Conproportionation route

The synthesis of lanthanide and actinide compounds was the subject of a book (Meyer and Morss 1991). Detailed information is given on the synthesis of lanthanide fluorides (Muller 1991), binary lanthanide halides, RX3 (X=Cl,Br,l) (Meyer 1991a), complex lanthanide(in) chlorides, bromides and iodides (Meyer 1991b), and on two alternative routes to reduced halides, the conproportionation route (Corbett 1991) and the action of alkaU metals on lanthanide(lll) halides (Meyer and Schleid 1991). Therefore, a brief outline of the main preparative routes and synthetic strat es might be sufficent. 

It should be noted that some of the dihalides in the literature are truly halide hydrides to be formulated as RX2H1 (Michaelis et al. 1992a-c). The source for this impurity is the hydrogen content of the rare-earth metal especially when metal powder is used in the conproportionation route. 

Meyer, G., and Th. Schleid, 1991, Action of alkali metals on lanthanide(III) halides an alternative to the conproportionation route to reduced lanthanide halides, in Synthesis of Lanthanide and Actinide Compounds, eds G. Meyer and L.R. Morss (Kluwer, Dordrecht) p. 175. 

The synthesis of lanthanide and actinide compounds is the topic of a book edited by Meyer and Morss (1991). Topics that relate to halides, with the author(s) in brackets, include Lanthanide fluorides [B.G. Muller], Actinide fluorides [N.P. Freestone], Binary lanthanide(III) halides, RX3, X = Cl, Br, and I [G. Meyer], Complex lan-thanide(III) chlorides, bromides and iodides [G. Meyer], Conproportionation routes to reduced lanthanide halides [J.D. Corbett], and Action of alkali metals on lanthanide(III) halides an alternative to the conproportionation route to reduced lanthanide halides [G. Meyer and T. Schleid]. Meyer and Meyer (1992) reviewed lanthanide halides in which the valence of the lanthanide was considered unusual, with unusual being defined as compounds in which the localized valence of an atom differs from its oxidation number. A metallic halide such as Lalj [oxidation number (0)= -1-2 valence (V)= -l-3, since the 5d electron is delocalized in the conduction band] or a semiconducting halide such as PrjBtj (O = -t- 2.5 V = -I- 3) is unusual by this definition, but Tmlj (O = -1-2 V = +2) is not. In this review synthesis, properties, and calculated electronic structures are considered with emphasis on praseodymium halides and hydrogen intercalation into lanthanide dihalides and monohalides . 

The synthesis of compounds of the lanthanides containing cluster complexes follows in general the same routes as described in The Divalent State in Solid Rare Earth Metal Halides, the conproportionation route and the metallothermic reduction route, for example... 

Conproportionation of ReCls and ReCls in a sealed tube at 300-600°C yields jS-ReCU containing dimeric confacial bioctahedral M2X9, units that share terminal chlorides as indicated by [Re2(/i-Cl3)Cl4]Cl2/2. Other routes to ReCU include heating Reds above 350 C under an N2 stream and hydrolyzing ReCU to Re02 prior to refluxing in thionyl chloride . In contrast to ReCU, the TcCU structure excludes metal-metal bonding. ... 

The most convenient route to M6Yi2 2+ clusters of niobium and tantalum is the conproportionation of the pentahalides NbY5 and TaY5 (Y = Cl, Br) with excess of the metal in molten alkali halide ... 

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