Spectroscopic and structural investigations of the ferrous and ferric high-spin state of a "picket-fence" porphyrinato acetato iron complex. A refined model for the P460 center of hydroxylamine oxidoreductase

Mössbauer investigations were performed in the ferrous and ferric form of the 'picket-fence' porphyrinato acetato iron complex |Fe(CH₃CO₂) (TP_pivP)|^1-,0 at temperatures varying from 1.5-200K and in fields of 0-6.2T. The ferrous complex has an unusually large quadrupole splitting, ΔE_Q=+4.25mms^-1. The quadrupole splitting in the ferric species, ΔE_Q=+1.1mms^-1, is as normally found in ferric high-spin iron porphyrins. Spin-Hamiltonian analysis of the magnetic spectra yields zero-field parameters D=-0.9mms^-1, E/D=0.33 and magnetic hyperfine parameters A_x,y=-17T, A_z=-13.3T in the ferrous high-spin (S=2) complex, and D=7.5cm^-1, E/D≈0 and A_x,y,z=20T in the ferric high-spin (S=5/2) species.