Vaporization lanthanide oxides

Oxides. Decomposition pressure measurements on the TbO system by Eyring and his collaborators (64) have been supplemented by similar and related studies on the PrO system (46) and on other lanthanide-oxygen systems (43, 44). Extensive and systematic studies of vaporization processes in lanthanide-oxide systems have been undertaken by White, et al. (6, 188,196) using conventional Knudsen effusion measurements of the rates of vaporization of the oxides into high vacuum. Combination of these data with information on the entropies and Gibbs energy functions of reactants and products of the reaction yields enthalpies of reaction. In favorable instances i.e., if spectroscopic data on the gaseous species are available), the enthalpies of formation and the stabilities of previously undetermined individual species are also derived. The rates of vaporization of 17 lanthanide-oxide systems (196) and the vaporization of lanthanum, neodymium, and yttrium oxides at temperatures between 22° and 2700°K. have been reported (188). 

With the lanthanide sesquioxides, the high-temperature vapor species encountered above the molten or solid oxides range from R, RO, RjO and R2O2. Thermodynamic properties of the lanthanide oxides have been given in section 1 and are therefore only reviewed briefly in this section for ease of comparison. 

It is not feasible to consider conventional-type studies (structure, vaporization behavior, etc.) for the transeinsteinium oxides, given their scarcity and short lifetimes. Presumably their oxide chemistry would be very similar to that of the lanthanide oxides, especially for the trivalent oxidation state. However, there is an increased tendency for actinides in the second half of the series toward divalency. This suggests that the monoxides of the higher actinides (e.g., transeinsteinium elements) could be potentially more stable, perhaps approaching the stability of Eu monoxide. With No (element 102 homolog of Yb), the monoxide could be its most stable oxide. 

The yield and rate of the tantalothermic reduction of plutonium carbide at 1975 K are given in Fig. 3. Producing actinide metals by metallothermic reduction of their carbides has some interesting advantages. The process is applicable in principle to all of the actinide metals, without exception, and at an acceptable purity level, even if quite impure starting material (waste) is used. High decontamination factors result from the selectivities achieved at the different steps of the process. Volatile oxides and metals are eliminated hy vaporization during the carboreduction. Lanthanides, Y, Ti, Zr, Hf, V, Nb, Ta, Mo, and W form stable carbides, whereas Rh, Os, Ir, Pt, and Pd remain as nonvolatile metals in the actinide carbides. Thus, these latter elements... 

There are just few examples of authentic lanthanide complexes in the oxidation state zero. Bis(arene) complexes of the lanthanides (l,3,5- Bu3C6H3)2Ln (Ln = Sc, Y, La, Nd, Pr, Sm, Gd, Tb, Dy, Ho, Er, Lu) have been synthesized by cocondensation of metal vapors (see Metal Vapor Synthesis of Transition Metal Compounds) with 1,3,5-tri(ferf-butyl)benzene at 75 K. A sandwich structure with coplanar arene ligands has been proven by X-ray crystal structure analysis of the Gd and Ho complexes (Figure 86a). 

The metal vapor technique, in which a metal is vaporized from a resistively heated tungsten container under high vacuum and is cocondensed with a potential ligand at -125 to -196°C, had proven useful in the synthesis of a variety of unusual low-valent transition metal complexes (67-71). With lanthanide metals, this method not only has generated low oxidation state species, but it has also provided the opportunity to study zero-valent lanthanide chemistry on an atomic/molecular basis for the first time. These studies have been important in identifying new directions in organolanthanide chemistry. 

Lanthanide metal vapor reactions with unsaturated hydrocarbons such as CsHft (75) or CgHg (76), which are readily reduced by electropositive metals to common anionic ligands, give products arising from the reduction of the ligand and oxidation of the metal [Eqs. (24)-(26)]. The products of... 

The interaction of a lanthanide metal with a substrate such as 3-hexyne could occur in several ways 60) by it complex formation, by oxidative addition into a C—H bond, or by reduction involving radical species. Subsequent lanthanide metal vapor studies were designed to test some of these possibilities. Co-condensation of lanthanide metal vapor with reagents containing acidic hydrogen atoms, e.g., terminal alkynes, demonstrated that oxidative addition of C—H was a viable reaction [Eqs. (32) and (33)] 51). These reactions also provided access to a new class of... 

Creating metal oxide based advanced materials using lanthanide alkoxide complexes as molecular precursors is another area where the lanthanide alkoxide chemistry has found significant applications [5, 7-10]. A technique heavily used in the semiconductor industry for the growth of metal oxides materials is the process of metal-organic vapor chemical vapor deposition... 

Enthalpies of sublimation based on Knudsen effusion measurements have been determined for LaBe by Gordienko, et al. (57). The thermodynamics of formation of lanthanide hexaborides from oxides have been deduced by Portnoi, et al. (162) vaporization and stabilities have been studied by Smith (168). 

Direct reactions of anhydrous triflic acid with lanthanide chlorides or oxides often resulted in complexes solvated by the acid, which are viscous liquids with a very low vapor pressure. Thus it is advisable to perform reactions with diluted trific acid in an aqueous solution. If anhydrous lanthanide chlorides are used, they are to be hydrated with care in water before use in order to avoid contamination by side products. For instance, anhydrous ScCl reacts violently with water, the sample is first cooled at -180 °C and water is added slowly. The mixture is then warmed in 12 h to room temperature. The anhydrous compound, ScCl -nH O (n= 3.7) is obtained as a white solid after boiling the solution to dryness. 

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