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, octaet hylporphyrin, tetra-p-methoxyphenylporphyrin, or picket fence porphyrin, ar e described. Crystal data: [Fe(Tp-OCH3PP)(NO2)(NO)]. CH2Cl2, tetragonal, sp ace 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 = 18.0 93(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) Angs trom, and beta = 90.971(6)degrees; [Fe(TpivPP)(NO2)(NO)]. C7H8 (4), monocli nic, 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 crysta l structures described, two tout of lour characterized) picket fence porphy rin 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 structura l 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 temperatu re dependence with lower values at high temperature. Mossbauer spectra in a pplied magnetic field at 4.2 K show that the molecules have diamagnetic gro und states which is pl presumed to result from antiferromagnetic coupling b etween the low-spin iron(III) and the S = 1/2 nitric oxide center.