engleski

Spin-coupling in dimers of 2, 3-dicyano-5, 6-dichlorosemiquinone radical anions in the crystalline state

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: LiDDQ2H2O(CH3)2CO, RbDDQ2H2O and CsDDQ2H2O. 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 A ˚ for the Li salt and the longest is 2.925 A ˚ 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.

semiquinone radical ; spin coupling ; solid state ; EPR spectroscopy ; IR spectroscopy ; DFT calculations ; crystallography

nije evidentirano