Unique Axial Imidazole Geometries of Fully Halogenated Iron(II) Porphyrin Complexes: Crystal Structures and Mössbauer Spectroscopic Studies

The synthesis and characterization of several electron-poor iron­(II) porphyrin (FeTFPPBr₈) complexes with axial imidazole ligands are reported. The single-crystal X-ray structures have been studied by a combination of crystal packing and Hirshfeld surface calculations, which explained the unusual axial-ligand geometries, e.g., the strong tilt of the Fe–N_Im bonds and the imidazole planes. The six-coordinate [Fe­(TFPPBr₈)­(1-MeIm)₂] was studied by multiple-temperature solid-state Mössbauer spectroscopy, which suggested that it is a low-spin complex with δ ∼ 0.32–0.38 mm/s and ΔE_Q ∼ 1.0 mm/s.