Category: publications

Microscopic Behavior of Active Materials inside a TCNQ-based Lithium Ion Rechargeable Battery by in-situ 2D ESR Measurements

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ACS Appl. Mater. Interfaces 10, pp.43631-43640 (2018) (DOI: 10.1021/acsami.8b14967) Real-time spectroscopic measurements in rechargeable batteries are important to understand the electrochemistry of the batteries at the molecular level and improve relevant functionalities. We have applied in-situ two-dimensional (2D) ESR spectroscopy to a well-known organic lithium ion battery, which is composed of 7,7,8,8-tetracyanoquinodimethane (TCNQ) as the cathode-active material and a lithium metal anode electrode. The TCNQ rechargeable battery is suitable for investigating electrochemistry in the battery in terms of behavior of electron spin at microscopic levels on both the cathode and anode electrodes. We have discussed two-stage oxidation/reduction reactions of TCNQ, Li deposited/stripped process and their resulting dendritic and/or mossy microstructures, clearly elucidating the cause […]

ESR analyses of picket fence MnII and 6th ligand coordinated FeIII porphyrins (S = 5/2) and a CoII(hfac) complex (S = 3/2) with sizable ZFS parameters revisited: a full spin Hamiltonian approach and quantum chemical calculations

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Dalton Trans., 47, 16429-16444 (2018). (DOI:10.1039/C8DT02988A) The fictitious spin-1/2 (effective spin-1/2) Hamiltonian approach has been the putative method to analyze the conventional fine-structure/hyperfine ESR spectra of high spin metallocomplexes with sizable zero-field splitting (ZFS) tensors since the early 1950s, and the approach gives salient principal geff-values far from g = 2 without explicitly affording their ZFS values in most cases. The experimental geff-values thus determined, however, never agree with those (gtrue-values) of the true principal g-tensors, which are obtainable from reliable quantum chemical calculations. We have recently derived exact or extremely accurate analytical expressions for the geff/gtrue relationships for the spin quantum number S‘s up to S = 7/2 (T. […]

Reversible solution pi-dimerization and long multicenter bonding in a stable phenoxyl radical

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Chemistry – A European Journal Chem. Eur. Journal, 24, pp.14906-14910 (2018). (DOI:10.1002/chem.201802204) Reversible solution p-dimerization is observed in the stable neutral phenoxyl radical 2,6-bis-(8-quinolylamino)-4-(tertbutyl) phenoxyl baqp and is spectroscopically characterized. This behavior, not previously observed for p-extended phenoxyl radicals, is relevant to the formation of long multicenter bonding in the p-dimer at low temperature akin to previously reported phenalenyl radicals. Our experimental data are supported in a quantitative manner by results from density functional theory (DFT) and ab initio molecular orbital theory calculations. Our theoretical results indicate that the solution dimer features strong bonding interactions between the two phenoxyl rings but that the stability of the dimer is also related […]

Fe-Transferrins or their homologues in ex-vivo mushrooms as identified by ESR spectroscopy and quantum chemical calculations: a full spin-Hamiltonian approach for the ferric sextet state with intermediate zero-field splitting parameters

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Food Chemistry Volume 266, 15 November 2018, Pages 24-30 http://doi.org/10.1016/j.foodchem.2018.05.092 Fe-transferrins/their homologues in ex-vivo mushrooms were identified by ESR spectroscopy at liquid helium temperature, 4 K. The ESR fine-structure signals from Grifola frondosa were analyzed by spectral simulation with a full spin-Hamiltonian approach, determining the spin Hamiltonian parameters of the ferric iron species bound in the biological environment: S = 5/2, g = (2.045, 2.01, 2.235), |D| = 0.28 cm−1, |E/D| = 0.05. The zero-field splitting (ZFS) parameters, D– and E-values, are very close to the reported values, |D| = 0.25 cm−1 and |E/D| = 0.06, for an Fe-transferrin with oxalate anion, and to |D| = 0.25 cm−1 and |E/D| = 0.04 for one with malonate anion in human sera, suggesting that the Fe3+ species are from Fe-transferrins or their […]

Using optimal control methods with constraints to generate singlet states in NMR

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J. Magn. Reson., 291, pp.14-22 (2018). DOI:10.1016/j.jmr.2018.03.005 A method is proposed for optimizing the performance of the APSOC (Adiabatic-Passage Spin Order Conversion) technique, which can be exploited in NMR experiments with singlet spin states. In this technique magnetization-to-singlet conversion (and singlet-to-magnetization conversion) is performed by using adiabatically ramped RF-fields. Optimization utilizes the GRAPE (Gradient Ascent Pulse Engineering) approach, in which for a fixed search area we assume monotonicity to the envelope of the RF-field. Such an approach allows one to achieve much better performance for APSOC; consequently, the efficiency of magnetization-to-singlet conversion is greatly improved as compared to simple model RF-ramps, e.g., linear ramps. We also demonstrate that the optimization […]

Behaviour of DFT-based approaches to the spin– orbit term of zero-field splitting tensors: a case study of metallocomplexes, MIII(acac)3 (M = V, Cr, Mn, Fe and Mo)

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Phys. Chem. Chem. Phys., 19, pp.30128-30138 (2017). DOI: 10.1039/C7CP05533a Spin–orbit contributions to the zero-field splitting (ZFS) tensor (DSO tensor) of MIII(acac)3 complexes (M = V, Cr, Mn, Fe and Mo; acac = acetylacetonate anion) are evaluated by means of ab initio (a hybrid CASSCF/MRMP2) and DFT (Pederson–Khanna (PK) and natural orbital-based Pederson–Khanna (NOB-PK)) methods, focusing on the behaviour of DFT-based approaches to the DSO tensors against the valence d-electron configurations of the transition metal ions in octahedral coordination. Both the DFT-based approaches reproduce trends in the D tensors. Significantly, the differences between the theoretical and experimental D (D = DZZ – (DXX + DYY)/2) values are smaller in NOB-PK than in PK, emphasising the usefulness of […]

Analyses of sizable ZFS and magnetic tensors of high spin metallocomplexes

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Phys. Chem. Chem. Phys., 19, pp.24769-24791 (2017). DOI: 10.1039/C7CP03850J The fictitious spin-1/2 Hamiltonian approach is the putative method to analyze the fine-structure/hyperfine ESR spectra of high spin metallocomplexes having sizable zerofield splitting (ZFS), thus giving salient principal g-values far from around g = 2 without explicitly providing their ZFS parameters in most cases. Indeed, the significant departure of the g-values from g = 2 is indicative of the occurrence of their high spin states, but naturally they never agree with true g-values acquired by quantum chemical calculations such as sophisticated DFT or ab initio MO calculations. In this work, we propose facile approaches to determine the magnetic tensors of high spin metallocomplexes having sizable ZFS, instead of performing advanced high-field/high-frequency […]

Synthesis and Magnetic Properties of Trioxytriphenylamine Dimers in Di(radical cationic) States

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Chem, Eur. J., accepted (2017). DOI: 10.1002/chem.201703220   Three structural isomers of trioxytriphenylamine (TOT) dimers, 4,4”’-bis(2,2′:6′,2″:6″,6-trioxytriphenylamine) (4), 3,3”’-bis(2,2′:6′,2″:6″,6-trioxytriphenylamine) (5), and 3,4”’-bis(2,2′:6′,2″:6″,6-trioxytriphenylamine) (6) were prepared and their electronic and magnetic properties in the di(radical cationic) states were investigated. The X-ray crystal structure analysis demonstrated that the TOT moieties of all the di(radical cation)s have planar structures similar to that of the structure of the parent TOT radical cation 3+. The UV-vis spectrum of the di(radical cation) showed characteristic absorptions depending on the connecting pattern. Thus, in the long wavelength region (600-900 nm), 4-2+ exhibited strong and broad characteristic absorptions, while compounds 5-2+ and 62+ exhibited weak absorptions. Notably, in the 450-600 […]