Structural studies tetravalent metals

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. 

The structure of platinum dioxide and its reactions with some di, tri, and tetravalent metal oxides have been investigated. Ternary platinum oxides were synthesized at high pressure (40 kUobars) and temperature (to 1600°C). Properties of the systems were studied by x-ray, thermal analysis, and infrared methods. Complete miscibility is observed in most PtO2-rutile-type oxide systems, but no miscibility or compound formation is found with fluorite dioxides. Lead dioxide reacts with Pt02 to form cubic Pb2Pt207. Several corundum-type sesquioxides exhibit measurable solubility in PtOz. Two series of compounds are formed with metal monoxides M2PtOh (where M is Mg, Zn, Cd) and MPt306 (where M is Mg, Co, Ni, Cu, Zn, Cd, and Hg). 

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M-N—M unit They have the stoichiometries M2NX8(H20)2]3 and [M2N(NH3)8Y2]3+ (M = Os, Ru X = Cl, Br Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal-oxo complexes is discussed briefly. 

Pyoverdin. Pyoverdin complexes of tetravalent actinides have been investigated due to the potential of this class of ligand to solubilize and sequester these metals (as they do for Fe ). At near-neutral pH pyoverdine forms a 1 1 Pu pyoverdine complex with Pu. The stoichiometry changes to 1 2 when excess ligand is present. Thorium(IV), U, and complexes have also been reported. Their optical absorbance spectroscopic properties, but no structural studies, are reported. The selectivity of pyoverdin for common actinides in the order Th > has been proposed. ... 

Americium was isolated first from plutonium, then from lanthanum and other impurities, by a combination of precipitation, solvent extraction, and ion exchange processes. Parallel with the separation, a vigorous program of research began. Beginning in 1950, a series of publications (1-24) on americium put into the world literature much of the classic chemistry of americium, including discussion of the hexavalent state, the soluble tetravalent state, oxidation potentials, disproportionation, the crystal structure(s) of the metal, and many compounds of americium. In particular, use of peroxydisulfate or ozone to oxidize americium to the (V) or (VI) states still provides the basis for americium removal from other elements. Irradiation of americium, first at Chalk River (Ontario, Canada) and later at the Materials Testing Reactor (Idaho), yielded curium for study. Indeed, the oxidation of americium and its separation from curium provided the clue utilized by others in a patented process for separation of americium from the rare earths. 

Extended X-ray absorption fine structure (EXAFS) and K edge absorption spectroscopy have been used to study vanadium in coaI7). In contrast to the common belief that vanadyl porphyrins are the major compounds present, these studies demonstrate that in the high vanadium content samples examined, the metal is tetravalent and coordinated to oxygen ligands. Similar investigations have been carried out on the vanadocytes of aci-dians to identify the form of vanadium in tunicate blood cells22 (vide infra). 

Nature of metallic cations. A great number of natural or synthetic LDHs containing various metallic cations have been studied the divalent cations are Mg, Mn, Fe, Co, Ni, Cu, Zn, and Ca and the trivalent ones are Al, Cr, Mn, Fe, Co, Ni, and La. The same structure is also attributed to compounds containing the Li-Al monovalent - trivalent association or the Co-Ti divalent -tetravalent association. In Table 7-1, we present a review of metallic cations associations reported in the hterature. 

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