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Probing semiconductivity in crystals of stable semiquinone radicals: organic salts of 5,6-dichloro-2,3-dicyanosemiquinone (DDQ) radical anion

Abstract

Structural parameters and semiconductivity of crystals with stacked 5,6-dichloro-2,3-dicyanosemiquinone (DDQ) radicals were studied on a series of first nine salts of DDQ with substituted N-ethyl- and N-methylpyridinium cations. Structures with stacks of equidistant radicals (interplanar separation < 3.3 Å) are fairly good semiconductors (10-9 S cm–1), while those with Peierls-distorted stacks comprising diamagnetic dimers of radicals (interplanar separations are < 3.1 Å within the dimers and > 3.4 Å between the dimers) are insulators. DFT calculations indicate covalent character (pancake bonding) of interactions between the DDQ radical anions. Inductive effect of the electronegative substituents (halogeno and cyano) on the quinoid ring stabilises the radicals, but also increases the HOMO-LUMO gap, resulting in lower electrical conductivity.

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Publication details

The article was received on 12 Dec 2017, accepted on 13 Feb 2018 and first published on 14 Feb 2018


Article type: Paper
DOI: 10.1039/C7CE02146A
Citation: CrystEngComm, 2018, Accepted Manuscript
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    Probing semiconductivity in crystals of stable semiquinone radicals: organic salts of 5,6-dichloro-2,3-dicyanosemiquinone (DDQ) radical anion

    K. Molcanov, D. Stalke, A. Santic, S. Demeshko, V. Stilinovic, M. Kertesz, Z. Mou and B. Kojic-Prodic, CrystEngComm, 2018, Accepted Manuscript , DOI: 10.1039/C7CE02146A

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