Rare earth trichlorides

Enthalpies of solution of rare-earth trichlorides in dimethyl sulfoxide are markedly more negative than in water, though the difference decreases on going from lanthanum across to ytterbium. Less favorable solvation of the chloride ions by the dimethyl sulfoxide must be more than balanced by favorable solvation of the rare-earth 3+ cations (cf. Section VI,B). This dimethyl sulfoxide-versus-water comparison should be contrasted with the alcohol-versus-water comparisons discussed earlier. 

Solubilities of Rare-Earth Trichlorides in Ethylene Glycol and in Glycerol... 

Chloride. — All the rare earth trichlorides except La and Pr crystallize with six molecules of water of crystallization La and Pr chlorides crystallize as heptahydrates. Thermal decomposition studies [280] on... 

Several adducts of amine hydrochlorides with rare earth trichlorides of the type [MCI3] [AHC1] containing varied amounts of solvent molecules have been isolated [365, 366] from alcoholic solution. 

The rare-earth trichlorides belong to the best studied systems at ambient as well as at high pressure. Voloshin et al. (1975) studied the effect of pressure on the free-ion parameters of NdCl3-6H20 up to 2.3 GPa. They found reductions of -0.26%, -0.29%, -0.12%, and -0.25% for F2, F4, F6, and f, respectively. Such variations can be explained neither by the CFC nor by the SRC model alone. 

Similar to the rare-earth trichlorides, also different ternary MYX compounds have been studied thoroughly under high pressure. The results for the pressure-induced changes of the Slater parameter F2 and the spin-orbit coupling parameter of these and other compounds are presented in table 5. Due to the difficulties with the DS model, the evaluation of the parameter shifts has been performed only in terms of the two covalency models. Assuming small changes for the free-ion parameters, the relative changes were approximated by ... 

Roesky introduced bis(iminophosphorano)methanides to rare earth chemistry with a comprehensive study of trivalent rare earth bis(imino-phosphorano)methanide dichlorides by the synthesis of samarium (51), dysprosium (52), erbium (53), ytterbium (54), lutetium (55), and yttrium (56) derivatives.37 Complexes 51-56 were prepared from the corresponding anhydrous rare earth trichlorides and 7 in THF and 51 and 56 were further derivatised with two equivalents of potassium diphenylamide to produce 57 and 58, respectively.37 Additionally, treatment of 51, 53, and 56 with two equivalents of sodium cyclopentadienyl resulted in the formation of the bis(cyclopentadienly) derivatives 59-61.38 In 51-61 a metal-methanide bond was observed in the solid state, and for 56 this was shown to persist in solution by 13C NMR spectroscopy (8Ch 17.6 ppm, JYc = 3.6 2/py = 89.1 Hz). However, for 61 the NMR data suggested the yttrium-carbon bond was lost in solution. DFT calculations supported the presence of an yttrium-methanide contact in 56 with a calculated shared electron number (SEN) of 0.40 for the yttrium-carbon bond in a monomeric gas phase model of 56 for comparison, the yttrium-nitrogen bond SEN was calculated to be 0.41. 

The organometalhc chemistry of the rare earths deals mainly with bis(cyclopentadienyl) derivatives due to the easy available bis(cyclopentadienyl) rare earth chlorides and other halides via reaction of the rare earth trichlorides with two equivalents of a cyclopentadienyl alkali salt. Bis(cyclopentadienyl)lanthanide chlorides are formed as chloride-bridged dimers (Figure 28a), as monomers stabihzed by a donor molecule like THF (Figure 28b) or as ate complexes with alkali hahdes (Figure 28c). 

For a better understanding of many successful applications of the rare earth-alkali metal containing LnM3tris (binaphthoxide) complexes (LnMB, Ln=rare earth, M=alkali metal) to catalytic asymmetric synthesis, intense investigations also focused on the determination of the structure. It has been shown that these complexes, which can be readily prepared from the corresponding rare earth trichlorides and/or rare earth isopropoxides [5],possess a structure as presented in Fig. 2. This structure was supported by various NMR spectroscopic, MS spectrometric, X-ray crystallographic and other analytic investigations of a variety of LnMB complexes. 

Although this has the effect of putting in doubt all the good fits between theory and experiment found by Peacock and his collaborators, it removes the somewhat embarrassing result that hypersensitive lines in the rare-earth trichlorides, which the theory would otherwise predict to be intense,are experimentally unexceptional. 

A direct precipitation technique for the preparation of the RE orthophosphates has been described by Hikichi et al. (1978) in which a 0.05 mol/1 solution of the rare-earth trichloride was added to a dilute, stirred H3(P04) solution. The mixed solutions were then maintained at 20, 50, and 90°C for 1 to 900 days and were titrated to maintain a constant pH by adding H3(P04) or other phosphates. Both the hydrated low-temperature hexagonal forms of the rare-earth phosphates (as discussed in the previous section on Chemical composition) and the anhydrous RE orthophosphates were produced by Hikichi et al. (1978). 

The tris(cyclopentadienyl) complexes of the rare earths were the first compounds discovered and the most intensively investigated class of organometallic compounds of these elements. They were reported for the first time in 1954 by Wilkinson and Birmingham, and generally prepared by reaction of anhydrous rare earth trichlorides with sodium cyclopentadienide in tetrahydrofuran at room temperature and isolated by sublimation of the crude products in vacuum at about 220°C (Wilkinson and Birmingham, 1954 Krasnova et al., 1971) ... 

Another method available for the synthesis of such derivatives is the reaction of the rare earth trichlorides with KC5H5 or TIC5H5 in benzene (E.O. Fischer and H. Fischer, 1965b Manzer, 1976a). This method allows the synthesis of tris(cyclo-pentadienyl) europium, which could not be prepared by the reaction in tetrahydro-furane, because of the decomposition of (CjH5)3Eu THF during sublimation ... 

Dicyclopentadienyl rare earth chlorides can be prepared by treating the rare earth trichlorides with two equivalents of cyclopen tadienyl sodium or with its respective tricyclopentadienyl derivative in tetrahydrofuran (Maginn et al., 1963 Schumann... 

Heptamethylindenyl complexes of lanthanum, neodymium and erbium were synthesized by the reaction of the appropriate rare earth trichloride with potassium heptamethylindenide in tetrahydrofuran by Tsutsui et al. in 1982. Corresponding to the ratio of the starting materials, the tris(heptamethylindenyl) derivatives of... 

Carboranyl derivatives of lanthanum, thulium and ytterbium are formed when the C-mercuro derivatives of methyl- and phenylcarboranes react with the rare earth metals in tetrahydrofuran at 20°C (Suleimanov et al., 1982a), or from the lithium derivatives of methyl- and phenylcarboranes with the rare earth trichlorides in benzene-ether at 20°C (Bregadze et al., 1983) as complexes with THF. A carboranyl derivative with a thulium-boron bond is also described. The reaction (eq. 62) may proceed via the formation of B-Tm-C derivatives, followed by disproportionation. 

The addition of trimethylmethylenephosphorane to a suspension of rare earth trichlorides in pentane or hexane results in the formation of pyrophoric phos-phonium salts in quantitative yields. While no dehydrochlorination of these salts was... 

The following carboranyl derivatives of La, Tm, and Yb have been prepared by interaction of the lithium derivatives of carboranes with the appropriate rare earth trichlorides in tetrahydrofuran benzene-ether in 1983 by Bregadze et al. MeCBioHioCLaCl2, m.p. 133-135°C,... 

Also rare earth metal-cobalt bonds are proposed for products from reactions of rare earth trichlorides and cobalt carbonyl derivatives (Suleimanov et al., 1982e). 

Travers et al. (1976). SCCI3 has the rhombohedral FeCl3 structure its enthalpy of solution does not correlate with that of any of the other rare-earth trichlorides. 

The thermochemistry of rare-earth trifluorides was summarized in Gmelin Hand-buch (1976) and the thermochemistry of rare-earth tribromides and triiodides was summarized in Gmelin Handbuch (1978). The thermochemistry of trivalent rare-earth trichlorides was critically assessed by Morss (1976). Enthalpies of formation of most of the lanthanide tribromides were determined by Hurtgen et al. (1980). Thermodynamic properties for europium halides were assessed by Rard (1985). Only enthalpies of formation of Sc, Y, Dy and Tm triiodides have been redetermined since the classical work of Hohmann and Bommer (Morss and Spence 1992). A recent set of literature values of enthalpies of formation of rare-earth solid and gaseous trihalides has been published, accompanied by Born-Haber cycle estimated values for all trihalides (Struck and Baglio 1992). 

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