Chiral Conducting Salts of Nickel Dithiolene Complexes
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Conducting and chiral [Ni(dmit)2] dithiolene salts were obtained by electrocrystallization of the radical [n-Bu4N][Ni(dmit)2] salt in the presence of chiral, enantiopure trimethylammonium cations. Three different cations were investigated, namely, (R)-Ph(Me)HC*-NMe3+, (S)-(tBu)(Me)HC*-NMe3+, and (S)-(1-Napht)MeHC*-NMe3+, 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·(CH3CN)2. They both crystallize in the P212121 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 (σRT = 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.
