5f —+ 6d transitions

Electronic spectra for the /-elements often contain many weak, sharp peaks in the visible to near-infrared region these originate from Laporte-forbidden f-f transitions, and are observed in the late-visible/near-infrared (700-1200 nm) for solutions of these U(III) complexes [29]. The groimd state of trivalent uranium is 5/ however, the 5f 6d state is sufficiently low-lying for 5/ 5f 6d transitions to occur in the early-visible region, often in the... 

The visible bands previously assigned to the ligand to metal u - f charge-transfer transitions were reassigned to the 5f -> 6d transition. Table 70 gives a summary of a few dipole-allowed electronic transitions of U(C8H8)2. The characteristic green color of... 

In the actinides, the 5f 6d transitions have comparatively smaller wave numbers. Fried and Hindman find nearly the same distribution of bands as of Ce(HI) by measuring Pa(IV) in IM HCl with bands at 36,300, 39,200, and 44,800 cm-i. In uranium(IV) aquo ions, no Laporte-allowed band is observed in the accessible range, while the U(IH) ions have Sp SpSd bands at rather low wave numbers, viz., 25,000, 28,600, and 31,200 cm. There is some influence of chloro complex formation, comparable... 

All of these criteria more-or-less follow simple common sense ideas about the characteristics of the two types of transition. Together, they enable distinctions to be drawn in most cases. Although the detailed study of the bands is in its infancy, it is interesting to note that f -> d transition energies seem to follow a spectrochemical series, just as do d -> d in the transition metal ions. So, the following 5f-> 6d transition energies, all xl0 cm" have been reported for complexes of U " and other similar ions ... 

A further group of elements, the transuranium elements, has been synthesized by artificial nuclear reactions in the period from 1940 onwards their relation to the periodic table is discussed fully in Chapter 31 and need not be repeated here. Perhaps even more striking today are the predictions, as yet unverified, for the properties of the currently non-existent superheavy elements.Elements up to lawrencium (Z = 103) are actinides (5f) and the 6d transition series starts with element 104. So far only elements 104-112 have been synthesized, ) and, because there is as yet no agreement on trivial names for some of these elements (see pp. 1280-1), they are here referred to by their atomic numbers. A systematic naming scheme was approved by lUPAC in 1977 but is not widely used by researchers in the field. It involves the use of three-letter symbols derived directly from the atomic number by using the... 

The transactinide elements are defined simply as those elements with atomic number greater than 103 (Lr), which completes the actinide series with the complete filling of the inner 5f shell. The schematic periodic table of 2004 given in Fig. 16.1 shows the lanthanide (4f) series, the actinide (5f) series, and the transactinides as a 6d transition series that begins with element 104 (rutherfordium, Rf). According to results of atomic relativistic calculations (Pershina and Fricke,... 

The first chemical experiments on the transactinides were designed to determine their placement in the periodic table and whether the 5f actinide series actually ended with Lr as predicted by Glenn Seaborg (Seaborg, 1945). Then elements 104 and 105 should have different chemistry from the actinides, and as members of the 6d transition series should be placed as the heaviest members of groups 4 and 5 and have similar properties. 

In addition to transitions within the UO2 entity (transitions from bonding orbitals to unfilled 5f or 6d uranium orbitals), the complexes of UOo show charge transfer bands (CTTM). The frequencies (primarily in the UV region), depend on the nature of the relevant ligands The... 

Since we believe that the trans-plutonium elements have localized 5f electrons, we are led to attempt to establish a relationship between their crystallographic properties and those of the rare earths. That is, we want to compare trivalent 6d transition... 

Viewed in terms of their conduction electrons the lanthanide metals are early 5d transition metals since the 5d shell is much less than half-filled and the 4f shell chemically inert. The actinides are more complex. The light actinides are 5f transition metals with bonding 5f electrons, while the heavy actinides, which have an essentially chemically inert 5f shell, are early 6d transition metals. 

---