Uranium Cyanides from Reactions in Liquid Ammonia Solution

So far there are only very few uranium cyanides. Three novel uranium cyanides have been obtained from reactions of uranium halides with cyanides in liquid ammonia as a solvent.

Abstract

Reactions of uranium tri- and tetrahalides, UBr₃, UI_3, UCl₄, and UI₄, with different cyanides MCN (M=K, Ag) in liquid anhydrous ammonia led to three novel uranium(IV) cyanide compounds. The reaction of UCl₄ in the presence of KCN resulted in the compound [U(CN)(NH₃)₈]Cl₃ ⋅ 3NH₃, while UBr₃ and UI₃ were oxidized in the presence of AgCN to form the compounds (μ-CN){(H₃N)₅U(μ-NH₂)₃U(NH₃)₅}]Br₄ ⋅ 2NH₃, and (μ-CN){(H₃N)₅U(μ-NH₂)₃U(NH₃)₅}]I₄ ⋅ 2NH₃. The reaction of UI₄ with KCN in aNH₃ also yielded the compound (μ-CN){(H₃N)₅U(μ-NH₂)₃U(NH₃)₅}]I₄ ⋅ 2NH₃. The compounds (μ-CN){(H₃N)₅U(μ-NH₂)₃U(NH₃)₅}]X ₄ ⋅ 2NH₃ (X=Br, I) crystallize in different space groups, Pmn2₁ (no. 31) and Imm2 (no. 44), respectively. In both cases, the (μ-CN){(H₃N)₅U(μ-NH₂)₃U(NH₃)₅}]⁴⁺ cation forms infinite strands. We conducted quantum-chemical calculations and Intrinsic Bond Orbital analyses on the observed [U(CN)(NH₃)₈]³⁺ cation and the [(μ-CN)₂{(H₃N)₅U(μ-NH₂)₃U(NH₃)₅}]³⁺ model cation to gain insight into the bonding situation.

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