Peculiarities of Spin Exchange in Nitroxide Biradicals Containing Two para-Phenylene Groups in the Bridge. EPR Investigation and DFT Calculations

Kokorin, Alex and Gromov, Oleg and Kálai, Tamás and Hideg, Kálmán (2016) Peculiarities of Spin Exchange in Nitroxide Biradicals Containing Two para-Phenylene Groups in the Bridge. EPR Investigation and DFT Calculations. Applied Magnetic Resonance, 47. pp. 1283-1293. ISSN 0937-9347, ESSN: 1613-7507

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Abstract

Abstract Two nitroxide biradicals of similar composition: R5-CC-Ph-Ph-CC-R5 (B3a) and R6-CC-Ph-Ph-CC-R6 (B3b), where Ph = p-C6H4, and R6 is 1-oxyl-2,2,6,6-tetramethyl piperidine-3,4-ene- , and R5 is 1-oxyl-2,2,5,5-tetramethylpyrroline-3,4-ene- nitroxide rings, have been studied by electron paramagnetic resonance (EPR) spectroscopy. Variations of the intramolecular electron spin exchange in the biradicals, dissolved in toluene, as a function of temperature were characterized by changes in the isotropic 14N hyperfine splitting (hfs) constant a, values of the exchange integral |J|, and compared with the data obtained by DFT calculations. Thermodynamic parameters of the conformational rearrangements were calculated. Geometries of nitroxide biradicals in PES local minima and transition states in the triplet state were calculated at UDFT/B3LYP level with split-valence basis set cc-PVTZ [43]. Probable differences in biradicals behavior are discussed.

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