Lanthanoid compounds

The neglect of the ligand field in Eq. (10.1) leads one to expect no satisfactory account of the experimental magnetism of lanthanoid complexes either. It is an empirical fact, however, that Eq. (10.1) accounts extremely well for observed magnetic moments in most lanthanoid compounds. We compare typical experimental moments for lanthanoid complexes with those calculated from Eq. (10.1) in Fig. 10-3. Significant discrepancies occur for/ and/ species and we will comment on these shortly. 

Block copolymers of olefins and acrylates or vinyl esters can be obtained with lanthanoid compounds as catalysts. Living polyethylene-biscyclopenta-dienyl samarium systems can continue the polymerization of cyclolactone monomers by ROMP (273, 274). 

Block copolymers of olefins and acrylates or vinylesters can be obtained by lanthanoid compounds. Living polyethylene-biseyclopentadienyl samarium systems can continue the polymerization with acrylate monomers by group transfer polymerization or cyclolactone monomers by ring opening polymerization [216, 217]. 

XANES is one of powerful tools for the study of chemical states of lanthanoid compounds. Most of the conclusions drawn from the XANES for the lanthanoid compounds have been concerned with the chemical states or characteristics of the electronic structures. In particular, valences of lanthanoids have been studied using such spectra (2). They were obtained by assigning some of the peaks in the spectra to different valences. By using the Anderson impurity model, the valences were derived from intensities of shake-up peaks (3). 

Table VIII.2. Methane carboxylation promoted by lanthanoid compounds ...

Because of the inner nature of the 4f orbitals, the dififerenees of eleetron configuration between the lanthanoid elements are associated to eleetrons relatively well screened from the chemical surroundings by the outer (5s p ) shell. This implies weak crystal fields splitting effects [28], and a relatively small eovalent contribution to the bonding, particularly in the sesquioxides. Accordingly, the ionic model plays an important role in determining their chemistry [21]. Also related to these chemical characteristics, the lanthanoid compounds exhibit a rich variety of stmctures, often reflected in the occurrence of polymorphism phenomena. 

Despite the extreme air and moisture sensitivity of organo-lanthanoid compounds, this is a rapidly expanding research area. An exciting aspect of organolanthanoid chemistry is the number of efficient catalysts for organic transformations that have been discovered (see Box 25.5). In contrast to the extensive carbonyl chemistry of the J-block metals (see Sections 24.4 and 24.9), lanthanoid metals do not form complexes with CO under normal conditions. Unstable carbonyls such as Nd(CO)g have been prepared by matrix isolation. Since organolanthanoids are usually air- and moisture-sensitive and may be pyrophoric, handling the compounds under inert atmospheres is essential. ... 

Due to the high bond ionicity of lanthanoid compounds the classical idea of a and n type bonding between organic ligand and metal atom in most cases does not fit to REM... 

One more lanthanoid compound containing both Cp and arene ligands has been obtained in the reaction of Cp2LuCl with mono- and disodium derivatives of anthracene [70]. The data of the element analysis correspond to the formula Cp2Lu(Ci4Hio)Na(THF). 

Two general types of lanthanoid compounds containing PR2 groups at the metal atom are known Ln(PR2)3 and Cp2LnPR2- The first of them are obtained from the reaction of LiPR2 with anhydrous lanthanoid chlorides in THF at room temperature [1] ... 

The first lanthanoid compound containing metallcarbonyl substituents, Er[Co(CO)4]3, was synthesized by Marianelli and Dumey in 1971 [38], Later the chemistry of REM metalcarbonyls has been developed in the works of Beletskaya [39-45], Andersen [46, 47] and other investigators. The most interesting point in this area of organolanthanoids is the problem of chemical bond between the lanthanoid atom and the transition metal. Elucidation of the nature of this bond became the central question in most papers on the given topic. Additionally, the titled compounds appear to be attractive as plausible catalysts in some processes of organic synthesis, specifically in the processes of CO transformation. 

In this section we briefly consider specific lanthanoid compounds with carbon containing ligands, which were not included in the previous chapters. The complexes with carbon monoxide, graphite intercalates, phtalocyanine and porphyrin complexes, some carbon-containing clusters and alkylhydroborates are attributed to such compounds. 

In Table XIII. 1 the lanthanoid compounds are listed, which already have a practical application or can find such an application in the future. Table XIII.1. Applications of REM derivatives. ... 

Lanthanoid compounds are active in oxidation reactions. The t-BuOSml2, promotes the alkylation of carbonyl compounds, catalyzes the reverse reaction as well the oxidation of alcohols to aldehydes and ketones (the Oppenauer reaction) [83]. Heterometallic oxides of the general composition Lai. M M 03 (M = Ce, Sr M = Fe, Co) [109, 141], LaMni. CUx03 [110] accelerate the O2 oxidation of alkanes and carbon oxide. The effectiveness of the oxides essentially depends on the molar ratio of the metals in them. 

See the general references in the Introduction, and some more-speciahzed books [4, 6-58], Some articles in journals discuss actinide complexation and thermodynamics at elevated temperatures [59] classifying lanthanoids by multivariate analysis, albeit with results that seem hard to defend [60] designing sequestering agents for Pu and other actinoids [61] lanthanoid compounds with complex inorganic anions, part of a thematic issue on lanthanoid chemistry [62] Pm, discovery and chemistiy [63] recent Sc chemistiy [64] actinoid complexes [65] the transuranium elements [66] actinoid complexes with OH and [67] coordination numbers [68] the aqueous chemistiy and thermodynamics of Eu [69] photooxidation-reduction of Np and Pu [70] review of Pm [71] Rth thermochemistiy [72] unusual oxidation states of Ln and An [73] and Rth chemistiy [74]. 

In the only isolated example of actinoid NHC-ligated compounds, namely uranium complexes, the NHC-U bond lengths were in the range of lanthanoid compounds. The few reported NMR spectra exhibited extremely downfield-shifted carbene resonances. Direct comparison to NHC-lanthanoid complexes was not straightforward, due to the different oxidation states, but, for instance, compound [(NHC)2U02] 25 showed a Ccarbene resonance at 262.8 ppm and the saturated examples 45 and 46 at 281.6 ppm and 283.6 ppm (Figure 6.5). ... 

Dolg M, Stoll H, Preuss H. A combination of quasirelativistic pseudopotential and ligand field calculations for lanthanoid compounds. Theor Chim Acta. 1993 85 441-50. 

M. Dolg, H. Stoll, H. Preuss, Homonuclear diatomic lanthanoid compounds a pseudopotential configuration interaction and correlation energy density functional study, J. Molec. Struct. (THEOCHEM), 277, 239-249 (1992). 

Albertsson, J., 1972d, On the Stereochemistry of Nine-Coordinate Lanthanoid Compounds, Thesis, Lund. 

The divalent state of Sm, Eu, Tm and Yb should become unstable under high pressure. This can be foreseen from the fact that they have smaller ionic radii in their trivalent state and hence high pressure could favor the higher valence state. Recent high pressure experiments on a series of lanthanoid compounds, in particular the monochalcogenides Sm, Eu, Yb, Tm, have demonstrated the occurrence of such transformations. 

Nauk SSSR, Neorg. Mater. 19, 151. In Russian. Hordijenko, S.P, B.V Fenoehka and G.Sh. Viksman, 1979, The Thermodynamies of Lanthanoid Compounds (Naukova Dumka, Kiev) pp. 136-152. In Russian. 

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