Structural and Electronic Characterization of Nitrosyl(Octaethylporphinato)iron(III) Perchlorate Derivatives

Abstract

The synthesis and crystallographic characterization of the five-coordinate iron(III) porphyrinate complex [Fe(OEP)(NO)]ClO4 are reported. This [FeNO]6 complex has a nearly linear Fe-N-O group (angle = 173.19(13) degrees) with a small off-axis tilt of the Fe-N(NO) vector from the heme normal (angle = 4.6 degrees); the Fe-N(NO) distance is 1.6528(13) A and the iron is displaced 0.32 A out-of-plane. The complex forms a tight cofacial pi-pi dimer in the solid state. Mössbauer spectra for this derivative as well as for a related crystalline form are measured both in zero applied magnetic field and in a 7 T applied field. Fits to the measurements made in applied magnetic field demonstrate that both crystalline forms of [Fe(OEP)(NO)]ClO4 have a diamagnetic ground state at 4.2 K. The observed isomer shifts (delta = 0.22-0.24 mm/s) are smaller than those typically observed for low-spin iron(III) porphyrinates. Analogous Mössbauer measurements are also obtained for a six-coordinate derivative, [Fe(OEP)(Iz)(NO)]ClO4 (Iz = indazole). The observed isomer shift for this species is smaller still (delta = 0.02 mm/s). All derivatives show a strong temperature dependence of the isomer shift. The data emphasize the strongly covalent nature of the FeNO group. The Mössbauer isomer shifts suggest formal oxidation states greater than +3 for iron, but the NO stretching frequencies are not consistent with such a large charge transfer to NO. Differences in the observed nitrosyl stretching frequencies of the two crystalline forms of [Fe(OEP)(NO)]ClO4 are discussed.

New precursor for the post-synthesis preparation of Fe-ZSM-5 zeolites with low iron content

“…[8]. This method lead, in our lab, to better results (in terms of [15,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] for Fe 3+ (NO) complexes; Refs. [15,17,18,35,[47][48][49][50][51][52] for Fe 2+ (NO); Refs.…”

Direct Probe of NO Vibration in the Naked Ferric Heme Nitrosyl Complex

“…[13] It is worth noting, however, that in condensed phases the iron porphyrin complex is prone to interact with solvent molecules and counterions and to form p-p interacting dimers. [13] The assay of gaseous FeÀheme(NO) + ions by IRMPD has provided the first unambiguous characterization of the IR absorption features of a genuine five-coordinate nitrosyl complex of the ferric heme.…”

“…[13] It is worth noting, however, that in condensed phases the iron porphyrin complex is prone to interact with solvent molecules and counterions and to form p-p interacting dimers. [13] The assay of gaseous FeÀheme(NO) + ions by IRMPD has provided the first unambiguous characterization of the IR absorption features of a genuine five-coordinate nitrosyl complex of the ferric heme. As the structural and electronic features of heme-nitrosyl complexes are the object of intense ongoing experimental and computational studies, [4,14] the observed vibrational n NO signature at 1842 cm À1 may stand as a reference for the free species in an isolated state.…”

Explorations in metalloporphyrin stereochemistry, physical properties and beyond

“…There are other effects on the structure around iron on the addition of the sixth ligand that have been summarized in references [87][88][89]. We have also characterized additional iron(III) species, espcially six-coordinate species and the original references include the following [90][91][92][93][94]. The nitrosyl derivatves were also the original imputus for my laboratory beginning to explore and develop the new vibrational technique NRVS (nuclear resonance vibration spectroscopy).…”