Halide trivalent lanthanides

Divalent lanthanide chemistry has been dominated by the most readily accessible divalent lanthanide metals samarium(II), europium(II), and ytterbium(II) (classical ) for decades, and a large number of divalent lanthanide compounds have been prepared [92], There are three routes to generate divalent organolanthanide complexes oxidative reaction of lanthanide metal, metathesis reaction of a divalent lanthanide halide, and reductive reaction of a trivalent lanthanide complex. 

To the melts containing a trivalent cation belong a great number of systems of alkali metal halide-rare earth metal halide systems. Lanthanide halides play an important role in the production of lanthanide metals by molten salt electrolysis and they are also used in a number of applications ranging from lighting to catalysis, through pyrochemical reprocessing of nuclear fuel. 

If the sample contains plenty of inorganic cations, the trace components of the solutions can be separated by precipitation of the main components with a suitable reagent or by increasing the pH of the solution. However, some suitable metal cation must usually be added into the solution to obtain sufficient precipitation. Commonly used cations are Fe Al, trivalent lanthanide, Mn , and Mg ions. Compounds to be precipitated are often hydroxides, halides, sulfides, or sulfates. The cation used must not cause any interference in the determination, and it must be added in sufficient quantity to ensure adequate precipitation. 

The formation and disruption of M-M bonds through chemical reactions can be performed reversibly with the hydride halides of the trivalent lanthanides whose structures are closely related to that of Gd2Q2C2. 

The Lewis acid and coordinating properties of trivalent lanthanides were used very early. In 1922, lanthanide trichlorides were compared to other metal halides as catalysts for acetalization (38). The first detailed study of the application of lanthanide derivatives to problems of organic synthesis seems to be the report of Pratt in 1962 (39) who showed that CeCl is a superior catalysts for the regioselective addition of p-toluidine on 5,8-quinoline-quinone (followed by reoxidation) (eq.j 26j). 

Several patents for the polymerization of ethylene using divalent and trivalent lanthanides have been applied for although details are very sketchy. Workers at Montell Co. filed a very broad patent disclosing the use of lanthanide and transition metal complexes containing polysubstituted ansa-bridged indenyl ligands as catalyst components (presumably in the presence of MAO) for olefin polymerization. Both mononuclear halides and binuclear hydride-bridged spe-... 

Table 14 summarizes the trivalent lanthanide halide vapor complexes which have been studied by means of spectrophotometry. Among the binary systems involving Group-IIIA trihalides, chlorides are by far the most extensively studied systems. The overall spectra of vapor complexes are similar to those observed in aqueous solutions (Carnall 1979) or in other (e.g. glass) media (Reisfeld 1975) in terms of transition energies but the hypersensitive transition intensities were foimd to vary. However, the hypersensitive intensity ( G5/2 <— 19/2) of Nd-Al-Cl vapor complexes compares well with the result... 

The study of coordination compounds of the lanthanides dates in any practical sense from around 1950, the period when ion-exchange methods were successfully applied to the problem of the separation of the individual lanthanides,131-133 a problem which had existed since 1794 when J. Gadolin prepared mixed rare earths from gadolinite, a lanthanide iron beryllium silicate. Until 1950, separation of the pure lanthanides had depended on tedious and inefficient multiple crystallizations or precipitations, which effectively prevented research on the chemical properties of the individual elements through lack of availability. However, well before 1950, many principal features of lanthanide chemistry were clearly recognized, such as the predominant trivalent state with some examples of divalency and tetravalency, ready formation of hydrated ions and their oxy salts, formation of complex halides,134 and the line-like nature of lanthanide spectra.135... 

No, the editor did not know what this name meant either.) It means salts of the trivalent anions of Group V, restricted in [1] to arsenides, antimonides and bismu-thides and prepared by reaction of sodium pnictides with anhydrous halides of transition and lanthanide metals. This violently exothermic reaction may initiate as low as 25°C. Avoidance of hydrated halides is cautioned since these are likely to react uncontrollably on mixing. Another paper includes a similar reaction of phosphides, initiated by grinding [2]. Nitrides are reported made from the thermally initiated reaction of sodium azide with metal halides, a very large sealed ampoule is counselled to contain the nitrogen [3]. 

The absence of reliable thermodynamic data for the tetrafluorides has contributed to difficulties in defining the chemistry of the rare earth elements. The fact that only Ce, Pr, and Tb form stable Rp4(s) phases has been established (see section 2.4) however, the thermochemistry of these fluorides has remained uncertain. Insight is provided by the work of Johansson (1978), who has correlated data for lanthanide and actinide oxides and halides and derived energy differences between the trivalent and tetravalent metal ions. The results, which have been used to estimate enthalpies of disproportionation of RF4 phases, agree with preparative observations and the stability order Prp4< TbP4 < CeP4. However, the results also indicate that tetravalent Nd and Dy have sufficient stability to occur in mixed metal systems like those described by Hoppe (1981). 

RXH. The hydride halides RXH of the divalent rare earth metals have been known for a long time. All of them, EuXH, YbXH with X = Cl, Br, 1, and SmBrH (Beck and Limmer 1982) crystallize in the PbFCl-type structure, which is also adopted by the hydride halides of the alkaline earth metals MXH (Ehrlich et al. 1956), by the mixed halides RXX of divalent lanthanides, and many oxyhalides ROX of the trivalent metals. The colorless compounds RXH of R = Sm, Eu, Yb therefore have to be addressed as normal salts. The hydrogen content of these compounds is strictly stoichiometric. 

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. 

The thermochemistry of rare-earth trifluorides was summarized in Gmelin Hand-buch (1976) and the thermochemistry of rare-earth tribromides and triiodides was summarized in Gmelin Handbuch (1978). The thermochemistry of trivalent rare-earth trichlorides was critically assessed by Morss (1976). Enthalpies of formation of most of the lanthanide tribromides were determined by Hurtgen et al. (1980). Thermodynamic properties for europium halides were assessed by Rard (1985). Only enthalpies of formation of Sc, Y, Dy and Tm triiodides have been redetermined since the classical work of Hohmann and Bommer (Morss and Spence 1992). A recent set of literature values of enthalpies of formation of rare-earth solid and gaseous trihalides has been published, accompanied by Born-Haber cycle estimated values for all trihalides (Struck and Baglio 1992). 

Aryls Alkyl Homogeneous Catalysis The Electronic Stmcture of the Lanthanides Variable Valency Solvento Complexes of the Lanthanide Ions Lanthanides Coordination Chemistry The Divalent State in Solid Rare Earth Metal Halides Lanthanides Comparison to 3d Metals Trivalent Chemistry Cyclopentadienyl Tetravalent Chemistry Organometallic Organic Synthesis. 

The first compounds with lanthanide chalcogen bonds were prepared with ancillary Cp or Cp Ugands (see Trivalent Chemistry Cyclopentadienyl), because at the time it was believed that Cp steric demands were necessary to control chemical reactivity, and because the solubility of products in hydrocarbon solvents limited potential side reactions. Metathesis reactions governed by the insolubility of alkali halides were initially investigated (Reaction 1), but eventually a host of synthetic approaches were successfully employed. Compounds have been prepared by reduction of RE-ER with divalent Ln (Reaction 2), where the driving force of the reaction is increased stability associated... 

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