Electronic and Magnetic Properties of the Actinides

Lanthanide and Actinide Chemistry S. Cotton 2006 John Wiley Sons, Ltd. 

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The interpretation of the electronic and especially of the magnetic properties of the actinides is much more complicated than in the lanthanides for the following reasons ... 

The first edition consisted of a serial description of the individual actinide elements, with a single chapter devoted to the six heaviest elements (lawrendum, the heaviest actinide, was yet to be discovered). Less than 15 % of the text was devoted to a consideration of the systematics of the actinide elements. In this edition nearly half of the work consists of survey chapters in which such subjects as the metallic state, thermochemistry, solid state chemistry, solution chemistry, atomic and electronic spectroscopy, magnetic properties, organometallic chemistry, and the biological and environmental properties of the actinide elements are treated in comparative fashion. Because of the expansion of the discipline and of the scope of the second edition, many cdleagues were asked to contribute chapters that reflected their expert knowledge. 

The transition metal ions generally have a number of d electrons in their outer shell, and because the energy difference between the various configurations is small, the arrangement adopted will depend upon a variety of external factors, such as the geometry of the crystal structure (see also Chapter 12 and Section S4.5). The lanthanides have an incomplete 4f shell of electrons, and the actinides an incomplete 5f shell. In these elements, the f orbitals are shielded from the effects of the surrounding crystal structure. The d and f electrons control many of the important optical and magnetic properties of solids. 

Some magnetic properties of the lanthanides are presented in section 3 in comparison with the actinides. Table 33 and fig. 27 should be consulted for specific electronic configurations and magnetic moments in each series. 

In 1972 a hybridized non-degenerate 6d and 5f virtual-bound-states model was used to describe the properties of the actinide metals, including berkelium [138]. It accounted for the occurrence of localized magnetism in Bk metal. In 1974 a review of the understanding of the electronic properties of berkelium metal as derived from electronic band theory was published [139]. Included was the relativistic energy band structure of face-centered cubic Bk metal (5f 6d 7s ), and the conclusion was that berkelium is a rare-earth-like metal with localized (ionic) 5f electrons resulting from less hybridization with the 6d and 7s itinerant bands than occurs in the lighter actinides. 

Most of the known borides are compounds of the rare-earth metals. In these metals magnetic criteria are used to decide how many electrons from each rare-earth atom contribute to the bonding (usually three), and this metallic valence is also reflected in the value of the metallic radius, r, (metallic radii for 12 coordination). Similar behavior appears in the borides of the rare-earth metals and r, becomes a useful indicator for the properties and the relative stabilities of these compounds (Fig. 1). The use of r, as a correlation parameter in discussing the higher borides of other metals is consistent with the observed distribution of these compounds among the five structural types pointed out above the borides of the actinides metals, U, Pu and Am lead to complications that require special comment. 

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