A redox active proton transfer and hydrogen-bonding system of tetrathiafulvalene-dicarboxylic acid and pyridine bases

Abstract

Hydrogen bonds are important in supramolecular chemistry and responsible for proton transfer processes. This manuscript reports new hydrogen-bonding systems of redox-active acid–base assemblies consisting of dimethylthio-tetrathiafulvalene dicarboxylic acid (H₂L) coupled with pyridine (py), 2,2′-bipyridine (2,2′-bpy), and 4,4′-bipyridine (4,4′-bpy). The ¹H NMR chemical shifts of the pyridines and the redox potential shifts of the tetrathiafulvalene moiety indicate that proton-transfer and strong hydrogen-bonding interactions exist between the acid and the bases in aprotic solvents. The results of cyclic voltammetry show a two-step square reaction with a redox and proton transfer coupled mechanism. The nature of the hydrogen bonds was characterized by X-ray single crystal analysis. In contrast to the mono-carboxyl–py system, in this ortho-substituted dicarboxyl–py system one proton of the H₂L transfers completely from the carboxyl to the py group. The conjugated intramolecular and intermolecular hydrogen bonds are responsible for the proton transfer.