Lanthanide vaporization

The unexpected finding that the oscillator strengths of the hypersensitive transitions in lanthanide vapor spectra are larger than in many... 

Co-deposition of a monoatomic lanthanide vapor (Sm, Eu, Tm, Yb) and tri-/-butylbenzene, 1 TS-Bu jCt.Hj, onto a cold (77 K) surface afforded matrices that contained zero-valent bis(r/ -arene (lanthanide complexes of the form Ln( 6-C6H3But3-l,3,5)2 as formed in macroscale co-condensation reactions using metal vapor synthetic (MVS)... 

The L absorption spectra in lanthanide vapors may be interpreted through this type of approximation. Figure 8 models an atomic Lm absorption spectrum through a superposition of a lifetime broadened distribution of atomic oscillator strengths and an arctan shaped continous absorption. Due to the relatively large core hole... 

Fig. 8. Lanthanide Lm absorption constructed from a superposition of 2p3/2-nd (n = 5 - 00) atomic absorption lines and an arctan curve representing the continuous absorption. The onset of the continuous absorption is fixed at the series limit (n = oo) of the underlying optical spectrum. F indicates the total L ] core level width (3 eV). The resulting spectral shape matches that of the Lm absorption in lanthanide vapors (fig. Ida).

The lanthanides are considered only slightly toxic in the Hodge-Stemer classification system and are safely handled with ordinary care (15). Inhalation of rare-earth vapors or dust should be avoided, and the skin washed thoroughly if it comes into contact with any dust or solution. 

The criterion based on the vapor pressure holds for actinide Th and U, being non-volatile (their vapor pressures are much lower than La), were recently found to be encapsulated in a form of dicarbide, ThC2[25] and UC2[26], like lanthanide. 

The metal vapor method also has played an important role in the development of organometallic lanthanide chemistry (6-10). This high energy technique demonstrated that the lanthanide metals had a much greater range of organometallic chemistry than had been assumed previously. The metal vapor technique applied to lanthanides identified reasonable new research goals which could subsequently be pursued by solution techniques. Not only the metal vapor reactions. 

Metal vapor chemistry showed that the lanthanides had quite an extensive chemistry with unsaturated hydrocarbons. Some of the early surveys of metal vapor reactions with unsaturated hydrocarbons included some lanthanide metals and showed that reactivity was present for these metals (14-18). Subsequent synthetic studies in which the products were isolated and characterized led to some of the most unusual organolanthanide complexes currently known (19-28). 

In each case, the metal was 500-1600°C depending on the vapor was cocondensed with vaporized at temperatures ranging from specific lanthanide involved and the the unsaturated hydrocarbon at -196°C. ... 

Although the structures of these species were not determined, this metal vapor chemistry clearly showed that unsaturated hydrocarbons were viable reagents for lanthanides. Furthermore, this high energy technique showed that new regimes of organolanthanide complexes were accessible under the appropriate conditions. In addition, attempts to understand the synthesis of the products in reac-... 

The simple hydrocarbon substrates included ethene, 1,2-propa-diene, propene and cyclopropane (22). Their reactivity with Sm, Yb and Er was surveyed. In contrast to the reactions discussed above, lanthanide metal vapor reactions with these smaller hydrocarbons did not provide soluble products (with the exception of the erbium propene product, Er(C H ) ). Information on reaction pathways had to be obtained primarily by analyzing the products of hydrolysis of the metal vapor reaction product. 

Lanthanide metal vapor studies with CO have also been done Slater, J. L. DeVore, T. C. Calder, V. Inorg. Chem. 1973, 12, 1918 1974, 13, 1808. 

Lanthanide metal vapor studies with acetylacetone have also been... 

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... 

Fig. I. Methods for forming metal vapors, (a) Evaporation from a resistance-heated, alumina-coated Mo or W spiral. This is a method suitable for Cr, Mn, Fe, Co, Ni, Cu, Pd, Ag, Au and other metals that do not attack alumina, (b) Evaporation from a resistance-heated Ta or W boat. This method is useful for V, Cr, and some lanthanides, (c) Sublimation from a resistance-heated free-hanging loop of wire, e.g., Ti, Mo, or W. (d) Evaporation from a cooled hearth using laser or electron bombardment heating. This method may be used with all metals.

Matrix isolation studies usually permit spectroscopic observation of the species M(CO), M(CO)2,. M(CO) , the coordinatively saturated molecule. In some early studies, species thought to be simple unsaturated carbonyls were in fact carbonyls of metal clusters Mx(CO) a very low concentration of metal in the matrix (e.g., I mol in 104 mol noble gas) has to be used to prevent clustering. All the partially coordinated carbonyls are only matrix species, that is, they only exist when completely isolated from other molecules of their own kind or from CO. The coordinately saturated carbonyls are of more interest in the context of this review. The following new molecules have been reported Au(CO)2 (84a) Ag(CO)3, Cu2(CO)6 (46, 87) Pd(CO)4 (22), Pt(CO)4 (69) Rh2(CO)g, Ir2(CO)g (37) M(CO)6[M = Pr, Nd, Gd, Ho, Yb (100), Ta (24), U (117)]. The Cu, Pd, Pt, Rh, and Ir carbonyls can be obtained by condensing the metal vapors with pure CO at 40 K and then pumping off excess CO to leave a film of the carbonyl. The Cu, Pd, and Pt carbonyls decompose under vacuum temperatures above -100°C, and the Rh and Ir carbonyls dimerize with loss of CO to give M4(CO)12 above -60°C. The gold and silver carbonyls are not stable outside matrix isolation conditions. Unfortunately, the literature is presently unclear about the stability of the Ta and lanthanide hexacarbonyls outside a matrix. 

The synthetic potential of transition metal atoms in organometallic chemistry was first demonstrated by the formation of dibenzenechrom-ium (127). Apart from chromium, Ti, V, Nb, Mo, W, Mn, and Fe atoms each form well-defined complexes with arenes on condensation at low temperatures. Interaction has also been observed between arenes and the vapors of Co, Ni, and some lanthanides. Most important, the synthesis of metal-arene complexes from metal vapors has been successful with a wide range of substituted benzenes, providing routes to many compounds inaccessible by conventional reductive preparations of metal-arene compounds. 

Lanthanide and actinide complexes. Ln(L-L)) and An(L-L)4, of sterically hindered diketonates [e.g.. [Me3CC(0)CHC(0)CMej] fdpm) and [F CCF2CF2-CfOICHQOJCMeJ (fed)], are of considerable interest because of their volatility. Despite their high molecular weights, they have measurable vapor pressures at temperatures below the boiling point of water. This volatility has been exploited in... 

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