Molecular conformation and intermolecular interactions in the crystal structures of free-base 5,15-diarylporphyrins

Nine crystal structures of free-base 5,15-diarylporphyrin derivatives are reported, and systematic analysis is made of the molecular conformations and intermolecular interactions in these and other comparable structures. In all cases, the porphyrins show minimal out-of-plane distortion in the solid state, but significant in-plane distortion, consistent with previous observations. The simplest 5,15-diarylporphyrin (with no further substitution on the macrocycle periphery) crystallizes as a solvate with features comparable to the structure of porphine itself, and also in an unsolvated form in which edge-to-face interactions between the phenyl substituent and the porphyrin faces give rise to one-dimensional porphyrin chains. The majority of the structures reported here are derived from a balance between these latter interactions and the common offset face-to-face-pi-stacking interaction. Introduction of substituents such as hydroxyl and methoxy groups on the phenyl rings does not disrupt the edge-to-face interactions. Introduction of bulky groups on both sides of the phenyl substituent can disrupt chain formation, and the structures in these cases are dominated by offset pi-stacking. In structures where the porphyrins bear solubilizing n-alkyl groups on the macrocycle periphery, the porphyrin chains generally may be considered to form layers that are stacked with n-alkyl groups filling space between them.