Uranium, oxidation state, promoted

While titanium substituted for antimony and this had a dramatic effect on catalytic activity as expected, there is a question as to how much of the uranium was converted from the +5 to the +6 oxidation state. The shifts in the infrared bands indicate a shortening of the bond distance and a lengthening of the Sb-0 bond distance which is consistent with an increase in hexavalent character, but the magnetic measurements show that a substantial portion of the uranium remained in +5 state. If the valence of uranium is not changed, then the replacement of Sb" by Ti must generate oxygen vacancies in the USb Oj Q lattice. It is these sites that may be responsible for the high activity of the promoted catalysts. 

For the lighter actinide elements, such as uranium, neptunium, plutonium, and americium, the promotion energy of 5f —> 6d is smaller than that of 4f 5d transition in the lanthanides. Due to this smaller promotion energy, the chemical bonding is complicated in the lighter actinides and these elements take from 3+ to 7+ oxidation states. However, the heavier actinides beyond curium more closely resemble the lanthanides and the trivalent state becomes stable. In order to understand the chemistry of transuranium elements, one has to consider the relative energy of the valence orbitals and the relativistic effects on... 

U(Tp )2CH2Ph] and the high thermodynamic stabihty of the +4 oxidation state.The trivalent uranium complex [U(Tp )2(CH2Ph)] has been investigated by DFT as catalyst to promote the fimctionahzation ofC02 and CS2-It has been found that the interaction between CO2 and CS2 is not with central uranium atom, but due to the steric hindrance the first step is the cleavage of the U—C benzyl bond to form a C—C covalent bond. " ... 

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