Syntheses, characterization, and structural studies of several (Nitro)(nitrosyl)iron(III) porphyrinates:: [Fe(Porph)(NO2)(NO)]

The preparation and characterization of several (nitro)(nitrosyl)iron(III) complexes. [Fc(PorDh)(NO2)(NO)], where Porph = tetraphenylporphyrin, octaethylporphyrin, tetra-p-methoxyphenylporphyrin, or picket fence porphyrin, are described. Crystal data: [Fe(Tp-OCH3PP)(NO2)(NO)]. CH2Cl2, tetragonal, space group I4(1)/a, Z = 4, with a = 15.620(3) Angstrom, 18.649(2) Angstrom; [Fe(TpivPP)(NO2)(NO)]. C6H5Cl (1), tetragqnal, P4/ncc, Z = 4, with a = 18.093(3) Angstrom, c = 18.939(4) Angstrom, and (2) with a 18.117(2) Angstrom, c = 19.0838(8) Angstrom: [Fe(TpivPP)(NO2)(NO)] (3), monoclinic, C2/c, Z = 2, with a 16.1559(5) Angstrom, b = 18.6920(8) Angstrom, c = 19.7779(10) Angstrom, and beta = 90.971(6)degrees; [Fe(TpivPP)(NO2)(NO)]. C7H8 (4), monoclinic, P2(1)/n, Z = 4, with a 12.7763(10) Angstrom, b = 27.192(2) Angstrom, c = 19.1716(8) Angstrom. and beta = 105.063(5)degrees. Of the several crystal structures described, two tout of lour characterized) picket fence porphyrin derivatives exhibited no crystallographic disorder that led to problems defining the axial ligand geometry. In these two derivatives the Fe-axial ligand distances are Fe-N(NO) = 1.668(2) or 1.671(2) Angstrom and Fe-N(NO2) = 2.002(2) or 1.998(2) Angstrom; NO does not cause a significant structural trans effect. The average Fe-N, distance of 1.998(4) A is consistent with a low-spin state for iron. The linear or near-linear (169.3(2)degrees) Fe-N-O angle observed is that expected for {FeNO}(6) (i.e., iron(III) nitrosyl) species. The solid-state NO stretching frequencies (1871-1893 cm(-1)) an also consistent with a linear Fe-N-O group. Mossbauer spectra show that the complexes have quadrupole splittings Delta E-q = 1.35-1.50 mm/s and isomer shifts delta = 0.0-0.11 mm/s; the isomer shifts display a strong temperature dependence with lower values at high temperature. Mossbauer spectra in applied magnetic field at 4.2 K show that the molecules have diamagnetic ground states which is pl presumed to result from antiferromagnetic coupling between the low-spin iron(III) and the S = 1/2 nitric oxide center.