title: Effects of imidazole deprotonation on vibrational spectra of high-spin iron(II) porphyrinates.
abstract: The effects of the deprotonation of coordinated imidazole on the vibrational dynamics of five-coordinate high-spin iron(II) porphyrinates have been investigated using nuclear resonance vibrational spectroscopy. Two complexes have been studied in detail with both powder and oriented single-crystal measurements. Changes in the vibrational spectra are clearly related to structural differences in the molecular structures that occur when imidazole is deprotonated. Most modes involving the simultaneous motion of iron and imidazolate are unresolved, but the one mode that is resolved is found at higher frequency in the imidazolates. These out-of-plane results are in accord with earlier resonance Raman studies of heme proteins. We also show the imidazole vs imidazolate differences in the in-plane vibrations that are not accessible to resonance Raman studies. The in-plane vibrations are at lower frequency in the imidazolate derivatives; the doming mode shifts are inconclusive. The stiffness, an experimentally determined force constant that averages the vibrational details to quantify the nearest-neighbor interactions, confirms that deprotonation inverts the relative strengths of axial and equatorial coordination.
authors.affiliation: Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China. cjhu@suda.edu.cn
authors.forename: Chuanjiang
authors.initials: C
authors.lastname: Hu
authors.forename: Qian
authors.initials: Q
authors.lastname: Peng
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Silvernail
authors.forename: Alexander
authors.initials: A
authors.lastname: Barabanschikov
authors.forename: Jiyong
authors.initials: J
authors.lastname: Zhao
authors.forename: E Ercan
authors.initials: EE
authors.lastname: Alp
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sturhahn
authors.forename: J Timothy
authors.initials: JT
authors.lastname: Sage
authors.forename: W Robert
authors.initials: WR
authors.lastname: Scheidt
mesh_terms: D007093:Imidazoles / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D013057:Spectrum Analysis; D014732:Vibration
chemical_list: D007093:Imidazoles; D008665:Metalloporphyrins; D011522:Protons; C029899:imidazole; D007501:Iron