Martin K. Safo

MOLECULAR STRUCTURE OF BIS(1-METHYLIMIDAZOLE)(MESO-TETRAPHENYLPORPHINATO)IRON(III) PERCHLORATE

The preparation and characterization of the bis(1-methylimidazole)( meso -tetraphenylporphinato)iron(III) perchlorate complex is described. The molecular structure has been determined by an X-ray crystal structure determination. The complex has two axial imidazole ligands that are nearly coplanar and close to eclipsing an FeN p bond. A rhombic distortion in the equatorial bonds is seen; the set that is approximately perpendicular to the imidazole ligand planes has an average value of 1.973(6) A while the other set has an average value of 1.991(4) A. The axial FeN(Im) bond distances average to 1.974 A. The complex has a rhombic EPR spectrum and the derived crystal field parameters are reported. Crystal data: a =10.730(1), b =21.207(4), c =21.231(4) A, and β= 96.82(1)°, monoclinic, space group P 2 1 / n , V =4796.8 A 3 , Z =4, R 1 =0.066, R 2 =0.074 based on 6429 observed data.

Characterization of the admixed intermediate-spin complex bis(3-cyanopyridine)(octaethylporphinato)iron(III) perchlorate

The preparation of bis(3-cyanopyridine)(octaethylporphinato)iron(III) perchlorate is described. The molecular structure has been determined by an X-ray crystal structure determination. The centrosymmetric complex has coplanar axial pyridine ligands that are close to eclipsing an FeN p bond (φ=4°).The average equatorial bond distance is 2.012(3) A. The axial Fe-N(Py) bond distance is 2.269(6) A. The complex has been further characterized by EPR and Mossbauer spectroscopy and temperature dependent magnetic susceptibility measurements between 1.8 and 300 K. The complex has an axial EPR spectrum with g ⊥ =4.28 and g∥=1.97. The Mossbauer spectrum in zero field at 77 K has an isomer shift of 0.38 mm/s and a quadrupole split doublet of 2.61 mm/s. The Mossbauer has also been studied in an applied magnetic field (6 T) at 4.2 K and fitted with a crystal field model. The structure and spin state of this compound serve to emphasize an emerging pattern in the relationship of axial ligand orientation (φ angles) and sopin state. Crystal data: [Fe(OEP)(3-CNPy) 2 ]ClO 4 ·3CHCl 3 : a =10.463(7), b =24.805(26), c = 11.661(4) A, and β= 109.60(6)°, monoclinic, space group P2 1 /m, V =2851.0 A3, Z =2, observed data = 3118, R 1 =0.099, R 2 =0.102.

Characterization of the mixed axial ligand complex (4-cyanopyridine)(imidazole)(tetramesitylporphinato)iron(iii) perchlorate. Stabilization by synergic bonding

The reaction of [Fe(TMP)(OClO3)], where TMP is the dianion of tetramesitylporphyrin, with a combination of a strong π-acceptor ligand and a π-donating imidazole can lead to the preparation of mixed-ligand complexes [Fe(Porph)(4-CNPy)(L)]+ where L is imidazole itself or 1-acetylimidazole and 4-cyanopyridine is the strong π acceptor ligand. The stability of the new mixed-ligand pair is the presumed result of synergic bonding between the two axial ligands. The molecular structure and other characterization of the new mixed axial ligand complex, [Fe(TMP)(4-CNPy)(HIm)]ClO4 is described. The axial ligands have a relative perpendicular arrangement with Fe-N(imidazole) = 1.945 Å and Fe-N(pyridine) = 2.021 Å The average equatorial Fe-Np distance is 1.963 Å, which is consistent with the S4-ruffled TMP core. Despite the relative perpendicular arrangement of axial ligands, the EPR spectrum of the complex is a rhombic signal and not a large gmax signal. The EPR g-values are g1 = 3.05, g2 = 2.07, and g3 = 1.22. A quadrupole doublet was seen in the Mössbauer spectrum with an isomer shift of 0.197 mm/s and quadrupole splitting of 1.935 mm/s. Two crystalline forms of [Fe(TMP)(4-CNPy)(HIm)]ClO4 have been characterized; the two forms differ only in the solvent content of the lattice. Crystal data for form A: a = 15.432 (12) Å, b = 20.696 (2) Å, c = 19.970 (5) Å, and β = 99.256 (14)°, monoclinic, space group P21/n, V = 6295 (2) Å3, Z = 4, formula FeCl3O4N8C69H69, 8397 observed data, R1 = 0.086, wR2 = 0.210, refinement on F2. Crystal data for form B: a = 15.267 (3) Å, b = 20.377 (6) Å, c = 19.670 (4) Å, and β = 98.14 (1)°, monoclinic, space group P21/n, V = 6058 (4) Å3, Z = 4, formula C65.25H60.5Cl1.5FeN8O4, 5464 observed data, R1 = 0.096, wR2 = 0.112, refinement on F.