A Reduced-Symmetry Pd2L4 Cage from a Heterotopic Dipyridyl Ligand

Two dipyridyl ligands, L 3,3 and L 3,4 , 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 (C 2h ) lantern-type cage is formed in one instance, [Pd2(L3,3)4]4+, while the isomeric ligand yields a larger double-walled square complex, [Pd4(L3,4)8]8+. [Pd2(L3,3)4]­(NO3)4 was isolated in crystalline form revealing two anions within the interior of the C 2h -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 NO3 – has sharp 1H nuclear magnetic resonance (NMR) signals at room temperature, while the BF4 – analogue has broad signals that sharpen at higher temperatures or upon addition of (Bu4N)­(NO3), 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 [Pd4(L3,4)8]­(NO3)8 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.