The role of sulfonate groups and hydrogen bonding in the proton conductivity of two coordination networks

<jats:p>The proton conductivity of two coordination networks, [Mg(H<jats:sub>2</jats:sub>O)<jats:sub>2</jats:sub>(H<jats:sub>3</jats:sub>L)]·H<jats:sub>2</jats:sub>O and [Pb<jats:sub>2</jats:sub>(HL)]·H<jats:sub>2</jats:sub>O (H<jats:sub>5</jats:sub>L = (H<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>PCH<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>-NCH<jats:sub>2</jats:sub>-C<jats:sub>6</jats:sub>H<jats:sub>4</jats:sub>-SO<jats:sub>3</jats:sub>H), is investigated by AC impedance spectroscopy. Both materials contain the same phosphonato-sulfonate linker molecule, but have clearly different crystal structures, which has a strong effect on proton conductivity. In the Mg-based coordination network, dangling sulfonate groups are part of an extended hydrogen bonding network, facilitating a “proton hopping” with low activation energy; the material shows a moderate proton conductivity. In the Pb-based metal-organic framework, in contrast, no extended hydrogen bonding occurs, as the sulfonate groups coordinate to Pb<jats:sup>2+</jats:sup>, without forming hydrogen bonds; the proton conductivity is much lower in this material.</jats:p>