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首页> 外文期刊>Chemistry: A European journal >Thermodynamic Parameters Governing the Self-Assembly of Head-Head-Head Lanthanide Bimetallic Helicates
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Thermodynamic Parameters Governing the Self-Assembly of Head-Head-Head Lanthanide Bimetallic Helicates

机译：热力学参数控制头-头-头镧系金属双金属螺旋的自组装

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摘要

The heterobitopic ligands L~(ABX) (X=1,2,3,4 or 5), differing only by a Cl or NEt_2 substituent, have been designed to complex with a pair of lanthanide ions to form triple-stranded bimetallic helicates of overall composition [Ln_2(L~(ABX))_3]~(6+). The percentage of HHH (head-head-head) isomer, in which each of the three ligand strands coordinates to the same lanthanide ion with the same coordination unit, is deciding the ability of the ligands to selectively form heterobimetallic complexes containing one luminescent andone magnetic or two different luminescent ions. It deviates significantly from the statistical value of 25% and ranges from 6-20% for L~(AB2) complexes to 93-96% for L~(AB4) complexes. The equilibrium between HHT (head-head-tail) and HHH isomers has been investigated in detail for homobimetallic helicates (Ln=Y, La, Ce, Pr, Nd, Sm, Eu, Lu) by means of variable temperature NMR and thermodynamic parameters have been determined. The equilibrium is characterized by small values of AH and DELTA S, which vary in opposite direction along the lanthanide series for complexes with the same ligand in a way that keeps the value of DELTA G almost constant. The results are interpreted in terms of differences in interstrand stacking, ion-dipole interactions and metal-metal repulsion.
机译：异双位配体L〜（ABX）（X = 1,2,3,4或5）仅与Cl或NEt_2取代基不同，已设计为与一对镧系元素离子络合形成三链双金属双螺旋整体组成[Ln_2（L〜（ABX））_ 3]〜（6+）。 HHH（头-头-头）异构体的百分比，其中三个配体链中的每一个均以相同的配位单元与相同的镧系元素配位，决定了配体选择性形成含有一种发光和一种磁性的异双金属配合物的能力或两个不同的发光离子。它与25％的统计值有显着偏差，范围从L〜（AB2）配合物的6-20％到L〜（AB4）配合物的93-96％。已通过可变温度NMR和热力学参数详细研究了同双金属螺旋产物（Ln = Y，La，Ce，Pr，Nd，Sm，Eu，Lu）的HHT（头-头尾）与HHH异构体之间的平衡已经确定。平衡的特征是AH和DELTA S的值较小，对于具有相同配体的配合物，它们沿镧系元素的方向相反，以使DELTA G值几乎恒定的方式变化。根据链间堆叠，离子-偶极相互作用和金属-金属排斥的差异来解释结果。

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