Uranium V Compounds

These are among the best characterized compounds in this somewhat rare oxidation state, although they do tend to be unstable (see the preparation of UCle) and UI5 does not exist. 

2 UCI5 + 6 COCI2 + CI2 (20 atm., 160 °C) 2 UBrs (Soxhlet extraction brown solid) 

Grey UF5 has a polymeric structure with 6- and 7-coordinate uranium, whilst red-brown UCI5 and brown UBrs have a dimeric structure in which two octahedra share an edge. 

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U(OEt)5 is easily prepared by oxidation of U(OEt)4 by bromine in ethanol, followed by addition of the calculated quantity of sodium ethoxide, a reaction which yields181 only Np(OEt)4Br in the case of Np(OEt)4. U(OEt)s is commonly used as the starting material for the preparation of other uranium(V) alkoxides by alcohol exchange reactions. A comprehensive review of metal alkoxides includes a useful discussion of the uranium(V) compounds.182... 

A few salts of composition (Et4N)2[MvOX5] (Mv = Pa, X = C1, Br MV = U, X = F) are known the uranium(V) compound is obtained from the dihydrate under vacuum, and the protactinium(V) chlorocompound is prepared by hydrolysis of the hexachloro complex salt in methyl cyanide containing 0.5% water. Salts of composition (Et4N)[Pa(OEt)2X4j (X = Cl, Br) are also known. 

Uranium(v) compounds are, as expected for an f system, paramagnetic, usually exhibiting Curie-Weiss behaviour, with large Weiss constants g-values, expected to be 6/7, are modified by the mixing in of higher states and by orbital-reduction effects (covalency), experimental -values including values of 1.2 in NasUFg and 0.71 in CsUFe. 

The dark red, volatile, tris[bis(trimethylsilyl)amido] uranium(III) can be made from a solution of UClaTHFn and the sodium bis(trimeth-ylsilyl)amide. It is monomeric and contains 3-coordinate uranium (285). It has no tendency to act as an acceptor, but it reacts with tri-methylamine oxide or oxygen to yield the uranium(V) compound OU[N(SiMe3)2l3. 

Selbin J, Ortego JD and Gritzner G 1968 Electronic spectral studies of some uranium(v) compounds. Inorg. Chem. 7(5), 976-982. 

The starting material is dissolved in thionyl chloride and stirred at room temperature. Oxidation to [(n-Bu)4N][U06]is complete within 2-3 hours. In addition to the uranium(V) compound, SO2 and S were identified as products. No H2S, SQ3, HO, or Q2 were found. 

Neptunium has the oxidation states (VI), (V), (IV), and (III) with a general shift in stability toward the lower oxidation states as compared to uranium. The compounds which are formed are very similar to the corresponding compounds of uranium. 

Bis(pentalene) uranium complexes, preparation, 4, 221—222 Bis(pentamethylcyclopentadienyl)actinide(IV) compounds, synthesis and reactions, 4, 210 Bis(pentamethylcyclopentadienyl)actinide(V) compounds, synthesis and reactions, 4, 210 Bis(pentamethylcyclopentadienyl)actinide(VI) compounds, synthesis and reactions, 4, 210... 

Among the elements known before transuranium elements started to be synthesized in 1940, uranium has a unique characteristic, the extreme stability of the triatomic uranyl ion OUO+z. Not only are the numbers of uranium(VI) compounds larger than of U(IV), and far larger than of the two other oxidation states U(V) and U(III) known from non-metallic compounds, but until the preparation of UOFj discussed below, the only two U(VI) compounds known to contain less than two oxygen atoms per uranium atom were the octahedral molecules UFe and UQ6. 

S). Similar compounds with bis(diphenylphoBphino)methane disulfide and the corresponding diselenide have also been prepared (Table X). These are the first examples of coordination of sulfur and selenium donors to actinide pentahalides and it will be interesting to see whether uranium pentahalides behave in a similar fashion since the analogous niobium(V) and tantalum(V) compounds are also known (43). 

Np (V) (3) and Pu (V) (8), the last two being the first non-oxygenated neptunium (V) and plutonium (V) compounds. Some of the preparative procedures used for uranium (V) fiuoro complexes are shown in Table IV. 

Uranium(V). In the case of uranium, gaseous fluorine will normally take UF4 on past UF5 to UF0. In contrast, we find that fluorine oxidation of UF4 in liquid anhydrous HF proceeds readily to UF5 and then goes only slowly to UF0. If alkali fluoride is also present, the method is especially useful in the preparation of MF UF5 compounds free from traces of U(IV) or U(VI). The technique is given below ... 

Alkoxide complexes. In contrast to the propensity of many uranium(V) species to disproportionate to uranium(IV) and uranium(VI), homoleptic uranium(V) alkoxide compounds are quite stable toward disproportionation. Gilman and co-workers reported the synthesis of dark brown uranium(V) pentakis(ethoxide) from a metathesis reaction between UCI4 and four equivalents of sodium ethoxide. . In this early report, it was noted that better yields were obtained when no great care was taken to exclude air from the reaction, and in the presence of oxygen, the product yield was 80%. The mechanism shown in Equations (36) and (37) was suggested for this reaction. 

A variety of mixed ligand/alkoxide uranium(V) products are also isolable. Substitution compounds (U(0R)4L, U(0R)3L2, U(0R)2L3) were prepared from the reactions of U(OCH2CH3)5 with FlCl, /3-ketoesters (2,2,2,-trifiuoroaceto acetate, methyl acetate, ethyl acetate), acetyl chlorides... 

Table 28 Some hydrates of protactinium(V), uranium(V), neptunium(V), and plutonium(V) compounds.

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