Crystal structure and electrical conductivity of [1,1′-bis(p-fluorophenyl)-4,4′-bipyridinium]2+(TCNQ)22− and electrical characterisation of 51 TCNQ simple salts3)

Abstract

The crystal structure of [1,1′‐bis(p‐fluorophenyl)‐4,4′‐bipyridinium]2+(7,7,8,8‐tetracyano‐p‐quinodimethanide) 22−,(FΦBP) (TCNQ)2, its electrical conductivity and the properties of 51 related simple salts are reported. (FΦBP) (TCNQ)2s triclinic, space group PI, with a = 7.112(7), b = = 13.702(11), c = 12.425(9) Å, α = 115.6(1)°, β = 85.6(1)°, γ = 105.3(1)°, U = 1053 Å3Dm = 1.21 Mg m−3, Z = 1, Dc 1.19 Mg m−3. Within the stoichiometric unit the TCNQ's overlap in an exocyclic bond to quinonoid ring manner with a mean intermolecular spacing of 3.14 A. In the direction of stacking the TCNQ diads are separated by the FΦBP dications and consequently the electrical conductivity, Órt = 6 × 10−9 S cm−1, of (FΦBP) (TCNQ)2 is low compared with values obtained for the congeneric pyridinium and bipyridinium TCNQ simple salts. These fall in the range 10−10 to 60 S cm−1 and eight salts have Órt <1 S cm−1.

Electrochemical investigation on hybrid viologen tetracyanoquinodimethanide LB films

“…In addition, there is a charge transfer band centred at 3300 cm À1 [22] whose intensity increases after the immersion of the film into the KClO 4 aqueous solution, which is evidence of the formation of a CT complex (this complex formation does not take place when a viologen film transferred from a pure water subphase is introduced into a KClO 4 aqueous solution). This result is in agreement with the well-known tendency of bipyridils to form charge transfer complexes when treated under suitable conditions with 7,7,8,8-tetracyanoquinodimethane or its derivatives [3,[23][24][25][26][27]. From a comparative study of these voltammograms, the following points are worth noting:…”

A Convenient N-Arylation Route for Electron-Deficient Pyridines: The Case of π-Extended Electrochromic Phosphaviologens

“…In addition to these anticipated results, we also came across two unexpected findings: (i) The most electron-rich phosphaviologen 5 features the lowest lying LUMO energy level with a first reduction at −0.38 V vs Fc/Fc + , and (ii) the introduction of the electron withdrawing p-F-Ph moiety (4) did not alter the LUMO energy level as compared to phenylsubstituted species 3. In contrast, in the case of regular viologens the latter actually does facilitate the electron injection by 0.1 V. 28 Photophysical Properties. The photophysical properties of 3−5 were investigated via UV−vis absorption spectroscopy in acetonitrile (Table 1).…”

Isolation and Characterization of Phenyl Viologen as a Radical Cation and Neutral Molecule

“…There are two published structures of 1,1′-diaryl viologen dications (the p-fluorophenyl 19 and p-cyanophenyl 20 derivatives), and in both structures the viologen cation has two coplanar central rings and two outer rings that are twisted relative to the central rings. In both compounds TCNQis the counterion, so it is likely that the charge on the cations is not a full 2+, resulting in the observed structures.…”

“…The radical cations of viologens, because they are odd-electron species, might be expected to be good electrical conductors as solid, crystalline materials. Several salts of viologens with the 7,7,8,8-tetracyanoquinodimethanide (TCNQ) anion have been synthesized and their solid-state electrical conductivity measured, − but the oxidation state of the viologen in these compounds is probably best considered to be close to 2 + , although the oxidation state is somewhat ambiguous because TCNQ can exist in either the anionic or neutral form. In any case, the majority of the conductivity in these compounds is likely due to the TCNQ, as indicated by the fact that the conductivity is highest when the TCNQ molecules are present as infinite stacks and are of mixed valence.…”