Lanthanide ions orbitals

Let us now consider MMCT for the case in which the donating ion is a lanthanide ion with a partly filled 4/ shell M(/")M(d°)CT. The trivalent lanthanide ions with a low fourth ionization potential are Ce, Pr ", Tb ". Their optical absorption spectra show usually allowed 4f-5d transitions in the ultraviolet part of the spectrum [6, 35]. These are considered as MC transitions, although they will undoubtedly have a certain CT character due to the higher admixture of ligand orbitals into the d orbitals. In combination with M(d°) ions these M(/") ions show MMCT transitions. An early example has been given by Paul [36] for Ce(III)-Ti(IV) MMCT in borosilicate glasses. The absorption maximum was at about 30000 cm ... 

The Slater—Condon integrals Ft(ff), Ft(fd), and Gj-(fd), which represent the static electron correlation within the 4f" and 4f 15d1 configurations. They are obtained from the radial wave functions R, of the 4f and 5d Kohn—Sham orbitals of the lanthanide ions.23,31... 

When a lanthanide ion is placed in a ligand environment with symmetry lower than spherical, the energies of its partly filled 4f orbitals are split by the electrostatic field of the ligand. The result is a splitting of the 2/ + 1 degeneracy of the free ion states (see Figure 1.2). 

Three-positive lanthanide ions are not so promising if the objective is building bulk molecular magnets because of the internal character of 4f orbitals, which... 

Spin-Orbit Multiplets of Free Lanthanide Ions Relativistic CASSCF/RASSI Method in Work... 

The lanthanides have electrons in partly filled 4/orbitals. Many lanthanides show colors due to electron transitions involving the 4/orbitals. However, there is a considerable difference between the lanthanides and the 3d transition-metal ions. The 4/ electrons in the lanthanides are well shielded beneath an outer electron configuration, (5.v2 5p6 6s2) and are little influenced by the crystal surroundings. Hence the important optical and magnetic properties attributed to the 4/ electrons on any particular lanthanide ion are rather unvarying and do not depend significantly upon the host structure. Moreover, the energy levels are sharper than those of transition-metal ions and the spectra resemble those of free ions. 

Equation (S6.1) is applicable to the salts of lanthanide ions. These have a partly filled 4f shell, and the 4f orbitals are well shielded from any interaction with the surrounding atoms by filled 5.9, 5p, and 6.9 orbitals, so that, with the notable exceptions, Eu3+ and Sm3+, they behave like isolated ions. For the transition metals, especially those of the 3d series, interaction with the surroundings is considerable. Because of this, the 3d transition-metal ions often have magnetic dipole moments corresponding only to the electron spin contribution. The orbital moment is said to be quenched. In such materials Eq. (S6.1) can then be replaced by a spin-only formula ... 

All lanthanide ions, with the exception of gadolinium(III) and europium(II), are likely to be relaxed by Orbach-type processes at room temperature. In fact, the f" configurations n l) of lanthanides(III) give rise to several free-ion terms that upon strong spin-orbit coupling, provide several closely spaced energy levels. Table III reports the multiplicity of the ground levels, which varies from 6 to 17, and is further split by crystal field effects. 

Table 2. Comparison of Coulomb, spin-orbit, crystal field and exchange interactions for actinides and lanthanide ions, (U Coulomb spin-orbit Hef crystal field, H,jch. = exchange)...

Since the unpaired 4f electrons in lanthanide ions occupy orbitals of extremely low radial extension, the Fermi contact term is small for lanthanide shift reagents, and... 

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