Gold-Clip-Assisted Self-Assembly and Proton-Coupled Expansion-Contraction of a Cofacial Fe

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Self-assembly of complex molecular architectures is crucial for developing novel functional materials.
• Iron-porphyrin complexes are versatile building blocks in coordination chemistry.
• Gold coordination compounds offer unique structural and electronic properties.

Purpose of the Study:

• To synthesize and characterize a novel molecular cage composed of gold and iron-porphyrin units.
• To investigate the structural changes and reversibility of the molecular cage upon external stimuli.
• To explore the potential applications of such dynamic molecular cages.

Main Methods:

• Self-assembly of the molecular cage using a gold clip and iron-porphyrin precursors.
• Structural characterization using X-ray crystallography.
• Spectroscopic analysis including NMR and UV/Vis titrations.
• Density Functional Theory (DFT) calculations to support structural assignments.

Main Results:

• Successful synthesis of a molecular cage {Au8 (μ-PAnP)4 [Fe(H2 O)2 (TPyP)]2 (OTf)2 }(OTf)8 with a height of 8.579(3) Å.
• Demonstration of reversible cage contraction and twisting to ≈4.4 Å height and ≈20° torsional angle upon base addition.
• Independent synthesis of the contracted cage and its unclipped analog, confirming structural integrity.
• Validation of cage structure and dynamics through spectroscopic methods and DFT calculations.

Conclusions:

• A novel, dynamic molecular cage based on gold and iron-porphyrin has been successfully constructed.
• The cage exhibits reversible structural transformations (expansion-contraction, untwisting-twisting) in response to chemical stimuli.
• The findings open avenues for designing responsive supramolecular systems and functional nanomaterials.