Low-spin bis(2-methylimidazole)(octaethylporphyrinato)iron(III) chloride (perp-[Fe(OEP)(2-MeHIm)(2)]Cl): a consequence of hydrogen bonding?

Crystal structure of bis(1-ethyl-1H-imidazole-κN 3)(meso-tetramesitylporphyrinato-κ4 N,N′,N′′,N′′′)iron(III) perchlorate chlorobenzene sesquisolvate

In the complex cation of title compound, [Fe(C56H52N4)(C5H8N2)2]ClO4·1.5C6H5Cl, the ironIII atom is coordinated in a distorted octahedral manner by four pyrrole N atoms of the porphyrin ring system in the equatorial plane, and by two N atoms of the 1-ethylimidazole ligands in the axial sites. A disordered perchlorate anion and one and a half chlorobenzene solvent molecules are also present. The cationic complex exhibits a highly ruffled porphyrin core. The average Fe—Np (Np is a porphyrin N atom) bond length is 1.988 (5), and the axial Fe—NIm (NIm is an imidazole N atom) bond lengths are 1.962 (3) and 1.976 (3) Å. The two 1-ethylimidazole ligands are inclined to each other by a dihedral angle of 68.62 (16)°. The dihedral angles between the 1-ethylimidazole planes and the planes of the closest Fe—Np vector are 28.52 (18) and 43.57 (13)°. Intermolecular C—H...Cl interactions are observed.

Crystal structure of bis-(2-methyl-1H-imidazole-κN (3))(meso-tetra-p-tol-ylporphyrinato-κ(4) N)iron(III) perchlorate tetra-hydro-furan sesquisolvate

In the title compound, [Fe(C48H36N4)(C4H6N2)2]ClO4·1.5C4H8O, the iron(III) metal is coordinated in a distorted octa-hedral geometry by four pyrrole N atoms of the porphyrin ligand in the equatorial plane and two N atoms of 2-methyl-imidazole ligands in the axial sites. The complex has a highly ruffled porphyrin core with mean absolute core-atom displacements C a, C b, C m and C av of 0.25 (5), 0.17 (12), 0.432 (16) and 0.25 (13) Å, respectively. One of the four phenyl groups of the porphyrin is disordered over two sets of sites with refined occupancy ratio of 0.718 (7):0.282 (7). The mean Fe-Np (Np is a porphyrin N atom) bond length [1.975 (9) Å] indicates the low-spin state of the iron atom. The two 2-methyl-imidazole ligands are nearly perpendicular and form a dihedral angle of 86.93 (10)°. The dihedral angles between the 2-methyl-imidazole ligands and the closest Fe-Np vector are 38.04 (9) and 35.00 (7)°. In the crystal, the complex cations inter-act with the perchlorate anions through N-H⋯O hydrogen bonds, forming chains running parallel to [110].

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

The reaction of [Fe(TMP)(OClO[Formula: see text]], where TMP is the dianion of tetramesitylporphyrin, with a combination of a strong [Formula: see text]-acceptor ligand and a [Formula: see text]-donating imidazole can lead to the preparation of mixed-ligand complexes [Fe(Porph)(4-CNPy)(L)][Formula: see text] where L is imidazole itself or 1-acetylimidazole and 4-cyanopyridine is the strong [Formula: see text] 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–N[Formula: see text] 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 [Formula: see text] 3.05, [Formula: see text] 2.07, and [Formula: see text] 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: [Formula: see text] 15.432 (12) Å, [Formula: see text] 20.696 (2) Å, [Formula: see text] 19.970 (5) Å, and [Formula: see text] 99.256 (14)[Formula: see text], monoclinic, space group P21/n, V [Formula: see text] 6295 (2) Å3, Z [Formula: see text] 4, formula FeCl3O4N8C[Formula: see text]H[Formula: see text], 8397 observed data, [Formula: see text] 0.086, [Formula: see text] 0.210, refinement on [Formula: see text]. Crystal data for form B: [Formula: see text]15.267 (3) Å, [Formula: see text]20.377 (6) Å, [Formula: see text] 19.670 (4) Å, and [Formula: see text] 98.14 (1)[Formula: see text], monoclinic, space group P[Formula: see text]/n, V = 6058 (4) Å3, Z = 4, formula C[Formula: see text]H[Formula: see text]Cl[Formula: see text]FeN8O4, 5464 observed data, [Formula: see text] 0.096, [Formula: see text] 0.112, refinement on F.

Synthesis and characterization of a modified "picket fence" porphyrin complex - stronger π bonding interactions between Fe(ii) and axial ligands

A new, modified "picket fence" porphyrin is synthesized and its bis(imidazole)-ligated iron(ii) derivative [Fe(MbenTpivPP)(1-MeIm)(2)] is investigated. X-ray structure determinations demonstrate that [Fe(MbenTpivPP)(1-MeIm)(2)] has structural features of a near planar porphyrin plane, a relative perpendicular ligand orientation, and one unusually large absolute ligand orientation (φ). The combination of these features leads to a new type of species that is different from previously reported analogues. Further structural examination reveals a strong correlation between the mutual ligand orientations (θ) and the axial Fe-N(Im) bond distances, which is detailed for the first time. Mössbauer spectroscopic characterization shows that the low spin derivative has a quadrupole splitting of 0.99 mm s(-1) at 100 K.

Explorations in metalloporphyrin stereochemistry, physical properties and beyond

A review of selected portions of our work in the area of porphyrin structure and physical characterization is presented. Topics covered include early work on periodic trends in first row transtion metalloporphyrins, a survey of electronic structure of iron derivatives including spin-state trends, ligand orientation effects and the elucidtion of unusual low-spin states for iron(II). A discussion of the different tlypes of high-spin iron(II) complexes and the effects of hydrogen bonding is given. A survey of nitric oxide (NO) derivatives is presented as well as a brief introduction into the use of nuclear resonance vibrational spectroscopy for the study of iron porphyrins and heme proteins.