Four-Coordinate Iron(II) Porphyrinates: Electronic Configuration Change by Intermolecular Interaction

The syntheses and structures of three four-coordinate iron(II)
porphyrinates are reported. The three derivatives are tetraarylporphyrin species, where the aryl is either phenyl, p-methylphenyl, or
p-methoxyphenyl. One of these derivatives, that of tetraphenylporphyrin, Fe(TPP), is a new crystalline phase that is distinct from
the earlier reported phase (Collman, J. P.; et al. J. Am. Chem.
Soc. 1975, 97, 2676). This new phase of Fe(TPP) has a very
saddled porphyrin core; the prior phase was ruffled. The iron atom
has close interactions (∼3.10 Å) with two pyrrole Cb−Cb bonds
above and below the porphyrin plane. Mössbauer spectra and
magnetic susceptibility measurements, different for the two phases,
provide strong evidence that the two phases of Fe(TPP) have
distinct electronic structures that originate from intermolecular
interactions.