Guest-Shape-Directed Structural Switching between Two Isomers of a Pd₆ Host and Its Structural Adaptability for...

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• The structure and function of metal-organic cages (MOCs) are dictated by their constituent building blocks.
• Previous work with tetramethyl-substituted ethylene diamine blocked cis-Pd(II) acceptors yielded double-square architectures in water.

Purpose of the Study:

• To design and synthesize a novel metal-organic cage (M1O) using a dimethyl-substituted propane diamine blocked cis-Pd(II) acceptor (A) and a tri-imidazole ligand (L).
• To investigate the guest-shape-dependent structural transformations of the synthesized cage.
• To explore the cage's potential for selective photodimerization and enzyme-like activity.

Main Methods:

• Self-assembly of a cis-Pd(II) acceptor (A) with a tri-imidazole ligand (L) to form an octahedral cage (M1O).
• Investigation of structural changes in M1O upon introduction of planar (Gn) and tetrahedral (G5/G6) guests.
• Photochemical studies of anthracene derivatives within the cage structure.
• Analysis of host-guest complex formation and dissociation.

Main Results:

• An unusual A6L4 octahedral cage (M1O) was formed, differing from expected double-square architectures.
• M1O transformed into a transient double-square cage (M1DS) in the presence of planar guests (Gn), forming (Gn)2@M1DS complexes.
• Tetrahedral guests (G5/G6) stabilized the octahedral M1O form and could displace planar guests from M1DS.
• Selective photodimerization of anthracene derivatives occurred within M1DS, leading to product expulsion and cage recovery.
• The cage mimicked enzymatic activity through its adaptive host behavior and selective photodimerization.

Conclusions:

• A multifunctional supramolecular host exhibiting reversible, guest-shape-driven structural switching was successfully developed.
• The cage demonstrates adaptive behavior, acting as a template for guest stabilization or transformation.
• The system shows potential for selective photodimerization and mimics enzymatic functions, highlighting its versatility in supramolecular chemistry.