Anisotropic Proton Conductivity Arising from Hydrogen-Bond Patterns in Anhydrous Organic Single Crystals, Imidazolium Carboxylates

Abstract

Organic acid–base salts have attracted increasing attention as a promising candidate of anhydrous proton conductors. In this study, we have successfully disclosed the relationship between proton conductivity and hydrogen-bond (H-bond) interactions in such kinds of organic salts, composed of dicarboxylic acid and imidazole. We have grown high-quality single crystals of imidazolium succinate (Im-Suc) or glutarate (Im-Glu) with two-dimensional H-bonding networks and measured the proton conductivity within and perpendicular to the networks. On the basis of the observed “intrinsic” proton conductivities without grain boundary contributions, their relationship to the crystal structure and molecular arrangement was investigated in detail. Importantly, in both materials, the proton conductivities within the H-bonding networks are almost 2 orders of magnitude higher than those perpendicular to the networks, demonstrating that the proton conduction is highly mediated by the H-bonds. In addition, a suitable combination and arrangement of acid and base molecules for realizing high proton conductivity is discussed in terms of their proton donating/accepting abilities (pK a) and molecular motions. These results provide important insights into the effects of H-bonds on proton conductivity in this kind of anhydrous organic acid–base salts.

pH-induced conformational changes in histamine in the solid state

“…In the present case, T o was ignored for simplicity. The natural logarithm of s is expressed as a function of temperature as follows: 51 Im-Suc (parallel to HB) 4.94 Â 10 À7 320 Im-Suc (perpendicular to HB) 3.55 Â 10 À9 378 Im-Glu (parallel to HB) 2.40 Â 10 À6 87 Im-Glu (perpendicular to HB) 5.92 Â 10 À8 157 Histamine 33 9.40 Â 10 À6 H1 (this work) 2.70 Â 10 À4 18.9 (at 330 K)…”

Spectroscopic and Structural Study of a New Conducting Pyrazolium Salt

“…Recent studies reveal the numerous requirements for a proton conductor to be used as an electrolyte in a fuel cell [ 5 , 6 ]. For instance, the conduction should be selective to protons, and the electrolyte must be an electrical insulator to prevent the internal short circuit of the cell.…”

Modulation of the electronic states and magnetic properties of nickel catecholdithiolene complex by oxidation-coupled deprotonation

“…[1][2][3][4][5][6][7][8][9] Its strength is intermediate between the strengths of van der Waals interaction and covalent/coordination bonds; therefore, it has been widely utilized to indirectly control functionalities through structural regulation. 8,[10][11][12][13][14][15][16][17][18] Recent studies have demonstrated that the electrostatic and dynamic properties of protons in H-bonds can directly modulate the electronic functionalities of molecular crystals in the solid state. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] A clear strategy for controlling functionalities based on such electron-proton coupling is crucial to significantly expand a range of material designs for desired functionalities to pioneer novel physical properties and functionalities.…”