Anion binding properties of a hollow PdL-cage

Abstract

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 (1^2A). These species bind further to the coordinating anions in the order Cl⁻ > N₃⁻ > 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 NO₃⁻ (∼10⁵ M⁻¹) » ClO₄⁻ and BF₄⁻ (∼10³ M⁻¹). As evidenced by crystal structure data, DFT calculations and {¹H–¹⁹F}-HOESY NMR with BF₄⁻, the anions are bound by charge assisted [C–H]⁺···anion interactions.