Neodymium precursors

Other neodymium precursors such as Nd phosphates and Nd allyls are most commonly applied in combination with alkyl aluminum chlorides. The principles outlined for the selection of the appropriate halide for Nd... 

Lasers are devices for producing coherent light by way of stimulated emission. (Laser is an acronym for light amplification by stimulated emission of radiation.) In order to impose stimulated emission upon the system, it is necessary to bypass the equilibrium state, characterized by the Boltzmann law (Section 9.6.2), and arrange for more atoms to be in the excited-state E than there are in the ground-state E0. This state of affairs is called a population inversion and it is a necessary precursor to laser action. In addition, it must be possible to overcome the limitation upon the relative rate of spontaneous emission to stimulated emission, given above. Ways in which this can be achieved are described below, using the ruby laser and the neodymium laser as examples. 

The addition of dopants is found to have beneficial effects. However, they are not restricted only to transition metals. The hydrogenation of acrylic acid can be promoted significantly by the addition of neodymium ions onto the palladium particles [142], The selective transformation of 3,4-dichloronitrobenzene to the corresponding aniline has been selected to test pre-prepared Pt hydrosols as heterogeneous catalyst precursors (see Figure 3.9) [143],... 

The lanthanide phthalocyanine complexes, obtained by conventional methods starting from metal salts at 170-290°C and phthalonitrile (Example 26), contain one or two macrocycles for each metal atom [5,6,8,63,82,84-98]. Thus, according to Refs. 6,63, and 85, the complexes having compositions LnPc2H, XLnPc (X- is halide anion), and Ln2Pc3 (a super-complex ) were prepared from phthalonitrile as a precursor the ratio of the reaction products depends on the synthesis conditions and the metal nature. The ionic structure Nd(Pc)+Nd(Pc)2 was suggested [85] and refuted [63] for the neodymium super-complex Nd2Pc3 the covalent character of the donor-acceptor bonds in this compound and other lanthanide triple-decker phthalocyanines was proved by the study of dissociation conditions of these compounds [63]. 

Nd2Ni04+5 powder was prepared by nitrate-citrate route as described by Courty, et a1. (1973). Stoichiometric amounts of neodymium and nickel oxides were dissolved in diluted nitric acid. After addition of a large excess of citric acid, the solution was dehydrated and heated until self-combustion of the precipitate to obtain submicronic precursor particles (Boehm, 2005). The final annealing was performed at 1000°C for 12 hours to obtain a single crystalline phase. The particles were then ball milled to obtain an average grain size (d0 5) of about 0.8 pm. A terpineol-based slurry was prepared from this powder and this was deposited on the electrolyte by screen printing and then sintered at 1100°C for three hours in air (Lalanne, 2008). 

Neodymium-based catalysts are favored over other Ln metals because they are highly active and the catalyst precursors are readily available for reasonable prices. In addition, Nd catalyst residues do not catalyze aging of the rubber. The use of didymium catalyst systems is also reported in the literature. Didymium consists of a mixture of the three lanthanides neodymium (72 wt. %), lanthanum (20 wt. %) and praseodymium (8 wt. %). 

Though a vast number of studies on the characteristics of neodymium-mediated polymerizations were performed to the present day, only a few studies focus on the influence of the anion of the Nd precursor. As already mentioned in Sect. 2.1.1.2 Wilson systematically varied the structure of carboxylates and studied the influence on hydrocarbon solubility and on polymerization activity [183]. The dependence of polymerization activity on various halogenated Nd-carboxylates Nd(OCOR)3 (R = CF3, CCI3, CHCI2, CH2C1, CH3) was the target of a study by Kobayashi et al. [ 177]. 

The solubility of neodymium carboxylates in organic solvents is also improved by the addition of electron donors such as acetylacetone, tetrahy-drofuran, N,N -dimethylformamide, thiophene, diphenylether, triethylamine, pyridine, organic phosphorus compounds etc. Also the storage stability of neodymium carboxylates in organic solutions (reduction of sediment formation) is increased by these additives. Mixtures of the Nd-precursor and the respective additives are reacted in the temperature range 0-80 °C. The sequential addition of Al-compound and halide donor yield the active polymerization catalysts [409,410]. 

Evans et al. sequentially reacted the Nd carboxylate precursor Nd[C>2CC (CH3)2CH2CH3]3 % first with DEAC and then with TIBA. By this reaction catalytically active systems are obtained which polymerize IP. In the first reaction step in which Nd carboxylate is reacted with DEAC mixed ligand complexes are formed which contain neodymium and aluminum as well as halide and ethyl groups. Upon crystallization NdC -based compounds are obtained in which solvent is coordinated. These compounds exhibit a more complex... 

In 2004 Carpentier and co-workers were the first who isolated and characterized the active species from a Nd alcoholate/MgR2 mixture. The reaction of either a trinuclear or a monomeric Nd alcoholate precursor with Mg(CH2SiMe3)2 (Et20) yields an alkyl neodymium complex and a new het-erobimetallic Nd-Mg complex. The latter complex is considered to be the active species for the investigated catalyst system [621],... 

Figure 2.33 ORTEP view of the two independent molecules in the asymmetric unit of Nd(L )3-monoglyme-HiO (ellipsoid probability 30%). Fluorine and hydrogen atoms have been omitted for clarity [72]. (Reprinted from Inorganica ChimicaActa, 362, R.L. Nigro, R.G. Toro, M.E. Fragala, P. Rossi, P. Dapporto and G. Malandrino, Neodymium -diketonate glyme complexes Synthesis and characterization of volatile precursors for MOCVD applications, 4623 629, 2009, with permission from Elsevier.)...

Nigro, R.L., Toro, R.G., Fragala, M.E., etal (2009) Neodymium -diketonate glyme complexes synthesis and characterization of volatile precursors for MOCVD applications. Inorganica Chimica Acta, 362, 4623 629. 

The use of neodymium borohydride complexes as precursors for (COT)lanthanide complexes has been reviewed by Ephritikhine et al. A comparison has been made to the corresponding uranium chemistry.801... 

Treatment of 1.3-pentadiene with tribenzylaluminum/tetrabenzyltitanium/(—)-menthol also gives optically active polymers. Interestingly, a change of optical rotation of the polymer sample is observed when the same catalyst is used but the order of mixing the catalyst components is inverted56. Neodymium(III) chloride modified with optically active sulfoxides in the presence of alkylaluminums as catalyst precursor is also used for asymmetric polymerization of 1,3-pentadiene57. 

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