Contractile and extensible molecular figures-of-eight

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Development of sophisticated molecular architectures is crucial for advanced materials.
• Macrocyclic ligands offer unique coordination environments for metal ions.
• Designing molecules with dynamic and responsive properties is a key challenge.

Purpose of the Study:

• To synthesize and characterize two new macrocycles, m-66 and m-78, with transition-metal-complexing units.
• To investigate the coordination behavior of these macrocycles with Fe(II) and Cu(I) ions.
• To explore the potential of these systems as molecular machine prototypes.

Main Methods:

• Synthesis of 66- and 78-membered macrocycles incorporating 2,9-diphenyl-1,10-phenanthroline (dpp) and 2,2',2'',6''-terpyridine (terpy) units.
• Complexation studies with Fe(II) and Cu(I) ions.
• Structural characterization of the resulting metal-macrocycle complexes.
• Analysis of molecular rearrangements and dynamic properties.

Main Results:

• Both macrocycles form figure-of-eight structures with Fe(II) via bis-terpy coordination.
• The larger m-78 macrocycle accommodates Cu(I) with a {Cu(dpp)2}+ complex and a twisted backbone.
• Macrocycle m-78 exhibits bimodal coordination, switching between terpy and dpp ligands.
• Significant changes in molecular height were observed based on the coordinated metal and ligand.

Conclusions:

• Macrocycle m-78 demonstrates versatile coordination capabilities with both Fe(II) and Cu(I).
• The observed large amplitude backbone rearrangements are promising for molecular machine applications.
• These figure-of-eight macrocycles represent a new class of molecular machine prototypes for dynamic systems.