EPR, the X-ray Structure and DFT calculations of the Nitroxide Biradical with One Acetylene Group in the bridge

Gromov, O. I. and Golubeva, E. N. and Khrustalev, V. N. and Kálai, Tamás and Hideg, Kálmán and Kokorin, Alex (2014) EPR, the X-ray Structure and DFT calculations of the Nitroxide Biradical with One Acetylene Group in the bridge. Applied Magnetic Resonance, 45. pp. 981-992. ISSN 0937-9347, ESSN: 1613-7507

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Abstract

Two short nitroxide biradicals of similar composition, R6'-R6' (B0) and R6'-(C≡C)-R6' (B1), where R6' is 1-oxyl-2,2,6,6-tetramethyl-3,4-ene-nitroxide ring, have been investigated by EPR spectroscopy and X-ray structural analysis. Quantum chemical calculations at UDFT/B3LYP/cc-pVDZ level were also performed and compared with the X-ray structural data. Zero field splitting parameters D for B0 and B1 were found to be equal 0.0048 cm-1 and 0.0022 cm-1 respectively in good agreement with quantum chemical prediction. Potential energy surface scans corresponding to pathways of the conformational rearrangements were calculated, rotation barriers for B0 and B1 were found to be 19.2 kJ/mol and 4.0 kJ/mol respectively, structural rigidity and probable differences in biradicals behavior are discussed. Calculations of spin density distribution in biradicals B0 and B1 were also carried out.

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