Zirconium 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. 

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer stmctures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer stmcture with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is - 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

The conditions under which the basic sulfates of tetraval-ent, Zr, Hf and Ce form provide analogies on which to base speculation about the hydrothermal hydrolysis of tetravalent plutonium. In the zirconium system at 100°C, the only basic sulfate observed is Zr2 (0H)2 (SOO3 ( 0), i.e., the zirconium analog of... 

The only crystalline phase which has been isolated has the formula Pu2(OH)2(SO )3(HaO). The appearance of this phase is quite remarkable because under similar conditions the other actinides which have been examined form phases of different composition (M(OH)2SOit, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction influences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate compounds, however, i.e., the existence of double hydroxide bridges between metal atoms. This structural feature persists from zirconium through plutonium for compounds of stoichiometry M(OH)2SOit to M2 (OH) 2 (S0O 3 (H20) i,. Spectroscopic studies show similarities between Pu2 (OH) 2 (SOO 3 (H20) i, and the Pu(IV) polymer and suggest that common structural features may be present. 

Complexes of tetravalent zirconium with organic acids, such as citric, tartaric, malic, and lactic acids, and a complex of aluminum and citric acid have been claimed to be active as dispersants. The dispersant is especially useful in dispersing bentonite suspensions [288]. Polymers with amine sulfide terminal moieties are synthesized by using aminethiols as chain transfer agents in aqueous addition polymerizations. The polymers are useful as mineral dispersants [1182]. 

The chemical properties of hafnium are very much similar to those of zirconium. In aqueous solutions, the metal exists in tetravalent state. The elec-... 

Zirconium phosphonates are solid materials typically synthesized in amorphous forms under aqueous conditions by the reaction of a soluble salt of a tetravalent metal and a phosphonic acid or an organophosphoric acid ... 

Zirconium oxide, Zr02 is widely known, both as a mineral, baddeleyite, and as an industrial product obtained horn zircon, Z1SO4. Moreover, the precipitate obtained by action of alkali hydroxides upon solutions of tetravalent zirconium is a hydrated oxide. The latter is readily soluble in acids to form oxysalts, which arc usually formulated in terms of the Zr02+ ion, without including its water of hydration, e.g., as Zr0(H2P04)2. The hydrated Zr02+ ion is not amphiprotic it does not dissolve in alkali hydroxides, While it does react on alkali carbonate fusions, the compounds formed have been shown to be mixed oxides rather than zirconates. 

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. 

Sokina, L.P., Solovkin, A.S., Teterin, E.G., Bogdanov, F.A., Shesterikov, N.N. 1978. Dibutyl phosphates of tetravalent plutonium, zirconium, and thorium, formed in solutions of tri-n-butyl phosphate (TBP). Soviet Radiochem. 20(1) 19-24. (Translated from Radiokhimiya 20(1) 28-34.)... 

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. 

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. 

Finally, the column is flushed with three volumes of 0.8 M HC1 to remove sorbed impurities, such as zirconium and plutonium. More precisely, the LiCl eluent solutions are adjusted to within 0.05 M of the desired concentration and are acidified to 0.10 + 0.05 M HC1 hydroxylamine hydrochloride is added (to a concentration of 0.1 M) as a reducing agent for any tetravalent cerium sorbed on the resin and methyl alcohol is added (to a concentration of 2.5% by volume) to suppress the rate of radiolytic destruction of HC1 and the corresponding generation of radiolytic gases (8) Typically, the eluents are added to the feed tank in small portions and pumped to the column thus, the eluents also serve to flush the feed system. The eluent flow rate is 1 L/h and the superficial column velocity is 140 iim/s. 

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. 

Unit cell dimensions for the tetravalent protactinium fluoro complexes are listed in Table VIII. LiPaFs is a member of an isostructural series of 1 1 complexes formed by the actinide elements thorium to curium inclusive (91). Structural details are available for LiUP5 (5S), but bond distances have not been reported for the protactinium complex. The 7 6 complexes, like their actinide(IV) analogs (Th-Cm with Na, Th-Cm with K, and Th-Pu with Rb) are all 4, 114) isostructural with Na7Zr F3 (60) in which each zirconium atom is 8-coordinate and the... 

The general area of zirconacyclopentane chemistry has been reviewed.76 Because these molecules are best viewed as zirconium or hafnium dialkyl complexes, and hence as tetravalent metal centers, this renders them beyond the scope of this review. It should be noted that these molecules display a rich reaction chemistry, serving as initiators for olefin polymerization,77-79 reagents for organic methodology,57,80-86 and key intermediates in natural product synthesis.87,88... 

In contrast to the conventional approach whereby various organic groups are subsequently bound to a previously prepared surface, we have been synthesizing a broad series of anchored, layered-structure solids by precipitating the pre-derived phosphonate salts with tetravalent metal ions. The two-dimensional backbone has the zirconium phosphate structure however, substituted for hydroxylic groups are the desired organics, oriented away from the basal surfaces in a bilayered fashion in the interlayer region. 

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