Issue 13, 2018

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

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 <3.3 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 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.

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

Supplementary files

Article information

Article type
Paper
Submitted
12 Dec 2017
Accepted
13 Feb 2018
First published
14 Feb 2018

CrystEngComm, 2018,20, 1862-1873

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

K. Molčanov, D. Stalke, A. Šantić, S. Demeshko, V. Stilinović, Z. Mou, M. Kertesz and B. Kojić-Prodić, CrystEngComm, 2018, 20, 1862 DOI: 10.1039/C7CE02146A

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