns. Although both lanthanum and actinium could be included in the d transition metal series, they are very similar physically and chemically to the elements in the f-block and therefore are considered to be f-type transition elements (4f-, 5f-type transition elements, respectively). The last element of the lanthanides series, lutetium, also has a partly filled d orbital (Table 2.6) and could also be included in the d transition metal group. However, it has similar properties to the 4f-type transition metals, where it is usually grouped with lanthanum and the rest of the lanthanides series. 

The rare earth minerals are composed of scandium, yttrium, and the lanthanides. The lanthanides comprise a group of 15 elements that include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Cerium is the most abundant element in the rare earth group at 60 ppm, followed by yttrium at 33 ppm, lanthanum at 30 ppm, and neodymium at 28 ppm. Thulium and lutetium are the least abundant at 0.5 ppm. 

The absorption spectra of the lanthanide ions are quite characteristic of the individual lanthanides. Scandium, yttrium, lanthanum, and lutetium do not absorb in the spectral region from 200-1000 nm. The remaining lanthanides all absorb in this region, although the molar absorptivities of even the most intense bands are less than 12 /mole cm as is shown in table 37A.1. 

It may be helpful to explain the use of the terms rare earths and lanthanides throughout the text. By convenience, the term lanthanides refers to the elements La (Z = 57) to Lu (Z = 71). The term rare earths is commonly used for the lanthanides with inclusion of the elements Y (Z = 39) and Sc (Z = 21). Although one speaks often about rare-earth spectroscopy, the term lanthanide spectroscopy is preferable. The main objects of study in lanthanide spectroscopy are the trivalent lanthanide ions from Ce (4f ) to Yb3+ (4f ), since these ions have unpaired f electrons and can interact with ultraviolet, visible or near-infrared radiation. Divalent ions like Eu " " have gained less interest and will not be discussed here. The trivalent lanthanide ions La " (4f ) and Lu (4f ) are not spectroscopically active, because of an empty or filled 4f shell. The same is true for and Sc. Yttrium, lanthanum and to a lesser extent lutetium compounds are used as transparent host crystals in which other trivalent lanthanide ions can be doped. The trivalent lanthanide ions can readily substitute for Y, La " and Lu. Expressions like point group of the rare-earth site and the crystal field in rare-earth compounds are thus meaningful. 

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides. 

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used. 

To avoid this confusion, and because many of the elements are actually far from rare, the terms lanthanide , lanthanon and lanthanoid have been introduced. Even now, however, there is no general agreement about the position of La, i.e, whether the group is made up of the elements La to Lu or Ce to Lu. Throughout this chapter the term lanthanide and the general symbol, Ln, will be used to refer to the fourteen elements cerium to lutetium inclusive, the Group 3 elements, scandium, yttrium and lanthanum having already been dealt with in Chapter 20. 

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