Actinide preparation

Table 16— Uptake of various lanthanide and actinide preparations in liver and skeleton at l and 24 hours and excretion in urine and feces at 3 or 4 hours after intravenous injection in female rats...

An Am (IV) silicate, AmSi04, having the structure of zhcon (a-form of the actinide(IV) silicates) was obtained by hydrothermal synthesis out of a mixed hydroxide precipitation of Am (OH) 4 + Si02 aq. The Am fraction, after precipitation by the method of Pennemann et al. (31), was oxidized with NaOCl in an alkaline solution to form Am (OH) 4. After 5-7 days at 230 °C. and a pH of 8.2-S.6, the components reacted to form crystalline AmSi04, which is isostructural with the silicates of the other tetravalent actinides prepared the same way. 

Gramme quantities of protactinium could be deposited when the dissociation wire was replaced by an induction heated tungsten or protactinium sphere (3). Table II lists selected methods of actinide preparation via the vapour phase. 

Table II. Examples of actinide preparation via the vapour phase...

Microchemical or ultramicrochemical techniques are used extensively ia chemical studies of actinide elements (16). If extremely small volumes are used, microgram or lesser quantities of material can give relatively high concentrations in solution. Balances of sufficient sensitivity have been developed for quantitative measurements with these minute quantities of material. Since the amounts of material involved are too small to be seen with the unaided eye, the actual chemical work is usually done on the mechanical stage of a microscope, where all of the essential apparatus is in view. Compounds prepared on such a small scale are often identified by x-ray crystallographic methods. 

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

The phosphido complex, Th(PPP)4 [143329-04-0], where PPP = P(CH2CH2P(CH2)2)2) has been prepared and fully characterized (35) and represents the first actinide complex containing exclusively metal—phosphoms bonds. The x-ray stmctural analysis indicated 3-3-electron donor phosphides and 1-1-electron phosphide, suggesting that the complex is formally 22-electron. Similar to the amido system, this phosphido compound is also reactive toward insertion reactions, especially with CO, which undergoes a double insertion (35,36). 

Uranium tetrachloride [10026-10-5], UCl, has been prepared by several methods. The first method, which is probably the best, involves the reduction/chlorination of UO [1344-58-7] with boiling hexachloropropene. The second consists of heating UO2 [1344-57-6] under flowing CCl or SOCI2. The stmcture of the dark green tetrachloride is identical to that of Th, Pa, and Np, which all show a dodecahedral geometry of the chlorine atoms about a central actinide metal atom. The tetrachloride is soluble in H2O, alcohol, and acetic acid, but insoluble in ether, and chloroform. Industrially the tetrachloride has been used as a charge for calutrons. 

Barium reduces the oxides, haUdes, and sulfides of most of the less reactive metals, thereby producing the corresponding metal. It has reportedly been used to prepare metallic americium via reduction of americium trifluoride (13). However, calcium metal can, in most cases, be used for similar purposes and is usually preferred over barium because of lower cost per equivalent weight and nontoxicity (see Actinides and transactinides). 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

The remaining actinide elements were prepared by various bombardment techniques fairly regularly over the next 25 years (Table 31.1) though, for reasons of national security, publication of the results was sometimes delayed. The dominant figure in this field has been G. T. Seaborg, of the University of California, Berkeley, in early recognition of which, he and E. M. McMillan were awarded the 1951 Nobel Prize for Chemistry. 

Because the sequence of neutron captures inevitably leads to looFrn which has a fission half-life of only a few seconds, the remaining three actinides, loiMd, 102N0 and losLr, can only be prepared by bombardment of heavy nuclei with the light atoms jHe to foNe. This raises the mass number in multiple units and allows the f Fm barrier to be avoided even so, yields are minute and are measured in terms of the number of individual atoms produced. 

Dioxides are known for all the actinides as far as Cf. They have the fee fluorite structure (p. 118) in which each metal atom has CN = 8 the most common preparative method is ignition of the appropriate oxalate or hydroxide in air. Exceptions are Cm02 and Cf02, which require O2 rather than air, and Pa02 and UO2, which are obtained by reduction of higher oxides. 

Several oxohalides are also known, mostly of the types An OaXa, An OaX, An OXa and An "OX, but they have been less thoroughly studied than the halides. They are commonly prepared by oxygenation of the halide with O2 or Sb203, or in case of AnOX by hydrolysis (sometimes accidental) of AnX3. As is to be expected, the higher oxidation states are formed more readily by the lighter actinides thus An02X2, apart from the fluoro compounds, are confined to An = U. Conversely the lower oxidation states are favoured by the heavier actinides (from Am onwards). 

One name, more than any other, is associated with the actinide elements Glenn Seaborg (1912-1999). Between 1940 and 1957. Seaborg and his team at the University of California, Berkeley, prepared nine of these elements (at no. 94-102) for the first time. Moreover, in 1945 Seaborg made the revolutionary suggestion that the actinides, like the lanthanides, were filling an f sublevel. For these accomplishments, he received the 1951 Nobel Prize in chemistry. 

Preparations and reactions of oxide fluorides of the transition metals, the lanthanides and the actinides. J. H. Holloway and D. Laycock, Adv. Inorg. Chem. Radiochem., 1984, 28, 73 (278). 

That magnetic measurements often raise more problems than they solve, is demonstrated for the indicated compound. We prepared a series of [ (C2H5N] i,An(NSC) e compounds (An = Th, U, Np, Pu) with cubic coordination of the actinide ion. We derived a consistent interpretation of the magnetic and optical properties of the uranium and the neptunium compounds (6 ). In the case of Pu we expect an isolated T1 ground state and a first excited state at about 728 cm-1. To our surprise we found a magnetic ground state much more pronounced than in the case of the hexachloro-complex, Fig. 4. 

A critical assessment of the chemical thermodynamic properties of the actinides and their compounds is presently being prepared by an international team of scientists under the auspices of the International Atomic Energy Agency (Vienna). As a result of this effort, four publications (1, 2, 3, 5) have already become available and a further ten 6-T4), including the halides (8) and aqueous complexes with Tnorganic ligands (12),... 

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