Large, heterometallic coordination cages based on ditopic metallo-ligands with 3-pyridyl donor groupsElectronic supplementary information (ESI) available. CCDC 1024735-1024740. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc03046j

Ditopic N-donor ligands with terminal 4-pyridyl groups are omnipresent in coordination-based self-assembly. The utilization of ligands with 3-pyridyl donor groups is significantly less common, because the intrinsic conformational flexibility of these ligands tends to favor the formation of small aggregates. Here, we show that large Pd 6 L 12 12+ cages can be obtained by reaction of Pd( ii ) salts with metallo-ligands L bearing terminal 3-pyridyl groups. The easy-to-access metallo-ligands contain an Fe( ii ) clathrochelate core. These sterically demanding clathrochelate complexes prevent the formation of smaller aggregates, which is observed for less bulky analogous building blocks. The cages were shown to bind BF 4 − and BPh 4 − anions in aqueous solvent mixtures, whilst the lateral size of the clathrochelate significantly affects their guest encapsulation behavior. The two-step synthesis of large, heterometallic coordination cages based on ditopic 3-pyridyl ligands is described.