Pd(II) Coordination Sphere Engineering: Pyridine Cages, Quinoline Bowls, and Heteroleptic Pills Binding One or Two Fullerenes

Cavity-based applications of metallo-supramolecular coordination cages (MSCCs)

This review describes cavity-based applications of cage-like SCCs such as molecular recognition and separation, stabilization of reactive species by encapsulation, as drug delivery systems and as molecular flasks.

Hydrophobicity controls guest uptake in Rh8 metallacages

The hydrophobic interaction plays a key role in the host–guest systems.

Tunable Fullerene Affinity of Cages, Bowls and Rings Assembled by PdII Coordination Sphere Engineering

For metal‐mediated host compounds, the development of strategies to reduce symmetry and introduce multiple functionalities in a non‐statistical way is a challenging task. We show that the introduction of steric stress around the coordination environment of square‐planar Pd^II cations and bis‐monodentate nitrogen donor ligands allows to control the size and shape of the assembled product, from [Pd₂L₄] cages over [Pd₂L₃] bowl‐shaped structures to [Pd₂L₂] rings. Therefore, banana‐shaped ligand backbones were equipped with pyridines, two different quinoline isomers and acridine, the latter three introducing steric congestion through hydrogen substituents on annelated benzene rings. Differing behavior of the four resulting hosts towards the binding of C₆₀ and C₇₀ fullerenes was studied and related to structural differences by NMR spectroscopy, mass spectrometry and single crystal X‐ray diffraction. The three cages based on pyridine, 6‐quinoline or 3‐quinoline donors were found to either bind C₆₀, C₇₀ or no fullerene at all.

Radical-Induced Hierarchical Self-Assembly Involving Supramolecular Coordination Complexes in Both Solution and Solid States

To explore a new supramolecular interaction as the main driving force to induce hierarchical self-assembly (HSA) is of great importance in supramolecular chemistry. Herein, we present a radical-induced HSA process through the construction of well-defined rhomboidal metallacycles containing triphenylamine (TPA) moieties. The light-induced radical generation of the TPA-based metallacycle has been demonstrated, which was found to subsequently drive hierarchical self-assembly of metallacycles in both solution and solid states. The morphologies of nanovesicle structures and nanospheres resulting from hierarchical self-assembly have been well-illustrated by using TEM and high-angle annular dark-field STEM (HAADF-STEM) micrographs. The mechanism of HSA is supposed to be associated with the TPA radical interaction and metallacycle stacking interaction, which has been supported by the coarse-grained molecular dynamics simulations. This study provides important information to understand the fundamental TPA radical interaction, which thus injects new energy into the hierarchical self-assembly of supramolecular coordination complexes (SCCs). More interestingly, the stability of TPA radical cations was significantly increased in these metallacycles during the hierarchical self-assembly process, thereby opening a new way to develop stable organic radical cations in the future.

Self-Assembled Amphiphilic Janus Double Metallacycle

A double metallacycle was prepared via the size-selective integrative self-sorting of four different building blocks driven by a reversible metal-ligand coordination interaction. A hydrophobic dendron was placed on a metallacycle and a hydrophilic dendron was attached to the other metallacycle, producing a two-faced Janus-type supramolecule with two distinct functionalities. In aqueous media, hierarchical self-assembly of the supramolecular system was induced by the combination of coordination interactions and hydrophobic-hydrophilic interactions resulting in the formation of micrometer-sized fiber-like structures, a morphology distinct from metallacycles bearing only one type of functionality. This study provides a versatile approach for the construction of Janus-type molecules and demonstrates that integrative self-sorting of a supramolecular coordination system can be utilized for the preparation of complex supramolecular systems with predesigned functionalities and morphologies.