Stable Radical Trianions from Reversibly Formed Sigma-Dimers of Selenadiazoloquinolones Studied by In Situ EPR/UV鈥搗is Spectroelectrochemistry and Quantum Chemical Calculations

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• 作者：Andrej Sta拧ko ; Karol Lu拧pai ; Zuzana Barbierikov谩 ; J谩n Rimar膷铆k ; Adam Vag谩nek ; Vladim铆r Luke拧 ; Maro拧 Bella ; Viktor Milata ; Michal Zalibera ; Peter Rapta ; Vlasta Brezov谩
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：October 11, 2012
• 年：2012
• 卷：116
• 期：40
• 页码：9919-9927
• 全文大小：510K
• 年卷期：v.116,no.40(October 11, 2012)
• ISSN：1520-5215

文摘

The redox behavior of the series of 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinolines and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f]quinolines with R₇, R₈ = H, COOC₂H₅, COOCH₃, COOH, COCH₃, and CN has been studied by in situ EPR and EPR/UV鈥搗is spectroelectrochemistry in dimethylsulfoxide. All selenadiazoloquinolones undergo a one-electron reduction process to form the corresponding radical anions. Their stability strongly depends on substitution at the nitrogen atom of the 4-pyridone ring. The primary generated radical anions from N-ethyl-substituted quinolones are stable, whereas for the quinolones with imino hydrogen, the initial radical anions rapidly dimerize to produce unusually stable sigma-dimer (蟽-dimer) dianions. These are reversibly oxidized to the initial compounds at potentials considerably less negative than the original reduction process in the back voltammetric scan. The dimer dianion can be further reduced to the stable paramagnetic dimer radical trianion in the region of the second reversible reduction step. The proposed complex reaction mechanism was confirmed by in situ EPR/UV鈥搗is cyclovoltammetric experiments. The site of the dimerization in the 蟽-dimer and the mapping of the unpaired spin density both for radical anions and 蟽-dimer radical trianions with unusual unpaired spin distribution have been assigned by means of density functional theory calculations.