Additions and Corrections - Synthesis, Crystal and Molecular Structure, and Spectroscopic Properties of Tris(2,2' -bipyridyl)iron(II) Nitroprusside Tetrahydrate [Fe(bpy)3][Fe(CN)5NO]-4H2O.

Single-atom catalysts with iron ions in the active site, known as FeNC catalysts, show high activity for the oxygen reduction reaction and hence hold promise for access to low-cost fuel cells. Because of the amorphous, multiphase structure of the FeNC catalysts, the iron environment and its electronic structure are poorly understood. While it is widely accepted that the catalytically active site contains an iron ion ligated by several nitrogen donors embedded in a graphene-like plane, the exact structural details, such as the presence or nature of axial ligands, are unknown. Computational chemistry in combination with Mössbauer spectroscopy can help unravel the geometric and electronic structures of the active sites. As a first step toward this goal, we present a calibration of computational Mössbauer spectroscopy for FeN 4-like environments. The uncertainty of both the isomer shift and the quadrupole splitting prediction is determined, from which trust regions for the Mössbauer parameter predictions of computational FeNC models are derived. We find that TPSSh, B3LYP, and PBE0 perform equally well; the trust regions with B3LYP are 0.13 mm s −1 for the isomer shift and 0.36 mm s −1 for the quadrupole splitting. The calibration data is made publicly available in an interactive notebook that provides predicted Mössbauer parameters with individual uncertainty estimates from computed contact densities and quadrupole splitting values. We show that a differentiation of common FeNC Mössbauer signals by a separate analysis of isomer shift and quadrupole splitting will most likely be insufficient, whereas their simultaneous evaluation will allow the assignment to adequate computational FeNC models.

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Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Gallenkamp

Kramm

Proppe

et al. 2020

Int J of Quantum Chemistry

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Solute Transport in Clay Media: Effect of Humic Acid

Fitch

1995

Environ. Sci. Technol.

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Syntheses, Crystal Structures, and Magnetic Properties of the Oxalato-Bridged Mixed-Valence Complexes [Fe^II(bpm)₃]₂[Fe^III₂(ox)₅]·8H₂O and Fe^II(bpm)₃Na(H₂O)₂Fe(ox)₃·4H₂O (bpm = 2,2‘-Bipyrimidine)

Armentano

Faus

et al. 2001

Inorg. Chem.

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The preparation and crystal structures of two oxalato-bridged FeII-FeIII mixed-valence compounds, [FeII(bpm)3]2[FeIII2(ox)5].8H2O (1) and FeII(bpm)3Na(H2O)2FeIII(ox)(3).4H2O (2) (bpm = 2,2'-bipyrimidine; ox = oxalate dianion) are reported here. Complex 1 crystallizes in the triclinic system, space group P1, with a = 10.998(2) A, b = 13.073(3) A, c = 13.308(3) A, alpha = 101.95(2) degrees, beta = 109.20(2) degrees, gamma = 99.89(2) degrees, and Z = 1. Complex 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 12.609(2) A, b = 19.670(5) A, c = 15.843(3) A, beta = 99.46(1) degrees, and Z = 4. The structure of complex 1 consists of centrosymmetric oxalato-bridged dinuclear high-spin iron(III) [Fe2(ox)5]2- anions, tris-chelated low-spin iron(II) [Fe(bpm)3]2+ cations, and lattice water molecules. The iron atoms are hexacoordinated: six oxygen atoms (iron(III)) from two bidentate and one bisbidentate oxalato ligands and six nitrogen atoms (iron(II)) from three bidentate bpm groups. The Fe(III)-O(ox) and Fe(II)-N(bpm) bond distances vary in the ranges 1.967(3)-2.099(3) and 1.967(4)-1.995(3) A, respectively. The iron(III)-iron(III) separation across the bridging oxalato is 5.449(2) A, whereas the shortest intermolecular iron(III)-iron(II) distance is 6.841(2) A. The structure of complex 2 consists of neutral heterotrinuclear Fe(bpm)2Na(H2O)2Fe(ox)3 units and water molecules of crystallization. The tris-chelated low-spin iron(II) ([Fe(bpm)3]2+) and high-spin iron(III) ([Fe(ox)3]3-) entities act as bidentate ligands (through two bpm-nitrogen and two oxalato-oxygen atoms, respectively) toward the univalent sodium cation, yielding the trinuclear (bpm)2Fe(II)-bpm-Na(I)-ox-Fe(III)(ox)2 complex. Two cis-coordinated water molecules complete the distorted octahedral surrounding of the sodium atom. The ranges of the Fe(II)-N(bpm) and Fe(III)-O(ox) bond distances [1.968(6)-1.993(5) and 1.992(6)-2.024(6) A, respectively] compare well with those observed in 1. The Na-N(bpm) bond lengths (2.548(7) and 2.677(7) A) are longer than those of Na-O(ox) (2.514(7) and 2.380(7) A) and Na-O(water) (2.334(15) and 2.356(12) A). The intramolecular Fe(II)...Fe(III) separation is 6.763(2) A, whereas the shortest intermolecular Fe(II)...Fe(II) and Fe(III)...Fe(III) distances are 8.152(2) and 8.992(2) A, respectively. Magnetic susceptibility measurements in the temperature range 2.0-290 K for 1 reveal that the high-spin iron(III) ions are antiferromagnetically coupled (J = -6.6 cm-1, the Hamiltonian being defined as H = -JS1.S2). The magnitude of the antiferromagnetic coupling through the bridging oxalato in the magneto-structurally characterized family of formula [M2(ox)5](2m-10)+ (M = Fe(III) (1), Cr(III), and Ni(II)) is analyzed and discussed by means of a simple orbital model.

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Additions and Corrections - Synthesis, Crystal and Molecular Structure, and Spectroscopic Properties of Tris(2,2' -bipyridyl)iron(II) Nitroprusside Tetrahydrate [Fe(bpy)₃][Fe(CN)₅NO]-4H₂O.

Cited by 4 publications

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Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Solute Transport in Clay Media: Effect of Humic Acid

Syntheses, Crystal Structures, and Magnetic Properties of the Oxalato-Bridged Mixed-Valence Complexes [Fe^II(bpm)₃]₂[Fe^III₂(ox)₅]·8H₂O and Fe^II(bpm)₃Na(H₂O)₂Fe(ox)₃·4H₂O (bpm = 2,2‘-Bipyrimidine)

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Additions and Corrections - Synthesis, Crystal and Molecular Structure, and Spectroscopic Properties of Tris(2,2' -bipyridyl)iron(II) Nitroprusside Tetrahydrate [Fe(bpy)3][Fe(CN)5NO]-4H2O.

Cited by 4 publications

References 0 publications

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Solute Transport in Clay Media: Effect of Humic Acid

Syntheses, Crystal Structures, and Magnetic Properties of the Oxalato-Bridged Mixed-Valence Complexes [FeII(bpm)3]2[FeIII2(ox)5]·8H2O and FeII(bpm)3Na(H2O)2Fe(ox)3·4H2O (bpm = 2,2‘-Bipyrimidine)

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Additions and Corrections - Synthesis, Crystal and Molecular Structure, and Spectroscopic Properties of Tris(2,2' -bipyridyl)iron(II) Nitroprusside Tetrahydrate [Fe(bpy)₃][Fe(CN)₅NO]-4H₂O.

Syntheses, Crystal Structures, and Magnetic Properties of the Oxalato-Bridged Mixed-Valence Complexes [Fe^II(bpm)₃]₂[Fe^III₂(ox)₅]·8H₂O and Fe^II(bpm)₃Na(H₂O)₂Fe(ox)₃·4H₂O (bpm = 2,2‘-Bipyrimidine)