Lanthanide chlorides, metathesis

For laboratory use, the dehydration of LnCl3 (H20)x (x = 6,7) using NH4C1 is the favorite method of preparing anhydrous lanthanide chlorides [96b]. However, simple thermal dehydration, as accessible to lanthanide trif-lates, leads to the formation of undesirable lanthanide oxychlorides. Because the Ln-halide precursor is insoluble in aliphatic and aromatic hydrocarbons, the preparation of organolanthanides via salt metathesis is performed in coordinating solvents such as THF. 

Inspection of the proposed nitration mechanism (Scheme 1) reveals that the mononitrate dipositive lanthanide species [Ln(H20)x(N03)](0Tf)2 (1) is the key intermediate. An independent preparation and characterisation of such a species enables possible indentification of 1 directly in situ in the reaction mixture. Additionally, spectroscopic examination of these salts may provide some evidence for our working model. We have developed a novel preparation of these mixed salts by simple metathesis of lanthanide chlorides with the requisite quantities of silver nitrate and silver triflate in water (Scheme 3).17 The resulting hydrated salts were white or lightly coloured (pink, green or yellow) solids which were found to be stable indefinitely at room temperature in the solid state. 

In contrast, less is known about La-(CNx) compounds. The composition La2(CN2)3 was reported many years ago [43], without any structural information. Solid-state metathesis reactions of lanthanum chloride with Li2(CN2) or Zn(CN2) have recently brought up three series of the lanthanide compounds Ln2(CN2)3 [44], LnCl(CN2) [45], and Ln2Cl(CN2)N [46], Syntheses routes for Ln-(CNx) compounds containing new anions such as [C2N4] are to be developed, as well as for compounds in the La-B-C-N system (Fig. 8.15). 

A metathesis reaction is a convenient route to lanthanide tetrahydroaluminate and lanthanide tetrahydroborate complexes. Using tetrahydroaluminate complexes as the hydride source, a number of structurally characterized lanthanide tetrahydroaluminate complexes are prepared via metathesis reactions in the presence of an excess of a Lewis base (Equation 8.24) [79]. Metathesis reaction of organolanthanide chlorides with alkali metal tetrahydroborate generates the corresponding lanthanide tetrahydroborate. The same reaction with sodium hydride in THE is reported to afford a lanthanide hydride however, no molecular structure for the hydride has been presented up till now. 

Anhydrous lanthanide halides are ionic substances with high melting points which take up water immediately when exposed to air to form hydrates (r>Br >Ch) [48]. Straightforward synthetic access and a favorable complexation/solva-tion behavior make the lanthanide halides the most common precursors in organolanthanide chemistry. Many important Ln-X bonds (X=C, Si, Ge, Sn, N, P, As, Sb, Bi, O, S, Se, Te) can be generated via simple salt metathesis reactions [4,8]. The so-called ammonium chloride route either starting from the lanthanide oxides or... 

From the diacetate chloride complexes, compounds containing other counterions, e.g. SCN (Bombieri et al. 1989a), Cl, Br (Bombieri et al. 1989b), or C104 (Bombieri et al. 1986) have been obtained by metathesis in methanol solution. Trinitrate or dinitrate perchlorate complexes of all lanthanide(III) ions except the three smallest ones, Tm(III), Yb(III) and Lu(lII), have also been obtained by trans-metallation from the barium perchlorate complex Ba(I)(C104)2 and the lanthanide nitrate in aqueous solution at room temperature (Arif et al. 1987). Structures have been determined for several of these compounds. 

Lanthanide(lII) alkanoates are salts of aUtanoic acids (fatty acids). They are also known as lanthanide soaps and their general formula is [R(C H2 + iCOO)3]. The first examples of lanthanide salts of the higher alkanoic acids were described by Mehrotra and coworkers (Mehrotra et al., 1966 Misra et al., 1963a), although shorter homologues have been reported much earlier (Wolff, 1905). The lanthanide(lll) alkanoates can be prepared by a metathesis reaction between the corresponding sodium alkanoate and the lanthanide salt (nitrate or chloride) in ethanol/water solution ... 

In the case of lithium nitride, YCI3 and LaCls were the first rare-earth chlorides investigated (Fitzmaurice et al. 1993). The highly exothermic reactions, once initiated at 400°C, were extremely rapid, leading to crystalline YN and LaN nitrides which were isolated from LiCl after tetrahydrofuran trituration. The same type of rapid exothermic solid-state metathesis reaction was then applied to produce all the RN rare-earth nitrides (R=Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) as well as mixed lanthanide nitrides (RR )N (RR =PrNd, DyHo, TbDy) (Fitzmaurice et al. 1994). Note that the reaction requires initiation via a conventional or microwave oven but is self-sustaining. The prepared nitrides have a stoichiometry LnN x (x = 0.1-0.2). 

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