Bis(pyridine)[meso-tetrakis(heptafluoropropyl)porphyrinato]iron(III), [Fe(THFPrP)Py2]+, was reported to be the low-spin complex that adopts the purest (dxz, dyz)4(d xy)1ground state where the energy gap between the iron dxyand dπ(dxz, dyz) orbitals is larger than the corresponding energy gaps of any other complexes reported previously (Moore, K. T.; Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 1999, 121, 5196-5209). Although the highly ruffled porphyrin core expected for this complex contributes to the stabilization of the (dxz, d yz)4(dxy)1ground state, the strongly electron withdrawing C3F7groups at the meso positions should stabilize the (dxy)2(dxz, d yz)3ground state. Thus, we have reexamined the electronic structure of [Fe(THFPrP)Py2]+by means of 1H NMR, 19F NMR, and electron paramagnetic resonance (EPR) spectroscopy. The CD2Cl2solution of [Fe(THFPrP)Py2] +shows the pyrrole-H signal at-10.25 ppm (298 K) in 1H NMR, the CF2(α) signal at-74.6 ppm (298 K) in 19F NMR, and the large gmaxtype signal at g = 3.16 (4.2 K) in the EPR. Thus, contrary to the previous report, the complex is unambiguously shown to adopt the (dxy)2(dxz, dyz) 3ground state. Comparison of the spectroscopic data of a series of [Fe(THFPrP)L2]+with those of the corresponding meso-tetrapropylporphyrin complexes [Fe(TPrP)L2]+with various axial ligands (L) has shown that the meso-C3F 7groups stabilize the (dxy)2(dxz, dyz)3ground state. Therefore, it is clear that the less common (dxz, dyz)4(dxy) 1ground state can be stabilized by the three major factors: (i) axial ligand with low-lying π* orbitals, (ii) ruffled porphyrin ring, and (iii) electron donating substituent at the meso position.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry