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.