Anionic complexes, trivalent uranium

Crown ethers. Metal and crown ether complexes have to fulfill two requirements to form stable complexes. First, the coordination sphere of the metal must be stabilized by the crown ether and any complexing anions. A trivalent uranium coordination sphere is typically satisfied... 

Dissolution of the calcium fluoride in aluminum nitrate-nitric acid oxidizes the plutonium to the tetravalent hexanitrate complex (3), while the transplutonium nuclides remain in the trivalent state. The only actinides retained by a nitrate-form anion-exchange column are thorium, neptunium, and plutonium. The uranium distribution coeflBcient under these conditions is about ten, but uranium should not be present at this point since hexavalent uranium does not carry on calcium fluoride (4). 

Uranium, unlike thorium, has an accessible trivalent oxidation state. It has been shown that uranocene can be reduced by lithium naph-thalide to the bis([8]annulene)uranate(III) anion.23 The same complex can be synthesized by the reaction of two equivalents of [8]annulene dianion with one equivalent of uranium trichloride.23... 

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