Experimental confirmation of proton conductivity predicted from intermolecular hydrogen-bonding in spatially-confined novel histamine derivatives

The new compounds with one (N-(2-(1H-imidazole-4-yl)ethyl)benzamide; A1), two (N,N′-bis(2-(1H-imidazole-5-yl)ethyl)terephthalamide; A2) and three (N,N′,N″-tris(2-(1H-imidazole-5-yl)ethyl)benzene-1,3,5-tricarboxamide; A3) histamine units were synthesized with an expectation of the realization of high proton conductivity in a high temperature region in the presence of imidazole groups. The X-ray crystal structure analysis revealed the network structures of the strong intra- and intermolecular hydrogen bonds. The thermal degradation temperatures were much higher than those for the original histamine. The proton conductivities of the single crystals were measured in a wide temperature range. The results of these three compounds were shown at different temperatures. Referring to the crystal structure, the water molecules are confined in a local position and the protons cannot spread freely over the whole crystal lattice. In this way, the information from X-ray analyzed crystal structure allowed us to predict the proton transfer behaviors of these compounds, which were confirmed by performing the proton conductivity experiment. [Display omitted] •Crystal packing modes of a series of novel molecules with the plural histamine units confined have been investigated.•Proton conductivities are speculated by investigating the detailed structural hydrogen-bonds formation.•High thermal properties are achieved corresponding to the strong hydrogen bonding network among neighboring molecules.•Proton conductivity of the packing model containing water molecule is supposed to occur by the Grotthuss-type mechanism.