Integration of Intrinsic Proton Conduction and Guest-Accessible Nanospace into a Coordination Polymer

We
report the synthesis and characterization of a coordination
polymer that exhibits both intrinsic proton conductivity and gas adsorption.
The coordination polymer, consisting of zinc ions, benzimidazole,
and orthophosphate, exhibits a degree of flexibility in that it adopts
different structures before and after dehydration. The dehydrated
form shows higher intrinsic proton conductivity than the original
form, reaching as high as 1.3 × 10–3 S cm–1 at 120 °C. We found that the rearranged conduction
path and liquid-like behavior of benzimidazole molecules in the channel
of the framework afforded the high proton conductivity. Of the two
forms of the framework, only the dehydrated form is porous to methanol
and demonstrates guest-accessible space in the structure. The proton
conductivity of the dehydrated form increases by 24 times as a result
of the in situ adsorption of methanol molecules, demonstrating the
dual functionality of the framework. NMR studies revealed a hydrogen-bond
interaction between the framework and methanol, which enables the
modulation of proton conductivity within the framework.