Cerium electronic structure

Cerium is especially intereshng because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer or valence electrons, and only small amounts of energy are required to change the relahve occupancy of these electronic levels. This gives rise to dual valency states. 

Optical Absorption Spectra and Electronic Structure The optical spectra of all the doubledeckers are listed in Table I, On first glance, Ce(0EP)2 has a "normal" spectrum (7), However, the spectrum shows extra bands and therefore should be called "hyper", A small band appears at 467 nm (maybe a ligand-to-metal charge transfer band), and broad features extend far into the near infrared (NIR), The latter absorption may be due to exciton interactions. Contrary to the known rare earth monoporphyrins (7), it has been shown for the closely related cerium(IV)... 

Gulino, A., Casarin, M., Conticellio, V.P. etal. (1988) Efficient synthesis, redox characteristics, and electronic structure of a tetravalent tris(cyclopentadienyl)cerium alkoxide complex. Organometallics, 1, 2360. 

The applications of ceria based materials are related to a potential redox chemistry involving Cerium(III) and Cerium(lV), high affinity of the element for oxygen and sulfur, and absorption / excitation energy bands associated with its electronic structure. Important areas for application of cerium based materials are catalysis and chemicals, glass and ceramics, phosphors and metallurgy. 

The electronic structures of the cerium(iv) alkoxide complexes Cp3Ce(OR) have been investigated by He I and He II UV photoelectron spectroscopy combined with SCF Xa-DVM calculations.503... 

In caesium (Z = 55) one electron occupies the 6s orbital of the P shell, and in barium (Z = 56) there are two electrons in this orbital. Thereafter the development of the P shell is interrupted, and lanthanum (Z = 57) initiates the third transition series with one electron in the 5 d orbital of the 0 shell. The development of this series, however, proceeds no further at this stage, and in the elements from cerium (Z = 58) to lutecium (Z = 71) electrons are entering the hitherto vacant 4/orbitals of the N shell. These elements constitute the rare earths or elements of the lanthanide series, and the fact that the differentiating electrons are so deep in the electronic structure is responsible for the close similarity of their chemical properties. 

Thin films of a rare earth on another metal (or the other way round) were investigated by various authors. Flowever, real alloys were rarely formed and most of the time such studies were performed from a purely surface science point of view (electronic structure, spectroscopic properties. ..) and with no direct relevance to catalysis. One may quote, for example, the oxidation studies of tantalum and aluminum with thin cerium overlayers, carried out at low temperature, which showed that cerium enhances the oxide growth on both substrates (Braaten et al. 1989). However, the mechanism was not identical. No alloy was formed with tantalum and a catalytic oxidation took place. On aluminum, the formation of an intermetallic Ce—Al-O oxide layer was evidenced. 

The pH of the test solution offers that a yellow solution is expected but in the presence of cerium(III) a red complex of the structure (Figure 6.5.3) is formed. Most likely it has a red color because the electronic structure of tiie chelate is similar to the red form of tiie pure substance in pH up to about 10. When the fluoride is added a new structure (6.5.4) is formed. This is blue. 

In this section, systematic results on the electronic structures and chemical bonding of rare-earth sesquioxides and fluorite-type oxides are introduced briefly. In the subsection 4-1, systematic results on the electronic structures and chemical bonding of sesquioxides are described and the description on rare-earth fluorite-type oxides is mainly focused on cerium dioxide in the subsection 4-2. 

This chapter deals extensively with the experimental data on the superconductivity of the rare earth metals at high pressure. The results are discussed from a phenomenological point of view emphasizing systematics. This seems appropriate at the present stage of understanding. The analysis results in rather clear-cut conclusions for the electronic structure of cerium and lanthanum. It is hoped that they will serve as a useful guide-line for future experimental and theoretical work. We would like to summarize the following results and problems. 

Kotzian et al. (1991) and Kotzian and Rosch (1992) applied their INDO/1 and INDO/S-CI methods to hydrated cerium(III), i.e. model complexes [Ce(H20) ] (n=8,9), in order to rationalize the electronic structure and the electronic spectrum of these species. Besides the scalar relativistic effects spin-orbit coupling was also included in the INDO/S-CI studies. The spin-orbit splitting of the 4f F and 5d states of the free Ce " ion was calculated as 2175cm" and 2320cm in excellent agreement with the experimental values of 2253 cm and 2489 cm" , respectively. The calculated energy separation between the F and states of approximately 44000cm" (estimated fi-om fig. 5 in Kotzian and Rosch 1992) is somewhat lower than the experimental value of 49943 cm" (Martin et al. 1978). 

The oxidation state of IV demonstrated by thorium is then analogous to the IV oxidation state of cerium. From the behavior of uranium, neptunium and plutonium it must be deduced that as many as three of the assumed 3f electrons are readily given up, so that the failure of thorium to demonstrate an oxidation state of III is accounted for. On the basis of this hypothesis, elements 95 and 96 should exhibit very stable III states in fact, element 96 should exhibit the III state almost exclusively because, with its seven 3f electrons, it should have an electron structure analogous to that of gadolinium, with its seven 4f electrons. 

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