The Structure and Internal Dynamics of R6-p-C6H4-R6 Biradical: EPR, X-ray Crystallography and DFT Calculations

A purposefully synthesized nitroxide biradical R 6 - p -C 6 H 4 -R 6 ( B1 ), where R 6 is the 1-oxyl-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine group with a relatively short distance between the two radical sites, has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy. Hyp...

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Bibliographic Details
Published in:Applied magnetic resonance 2019-03, Vol.50 (1-3), p.425-439
Main Authors: Kokorin, A. I., Gromov, O. I., Dorovatovskii, P. V., Lazarenko, V. A., Khrustalev, V. N., Hideg, K., Kálai, T.
Format: Article
Language:English
Subjects:
Atoms and Molecules in Strong Fields
Attenuation coefficients
Chromatography
Crystallography
Density functional theory
Electron paramagnetic resonance
Electron spin
Electrons
Laser Matter Interaction
Mathematical analysis
Organic Chemistry
Original Paper
Physical Chemistry
Physics
Physics and Astronomy
Quantum chemistry
Solid State Physics
Solvents
Spectroscopy/Spectrometry
Spin exchange
Superhigh frequencies
Temperature
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Summary:A purposefully synthesized nitroxide biradical R 6 - p -C 6 H 4 -R 6 ( B1 ), where R 6 is the 1-oxyl-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine group with a relatively short distance between the two radical sites, has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy. Hyperfine splitting (hfs) constants on the 14 N atoms, electron spin exchange integral | J |, and the distance between the two N–O fragments r NO–NO were experimentally measured. Density functional theory, DFT, calculations were performed using the ORCA 4.0.1.2 program package. The optimized geometry was compared with X-ray crystallographic data and theoretical hfs constants were compared with the respective experimental EPR values. It is concluded that the current quantum chemical approaches provide good results in calculating hfs constants as well as some other EPR parameters. It is confirmed that the intramolecular electron spin exchange in biradicals analogous to B1 is realized by the indirect mechanism rather than direct collision of the N–O· groups. It is also shown that one can calculate and predict values of | J | in other similar biradicals based on the principle of “attenuation coefficients.
ISSN:0937-9347
1613-7507
DOI:10.1007/s00723-018-1089-8