Scrutinizing “Ligand Bands” via Polarized Single-Crystal X-ray Absorption Spectra of Copper(I) and Copper(II) Bis-2,2′-bipyridine Species

DiMucci, Ida M.; MacMillan, Samantha N.; Walroth, R. C.; Lancaster, Kyle M.

doi:10.1021/acs.inorgchem.0c01800

Cited by 5 publications

(6 citation statements)

References 38 publications

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“…In 2015, Tomson et al investigated the Cu K-edges of a range of covalent β-diketiminate Cu complexes with co-ligands exhibiting various degrees of π acidity . In this work, pre-edge features with energies typical of Cu(III) species were found to be accompanied by uncharacteristically low energy rising edges, specifically Cu 1s → 4p excitations, something which was also subsequently observed in bipyridine coordinated Cu(I/II) complexes . Here the authors stress that an analysis based solely on the pre-edge energies of these complexes would have led to a Cu(III) assignment on many complexes that were shown via quantum chemical calculations to have ground states dominated by Cu(I)/Cu(II) configurations.…”

Section: Discussionmentioning

confidence: 83%

“… 18 In this work, pre-edge features with energies typical of Cu(III) species were found to be accompanied by uncharacteristically low energy rising edges, specifically Cu 1s → 4p excitations, something which was also subsequently observed in bipyridine coordinated Cu(I/II) complexes. 62 Here the authors stress that an analysis based solely on the pre-edge energies of these complexes would have led to a Cu(III) assignment on many complexes that were shown via quantum chemical calculations to have ground states dominated by Cu(I)/Cu(II) configurations. Hence, this study emphasizes the importance of examining both the pre-edge and rising edge energy trends in the evaluation of the electronic structure of copper complexes.…”

Section: Discussionmentioning

confidence: 99%

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Combining Valence-to-Core X-ray Emission and Cu K-edge X-ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu(I)/(II)/(III) Complexes

et al. 2022

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A series of organometallic copper complexes in formal oxidation states ranging from +1 to +3 have been characterized by a combination of Cu K-edge X-ray absorption (XAS) and Cu Kβ valence-to-core X-ray emission spectroscopies (VtC XES). Each formal oxidation state exhibits distinctly different XAS and VtC XES transition energies due to the differences in the Cu Z eff , concomitant with changes in physical oxidation state from +1 to +2 to +3. Herein, we demonstrate the sensitivity of XAS and VtC XES to the physical oxidation states of a series of N-heterocyclic carbene (NHC) ligated organocopper complexes. We then extend these methods to the study of the [Cu(CF 3 ) 4 ] − ion. Complemented by computational methods, the observed spectral transitions are correlated with the electronic structure of the complexes and the Cu Z eff . These calculations demonstrate that a contraction of the Cu 1s orbitals to deeper binding energy upon oxidation of the Cu center manifests spectroscopically as a stepped increase in the energy of both XAS and Kβ 2,5 emission features with increasing formal oxidation state within the [Cu n +(NHC 2 )] n+ series. The newly synthesized Cu(III) cation [Cu III (NHC 4 )] 3+ exhibits spectroscopic features and an electronic structure remarkably similar to [Cu(CF 3 ) 4 ] − , supporting a physical oxidation state assignment of low-spin d 8 Cu(III) for [Cu(CF 3 ) 4 ] − . Combining XAS and VtC XES further demonstrates the necessity of combining multiple spectroscopies when investigating the electronic structures of highly covalent copper complexes, providing a template for future investigations into both synthetic and biological metal centers.

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Section: Discussionmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Combining Valence-to-Core X-ray Emission and Cu K-edge X-ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu(I)/(II)/(III) Complexes

et al. 2022

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“…The feature that is approximately 5 eV higher in energy results from a transition into a ligand π* dominated final state (a Co(1s) → L(π*) transition). As demonstrated by single crystal XAS studies of [Cu(bpy) 2 ] 2+/+ complexes by Lancaster and co-workers, these transitions are best thought of as M(1s → 4p) transitions, not XAS-MLCT transitions; although the acceptor state is dominated by oxygen, nitrogen and phenyl carbon 2p character, the minor degree of Co(4p) character (∼2% Co(4p)) in the L(π*) acceptor state allows the transition to gain intensity.…”

Section: Results and Analysismentioning

confidence: 99%

The Oxo-Wall Remains Intact: A Tetrahedrally Distorted Co(IV)–Oxo Complex

et al. 2021

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In this paper, we report the preparation, spectroscopic and theoretical characterization, and reactivity studies of a Co(IV)−oxo complex bearing an N4-macrocyclic coligand, 12-TBC (12-TBC = 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane). On the basis of the ligand and the structure of the Co(II) precursor, [Co II (12-TBC)(CF 3 SO 3 ) 2 ], one would assume that this species corresponds to a tetragonal Co(IV)−oxo complex, but the spectroscopic data do not support this notion. Co K-edge XAS data show that the treatment of the Co(II) precursor with iodosylbenzene (PhIO) as an oxidant at −40 °C in the presence of a proton source leads to a distinct shift in the Co K-edge, in agreement with the formation of a Co(IV) intermediate. The presence of the oxo group is further demonstrated by resonance Raman (rRaman) spectroscopy. Interestingly, the EPR data of this complex show a high degree of rhombicity, indicating structural distortion. This is further supported by the EXAFS data. Using DFT calculations, a structural model is developed for this complex with a ligand-protonated structure that features a CoO•••HN hydrogen bond and a four-coordinate Co center in a seesaw-shaped coordination geometry. Magnetic circular dichroism (MCD) spectroscopy further supports this finding. The hydrogen bond leads to an interesting polarization of the Co−oxo π-bonds, where one O(p) lone-pair is stabilized and leads to a regular Co(d) interaction, whereas the other π-bond shows an inverted ligand field. The reactivity of this complex in hydrogen atom and oxygen atom transfer reactions is discussed as well.

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“…The Cu K-edge XAS of 1 (15 mM in frozen DCM or in the solid state) is consistent with Cu I , with a prominent edge feature at 8985.8 eV ascribed to the characteristic Cu I 4p ← 1s peak. 40,41 The Cu K-edge XAS of 2 (made with 3 equiv of DIAD, 15 mM in frozen DCM solution), on the other hand, exhibits features more characteristic of a Cu II species, with an edge at 8985.0 eV, shifted 2.2 eV with respect to that of 1, and a weak low-energy Cu 3d ← 1s pre-edge feature at 8977.6 eV. 40 DFT and EXAFS data support that the (ArNO) •− moiety in 2 is coordinated to Cu II in a κN fashion.…”

mentioning

confidence: 99%

Five Nitrogen Oxidation States from Nitro to Amine: Stabilization and Reactivity of a Metastable Arylhydroxylamine Complex

et al. 2020

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Redox noninnocent ligands enhance the reactivity of the metal they complex, a strategy used by metalloenzymes and in catalysis. Herein, we report a series of copper complexes with the same ligand framework, but with a pendant nitrogen group that spans five different redox states between nitro and amine. Of particular interest is the synthesis of a unprecedented copper(I)-arylhydroxylamine complex. While hydroxylamines typically disproportionate or decompose in the presence of transition metal ions, the reactivity of this metastable species is arrested by the presence of an intramolecular hydrogen bond. Two-electron oxidation yields a copper(II)-(arylnitrosyl radical) complex that can dissociate to a copper(I) species with uncoordinated arylnitroso. This combination of ligand redox noninnocence and hemilability provides opportunities in catalysis for two-electron chemistry via a one-electron copper(I/II) shuttle, as exemplified with an aerobic alcohol oxidation.

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Scrutinizing “Ligand Bands” via Polarized Single-Crystal X-ray Absorption Spectra of Copper(I) and Copper(II) Bis-2,2′-bipyridine Species

Cited by 5 publications

References 38 publications

Combining Valence-to-Core X-ray Emission and Cu K-edge X-ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu(I)/(II)/(III) Complexes

Combining Valence-to-Core X-ray Emission and Cu K-edge X-ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu(I)/(II)/(III) Complexes

The Oxo-Wall Remains Intact: A Tetrahedrally Distorted Co(IV)–Oxo Complex

Five Nitrogen Oxidation States from Nitro to Amine: Stabilization and Reactivity of a Metastable Arylhydroxylamine Complex

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