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 π-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 π-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.