Geometrically Complementary Self-Assembly of a Hexarhomboid Architecture from Two Ruthenium(II)-Organic Building Blocks

Assembly of Six Types of Heteroleptic Pd2L4 Cages under Kinetic Control

Heteroleptic assemblies composed of several kinds of building blocks have been seen in nature. It is still unclear how natural systems design and create such complicated assemblies selectively. Past efforts on multicomponent self-assembly of artificial metal-organic cages have mainly focused on finding a suitable combination of building blocks to lead to a single multicomponent self-assembly as the thermodynamically most stable product. Here, we present another approach to selectively produce multicomponent Pd(II)-based self-assemblies under kinetic control based on the selective ligand exchanges of weak Pd-L coordination bonds retaining the original orientation of the metal centers in a kinetically stabilized cyclic structure and on local reversibility given in certain areas of the energy landscape in the presence of the assist molecule that facilitates error correction of coordination bonds. The kinetic approach enabled us to build all six types of Pd2L4 cages and heteroleptic tetranuclear cages composed of three kinds of ditopic ligands. Although the cage complexes thus obtained are metastable, they are stable for 1 month or more at room temperature.

Construction of 1,3,5-Triazine-Based Prisms and Their Enhanced Solid-State Emissions

In this study, two trigonal prisms based on the 1,3,5-triazine motif (SA and SB), distinguished by hydrophobic groups, were prepared by the self-assembly of tritopic terpyridine ligands and Zn(II) ions. SA and SB exhibited high luminescence efficiencies in the solid state, overcoming the fluorescence quenching of the 1,3,5-triazine group caused by π-π interactions. Notably, SA and SB exhibited different luminescence behaviors in the solution state and aggregation state. SB with 12 alkyl chains exhibited extremely weak fluorescence in a dilute solution, but its fluorescence intensity and photoluminescence quantum yield (PLQY) were significantly enhanced in the aggregated state (with the increase in the water fraction), especially in the solid state. Different from the gradually enhanced efficiency of SB, the PLQY of SA gradually decreased with the increase in aggregation but still maintained a high luminescence efficiency. These two complexes exhibited different modes to solve the fluorescence quenching of 1,3,5-triazine in the solid state. The hierarchical self-assembly of SB exhibited nanorods owing to the hydrophobic interactions of alky chains, while SA aggregated into spheres under the influence of π-π interactions.

Tetratopic Terpyridine Building Unit as a Precursor to Wheel-Like Metallo-Supramolecules

In an effort to construct molecules with distinct shapes and functions, the design and synthesis of multitopic ligands are often able to play an important role. Here, we report the synthesis of a novel tetratopic organic ligand LA, which can be viewed as a bis-tenon with successive angular orientations in space. The particular ligand has been treated with different tailored metal-organic ligands to afford new members of the molecular wheel family (multi-rhomboidal-shaped wheel and bis-trapezium-shaped wheel) that show enhanced stability. Two-dimensional (2D) diffusion nuclear magnetic resonance (NMR) spectroscopy (DOSY), electrospray ionization (ESI) mass spectrometry, traveling wave ion mobility (TWIM), and gradient tandem mass spectrometry (gMS₂) experiments, as well as molecular modeling, have been employed to provide structural information and differentiate the isomeric separation process. In addition, considering that LA has rotational properties, it is expected to open the door to functional supramolecules and stimuli-responsive materials.