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Mn K-edge X-ray absorption studies of oxo- and hydroxo-manganese(IV) complexes: experimental and theoretical insights into pre-edge properties.

Leto DF, Jackson TA - Inorg Chem (2014)

Bottom Line: Mn 3d-4p mixing, which primarily accounts for the pre-edge intensities, is not solely a function of the Mn-O(H) bond length; the coordination geometry also has a large effect on the distribution of pre-edge intensity.These results underscore the importance of reporting experimental pre-edge areas rather than peak heights.Finally, the TD-DFT method was applied to understand the pre-edge properties of a recently reported S = 1 Mn(V)═O adduct; these findings are discussed within the context of previous examinations of oxomanganese(V) complexes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States.

ABSTRACT
Mn K-edge X-ray absorption spectroscopy (XAS) was used to gain insights into the geometric and electronic structures of [Mn(II)(Cl)2(Me2EBC)], [Mn(IV)(OH)2(Me2EBC)](2+), and [Mn(IV)(O)(OH)(Me2EBC)](+), which are all supported by the tetradentate, macrocyclic Me2EBC ligand (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). Analysis of extended X-ray absorption fine structure (EXAFS) data for [Mn(IV)(O)(OH)(Me2EBC)](+) revealed Mn-O scatterers at 1.71 and 1.84 Å and Mn-N scatterers at 2.11 Å, providing the first unambiguous support for the formulation of this species as an oxohydroxomanganese(IV) adduct. EXAFS-determined structural parameters for [Mn(II)(Cl)2(Me2EBC)] and [Mn(IV)(OH)2(Me2EBC)](2+) are consistent with previously reported crystal structures. The Mn pre-edge energies and intensities of these complexes were examined within the context of data for other oxo- and hydroxomanganese(IV) adducts, and time-dependent density functional theory (TD-DFT) computations were used to predict pre-edge properties for all compounds considered. This combined experimental and computational analysis revealed a correlation between the Mn-O(H) distances and pre-edge peak areas of Mn(IV)═O and Mn(IV)-OH complexes, but this trend was strongly modulated by the Mn(IV) coordination geometry. Mn 3d-4p mixing, which primarily accounts for the pre-edge intensities, is not solely a function of the Mn-O(H) bond length; the coordination geometry also has a large effect on the distribution of pre-edge intensity. For tetragonal Mn(IV)═O centers, more than 90% of the pre-edge intensity comes from excitations to the Mn═O σ* MO. Trigonal bipyramidal oxomanganese(IV) centers likewise feature excitations to the Mn═O σ* molecular orbital (MO) but also show intense transitions to 3dx(2)-y(2) and 3dxy MOs because of enhanced 3d-4px,y mixing. This gives rise to a broader pre-edge feature for trigonal Mn(IV)═O adducts. These results underscore the importance of reporting experimental pre-edge areas rather than peak heights. Finally, the TD-DFT method was applied to understand the pre-edge properties of a recently reported S = 1 Mn(V)═O adduct; these findings are discussed within the context of previous examinations of oxomanganese(V) complexes.

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Fourier transforms of Mn K-edge EXAFS data [k3χ(k)] and raw EXAFS spectra (insets),experimental data (···) and fits (−) for (A)[MnII(Cl2)(Me2EBC)] (1), (B) [MnIV(OH)2(Me2EBC)]2+ (2), and (C) [MnIV(O)(OH)(Me2EBC)]+ (3). Details regarding EXAFSfits are in Table 1.
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fig2: Fourier transforms of Mn K-edge EXAFS data [k3χ(k)] and raw EXAFS spectra (insets),experimental data (···) and fits (−) for (A)[MnII(Cl2)(Me2EBC)] (1), (B) [MnIV(OH)2(Me2EBC)]2+ (2), and (C) [MnIV(O)(OH)(Me2EBC)]+ (3). Details regarding EXAFSfits are in Table 1.

Mentions: The Fourier transform (R′ space) of the EXAFSspectrum of 1 exhibits a broad peak at R′ ≈ 2.0 Å that is best accounted for by two shellsof scatterers 2.47 (two Cl scatterers) and 2.29 Å (four N scatterers),as shown in Figure 2A and Table 1. The distances of the Cl and N scatterers are in good agreementwith the average Mn–Cl and Mn–N distances of 2.455 and2.334 Å observed in the X-ray diffraction structure of 1 (Table 2).54 Fits modeling the two smaller peaks at R′≈ 2.6 and 2.9 Å using two Mn···C shellsat 3.03 and 3.21 Å (4 and 6 C atoms, respectively) improve theoverall goodness-of-fit (Table 1 and Table S1, Supporting Information). In the X-raydiffraction structure of 1, two C atoms are located ata Mn···C distance of ∼3.00 Å, 10 C atomsat Mn···C distances ranging from 3.10 to 3.26 Å(average Mn···C distance 3.18 Å), and 2 C atomsare located at a Mn···C distance of ∼3.65 Å.54 Thus, all structural parameters obtained fromEXAFS fits of 1 are in excellent agreement with the correspondingXRD structure.


Mn K-edge X-ray absorption studies of oxo- and hydroxo-manganese(IV) complexes: experimental and theoretical insights into pre-edge properties.

Leto DF, Jackson TA - Inorg Chem (2014)

Fourier transforms of Mn K-edge EXAFS data [k3χ(k)] and raw EXAFS spectra (insets),experimental data (···) and fits (−) for (A)[MnII(Cl2)(Me2EBC)] (1), (B) [MnIV(OH)2(Me2EBC)]2+ (2), and (C) [MnIV(O)(OH)(Me2EBC)]+ (3). Details regarding EXAFSfits are in Table 1.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4066903&req=5

fig2: Fourier transforms of Mn K-edge EXAFS data [k3χ(k)] and raw EXAFS spectra (insets),experimental data (···) and fits (−) for (A)[MnII(Cl2)(Me2EBC)] (1), (B) [MnIV(OH)2(Me2EBC)]2+ (2), and (C) [MnIV(O)(OH)(Me2EBC)]+ (3). Details regarding EXAFSfits are in Table 1.
Mentions: The Fourier transform (R′ space) of the EXAFSspectrum of 1 exhibits a broad peak at R′ ≈ 2.0 Å that is best accounted for by two shellsof scatterers 2.47 (two Cl scatterers) and 2.29 Å (four N scatterers),as shown in Figure 2A and Table 1. The distances of the Cl and N scatterers are in good agreementwith the average Mn–Cl and Mn–N distances of 2.455 and2.334 Å observed in the X-ray diffraction structure of 1 (Table 2).54 Fits modeling the two smaller peaks at R′≈ 2.6 and 2.9 Å using two Mn···C shellsat 3.03 and 3.21 Å (4 and 6 C atoms, respectively) improve theoverall goodness-of-fit (Table 1 and Table S1, Supporting Information). In the X-raydiffraction structure of 1, two C atoms are located ata Mn···C distance of ∼3.00 Å, 10 C atomsat Mn···C distances ranging from 3.10 to 3.26 Å(average Mn···C distance 3.18 Å), and 2 C atomsare located at a Mn···C distance of ∼3.65 Å.54 Thus, all structural parameters obtained fromEXAFS fits of 1 are in excellent agreement with the correspondingXRD structure.

Bottom Line: Mn 3d-4p mixing, which primarily accounts for the pre-edge intensities, is not solely a function of the Mn-O(H) bond length; the coordination geometry also has a large effect on the distribution of pre-edge intensity.These results underscore the importance of reporting experimental pre-edge areas rather than peak heights.Finally, the TD-DFT method was applied to understand the pre-edge properties of a recently reported S = 1 Mn(V)═O adduct; these findings are discussed within the context of previous examinations of oxomanganese(V) complexes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States.

ABSTRACT
Mn K-edge X-ray absorption spectroscopy (XAS) was used to gain insights into the geometric and electronic structures of [Mn(II)(Cl)2(Me2EBC)], [Mn(IV)(OH)2(Me2EBC)](2+), and [Mn(IV)(O)(OH)(Me2EBC)](+), which are all supported by the tetradentate, macrocyclic Me2EBC ligand (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). Analysis of extended X-ray absorption fine structure (EXAFS) data for [Mn(IV)(O)(OH)(Me2EBC)](+) revealed Mn-O scatterers at 1.71 and 1.84 Å and Mn-N scatterers at 2.11 Å, providing the first unambiguous support for the formulation of this species as an oxohydroxomanganese(IV) adduct. EXAFS-determined structural parameters for [Mn(II)(Cl)2(Me2EBC)] and [Mn(IV)(OH)2(Me2EBC)](2+) are consistent with previously reported crystal structures. The Mn pre-edge energies and intensities of these complexes were examined within the context of data for other oxo- and hydroxomanganese(IV) adducts, and time-dependent density functional theory (TD-DFT) computations were used to predict pre-edge properties for all compounds considered. This combined experimental and computational analysis revealed a correlation between the Mn-O(H) distances and pre-edge peak areas of Mn(IV)═O and Mn(IV)-OH complexes, but this trend was strongly modulated by the Mn(IV) coordination geometry. Mn 3d-4p mixing, which primarily accounts for the pre-edge intensities, is not solely a function of the Mn-O(H) bond length; the coordination geometry also has a large effect on the distribution of pre-edge intensity. For tetragonal Mn(IV)═O centers, more than 90% of the pre-edge intensity comes from excitations to the Mn═O σ* MO. Trigonal bipyramidal oxomanganese(IV) centers likewise feature excitations to the Mn═O σ* molecular orbital (MO) but also show intense transitions to 3dx(2)-y(2) and 3dxy MOs because of enhanced 3d-4px,y mixing. This gives rise to a broader pre-edge feature for trigonal Mn(IV)═O adducts. These results underscore the importance of reporting experimental pre-edge areas rather than peak heights. Finally, the TD-DFT method was applied to understand the pre-edge properties of a recently reported S = 1 Mn(V)═O adduct; these findings are discussed within the context of previous examinations of oxomanganese(V) complexes.

Show MeSH
Related in: MedlinePlus