Self-Assembly and Host-Guest Interactions of Pd3L2 Metallo-cryptophanes with Photoisomerizable Ligands.

New photoswitchable pyridyl-azo-phenyl-decorated tripodal host ligands (L-az) that belong to the cyclotriveratrylene family have been synthesized, and their photoswitching behavior and crystal structures determined. The latter includes a remarkable 7-fold Borromean-weave entanglement of pi-pi stacked layers. Trigonal bipyramidal {[Pd(en)](3)(L-az)(2)}(6)+ metallo-cryptophanes (en = ethylenediamine) were formed from these and a previously known pyridyl-azo-phenyl-decorated tripodal host ligand. These coordination cages dissociate at low concentrations and are less robust to photoswitching of the Laz ligands than were previously reported Ir(III)-linked metallo-cryptophanes with similar ligands, reflecting the greater lability of the PdN bonds. The {[Pd(en)](3)(L-az)(2)}(6+) cages all act as hosts, binding octyl sulfate anions, or N-[2-(dimethylamino)ethyl]-1,8-naphthalimide in a dimethyl sulfoxide solution.