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

Using N-15 high-resolution solid-state NMR and X-ray diffraction, the structure of N-confused porphyrin (NCP) in the solid state was studied. A ID N-15 magic angle spinning (MAS) experiment and a 2D dipolar assisted rotational resonance (DARR) N-15-N-15 spin exchange experiment of N-confused tetratolylporphyrin (Tol) crystallized from CH2Cl2/hexane indicate that Tol is the inner 3H-type tautomer and has two magnetically different molecules in the unit cell. Further, a FSLG-2 (4) over bar2 H-1-N-15 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 pi-pi stacking and CH-pi interactions. Copyright (c) 2007 John Wiley & Sons, Ltd.