Discrete and Interlocked Metal–Organic Cages: A Rationally Designed Laboratory Platform for Investigating Self-Assembly and the Conversion of Kinetic to Thermodynamic Supramolecular Complexes

In this two-part undergraduate laboratory experiment, students synthesize a bis(pyridyl) ligand and subsequently investigate its coordination-driven self-assembly using nuclear magnetic resonance (NMR) spectroscopy within a problem-based inquiry framework. The reaction of the ligand with palladium(II) ions in acetonitrile at a 2:1 stoichiometric ratio gives rise to two distinct cage architectures: a kinetically favored M2L4 assembly and a thermodynamically stable interlocked M4L8 complex, with their relative distributions governed by reaction conditions. This experiment not only develops essential experimental skills but also reinforces key concepts spanning organic synthesis, coordination chemistry, and chemical thermodynamics. The modular design and operational simplicity make it readily adaptable to a wide range of undergraduate curricula.