title: Ligand orientation control in low-spin six-coordinate (porphinato)iron(II) species.
abstract: The synthesis of a low-spin six-coordinate iron(II) porphyrinate in which the two axial ligands are forced to have a relative perpendicular orientation has been successfully accomplished for the first time. The reaction of four-coordinate (tetramesitylporphinato)iron(II) with 2-methylimidazole leads to the preparation of [Fe(TMP)(2-MeHIm)(2)] which cocrystallizes with five-coordinate [Fe(TMP)(2-MeHIm)]. The six-coordinate complex accommodates the sterically crowded pair of imidazoles with a strongly ruffled core and relative perpendicular orientation. This leads to shortened equatorial bonds of 1.963(6) A and slightly elongated axial Fe-N bond lengths of 2.034(9) A that are about 0.04 A shorter and 0.03 A longer, respectively, in comparison to those of the bis-imidazole-ligated iron(II) species with parallel oriented axial ligands. The Mossbauer spectrum shows a pair of quadrupole doublets that can be assigned to the components of the cocrystallized crystalline solid. High-spin five-coordinate [Fe(TMP)(2-MeHIm)] has DeltaE(Q) = 2.25 mm/s and delta = 0.90 mm/s at 15 K. The quadrupole splitting, DeltaE(Q), for [Fe(TMP)(2-MeHIm)(2)] is 1.71 mm/s, and the isomer shift is 0.43 mm/s at 15 K. The quadrupole splitting value is significantly larger than that found for low-spin iron(II) derivatives with relative parallel orientations for the two axial ligands. Mossbauer spectra thus provide a probe for ligand orientation when structural data are otherwise not available.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Chuanjiang
authors.initials: C
authors.lastname: Hu
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Noll
authors.forename: Charles E
authors.initials: CE
authors.lastname: Schulz
authors.forename: W Robert
authors.initials: WR
authors.lastname: Scheidt
mesh_terms: D018360:Crystallography, X-Ray; D004563:Electrochemistry; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008665:Metalloporphyrins / Q000138:chemical synthesis*; D008968:Molecular Conformation; D015204:Spectroscopy, Mossbauer
chemical_list: D008024:Ligands; D008665:Metalloporphyrins; D007501:Iron