Lanthanides formation

The lanthanide formates decompose above 670 K [1040] and the chemical changes proceed through the oxyformate [1041] and the oxy-carbonate to Ln203. Values of E determined by non-isothermal methods [1040] decreased with increase in atomic number for reaction in air but were approximately equal for reactions in vacuum. 

Furmanova, N.G, Soboleva, L.V., Khapaeva, L.I., and Belov, N.V. (1983) Crystal structure of ytterbium formate dihydrate. Morphotropy in the lanthanide formate (Ln(HCOO)3) dihydrate series. Kristallografiya (Crystallography Reports) (in Russian), 28 (1), 62—66. 

A number of simple carboxylic acids are known to be produced within the body, and so can be classed as endogenous ligands. Diacids such as fumaric, succinic, and malic acid are constantly synthesized and metabolized in cells during the Krebs cycle, whereas formic, oxahc, lactic, glutaric, and tartaric acid also play significant roles in biological processes (amino acids are discussed in Section 4.3). These endogenous linkers can be considered edible and have been extensively employed in MOF assembly—both transition metal and lanthanide formates with extended structures are commonplace, as well as... 

Lanthanide Formate Frameworks Incorporating Ammonium Cations... 

Fig. 5. Predicted lanthanide formation constants obtained in the linear free-energy relationship (LFER) analysis of Byrne and Li (1995) are shown as a function of atomic number and the magnitude of logL/3 (Dy) for a...

The lanthanides, distributed widely in low concentrations throughout the earth s cmst (2), are found as mixtures in many massive rock formations, eg, basalts, granites, gneisses, shales, and siUcate rocks, where they are present in quantities of 10—300 ppm. Lanthanides also occur in some 160 discrete minerals, most of them rare, but in which the rare-earth (RE) content, expressed as oxide, can be as high as 60% rare-earth oxide (REO). Lanthanides do not occur in nature in the elemental state and do not occur in minerals as individual elements, but as mixtures. 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

Catalysts for SW tube formation are not confined to the iron-group metals. Some elements of the lanthanide series can catalyze the formation of SW tubes. 

Using tables of free energies of formation it is clear that most metals will react with most HX. Moreover, in many cases, e.g. with the alkali metals, alkaline earth metals, Zn, A1 and the lanthanide elements, such reactions are extremely exothermic. It is also clear that Ag should react with HCl, HBr and HI but not with HF, and... 

For all three halates (in the absence of disproportionation) the preferred mode of decomposition depends, again, on both thermodynamic and kinetic considerations. Oxide formation tends to be favoured by the presence of a strongly polarizing cation (e.g. magnesium, transition-metal and lanthanide halates), whereas halide formation is observed for alkali-metal, alkaline- earth and silver halates. 

The most important minerals of the lanthanide elements are monazite (phosphates of La, Ce, Pr, Nd and Sm, as well as thorium oxide) plus cerite and gadolinite (silicates of these elements). Separation is difficult because of the chemical similarity of the lanthanides. Fractional crystallization, complex formation, and selective adsorption and elution using an ion exchange resin (chromatography) are the most successful methods. 

PEO is found to be an ideal solvent for alkali-metal, alkaline-earth metal, transition-metal, lanthanide, and rare-earth metal cations. Its solvating properties parallel those of water, since water and ethers have very similar donicites and polarizabilities. Unlike water, ethers are unable to solvate the anion, which consequently plays an important role in polyether polymer-electrolyte formation. 

A review article entitled "Bulky amido ligands in rare-earth chemistry Syntheses, structures, and catalysis" has been published by Roesky. Benzamidinate ligands are briefly mentioned in this contexD The use of bulky benzamidinate ligands in organolanthanide chemistry was also briefly mentioned in a review article by Okuda et al. devoted to "Cationic alkyl complexes of the rare-earth metals S mthesis, structure, and reactivity." Particularly mentioned in this article are reactions of neutral bis(alkyl) lanthanide benzamidinates with [NMe2HPh][BPh4] which result in the formation of thermally robust ion pairs (Scheme 55). ... 

Metathetical routes using bulky lithium guanidinates as starting materials have also been employed to synthesize bis(guanidinato) lanthanide halides as well as reactive alkyls and hydrides. Scheme 63 shows as a typical example the formation of the lutetium chloro precursor, which was isolated in 76% yield. ... 

Homoleptic lanthanide(III) tris(amidinates) and guanidinates are among the longest known lanthanide complexes containing these chelating ligands. In this area the carbodiimide insertion route is usually not applicable, as simple, well-defined lanthanide tris(alkyls) and tris(dialkylamides) are not readily available. A notable exception is the formation of homoleptic lanthanide guanidinates from... 

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