Asymmetrical
and dissymmetrical structures are widespread and play
a critical role in nature and life systems. In the field of metallo-supramolecular
assemblies, it is still in its infancy for constructing artificial
architectures using dissymmetrical building blocks. Herein, we report
the self-assembly of supramolecular systems based on two dissymmetrical
double-layered ligands. With the aid of ultra-high-vacuum, low-temperature
scanning tunneling microscopy (UHV-LT-STM), we were able to investigate
four isomeric structures corresponding to four types of binding modes
of ligand LA with two major conformations complexes A. The distribution of isomers measured by STM and total binding
energy of each isomer obtained by density functional theory (DFT)
calculations suggested that the most abundant isomer could be the
most stable one with highest total binding energy. Finally, through
shortening the linker between inner and outer layers and the length
of arms, the arrangement of dissymmetrical ligand LB could
be controlled within one binding mode corresponding to the single
conformation for complexes B.
In nature as well as life systems, the presence of asymmetrical and dissymmetrical structures with specific functions is extremely common. However, the construction of metallo‐supramolecular assemblies based on dissymmetrical ligands still remains a considerable challenge for avoiding the generation of unexpected isomers with similar thermodynamic stabilities, especially for three‐dimensional supramolecular structures. In this study, a strategy for the conformational control of metallo‐supramolecular cages via the enhancement of ligand dissymmetry was proposed. Four dissymmetrical ditopic ligands were designed and synthesized. By increasing the dissymmetry of length or angle, conformations of assemblies were precisely controlled to form discrete cis‐PdnL2n molecular cages.
Mechanically interlocked molecules (MIMs) and host-guest chemistry have received great attention in the past few decades. However, it remains challenging to design architectures with mechanically interlocked features and construct cavities for guest molecule recognition using similar building blocks. In this study, we designed and constructed a series of novel twisted supramolecular structures by assembling various multitopic terpyridinyl (tpy) ligands with the same diameter and Zn(II) ions. The obtained complexes exhibited evolutional architectures and showed distinctively different space-constraint effects. Specifically, the assembled dimer SA, SB, and SBH displayed mechanically interlocked phenomena with the increase of concentration, including [2]catenane and [3]catenane. However, no interlocked structures were observed in complexes SC and SCH constructed by hexatopic tpy ligands, due to the significant space constraints. The single-crystal data of complex SCH further proved significant space constraints and illustrated the formation
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