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Chiral Metal‐Dithiolene/Viologen Ion Pairs: Synthesis and Electrical Conductivity
Author(s) -
Kisch Horst,
Eisen Bernhard,
Dinnebier Robert,
Shankland Kenneth,
David William I. F.,
Knoch Falk
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010202)7:3<738::aid-chem738>3.0.co;2-6
Subject(s) - chemistry , dication , enantiomer , tetrathiafulvalene , viologen , ion , crystallography , electrochemistry , crystal structure , diastereomer , dithiol , stereochemistry , photochemistry , molecule , organic chemistry , electrode
Enantiomerically pure dithiolene complexes NBu 4 [Ni{( R , R )‐diotte} 2 ] and NBu 4 [Ni{( S , S )‐diotte} 2 ] (diotte 2− =a 1,3‐dioxolane‐tetrathiaethylene), were prepared from the corresponding enantiomers of a diotte 2− precursor. The structure of the precursor was solved by single‐crystal X‐ray analysis; desulfurization afforded a novel tetrathiafulvalene derivative. Combination of the complex monoanion with the enantiomers of the viologen derivative bis(2‐methyl‐3‐hydroxypropyl)‐4,4′‐dipyridinium (HiBV 2+ ) afforded enantiomeric and diastereomeric ion–pair complexes of the type HiBV[Ni(diotte) 2 ] 2 . For comparison, the analogous compounds A[Ni(diotte) 2 ] 2 , (A 2+ =methyl (MV 2+ ), octyl (OV 2+ ), stearyl (StV 2+ ) viologen or two 2,2′‐bipyridinium acceptors), HiBV[Ni(diotte)L] {L=mnt 2− (maleonitrile‐1,2‐dithiolate), dmit 2− (2‐thioxo‐1,3‐dithiol‐4,5‐dithiolate)}, MV[Ni(dmit) 2 )] 2 , [Ni(diotte) 2 ], and [Ni(diotte)(dmit)] were synthesized. An X‐ray powder diffraction structural analysis of MV[Ni(dmit) 2 )] 2 revealed the presence of mixed stacks that contain the sequence anion–anion–cation. While no short contacts are observable within a stack, these are observed between the stacks for the dication–anion interaction by short S⋅⋅⋅H distances in the range of 2.77 to 2.86 Å, and for the anion–anion interaction short S⋅⋅⋅S distances of 3.55 to 3.65 Å. In agreement with the absence of intrastack interactions, no ion–pair charge‐transfer band can be detected in this 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 ( σ ) of pressed powder pellets ranges from 10 −2 to 10 −12 Ω −1 cm −1 and in all cases increases with increasing temperature (293–393 K) according to an Arrhenius law. Corresponding activation energies vary from 0.14 to 0.93 eV and increase linearly with log σ for structurally similar ion pairs. Charge generation is postulated to occur by disproportionation of the monoanion as suggested by the almost linear increase of log σ with decreasing disproportionation energy. The conductivity of diastereomers of ions with two unlike configurations like [( S , S ) ‐ HiBV][Ni{( R , R )‐diotte} 2 ] 2 (1.1×10 −11 Ω −1 cm −1 ) is one to two orders of magnitude higher as compared to the diastereomers with two like‐configured ions.