Hydrogen Bonding Influence of 1,10-Phenanthroline on Five-Coordinate High-Spin Imidazole-Ligated Iron(II) Porphyrinates

The influence of a hydrogen bond to the coordinated imidazole on the geometric and electronic structure of iron has been further studied in new complexes of five-coordinate high-spin imidazole-ligated iron(II) porphyrinates. With 1,10-phenanthroline (1,10-phen) as the hydrogen-bond acceptor, several new octaethylporphyrin dianion (OEP) and meso-tetraphenylporphyrin dianion (TPP) derivatives have been synthesized and characterized by X-ray crystallography and Mössbauer spectroscopy. In all three new structures, the porphyrin molecules and 1,10-phenanthroline molecules have been found with a ratio of 1:1. All the porphyrin derivatives are five-coordinate 2-methylimidazole-ligated iron(II) species. 1,10-Phenanthroline is hydrogen bonded to the coordinated imidazole to form two unequal hydrogen bonds. The Fe−Np and Fe−NIm bond lengths and displacement of the iron atom out of the porphyrin plane are similar to those in imidazole-ligated species. Mössbauer measurements showed remarkable temperature dependence; the analysis of the data obtained in applied magnetic field for [Fe(OEP)(2-MeHIm)]·(1,10-phen) gave a negative quadrupole splitting value and large asymmetry parameters. All the structural and Mössbauer properties suggest that these new hydrogen-bonded species have the same electronic configuration as imidazole-ligated species.