Wide variability in the stability of Pd₆L_x-type coordination cages

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Hexanuclear palladium (Pd)-based coordination cages, specifically [Pd6L12]12+ and [Pd6L8]12+ types, are of interest for their structural properties.
• Understanding the stability of these self-assembled structures is crucial for their potential applications.

Purpose of the Study:

• To investigate the relative thermodynamic and kinetic stability of eight hexanuclear Pd-based coordination cages.
• To identify the key factors governing the stability of these supramolecular assemblies.
• To explore the synthesis of larger cage structures based on stability insights.

Main Methods:

• Synthesis of eight [Pd6L12]12+ or [Pd6L8]12+ cages, including two novel compounds with crystallographic analysis.
• Stability studies conducted by exposing cage solutions (in DMSO-d6 or CD3CN) to varying concentrations of pyridine.
• Monitoring cage degradation using proton nuclear magnetic resonance (1H NMR) spectroscopy.

Main Results:

• Significant variability in cage stability was observed, with thermodynamic stability differing by nearly two orders of magnitude and kinetic stability by over four orders of magnitude.
• The primary determinant of cage stability is the nature of the donor group within the ligand, while denticity plays a secondary role.
• High kinetic stability, particularly with imidazole-based ligands, enabled the formation of a rare octanuclear cage, [Pd8L16]16+.

Conclusions:

• The stability of Pd-based coordination cages is highly tunable through ligand design.
• Imidazole-based ligands offer superior kinetic stability, facilitating the construction of complex, larger supramolecular architectures.
• These findings provide a foundation for designing robust coordination cages with tailored properties.