Multinuclear uranium-nitrogen cluster formation from exploration of organouranium-ammonolysis.

Uranium-nitrogen compounds (UxNy) pose interesting structural and electronic questions. Understanding the formation and speciation of UxNy may provide insights in nitrogen fixation as well as the preparation of potential uranium nitride nuclear fuels, a promising Gen IV nuclear reactor fuel. Small molecular clusters offer the opportunity to study UxNy using solution and dynamic spectroscopies. Herein, we have explored a new method for  the synthesis of multinuclear uranium-nitrogen clusters containing uranium-nitride, -imide, and -amide moieties in excellent yield. Ammonolysis of (C5Me5)UBn3 gives a mixture of the tetra- and hexa-nuclear clusters (C5Me5)4U4(µ4-N)(µ-NH)(μ-NH2)7, 1, (C5Me5)6U6(µ6-N)(µ3-NH2)(µ3-NH)7, 2, and (C5Me5)6U6(µ3-N)2(µ-NH2)12, 3. Compound 1 was readily separated from 2 and 3, but compounds 2 and 3 display similar solubilities. Various reaction conditions, including changing the stoichiometry, reaction time, solvent free conditions, or the use of an ammonia/dioxane solution, did not alter the identity of what clusters were produced. Only small variations in the amount of each cluster produced were observed. Once formed, the clusters do not interconvert. The clusters were characterized by single crystal X-ray diffraction as well as 1H NMR, UV-vis-NIR, and IR spectroscopies.