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EPR,the X-ray Structure and DFT Calculations of the Nitroxide Biradical with One Acetylene Group in the Bridge |
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| Authors: | O I Gromov E N Golubeva V N Khrustalev T Kálai K Hideg A I Kokorin |
| Institution: | 1. Chemistry Department, M. Lomonosov Moscow State University, 11991, Leninskiye Gory 1-3, Moscow, Russian Federation 2. Institute of Organoelement Compounds of Russian Academy of Sciences, 119991, Vavilov St., 28, Moscow, Russian Federation 3. Institute of Organic and Medical Chemistry, University of Pécs, PO Box 99, Pécs, H-7602, Hungary 4. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russian Federation |
| 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 electron paramagnetic resonance 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 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 and 4.0 kJ/mol, respectively; and 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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