Lanthanide atom

THE ELECTRON CONFIGURATIONS OF GASEOUS ACTINIDE AND LANTHANIDE ATOMS... 

A new class of organolanthanide complex has been reported from the metal-atom reaction of lanthanide atoms and butadiene (BD) or 2,-... 

Structures of the lanthanide nitridoborates appear as layered structures with approximate hexagonal arrangements of metal atoms, and typical coordination preferences of anions. As in many metal nitrides, the nitride ion prefers an octahedral environment such as in lanthanum nitride (LaN). As a terminal constituent of a BNx anion, the nitrogen atom prefers a six-fold environment, such as B-N Lns, where Ln atoms form a square pyramid around N. Boron is typically surrounded by a trigonal prismatic arrangement of lanthanide atoms, as in many metal borides (Fig. 8.10). All known structures of lanthanide nitridoborates compromise these coordination patterns. 

Lanthanides in combination with transition metals have been shown to have a positive effect in promoting heterogeneous catalytic reactions. The bimetallic Yb—Pd catalyst obtained from the precursor (pMF)i0Yb2 Pd(CN)4]3 K on a titania surface offers improved performance over a palladium-only catalyst for the reduction of NO by CH4 in the presence of 02.99 100 The structure, shown in Figure 6, consists of two inverted parallel zigzag chains that are connected through the lanthanide atoms by trans-bridging [Pd(CN)4]2- anions.101... 

Figure 6 Bimetallic Yb—Pd catalyst obtained from the precursor (DMF)1oYb2[Pd(CN)4]3

The trend toward greater complex stability with increasing lanthanide atomic number (see Table 3 for EDTA, DCTA, and DTPA complexes) has also been demonstrated for lanthanide complexes with... 

Fig. 4.15 The system La(III) acetylacetone (HA) - IM NaC104/benzene at 25°C as a function of lanthanide atomic number Z. (a) The distribution ratio Hl (stars, right axis) at [A ] = 10 and [HA] rg = 0.1 M, and extraction constants (crosses, left axis) for the reaction Ln + 4HA(org) LnA3HA(org) + 3FE. (b) The formation constants, K , for formation of LnA " lanthanide acetylacetonate complexes (a break at 64Gd is indicated) circles n = 1 crosses n = 2 triangles w = 3 squares w = 4. (c) The self-adduct formation constants, for the reaction of LnA3(org) + HA(org) LnA3HA(org) for org = benzene. (A second adduct, LnA3(HA)2, also seems to form for the lightest Ln ions.) (d) The distribution constant Ajc for hydrated lanthanum triacetylacetonates, LnAs (H20)2 3, between benzene and IM NaC104. (From Ref. 28.)...

SYMBOL La PERIOD 6 SERIES NAME Lanthanide ATOMIC NO 57... 

SYMBOL Eu PERIOD 6 SERIES NAME Lanthanide ATOMIC NO 63 ATOMIC MASS 151.964 amu VALENCE 2 and 3 OXIDATION STATE +2 and +3 NATURAL STATE Solid ORIGIN OF NAME Named for the continent of Europe. 

The energy level values of the lowest spectroscopic term of the electronic configuration of lanthanide as well as actinide atoms, were tabulated by Brewer. Such tables are very useful for phenomenological correlations concerning actinide metals (see Chap. C). From these tables one can obtain Table 1 giving the ground state and the first excited level of the actinide atoms as well as of the lanthanide atoms for comparison ... 

Note that the Lanthanide (atomic numbers 58-71) and Actinide (90-103) series elements, as well as the synthetic elements of atomic number greater than 87, are omitted from all the periodic tables in this text. With the possible exception of nuclear fuels such as uranium and plutonium, these elements are of little general engineering interest. 

Fig. 8. Angular distribution of the 4f charge density of lanthanide atoms for Jz = J (effective moment parallel to the z-axis). After Thole in Coehoom (1990). In Ce, Pr, Nd, Tb, Dy, Ho the charge density is oblate (aj < 0), in Pm, Sm. Er, Tm, Yb it is prolate (aj > 0). In Gd, Lu (L = 0), the charge density has spherical symmetry.

The atomisation enthalpies of the lanthanides as metallic elemental substances exhibit very different trends. From La to Eu, we see a steady decrease, followed by an abrupt increase at Gd. The atomisation enthalpies then decrease (not quite monotonically) to Yb, then increase at Lu. These trends may be rationalised as follows. According to magnetic studies, the lanthanide atoms in the elemental substances have the electronic configurations 6s25d14f" Eu and Yb are exceptions, discussed further below. The band structure is evidently complex and will not be described in detail. The atomisation enthalpy can be broken down for thermochemical purposes into two steps ... 

Fig. 4. Model of filled skutterudite structure that emphasizes the pnicogen-pnicogen bonding that results in nearly square pnicogen rings. The transition metal atoms (small white spheres) form a simple cubic lattice as shown. The lines connecting the transition metal atoms have been added for clarity and do not correspond to a chemical bond. The only chemical bonds shown in this model are those that form the pnicogen rings. The lanthanide atoms (large dark spheres) occupy the two voids without a pnicogen ring.

The filled skutterudite antimonides appear to represent excellent examples of electron-crystal, phonon-glass materials. The incoherent rattling of the loosely bound lanthanide atoms in these materials is inferred from the large values of the ADP parameters obtained in single-crystal structure refinements. This rattling lowers the thermal conductivity at room temperature to values within two to three times Km... 

M. Dolg and H. Stoll, Electronic structure calculations for molecules containing lanthanide atoms 60 7 Author index 731... 

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