Hyperfine shifts of the 13C-NMR. in low spin iron(3) porphyrin complexes

The ¹³C-NMR. in Zn(II)(Porphin), Fe(III)(Porphin)(CN₂), Zn(II)(Tetraphenyl-porphin), and Fe(III)(Tetraphenylporphin)(CN₂) have been identified, and the ¹³C hyperfine shifts in the iron complexes evaluated. It was found that dipole-dipole coupling with the electron spin localized in the π-orbitals of the aromatic carbon atoms makes an important contribution, to the ¹³C hyperfine shifts. In a preliminary analysis the experimental spin density distribution obtained from the combined ¹H- and ¹³C-NMR.-data is compared with theoretical models of the iron porphyrin complexes.