Blue coloration of uranium in aqueous solution

A mixed valence hydroxo complex of uranium in aqueous solution is prepared by mixing an uranyle-chlorid solution with a tetramethyl-ammonium or tetrabuthyl-ammonium hydroxid solution at pH=10.5 - 12.5. The blue coloration is caused by the absorption band in the visible spectrum. Absorption spectrum of this complex suggests that it contains U(VI) and U(V) ions. Charge transfer bands *U(VI)+U(V)+hν → * U(V)+U(VI) are also observed. All the band intensities are in direct proportion to the concentration of uranium. The oxidation number is close to 5.75 showing that the complex contains one U(V) for three U(VI) atoms. (N.L.Gy.)