Uranyl chloro complexes

Chaumont, A., Wipff, G. (2004), Solvation of Uranyle 11, Europium 111 Cations and their Chloro complexes in a Room-Temperature Ionic Liquid. A Theoretical Study of the effect of Solvent Humidity, Inorg. Chem. 43, in press. 

Treatment of U02C12(THF)3 in THF with 1 equiv. of Na[CH(Ph2P=NSiMe3)2] led to formation of an unusual red uranyl chloro-bridged dimer (70% yield) containing a uranium(vi)-carbon bond as part of a tridentate bis(imino-phosphorano)methanide chelate complex (Scheme 9). This was the first example of a uranyl-methine carbon bond. The methine carbon is displaced significantly from the uranyl equatorial plane.33... 

Ions comprise another class of solutes which have been studied extensively by Wipff and coworkers, who have been particularly interested in lanthanide and uranyl ions and their chloro-complexes [44,142]. Their studies show that the chloro-complexes are stabHized by solvation in the ionic liquids based on imidazolium cations and the [PFe]" anion. The principal interaction of the naked ions is with the anions, but on chlorination the cations move closer to complexes such as [EuQe] and [U02Cl4] . In a further study [45] they showed that in an equimolar mixture of water and ionic liquid, water molecules tend to fill the first solvation shell of naked ions in preference to [PFs]" ions, and tend to solvate the chloro-complexes in preference to the imidazolium cations. 

Of all uranium species existing in solutions those containing uranium in the oxidation state d-5 (normally in the form of U02 moieties) are the least studied. Aqueous solutions of U02 are prone to disproportionation, with the carbonato-complex 002(003)3 being the best known. A number of uranium(V) complexes were characterised in organic solvents [1]. In solutions uranium(V) species are most stable in ionic solvents including molten salts. In the chloride-based melts uranyl(V) chloro-complexes were reported over half of a century ago [2, 3] and their electrochemical, thermodynamic and structural properties have subsequently been studied to a certain extent [4-9]. 

The reduction of uranyl ion by titanium(m) has been investigated in various solvents. In acetonitrile or DMF, at ambient temperature, there is a rapid reaction involving the chloro-complexes of the reductant and the complexed uranyl ion to yield TiOCla and UCls , whereas in acetone or (BuO)bPO the uranium product is UCU". The uncharged UCI5 complex predominates in methanol. The mechanism of the reaction is however attributed to direct electron- and oxygen-atom-transfer between the inner co-ordination spheres of the titanium(in) and uranium. 

The stability constants of uranyl amino- and mercapto-acid complexes have been determined. Among the acids investigated were cysteine, methionine, P-alanine, anthranilic acid, serine, threonine, and JV-ac tylglycine. Stability constants of a series of chloro-, bromo-, iodo-, and nitro-substituted salicylic acid and of o-pyrocatechinic, y-resorcylic, and gentisic acids complexes of UOj" have been measured 1 1 and 1 2 species were identified. It was observed that there was a distinct dependence of stability constant on the charge of the central metal atom in UO ", NpO, and Pu " tropolonato complexes. ... 

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