Synthesis and characterization of charge transfer salts based on [M(dcdmp)2 ] (M = Au, Cu and Ni) with TTF type donors

Abstract

The charge transfer salts α-DT-TTF[Au(dcdmp)2 ] (1), BET-TTF[Au(dcdmp)2 ] (2M and 2T), α-DT-TTF[Cu(dcdmp)2 ] (3), ET[Cu(dcdmp)2 ] (4), (BET-TTF)2 [Cu(dcdmp)2 ] (5), (ET)2 [Ni(dcdmp)2 ] (6), and α-mtdt[Cu(dcdmp)2 ] (7) were obtained by electrocrystallization of different electron donor molecules derived from TTF (α-DT-TTF = alpha-dithiophene-tetrathiafulvalene; BET-TTF = (bis(ethylenethio)tetrathiafulvalene; ET = bis(ethylenedithio)-tetrathiafulvalene; α-mtdt = alpha-methylthiophenetetrathiafulvalene) in the presence of transition metal complex [M(dcdmp)2 ] (M = Au (III), Cu (III) and Ni (II)) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 2 (2M and 2T) have a similar packing pattern composed of mixed stacks of alternating donor-acceptor molecules. For (BET-TTF)[Au(dcdmp)2 ] two different crystal structures (2M and 2T) were obtained indicating polymorphism. Compounds 3 and 4 are isostructural being composed of zigzag chains of alternating donor and acceptor molecules. The salts with a 2:1 stoichiometry, (BET-TTF)2 [Cu(dcdmp)2 ] (5), and (ET)2 [Ni(dcdmp)2 ] (6) present the donor molecules fully oxidized and [M(dcdmp)2 ] (M = Ni and Cu) in a dianionic state. The salt of the dissymmetric donor α-mtdt with [Cu(dcdmp)2 ], α-mtdt[Cu(dcdmp)2 ] (7) has a crystal structure composed of segregated donor stacks that are positioned in a head-to-head fashion and alternate with the anion stacks. All charge transfer salts (1–7) are modest semiconductors with conductivities in the range 10−1 –10−5 S/cm, with the highest values obtained in α-DT-TTF salts, compounds 1 and 3.