Samarium dichloride

SiBr2[g] SILICON DIBROMIDE (GAS) 1485 SmCI2 SAMARIUM DICHLORIDE 1533... 

While it is recognized that samarium diiodide (Sml2) is by far the most utilized reductant among Sm(II) halides, samarium dichloride (SmCh) and samarium dibromide (SmBr2) have been used in a number of applications. The main limitation of these two reductants is their... 

Samarium dichloride has been prepared by reduction of ethanolic solutions of SmCl3 with magnesium and hydrochloric acid (aqueous or anhydrous). Nevertheless, isolation of the pure compound from the reaction medium has not been achieved (Clifford et al., 1948). 

Reduction of diaryltellurium dichlorides with samarium diiodide (typical procedure). Diaryl tellurium dichloride (1 mmol) was added to the deep blue solution of Sml2 (2.2 mmol) in THF (22 mL) at room temperature under nitrogen with stirring. The deep blue colour of the solution disappeared immediately and became yellow. The resulting solution was stirred at room temperature under nitrogen for 30 min. To the solution was added dilute hydrochloric acid, and the mixture was extracted with ether. The ethereal solution was washed with brine and dried over MgS04. The solvent was evaporated in vacuo, and the residue was purified by preparative TLC on silica gel (petroleum ether-methylene dichloride as eluent). 

By controlling the stoichiometry of the reaction between lanthanide trichlorides and sodium cyclopentadienide it is possible to replace the chloride ions stepwise. Equihbria are rapidly established, so the addition of Ln(C5H5)3 to one or two equivalents of LnCls will produce M(C5H5)2C1 and M(C5H5)Cl2, respectively. The dichlorides are known only for the lanthanides from samarium to lutetium and are obtained from THF solutions as tris-THF adducts. 

The divalent compounds of samarium primarily are halides, the reddish-brown crystalline dichloride, SmCb [13874-75-4] the dark-brown diiodide, Sml2 [32248-43-4] and the dark brown dibromide, SmBr2 [50801-97-3]. Samarium also forms a difluoride, SmF2 [15192-17-3]. The trivalent salts of these halogens are more stable than their divalent counterparts. 

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. 

Chromium carbene complexes. phloroglucinols Malonyl dichloride. phthalides Thallium(III) trifluoroacetate. pinacols Samarium(II) iodide. Tetra-w-butylammonium fluoride. 

The same reaction products are obtained from epoxides and TMS-CN in the presence of aluminum al-koxides, samarium, cerium or lanthanum chlorides as well as titanium tetraisopropanoate, which may all be considered comparatively hard Lewis acids. On the other hand various groups demonstrated that softer Lewis acids like zinc, tin and palladium dichloride may give rise to isocyanides (Scheme 15). 

Dialkyltin dichlorides, R2SnCl2 (R = Me, Et, or C6H13), react with samarium iodide or with magnesium or calcium vapour to give polystannanes with M u/ > 103 and a narrow molecular weight distribution (e.g. equation 18-48). 

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. 

Jia (1990) has described the molecular constants of RX2 (R = La-Lu X = F, Cl, Br, I) by taking into accoimt the data reported by Krasnov and Timoshinin (1969), the molecular characteristics of samarium, europium, and ytterbium dichlorides and difluorides obtained from their IR spectra (DeKock et al., 1972 Hastie et al., 1971), as well as estimates by Filippenko... 

Indeed, when Johnson (1969) published his paper, four experimental values of AfH°(RCl2, cr, 298) were known, for neodymium, samarium, europium, and ytterbium dichlorides. One decade later, Kim and Oishi (1979) could compare their estimates with the experimental values for six dichlorides, dysprosium and thulium dichlorides data having been added in the meantime. 

Such a close agreement between the calculated and experimental enthalpies of formation for samarium, europium, thulium, and ytterbium dichlorides allows us to claim that the calculation scheme used in the framework of this study leads to reliable results provided that the reference values are chosen adequately. 

The most reliable characteristic parameters for compoimds of the other crystal structure t5q>es can be obtained by processing the experimental data on samarium and eiuopium dictilorides. Indeed, the cooperative magnetic transition characteristic of the Eu ion in eiuopium dichloride should be observed at temperatures lower than the minimum temperature limit at which heat capacity measiuements have been performed by Tolmach et al. (1986). It follows that these data can be treated as the lattice contribution to the heat capacity of EuQ2. 

Pogrebnoi, A.M., 2004. Molecular and ion associates in vapors over lanthanide chlorides and solid electrolytes. Extended Abstract of Doctoral (Chem) Dissertation, Ivanovo (in Russian). Pogrebnoi, A.M., Kudin, L.S., 2003a. Neutral and charged species in saturated vapour over samarium, europium and ytterbium dichlorides. In Proceedings of the II International Symposium on High Temperature Mass Spectrometry (Plyos, 2003), Ivanovo, pp. 110-117. 

The Heats of Reaction of the Dichlorides of Samarium and Ytterbium with Hydrochloric Acid. A Microcalorimeter, G.R. Machlan, C.T. Stubblefield and L. Eyring, J. Amer Chem. Soc., 77, 2975-2978 (1955). 

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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