Bis(cyano) Iron(III) Porphyrinates: What Is the Ground State?

The
synthesis of six new bis­(cyano) iron­(III) porphyrinate derivatives
is reported. The anionic porphyrin complexes utilized tetraphenylporphyrin,
tetramesitylporphyrin, and tetratolylporphyrin as the porphyrin ligand.
The potassium salts of Kryptofix-222 and 18-C-6 were used as the cations.
These complexes have been characterized by X-ray structure analysis,
solid-state Mössbauer spectroscopy, and EPR spectroscopy, both in
frozen CH2Cl2 solution and in the microcrystalline
state. These data show that these anionic complexes can exist in either
the (dxz,dyz)4(dxy)1 or the
(dxy)2(dxz,dyz)3 electronic configuration
and some can clearly readily interconvert. This is a reflection that
these two states can be very close in energy. In addition to the effects
of varying the porphyrin ligand, subtle effects of the cyanide ligand
environment in the solid state and in solution are sufficient to shift
the balance between the two electronic states.