Plutonium dioxide ions

Plutonium compounds, 19 687-691 protection against, 19 702 Plutonium dioxide, 19 688—689 Plutonium fuel fabrication facilities, 17 547 Plutonium-gallium alloys, 19 683-684 Plutonium halides, 19 689-690 Plutonium hexafluoride, 19 689 Plutonium hydrides, 19 690 Plutonium ions... 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

With the exception of thorium, the actinides form trihalides. For uranium and neptunium, reduction of the MX4 compounds with hydrogen is necessary, but for the elements from plutonium onwards the action of the carbon tetrahalide or aluminium halide on the dioxide is usually employed. The trifluorides are insoluble but the rest dissolve to give solutions containing ions. 

Plutonium also forms a similar series of cations. In this instance the redox potentials indicate that Pu + is the most stable ion. Hot bromate solutions are required to oxidise it to Pu02+, but reduction to the terpositive state is easier than with and Np + ions, being effected by sulphur dioxide, hydrazine or the iodide ion. In solution, the Pu + ion is not oxidised... 

Semiempirical calculations of free energies and enthalpies of hydration derived from an electrostatic model of ions with a noble gas structure have been applied to the ter-valent actinide ions. A primary hydration number for the actinides was determined by correlating the experimental enthalpy data for plutonium(iii) with the model. The thermodynamic data for actinide metals and their oxides from thorium to curium has been assessed. The thermodynamic data for the substoicheiometric dioxides at high temperatures has been used to consider the relative stabilities of valence states lower than four and subsequently examine the stability requirements for the sesquioxides and monoxides. Sequential thermodynamic trends in the gaseous metals, monoxides, and dioxides were examined and compared with those of the lanthanides. A study of the rates of actinide oxidation-reduction reactions showed that, contrary to previous reports, the Marcus equation ... 

Tetravalent plutonium in aq soln is reduced to the trivalent form by sulfur dioxide, hydroxylamine hydrochloride, hydrazine hydrochloride, the uranous ion, the iodide ion by shaking with mercury in chloride soln electrolytically at a platinum cathode. Tetravalent salts are pink or greenish form complexes very readily. 

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