Crystal structures and optical properties of cation radical salts of a tetrathiafulvalene trisannulated macrocycle

Cation radical salts of the bis(methylthio)tetrathiafulvalene (DMT-TTF) trisannulated macrocycles, [tris(DMT-TTF)]I₃^- (1) and [tris(DMT- TTF)]IBr₂^- (2), were prepared and the crystal structures and polarized reflectance spectra of the salts 1 and 2 were investigated. An isostructural character is observed for the two salts. The C₃ symmetry of tris(DMT-TTF) bearing three equivalent DMT-TTF units (A, B, and C) within a molecule is broken through the formation of cation radical salts. Two DMT-TTF units (B and C) of three equivalent units form an intramolecular dimer structure through the face-to-face π-π overlap, whereas the plane of the A unit is orthogonal to the dimer plane and isolated from the other units. The intramolecular dimers are further dimerized through the intermolecular B-B' interaction, resulting in a DMT-TTF tetramer unit (C-B-B'-C') within the crystal. The intramolecular bond lengths and polarized reflectance spectra indicate the localization of a unit charge on the B unit rather than A or C. The charge separated A⁰-B⁺-C⁰ electronic structure is confirmed.