Self-Assembly of Polymer and Sheet Structures from Palladium(II) Complexes by Hydrogen Bonding between Carboxamide Substituents

The self-assembly of supramolecular structures from either neutral or cationic palladium(II) complexes containing primary or secondary carboxamide groups as substituents on pyridine ligands has been explored. The displacement of PhCN in trans-[PdCl2(PhCN)2] by L = N-methylnicotinamide (MNA), isonicotinamide (INA), or nicotinamide (NA) gave the corresponding complexes trans-[PdCl2L2] 1−3, respectively. Complex 1·H2O forms a 2D sheet network via amide−amide hydrogen bonding supported by chloride ligand-to-water hydrogen-bonding interactions. Several cationic complexes, [Pd(L‘L‘)L2]2+ 4−9 and 11−16, containing the above ligands and with PPh3, dppp, dppm, or bu2bipy as ancillary ligand(s) were prepared. Complex 4 (L = MNA, L‘L‘ = dppp) forms dimers through amide−amide hydrogen bonding, forming macrocycles which further propagate to form chains via weak C−H···OC hydrogen bonding. Complex 6 (L = NA, L‘L‘ = dppp) forms zigzag chains connected by amide head-to-head hydrogen bonds. Complex 8 (L = INA, L‘L‘ = dppm) gives interesting double-stranded ribbons linked by two types of amide−amide hydrogen-bonding interactions. Complex 13 (L‘ = PPh3, L = NA) forms an infinite chain via complementary amide−amide hydrogen bonds. Complex 14 (L = MNA, L‘L‘ = bu2bipy) forms infinite ribbons via the combination of amide hydrogen bonding mediated by a BF4 anion and weak C−H···OC hydrogen bonding. Complex 15 (L = INA, L‘L‘ = bu2bipy) gives a ladder polymer formed through amide−amide hydrogen bonds. The structure of cis-[Pd(PPh3)2(OH2)2] (OTf)2 (10) is also reported.