A Reduced-Symmetry Pd 2 L 4 Cage from a Heterotopic Dipyridyl Ligand.

Samuel E WalkerNicholas KyratzisDiksha U SawantAlasdair I McKayKellie L TuckDavid R Turner
Published in: Inorganic chemistry (2024)
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 2 h ) lantern-type cage is formed in one instance, [Pd 2 (L 3,3 ) 4 ] 4+ , while the isomeric ligand yields a larger double-walled square complex, [Pd 4 (L 3,4 ) 8 ] 8+ . [Pd 2 (L 3,3 ) 4 ](NO 3 ) 4 was isolated in crystalline form revealing two anions within the interior of the C 2 h -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 3 - has sharp 1 H nuclear magnetic resonance (NMR) signals at room temperature, while the BF 4 - analogue has broad signals that sharpen at higher temperatures or upon addition of (Bu 4 N)(NO 3 ), 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 4 (L 3,4 ) 8 ](NO 3 ) 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.