Catenation and Aggregation of Multi-Cavity Coordination Cages

A series of metal-mediated cages, having multiple cavities, was synthesized from Pd-II cations and tris- or tetrakis-monodentate bridging ligands and characterized by NMR spectroscopy, mass spectrometry, and X-ray methods. The peanut-shaped [Pd3L41] cage deriving from the tris-monodentate ligand L-1 could be quantitatively converted into its interpenetrated [5Cl@Pd6L81] dimer featuring a linear {[Pd-Cl-](5)Pd} stack as an unprecedented structural motif upon addition of chloride anions. Small-angle neutron scattering (SANS) experiments showed that the cigar-shaped assembly with a length of 3.7nm aggregates into mono-layered discs of 14 nm diameter via solvophobic interactions between the hexyl sidechains. The hepta-cationic [5Cl@Pd6L81] cage was found to interact with polyanionic oligonucleotide double-strands under dissolution of the aggregates in water, rendering the compound class interesting for applications based on non-covalent DNA binding.