Steric Hindrance and Secondary Interactions Govern Reconfiguration Between Two Complex Cu^I Coordination Cages

Area of Science:

• Coordination chemistry
• Supramolecular chemistry
• Materials science

Background:

• Metal-organic cages (MOCs) are versatile supramolecular structures with applications in catalysis, sensing, and drug delivery.
• Controlling the self-assembly of MOCs is crucial for tailoring their properties and functions.
• Steric hindrance and non-covalent interactions play significant roles in directing the formation of specific MOC architectures.

Purpose of the Study:

• To design and synthesize novel tetramine-based copper(I) coordination cages with controllable architectures.
• To investigate the influence of steric factors and secondary interactions on cage formation and structural interconversion.
• To establish design principles for generating diverse supramolecular structures from identical building blocks.

Main Methods:

• Design of a tetramine ligand with 1,5-naphthylene arms for assembly with Cu(I) ions.
• Synthesis of two distinct Cu(I) coordination cages, [Cu^I₁₂L₆]¹²⁺ and [Cu^I₈L₄]⁸⁺, using different pyridine-based aldehyde components.
• Structural characterization using X-ray crystallography to analyze intermolecular interactions (C-H···π and arene stacking).
• Investigation of structural interconversion by introducing one ligand into a pre-formed cage of the other.

Main Results:

• Formation of a pseudo-hexagonal prismatic [Cu^I₁₂L₆]¹²⁺ cage stabilized by extensive C-H···π and arene stacking interactions when using 6-methyl-2-formylpyridine.
• Formation of a rectangular open prismatic [Cu^I₈L₄]⁸⁺ cage due to steric clashes introduced by 3-methyl-2-formylpyridine, hindering secondary interactions.
• Demonstration of structural interconversion: the [Cu^I₈L₄]⁸⁺ cage transformed into the [Cu^I₁₂L₆]¹²⁺ cage upon addition of 6-methyl-2-formylpyridine, with selective displacement of aldehyde residues.
• Correlation between steric hindrance, secondary interactions, and the resulting cage architecture.

Conclusions:

• Rational control over the architecture of copper(I) coordination cages is achievable by fine-tuning steric factors of the organic ligands.
• Secondary interactions, such as C-H···π and arene stacking, are critical for stabilizing specific cage structures.
• The study provides a versatile platform for designing diverse supramolecular architectures by manipulating ligand design and assembly conditions.
• This work offers valuable design principles for the construction of complex molecular cages with tailored properties.