title: EPR, resonance Raman, and DFT calculations on thiolate- and imidazole-bound iron(III) porphyrin complexes: role of the axial ligand in tuning the electronic structure.
abstract: Iron(III) porphyrin complexes bearing covalently attached imidazole and thiolate axial ligands are investigated using resonance Raman, electron paramagnetic resonance, and cyclic voltammetry. The thiolate ligand stabilizes a low-spin ground state in solvent-bound six-coordinate species, weakens the Fe-N(pyr) bonds, and shifts the Fe(III/II) potential more negative by ~500 mV relative to an imidazole-bound species. Density functional theory calculations reproduce the experimental observation and indicate that the covalent charge donation from thiolate to iron reduces the Z(eff) on the iron. This increases the Fe(3d) orbital energies, which changes the bonding interaction present in these complexes significantly. In particular, the increase of the Fe(3d) energies activates an iron-to-porphyrin π*-back-bonding interaction not present in the imidazole-bound complex.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata, India 700032.
authors.forename: Pradip Kumar
authors.initials: PK
authors.lastname: Das
authors.forename: Sudipta
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Subhra
authors.initials: S
authors.lastname: Samanta
authors.forename: Abhishek
authors.initials: A
authors.lastname: Dey
mesh_terms: D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007093:Imidazoles / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D014732:Vibration
chemical_list: D007093:Imidazoles; D008024:Ligands; D008665:Metalloporphyrins; D013438:Sulfhydryl Compounds; C029899:imidazole; D007501:Iron