Yb metal vapor

Acetylide hydride complexes of samarium, erbium and ytterbium have been made by the cocondensation reactions of Sm, Er, and Yb metal vapor with 1-hexyne at 77K. Polymeric compounds containing [(BuC C)2SmH], [(BuC C)2ErH] and [(BuC=C)3Yb2H] units are isolated and shown to be active catalysts for hydrogenation reactions (W.J. Evans et al., 1981c). 

The same authors also investigated co-condensation of the Yb metal vapor with 1-hexyne. Organolanthanide products were made in which ytterbium is present predominantly as Yb " " (85-92%). These complexes are highly associated in solution. Oligomerisation may occur via alkylnide bridge (W.J. Evans et al., 1981b). 

In order to explain the experimental results observed in the reaction of 1-hexyne with Yb metal vapor, W.J. Evans (1981b) proposed the following scheme ... 

Thermochemical properties of the lanthanide elements and ions have recently been reviewed by Johnson (1977) and Morss (1976). It is well known that with any particular ligand, the thermodynamic stability of the dipositive oxidation state of the lanthanide varies according to the sequence Eu > Yb > Sm. The ease of preparation of divalent compounds is in the same order. For example, co-condensation of Yb metal vapor with 1-hexyne yields a compound in which Yb is present as 85-92% Yb " in the case of samarium, trivalent products are obtained (W.J. Evans et al., 1981). Eu and Yb cyclooctatetraenyl have been prepared (Hayes et al., 1969), but the samarium compound is as yet unknown. 

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. 

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. 

Terminal alkyne H—C bonds add to Pt(PPh3)j e.g., the reaction with 1-ethynylcyclohexanol gives the trans-dihydride, H2Pt(CCR)2(PPhj)2. Metal vapors of Yb, Sm and Er react with 1-hexyne, and the first step is oxidative addition of the terminal H—C bond. ... 

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)... 

Co and Ni are normally active for the hydrogenolysis of alkanes, whereas Eu and Yb metal powders prepared by the metal vapor technique are not active under similar reaction... 

The Yb metal was the first rare earth metal studied with the de Haas-van Alphen measurement. Tanuma et al. (1967) purified a piece of raw metal by the vacuum distillation method. A single crystal specimen was obtained by spark cutting a large grain in a vapor condensed ingot. The resistivity ratio of the specimen was not reported. The crystal structure was determined to be fee by X-ray analysis at room temperature. Two de Haas-van Alphen frequencies were observed, and the authors suggested that they came from two separate pieces of Fermi surface. Datars and Tanuma (1968) deduced from magnetoresistance measurements at 1.3 K with fields up to 20 KG that there were no open orbits in Yb. Therefore, they concluded that Yb is semimetallic with two small, closed pieces of Fermi surface. ... 

The problem of mixed-valence behavior which is sensitive to particle size has been studied for Sm, Tm and Yb metals. A review paper by Connerade and Kamatak (1990) points out, for vapors and clusters, the main calculations and interpretations which have been done to explain this property. The authors report numerous XAS results which demonstrate experimentally the valence change with cluster size. 

A metal vapor technique provides a very interesting route to the preparation of Sm(II) or Yb(II) organometallic species. Thus W.J. Evans et al. (1980, 1981a, 1982) were able to prepare several substituted dicyclopentadienyl samarium and ytterbium complexes. Sm(C5Mes)2 was the first known soluble divalent organosamarium complex. 

Figure 4 shows vapor pressure curves of rare-earth metals[24], clearly showing that there is a wide gap between Tm and Dy in the vapor pressure-temperature curves and that the rare-earth elements are classified into two groups according to their volatility (viz.. Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, non-volatile elements, and Sm, Eu, Tm, and Yb, volatile elements). Good correlation between the volatility and the encapsulation of metals was recently... 

Some inner transition metals are prepared from oxides on the research scale. Most of the lanthanoid metal are prepared from oxides via halides (see Section 9.2.2.3). A powerful reductant however, is required to produce Sm, Eu, Tm, and Yb, because of the stability of the difluorides of these metals. Since Sm, Eu, Tm, and Yb also have relatively high vapor pressures, they are best prepared by reduction of their oxides ... 

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