Proton
conductive materials have attracted extensive interest in
recent years due to their fascinating applications in sensors, batteries,
and proton exchange membrane fuel cells. Herein, two Fe-diphosphonate
chains (H4-BAPEN)0.5·[FeIII(H-HEDP)(HEDP)0.5(H2O)] (1) and (H4-TETA)2·[FeIII
2FeII(H-HEDP)2(HEDP)2(OH)2]·2H2O (2) (HEDP = 1-hydroxyethylidenediphosphonate, BAPEN = 1,2-bis(3-aminopropylamino)ethane,
and TETA = triethylenetetramine) with different templating agents
were prepared by hydrothermal reactions. The valence states of the
Fe centers were demonstrated by 57Fe Mössbauer spectra
at 100 K, with a high-spin FeIII state for 1 and mixed high-spin FeIII/FeII states for 2. Their magnetic properties were determined, which featured
strong antiferromagnetic couplings in the chain. Importantly, the
proton conductivity of both compounds at 100% relative humidity was
explored at different temperatures, with 2.79 × 10–4 S cm–1 at 80 °C for 1 and 7.55
× 10–4 S cm–1 at 45 °C
for 2, respectively. This work provides an opportunity
for improving proton conductive properties by increasing the relative
number of protons and the carrier density using protonated flexible
aliphatic amines.