Dual-Site Molecular Recognition in a Truncated-Octahedral Pd ₆ L ₈ Cage via Symmetry-Selective Endo and Peripheral Binding

A primary objective of supramolecular chemistry is to mimic the functions of proteins in biological systems for molecular recognition, which utilizes both surface interactions and internal binding pockets. Herein, we report a truncated octahedral Pd₆L₈ cage (MOC-35), constructed through coordination-driven self-assembly from a C₃-symmetric triphenylamine-based monodentate pyridyl ligand L and naked Pd(II) ions. NMR spectroscopy, DOSY, HR-ESI-MS, and single-crystal X-ray diffraction confirm the formation of a discrete cage featuring a hydrophobic cavity (∼643 ų) and 12 rhombic peripheral pockets. Host-guest studies reveal pronounced shape- and symmetry-dependent binding. Nonplanar threefold or pseudo-threefold aromatic guests, such as triphenylamine and triphenylbenzene derivatives (G1-13), are encapsulated within the central cavity, whereas bulkier triptycene derivatives (G16-17) and cationic triphenylsulfonium G18 were preferentially bound in the peripheral pockets in a fast-exchange manner. Crystallographic and spectroscopic analyses indicate that peripheral binding is stabilized by π-π and C-H···π interactions. Notably, internal and peripheral guests can bind concurrently without significant allosteric interference, demonstrating a rare dual-site binding mode governed by cavity topology, portal size, and ligand nonplanarity.