Praseodymium halides

Praseodymium halides (except the fluoride), nitrate, and acetate are soluble. The hydroxide, carbonate, oxalate phosphate, and oxide compotmds are insoluble. Praseodymium s solutions and most of its solids are green. 

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 . 

Neodymium, along with lanthanum, cerium and praseodymium, has low melting points and high boiling points. The fluorides of these and other rare earth metals are placed under highly purified helium or argon atmosphere in a platinum, tantalum or tungsten crucible in a furnace. They are heated under this inert atmosphere or under vacuum at 1000 to 1500°C with an alkali or alkaline earth metal. The halides are reduced to their metals ... 

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

Compounds of divalent samarium, europium, and ytterbium are well-known. In recent years, lower halides of other lanthanides, such as neodymium 48), praseodymium 45, 49, 90), and thulium 4) have been obtained by reducing the trihalide with the metal. The corresponding reaction of thorium tetraiodide with thorium metal has led to the identification of two crystalline forms of Thl2 41, 91) it is unlikely that the Th ", or even Th ", ion is present in Thl2, but like Prl2, which is formulated as Pr " (r)2( ) (2), the compound is probably of the type Th " (r)2(2 ) 41). Certainly one crystal form is diamagnetic 41), suggesting the latter formulation. 

The absolute values of the oscillator strengths may be in error by as much as 25% however, the relative intensities, which determine the relative magnitudes of t, are known to within d= 5% except for the very weak transitions of the less volatile praseodymium and neodymium halides for which the errors may be as large as 25%. 

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