Brønsted acid-base reactions between phosphoric acid (H3PO4) and haloanilines in alcohols formed 1:1 proton-transferred ionic salts of (X-anilinium+)(H2PO4-) and 2:1 ones of (X-anilinium+)2(HPO42-) (X = F, Cl, Br, and I at o, m, and p positions of anilinium). Only the former 1:1 single crystals showed proton conductivity under the N2 condition, and the latter 2:1 crystals became protonic insulators. In crystals, diverse hydrogen-bonding structures from 1D to 2D networks were achieved by modification of the molecular structure of X-anilinium cations. The protonic conductivity was associated with the connectivity of H2PO4- anions in the hydrogen-bonding networks. The hydrogen-bonding ladder chains in (o-cloroanilinim)(H2PO4-) and (o-bromoanilinim)(H2PO4-) resulted in the highest protonic conductivity of 10-3 S cm-1. The protonic conductivity of the ladder-chain (H2PO4-) arrangements was higher than that of 2D sheets. The motional freedom of protons was analyzed by difference Fourier analysis of the single-crystal X-ray structure. The 2D layer, including (H2PO4-)2 dimers and (H2PO4-)4 tetramers, showed relatively low protonic conductivity, and the activation energy for proton conductivity was lowered by increasing the hydrogen-bonding connectivity and uniformity between H2PO4- anions.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films