Charge-transfer complexes of metal dithiolenes, part XXVII - Chiral metal-dithiolene/viologen ion pairs: Synthesis and electrical conductivity

Enantiomerically pure dithiolene complexes NBu4[Ni{(R,R)-diotte}(2)] and NB u4[Ni{(S,S)-diotte}(2)] (diotte(2) = a 1,3-dioxolane-tetrathiaethylene), we re prepared from the corresponding enantiomers of a diotte(2) precursor. Th e structure of the precursor was solved by single-crystal X-ray analysis. d esulfurization afforded a novel tetrathiafulvalene derivative. Combination of the complex monoanion with the enantiomers of the viologen derivative bi s(2-methyl-3-hydroxypropyl)-4,4'-dipyridinium (HiBV(2+)) afforded enantiome ric and diastereomeric ion-pair complexes of the type HiBV[Ni(diotte)(2)](2 ). For comparison, the analogous compounds A[Ni(diotle)(2)](2), (A(2+) = me thyl (MV2+). octyl (OV2+), stearyl(StV(2+)) viologen or two 2,2'-bipyridini um accepters). HiBV[Ni(diotte)L] {L-mnt(2) (maleonitrile-1,2-dithiolate), d mit(2) (2-thioxo-1,3-dithiol-4,5-dithiolate)}. MV[Ni(dmit)(2))](2) [Ni(diot te)(2)], and [Ni(diotte)(dmit)] were synthesized. An X-ray powder diffracti on structural analysis of MV[Ni(dmit)(2))](2) revealed the presence of mixe d stacks that contain the sequence anion-anion-cation, While no short conta cts are observable within a stack. these are observed between the stacks fo r the dication-anion interaction by short S . . .H distances in the range o f 2.77 to 2.86 Angstrom, and for the anion-anion interaction short S . . .S distances of 3.55 to 3.65 Angstrom. In agreement with the absence of intra stack interactions, no ion-pair charge-transfer band can be detected in thi s and the other complexes. ESR and UV/Vis data suggest that in [Ni(diotte)( 2)](-) electron delocalization is less pronounced than in the corresponding mnt(2) and dmit(2-) complexes. The specific electrical conductivity (sigma ) of pressed powder pellets ranges from 10(-2) to 10(-12) Omega (-1) cm(-1) and in all cases increases with increasing temperature (293-393 K) accordi ng to an Arrhenius law. Corresponding activation energies vary from 0.14 to 0.93 eV and increase linearly with log sigma for structurally similar ion pairs. Charge generation is postulated to occur by disproportionation of th e monoanion as suggested by the almost linear increase of logo with decreas ing disproportionation energy. The conductivity of diastereomers of ions wi th two unlike configurations like [(S,S)-HiBV][Ni((R.R)-diotte)(2)](2) (1.1 x10(-11) Omega (-1) cm(-1)) is one to two orders of magnitude higher as com pared to the diastereomers with two like-configured ions.