Tris(thianthrene)2+ bis(dodecamethylcarba-closo-dodecaborate) dichloromethane tetrasolvate: a crossed triple-decker pi-trimer dication.

The title compound, (3C(12)H(8)S(2))(2+).2C(13)H(36)B(11)(-).4CH(2)Cl(2), contains an unusual cation-radical association comprising a pi-trimer dication of crossed thianthrenes. The thianthrene molecular planes are essentially cofacial, but the S...S axes of adjacent molecules are orthogonal to each other. The outer thianthrenes (both located on mirror planes bisecting the units at the S atoms) are bent slightly towards the inner and planar thianthrene (residing on a 2/m symmetry element with the S atoms on the twofold rotation axis), with close noncovalent separations of 3.1 A indicating strong interplanar interactions within the trimeric dication. Bond-length analysis indicates that the 2+ charge is delocalized over the three stacked thianthrenes with the maximum charge on the central unit. The crossed monomer arrangement is attributed to the frontier-orbital symmetry that allows various pi-bonding orientations between thianthrene molecules. The CB(11)(CH(3))(12)(-) counter-ion resides on a mirror plane. One of the CH(2)Cl(2) solvent molecules resides on a twofold rotation axis, whereas the other is located on a mirror plane.