Highly Proton-Conducting Mixed Proton-Transferred [(H2PO4-) (H3PO4)]∞ Networks Supported by 2,2′-Diaminobithiazolium in Crystals

Hydrogen-bonding organic acid-base salts are promising candidates for the chemical design of high-performance anhydrous proton conductors. The simple molecular crystals between the pi-planar molecules of 2,2'-diaminobithiazolium (DABT) derivative and hydrogen-bonding H3PO4 formed the proton-transferred salts with proton conductivities above similar to 10(-4) S cm(-1) and anisotropic behavior. Controlling the crystallization condition facilitated the formation of binary salts between di-cationic H2DABT(2+) and (H3PO4-)(2) or mixed proton-transferred (H2PO4-)(2) (H3PO4)(2 )with different hydrogen-bonding networks, including one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) networks. The structural isomers of 2,2'-diamino-4,4'-bithiazolium (2,4-DABT) and 2,2'-diamino-5,5'-bithiazolium (2,5DABT) formed a different type of packing structure even with the same crystal stoichiometry of (H2DABT(2+))(H2PO4-)(2) and/or (H2DABT(2+))(H2PO4-)(2) (H3PO4)(2) where the latter salt had different protonated species of H2PO4- and H3PO4 in the hydrogen-bonding network. Four and 10 protons per H2DABT(2+) molecule (H+: carrier concentration) were present in the (H2DABT(2+))(H2PO4-)(2) and (H2DABT(2+))(H2PO4-)(2) (H3PO4)(2) salts, respectively, which accounted for the highly proton-conducting behavior in the latter mixed protonated crystal. To design anhydrous intrinsic H+ conductors, both the mixed proton transfer state and uniform O-H center dot center dot center dot O= hydrogen-bonding interaction are essential factors that must be considered.