Supramolecular reactivity of porphyrins with mixed iodophenyl and pyridyl meso-substituents

This study evaluates the supramolecular reactivity of the 5-(4′-pyridyl)-10,15,20-tris(4′-iodophenyl)porphyrin (PyTIPP) and 5,15-bis(4′-pyridyl)-10,20-bis(4′-iodophenyl)porphyrin (PyDIPP) platforms in their free base and metalated forms, utilizing metal-ligand coordination and halogen bond synthons in the construction of polymeric as well as oligomeric assemblies. Free base PyTIPP and PyDIPP moieties form extended supramolecular layers held together by intermolecular N···I and I···π interactions, which π·· ·π stack in an offset manner to yield layered crystals. The metalated monopyridyl derivative Co-PyTIPP (as well as its Zn-PyTIPP analogue) assembles into cyclic tetrameric supermolecule via coordination of the pyridyl function of one species to the core metal ion of an adjacent unit. On the other hand, the bis-pyridyl Zn-PyDIPP scaffold constructs a robust framework solid of extended honeycomb architecture by polymeric self-coordination. These findings provide useful protocols for rational design of the different modes of supramolecular porphyrin ensembles, which are valid in reaction media lacking polar reagents with competing affinity for the functional groups of the porphyrin units. In the latter context, PyDIPP in the presence of benzoic acid forms discrete solvated entities, where the pyridyl N-sites engage in hydrogen bonds to the carboxylic acids, preventing direct inter-porphyrin association.