Binary compounds actinides

Table 8. Properties and Crystal Structure Data for Important Actinide Binary Compounds...

In actinide binary compounds an equation of state can also be developed on the same lines. The difference in electronegativity of the actinide and the non-actinide element plays an important role, determining the degree of mixing between the actinide orbitals (5 f and 6 d) and the orbitals of the ligand. A mixture of metallic, ionic and covalent bond is then encountered. In the chapter, two classes of actinide compounds are reviewed NaCl-structure pnictides or chalcogenides, and oxides. 

One of the aims of the chapter is to inspire new research in actinide magnetism. To this purpose, tables collecting the main magnetic data for a large number of actinide binary compounds are provided. 

TABLE 4. PROPERTIES AND CRYSTAL STRUCTURE DATA FOR IMPORTANT ACTINIDE BINARY COMPOUNDS... 

Table 14.8 Properties and crystal structure data for some important actinide binary compounds. 

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Synthesis in liquidAl Al as a reactive solvent Several intermetallic alu-minides have been prepared from liquid aluminium very often the separation of the compounds may be achieved through the dissolution of Al which dissolves readily in several non-oxidizing acids (for instance HC1). For a review on the reactions carried out in liquid aluminium and on several compounds prepared, see Kanatzidis et al. (2005) binary compounds are listed (Re-Al, Co-Al, Ir-Al) as well as ternary phases (lanthanide and actinide-transition metal aluminides). Examples of quaternary compounds (alumino-silicides, alumino-germanides of lanthanides and transition metals) have also been described. As an example, a few preparative details of specific compounds are reported in the following. 

Table 7. The density of states at the Fermi level and the Stoner product in some NaCl-structure binary compounds of actinides...

In this chapter, preparation and purification methods are reviewed. In view of the expected role of 5 f electrons in the metallic bond of actinides, methods for the preparation of metals have been particularly studied. There has also been important progress in the preparation of simple binary compounds. Special emphasis has been given to the growth of single crystals, particularly needed for the most refined physical techniques. 

Among the actinide compounds the interest is concentrating on binary compounds of simple structure (e.g. 1 1 compounds with elements of the groups V and VI of the periodic table) for which the theoretical treatment is rather advanced, and on intermetal-lic (e.g. Laves-) phases. 

A formalism similar to that presented for actinide metals has been developed for the ground state properties of binary compounds by Andersen et al. leading to a general form of equation of state (see Chap. F). However, this analysis of bonding contributions must draw from detailed results of band calculations more heavily than for the metals case (where the explanation of the qualitative behaviour of ground state properties vs. atomic number needed only the hypothesis of a constant 5f-bandwidth and its volume dependence as predicted by the general theory). In fact, the bond is more complicated ... 

In this section, magnetic data for most actinide binary or ternary compounds are presented. The table presentation seemed to us the most convenient form for this reference section. 

A new field of coordination chemistry is that of polymetallic cage and cluster complexes [Mm(p-X)xLJz with molecular (i.e. discrete) structure. They contain at least three metal atoms, frequently with bridging ligands X and terminal ligands L. These compounds link the classical complexes (m = 1) and the non-molecular (m - oo) binary and ternary compounds of the metals.1 Molecular polymetallic clusters (with finite radius) also provide a link with the surfaces (infinite radius) of metals and their binary compounds.2"5 Polymetallic complexes are known for almost all metals except the actinides. 

Solid Compounds. Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 4. 

This chapter examines some of the most important binary compounds of the actinides, especially the halides. Despite the problems caused by their radioactivity, some binary compounds of most of these elements have been studied in considerable detail, and form a good vehicle for understanding trends in the actinide series. 

The actinides are reactive metals, typified by the reactions of thorium and uranium shown in Figures 10.1 and 10.2. These binary compounds frequently have useful properties. Thus, choosing examples from thorium chemistry, Th2S3 is a high-temperature crucible material, ThN is a superconductor, and Th3P4 and Th3As4 are semiconductors. 

Although not binary compounds, a discussion of actinide oxyhalides is not out of place here. A number of these are formed by the earlier actinides, another difference between the 4f and 5f metals. 

The succeeding actinides (Cm, Bk, Cf, Es, Em, Md, No, Lr) mark the point where the list of isolated compounds tends to involve binary compounds (oxides, halides and halide complexes, chalcogenides, and pnictides) rather than complexes. Those studies of complexes that have been made are usually carried out in solution and, from Em, onwards, have been tracer studies. 

The hydrides formed in reaction (a) may be classified as (1) saline or ionic hydrides, (2) metallic hydrides and (3) covalent hydrides. The saline hydrides include the hydrides of the alkali and alkaline-earth metals, except BeHj, which is covalent. Transition metals form binary compounds with hydrogen that are classified as metallic hydrides including rare-earth and actinide hydrides. Intermetallic compound hydrides, such as TiFeHj and LaNijH, may be thought of as pseudobinary metallic hydrides. 

Figure 1. Uranium-aluminum phase diagram. (From P. Chiotti, V. V. Akhachinskij, I. Ansara, M. H. Rand, The Chemical Thermodynamics of Actinide Elements and Compounds, Part 5, The Actinide Binary Alloys, International Atomic Energy Agency, Vienna, 1981, Fig. 5.22, with permission.)...

Just as the lanthanides form a series of closely related elements following La in which the characteristic ions M have from 1 to 14 4f electrons, so the actinide series might be expected to include the 14 elements following the prototype Ac (which, like La, is a true member of Group III), with from 1 to 14 electrons entering the 5f in preference to the 6d shell. In fact there are probably no 5f electrons in Th and the number in Pa is uncertain, and these elements are much more characteristically members of Groups IV and V respectively than are the corresponding lanthanides Ce and Pr. Thus the chemistry of Th is essentially that of Th(iv), whereas there is an extensive chemistry of Ce(iii) but only two solid binary compounds of Ce(iv), namely, the oxide and fluoride. In contrast to Pa, the most stable oxidation state of which is v, there are no compounds of Pr(v). 

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