A Methyl-Substituted Thiophene-Tetrathiafulvalene Donor and Its Salts

alpha-Methyldithiophene-tetrathiafulvalene (-mDT-TTF), the first alkyl-substituted thiophene-tetrathiafulvalene electronic donor, and some of its charge-transfer salts were explored. The crystal structure of -mDT-TTF is composed of molecular stacks aligned parallel to each other. Its cyclic voltammetry shows higher electron-donor ability than the unsubstituted analogue. This material was employed as a semiconductor in an organic field-effect transistor and showed a mobility of 4x10(-4) cm(2)V(-1)s(-1). Two charge-transfer salts of this donor with [M(mnt)(2)](-) anions (mnt = maleonitriledithiolate), M = Co and Au, were obtained by electrocrystallization; they present unusual stoichiometries: (-mDT-TTF)[Co(mnt)(2)] and (-mDT-TTF)(3)[Au(mnt)(2)](2). In the cobalt compound, the donor molecules are fully oxidized and the Co complex is dimerized; it presents semiconducting behavior (7x10(-3) Scm(-1)). The gold compound is composed of alternating stacks of donor trimers and pairs of anions.