Uranium selenides

The first poly chalcogenide complex, K4USeg, was obtained by a solid-state reaction. It has a molecular sfructure with a distorted dodecahedral anion, [U(Se2)4] , which is isosfructural with the known peroxoanions [M(02)4]" , where M = V, Nb, Ta, Cr (n = 3) or Mo, W (n = 2). Recently, two additional uranium selenides have been synthesized, MU2Se6 (M = K+, Cs+), using a reactive flux method. The oxidation state of the uranium in these compounds was found to be tetravalent. The selenium has two distinct oxidation states, Se and one similar to a polyselenide network. 

Thermodynamic data for uranium selenides were previously assessed in the book on uranium compounds and complexes [92GRE/FUG]. Comparisons are frequently made with this source in the following sections but a number of selections made there are not made by the review since they were based entirely on estimates. 

Selenium and Tellerium Tantalum is attacked by selenium and tellurium vapours at temperatures higher than 80°C. Only slight attack is observed on the metal by liquid selenides and tellurides of ytirum, the rare earths, and uranium at temperatures of 1300 to 2100°C, and tantalum is considered to be a satisfactory material in which to handle these intermetallic compounds. 

The structural chemistry of the actinides is often similar to that of lighter transition metals, such as Zr and Hf, and to that of the lanthanides however, the diffuse nature of the 5/ orbitals leads to some differences and specifically to interesting magnetic and electrical properties. The actinide sulfides are generally isostructural with the selenides, but not with the analogous tellurides. The binary chalcogenides of uranium and thorium have been discussed in detail [66], but the structural... 

Nickel and selenium interact with incandescence on gentle heating [1], as do also sodium and potassium, the latter mildly explosively [2], Uranium [3] and zinc [4] also incandesce when their mixtures with selenium are heated, and platinum sponge incandesces vividly [5], The particle size of cadmium and selenium must be below a critical size to prevent explosions during synthesis of cadmium selenide by heating the elements together. Similar considerations also apply to interaction of cadmium or zinc with sulfur, selenium or tellurium [6], Interaction of powdered tin and selenium at 350° C is extremely exothermic [7],... 

Phosphine complexes, osmium, 19 642 Phosphine coordination complexes, of uranium, 25 436 Phosphine derivatives, 19 28 Phosphine oxide(s), 11 495-496 19 66 predicted deviations from Raoult s law based on hydrogen-bonding interactions, 8 814t in salicylic acid manufacture, 22 8 Phosphine oxide diols/triols, 11 501 Phosphine selenides, 22 90 Phosphinic acid, 19 20, 54-55 Phosphinic anhydride, 11 499 Phosphinothricin acetyltransferase (PAT) proteins, 13 360 Phosphite esters, 19 20 Phosphites, in VDC polymer stabilization, 25 720... 

Aluminium and magnesium selenides are very similar light brown powders, unstable in air. Zinc and iron (ferrous) selenides are more stable in air, the zinc compound being citron-yellow and the iron compound black and metallic in appearance.8 The latter becomes brown in air owing to oxidation. Ferric selenide is difficult to obtain pure. Cadmium selenide, which is dark brown, is very stable in colour and is used as a pigment. With thallium, selenium is said to form three distinct compounds,9 but analyses of these compounds have led to discordant results. The selenides of aluminium, chromium and uranium cannot be prepared in the wet way. Nickel selenide, unlike the sulphide, shows no tendency to form a colloidal solution. 

Metals. Nickel, sodium, potassium, uranium, zinc, and platinum sponge interact with selenium with incandescence when gently heated.3-7 The particle size of cadmium and selenium must be below a critical size to prevent explosions when making cadmium selenide this also applies to zinc.8... 

Compounds Bis-dimethylstibinyl oxide Bis(dimethylthallium) acetylide Butyllithium Nonacarbonyldiiron Octacarbonyldicobalt Pentacarbonyliron Tetracarbonylnickel Dibismuth trisulphide Dicaesium selenide Dicerium trisulphide Digold trisulphide Europium (II) sulphide Germanium (II) sulphide Iron disulphide Iron (II) sulphide Manganese (II) sulphide Mercury (II) sulphide Molybdenum (IV) sulphide Potassium sulphide Rhenium (VII) sulphide Silver sulphide Sodium disulphide Sodium polysulphide Sodium sulphide Tin (11) sulphide Tin (IV) sulphide Titanium (IV) sulphide Uranium (IV) sulphide ... 

Uranium Diselenide, Uranous Selenide, UScj, is formed when a current of hydrogen bearing excess of selenium vapour is passed over the double chloride at low red heat or by fusing the same chloride... 

EXPLOSION and FIRE CONCERNS combustible solid NFPA rating (NA) reacts to form explosive products with metal amides contact with acids may cause formation of poisonous hydrogen selenide gas incompatible or reacts violently with barium carbide, bromine pen-tafluoride, chromic oxide, fluorine, lithium carbide, lithium silicon, metals, nickel, sodium, nitric acid, nitrogen trichloride, oxygen, potassium, potassium bromate, rubidium carbide, zinc, silver bromate, uranium, strontium carbide, and thorium carbide toxic gases and vapors may be released in a fire involving selenium, sodium selenite, sodium selenate, and selenium dioxide use water for firefighting purposes. 

An example of veins with complex mineralogy is the mined-out uranium deposit at Shinkolobwe, Zaire, at the northwest end of the African Copperbelt. It occurs in a faulted transported fold in metamorphosed dolomitic shales of the middle Proterozoic Mine Series of the Roan Group.Uraninite and uranophane mineralization (about 620m.y. ago) was followed by several later mineralizations in which pyrite, molybdenite, monazite, selenium, Co-Ni sulphides and selenides and copper minerals were formed. It is believed that this orebody was formed by redistribution of metals originally deposited in marine sedimentary rocks." The uranium, originally weathered from granites and deposited in the marine sediments, was in low... 

At red heat tantalum reacts with sulfur or hydrogen sulfide to form tantalum sulfide (Ta2S4). At lower temperatures the metal is completely inert. In like maimer, at elevated temperatures on the order of at least 800°C, tantalum powder or shavings react with elemental carbon, boron, and silicon to form the corresponding binary compoimds. Tantalum also reacts with vapors of phosphorus, selenium, and tellurium at comparable temperatures. In contrast, there is only slight attack on the metal by liquid selenides and tellurides of the rare earths and uranium in the range 1300-2100°C, and tantalum is considered a satisfactory material for handling these intermetallic compoimds. 

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