Functionalized Triptycene-Derived Tripodal Ligands: Privileged Formation of Tetranuclear Cage Assemblies with Larger Ln(III)

In
this Article, we report the self-assembly of lanthanide complexes
formed with two new tripodal ligands, L2 and L3, where binding strands are connected to a rigid triptycene anchor.
The pyridine moieties are functionalized with methoxy and PEG groups
to enhance ligand solubility and to evaluate the effect of these substituents
on lanthanide coordination. These ligands were successfully synthesized
and characterized, and their coordination properties were examined
along the lanthanide series through speciation studies with NMR and
ESI-MS. Well-defined tetranuclear complexes are formed with both ligands,
but their stabilities with heavier lanthanides are considerably reduced,
especially for complexes with L3. This is attributed
to a destabilizing effect of pending PEG arms in combination with
increased steric hindrance between binding strands upon complexation
with smaller cations. The sensitization of lanthanide luminescence
in tetranuclear complexes occurs despite one water molecule being
coordinated to a metal ion.

本文报道了由两种新型三脚配体L2和L3形成的镧系金属络合物的自组装，其中配位链连接到一个刚性的三联苯基锚。吡啶官能团通过甲氧基和聚乙二醇基团的修饰以提高配体的溶解性，并评估这些取代基对镧系金属配位的影响。这些配体已成功合成并进行了表征，其配位性质通过核磁共振(NMR)和电喷雾电离质谱(ESI-MS)的物种研究在镧系元素系列中得到了考察。两种配体均形成了定义明确的四核络合物，但与较重的镧系金属形成的络合物的稳定性显著降低，尤其是对于L3配体。这种现象归因于未配位的聚乙二醇臂产生的去稳定效应，以及在与较小的阳离子配位时，配位链之间空间位阻的增大。尽管有一个水分子与金属离子配位，四核络合物中的镧系金属发光仍然得到了增强。