Halogen bonding (XB) interactions are investigated in cation radical salts of bis(methylthio)-5,5'-diiodotetrathiafulvalene (1). Electrocrystallization of 1 in the presence of Bu4 NCl affords a 1 : 1 salt formulated as (E-1)Cl. Particularly strong I⋅⋅⋅Cl- XB interactions are observed around the Cl- anion with the distances at 78 % the sum of the van der Waals radii, a consequence of the XB charge activation in the cation radical. Moreover, the Cl- environment is complemented by two extra S⋅⋅⋅Cl- chalcogen bonding (ChB) interactions, an original feature among reported halide salts of TTF derivatives. Electrostatic potential calculations on the cation radical further demonstrate the efficient activation of the S atoms of the 1,3-dithiole rings (Vs,max =87.2 kcal/mol), as strong as with the iodine atoms (Vs,max =87.9 kcal/mol). The radical cations form weakly dimerized stacks, as confirmed by the variable-temperature magnetic susceptibility and the weak conductivity (4.8×10-5 S cm-1 ).
Keywords: chalcogen bonding; crystal engineering; halogen bonding; tetrathiafulvalenes; σ-hole interactions.
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