In the present volume, comparisons of the chemistry of the lanthanide and actinide elements are considered. The chemistry of the lanthanides played an important role in establishing the actinide hypothesis.
Background
Thus, the structures of the elements above radon (element 86) through uranium were written to show the addition of the next two electrons in the 7s shell for element 87 (francium) and element 88 (radium) and addition in the 6d shell for actinium. thorium, protactinium and uranium (Latimer and Hildebrand 1940; Richtmeyer and Kennard 1942; Taylor and Glasstone 1942). Saha and Saha (1934) proposed as an alternative possibility for filling the 6d shell, entry of the first 5f electron at thorium.
Suggestion of actinide eoncept
So it seems certain that the transition in elements 89 to 94 does not involve simply filling in the 6d scale. The persistence of the IV oxidation state by the elements thorium, uranium, neptunium and plutonium is certainly good evidence that electrons enter the 5f shell.
Further development of actinide concept
In the case of the elements thorium and protactinium, the relative energy positions of these levels are even more uncertain. Uranium differs significantly from tungsten and molybdenum in the chemistry of its lower oxidation states.
Completion of actinide series
Nevertheless, the electronic structures given in Table 6 will be somewhat relevant to the electronic structures of the ions and compounds of these elements. Chiefly for the sake of completeness we might add that the filling is 6d.
Superactinide elements
Disproportionation reactions are an important part of the chemistry of the actinide elements, especially for the + 4 and + 5 oxidation states. N o 2 + is the most stable oxidation state of nobelium, as a result of the stability of the filled 5f ag shell completely.
Transactinide elements
THE ORIGIN OF THE ACTINIDE CONCEPT 23 Similarly, Türler et al. 1992) showed that RfBr 4 is unexpectedly more volatile than HfBr4 and RfC14 has a surprisingly high volatility. Modern periodic table of the elements (atomic numbers of undiscovered elements are shown in parentheses).
Modern periodic table
The close similarity of the chemical behavior of hahnium to that of protactinium and niobium motivated Gober et al. 1992) to investigate this further using diisobutylcarbinol (DIBC) as an extractant. Seaborg, G.T., 1949, Electronic Structure of the Heaviest Elements, Paper 21.1, in: The Transuranium Elements - Research Papers, National Nuclear Energy Series IV, Vol.
BALASUBRAMANIAN*
Introduction
The electronic structures of molecules containing lanthanide and actinide atoms are extremely interesting because of the complex array of electronic states that result from open f-shell electronic configurations. Just before the 1970s, quantum mechanics made a significant impact on the chemistry of molecules containing light elements in the periodic table due to the advent of computers.
Relativistic effects and methods
Physically, it arises from the coupling of the orbital angular m o m e n t u m (1) of the electron with its spin (s). This means that the effect of the lanthanide contraction is comparable to the effect of relativity.
This method is one of the most widely used ab initio RECP methods to include both spin-orbit and electron correlation effects. The coupled electron pair formalism (GPF) (Arhlichs 1985), modified coupled pair formalism (MCPF) and more recently average coupled pair formalism (ACPF) have been used (see e.g. the papers by Bauschlicher and Langhoff.
Electronic structure.of lanthanide hydrides
Mulliken population analysis (net and overlap) of low-lying ScH 2 states at their equilibrium geometries. Contribution of different conductor configurations to SOCI wavefunctions at equilibrium geometries of LaH electronic states. D a s and Balasubramanian (1991a) studied the potential energy bending surfaces of the four doublet and four quartet electronic states of the L a H 2 molecule.
The total gross population of the lanthanum atom is less than 3.0 for all L a H 2 electronic states, which indicates L a + H - the polarity of the L a - H bond. The lengths of the L a - H bonds in the linear high-spin states are longer than the bonds L a - H in bent states. Spin-orbit coupling has noticeable effects on some electronic states of HfH (see Table 30).
The effect of lanthanide contraction is not fully manifested in Res of the three species compared to Des. The steep increase in energy in the 40 state is due to the lanthanide contraction.
0 (Degree)
Electronic states of diatomic lanthanide and actinide halides
The rotational analysis of the observed bands has yielded very accurate molecular constants for the X and B states of YC1. Recently, Shirley et al. 1991) have used the molecular beam millimeter-wave optical pump-probe spectroscopy to study pure rotational transitions of the YF ~ ÷ ground state. Reproduced from Langhoff et al. 1988) have calculated the spectroscopic constants for scandium and yttrium halides using the ab initio method.
These authors calculated the spectroscopic constants of 18 electronic states of YC1 and the observed spectra of Fischell et al. As seen from table 49, A and B conditions were assigned to 1A and 1H respectively by Langhoff et al. The lifetime of the B 1H state was calculated to be ~ 291 ns by Langhoffet al. 1991) Langhoff et al. s calculated properties of the B 1FI state confirmed.
Dissociation energies of rare earth monofluorides (eV) [AC shows the CI (SD) + Q results after applying the energy correction to the experimentally observed atomic ground state of the rare earth atom]. The predicted ground state of YbF was consistent with the ESR studies of Van Zee et al.
Electronic states of lanthanide oxides
Recently, Kotzian et al. 1967) extended to spin-orbit coupling [see also Kotzian et al. Table 52, reproduced from the work of Kotzian et al., compares the I N D O / S C I energy splitting with experiment for several electronic states of LaO. However, as noted by Linton et al., the spectroscopic data for the above states are less complete and are shown in Table 54.
Note that Kotzian et al. have also compared the INDO/S-CI results with ligand field theories LFT1 and LFT2. We use the Kotzian et al. 1990a, b) works as a basis for discussion of the electronic states of GdO. Therefore, the calculation of Kotzian et al. also supports that the majority of the separately occupied 4cy orbital consists of Gd 6s.
This table is reproduced from Kotzian et al. 1986) have studied D y O using the laser spectroscopic method. They have also summarized the results of their I N D O / S - C I technique with the ligand field theory study by Dulick et al.
Accordingly, the reader is referred to the excellent review by Pepper and Bursten (1991) for a comprehensive summary of the electronic structure of actinide-containing species. They found that the theoretical calculations of the large variation in U - O , x distance as a function of U Oeq distance for UO 6 6 (Dgh) followed the experimental curve. The 6d and 5f orbitals appear to be more important for the covalent bonding of the early actinides (Th-Am) and the 6p semi-core orbital.
The second set of states (SAg) has a relatively shorter Re (2.2 ~,); the bonds in these states consist of the 5£ 6d and 7s orbitals of the two atoms. 1991a, b) that due to the compactness of the 4f shell, the 4f Ce ÷3 valence electron does not contribute to the metal-ligand bond. Many actinocenes have a beautiful color with strong absorption in the visible region of the spectrum.
The Mulliken population analysis of the SCF orbitals obtained by Chang and Pitzer (1989) shows that the charge at U is +0.98 (rather than the formal +4 charge). This is consistent with the primary role of the 6d orbitals in the binding of U(CBHs)2.
BALASUBRAMANIAN
- Conclusion
This was achieved by Chai et al. 1991) by laser evaporation of a composite lanthanum oxide/graphite rod in an Ar gas stream at 1200°C. The recent study by Chang et al. 1991) in La®C60 showed that the lanthanum atom donates two electrons from the 6s orbital to the carbon cage. Calculations by Chang et al. 1991) showed a strong destabilizing interaction between the 6s orbitals of La and C orbitals.
Although the exact mechanism of the formation of these species is not currently clearly established, Chai et al. 1991) speculated that they are generated by (La®C,) (La®C,) fusion reactions. The recent synthesis of macroscopic quantities of La® C 8 z and other carbon cages containing small clusters of La containing up to three atoms by Chai et al. 1991) should certainly stimulate further theoretical calculations on carbon cages containing one or more lanthanides inside. The calculations by Chang et al. 1991) on La®C6o, U®C6o, Eu®C6o, etc., provided significant insight which in fact served as the basis for qualitative interpretation of the unusual stability of La®C82.
The RECP/RHF calculation of Chang et al. in La®C6o showed that the La atom donates two 6s electrons to the carbon cage. Certainly, recent calculations by Chang and Pitzer (1989) and Chang et al. 1991) for both uranocene and lanthanide-containing carbon cages have clearly shown that indeed such calculations are feasible and play an important role in our understanding of the nature of bonding in lanthanide- and actinide-containing polyatomics .
V. BEITZ
- Observed spectra of aquated trivalent lanthanidc and aetinide ions
- Theoretical treatment of f-state spectra
- L u m i n e s c e n c e of trivalent-ion f s t a t e s
Evidence for the close similarity between the 4f state energy level structure of trivalent lanthanide ions in solids such as LaC13 and LaF3 and aqueous ions in solution has been reviewed by Carnall (1979). Carnall and Wybourne (1964) carried out the first systematic interpretation of the 5f state energy level structure of trivalent actinide ions in solution using observed absorption spectra for U 3 + to Cm 3 . The first comprehensive review of the absorption spectra of transuranic actinide ions (including U 3 + ) in dilute acid solution was published by Carnall (1973).
Comparing the absorption spectra of lanthanide and actinide ions with the same number of f-electrons, the most striking differences in molar absorptivity occur at the light end of the actinide series. The energy level differences between the 4f states of aquatated trivalent lanthanide ions (that is, the experimentally determined centers of gravity of observed 4f-4f bands) are quite similar to those deduced from studies of the same ions doped in LaCl3 (Dieke 1968, Morrison and Leavitt 1982) or LaF 3 (Carnall et al. 1989) as Carnall (1979) emphasized in his discussion of lanthanide ion spectroscopy. 1-21 are those determined in systematic interpretations of the spectra of trivalent lanthanide ions doped in LaF 3 (Carnall et al. 1989) and actinide ions doped in LaCl 3 (Carnall 1992).
Tables 1 and 2 list the values of the "free ion" parameters used to calculate the energies of the f-state, shown in Figures 1 and 2. Values of U(2) for 5f-5f transitions of the actinide ions from U 3+ to Md 3+ have been reported by Carnall (1992) in his analysis of the spectra of trivalent actinides in LaCl3.
