Five-coordinate nitrosyl iron(II) tetraphenylporphyrin exhibits porphyrin ring 14N symmetry about the Fe–N–O plane: a hyperfine sublevel correlation spectroscopy study Original Research Article

Hyperfine sublevel correlation experiments were performed on five-coordinate nitrosyl iron(II) tetraphenylporphyrin (ON–FeTPP) in frozen toluene solution. The spectrum exhibits pairs of equivalent pyrrole nitrogens N1,2 and N3,4. The quadrupole parameters agree with literature values for other pyrrole nitrogens. N 2s spin densities of −0.0021 to −0.0022 and −0.00096 on N1,2 and N3,4, respectively, are found. The anisotropic hyperfine interaction results from magnetic dipole interactions between the pyrrole 14N nuclei and electron spin located in the Fe 3dz2-type orbital and in the N 2p orbitals in the (yz) plane bisecting the pyrrole C–N–C angles. The spin density in the Fe 3dz2-type orbital along the normal to the porphyrin plane (y axis) is ∼0.7. The two pyrrole N 2p orbitals are quantized along axes y′ and z′, 9–10° from y and z, respectively. The N 2py′ and N 2pz′ spin densities range from −0.005 to −0.009 and +0.007 to +0.010, respectively.