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

A tetramine subcomponent featuring 1,5-naphthylene arms was designed to exhibit extensive secondary interactions when assembled around stereochemically flexible tetracoordinate Cu^I ions. Using 6-methyl-2-formylpyridine, a [Cu^I ₁₂L₆]¹²⁺ pseudo-hexagonal prismatic cage formed, stabilized by 29-32 C─H···π interactions and 12 arene stacking interactions. Replacing the aldehyde component with 3-methyl-2-formylpyridine introduced steric clashes that partially prevented these interactions, leading instead to the formation of a [Cu^I ₈L₄]⁸⁺ rectangular open prism. The system exhibited structural interconversion: adding 6-methyl-2-formylpyridine to the [Cu^I ₈L₄]⁸⁺ cage transformed it into the [Cu^I ₁₂L₆]¹²⁺ structure through selective displacement of 8 out of 24 aldehyde residues per cage, matching the number of sterically-hindered positions predicted from structural analysis. This work demonstrates rational control over cage architecture through fine-tuning of steric factors and intermolecular interactions, providing design principles for generating diverse structures from identical building blocks.