Versatile Molecular Recognition Features of Tetra(3-pyridyl)porphyrin in Crystal Engineering

This study explores the supramolecular reactivity of the meso-tetra(3-pyridyl)porphyrin ((TPyP)-Py-3) building block in the context of crystal engineering. This ligand has coordination as well as hydrogen bonding tetradentate functionalities and exhibits orientational versatility of the 3-pyridyl substituents. Reactions of the (TPyP)-Py-3 with copper and manganese chlorides afforded hybrid coordination polymers with uniquely interesting and novel architectures of three-dimensional connectivity, in which the metal ions have multiple oxidation states. Several different modes of intermolecular association have been observed in crystalline adducts of (TPyP)-Py-3 with various aqua nitrate salts of lanthanoid metal ions, which bear multiple molecular recognition sites on their nitrate and water ligands. The porphyrin component in these structures is characterized by differently protonated states. It is either interlinked through the inorganic connectors into self-assembled three-dimensional architectures or exhibits self-complementary hydrogen bonding into homogeneous porphyrin layers which cocrystallized with hydrogen bonded chains of the lanthanoid complex. In addition, the molecular and crystal structures of the freebase ligand, its discrete tin dichloride complex, and polymeric chains of self-coordinated (CuTPyP)-Py-3 complex have been characterized as well. These findings demonstrate that the (TPyP)-Py-3 scaffold may effectively engage in diverse supramolecular constructs with transition metal ions, either through direct coordination to the metal center or by hydrogen bonding to their coordination sphere ligands, as well as in multiporphyrin self-hydrogen bonded networks.