Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers

Abstract

We report the synthesis and characterization of dimeric viologen salts (1',1''-(alkane-1,n-diyl)bis(1-ethyl-4,4'-bipyridinium) with n = 4-10) with bis(trifluoromethanesulfonyl)amide (bistriflimide, Tf(2)N(-)) as a counteranion. For n = 4, 5 and 6, and for the nonylviologen cation (1,1'-dinonyl-4,4'-bipyridinium) we also prepared salts with the totally inorganic dodecatungstosilicate anion, SiW(12)O(40)(4-), featuring a poly-charged surface and nanosized dimensions. The materials have been characterized by means of calorimetric techniques, X-ray diffraction and solid state NMR and a comparison is made with analogous monomeric viologen salts exhibiting smectic mesophases. A strong odd-even effect is observed in the melting points and in the thermal behaviour of the bistriflimide dimeric systems, similar to what was reported for dipolar calamitic liquid crystal dimers, although the studied viologen dimers are not mesomorphic. By increasing the size of the counteranion we have observed a destabilization of the crystal phases and of the mesophases in favour of a glassy amorphous state. Implications on the design of novel ionic liquid crystals are discussed. The electrochemical behaviour in solution has been investigated by cyclic voltammetry measurements: interestingly, the odd-even effect is clearly visible also in the redox potentials. The spin-pairing of the viologen radical cations formed at each end of the dimer is responsible for the observed redox trend. Insights on the structure of the spin-paired dimer have been obtained by DFT calculations.

Photoresponsive Supramolecular Complexes as Efficient DNA Regulator

“…1-(4-(Bromomethyl)phenyl)-2-phenyldiazene ( 4 )20, 1-(6-bromohexyl)-1′- methyl-4,4′-bipyridine-1,1′-diium ( 6 )30, ( E )-1-(4-(6-bromohexyloxy)phenyl)- 2-phenyldiazene ( 7 )31 1-methyl-4-(pyridin-4-yl)pyridinium ( 8 )32 were prepared according to the literatures procedures. NMR data were recorded on 300 M, 400 M and 600 M spectrometers, respectively, and chemical shifts were recorded in parts per million (ppm).…”

Synthesis of tetracationic organic salt from 4,4'-bipyridine

“…This is attributed to the high speed of mobility of the ions due to the nature of the cation. This is a consequence of the very long dimeric, rodlike cation contained relatively long hydrophobic alkyl chain; its positive charge is highly delocalized throughout the aromatic ring portion; subsequently, become amphiphilic [30]. This reduces the drifting (counter directional) speed due to the interaction with the solvent cavity surrounding the cation.…”

“…Several reports appeared in literature describing the synthesis and applications of organic salts derived from 4,4'-bipyridine [3,[24][25][26][27][28][29]. In this regard, tetracationic salts derived from 4,4'-bipyridine have been reported using ethylbromide as primary quaternizing and X(CH 2 ) n X, n = 4-10 as spacers [30][31][32]. The nature and compositions of the first quaternizing and the spacer alkyl chain significantly influence the characteristics of the polycharged salt.…”

Ionic Liquid Crystals Based on Pyridinium Salts

“…Additionally, it is of interest to note here that many dicationic and tetracationic ILC based on the 4,4'-bipyridinium rigid core (viologen-based ILC) have been investigated so far, displaying mesomorphic properties typically of calamitic and discotic materials [55][56][57][58][59].…”