Polyoxometalates in Imidazolim-based Ionic Liquids: Acceptor Number and Polarity Estimated from Their Voltammetric Behaviour

Abstract

The selection of an appropriate solvent is essential for achieving high yields and selectivity in chemical reactions. The chemical and physical parameters of organic solvents have been classified into several groups, and solvents can be compared with each other with respect to these properties. The acceptor number (A_N), donor number (D_N) and polarity (E_T^N) have been widely accepted and used for theoretically and quantitatively evaluating the properties of organic solvents. In a similar manner, the A_N, D_N and E_T^N of room temperature ionic liquids (RTILs) have been estimated from spectral changes in solvatochromic compounds. In this paper, the A_N and E_T^N of eight types of imidazolium-based RTILs were estimated from the relationship between the A_N and E_T^N values and the first redox potential obtained from the voltammograms of polyoxometalates (POMs) in various organic solvents. The obtained parameters were compared with those estimated by spectrophotometric methods reported previously by several groups. This new method for estimating the A_N and E_T^N of RTILs using the voltammetric behaviour of POMs with low charge density and high symmetry could provide the other path to obtain more reliable A_N and E_T^N of RTILs.