5fs ions

One can envision two ground states with parallel electronic spins for the 5f ions in the strong electrostatic field of the Me-0 bonds (28) ... 

In closing this paragraph we mention the emission spectroscopy of the U6 + ion. This ion shows emission spectra with clear vibrational structure. It is mentioned here because the optical transition is of the charge-transfer type, and the U6+ ion may be described in the present context as a 5f° ion. The vibrational structure in the emission spectra depends strongly on the ligands of... 

In NagUFg (and the isostructural Pa and Np compounds) there is almost perfect cubic 8-coordination of the 5f ion. ... 

A yellow form of the pentacyanocobaltate(II) ion has been observed in DMF solution. Various monomeric (NR4)3[Co(CN)5] complexes have been crystallized and a structural study on one shows the anion to possess a truly five-coordinate square-pyramidal geometry. Electron irradiation of solid K3[Co(CN)j] gives a presumed pentacyanocobaltate(II) ion, the visible spectrum of which is virtually identical with that of [Co(C1 5](, ). The structural parallels between the green and yellow forms of [Co(CN)5] and isoelectronic [Co(CNR)5f" ions indicate that all the green forms observed both in the solid state and in solution are weakly coordinated in the sixth axial position. 

Formation of the LiF MFs compounds with the lanthanides is size discriminatory (132), and stops abruptly with trivalent lanthanide ions larger than Eu3+. Because of the shift in 5f ion size equivalence versus the 4f series, as previously mentioned, the beginning of LiF actinide trifluoride compound formation is expected at cahfomium(III) and hkely not at the Bk + radius (or larger). Both the larger M + ions of americium and curium failed to 3deld LiF MF3 compounds as expected (132). 

The main impact of p,SR studies on HF materials is the realization that a pure Fermi-liquid ground state with only Pauli paramagnetism is the exception rather than the rule, even when superconductivity is present. Many systems form weak magnetic states at low temperatures, which in the majority of cases could only be detected by [tSR. This weak magnetic state consists of quasistatic moments on the 4f or 5f ion having extremely low... 

It is of interest to compare the radial wave functions between 4f and 5f elements. O Figure 18.19 shows relativistic calculations of and Am valence wave functions of the radial part. This figure indicates that the 4f subshell of Eu is core like because of the lower density around the ionic radius of the ion. In the corresponding 5f ion, Am, 5f subshell penetrates the 6s and 6p orbitals. The wider distribution of the 5f orbital allows much participation in bonding for the actinides than for the lanthanides. The 4f orbitals of lanthanide atoms are mainly localized in the core and do not contribute to the chemical bonding. 

In general, the two emphases of this chapter are (1) to correlate the energetics of ions that change their f-electron configuration smoothly and (2) to contrast energetics of reactions of 4f ions with those of 5f ions. We may generalize a recent concept enunciated by Johnson (1980) as follows The lanthanide elements are a series, and the actinide elements are a second series, that behave similarly in reactions in which the number of 4f or 5f electrons is conserved. The elements behave differently in reactions in which the number of 4f or 5f electrons changes. We accept this principle for intra-series comparisons that conserve the number of/electrons (4f" 4f" or 5f" -> 5f" reactions, such as coordina-... 

Fig. 4. S-shaped variation of the overall hydration number, h, derived from diflii-sion measurements, as a function of crystallographic radius, (C = 8) for some trivalent 4f and 5f ions.

If we examine the spectra of (aquo) and Np (aquo), both 5f ions (Fig. 16.13), we can interpret the apparent similarities in the band structure based on the analysis of U (aquo) cited above. If the crystal field splitting in both cases is relatively small, then the apf>arent shift of corresponding band structure to higher... 

Table 14.9 showed that all the dioxides from Th02 through Cf02 are known, but that several have not been studied thermodynamically. Morss and Fuger [39-41, 157] have established an enthalpy-of-solution plot (Fig. 17.7) for f-block dioxides that is similar in principle to that discussed above for sesquioxides but shows no shift between 4f and 5f elements. (If greater covalence of 5f ions than 4f ions with... 

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