Abstract
Understanding the solvation and ion-pairing interactions of anionic substrates in room-temperature ionic liquids (RTIL) is key for the electrochemical applications of these new classes of solvents. In this work, cyclic voltammetry and visible and infrared spectroelectrochemistry of tetracyanoquinodimethane (TCNQ) was examined in molecular (acetonitrile) and RTIL solvents, as well as mixtures of these solvents. The overall results were consistent with the formation of RTIL/acetonitrile nanodomains. The voltammetry indicated that the first electrogenerated product, TCNQ−, was not incorporated into the RTIL nanodomain, while the second electrogenerated product, TCNQ2−, was strongly attracted to the RTIL nanodomain. The visible spectroelectrochemistry was also consistent with these observations. Infrared spectroelectrochemistry showed no discrete ion pairing between the cation and TCNQ− in either the acetonitrile or RTIL solutions. Discrete ion pairing was, however, observed in the acetonitrile domain between the tetrabutylammonium ion and TCNQ2−. On the other hand, no discrete ion pairing was observed in BMImPF6 or BMImBF4 solutions with TCNQ2−. In BMImNTf2, however, discrete ion pairs were formed with BMIm+ and TCNQ2−. Density function theory (DFT) calculations showed that the cations paired above and below the aromatic ring. The results of this work support the understanding of the redox chemistry in RTIL solutions.
Highlights
The use of room-temperature ionic liquids (RTILs) has attracted considerable interest among electrochemists because of their electrical conductivity and their ability to solvate ionic species, especially anions
The electrogenerated anion might not be able to form a discrete ion pair might not be able to displace the strong interactions between the cation and the RTIL anion
Shows the molecular structure of TCNQ and the anions/cations of the RTILs used in this work
Summary
The use of room-temperature ionic liquids (RTILs) has attracted considerable interest among electrochemists because of their electrical conductivity and their ability to solvate ionic species, especially anions. RTILs, the voltammetric may be due toofgeneral of the substrate by ion RTIL pairs (loose (at least enough to bebe observed spectroscopically) with and a specific geometric structure the ionlong pair), or it might due to the formation of discrete relatively long-lasting ion and atomic interactions (i.e., ion pairs). Pairs (at least long enough totight be observed spectroscopically) with a specific geometric structure and Recent work has shown that mixed molecular/RTIL solutions are often not homogeneous atomic interactions (i.e., tight ion pairs). The electrogenerated anion might not be able to form a discrete ion pair might not be able to displace the strong interactions between the cation and the RTIL anion. For RTIL-rich solutions, reverse with molecular result, theRTIL electrogenerated anion might not be the ablesolvents to form will a discrete ionthemselves pair with the cation.
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