On the structure of unsolvated free-base 5,10,15,20-tetra(3-pyridyl)porphyrin

A combined X-ray and density functional theory (DFT) study on the structure of 5,10,15,20-tetra(3-pyridyl)porphyrin (1) has been undertaken. Single-crystal X-ray diffraction revealed molecules of 1 in the ααββ conformation with molecular and crystallographic Ci point group symmetry. The porphyrin macrocycle shows no marked deviation from planarity. Positional disorder of the pyrrole NH atoms is discussed. The crystal packing of 1 is achieved through common off-set stacking of the porphyrin entities. Bulk material of 1 was further investigated by scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). The crystal and molecular structure of 1 is compared to the known structures of the unsolvated free-base 2- and 4-pyridyl isomers. The molecular structure of 1 in solution has been investigated by variable temperature 1H NMR spectroscopy in CDCl3.