Complexes with rare earth metals

Compound Metal combination Bond length(s) (pm) Coordination number of f-element ) References 

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Alkylated rare-earth metal complexes with rare-earth metal centers surrounded exclusively by oxygen donor ligands were reported from facile ligand redistribution processes in 2,6-dimethylphenolate/trialkylaluminum mixtures. As shown in Scheme 29 for the yttrium derivatives Y(0ArMe,II)2[(//-OArMe>H)2AlR2](THF)2 (R= Me, Et), heterobimetallic 1 1-species were ac-... 

Special substrates comprising a phosphine oxide function and a phenolic moiety served as as5mmetric bifunctional catalysts after complexation with rare earth metal... 

Harrowfield et al. [37-39] have described the structures of several dimethyl sulfoxide adducts of homo bimetallic complexes of rare earth metal cations with p-/e rt-butyl calix[8]arene and i /i-ferrocene derivatives of bridged calix[4]arenes. Ludwing et al. [40] described the solvent extraction behavior of three calixarene-type cyclophanes toward trivalent lanthanides La (Ln = La, Nd, Eu, Er, and Yb). By using p-tert-huty ca-lix[6Jarene hexacarboxylic acid, the lanthanides were extracted from the aqueous phase at pH 2-3.5. The ex-tractability is Nb, Eu > La > Er > Yb. 

Fig. 21 Stoichiometric reaction of C02 with rare-earth metal alkyl complexes to produce carboxylate dimeric catalysts...

Cyanide-bridged squares with rare earth metal ions, namely, [(phen)2 Fe°(CN)2]2[Yb Cl3(H20)2]2 (155) and [Cr (CN)6]2[Gd (urea)4(H20)2]2 (156), also were reported. Both complexes possess multiple open sites (Fig. 27) for further chemistry to take place crystallization from aqueous solution is most likely driven by electroneutrality of the complexes. 

The rare earth complexes of octamethylpyrophosphoramide are the first examples of isolated complexes with rare earth ions coordinated to the pyrophosphate linkage. Experimental evidence supports the coordination of the phosphoryl oxygens to the metal ion with additional coordination positions occupied by water. 

The first dye used in an electrophosphorescent LED was the terbium-complex Tb(acetyhlacetonate)3 (Tb(acac)3, see Fig. 11.2) [21], LEDs based on complexes with rare-earth central metals such as terbium or europium are very interesting for display applications, because they emit light with a very small spectral line width. These sharp emission lines are due to f-f transitions located on the central metal ion. Disadvantages of these complexes are, however, that color tuning via the chemical modification of the ligand is not possible and that the radiative lifetime of phosphorescence is rather long. 

Thus no success has yet been achieved in synthesizing syndiotactic polystyrene with rare earth metal complexes, in contrast to the synthesis of highly syndiotactic polystyrene with TiCl3(C5Me5)/(AlMe-0-)n (syndiotacticity >95%) [63,64]. 

One of the most interesting applications of the HSAB concept consists in the prediction of the stability of the complexes formed owing to interaction of alkali metal halides with rare-earth metal halides. These systems are of great interest for the materials science of scintillation materials the said complex halides are now considered among the most promising scintillation detectors and sensors. Besides, the Li- and Gd-based materials are especially convenient as effective detectors of thermal neutrons. The compositions and stability of the formed compounds depend considerably on the kind of acids and bases from which the compound is formed. So, Li+ cation is one of the hardest cation acids, and, therefore, the formation of stable complex halides of Li and lanthanides according to reaction ... 

Arene complexes of rare-earth metals, among them complexes with heterocyclic ligands 00UK856. 

Chem. Descrip. Cobalt compd. complexed with rare earth and alkaline earth metals... 

When these macrocycles are complexed with rare-earth and actinide ions through binding with the four nitrogen atoms in the core, the unique nature of the metal ions... 

By virtue of a deep understanding of his LnM3tris(BINOLate)3 complexes (Ln = rare-earth metal, M = alkali metal) based on evidence from X-ray analysis and other experiments, Shibasaki developed chiral heterobimetallic yttrium(in) lithium(i) tris(binaphtholate) complex 22, which can promote the catal) ic enantioselective aza-Michael reaction of metho g lamine to enones in excellent yields with up to 97% ee as a Lewis-acid-Lewis-acid cooperative catalyst (Scheme 2.17). Transformation of the 1,4-adducts 23 afforded the corresponding optically active aziridines 24 in high yields. 

The structural chemistry of the dianionic disiloxide ligand, [(OSiPh2)20] , is somewhat different from the aforementioned systems as in all cases either spirocyclic ate complexes (type VII) or spirocychc salt adducts (type VI) are formed with rare earth metal ions. The formation of these two structural types is heavily dependent on the size of the rare earth ion and synthetic protocol applied (Scheme 4). Thus, the smaller ions Y + and Sc + preferentially form salt... 

Ternary and quaternary a-hydroxy-phosphonates, an important class of biologically active compounds, are commonly obtained by addition of dialkylphosphites onto aldehydes or ketones [30]. Well-defined mono- or bimetallic complexes of rare-earth metals, titanium, or aluminum have emerged over the past two decades as effective catalysts for this so-called hydrophosphonylation of aldehydes [31] and, with more difficulty, that of ketones [31c,d, 32], which are far less reactive because of their lower electrophilicity. In some cases, good enantioselectivities could be achieved thanks to the use of chiral metal-based precatalysts [31, 32], Despite their several similarities with rare-earth elements, we were surprised to see that discrete complexes of the large Ae metals had never been utilized to catalyze hydrophosphonylation reactions. 

Of great interest is the use of intermetallic compounds of platinum with rare-earth metals such as cerium and praseodymium for anodic methanol oxidation, known from the work of Lux and Cairns (2006). This combination is attractive inasmuch as it involves two metals that differ strongly in their own electrode potentials Pt with = -1-1.2 V and Pr with = —2.3 V(SHE), and thus in their electronic structure. However, for the same reason, traditional methods of preparing joint disperse deposits of these metals by chemical or electrochemical reduction in a solution of the corresponding salts fail in such a situation. Lux and Cairns developed a new technology for preparing disperse powders of such compounds by thermal decomposition of complex cyanide salts of these metals. The catalyst obtained had some activity in ethanol oxidation (although somewhat... 

A low value of the frequency of the stretching mode of La-CgHg (202 and 216 cm ) in comparison with Th-CgHg (226 and 245 cm ) shows at a less stable metal-carbon bond in the complexes of rare earth metals [52]. It is supposed [24, 30], that the stability of M-C bond increases from Ce to Nd. 

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