M. Nakamura et al., Electron configuration of ferric ions in low-spin (dicyano)(meso-tetraarylporphyrinato)iron(III) complexes, INORG CHEM, 38(17), 1999, pp. 3857-3862
The electron configuration of a series of low-spin (dicyano){meso-tetrakis(
2,4,6-trialkylphenyl)porphyrinato}iron(III) complexes, [Fe(R-TPP)(CN)(2)](-
) where R = Me, Et, or Pr-i, together with the parent [Fe(TPP)(CN)(2)](-),
has been examined in dichloromethane-methanol solution by H-1 NMR, C-13 NMR
, and EPR spectroscopies. While the ferric ion of [Fe(TPP)(CN)(2)](-) has s
hown a common (d(xy))(2)(d(xz),d(yz))(3) configuration, the ferric ions of
the alkyl-substituted complexes [Fe(R-TPP)(CN)(2)](-) have exhibited the pr
eference of a less common (d(xz),d(yz))(4)(d(xy))(1) configuration. Spectro
scopic characteristics of the complexes in which ferric ions take the (d(xz
),d(yz))(4)(d(xy))(1) configuration are (i) axial type EPR spectra, (ii) do
wnfield shifted pyrrole and meta signals in H-1 NMR spectra, and (iii) down
field shifted meso-carbon signals in C-13 NMR spectra. Occurrence of the le
ss common (d(xz),d(yz))(4)(d(xy))(1) configuration in [Fe(R-TPP)(CN)(2)](-)
has been ascribed to the electronic interaction between iron (d(pi)) and c
yanide (p(pi)*) orbitals. The interaction stabilizes the d(pi) orbitals and
induces (d(xz),d(yz))(4)(d(xy))(1) configuration. Since the electron confi
guration of (dicyano){meso-tetrakis(2,6-dichlorophenyl)porphyrinato}iron(II
I), [Fe(Cl-TPP)(CN)(2)](-), which carries bulky electronegative chlorine at
oms at the ortho positions, is presented as a common (d(xy))(2)(d(xz),d(yz)
)(3), the less common (d(xz),d(yz))(4)(d(xy))(1) configuration in [Fe(R-TPP
)(CN)(2)](-) can be ascribed, at least partially, to the electron-donating
ability of the meso-aryl groups.