Zirconium trivalent

Whereas zirconium was discovered in 1789 and titanium in 1790, it was not until 1923 that hafnium was positively identified. The Bohr atomic theory was the basis for postulating that element 72 should be tetravalent rather than a trivalent member of the rare-earth series. Moseley s technique of identification was used by means of the x-ray spectra of several 2ircon concentrates and lines at the positions and with the relative intensities postulated by Bohr were found (1). Hafnium was named after Hafma, the Latin name for Copenhagen where the discovery was made. 

In the case of the allyl compounds, displacement of the allyl group seems to be required. Thus the reaction of Zr(allyl)4 with pyridine follows a fundamentally different course to the corresponding benzyl compound. In this instance the reaction is irreversible, and an allyl group is displaced to give a trivalent zirconium compound (9) as shown by the equation... 

Zirconium exhibits quadrivalency in most of its compounds although divalent and trivalent compounds also exist. Zirconium reacts with oxygen to form zirconium oxide, Zr02. In powder form, Zr metal ignites spontaneously forming oxide. Solid metal, however, is stable in air at ordinary temperatures, but reacts slowly at 200°C. Reaction is rapid at high temperatures. 

On the basis of his quantum theory of atomic structure, Niels Bohr believed that, since Urbain s celtium had been obtained from the rare earths, it could not be element 72, for the latter must be quadrivalent rather than trivalent and must belong to the zirconium family. He showed that the chemical properties of an atom are determined by the number and arrangement of the electrons within it and especially by the number... 

The ZEALEX Process Researchers from KRI have shown that the zirconium salt of dibutyl phosphoric acid (ZS-HDBP) was soluble in Isopar-L in the presence of 30% TBP. This super PUREX solvent, known as ZEALEX, extracts actinides (Np-Am) together with lanthanides and other fission products, such as Ba, Cs, Fe, Mo, and Sr from nitric acid solutions. The extraction yields depend on both the molar ratio between Zr and HDBP in the 30% TBP/Isopar-L mixture and the concentration of HN03 (232). Trivalent transplutonium and lanthanide elements can be stripped together from the loaded ZEALEX solvent by a complexing solution, mixing ammonium carbonate, (NH4)2C03, and ethylenediamine-N.N.N. N -tetraacetic acid (EDTA). An optimized version of the process should allow the separation of... 

For several ions plausible structures require trivalent or divalent zirconium, e.g., [C5H5ZrCl]+, [(C5H5)2Zr]+, [ZrCl2]+, and [(C5H5)(C1) ZrOZrCl]+. In the last ion the resonance structure includes contributions in which both zirconium atoms are formally trivalent and others in which one is tetravalent and the other divalent. 

In this chapter we will review the synthesis, structural aspects, and basic chemical properties of formally divalent and trivalent titanium and zirconium metallocene complexes. We have restricted our coverage to the low-valent bis(rj-cyclopentadienyl) and related metallocenes metal halide complexes and organometallic mixed metal systems will not be discussed here. We have not attempted to present an exhaustive coverage of the field. Rather, our aim has been to describe critically and to evaluate the often confusing chemistry that has been reported for the reactive low-valent titanium and zirconium metallocenes. More general reviews (7) and a book (2) on the organometallic chemistry of titanium, zirconium, and hafnium have been published. 

If it becomes easy now to obtain open structures with di and trivalent transition metals, the litterature is very poor concerning tetravalent cations. However, very recently, two zirconium [72,73] and two titanium [74,75] fluorophosphates were evidenced. The titanium family provides the first example [74], of a mixed valence compound, X iIIITilvF(P04)2, 2 H20 (Fig. 13) in the series of oxyfluorinated solids with an open framework. 

Aluminum oxide is the only trivalent oxide that has been used to form a ceramic some heat treatment is needed. Kingery claims to have observed a setting reaction between trivalent iron oxide and phosphoric acid, but this reaction may have been caused by traces of magnetite in the trivalent oxide. Pure trivalent iron oxide such as hematite (Fe203) does not react with phosphoric acid. Overall, trivalent metal oxides have a solubility that is only marginal and falls below that of even sparsely soluble divalent oxides, while the solubility of oxides of most quadrivalent metals (zirconium is an exception) is too low to form a ceramic. 

The crystalline form of interest in Zr-based ceramic compounds is the cubic fluorite structure based on the mineral CaF2. In this structure, consisting of interpenetrating face-centered-cubic and simple cublic arrays of cations (Zr ) and anions (O ), respectively, oxygen ion conductivity is enhanced by replacing zirconium (Zr ) ions on the cation lattice with soluble dopant cations having a valence less than 4, typically divalent (Mg, Ca ) and trivalent (Y, Yb , Sc ) cations. These dopants, which are in solid solution, are incorporated into the zirconia structure by the following types of defect reaction ... 

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