Acta Cryst. (2014). B70, 141-148 [ doi:10.1107/S2052520613032629 ]
Abstract: Oxidation of diiodoethylenedithiotetrathiafulvalene (EDT-TTF-I2), C8H4I2S6, with the strong oxidizer tetrafluorotetracyanoquinodimethane (TCNQF4), C12F4N4, affords, depending on the crystallization solvent, two polymorphs of the 2:1 charge-transfer salt (EDT-TTF-I2)2(TCNQF4), represented as D2A. In both salts, the TCNQF4 is reduced to the radical anion state, and is associated through short C-INC halogen bonds to two EDT-TTF-I2 molecules. The two polymorphs differ in the solid-state association of these trimeric D-A-D motifs. In polymorph (I) the trimeric motif is located on an inversion centre, and hence both EDT-TTF-I2 molecules have +0.5 charge. Together with segregation of the TTF and TCNQ derivatives into stacks, this leads to a charge-transfer salt with high conductivity. In polymorph (II) two crystallographically independent EDT-TTF-I2 molecules bear different charges, close to 0 and +1, as deduced from an established correlation between intramolecular bond lengths and charge. Overlap interactions between the halogen-bonded D0-A-D motifs give rise, in a perpendicular direction, to diamagnetic A22- and D0-D22+-D0 entities, where the radical species are paired into the bonding combination of respectively the acceptor LUMOs and donor HOMOs. The strikingly different solid-state organization of the halogen-bonded D-A-D motifs provides an illustrative example of two modes of face-to-face interaction between -type radicals, into either delocalized, uniform chains with partial charge transfer and conducting behaviour, or localized association of radicals into face-to-face A22- and D22+ dyads.
Keywords: charge-transfer salt; solid state; radical species.
Structure factor file (CIF format) (206.5 kbytes)
Structure factor file (CIF format) (81.5 kbytes)
Structure factor file (CIF format) (217.2 kbytes)
Structure factor file (CIF format) (428.0 kbytes)
To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.
The download button will force most browsers to prompt for a file name to store the data on your hard disk.
Where possible, images are represented by thumbnails.
Copyright © International Union of Crystallography