Pt over Pd, Phenyl over Pyridyl: Determining Factors for Host-Guest Complex Formation in M₂L₄ Architectures

Pd₂L₄ cages have been extensively investigated for a range of applications but are prone to disassembly under acidic conditions or in the presence of competing ligands. More recently, Pt^II analogues became more accessible and allow addressing some of the issues limiting the further development of M₂L₄ cage structures, in particular around the stability of the architectures. We explored a range of structurally analogous Pd- and Pt-based M₂L₄ structures as hosts for the binding of a range of neutral guest molecules. We selected the guests for their varying structural features to affect their binding to these cages. We characterized the latter by qualitative and quantitative means, as well as structurally by X-ray diffraction analysis and supported the interpretation of the data by modeling. We found that the Pt₂L₄ cages exhibited superior guest binding abilities when compared to their Pd analogues as they were less prone to disassembly, while the binding strengths of the cages with 2-hydroxy-1,4-naphthoquinone were similar. This allows the use of a wider range of guest molecules to be encapsulated into supramolecular architectures. The cages built from bridging phenyl-based ligands were found to form stronger host-guest complexes than those featuring a pyridyl unit.