Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, United Kingdom.
Inorg Chem. 2013 May 6;52(9):4993-5005. doi: 10.1021/ic3026842. Epub 2013 Apr 24.
Two members of the tetradentate N-donor ligand families 6,6'-bis(1,2,4-triazin-3-yl)-2,2'-bipyridine (BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) currently being developed for separating actinides from lanthanides have been studied. It has been confirmed that CyMe4-BTPhen 2 has faster complexation kinetics than CyMe4-BTBP 1. The values for the HOMO-LUMO gap of 2 are comparable with those of CyMe4-BTBP 1 for which the HOMO-LUMO gap was previously calculated to be 2.13 eV. The displacement of BTBP from its bis-lanthanum(III) complex by BTPhen was observed by NMR, and constitutes the only direct evidence for the greater thermodynamic stability of the complexes of BTPhen. NMR competition experiments suggest the following order of bis-complex stability: 1:2 bis-BTPhen complex ≥ heteroleptic BTBP/BTPhen 1:2 bis-complex > 1:2 bis-BTBP complex. Kinetics studies on some bis-triazine N-donor ligands using the stopped-flow technique showed a clear relationship between the rates of metal ion complexation and the degree to which the ligand is preorganized for metal binding. The BTBPs must overcome a significant (ca. 12 kcal mol(-1)) energy barrier to rotation about the central biaryl C-C axis in order to achieve the cis-cis conformation that is required to form a complex, whereas the cis-cis conformation is fixed in the BTPhens. Complexation thermodynamics and kinetics studies in acetonitrile show subtle differences between the thermodynamic stabilities of the complexes formed, with similar stability constants being found for both ligands. The first crystal structure of a 1:1 complex of CyMe4-BTPhen 2 with Y(NO3)3 is also reported. The metal ion is 10-coordinate being bonded to the tetradentate ligand 2 and three bidentate nitrate ions. The tetradentate ligand is nearly planar with angles between consecutive rings of 16.4(2)°, 6.4(2)°, 9.7(2)°, respectively.
两种四齿氮供体配体家族成员 6,6'-双(1,2,4-三嗪-3-基)-2,2'-联吡啶（BTBP）和 2,9-双(1,2,4-三嗪-3-基)-1,10-菲咯啉（BTPhen）目前正在开发用于分离锕系元素和镧系元素。已经证实 CyMe4-BTPhen 2 的络合动力学比 CyMe4-BTBP 1 更快。2 的 HOMO-LUMO 能隙值与 CyMe4-BTBP 1 的 HOMO-LUMO 能隙值相当，先前计算 CyMe4-BTBP 1 的 HOMO-LUMO 能隙值为 2.13 eV。通过 NMR 观察到 BTBP 从其双镧（III）配合物中被 BTPhen 取代，这构成了 BTPhen 配合物具有更大热力学稳定性的唯一直接证据。NMR 竞争实验表明双配合物稳定性的以下顺序：1:2 双 BTPhen 配合物≥杂配 BTBP/BTPhen 1:2 双配合物＞1:2 双 BTBP 配合物。使用停流技术对一些双三嗪氮供体配体的动力学研究表明，金属离子络合的速率与配体结合金属的预组织程度之间存在明显的关系。BTBPs 必须克服约 12 kcal mol(-1)的中央联苯 C-C 轴旋转的能垒，才能形成所需的顺式-顺式构象以形成配合物，而 BTPhens 中的顺式-顺式构象是固定的。在乙腈中的配合物热力学和动力学研究表明，所形成的配合物的热力学稳定性存在细微差异，两种配体都发现了相似的稳定常数。还报道了 CyMe4-BTPhen 2 与 Y(NO3)3 的 1:1 配合物的第一个晶体结构。金属离子是 10 配位的，与四齿配体 2 和三个双齿硝酸根离子键合。四齿配体几乎是平面的，相邻环之间的角度分别为 16.4(2)°、6.4(2)°和 9.7(2)°。
