Lanthanide oxide halides

LANTHANIDE AND ACTINIDE HALIDES AND OXIDE HALIDES 9.3.1 Reactions of phosgene with lanthanide oxide halides... 

This is the most common oxidation state, although for Th, Pa, and U it is of secondary importance. The general chemistry closely resembles that of the lanthanides. The halides MX3 may be readily prepared and are easily hydrolyzed to MOX. The oxides M203 are known only for Ac, Pu, and heavier elements. In aqueous solution... 

Relatively little is known about the chemistry of promethium, although the established facts highlight the resemblance of promethium to the lanthanides that flank it. The halides are well defined, and have been shown to have the expected structures (Table 2). Thus in a recent study, starting with some 100 J,g of Pm203, the halides were synthesized microchemically, using the reaction with fluorine for PmFs and the reaction with HX (X = Cl, Br) for the chloride and bromide the latter two reacted with HI to give the iodide. Pm203 is one of the few lanthanide oxides to crystallize in three modifications. 

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... 

Idemitsu Kosan Co. report that the addition of alkali halides to basic oxides (such as alkaline earth oxides or lanthanide oxides) resulted in methane oxidation catalysts that produced good yields of ethylene. A LiCl/EUjOj catalyst at 750 C gave a methane conversion of 37% with an ethylene selectivity of 46% and an ethane selectivity of 4.5%. 

The rare-earth elements constitute together with the actinide elements group 3 of the Periodic Table of the elements, a total of 32 elements The actinides excluded, there are 17 elements left with electron configurations of 4s 3d (Sc), 5s 4d (Y), and 6s 5d 4f (the lanthanides, La, Ce-Lu = 0-14). Hence, they all have an outer valence electron configuration of s d in common that qualifies them for all becoming trivalent in numerous compounds, in oxides, halides, as aqua conqilexes in aqueous solutions. 

Additional areas of lanthanide halide chemistry that have been reviewed include the synthesis, phase studies, and structures of complex lanthanide halides - compounds formed between one or more group 1 cation and lanthanide element halides (Meyer 1982). Halides in combination with lanthanide elements in the II, III, and IV oxidation states were considered with the chemistry of the heavier halides being emphasized. More recently the reduced ternary lanthanide halides (Meyer 1983) and the reduced halides of the lanthanide elements were reviewed (Meyer 1988). The latter review considered lanthanides in which the formal oxidation state of the cation was 2 and included hydride halides, oxide halides, mixed-valence ternary halides, and reduced halide clusters. Corbett et al. (1987) discussed the structures and some bonding aspects of highly reduced lanthanide halides and compounds stabilized by a second-period element bound within each cluster, e.g., SC7CIJ2B, SC5CI5B, YjCljC. 

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 . 

Comparable recent detailed reviews of the actinide halides could not be found. The structures of actinide fluorides, both binary fluorides and combinations of these with main-group elements with emphasis on lattice parameters and coordination poly-hedra, were reviewed by Penneman et al. (1973). The chemical thermodynamics of actinide binary halides, oxide halides, and alkali-metal mixed salts were reviewed by Fuger et al. (1983), and while the preparation of high-purity actinide metals and compounds was discussed by Muller and Spirlet (1985), actinide-halide compounds were hardly mentioned. Raman and absorption spectroscopy of actinide tri- and tetrahalides are discussed in a review by Wilmarth and Peterson (1991). Actinide halides, reviewed by element, are considered in detail in the two volume treatise by Katzet al. (1986). The thermochemical and oxidation-reduction properties of lanthanides and actinides are discussed elsewhere in this volume [in the chapter by Morss (ch. 122)]. 

Oxide-halides of the alkaline-earth-hke divalent lanthanides, OlGlXe (R = Eu, Yb, Sm) are discussed in The Divalent State in Solid Rare Earth Metal Halides. Although, these have the topology of cluster complexes with isolated... 

For all three halates (in the absence of disproportionation) the preferred mode of decomposition depends, again, on both thermodynamic and kinetic considerations. Oxide formation tends to be favoured by the presence of a strongly polarizing cation (e.g. magnesium, transition-metal and lanthanide halates), whereas halide formation is observed for alkali-metal, alkaline- earth and silver halates. 

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