¹⁵N solid-NMR and X-ray diffraction studies of N-confused porphyrins

Using ¹⁵N high-resolution solid-state NMR and X-ray diffraction, the structure of N-confused porphyrin (NCP) in the solid state was studied. A 1D ¹⁵N magic angle spinning (MAS) experiment and a 2D dipolar assisted rotational resonance (DARK) ¹⁵N-¹⁵N spin exchange experiment of N-confused tetratolylporphyrin (Tol) crystallized from CH ₂Cl₂/hexane indicate that Tol is the inner 3H-type tautomer and has two magnetically different molecules in the unit cell. Further, a FSLG-24̄2 ¹H-¹⁵N dipolar recoupling NMR measurement indicates no fast ring flipping motion which is consistent with the planar structure in the X-ray analysis. The planarity of Tol is ascribed to crystal packing enforced by π-π stacking and CH-π interactions.