Rare earth elements, and compounds

M. Bode, M. Getzlaff, R. Pascal, S. Heinze, R. Wiesendanger, in Magnetism and Electronic Correlations in Local-Moment Systems Rare Earth Elements and Compounds, ed. by M. Donath, P. Dowben, W. Nolting (World Scientific, Singapore, 1998)... 

Many of the factors which control the properties and chemistry of rare earth elements and compounds have been considered in Section 1.2 - rare earth elements and their place in the periodic system. These factors are electronic configurations, ionic radii, lanthanoid contraction and redox potentials/oxidation states (Table 1.1). Some general properties are listed in Table 1.1. For a more detailed account see refs 32-34. 

Yost, D. M., Russell, H. Jr. and Garner, C. S. (1947). The Rare-Earth Elements and Their Compounds (John Wiley and Sons, Inc., New York). 

Abell, J.F. (1989) Preparation and crystal growth of rare earth elements and intermetallic compounds. In Handbook on the Physics and Chemistry of Rare Earths, eds. Gschneidner Jr., K.A. and Eyring, L.R. (North-Holland, Amsterdam), Vol. 12. 

For many elements, the atomization efficiency (the ratio of the number of atoms to the total number of analyte species, atoms, ions and molecules in the flame) is 1, but for others it is less than 1, even for the nitrous oxide-acetylene flame (for example, it is very low for the lanthanides). Even when atoms have been formed they may be lost by compound formation and ionization. The latter is a particular problem for elements on the left of the Periodic Table (e.g. Na Na + e the ion has a noble gas configuration, is difficult to excite and so is lost analytically). Ionization increases exponentially with increase in temperature, such that it must be considered a problem for the alkali, alkaline earth, and rare earth elements and also some others (e g. Al, Ga, In, Sc, Ti, Tl) in the nitrous oxide-acetylene flame. Thus, we observe some self-suppression of ionization at higher concentrations. For trace analysis, an ionization suppressor or buffer consisting of a large excess of an easily ionizable element (e g. caesium or potassium) is added. The excess caesium ionizes in the flame, suppressing ionization (e g. of sodium) by a simple, mass action effect ... 

Boron has a particular affinity with rare earth elements, and forms rare earth borides which are of particular interest. The rare earth atoms supply electrons to the boron atomic framework to stabilize and form novel structures, while the shell of f electrons supplies further attractive properties like magnetism. Borides with lower boron content, like the hexaborides RB6 and tetraborides RB4 are well known metallic compounds and have been studied throughout the years, revealing interesting magnetic properties (e.g. Gignoux and Schmitt, 1997). 

J.S. Abell, Preparation and crystal growth of rare earth elements and intermetallic compounds 1... 

Diagrammatic representation of the system of fractional crystallization used to separate salts of the rare-earth elements (reproduced with permission from D.M. Yost, H. Russell and C.S. Garner, The Rare Earth Elements and their Compounds, John Wiley, 1947.)... 

The hydroxides of berklium(III), Bk(OH)3, and califomium(III), Cf(OH)s, behave in a similar fashion [3]. In their crystalline forms, Am(OH)s and Cm(OH)3 are anhydrous (as are hydroxides of light rare-earth elements), and are hexagonal, C 6h P s/m space group, a = 6.420 and 6.391 A, c = 3.745 and 3.712 A, for Am and Cm compounds, respectively. Due to self-irradiation, the unit-cell parameters increase with time, as does the sample amorphization. In the case of " Cm(OH)3, the stmcture decomposes within 1 day, but the same process for " Am(OH)3 takes up to 4-6 months [4]. The Mossbauer spectrum of Am(OH)3 [5] is characterized by 5 = 4.6 cm/c (relative to Am02). The nuclear magnetic resonance (NMR) studies indicate that, among the TUE(III) hydroxides, the Am compound has the most covalent chemical bonds. The TUE(III) hydroxides are readily soluble in different mineral acids under these conditions, the solutions of hydrated An ions are produced. 

Examples of o-hydroxyarylazo compounds are Chromotrope 2B (formula 4.14), a reagent for thorium and rare-earth elements, and 2-(4-sulphophenylazo)chromotropic acid (SPADNS) (formula 4.15) used in determinations of Al, Zn, Th, U and other metals [35]. In both these groups of azo reagents the oxygen atom of the o-hydroxyl group and the nitrogen atom of the azo group participate in complex formation with metal ions. 

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