2,6-dialkoxy-9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene derivatives: Synthesis, electrochemistry and X-ray crystal structures of neutral and dication species

The synthesis of 2,6-dialkoxy-9,10-bis(1,3-dithiol-2-ylidene 9,10-dihydroan thracene derivatives 15 and 16 is described. Solution electrochemistry show s that 15 and 16 display three redox waves, representing the sequential for mation of the dication, radical trication and tetracation species in an EqE qEq process. The X-ray crystal structures of neutral compounds 15 and 16 an d the charge transfer complex (15)(2+)(TCNQ(-.))2 2MeCN are reported. The n eutral molecules adopt a saddlelike conformation; the bis(1,3-dithiole)benz oquinone system is U-shaped through an 'accumulating bend' comprising the b oat conformation of the central (quinonoid) ring and folding of both 1,3-di thiole rings. In the complex (15)(2+)(TCNQ(-.))(2.) 2MeCN the anthracene sy stem is planar and aromatic; the dithiolium cations form a dihedral angle o f 78 degrees with the anthracene plane. The TCNQ anion radicals form a stac k of dimers with interplanar separations of 3.15 Angstrom within a dimer an d 3.50 Angstrom between the dimers. The structure contains unusually short intermolecular S ... N contacts [2.865(3) Angstrom].