1. Probing semiconductivity in crystals of stable semiquinone radicals: organic salts of 5,6-dichloro-2,3-dicyanosemiquinone (DDQ) radical anions
- Author
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Ana Šantić, Vladimir Stilinović, Krešimir Molčanov, Zhongyu Mou, Miklos Kertesz, Dietmar Stalke, Biserka Kojić-Prodić, and Serhiy Demeshko
- Subjects
Chemistry ,Radical ,semiquinones ,pi-stacking ,semiconductivity ,magnetic properties ,Stacking ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Ring (chemistry) ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Electrical resistivity and conductivity ,Covalent bond ,Semiquinone radicals ,General Materials Science ,0210 nano-technology - Abstract
The structural parameters and semiconductivity of crystals with stacked 5, 6-dichloro-2, 3-dicyanosemiquinone (DDQ) radicals were studied for a series of the first nine salts of DDQ with substituted N-ethyl- and N-methylpyridinium cations. Structures with stacks of equidistant radicals (interplanar separation 3.4 Å between the dimers) are insulators. DFT calculations indicate the covalent character (pancake bonding) of the interactions between the DDQ radical anions. The inductive effects of electronegative substituents (halogeno and cyano) on the quinoid ring stabilise the radicals, but also increase the HOMO–LUMO gap, resulting in lower electrical conductivity.
- Published
- 2018