Floquet Sébastien, Ouali Nadjet, Bocquet Bernard, Bernardinelli Gérald, Imbert Daniel, Bünzli Jean-Claude G, Hopfgartner Gérard, Piguet Claude
Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, Switzerland.
Chemistry. 2003 Apr 14;9(8):1860-75. doi: 10.1002/chem.200390214.
The segmental tris-tridentate ligand L7 reacts with stoichiometric quantities of Ln(III) (Ln=La-Lu) in acetonitrile to give the complexes Ln(2)(L7)(3) and Ln(3)(L7)(3). Formation constants point to negligible size-discriminating effects along the lanthanide series, but Scatchard plots suggest that the self-assembly of the trimetallic triple-stranded helicates Ln(3)(L7)(3) is driven to completion by positive cooperativity, despite strong intermetallic electrostatic repulsions. Crystallization provides quantitatively Ln(3)(L7)(3)(9) (Ln=La, Eu, Gd, Tb, Lu) and the X-ray crystal structure of Eu(3)(L7)(3)(9).(CH(3)CN)(9).(H(2)O)(2) (Eu(3)C(216)H(226)N(48)O(35)F(27)S(9), triclinic, P1, Z=2) shows the three ligand strands wrapped around a pseudo-threefold axis defined by the three metal ions rigidly held at about 9 A. Each metal ion is coordinated by nine donor atoms in a pseudo-trigonal prismatic arrangement, but the existence of terminal carboxamide units in the ligand strands differentiates the electronic properties of the terminal and the central metallic sites. Photophysical data confirm that the three coordination sites possess comparable pseudo-trigonal symmetries in the solid state and in solution. High-resolution luminescence analyses evidence a low-lying LMCT state affecting the central EuN(9) site, so that multi-metal-centered luminescence is essentially dominated by the emission from the two terminal EuN(6)O(3) sites in Eu(3)(L7)(3). New multicenter equations have been developed for investigating the solution structure of Ln(3)(L7)(3) by paramagnetic NMR spectroscopy and linear correlations for Ln=Ce-Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second-rank crystal-field parameters, obtained by LIS analysis, for the LnN(6)O(3) and LnN(9) sites with respect to the parameters extracted for Eu(III) from luminescence data, suggests that the geometry of the central LnN(9) site is somewhat relaxed in solution.
分段三齿配体L7在乙腈中与化学计量的Ln(III)（Ln = La - Lu）反应，生成配合物Ln(2)(L7)(3)和Ln(3)(L7)(3)。形成常数表明沿镧系元素系列尺寸区分效应可忽略不计，但Scatchard图表明，尽管存在强烈的金属间静电排斥作用，三金属三链螺旋体Ln(3)(L7)(3)的自组装仍因正协同作用而趋于完成。结晶定量得到Ln(3)(L7)(3)(9)（Ln = La、Eu、Gd、Tb、Lu），Eu(3)(L7)(3)(9)·(CH(3)CN)(9)·(H(2)O)(2)（Eu(3)C(216)H(226)N(48)O(35)F(27)S(9)，三斜晶系，P1，Z = 2）的X射线晶体结构显示，三条配体链围绕由三个刚性固定在约9 Å处的金属离子定义的伪三重轴缠绕。每个金属离子由九个供体原子以伪三角棱柱排列配位，但配体链中末端羧酰胺单元的存在使末端和中心金属位点的电子性质有所不同。光物理数据证实，在固态和溶液中，三个配位点具有可比的伪三角对称性。高分辨率发光分析表明，一个低能的配体到金属电荷转移（LMCT）态影响中心EuN(9)位点，因此在Eu(3)(L7)(3)中，多金属中心发光基本上由两个末端EuN(6)O(3)位点的发射主导。已开发出新的多中心方程，用于通过顺磁核磁共振光谱研究Ln(3)(L7)(3)的溶液结构，对于Ln = Ce - Tb的线性相关性表明这些较大的镧系元素具有同构性。核磁共振光谱表明三螺旋结构在溶液中得以保持，但通过配体诱导位移（LIS）分析获得的LnN(6)O(3)和LnN(9)位点的二级晶体场参数大小相对于从发光数据中提取的Eu(III)的参数发生了反转，这表明中心LnN(9)位点的几何结构在溶液中有所松弛。
