A Reduced-Symmetry PdL Cage from a Heterotopic Dipyridyl Ligand.

Two dipyridyl ligands, and , have been used in combination with palladium(II) in the construction of metallosupramolecular species that show anion-dependent behavior in solution. A rare example of a low-symmetry () lantern-type cage is formed in one instance, [Pd(L)], while the isomeric ligand yields a larger double-walled square complex, [Pd(L)]. Pd(L) was isolated in crystalline form revealing two anions within the interior of the -symmetry cage. The cage itself is held together by hydrogen bonding between "head-to-tail" pairs of ligands that reinforces the symmetry generated by the ditopic ligands. In solution, the cage with NO has sharp H nuclear magnetic resonance (NMR) signals at room temperature, while the BF analogue has broad signals that sharpen at higher temperatures or upon addition of (BuN)(NO), highlighting the importance of the anion in templating or otherwise influencing self-assembly in solution. Altering the substitution position of one of the pyridyl rings yields a more "open" complex, with Pd(L) being isolated as a crystalline solid. The double-walled square complex has a greater Pd···Pd separation due to the increased angle that the pyridyl groups subtend at the core of the ligand. NMR spectroscopy and mass spectrometry studies suggest a single species in the presence of nitrate but multiple species with tetrafluoroborate.