Engineered π⋯π interactions favour supramolecular dimers X@[FeL₃]₂ (X = Cl, Br, I): solid state and solution...

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Ditopic bis-pyrazolylpyridine ligands typically form dinuclear helicates or dimers with M2+ ions.
• Increased aromatic contacts in ligands can enhance self-recognition and alter aggregate formation.
• Understanding ligand design is crucial for controlling supramolecular assembly.

Purpose of the Study:

• To investigate the self-assembly of new bis-pyrazolylquinoline ligands (L2) with iron(II) halides.
• To characterize the structure and stability of the resulting supramolecular assemblies.
• To explore the influence of halide guests on the stability and behavior of these assemblies in solution.

Main Methods:

• Synthesis and crystallization of tripartite high-spin assemblies (X@[Fe(L2)3]2)3+.
• Structural characterization using X-ray diffraction (implied by crystallization).
• Stability studies in solution using paramagnetic 1H NMR spectroscopy.

Main Results:

• The new ligand L2 irreversibly drives the formation of tripartite high-spin assemblies with FeX2.
• These assemblies, (X@[Fe(L2)3]2)3+, exhibit exceptional stability in solution.
• Bromide and iodide guests are retained within the assembly, while chloride is released, forming an empty supramolecular dimer.

Conclusions:

• Enhanced aromaticity in bis-pyrazolylquinoline ligands promotes the formation of robust, tripartite supramolecular assemblies.
• The stability of these iron complexes in solution is confirmed by NMR studies.
• The selective retention or release of halide guests offers insights into host-guest interactions within supramolecular structures.