Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-34, O-okayama, Meguro-ku, Tokyo 152-8550, Japan.
Inorg Chem. 2010 Mar 1;49(5):2349-59. doi: 10.1021/ic902225f.
The U(VI) complex with a pentadentate Schiff base ligand (N,N'-disalicylidenediethylenetriaminate = saldien(2-)) was prepared as a starting material of a potentially stable U(V) complex without any possibility of U(V)O(2)(+)...U(V)O(2)(+) cation-cation interaction and was found in three different crystal phases. Two of them had the same composition of U(VI)O(2)(saldien) x DMSO in orthorhombic and monoclinic systems (DMSO = dimethyl sulfoxide, 1a and 1c, respectively). The DMSO molecule in both 1a and 1c does not show any coordination to U(VI)O(2)(saldien), but it is just present as a solvent in the crystal structures. The other isolated crystals consisted only of U(VI)O(2)(saldien) without incorporation of solvent molecules (1b, orthorhombic). A different conformation of the coordinated saldien(2-) in 1c from those in 1a and 1b was observed. The conformers exchange each other in a solution through a flipping motion of the phenyl rings. The pentagonal equatorial coordination of U(VI)O(2)(saldien) remains unchanged even in strongly Lewis-basic solvents, DMSO and N,N-dimethylformamide. Cyclic voltammetry of U(VI)O(2)(saldien) in DMSO showed a quasireversible redox reaction without any successive reactions. The electron stoichiometry determined by the UV-vis-NIR spectroelectrochemical technique is close to 1, indicating that the reduction product of U(VI)O(2)(saldien) is U(V)O(2)(saldien), which is stable in DMSO. The standard redox potential of U(V)O(2)(saldien)/U(VI)O(2)(saldien) in DMSO is -1.584 V vs Fc/Fc(+). This U(V) complex shows the characteristic absorption bands due to f-f transitions in its 5f(1) configuration and charge-transfer from the axial oxygen to U(5+).
以五齿席夫碱配体（N，N'-二水杨醛缩乙二胺 = saldien(2-)）与六价铀配合物作为潜在稳定的五价铀配合物的起始原料，该配合物没有 U(V)O(2)(+)…U(V)O(2)(+)阳离子-阳离子相互作用的可能性，并在三种不同的晶体相中被发现。其中两种具有相同的组成，在正交和单斜晶系中为 U(VI)O(2)(saldien)xDMSO（DMSO = 二甲亚砜，分别为 1a 和 1c）。在 1a 和 1c 中，DMSO 分子均不与 U(VI)O(2)(saldien)配位，而只是作为溶剂存在于晶体结构中。另一种分离出来的晶体仅由 U(VI)O(2)(saldien)组成，不包含溶剂分子（1b，正交晶系）。在 1c 中，与 1a 和 1b 中观察到的配位 saldien(2-)的构象不同。在溶液中，通过苯环的翻转运动，构象相互转化。即使在强路易斯碱性溶剂 DMSO 和 N，N-二甲基甲酰胺中，U(VI)O(2)(saldien)的五边形赤道配位也保持不变。在 DMSO 中，U(VI)O(2)(saldien)的循环伏安法显示出准可逆的氧化还原反应，没有任何连续反应。通过紫外可见近红外光谱电化学技术确定的电子化学计量接近 1，表明 U(VI)O(2)(saldien)的还原产物为[U(V)O(2)(saldien)]-，在 DMSO 中稳定。在 DMSO 中，[U(V)O(2)(saldien)]-/U(VI)O(2)(saldien)的标准氧化还原电位为-1.584 V 相对于 Fc/Fc(+)。该 U(V)配合物显示出其 5f(1)构型的 f-f 跃迁和轴向氧到 U(5+)的电荷转移引起的特征吸收带。
