Macak Peter, Tsushima Satoru, Wahlgren Ulf, Grenthe Ingmar
Theoretical Chemistry, Royal Institute of Technology (KTH), AlbaNova University Center, 106 91 Stockholm, Sweden.
Dalton Trans. 2006 Aug 14(30):3638-46. doi: 10.1039/b605819a. Epub 2006 Jun 5.
Experimental data on the thermodynamics and reaction mechanism of the inner-sphere fluoride exchange reaction U17O2(2+) + UO2F+ <==> U17O2F+ + UO2(2+) have been compared with different intimate reaction mechanisms using quantum chemical methods. Two models have been tested that start from the outer sphere complexes, (H2O)[U(A)O2F(OH2)4+]...[U(B)O2(OH2)5(2+)] and [U(A)O2F(OH2)4+]...[U(B)O2(OH2)5(2+)]; the geometry and energies of the intermediates and transition states along possible reaction pathways have been calculated using different ab initio methods, SCF, B3LYP and MP2. Both the experimental data and the theoretical results suggest that the fluoride exchange takes place via the formation and breaking of a U-F-U bridge that is the rate determining step. The calculated activation enthalpy DeltaH( not equal) = 30.9 kJ mol(-1) is virtually identical to the experimental value 31 kJ mol(-1); however this agreement may be a coincidence as we do not expect a larger accuracy than 10 kJ mol(-1) with the methods used. The calculations show that the fluoride bridge is formed as an insertion of U(A)O2)F(OH2)4+ into U(B)O2(OH2)5(2+) followed by a subsequent transfer of water from the first to the second coordination sphere of U(B).
关于内球氟交换反应U17O2(2+) + UO2F+ <==> U17O2F+ + UO2(2+)的热力学和反应机理的实验数据，已使用量子化学方法与不同的亲密反应机理进行了比较。测试了两种从外球络合物(H2O)[U(A)O2F(OH2)4+]...[U(B)O2(OH2)5(2+)]和[U(A)O2F(OH2)4+]...[U(B)O2(OH2)5(2+)]开始的模型；沿着可能的反应途径，使用不同的从头算方法，即SCF、B3LYP和MP2，计算了中间体和过渡态的几何结构和能量。实验数据和理论结果均表明，氟交换是通过U-F-U桥的形成和断裂发生的，这是速率决定步骤。计算得到的活化焓ΔH(≠)=30.9 kJ mol(-1)与实验值31 kJ mol(-1)几乎相同；然而，这种一致性可能是巧合，因为我们预计使用的方法的精度不会超过10 kJ mol(-1)。计算表明，氟桥是通过U(A)O2)F(OH2)4+插入U(B)O2(OH2)5(2+)形成的，随后水从U(B)的第一配位球转移到第二配位球。
