Anion binding properties of a hollow PdL-cage

The hollow [PdL][BAr(F)](2) complex 1 of a tetra-pyridyl (py) ligand (L) has a [Pd(py)(4)](2+) coordination environment. Addition of coordinating anions resulted in the formation of a neutral species with Pd(py)(2)(anion)(2) coordination environment (12A). These species bind further to the coordinating anions in the order Cl(−) > N(3)(−) > Br(−) > I(−) > AcO(−) with K(a)(1 : 1) ≤ 414 M(−1). With relatively non-coordinating anions 1 remains intact and displays 1 : 2 binding behaviour dominated by the 1 : 1 stoichiometry in the order NO(3)(−) (∼10(5) M(−1)) » ClO(4)(−) and BF(4)(−) (∼10(3) M(−1)). As evidenced by crystal structure data, DFT calculations and {(1)H–(19)F}-HOESY NMR with BF(4)(−), the anions are bound by charge assisted [C–H](+)···anion interactions.