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Issue 13, 2017
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Spin pairing, electrostatic and dipolar interactions influence stacking of radical anions in alkali salts of 4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile (DDQ)

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Abstract

A series of five novel air-stable alkali salts of the 4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile radical anion (DDQ) were prepared and structurally characterised. Four of them (Li, Na and two Cs salts) involve Peierls-distorted π-stacks of radicals, while the K salt-structure comprises equidistant stacks of radicals. Different orientations of radicals in the stacks and different directions of the offset have been observed. For an unambiguous description of the π-stacking geometry of quinones and semiquinone radicals, the geometric parameters calculated by the program PLATON are not sufficient. Therefore, two additional geometric parameters are introduced: δ (torsion angle between molecular axes O[double bond, length as m-dash]C⋯C[double bond, length as m-dash]O of contiguous rings) and ε (angle between the molecular axis O[double bond, length as m-dash]C⋯C[double bond, length as m-dash]O and direction of the offset). On the basis of these geometric parameters, the optimal stacking orientations can be quantified and correlated with the polarity and steric effects.

Graphical abstract: Spin pairing, electrostatic and dipolar interactions influence stacking of radical anions in alkali salts of 4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile (DDQ)

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Publication details

The article was received on 07 Feb 2017, accepted on 04 Mar 2017, published on 08 Mar 2017 and first published online on 08 Mar 2017


Article type: Paper
DOI: 10.1039/C7CE00261K
Citation: CrystEngComm, 2017,19, 1801-1808
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    Spin pairing, electrostatic and dipolar interactions influence stacking of radical anions in alkali salts of 4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile (DDQ)

    K. Molčanov and B. Kojić-Prodić, CrystEngComm, 2017, 19, 1801
    DOI: 10.1039/C7CE00261K

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