Electronic ground state of iron in octamethyltetrabenzporphyriniron(II), a new square planar ferrous porphyrin

Electronic structure and bonding in unligated and ligated FeII porphyrins

“…The larger ring size of OTBP gives rise to a smaller ligand field, and the Fe-OTBP bond energy is 1.0 eV smaller than for FeTPP. Mössbauer data indicate that the strength of the bond to the tetradentate ligands is stronger for TPP than for OTBP, 18 consistent with the calculation.…”

“…This result agrees with experimental measurements on FeTPP, 3-7 but argues against the resonance Raman assignment 8 of FeOEP as 3 E g , and the assignment of FeOTBP as 5 B 2g based on mag- netic and Mössbauer measurements in the early literature. 18 The alternation of the porphyrin ligand does not have strong effects on the relative energetics of the spin states of Fe II in unligated iron porphyrin. The calculated excitation energies, Fe-porphyrin bond energies, ionization potentials, and electron affinities agree very well with available experimental data.…”

“…[3][4][5][6][7] Hence, the calculation does not support the experimental assignment of unligated FeOTBP as a high-spin (Sϭ2) state. 18 The 3 E g state is second lowest, between 0.12 and 0.18 eV higher in energy. Mössbauer studies of FeTPP suggest a separation of 1.35ϫ435 cm Ϫ1 ͑0.07 eV͒ between the 3 A 2g and 3 E g states, 4 agreeing very well with the calculated value.…”

“…Its magnetic moment was reported to be 5.9 B , 18 suggesting a high-spin ground state. Furthermore, a 5 B 2g ground state was based first on the assumption of a similar state for FeTPP, which was later shown to be erroneous.…”

Importance of Many-Body Effects in the Kernel of Hemoglobin for Ligand Binding

“…In particular, this accounts for the striking differences obtained experimentally for very similar porphyrin systems, e.g. it was found that unligated FeP is a triplet [24] in the tetraphenylporphine configuration, a triplet with different orbital symmetry in the octaethylporphine configuration [25], and a quintet in the octamethyltetrabenzporphine configuration [26]. The strong dependence of the spin state with respect to small modifications in the structure is consistent with an entangled spin state.…”