Exploiting N-H•••Cl Hydrogen Bonding Interactions in Cooperative Metallosupramolecular Polymerization

The self-assembly features of hydrophobic bispyridyldichlorido Pd(II) complexes, equipped with an extended aromatic surface derived from oligophenyleneethynylene (OPE) and polarizable amide functional groups, are reported. The cooperative supramolecular polymerization of these complexes results in bundles of thin fibers in which the monomer units are arranged in a translationally displaced or slipped fashion. Spectroscopic and microscopy studies reveal that these assemblies are held together by simultaneous pi-stacking of the OPE moieties and N-H center dot center dot center dot Cl-Pd hydrogen bonds. These unconventional forces are often observed in crystal engineering but remain largely unexploited in supramolecular polymers. Both steric and electronic effects (the presence of bulky and polarizable metal-bound Cl ligands as well as hydrogen bonding donor N-H units) prevent the establishment of short Pd-Pd contacts and strongly condition the aggregation mode of the reported complexes, in close analogy to the previously reported amphiphilic Pd(II) complex 4. The results presented herein shed light on the subtle interplay between different noncovalent interactions and their impact on the self-assembly of metallosupramolecular systems.