REACTIONS OF BIS(NITRO) ALPHA,ALPHA,ALPHA,ALPHA-TETRAKIS(ORTHO-PIVALAMIDOPHENYL)PORPHINATO)FERRATE(III) WITH PYRIDINE AND IMIDAZOLE - EPR AND MOSSBAUER-SPECTRA AND MOLECULAR-STRUCTURES OF THE MIXED-LIGAND SPECIES

The reactions of the bis(nitro)ferrate(III) picket fence porphyrin derivative [K(18-C-6)(H2O)][Fe(NO2)2(TpivPP)] with the neutral nitrogen donors pyridine and imidazole have been examined. Both reactions yield crystalline mixed nitro-neutral nitrogen donor [Fe(NO2)(L)(TpivPP)] species that have been characterized by UV-vis, IR, NMR, EPR, and Mossbauer spectroscopies. The EPR spectra are those of low-spin rhombic ferric porphyrinates with g1 = 2.98, g2 = 2.37, and g3 = 1.35 (pyridine adduct) and g1 = 2.87, g2 = 2.34, and g3 = 1.56 (imidazole adduct). Mossbauer spectra of the starting complex and the pyridine mixed-ligand product are reported. The isomer shifts are delta = 0.23 +/- 0.02 and 0.25 +/- 0.02 mm/s; the quadrupole splittings are DELTA-E(q) = 2.01 +/- 0.03 and 2.13 +/- 0.03 mm/s, respectively, at 150 K. Mossbauer spectra have also been obtained at 4.2 K in an applied magnetic field. The magnetic spectra have been fit with a crystal field model. The crystal structure of the pyridine and imidazole adducts shows that the nitro group is in the pocket defined by the four pickets while the pyridine or imidazole is coordinated on the open face of the porphyrin. For the pyridine derivative the equatorial bonds average to 1.985 (3) angstrom, the axial Fe-N(NO2) distance is 1.960 (5) angstrom, and the Fe-N(Py) distance is 2.093 (5) angstrom. Similar distances are observed in the imidazole derivative. Crystal data for the pyridine derivative: a = 18.589 (20) angstrom, b = 19.117 (18) angstrom, c = 18.667 (8) angstrom, and beta = 90.53 (7)-degrees, monoclinic, space group C2/c, V = 6633 angstrom-3, Z = 4, FeClO6N10C75H74, 5263 observed data, final data/variable = 12.3, R1 = 0.072, R2 = 0.082, all observations at 123 K. Crystal data for the imidazole derivative: a = 18.318 (5) angstrom, b = 19.196 (2) angstrom, c = 18.802 (6) angstrom, and beta = 91.72 (1)-degrees, monoclinic, space group C2/c, V = 6608 angstrom-3, Z = 4, FeClO6N11C73H71, 3820 observed data, final data/variable = 9.8, R1 = 0.100, R2 = 0.100, all observations at 294 K.