Rare-earth dichlorides

Solvent-free cyclopentadienyl rare earth dichlorides have not been prepared. Only the cyclopentadienyl lanthanide dichlorides coordinated by three tetrahydrofuran molecules of the heavier lanthanides could be isolated and some of their properties were investigated (Manastyrskyj et al., 1963 Ely and Tsutsui, 1975). The corresponding yttrium complex was mentioned in a paper by Jamerson et al. (1974), but no characterization of the compound was given. The preparation of the cyclopentadienyl rare earth dichloride complexes with 2 coordinated tetrahydrofuran Ugands of Eu, with 3 THE ligands of La and TM and with 4 THE ligands of La, Sm, Eu, Tm, and Yb was also described in the meantime (Suleimanov et al., 1982c, d). 

Mixed sandwich complexes of the rare earths containing cyclopentadienyl and cyclooctatetraenyl ligands were prepared either by the reaction of cyclopentadienyl rare earth dichlorides with dipotassium cyclooctatetraenide or form cyclooctatetraenyl rare earth chlorides and sodium cyclopentadienide in tetrahydrofuran (Jamerson et al., 1974) ... 

The preparation of cyclopentadienyl rare earth dichloride complexes with two coordinated THF ligands of Eu, and with four THF ligands of La, Sm, Eu, Tm, and Yb was also described (68,69). Figure 6 shows the ligand arrangement of C5H5ErCl2(THF)3 (70). 

Enthalpies of formation of several rare-earth dichlorides (Morss and Fahey 1976) and of dysprosium diiodide (Morss and Spence 1992) have been published and have been used to calculate the aqueous reduction potentials (R /R ) see section 4.5 for details. Others (Kim and Oishi 1979, Johnson and Corbett 1970, Johnson 1974, 1977) have calculated enthalpies of formation and used them as part of a cycle to calculate aquo-ion properties see section 3.3 for details. 

Chervonnyi, A.D., ITin, V.K., Charkin, O.P., Baluev, A.V., Evdokimov, V.I., 1974. Mass-Specrometrical and Theoretical Investigation of Atomization Ehergies of Rare-Earth Dichlorides. Moscow. Available from VINITT, No. 1657-1674 (in Russian). 

Chervonnyi, A.D., ITin, V.K., Krenev, V.A., 1975. Thermodynamics of vaporization of some rare-earth dichlorides. Proceedings of the II All-Union Meeting on Alloys of Rare Metals with Peculiar Physicochemical Properties. Nauka, Moscow, pp. 133-136 (in Russian). 

Vibrational frequencies (in cm" ) of bent (Cj,) gaseous rare-earth dichlorides... 

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. 

Gao, W. and Cui, D.M. (2008) Highly cis-1,4 selective polymerization of dienes with homogeneous Ziegler-Natta catalysts based on NCN-pincer rare earth metal dichloride precursors. Journal of the American Chemical Society, 130, 4984. 

Because of the extensive amount of waste generated in traditional Friedel-Crafts reactions, it is not surprising that this reaction has been studied in RTIL. Early examples included the use of catalytic chloroaluminate ionic liquids. However, the moisture sensitivity of such systems was a drawback. Therefore, water-stable rare-earth Lewis acids, such as Sc(CF3S03)3, have come to be used for these reactions.The same Lewis acid has also been used to catalyse Diels-Alder reactions in RTILs.Interestingly, in this example, the RTIL not only provided a means for recycling the catalyst but also accelerated the rate and improved selectivity. It has also been demonstrated that a moisture stable, Lewis acidic, catalytic ionic liquid could be prepared from choline chloride and zinc dichloride, and that this was an excellent medium for the Diels-Alder reaction. Yields of 90% or more were achieved in reaction times of between 8 min and 5h for a range of dienes and dienophiles. 

The dimeric rare-earth metal dichloride complexes [Ln(L30)Cl2]2 (Ln = Y (135), Sm (136), Dy (137), Er (138), Yb (139), Lu (140)) were obtained from the salt metathesis reaction of potassium bis(phosphinimino)methanide KL30 with anhydrous yttrium or lanthanide trichlorides (Scheme 49) [104]. When the metal center is larger than samarium, bis(phosphinimino)methanide lanthanide dichloride complexes could not be obtained. 

Since only a few standard aqueous electrode potentials °(Ln /Ln ) have been determined electrochemically, others have been estimated [e.g., (Dy /Dy ) (Morss and Fahey 1976, Morss and Spence 1992)] from calorimetric measurements on their dichlorides or from spectroscopic correlations. The only experimental values of °(An /An " ) are from radioelectrochemical measurements on Fm-No (David 1986a) and coprecipitation studies (Mikheev 1988,1992). Spectroscopic correlations of (An /An ) have also been made (section 3.4). These reduction potentials have been assessed for the rare earths (Morss 1985), for the lighter actinides (Martinot and Fuger 1985), and for the heavier actinides (David 1986a, Morss 1986). With the exception of uranium, neptunium and plutonium species [(Fuger 1992, table 1), discussed in section 2.4.1] and No + (discussed in section 2.4.1), these potentials are still valid. We note that the (An /An) values depend on the S°[An (aq)] which are referenced to a value for Pu (aq) that is based in part on experiment but also required estimation of S°[PuClj 6H20(s)]. 

Morss, L.R. and J.A. Fahey, 1976, Enthalpies of Formation of the Lanthanide Dichlorides, in Proceedings of the Twelfth Rare Earth Research Conference, Vail, Colorado, pp. 443-450. 

Unusual for the cyclopolyene compounds of rare earth elements properties of cyclopentadienyl and indenyl Ce(lV) complexes described in the papers of Indian researchers have prompted Deacon and coworkers [21] to repeat the synthesis of Cp4Ce and its derivatives. They have established [21] that the reaction of (C5H5NH)2-CeCl with CpNa does not lead to tetracyclopentadienide of cerium but to the well known trivalent derivative Cp3Ce under the conditions given in paper [1]. The attempts to reproduce the synthesis of tetrafluorenylcerium and dichloride of dicyclo-heptatrienylcerium failed as well [22]. 

For the preparation of samarium or europium carbonates, the rare earth(II) sulfate crystals were suspended in water, then concentrated (NH4)2C03 or K2CO3 solutions were introduced and allowed to contact the sulfate crystal. Some oxidation of the lanthanide occurs simultaneously (Asprey et al., 1964). Clifford et al. (1948) also reported preparation of samarium carbonate by metathesis of the dichloride. The water insoluble and unstable citrate was prepared in the same way (Clifford et al., 1948). 

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