Uranium v

The pH region in which uranium(V) could become an important species is less than 5. As the dominant ion is UOj, the ion will not hydrolyse in this pH region. At higher pH, where hydrolysis might be expected, uranium(V) will disproportionate (Grenthe et al., 1992). Consequently, uranium(V) hydrolysis species are unlikely to form. 

Four transitions are thus expected in the electronic spectrum and generally, in practice, four groups of lines are seen, between the near-IR and the visible, bearing out this prediction. The ground state is a Kramers doublet (F7), so compounds are EPR active. 

The effect of increasing crystal field upon the energy of an electron in an f system such as U (reproduced with permission from S. A. Cotton. Lanthanides and Actinides, Macmillan, 1991, p. 109). 

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Recently Suglobova et al. (3, 4, 5) reported structural data, phase diagrams, and enthalpies of reaction of several complex fluorides of uranium(V) with alkali metals. Their observations indicate that the enthalpy of stabilization represented by the equation... 

Table 49 Some Hydrates of Protactinium(V), Uranium(V), Neptunium(V) and Plutonium(V)...

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. 

Kniewald, G. and Branica, M. (1988) Role of uranium (V) in marine sedimentary environments a geochemical possibility. Mar. Chem., 24, 1-12. 

Uranium (V) chloride, formation of, in preparation of uranium (IV) chloride, 5 144... 

The uranium(v) species UO2+ exists, but is less stable than possibly owing to... 

Since E is positive, the reaction is energetically feasible although this only predicts that the UOj (aq) ion is thermodynamically unstable with respect to disproportionation and says nothing about kinetic stability, the fact is that the uranium(v) aqua ion is very short-lived. 

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. 

Electrochemical investigations have dealt with either U02(dik)2, or U(dik)4 complexes. Most investigations on U02(dik)2 derivatives have been carried out in coordinating solvents such as dmso or dmf, so that they actually refer to solvated molecules such as U02(dik)2(solvent)2 . Only in CHCI3 solution has it been assumed that the complex under study is actually U02(dik)2. In this medium, both U02(acac)2 and U02(dbm)2 undergo a chemically reversible U(VI) U(V) reduction. On the other hand, in coordinating solvents such as dmso or dmf, the one-electron reduction of most complexes is accompanied by chemical complications, which are probably due to the competitive coordination of the solvent itself (it is assumed that the diketonate may act as unidentate ligand in the uranium(V) species). The formal electrode potentials of the U(VI) U(V) process for selected complexes in various solvents are compiled in Table 18. 

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