Acta Cryst. (2014). B70, 181-190 [ doi:10.1107/S2052520613027170 ]
Abstract: A crystal engineering approach is used to stabilize a radical anion in the crystalline state and to modulate the separation distance within -stacks of anion radicals. Alkali metal salts of 2,3-dicyano-5,6-dichlorosemiquinone (C8Cl2N2O2, DDQ) radical anions were prepared and their crystal structures determined: LiDDQ·2H2O·(CH3)2CO, RbDDQ·2H2O and CsDDQ·2H2O. In these structures, stacked dimers of radical anions are formed within -stacked columns. Within the stacked dimers, interplanar separation distances are significantly shorter than the sum of the van der Waals radii for two C atoms; the shortest is 2.812 Å for the Li salt and the longest is 2.925 Å for the Cs salt. Diamagnetic character, observed by electron paramagnetic resonance spectroscopy, indicates spin-coupling of the unpaired electrons within the radical anion dimer. The electron-rich cyano substituents on DDQ influence the electron redistribution within the ring skeleton. The crystalline compounds are also characterized by IR spectroscopy, complemented by quantum-chemical calculations based on both isolated and periodic models.
CCDC references: 964468, 964469, 964470, 964471 and 964472
Keywords: semiquinone radical; spin coupling; -interaction; diamagnetism; thermal analysis; IR spectroscopy; density functional theory calculations.
Structure factor file (CIF format) (143.3 kbytes)
Structure factor file (CIF format) (101.4 kbytes)
Structure factor file (CIF format) (107.9 kbytes)
Structure factor file (CIF format) (109.8 kbytes)
Structure factor file (CIF format) (100.9 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.