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• 作者：Gé ; rard Simonneaux ; Volker Schü ; nemann ; Christophe Morice ; Laurence Carel ; Loï ; c Toupet ; Heiner Winkler ; Alfred X. Trautwein ; and F. Ann Walker
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：May 10, 2000
• 年：2000
• 卷：122
• 期：18
• 页码：4366 - 4377
• 全文大小：185K
• 年卷期：v.122,no.18(May 10, 2000)
• ISSN：1520-5126

文摘

The synthesis and characterization of the trifluoromethanesulfonate salt of bis(2,6-xylyl isocyanide)tetrakis(p-tolyl)porphyrinatoiron(III), [(p-TTP)Fe(2,6-xylylNC)₂]CF₃SO₃ (1), is reported. The crystal structureshows that the porphyrinate ring is strongly ruffled. The equatorial Fe-N bond distances average to 1.961(7)Å for 1, which is quite short for low-spin iron(III) porphyrinate derivatives. Two additional complexes, havingTPP (2) and m-TTP (3) as the porphyrinates, were also synthesized and studied by NMR, EPR, and Mössbauerspectroscopy. All physical properties are consistent with a low-spin iron(III) porphyrinate with the less-commonground-state configuration (d_xz,d_yz)⁴(d_xy)¹. The ¹H NMR chemical shift of the pyrrole protons at 297 K is+10.7 ppm for 1. The EPR spectrum of 1 in solution is axial, with g_{s/entities/bottom.gif">} = 2.15 and g_{s/entities/verbar.gif">s/entities/verbar.gif">} = 1.94, s/entities/sum.gif">g² = 13.0,while in the solid state g_{s/entities/bottom.gif">} = 2.2 and g_{s/entities/verbar.gif">s/entities/verbar.gif">} = 1.94, s/entities/sum.gif">g² = 13.4. The Mössbauer spectrum of 1 at 190 K has anisomer shift of 0.14 mm/s and quadrupole splitting of 1.81 mm/s. Magnetic Mössbauer spectra analyzed in theintermediate spin-spin relaxation regime by the dynamic line-shape formalism of Blume and Clauser confirmthis electron configuration and yield large negative quadrupole splittings, s/gifchars/Delta.gif" BORDER=0 >E_Q = -1.8 to -2.0 mm/s for thethree complexes. To our knowledge, this is the first case in which the Mössbauer spectra of low-spin ferrihemesystems have been analyzed in terms of the effect of intermediate rates of spin fluctuations on the appearanceof the spectra. Analysis of the temperature dependence of the quadrupole splitting, s/gifchars/Delta.gif" BORDER=0 >E_Q, for 2 yielded a differentestimate of the energy separation between the (d_xz,d_yz)⁴(d_xy)¹ ground state and an excited state than did thetemperature dependence of the NMR isotropic shifts. It is postulated that the excited state is actually theplanar transition state between the two ruffled conformations of the porphyrinate that are related by "inversion".To explain the temperature dependence of both NMR isotropic shifts and Mössbauer quadupole splittings, theplanar transition state must have the (d_xy)²(d_xz,d_yz)³ electron configuration. The energy barrier appears to besmaller in homogeneous solution than in the solid state and is considerably lower than that predicted for the(d_xz,d_yz)³(d_xy)² excited electronic state of the ruffled conformation on the basis of the EPR g values.