Chiral Conducting Salts of Nickel Dithiolene Complexes

Abstract

Conducting and chiral [Ni(dmit)(2)] dithiolene salts were obtained by electrocrystallization of the radical [n-Bu(4)N][Ni(dmit)(2)] salt in the presence of chiral, enantiopure trimethylammonium cations. Three different cations were investigated, namely, (R)-Ph(Me)HC*-NMe(3)(+), (S)-((t)Bu)(Me)HC*-NMe(3)(+), and (S)-(1-Napht)MeHC*-NMe(3)(+), noted (R)-1, (S)-2, and (S)-3. Salts of 1:3 stoichiometry were obtained with (R)-1 and (S)-2, formulated as [(R)-1][Ni(dmit)(2)](3) and [(S)-2][Ni(dmit)(2)](3)·(CH(3)CN)(2). They both crystallize in the P2(1)2(1)2(1) chiral space group, with three crystallographically independent complexes exhibiting different oxidation degrees. Another salt with 2:5 stoichiometry was isolated with (S)-3. The semiconducting character of the three salts (σ(RT) = 20-30 × 10(-3) S cm(-1)) finds its origin in a strong electron localization, favored by the large number of crystallographically independent [Ni(dmit)(2)] complexes in these chiral structures and their association into weakly interacting dimeric or trimeric motifs. Racemic salts with the same cations, obtained only with difficulties with the tert-butyl-containing (rac)-2 cation, afforded similar trimerized structures. The observed unusual stoichiometry and strong charge localization is tentatively assigned to the size and anisotropic charge distribution of the cations.