Toward a new type of proton conductor based on imidazole and aromatic acids

A new approach towards achieving proton conducting materials based on aromatic acids and heterocyclic bases was proposed. It can lead to a new material in which all hydrogen bonding interactions are of medium or weak strength and rotations of the base and acid molecules are possible. If the above conditions are met, one can expect a high value of proton conductivity governed by the Grotthuss mechanism. Two salts of imidazole, one with benzoic acid having one carboxylic acid group and another with salicylic acid having a carboxylic and hydroxyl group located in the ortho position, were synthesized. Physical properties of these newly synthesized proton conducting salts were investigated using experimental and theoretical methods. The structures of these salts were studied by X-ray diffraction and ¹H and ¹³C NMR techniques. The intermolecular interactions in the salts were analyzed by DFT calculations, within the QTAiM theory, and by Hirshfeld surface analysis. The π-π interactions, the proton conduction pathways, and the transport mechanism are also discussed.