UC Riverside

The proton NMR spectra of unligated ferrous porphyrins, proposed to exist in the intermediate S = 1 spin state, have been recorded and analyzed. The dominant dipolar shifts for the phenyl protons in tetraphenylporphinatoiron(II) result in a quantitative measure of the axial magnetic anisotropy, which, together with the average moment, yield μ⊥ = 4.9 μB and μ|| = 3.2 μB. The resultant contact shifts for pyrrole substituents reflect extensive π spin transfer, which originates solely from porphyrin → iron change transfer. The contact shift pattern indicates that dx2y2 is unoccupied, confirming the spin-triplet ground state. The large π contact shifts require unpaired spins in dxz, dyz, and strongly support the ground state configuration, (dxy)2(dzi)2(dxz, dyz)2, which has been previously shown to be the one favored by the average moment and Mössbauer data. © 1977, American Chemical Society. All rights reserved.