A mono-metallic Pd(II)-cage featuring two different polar binding sites

The tetra-α isomer of a super aryl-extended tetra-pyridyl calix[4]pyrrole self-assembles into a mono-metallic Pd(II)-cage featuring two different and converging polar binding sites. Mono- and di-topic polar guests are bound reversibly in the cage. A mechanism for guest exchange in the cage complexes is proposed.