Titanium tetravalent

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. 

If a chemical reaction regenerates the initial substance completely or partially from the products of the electrode reaction, such case is termed a chemical reaction parallel to the electrode reaction (see Eq. 5.6.1, case c). An example of this process is the catalytic reduction of hydroxylamine in the presence of the oxalate complex of TiIV, found by A. Blazek and J. Koryta. At the electrode, the complex of tetravalent titanium is reduced to the complex of trivalent titanium, which is oxidized by the hydroxylamine during diffusion from the electrode, regenerating tetravalent titanium, which is again reduced. The electrode process obeys the equations... 

Physical properties of binary or ternary Ru/Ir based mixed oxides with valve metal additions is still a field which deserves further research. The complexity of this matter has been demonstrated by Triggs [49] on (Ru,Ti)Ox who has shown, using XPS and other techniques (UPS, Mossbauer, Absorption, Conductivity), that Ru in TiOz (Ti rich phase) adopts different valence states depending on the environment. Possible donors or acceptors are compensated by Ru in the respective valence state. Trivalent donors are compensated by Ru5+, pentavalent acceptors will be compensated by Ru3+ or even Ru2+. In pure TiOz ruthenium adopts the tetravalent state. The surface composition of the titanium rich phase (2% Ru) was found to be identical to the nominal composition. 

Another application of an isomerisation reaction can be found in the production of the third monomer that is used in the production of EPDM rubber, an elastomeric polymerisation product of Ethene, Propene and a Diene using vanadium chloride catalysts. The starting diene is made from vinylnorbomene via an isomerisation reaction using a titanium catalyst. The titanium catalyst is made from tetravalent salts and main group hydride reagents, according to patent literature. 

Pia. 21. Spectra of four compounds of tetravalent titanium coordinated through four oxygens to various organic groups or hydrogen. 

The four spectra of tetravalent titanium shown in Fig. 21 are closely related. All have a low energy peak at about 5 ev., similar to the characteristic low energy peak in the chromate and permanganate spectra. This peak is also present in the spectra of the other tetravalent titanium compounds, Ti02 and the lactate. In Fig. 21 the principal peak reaches a maximum at about 22 ev. However, it is split and reaches a second maximum... 

Figure 22 presents the spectra of the common oxides of titanium. The two common forms of TiOj, anatase and rutile, give clearly distinguishable spectra. These distinctions in the spectra have been confirmed in several samples extending over a wide range of crystallite size. The packing within the first coordination shells of anatase and rutile is different and may account for the spectral differences. The tetravalent titanium spectra are... 

The spectrum of Ti208 retains the 5 ev. peak of the tetravalent form. This spectrum is compatible with the assumption that TijOs is a mixture of tetra- and divalent titanium. 

Fia. 23. Spectra of titanium metal, of metallic appearing TiSi-z phase, of organome-tallic compound of divalent titanium, and of the tetravalent titanium lactate. 

The TiS2 spectrum does not show the low energy peak characteristic of tetravalent titanium, and in other ways is difficult to classify. Again sulfur as a coordination atom does not give rise to fine structure of appreciable amplitude. 

The titanium carbide spectrum shows strong absorption at 0 ev., which may be attributed to the metallic nature of this carbide or to the tetravalent state of titanium. This ambiguity is not appreciably resolved by the discussion of Bundle 18), who explains how the tetravalent nature of the titanium in TiC leads to its metallic character. The TiO spectrum does not show this low-lying absorption peak TiO is not metallic and does not contain tetravalent titanium. 

The picture of the nitrogen atoms in diazadiboretidines acting as Lewis base centers is also supported by the formation of a 1 1 coordination compound with TiCl4 [Eq. (58)] (91). The B-NMR signal of 22.7 ppm indicates a highfield shift, which cannot be due to d-electrons from tetravalent d -titanium. X-Ray structural analysis shows that bridging chlorine atoms provide the observed electronic saturation of the boron atoms. 

We have observed that the radioactive contamination is practically independent of the temperature A9). We believe that this radioactive contamination is due to the presence of traces of radioactive polyethylene resulting from ethylene polymerization. Ethylene can result, in fact, from the disproportionation of C2Hs radicals released by decomposition of ethyl titanium compounds, which derive from the reaction between ethylalu-minum and traces of titanium tetrachloride or other tetravalent titanium compounds that are sometimes present as impurities in the a-titanium trichloride. 

The inverse spinel structure differs in that one type of cation occupies the tetrahedral and half of the octahedral sites of the spinel lattice, and the other cations occupy the remaining octahedral sites. This is indicated by writing the formula of, for example, zinc titanium spinel as Zn(TiZn)04. Spinels containing di- and tetravalent cations are mostly of the inverse type. Normal and inverse spinels should be regarded as idealized limiting structures, intermediate forms are often observed in practice. A... 

Unlike titanium, zirconium forms a few normal tetravalent salts, such as a tetranitrate and a tetrasulfate. as well as its more common basic salts. However, the normal salts readily undergo hydrolysis to form the basic salts. 

The salts of tetravalent titanium, zirconium, and thorium and of pentavalent niobium and tantalum are diamagnetic, as would be expected, and have colors ranging from white to orange, depending upon the halogen. 

A2Pt207, similar to those reported for tin, ruthenium, titanium, and several other tetravalent ions. Trivalent ions which form cubic platinum pyrochlores range from Sc(III) at 0.87 A to Pr(III) at X.14 A. Distorted pyrochlore structures are formed by lanthanum (1.18 A) and by bismuth (1.11 A). Platinum dioxide oxidizes Sb203 to Sb2(>4 at high pressure. The infrared spectra and thermal stability of the rare earth platinates have been reported previously and will not be repeated here, except to point out the rather remarkable thermal stability of these compounds decomposition to the rare earth sesquioxide and platinum requires temperatures in excess of 1200 °C. 

Titanium is the only member of its family forming +3 compounds of appreciable stability (Zr, Hf, and Th are almost exclusively tetravalent). In group Va, only vanadium assumes a +4 oxidation state (its congeners almost invariably are pentavalent). In Group VIII, osmium and ruthenium can assume a valence of + 8, but their lighter congener, iron, apparently does not. 

The type of cleavage of the alkyl titanium bond is certainly dependent upon the titanium valence state. Tetravalent compounds will tend to cleave homolytically, but heterolytic cleavage will become more favorable at the lower valence states because of higher bond polarity (290). Ethylene polymerization takes place more readily on alkyl vanadium compounds than on alkyl titanium compounds and yields higher molecular weight linear polymer (340). This is attributable to the fact that... 

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. 

FIGURE 21.23 Potential-pH equilibrium diagram for the titanium-water system at 25 °C. [Figure established by considering, as derivatives of tri and tetravalent titanium, the anhydrous oxides Ti203 and Ti02 (rutile).] (from Ref. 35). 

Unlike aluminum, titanium is tetravalent and can exhibit different oxidation states. Thus TS-1 is non-acidic if isomorphously substituted. TS-1 is relatively difficult to synthesize, which is probably one of the reasons the site structure was under debate for quite some time. TS-1 can only be synthesized with a maximum of 3 wt% Ti if more Ti is added extra-framework titanium is formed. Inihally, it was suggested from XAS that octahedral sites are formed in the silicalite framework [60]. However, later more and more groups suggested tetrahedral isomorphous substitution of the titanium sites in the MFl framework [61-63], It is now more or less generally accepted that the Ti is four-coordinate and has a Ti—O distance of 1.79-1.81 A. This is a significantly increased distance compared to the Si—O distance 1.605 A, which is constant for a vast number of oxides [4]. The increase in... 

The two most important sources of uranium are the minerals carnotite, where uranium occurs in the hexavalent oxide or hydrated oxide, and pitchblende, where uranium occurs mostly in the tetravalent state as a compound salt with other metals. It also occurs as a mixed oxide with titanium, thorium, and niobium in the tetravalent form. The tetravalent uranium minerals appear to have been geologically formed in the presence of reducing agents such as hydrocarbon minerals, graphite, native metals, and sulfide minerals, while such association is rarely observed with the hexavalent uranium minerals. 

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