Hu Shao-Wen, Wang Xiang-Yun, Chu Tai-Wei, Liu Xin-Qi
Department of Applied Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing, China 100871.
J Phys Chem A. 2008 Sep 18;112(37):8877-83. doi: 10.1021/jp804797a. Epub 2008 Aug 23.
The mechanism of the gas-phase reaction UF 6 + H 2O --> UOF 4 + 2HF is explored using relativistic density functional theory calculations. Initially, H 2O coordinates with UF 6 to form a 1:1 complex UF 6.H 2O. Over an activation energy barrier of about 19 kcal/mol, H 2O transfers a H atom to a nearby ligand F, resulting in UF 5OH + HF. The eliminated HF or another H 2O molecule may form a hydrogen bond with UF 5OH. Starting from UF 5OH, the second HF elimination results in UOF 4. If UF 5OH is in the isolated form, UF 5OH --> UOF 4 + HF takes place over a barrier of 24 kcal/mol. If UF 5OH is hydrogen-bonded with H 2O or HF, the conversion barrier is less than 10 kcal/mol. Once formed, the unstable UOF 4 tends to associate with additional ligands and hydrogen-bonding donors. The calculated binding energies indicate the significance of such interactions, which may have profound impact on further HF eliminating reactions. The IR spectra features can be used to indicate the formation and interaction type of the intermediates and products.
利用相对论密度泛函理论计算，探究了气相反应UF₆ + H₂O --> UOF₄ + 2HF的反应机理。起初，H₂O与UF₆配位形成1:1络合物UF₆·H₂O。越过约19千卡/摩尔的活化能垒后，H₂O将一个H原子转移至附近的配体F，生成UF₅OH + HF。消除的HF或另一个H₂O分子可能与UF₅OH形成氢键。从UF₅OH开始，第二次HF消除生成UOF₄。如果UF₅OH处于孤立形式，UF₅OH --> UOF₄ + HF的反应需越过24千卡/摩尔的能垒。如果UF₅OH与H₂O或HF形成氢键，转化能垒小于10千卡/摩尔。一旦形成，不稳定的UOF₄倾向于与额外的配体和氢键供体缔合。计算得到的结合能表明了此类相互作用的重要性，这可能对进一步的HF消除反应产生深远影响。红外光谱特征可用于指示中间体和产物的形成及相互作用类型。
