Chiral Conducting Salts of Nickel Dithiolene Complexes

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.