On the electronic structure of <i>N,N′</i>-ethylenebis(acetylacetonatiminato)Co(II), Co(II)acacen

Rudin, Markus; Schweiger, A.; Berchten, N.; Günthard, Hs. H.

doi:10.1080/00268978000103561

Cited by 15 publications

(6 citation statements)

References 30 publications

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“…The spectrum can be well reproduced assuming only the 59 Co hyperfine interaction and a 59 Co nuclear quadrupole coupling of | e 2 qQ / h | = 90 ± 10 MHz and η = 0.7 ± 0.4 (Figure c). 59 Co nuclear quadrupole values on the same order have been observed for Co(II)(acacen) ( e 2 qQ / h = −116 MHz) . There was no need to assume an interaction with a strongly coupled 14 N nucleus to explain the Davies ENDOR spectrum.…”

Section: Resultsmentioning

confidence: 53%

“…59 Co nuclear quadrupole values on the same order have been observed for Co(II)(acacen) (e 2 qQ/h = -116 MHz). 51 There was no need to assume an interaction with a strongly coupled 14 N nucleus to explain the Davies ENDOR spectrum. Furthermore, X-band matched HYSCORE and W-band ELDORdetected NMR experiments also proved unsuccessful at detecting a contribution of a strongly coupled 14 N nucleus.…”

Section: Resultsmentioning

confidence: 99%

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Formation of a Cobalt(III)−Phenoxyl Radical Complex by Acetic Acid Promoted Aerobic Oxidation of a Co(II)salen Complex

et al. 2010

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The activation of N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II), [Co(II)(1)], by the addition of acetic acid under aerobic conditions has been investigated by a range of spectroscopic techniques including continuous-wave EPR, HYSCORE, pulsed ENDOR, and resonance Raman. These measurements have revealed for the first time the formation of a coordinated cobalt(III)-bound phenoxyl radical labeled [Co(III)(1(*))(OAc)(n)](OAc)(m) (n = m = 1 or n = 2, m = 0). This cobalt(III)-bound phenoxyl radical is characterized by the following spin Hamiltonian parameters: g(x) = 2.0060, g(y) = 2.0031, g(z) = 1.9943, A(x) = 17 MHz, A(y) = 55 MHz, and A(z) = 14 MHz. Although the radical contains coordinated acetate(s), the experiments unambiguously proved that the phenoxyl radical is situated on ligand (1) as opposed to a phenoxyl radical ligated to cobalt in the axial position. Density functional theory computations on different models corroborate the stability of such a phenoxyl radical species and suggest the ligation of one or two acetate molecules to the complex. A mechanism is proposed, which accounts for the formation of this unusual and extremely robust phenoxyl radical, never previously observed for [Co(1)].

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Section: Resultsmentioning

confidence: 53%

Section: Resultsmentioning

confidence: 99%

Formation of a Cobalt(III)−Phenoxyl Radical Complex by Acetic Acid Promoted Aerobic Oxidation of a Co(II)salen Complex

et al. 2010

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“…However, in (OEC)Co(C 6 H 5 ) we suggest that ligand-atom spin−orbit coupling causes the noncoaxiality of the g and A Co principal axes . The (OEC)Co(C 6 H 5 ) complex has some features in common with several cobalt(II) complexes with Schiff bases and related ligands also possessing a (d xy ) 2 (d xz d yz ) 3 ground state. , For example, the Co(II)CF 3 (acacen) complex shown in Table has a A Co matrix with the largest principal value in the molecular plane of the molecule, and a large difference between the two g values in this plane ( g 1 and g 2 ). The absolute values are not comparable however since this Co(II) complex has the electron localized on the metal ion.…”

Section: Discussionmentioning

confidence: 99%

A Pulse EPR and ENDOR Investigation of the Electronic Structure of a σ-Carbon-Bonded Cobalt(IV) Corrole

et al. 2002

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In this contribution we present a continuous wave (CW), pulse electron paramagnetic resonance (EPR), and pulse electron nuclear double resonance (ENDOR) study of (OEC)Co(C6H5), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. To facilitate spectral assignments isotopic substitutions were employed (2H and 13C). From the analysis of the frozen solution CW EPR, ESEEM, and ENDOR spectra measured at X- and Q-band, we determined the electronic coupling parameters of the unpaired electron with the cobalt nucleus, corrole nitrogen nuclei, phenyl 13C, 1H and 2H nuclei, meso 1H and 2H nuclei, and ethyl 1H nuclei. Determination of the g matrix alignment in the molecular frame was achieved by successfully simulating the orientationally selective powder ENDOR spectra of the meso nuclei. The g principal values are g 1 = 1.9670, g 2 = 2.1122, and g 3=2.0043, with the g 1 and g 2 axes pointing at the nitrogens of the corrole macrocycle and the g 3 axis directed perpendicular to the plane. The cobalt hyperfine matrix A has principal values A 1 Co = 72, A 2 Co = 8, A 3 Co = 10 MHz, with the A 3 Co and g 3 axes parallel to each other and the A 1 Co axis rotated from the g 1 axis by 45°, so that it points at the meso proton H10. Relatively large 1H ENDOR couplings with the ethyl protons were observed, indicating that significant spin density also exists on the macrocycle. A good description of the electronic structure, consistent with the experimental data, was achieved using density functional theory simulations. Both the experimental and calculated data support the conclusion that there is significant spin density on both the macrocycle and in the cobalt d yz orbital.

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“…In their single-crystal ENDOR study of N,N′ethylenebis(acetylacetonatiminato)Co(II), Rudin et al determined the cobalt nuclear quadrupole principal values to be Q x ) -2.76 MHz, Q x ) 2.61 MHz, and Q z ) 0.15 MHz. 47 N,N′ethylenebis(acetylacetonatiminato)Co(II) has no axial ligands, and the unpaired electron resides mainly in the cobalt d yz orbital. The different electronic structure is probably responsible for the difference in magnitude between the cobalt nuclear quadrupole couplings reported for N,N′-ethylenebis(acetylacetonatiminato)Co(II) and the couplings estimated for the complexes under study.…”

Section: Discussionmentioning

confidence: 99%

“…There exists relatively few cobalt nuclear quadrupole data for Co(II) complexes. In their single-crystal ENDOR study of N , N ‘ -ethylenebis(acetylacetonatiminato)Co(II), Rudin et al determined the cobalt nuclear quadrupole principal values to be Q x = −2.76 MHz, Q x = 2.61 MHz, and Q z = 0.15 MHz …”

Section: Discussionmentioning

confidence: 99%

A Continuous Wave and Pulse EPR and ENDOR Investigation of Oxygenated Co(II) Corrin Complexes

2001

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Heptamethyl cobyrinate perchlorate, [Cob(II)ester]ClO 4 , has the relevant structural features of base-off B 12r , the reduced Co(II) form of vitamin B 12 . The reversible oxygenation behavior of this complex in different solvents is investigated using continuous wave (cw) EPR at X-band and compared with that of Co(II) porphyrin complexes. Furthermore, the influence of the addition of a nitrogen base (pyridine or 1-methylimidazole) to the solutions is investigated. To determine the electronic structure of the oxygenated complexes, different pulse electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) techniques are applied. The g and cobalt hyperfine matrix and their principal axes are determined using a combination of cw-EPR at X-and Q-band, ESE (electron spin-echo)-detected EPR at W-band and Davies-ENDOR at Q-band. The experimental g and cobalt hyperfine values are found to be sensitive to the change of solvent, addition of a nitrogen base, and change in the ring structure. From the HYSCORE (hyperfine sublevel correlation) spectra measured at X-band, the interactions with the corrin nitrogen nuclei and the nitrogens of the axial base are deduced. Comparison of these data with those of oxygenated base-on Co(II) porphyrin complexes revealed shorter axial cobalt-nitrogen bonds in the Co(II) corrin than in the porphyrin case. On the other hand, the nitrogen atoms of the corrin and of the porphyrin ligands show similar, small interactions, which is due to the fact that the unpaired electron resides mainly on the O 2 fragment.

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On the electronic structure of N,N′-ethylenebis(acetylacetonatiminato)Co(II), Co(II)acacen

Cited by 15 publications

References 30 publications

Formation of a Cobalt(III)−Phenoxyl Radical Complex by Acetic Acid Promoted Aerobic Oxidation of a Co(II)salen Complex

Formation of a Cobalt(III)−Phenoxyl Radical Complex by Acetic Acid Promoted Aerobic Oxidation of a Co(II)salen Complex

A Pulse EPR and ENDOR Investigation of the Electronic Structure of a σ-Carbon-Bonded Cobalt(IV) Corrole

A Continuous Wave and Pulse EPR and ENDOR Investigation of Oxygenated Co(II) Corrin Complexes

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