Rare earth element complexes with

Preparation of rare-earth element complexes with ascorbic acid. 

A Comparison of the Dissociation Kinetics of Rare Earth Element Complexes with Synthetic Polyelectrolytes and Humic Acid... 

In addihon to the more generally reachve group 3 elements, examples of group 4 metals with amidate, pyridonate, and sulfonamidate ligands have been reported for ROP of cyclic esters. Such group 4 metals, and in particular titanium, are attractive due to their low cost, low toxicity, and high earth abundance. Furthermore, such complexes are known to be more robust than rare earth element complexes and thus less sensitive to the purity of the monomeric feedstock that is used for ROP. 

The fluorescence properties of several europium and samarium ) -diketonates have been measured and assignments of the transitions made. Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to fluoresce. The luminescence of the heptafluoroheptane-2,4-dione complexes of Sm, Eu, and Tb has been measured in dilute ethanol at pH8 and 610nm mixed-ligand complexes with 1,10-phenanthroline exhibited an enhanced luminescence. Photolysis of the Tb chelate of 2,2,6,6-tetramethylheptane-3,5-dione has been examined at 311 nm in various alcohols, and loss of one -diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 

An additional major speciation assessment provided a greatly improved, comprehensive view of inorganic complexation in seawater. Based on the analogous characteristics of metal complexation by carbonate and oxalate, Turner et al. concluded that rare earth element complexation in seawater is dominated by carbonate. Subsequently, as the result of approximately twenty years of progress in seawater speciation, the Principal Species assessment of Bruland listed seventeen elements with carbonate-dominated Principal Species. 

Another method often employed is to minimize vaporization differences by using a spark-type of excitation which introduces the sample into the excitation zone by a sputtering process. At the Ames Laboratory, this second approach has been emphasized. Uniarc excitation, which is a combination of a spark and a unidirectional ac arc, has provided reliable analyses with adequate sensitivity for many impurities in most of the rare earth elements, and with a precision of better than 10%. A briquetted sample of one part rare earth oxide mixed with nine parts of pelleting graphite is used. The complex rare earth matrix spectra often causes spectral interference with the more sensitive spectral lines of impurity elements. For Pr and Nd, which have the most complex spectra, this problem is particularly serious, and alternate analytical approaches must be used if determinations at lower concentration levels are required. 

Terbium — Ytterby, village in Sweden), Tb at. wt. 158.92534(2) at. no. 65 m.p. 1356°C b.p. 3230"C sp. gr. 8.230 valence 3, 4. Discovered by Mosander in 1843. Terbium is a member of the lanthanide or rare earth group of elements. It is found in cerite, gadolinite, and other minerals along with other rare earths. It is recovered commercially from monazite in which it is present to the extent of 0.03%, from xenotime, and from euxenite, a complex oxide containing 1% of more of terbia. Terbium has been isolated only in recent years with the development of ion-exchange techniques for separating the rare-earth elements. As with other rare earths, it can be produced... 

Sal nikov, Yu I, Devyatov FV (1980) Complexing of yttrium group rare earth element ions with citric acid. ZhumNeoig Khim 25 1216-1222... 

The X-ray determination of REE in geological samples is normally complicated by the relatively low concentrations of the REE, their complex X-ray spectra, the high concentration of matrix elements and the lack of reference standards with certified values for REE. A rapid and sensitive ion exchange and X-ray fluorescence procedure for the determination of trace quantities of rare earths is described. The REE in two U.S.G.S. standards, two inhouse synthetic mixtures and three new Japanese standards have been determined and corrections for inter-rare earth element interferences are made. 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

Rare earth elements are the general term for 15 kinds of lanthanide elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Py, Ho, Er, Tm, Yb, Lu) together with Sc and Y elements. They prefer trivalent states in the complex formation, though three elements (Eu, Sm, Yb) can assume tri- and divalent stateos and Ce a tri- or tetravalent state. Their ionic radii are fairly large (1.0-1.17 A) and their electronegativities are low (1.1-1.2). In fact, the former are much larger than those of... 

Minerals such as euxenite, fergusonite, samarskite, polycrase and loparite are highly refractory and complex in nature. These minerals may be opened up by treatment with hydrofluoric acid. While metals such as niobium, tantalum and titanium form soluble fluorides, rare earth elements form an insoluble residue of their fluorides. Such insoluble fluorides are filtered out of solution and digested with hot concentrated sulfuric acid. The rare earth sulfates formed are dissolved in cold water and thus separated from the insoluble mineral impurities. Rare earth elements in the aqueous solution are then separated by displacement ion exchange techniques outlined above. 

---