Comparison of [Pd₂L₄][BF₄]4 cages for binding of n-octyl glycosides and nitrate (L = isophthalamide or dipicolinamide linked dipyridyl ligand)

Two dipyridyl ligands were synthesized, where the pyridyl donor fragments were separated by an isophthalamide (1) or a dipicolinamide moiety (2). Both ligands formed [Pd₂(Ligand)₄][BF₄]₄ complexes in CD₂Cl₂ containing 5% dmso-d₆. It was found that while [Pd₂(1)₄][BF₄]₄ readily binds to n-octyl glycosides and to nitrate anions, [Pd₂(2)₄][BF₄]₄ did not. The difference in binding properties could be rationalized based on the reduced flexibility and size of the [Pd₂(2)₄]²⁺ cage and/or stronger interior binding of a BF₄⁻ counter anion.