Nickel(II) Complex of N4 Schiff Base Ligand as a Building Block for a Conducting Metallopolymer with Multiple Redox States

Mikhail Karushev,Evgenia Smirnova,Irina Chepurnaya

doi:10.3390/molecules26092646

Abstract

Metal–ligand interactions in monomeric and polymeric transition metal complexes of Schiff base ligands largely define their functional properties and perspective applications. In this study, redox behavior of a nickel(II) N4-anilinosalen complex, [NiAmben] (where H2Amben = N,N′-bis(o-aminobenzylidene)ethylenediamine) was studied by cyclic voltammetry in solvents of different Lewis basicity. A poly-[NiAmben] film electrochemically synthesized from a 1,2-dichloroethane-based electrolyte was investigated by a combination of cyclic voltammetry, electrochemical quartz crystal microbalance, in situ UV-Vis spectroelectrochemistry, and in situ conductance measurements between −0.9 and 1.3 V vs. Ag/Ag+. The polymer displayed multistep redox processes involving reversible transfer of the total of ca. 1.6 electrons per repeat unit, electrical conductivity over a wide potential range, and multiple color changes in correlation with electrochemical processes. Performance advantages of poly-[NiAmben] over its nickel(II) N2O2 Schiff base analogue were identified and related to the increased number of accessible redox states in the polymer due to the higher extent of electronic communication between metal ions and ligand segments in the nickel(II) N4-anilinosalen system. The obtained results suggest that electrosynthesized poly-[NiAmben] films may be viable candidates for energy storage and saving applications.

Highlights

Sustainable energy has fast become the need of the century [1]
We investigate functional properties of the generated poly-[NiAmben] films by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), in situ UV-Vis spectroelectrochemistry, and in situ conductance measurements to identify the redox states available in the polymer upon p-doping
The CV curve of [NiAmben] obtained in the range of potentials from −0.9 to 0.9 V vs. Ag/Ag+ in the dimethyl sulfoxide (DMSO)-based electrolyte displays three well pronounced irreversible oxidation waves with peak potentials at −0.05 V, 0.47 V, and 0.67 V, respectively (Figure 2a)

Summary

Introduction

Sustainable energy has fast become the need of the century [1]. Sustainable energy involves various technologies out of which energy storage systems (e.g., supercapacitors, rechargeable batteries) [2] and energy saving technologies (e.g., low energy-consumption displays, smart windows) [3] are of utmost importance. The challenge of developing new materials to obtain more efficient energy storage and saving devices is often met through controlled modification of electrode surfaces. Electrodes for electrochemical energy storage are coated with conductive and highly capacitive materials capable of multi-electron transfer [4], whereas electrodes for energy saving systems are modified with materials that undergo significant color changes by electrochemically induced redox reactions, i.e., display electrochromic properties [5]. Substances possessing dual functionality attract special attention as they are suitable for electrode modification in both types of devices

Results

Discussion

Conclusion