Solid rare earth complexes

The field of rare earth complexes is quite large and hence it is important to define the scope of discussion to be presented here. We will confine the discussion to representative types of ligands which form solid rare earth complexes and have been identified and characterized. The coverage will of necessity be brief and not encyclopedic in nature. However, as far as possible, examples of all the major types of complexes will be given, especially complexes of unusual significance. Some reviews on solid rare earth complexes of common ligands have appeared in the literature [134-136]. 

The first reported laser action in rare earth complexes was obtained by Lempicki and Samelson [656] for europium benzoylacetonate in alcoholic solution. The laser parameters for this complex have also been evaluated by Lempicki and coworkers [656, 660] who found a slightly better quantum efficiency (0.8) for europium benzoylacetonate than for ruby (0.7), the solid state laser. The laser action of europium benzoylacetonate has also been investigated by Schimitschek [661] and Bhatjmik et al. [662]. Some other complexes of Eu3+ viz. dibenzoylmethide [665,664], m-4,4,4-trifluoro-l(2-thienyl)-l,3-butanedione [665], thenoyl-trifluoroacetonate [666, 667] were also found to lase. 

TMOS, TEOS, ORMOSIL, and TEOS/polystyrene hybrid gels compared to corresponding crystalline solids (124, 125, 129, 130). The presence of heterogeneous microenvironments that encapsulate the rare earth complexes within xerogel matrices explains this broadening phenomenon (128). 

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. 

In order to fully understand the crystal chemistry of the anhydrous LnXs and their solvates ([LnXj(solv) ]), the Ln atomic properties of these species must be considered. The predominant oxidation state for LnX species is the +3 state however, for a number of these cations, tiie +2 (see The Divalent State in Solid Rare Earth Metal Halides) and +4 (see Tetravalent Chemistry Inorganic) states are available. Since the bonding in these compounds is mainly ionic, the cation size and sterics of the binding solvent play a significant role in determining the final crystal structures isolated. The ionic nature of the LnX complexes makes... 

The pattern as seen in Figure 5 may be transferred to a periodic table of the rare earth elements, see Figure 6. Only elements underlaid in red form clusters. The lower I3 is, the easier it is to produce cluster complexes. Elements underlaid in blue form stable divalent compounds, for example EUCI2 the divalent state with the electronic configuration 4f 5d° (with n =7, 14, 6, 13 for R = Eu, Yb, Sm, Tm) has the highest stability and, thus, is the easiest to achieve when the third ionization potential is the highest. The divalent chemistry of these elements is alkaline-earth and saltlike this is described in The Divalent State in Solid Rare Earth Metal Halides. 

The synthesis of compounds of the lanthanides containing cluster complexes follows in general the same routes as described in The Divalent State in Solid Rare Earth Metal Halides, the conproportionation route and the metallothermic reduction route, for example... 

Oxide-halides of the alkaline-earth-hke divalent lanthanides, OlGlXe (R = Eu, Yb, Sm) are discussed in The Divalent State in Solid Rare Earth Metal Halides. Although, these have the topology of cluster complexes with isolated... 

It is easy to understand that, the precondition for the research on atypical amphiphilic rare earth complexes in Langmuir-Blodgett (LB) films is to fabricate them into LB films, which generally involves two steps i) obtain stable monolayers, ii) successfully transfer them from monolayers to solid substrates. Since all the complex molecules in a sphere shape have no long aliphatic chains, necessary procedures should be adopted during each step. Here we would emphasis on the optimised fabrication conditions as follows. 

The composite subphase mentioned above is the key factor for the stable rare earth complex monolayers at air/liquid interface. During monolayer transfer process, it is found that the monolayers are too rigid to transfer onto solid substrates. The conventional film-forming molecule AA with a long aliphatic chain was mixed with them in the spreading solution in a molar ratio of 1 1. The obtained mixed LB films emitted homogeneous intense fluorescence. So the use of a fatty acid AA is the key factor for the monolayer transfer during LB film fabrication. 

In a summary for the LB film fabrication of the atypical amphiphilic rare earth complexes, the optimised experimental conditions are a composite subphase, AA mixed with rare earth complexes in a molar ratio of 1 1, hydrophobic substrate, a deposition speed of 5mm min and air-dry the LB films after the even layers. The deposition surface pressure is 20 mN-m", corresponding to a solid state monolayer. All experiments were carried out at room temperature (25 1°C). 

The optical luminescence exhibited by some of the rare earth complexes and ions in solids has been utilized for the detection and determination of the rare earths at the trace and ultratrace levels for many years (El Yashevich, 1953 Dieke, 1968 Sinha, 1966). To date, optical luminescence of the rare earth ions in solids has been excited by flames (candoluminescence) (Neunhoeffer, 1951 Sweet et al., 1970) by ultraviolet or visible radiation (photoluminescence or UVEOL) (Ankina Ozawa/snrf ]trp 1968 Poluektov et al., 1971 ) by... 

The primary products from iron catalysts are linear polyethylenes and aluminum polymeryls. The iron complexes can be prepared in a few simple steps and are not particularly sensitive to air, contrasting with many metallocenes of group 111 and IV or rare earth complexes. A body of literature on ethylene polymerization studies with these complexes allows a picture to be created of the catalytic action [31]. Here, a summary is given oti the catalytic activity of these complexes, also in combination with solid supports, and an outlook towards the preparation of composites. 

In general, the ionic radii give an indication of the expected coordination number in a rare earth complex, though this is more apparent in aqueous solutions than in the solid state, where bulky ligands and different coordination modes may result in unexpected CNs. Scandium with its smaller ionic size has a significantly lower average coordination number than the other rare earths. The properties of scandium and yttrium, which are partly due to the ionic radii, are discussed in relation to those of the lanthanides in section 1.3.4. 

A number of different factors have directed attention to the oxohalogen rare earth compounds and classes of compounds. For instance, the perchlorates have mainly in solution been studied for their coordination types, while the iodates have been studied for their solid state properties. Because of the great number of papers published in this area, the present review will focus almost exclusively on the investigations of solid compounds. A brief account of perchlorate solutions, which are of central importance in rare earth complexation studies, is given in section 6.3. 

Solid rare earth chlorites can be synthesized only at lowered temperatures because at room temperature the concentrated solution decomposes before crystallization. Anhydrous chlorites are known for scandium and cerium. Sc(C102)3 is formed only in a reaction of aqueous suspension of Sc(OH)3 with gaseous CIO2. The formation of a complex in solution has been confirmed by... 

It has been established that the apparent volatilities of transition and rare-earth metal halides are increased by several orders of magnitude through reactions of type (1) and (2) giving rise to vapor complex formation. The enhancement of the vapor densities of transition metal and/or rare-earth metal ions has commonly (see for example Papatheodorou 1982) been reported in the form of the uolatility enhancement factor. That is, when a reaction occurs between a solid rare-earth halide with low vapor pressure Ps (e.g. NdCb) and a more volatile salt (carrier gas) with partial pressure P (e.g. AlCl3,NaCl), and the partial pressure of the vapor complex is Pq, then the volatility enhancement factor is determined at unit pressure of the carrier gas as ... 

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