The electronic structure of TEMPO, its cation and anion

Kubala, D.; Regeta, Khrystyna; Janečková, Radmila; Fedor, Juraj; Grimme, Stefan; Hansen, Andreas; Nesvadba, Peter; Allan, Michael

doi:10.1080/00268976.2013.781695

Cited by 20 publications

(16 citation statements)

References 69 publications

(73 reference statements)

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“…However, for molecules with larger alkyl chains, the term energy is decreased due to the hindered approach of the Rydberg electron to the cationic core, thus decreasing the attraction energy and decreasing the term energy [48,49]. An extreme example was shown in the recent study of the TEMPO (2,2,6,6-Tetramethylpiperidine-N-oxyl) [50] where the shift between DEA and PES bands was only 2.1 eV. In the present case we have the advantage of knowing the shift between PES and VUV spectra to be 3 eV due to the high-resolution data of Giuliani et al [21].…”

Section: Assignment Of Dea Bandsmentioning

confidence: 99%

Partial cross sections for dissociative electron attachment to tetrahydrofuran reveal a dynamics-driven rich fragmentation pattern

Janečková

May

Milosavljević

et al. 2014

International Journal of Mass Spectrometry

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We report partial absolute cross sections for dissociative electron attachment (DEA) to tetrahydrofuran C 4 H 8 O. The high sensitivity of the present setup, quantitative DEA spectrometer with time-of-flight analyzer, led to identification of a number of previously unreported fragments (CH 2− ) thus revealing complex dissociation dynamics of the involved resonant states. The chemical composition of fragment anions was assigned by experiments with completely deuterated tetrahydrofuran. We also show that the dominant heavy anionic fragment with m/z = 41 is C 3 H 5 − anion rather than C 2 HO − as reported in the previous studies, in spite of the fact that formation of the latter one is energetically more favorable. The dynamics on the resonant state is thus more decisive for the reaction outcome than the asymptotic energetics. The assignment of resonances and their dynamic pathways is discussed by using comparison with recent complementary experiments that characterize electronic states of neutral and ionic tetrahydrofuran.

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Section: Assignment Of Dea Bandsmentioning

confidence: 99%

Partial cross sections for dissociative electron attachment to tetrahydrofuran reveal a dynamics-driven rich fragmentation pattern

Janečková

May

Milosavljević

et al. 2014

International Journal of Mass Spectrometry

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“…[25] However,r adicals do not necessarily have al arge FOD and the ones with relatively local SEC effects may not be problematic in standard WFT or DFT treatments.O ften, these cases involve localized spincenters on metal atoms or open-shell functional groups in organic molecules. Figure 2h,r show the persistent TEMPO [38] and trityl radicals,r espectively.I na greement with chemical intuition, the FOD is spatially localized and relatively small. Hence,b oth radicals can be treated with single-reference methods although the trityl radical shows al arge spincontamination in unrestricted HF wave functions and is considered as aborderline case.…”

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confidence: 98%

“…This is even more pronounced for the reactant complex [36] of the reaction of Ni 0 with NH 3 (Figure 2m). Figure 2h,r show the persistent TEMPO [38] and trityl radicals,r espectively.I na greement with chemical intuition, the FOD is spatially localized and relatively small. [37] Further critical test cases are open-shell systems.The FOD of the cyanide radical (Figure 2d)i sl arge and delocalized over the bond thus correctly identifying this molecule as difficult case for most QC methods.…”

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confidence: 99%

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A Practicable Real‐Space Measure and Visualization of Static Electron‐Correlation Effects

2015

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The inclusion of dynamical and static electron correlation (SEC) is mandatory for accurate quantum chemistry (QC). SEC is particularly difficult to calculate and hence a qualitative understanding is important to judge the applicability of approximate QC methods. Existing scalar SEC diagnostics, however, lack the important information where the SEC effects occur in a molecule. We introduce an analysis tool based on a fractional occupation number weighted electron density (ρ(FOD) ) that is plotted in 3D for a pre-defined contour surface value. The scalar field is obtained by finite-temperature DFT calculations with pre-defined electronic temperature (e.g. TPSS at 5000 K). FOD plots only show the contribution of the "hot" (strongly correlated) electrons. We discuss illustrative plots for a broad range of chemical systems from small molecules to large conjugated molecules with polyradicaloid character. Spatial integration yields a single number which can be used to globally quantify SEC.

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“…A recent study of the gas phase TEMPO cation, neutral radical, and anion was performed by Grimme, Allan, and co-authors, combining computations and various gas phase photoelectron spectroscopy techniques. 55 (ch < ch-ax < tbt-1 < tbt-3 < tbt-2), 1c (ch-ax < ch < tbt-3 < tbt-1 < tbt-2), and free anionic TEMPO (ch < tbt-2 < ch-ax < tbt-1 < tbt-3). This difference is likely due to the different steric environments of the two TEMPO ligands in 1t versus 1c.…”

Section: A) Relative Free Energies Of Ni(η 2 -Tempo) 2 and Free Tempomentioning

confidence: 99%

The trans–cis isomerization of Ni(η2-TEMPO)2: Interconnections and conformational complexity

DeYonker

Webster

2015

Inorganica Chimica Acta

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Please cite this article as: N.J. DeYonker, C.E. Webster, The trans-cis Isomerization of Ni(η 2 -TEMPO) 2 : Interconnections and Conformational Complexity, Inorganica Chimica Acta (2015), doi: http://dx. ABSTRACTPreviously, reactions of the "bow-tie" Ni(η 2 -TEMPO) 2 complex with an assortment of donor ligands have been characterized experimentally and computationally. The X-ray crystal structures afforded Ni(η 2 -TEMPO) 2 with trans-disposed TEMPO ligands, which was validated theoretically. Surprisingly, proton transfer from the C-H bond of a variety of alkyne substrates (R) mostly produced cis-disposed ligands of the form Ni(η 2 -TEMPO)(κ 1 -TEMPOH)(κ 1 -R).While computations validated that the experimentally observed cis-disposed products were thermodynamically favored, in all cases, the proposed mechanisms of alkyne addition to cisNi(η 2 -TEMPO) 2 were kinetically disfavored. Therefore, a trans-cis isomerization must occur along the addition pathway. In order to better understand this phenomenon, an exhaustive theoretical conformational search of cis-/trans-Ni(η 2 -TEMPO) 2 and Ni(η 2 -TEMPO)(η 1 -TEMPO) structures has been performed. Our results show profound conformational and fluxional complexity for the trans-cis isomerization of the Ni(η 2 -TEMPO) 2 precursor. Surprisingly, the proposed mechanism for trans-cis isomerization indicates that conformational distortion of one of the TEMPO ligands of trans-Ni(η 2 -TEMPO) 2 before ring-opening provides a transition state free energy of activation stabilization of nearly 4.0 kcal mol -1 versus the most "straightforward" isomerization mechanism. 2 KEYWORDSDensity Functional Theory, TEMPO ligand, reaction mechanisms, conformational distortion HIGHLIGHTSThe trans-cis isomerization of Ni(TEMPO) 2 has been modeled with Density Functional Theory.The cis and trans isomer of Ni(TEMPO) 2 exhibit fascinating conformational complexity and fluxionality of the coordinated TEMPO ligand.New visualization techniques are needed for the presentation of the conformational dynamics of Ni(TEMPO) 2 .

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The electronic structure of TEMPO, its cation and anion

Cited by 20 publications

References 69 publications

Partial cross sections for dissociative electron attachment to tetrahydrofuran reveal a dynamics-driven rich fragmentation pattern

Partial cross sections for dissociative electron attachment to tetrahydrofuran reveal a dynamics-driven rich fragmentation pattern

A Practicable Real‐Space Measure and Visualization of Static Electron‐Correlation Effects

The trans–cis isomerization of Ni(η2-TEMPO)2: Interconnections and conformational complexity

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