Ytterbium oxidation states

Ytterbium, trinitratotris(dimethyl sulfoxide)-structure, 1, 97 Ytterbium, tris(acetylacetone)(4-ammo-3-penten-stereochemistry, 1,81 Ytterbium complexes acetylacetone, 2,373 dipositive oxidation state hydrated ions, 3,1109 polypyrazolylborates, 2,255 Ytterbium(III) complexes ethyl glycinate, diacetate... 

Rare-earth ions inserted in the tetraborides have the 34- oxidation state, except for CeB4 and YbB4 (see Fig. 2). The abnormal volume contraction for the CeB4 unit cell can be explained by the presence of some Ce ions . Recoilless y-ray emission spectra and magnetic measurements indicate that ytterbium in YbB4 has an intermediate valence state as in YbAl3... 

Europium and ytterbium di-valence. The oxidation state II for Eu and Yb has already been considered when discussing the properties of a number of divalent metals (Ca, Sr, Ba in 5.4). This topic was put forward again here in order to give a more complete presentation of the lanthanide properties. The sum of the first three ionization enthalpies is relatively small the lanthanide metals are highly electropositive elements. They generally and easily form in solid oxides, complexes, etc., Ln+3 ions. Different ions may be formed by a few lanthanides such as Ce+4, Sm+2, Eu+2, Yb+2. According to Cotton and Wilkinson (1988) the existence of different oxidation states should be interpreted by considering the ionization... 

Since ytterbium has both a +2 and +3 oxidation state, it can form two different compounds with the halogens. See the following examples ... 

Changes in oxidation state can have a significant effect on the volatility of some elements, including cerium, ytterbium, tungsten, and molybdenum, all of which are refractory in reducing conditions but become increasingly volatile as conditions become more oxidizing. 

This chapter commences with a review of a limited number of ternary hydride systems that have two common features. First, at least one of the two metal constituents is an alkali or alkaline earth element which independently forms a binary hydride with a metal hydrogen bond that is characterized as saline or ionic. The second metal, for the most part, is near the end of the d-electron series and with the exception of palladium, is not known to form binary hydrides that are stable at room temperature. This review stems from our own more specific interest in preparing and characterizing ternary hydrides where one of the metals is europium or ytterbium and the other is a rarer platinum metal. The similarity between the crystal chemistry of these di-valent rare earths and Ca2+ and Sr2+ is well known so that in our systems, europium and ytterbium in their di-valent oxidation states are viewed as pseudoalkaline earth elements. 

Although all the lanthanides are stable in the solid state as M2+ ions doped into CaF2 crystals, only in the cases of europium, ytterbium and samarium is there any real coordination chemistry, and that is very limited. There is a small but developing organometallic chemistry of the lower oxidation states,641 but that is not within the scope of the present review. Much of the chemistry of the dipositive state depends on solvated species642 and it is convenient to begin with these. 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniste. M(NHJ)jr, is formed. Lanthanide elements with stable +2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and teUraalkybmmonium halides yields blue solutions, presumably containing AP+, 3e Be2, 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexameihytphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

In 1956 it was found that europium and ytterbium dissolve in liquid ammonia with the characteristic deep blue color known for the alkali and alkaline earth metals [36-40]. This behavior arises from the low density and high volatility of those metals compared to the other lanthanide elements [41]. Samarium, which normally also occurs in the divalent oxidation state, does not dissolve under... 

Active catalyst species or catalysis intermediates can often be trapped by stoichiometric reactions of the precatalyst with the substrate. The following example describes the successful isolation of such an intermediate with participation of Ln-O cr-bonds. Reduction processes mediated by low oxidation states of the lanthanide elements are of special interest in organic synthesis [256]. One of the most intensively studied reactions is the stoichiometric reduction of arylketones by rare earth metals ytterbium and samarium [277]. Thus formed dianions possess high nucleophilic character and excess lanthanide metal can even accomplish complete cleavage of the C-O double bond (Scheme 36). 

The rare earth must have a reasonably stable +2 oxidation state, although the majority of the material must be in the +3 state. The elements europium (Eu) and ytterbium (Yb) have by far the most stable +2 oxidation states of the rare earths, and the oxides of these elements make the most effective matrices for anion emission. Eu is approximately two orders of magnitude more effective as a matrix that Nd when perrhenate emission is not pushed to high levels. 

Xe-like electronic configuration is adopted. The + 2 oxidation state is most relevant for samarium (f6, near half-filled), europium (f7, half-filled), thulium (f13, nearly filled) and ytterbium (f14, filled). In order to attain the more stable + 3 oxidation state, Sml2 readily gives up its final outer-shell electron, in a thermodynamically driven process, making it a very powerful and synthetically useful single-electron transfer reagent. 

In halides lower oxidation states are more stable than in oxides. In most oxide lattices europium and ytterbium are the only lanthanide ions which, because of... 

Consistent with the stability of the divalent oxidation states see Formal Oxidation State) of ytterbium and europium, the triflates of Yb(III) and Eu(III) are reduced by the bis(trimethylsilyl)allyl anion, leading to Ln(II) species (equation A) The same compounds can be made in higher yield by starting with Yb(II) and Eu(II) triflates directly. 

In aqueous solution, lanthanides are most stable in the tripositive oxidation state, making them difficult to separate and purify. The preference for this oxidation state is due in part to the energy of the 4f electrons being below those of the 5d and 6s electrons (except in the cases of La and Ce). When forming ions, electrons from the 6s and 5d orbitals are lost first so that all Ln + ions have [Xe] 4f electronic configurations. Under reducing conditions, certain lanthanides (europium, samarium, and ytterbium) can be stable as dipositive ions, and cerium can adopt a +4 oxidation state (5). 

Boussie, T.R., Eisenberg, D.C., Rigsbee, J. et al. (1991) Structures of organo-f-element compounds differing in the oxidation state of the central metal crystal structures of bis([8]annulene) complexes of cerium(lV), ytterbium(III), and uranium(III). Organometallics, 10, 1922. 

Ytterbium has the oxidation states 4-2 and -t-3. A stereochemical dichotomy exists in their enolate chemistry . Yb(II) enolates react with aldehydes to form the erythro-fi-hydroxyketones while Yb(III) enolates yield the threo stereoisomers. We fail to understand this by either thermodynamic or mechanistic reasoning. Analogous to corresponding reaction chemistry for samarium, preformed ytterbium benzophenone dimer, [Yb(Ph2CO) (HMPA)2]2, reacts " with sterically crowded phenols to form in low yield (5%) the enolate complex 22b by dearomatization of benzophenone. The major product (80%) is the... 

Organolanthanide(III) compounds form the bulk of all the known organo-lanthanides. However, in addition to the + 3 oxidation state, the + 2 oxidation state is chemically accessible for samarium, europium and ytterbium (an organocerium(II) [1] and an organoneodynium(II) [2] complex have also been reported but not structurally confirmed) and the +4 oxidation state is accessible for cerium. A few organolanthanide(O) compounds are also known,... 

Organolanthanide chemistry is dominated by the trivalent compounds. " Compounds in oxidation state (II) are restricted to derivatives of europium, samarium, and ytterbium, but they have considerable importance in both organic and organometallic syntheses because of their reducing properties. " Redox transmetalation reactions of organomercurials with lanthanide metals provide convenient syntheses of a number of diorganolanthanides, for example, R2M, R = CgFj or PhCC, M = Yb or Eu. " °... 

All the rare-earth elements occur in the HI oxidation state in compounds, and can be separated and determined in this form to provide what is known as the total REE. Samarium, europium, and ytterbium also occur in the unstable n oxidation state, whereas cerium, praseodymium, and terbium can be found in the IV oxidation state. 

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