Hydrogen-Bonding Effects in Five-Coordinate High-Spin Imidazole-Ligated Iron(II) Porphyrinates

• Published in: Inorganic chemistry 2018-01, Vol.57 (2), p.793-803
• Main Authors: Hu, Chuanjiang, Noll, Bruce C, Schulz, Charles E, Scheidt, W. Robert
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b02744

The influence of hydrogen binding to the N–H group of coordinated imidazole in high-spin iron­(II) porphyrinates has been studied. The preparation and characterization of new complexes based on [Fe­(TPP)­(2-MeHIm)] (TPP is the dianion of tetraphenylporphyrin) are reported. The hydrogen bond acceptors are ethanol, tetramethylene sulfoxide, and 2-methylimidazole. The last acceptor, 2-MeHIm, was found in a crystalline complex with two [Fe­(TPP)­(2-MeHIm)] sites, only one of which has the 2-methylimidazole hydrogen bond acceptor. This latter complex has been studied by temperature-dependent Mössbauer spectroscopy. All new complexes have also been characterized by X-ray structure determinations. The Fe–NP and Fe–NIm bond lengths, and displacement of the Fe atom out of the porphyrin plane are similar to, but marginally different than, those in imidazole-ligated species with no hydrogen bond. All the structural and Mössbauer properties suggest that these new hydrogen-bonded species have the same electronic configuration as imidazole-ligated species with no hydrogen bond. These new studies continue to show that the effects of hydrogen bonding in five-coordinate high-spin iron­(II) systems are subtle and challenging to understand.