Rare-earth halides

Fig. 6.1b) in which twelve inner ligands bridge the edges of the Me octahedron, and six outer ligands occupy apical positions, predominate. These units are found in reduced zirconium, niobium, tantalum, and rare-earth halides, and niobium, tantalum, molybdenum and tungsten oxides [la, 6, 10]. 

Ames Laboratory (Iowa State University, USA) investigating new solid state phases based on reduced rare earth halides. Since 1993, she has held a position at the University Jaume 1 of Castello (Spain) and became Associate Professor of Physical Chemistry in 1995. During the second semester of 2005, she held a visiting professor position at the Laboratory of Chemistry, Molecular Engineering and Materials of the CNRS-Universtity of Angers (France). Her research has been focussed on the chemistry of transition metal clusters with special interest in multifunctional molecular materials and the relationship between the molecular and electronic structures of these systems with their properties. She is currently coauthor of around 80 research papers on this and related topics. 

G. Meyer, The syntheses and structures of complex rare-earth halides, Progr. Solid State Chem. 14 (1982) 141. 

SmCl3 resulted in the reduction only to SmC. From NdCl3 + Ca with the addition of Fe powder, the alloy Nd2Fei7 was obtained. In a discussion of the results it was observed that the products obtained at ambient temperature by mechanical alloying are the same which result from the conventional metallothermic reduction of the rare earth halides. However, the metallothermic reduction requires a temperature of 800-1000°C for the reduction of the chlorides and 1400-1600°C for the fluorides. The products of the mechanical process, on the other hand, are fine, amorphous or microcrystalline, highly reactive metal powders mixed with CaCl2. 

Various methods [282] have been used to prepare anhydrous chlorides of the rare earths. Taylor and Carter [283] describe a general method for the preparation of high purity anhydrous halides in good yield. This method involves heating in vacuo, a molecularly dispersed mixture of hydrated rare earth halide with proper ammonium halide until the water and ammonium halide are expelled. All the trihalides except the iodides of Sm and Eu can be obtained using this proceedure. In the case of Sm and Eu the divalent iodides, Sml2 and Eul2 are obtained. 

It is easy to reduce anhydrous rare-earth halides to the metal by reaction of more electropositive metals such as calcium, lithium, sodium, potassium, and aluminum. Electrolytic reduction is an alternative in the production of the light lanthanide metals, including didymium, a Nd—Pr mixture. The rare-earth metals have a great affinity for oxygen, sulfur, nitrogen, carbon, silicon, boron, phosphorus, and hydrogen at elevated temperature and remove these elements from most other metals. 

The first suggestions on active species in rare earth halide-based catalyst systems date back to 1976 [603,604]. In 1980 Shen et al. formulated the structural element of the active species in Ln-halide-based systems on the basis of these early suggestions (Scheme 19) [92]. 

Rare earth halide (in particular NdCl3)-based compounds are very active catalysts for polymerization of dienes. The products are polymers with improved elastic and thermoplastic properties caused by high stereo regularity. The polymerization process is highly efficient (i.e.) 60 000 moles of butadiene are polymerized by one atom of rare earth. Hence the demand for rare earth compounds as polymerization catalysts is low. 

According to the coordination states of rare earth, previous studies have classified the rare earth halides complex A ,RX (A = alkali and /or... 

During the past two decades, nanomaterials have captivated the materials research field wifh fhe great promise of exciting applications in science and technology. Manipulation of lanthanide-doped rare earth halide NCs has led to important modulations of their optical properties in terms of excited sfafes, emission profiles, and efficiencies. Meanwhile, fhe successful preparation of rare earth halide nanomaterials have opened the pathways for finding new properties, and concurrently, the performance of fheir macroscopic counterparts can be conserved in the nanometer regime. In this chapter, we will focus primarily on the developments in the s)mthesis, properties, and potential applications of rare earth halides and their derivative NCs. 

Some General Remarks. The energies and intensities of the absorption maxima found in rare-earth halide vapor spectra are brought together in Table VI. 

Gaseous Rare-Earth Halide Absorption Maxims... 

Bromides and Iodides. The absorption spectra of the gaseous rare-earth halides were measured with a Cary 14 H spectrophotometer. The experimental procedure has been described previously 11). In this study a double furnace was used, allowing the rare-earth halide vapor to be heated to a higher temperature than the solid or liquid and allowing a baseline determination at the temperature of interest. In addition, a 0 0.1 full scale optical density slidewire was employed with the Cary... 

Since no accurate vapor pressure data are available for the erbium and thulium hahdes, the molar absorptivities were determined directly from a weighed amount of the respective rare-earth halides. Good results could be obtained from this method if the respective halogen, bromine, or iodine were added to the cell such that its pressure at 1000°C. was 1 atm. This procedure greatly reduced the reaction of the rare-earth... 

All the rare-earth halides were prepared by the ammonium halide method described by Taylor and Carter (24) and were used without further purification. The rare-earth oxides (Michigan Chemical) used to prepare the halides were of 99.8% purity or better. 

Boghosian S, Papatheodorou GN (1996) Rare earth halide vapors and vapor complexes. In Gschneidner KA, Eyring LR (eds) Handbook on the physics and chemistry of rare earths. North Holland Elsevier, Amsterdam... 

Very recently, a process for dehydrating hydrated rare earth halides, typically hexahydrates, with phosgene was patented [1612a]. 

This method has been applied by Gaune-Escard et al. (1996a), Rycerz and Gaune-Escard (1999), and Gaune-Escard and Rycerz (1999) to several rare earth halides and their compounds with alkali metal halides. 

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