Spectroscopic investigation of effect of Lewis basicity on the valent-state stability of an uranium(V) chloride complex in ambient temperature melts

The visible and NIR absorption spectrum of uranium(V) chloride in room temperature acidic melts has been measured. This spectrum was obtained by the direct dissolution of an uranium(V) chloride compound into a room temperature melt. Changing the acidic melt to a basic melt by adding EMIC caused the gradual disappearance of the U(V) spectrum and the concomitant appearance of a new set of bands. The absorption spectrum recorded in the basic melt of composition AlCl3:EMIC = 45:55 is identical to that from the uranium(IV) hexachloride complex in the same melt. This conversion of U(V) to U(IV) establishes that the uranium(V) chloride complex underwent a reduction reaction to form the uranium(IV) hexachloride complex. The stoichiometric ratio of U(total):U(IV) in this redox process was experimentally determined to be 1.00:1.00. The standard deviation for this ratio is 0.02. This suggests that the formation of uranium(IV) hexachloride in the basic melt is not via the disproportionation reaction of U(V).