Dh. Jones et al., DENSITY-FUNCTIONAL STUDIES OF IRON(III) PORPHINES AND THEIR ONE-ELECTRON-OXIDIZED DERIVATIVES, Inorganic chemistry, 32(10), 1993, pp. 2092-2095
The relative energies of selected states for one-electron-oxidized dif
luoro(porphinato)iron(III) and fluoro(porphinato)iron(III) have been s
tudied using approximate density functional methods. For the difluoro
derivative an iron(IV) (S = 1) state is stabilized relative to an iron
(III) A2u pi-cation-radical (S = 3) state. For the monofluoro species
this ordering of states is reversed. The molecular structures of diflu
oro(porphinato)iron(III) and the corresponding iron(IV) and iron(III)
A2u pi-cation-radical species have been investigated using a full geom
etry optimization. The A2u pi-cation-radical species has a geometry ve
ry similar to the parent compound. In contrast, the iron(IV) derivativ
e displays significantly shortened Fe-N and Fe-F bond distances. A pos
sible relationship between iron(III) spin state and the site of one-el
ectron oxidation in iron(III) porphyrins is rationalized in terms of e
xchange energy stabilization and the sigma- and pi-donor properties of
the axial ligand(s). The pi --> pi singlet transition energies of ch
loro(porphinato)iron(III) have been calculated. Good agreement with ex
perimental values is found, and an assignment of the Q-band region as
arising from 14a1 --> 18e (a2u --> eg) and 5a2 --> 18e (a1u --> e(g)*
) transitions is proposed. The B-band (Soret) region is suggested to a
rise from 8b, --> 18e (b2u --> e(g)) and 13a1 --> 18e (a2u' --> e(g)*
) transitions.