Characteristics of the Lanthanides

The lanthanides exhibit a number of features in their chemistry that differentiate them from the d-block metals. The reactivity of the elements is greater than that of the transition metals, akin to the Group n metals  

A very wide range of coordination numbers (generally 6-12, but numbers of 2, 3 or 4 are known). 

Coordination geometries are determined by ligand steric factors rather than crystal field effects. 

They form labile ionic complexes that undergo facile exchange of ligand. 

The 4f orbitals in the Ln + ion do not participate directly in bonding, being well shielded by the 5s and 5p orbitals. Their spectroscopic and magnetic properties are thus largely uninfluenced by the ligand. 

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The reason why lanthanides of high atomic number emerge first is that the stability of a lanthanide ion-citrate ion complex increases with the atomic number. Since these complexes are formed by ions, this must mean that the ion-ligand attraction also increases with atomic number, i.e. that the ionic radius decreases (inverse square law). It is a characteristic of the lanthanides that the ionic radius... 

In this article I will elaborate on the knowledge, which was obtained by Professor Leroy Eyring and his colleagues in more than 50 years of research on the lanthanide higher oxides and their ideas for the applications of these oxides. Also the unique non-stoichiometric characteristics of the lanthanide higher oxides are emphasized and the intrinsic relationship between the macroscopic properties and nano-scale structures is demonstrated. 

The striking characteristics of the lanthanide higher oxides are rooted in the electronic structure of Ce, Pr, and Tb atoms. The lanthanide elements located in the third group of the periodic table have a normal 3+ valence state and the normal oxides have the R2O3 formula. Due to the special electron configurations of Ce... 

The hysteresis loop of the oxygen content of the PrO and TbO is a obvious peculiar characteristic of the lanthanide higher oxides, but the hysteresis of the oxygen content of the CeO is difficult to observe directly in the isobaric curves because... 

The lanthanide series of metals includes the 15 elements with atomic numbers 57-71, plus yttrium (atomic number 39). The lanthanides occur in the earth s crust at concentrations exceeding some commonly used industrial elements making the term rare earths something of a misnomer. For example, yttrium, cerium, lanthanum, and neodymium are present in the earth s crust at higher concentrations than lead. Of the 15 lanthanides, only promethium does not occur in nature - it is a man-made element. All of the lanthanides have similar physical and chemical properties. Because of similarities in their chemistry and toxicity, the characteristics of the lanthanides are often described as a group. Within the lanthanide group, however, there are differences between the toxicity of the individual lanthanide elements and their compounds. 

To achieve reasonable conversions, the polymerisation with the catalyst NdCl3 3TBP-i-CgHiyMgC4H9 was conducted for several days (compound i-CgHj7MgC4H9 is catalytically inactive under these conditions). For this catalyst, the yield of the polymer depends on the ratio between the starting components with a sharply pronounced maximum at Mg/Nd = 12/13, which is not characteristic of the lanthanide systems. 

In this section we summarize the results of investigations of several types of configurations characteristic of the lanthanide spectra, which, in the first approximation, may be considered as isolated and therefore treated separately. In this case, the electrostatic interaction with other configurations is introduced only to second order perturbation theory, namely, by including in the hamil-tonian of the investigated configuration effective electrostatic interactions in addition to the real electrostatic and spin-orbit interactions. It is shown that further improvement between calculated and observed levels can be obtained through the inclusion of the spin-dependent interactions (SDI), i.e. ss, soo and effective EI SO. 

Ma CG, Brik MG, Tian Y, Li QX (2014) Systematic analysis of spectroscopic characteristics of the lanthanide and actinide ions with the 4f 5d and 5f 6d electronic configurations in a free state. J Alloys Compds 603 255... 

The two outer electron shells in neutral atoms of each lanthanide element have the same number of valence electrons as lanthanum, 2 and 1 respectively. This is the reason for the great similarities between them. And this is also the background to the enormously difficult discovery and separation work, characteristic of the lanthanides. But there are in fact some differences. In the third shell, the numbers of the so-called f-electrons differ. Lanthanum itself has no f-electron, the first lanthanide, cerium Ce, has 1, the second, praseodymium Pr, has 2 and the fourteenth, lutetium Lu, has 14 (see below, section 17.5.1). 

The crystal structure characteristics of the lanthanide and actinide series are similar in one respect the hep structure has a doubled c-axis in the actinide elements Am through Es, as it does in the lanthanide series for La through Pm. 

The steady-state absorption spectra of La Cg2 show the absorption bands at 1412, 1002, and 636 nm, which are characteristic of the lanthanide metal-encapsulated 32-fullerenes. Since it has been reported that the change of central metal does not affect the positions of absorption maxima, the electronic transitions take place within the Cg2 . The absorption spectrum of La2 Cgg shows a broad band around 900 nm and a relatively sharp shoulder at 400-450 nm, which are characteristic bands of endohedral metallofullerenes. 

As noted earlier, bands characteristic of the lanthanides are observed in non-aqueous solvents at lower energies than is possible in DCIO4. In a subsequent section, the quantitative treatment of band intensities is discussed. As a result of this work, the energies and intensities of all the transitions characteristic of the lanthanides in aqueous solution in the energy range 0-5500 cm can be computed. The corresponding bands are included in the spectra shown in figs. 24.4-24.12 and discussed in section 3.7. 

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