Scandium electronic structure

Ans. Mendeleev had used the prefix eka- (Sanskrit word for first) to name elements whose existence he predicted, applying the prefix to a known element in the same periodic group as the predicted element. His eka-boron, eka-aluminum, and e a-silicon were later discovered, confirmed, and named scandium, gallium, and germanium. Elements 104 and 105 were predicted to have electronic structures analogous to Hf and Ta. 

By the MEM charge density studies, the different features of encapsulated metal atoms in C82 were revealed for La C82 [2] and Sc C82 [3]. To compare the three-dimensional shape of the metal-atom charge distribution, a section of the equi-density surface of a La C82 molecule is presented in Fig. 9 together with the result for Sc C82 (Isomer I). The equi-density level is 1.8 e/A3. The number of electrons belonging to the Sc atom of Sc C82 was 18.8(2) e, which is close to the 19.0 e of a divalent state of the scandium atom, Sc2+. This indicates that the Sc C82 (I) is an endohedral metallofullerene whose formal electronic structure is Sc2+C82. This result has brought the long discussion as to whether the Sc atom is in a divalent or trivalent state inside the carbon cage [26-29] to an end experimentally. 

Scandium metallofullerenes were also produced in macroscopic quantity and solvent-extracted by Shinohara et al. (1992b) and Yannoni et al. (1992). The Sc fullerenes exist in extracts as a variety of species (mono-, di-, tri-and even tetra-scandium fullerenes), typically as Sc Cs2/ Sc2 C74, Sc2 Cs2, Sc2 Cg4, Sc3 Cs2, and Sc4 C82- It was found that Scs C82 was also an ESR-active species whereas di-and tetra-scandium fullerenes like Sc2 C84 and Sc4 C82 were ESR-silent. (See Section 5 for the present correct assignment for some of the di- and tri-scandium metallofullerenes.) A detailed discussion on the electronic structures of the scandium fullerenes accrued from these ESR experiments is given in Section 6.1. 

We have performed ab initio calculations on the diatomic molecule scandium boride cation, ScB", determining the electronic structure both of its ground state and of a series of low-lying excited states. 

The elements titanium to copper are known as the first transition series. The electronic structures of these atoms (and of zinc and scandium) in their lowest energy states are shown in Table 3.4. 

On the electronic structure of the carbides of the group III elements (scandium, yttrium and the lanthanides), only a few theoretical investigations are available. The bond structure of ScC was calculated by Schwarz et al, (1969) using the augmented-plane-wave method, Ivashchenko et al, (1984) applied the same method to YC and presented the densities of states for YC,, = O-Sj 0-7 and 0.6, which were calculated by using the coherent potential approximation. The results have been used to analyze the stability of the compounds. However, both calculations (Schwarz et al. 1969, Ivashchenko et al. 1984) were not performed self-consistently. Zhukov et al. (1987)... 

Electronic Structures. Almost all the physical properties and chemical behavior of the rare earth elements find a logical explanation in terms of their electronic structures. Scandium, yttrium, lanthanum, and actinium are the first members, respectively, of the first, second, third, and fourth transition sequences of elements. In other words, each such element marks the beginning of an inner building where a stable group of 8 electrons is expanding to a completed (or more nearly complete) group of IS. This situation is illustrated for the first transition sequence. 

THE RARE EARTH elements are those from atomic numbers 57 (lanthanum) to 71 (lutetium) inclusive and elements 21 (scandium) and 39 (yttrium). They represent the largest group of chemically similar elements, but their physical properties differ markedly due to subtle features of electronic structure. Because of the similarity between... 

Some relevant material is contained in reviews on Qi-actinide chemistry, the electronic structure of actinide-containing molecules, ab initio calculatimis on transition metal organometallics/ a survey on the landiankfes and actinides fm the literature years 1984-6, and alkoxo and aryloxo chemistry of scandium, yttrium, and lanthanoids/ ... 

This chapter summarized recent advances in the reduction chemistry of rare earth metals and described our own efforts in synthesizing inverse sandwiches of rare earth arene complexes using ferrocene-based diamide ligands. Unprecedented molecules were synthesized and their unusual electronic structures were studied. Highlights included the synthesis of the first scandium naphthalene complex and its reactivity toward P4 activation and the isolation and characterization of a 6-carbon, lOTi-electron aromatic system stabilized by coordination to rare earth metals. The reactivity of those complexes was also discussed. 

The connection between the phenomenological shell model (PSM) and aromaticity of metal clusters is presented in this chapter. This model allows us to probe the aromaticity of metal clusters, and also organic compounds, in a general framework and context. The 4n + 2 rule of planar rings is shown to be a special case of this model. It can be applied to the cases of planar, spherical, and distorted (oblate and prolate) clusters. The different criteria (stability, symmetry, magnetic properties, electronic structure) are considered with the examples of different scandium-doped copper clusters Cu c and Cu c+. In summary, a closed electronic structure according to the PSM often results in an aromatic behavior. 

A comparison of the volumes per formula unit for the trifluorides is more complicated than for the difluorides because of the changes in structure type. If these changes are ignored, then some correlation with electronic configuration is possible. For the first transition series the volume decreases from scandium to chromium, increases from chromium to iron, and decreases to cobalt. This is as expected for the characteristic ligand-field stabilization effects (49), comparable with those for the difluorides. In the second series, there is a decrease from... 

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