Azaporphine guest-host complexes in solution and gas-phase: evidence for partially filled nanoprisms and exchange reactions

Supramolecular guest-host complexes comprising various azaporphines stacked in a coordination nanoprism consisting of tris(4-pyridyl)triazines as panels{,} 1{,}4-bis(pyridyl)benzenes as pillars and (en)Pd as hinges were synthesized according to the procedure of Fujita and coworkers and characterized as ions in the gas-phase by high-resolution electrospray ionization mass spectrometry and collision induced dissociation as well as in solution by analytical ultracentrifugation. Apart from fully filled nanoprisms we have also prepared and observed partially filled as well as empty congeners in aqueous solutions. Upon mixing room temperature solutions of two types of nanoprisms{,} we observe that azaporphine guest exchange reactions occur on a timescale of minutes{,} indicating that the formation of the guest-host complexes is reversible.