Manganese K-Edge X-Ray Absorption Spectroscopy as a Probe of the Metal–Ligand Interactions in Coordination Compounds

Abstract.Terminal high-valent metal-oxygen species are key reaction intermediates in the catalytic cycle of both enzymes (e.g., oxygenases) and synthetic oxidation catalysts. While tremendous efforts have been directed towards the characterization of the biologically relevant terminal manganese-oxygen and iron-oxygen species, the corresponding analogues based on late-transition metals such as cobalt, nickel or copper are relatively scarce. This is in part related to the "Oxo Wall" concept, which predicts that late transition elements cannot support a terminal oxido ligand in a tetragonal environment. Here, the nickel(II) complex (1) of the tetradentate macrocyclic ligand bearing a 2,6-pyridinedicarboxamidate unit is shown to be an effective catalyst in the chlorination and oxidation of C-H bonds with sodium hypochlorite as terminal oxidant in the presence of acetic acid (AcOH). Insight into the active species responsible for the observed reactivity was gained through the study of the reaction of 1 with ClO -at low temperature by UV/Vis absorption, resonance Raman, EPR, ESI-MS, and XAS analyses. DFT calculations aided the assignment of the trapped chromophoric species (3) as a nickel-hypochlorite species. Despite the fact that the formal oxidation state of the nickel in 3 is +4, experimental and computational analysis indicate that 3 is best formulated as a Ni III complex with one unpaired electron delocalized in the ligands surrounding the metal center. Most remarkably, 3 reacts rapidly with a range of substrates including those with strong aliphatic C-H bonds, indicating the direct involvement of 3 in the oxidation/chlorination reactions observed in the 1/ClO -

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“…46,70,71 Spin unrestricted, time-dependent calculations for XAS spectra were ) using acetonitrile as solvent.…”

Section: Computational Detailsmentioning

confidence: 99%

Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel–Oxygen Species

et al. 2016

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“…Thus, the energetic shift applied becomes non-trivial; the applied energetic shift in the present case was made such that the closed-shell solution fits appropriately. A more rigorous consideration of the energetic shift would require a calibration of the employed method across a series of varying nickel complexes, as has been shown previously for Mn and Fe [99,100].…”

Section: Simulated Core Level Excited State Spectramentioning

confidence: 99%

Distorted tetrahedral nickel-nitrosyl complexes: spectroscopic characterization and electronic structure

et al. 2016

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The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh 3 ) 2 ]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh 3 ) 2 ] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV-Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [Ni (II) (NO (-) )(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [Ni (II) (NO (-) )(X)(PPh 3 ) 2 ] ground state.

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“…[3,7,10,11]) and to investigate biological or biomimetic systems containing transition metal centers (see, e.g., Refs. [12][13][14][15][16][17][18]). Usually, XAS and XES are used as fingerprint techniques in such studies to identify the oxidation state, spin state, and local coordination environment of a metal center.…”

Section: Introductionmentioning

confidence: 99%

Origin-independent calculation of quadrupole intensities in X-ray spectroscopy

Bernadotte

Atkins

Jacob

2012

The Journal of Chemical Physics

147

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For electronic excitations in the ultraviolet and visible range of the electromagnetic spectrum, the intensities are usually calculated within the dipole approximation, which assumes that the oscillating electric field is constant over the length scale of the transition. For the short wavelengths used in hard X-ray spectroscopy, the dipole approximation may not be adequate. In particular, for metal K-edge X-ray absorption spectroscopy (XAS), it becomes necessary to include higher-order contributions. In quantum-chemical approaches to X-ray spectroscopy, these socalled quadrupole intensities have so far been calculated by including contributions depending on the square of the electric-quadrupole and magnetic-dipole transition moments. However, the resulting quadrupole intensities depend on the choice of the origin of the coordinate system. Here, we show that for obtaining an originindependent theory, one has to include all contributions that are of the same order in the wave vector consistently. This leads to two additional contributions depending on products of the electric-dipole andelectric-octupole and of the electric-dipole and magnetic-quadrupole transition moments, respectively. We have implemented such an origin-independent calculation of quadrupole intensities in XAS within timedependent density-functional theory, and demonstrate its usefulness for the calculation of metal and ligand K-edge XAS spectra of transition metal complexes.2

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Manganese K-Edge X-Ray Absorption Spectroscopy as a Probe of the Metal–Ligand Interactions in Coordination Compounds

Cited by 114 publications

References 58 publications

Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel–Oxygen Species

Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel–Oxygen Species

Distorted tetrahedral nickel-nitrosyl complexes: spectroscopic characterization and electronic structure

Origin-independent calculation of quadrupole intensities in X-ray spectroscopy

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