Description:
<jats:p>In our contribution to the development of new proton conductive coordination polymers (CPs) we focus on the impact of a partial replacement of Ga<jats:sup>3+</jats:sup> by Mg<jats:sup>2+</jats:sup>. This approach should come along with the introduction of additional protons due to charge balances. In a first step we have synthesized an isostructural compound to the literature known compound AlH<jats:sub>3</jats:sub>P3N [H<jats:sub>6</jats:sub>P3N = nitrilotris(methylene)triphosphonic acid], where Al<jats:sup>3+</jats:sup> is replaced by Ga<jats:sup>3+</jats:sup>, since all attempts to incorporate Mg<jats:sup>2+</jats:sup> ions directly into AlH<jats:sub>3</jats:sub>P3N were not successful. The relative amount of Mg<jats:sup>2+</jats:sup> and Ga<jats:sup>3+</jats:sup> was established by EDX analysis. Rietveld refinement of the synchrotron data located the Ga<jats:sup>3+</jats:sup> and Mg<jats:sup>2+</jats:sup> ions on a split position, proving the disordered incorporation of the Mg<jats:sup>2+</jats:sup> ions. Solid‐state NMR spectroscopy confirms a disordered protonation of the phosphonate groups as well and shows that all amine groups are protonated. In order to investigate the effect on the proton conductivity the compounds Ga[H<jats:sub>3</jats:sub>(O<jats:sub>3</jats:sub>PCH<jats:sub>2</jats:sub>)<jats:sub>3</jats:sub>N], denoted GaH<jats:sub>3</jats:sub>P3N as well as Ga<jats:sub>0.80</jats:sub>Mg<jats:sub>0.20</jats:sub>[H<jats:sub>3.20</jats:sub>(O<jats:sub>3</jats:sub>PCH<jats:sub>2</jats:sub>)<jats:sub>3</jats:sub>N], denoted GaMgH<jats:sub>3.20</jats:sub>P3N, were characterized by electrochemical impedance spectroscopy (EIS). Arrhenius behavior in the investigated temperature range (70–130 °C) was found for both compounds (activation energies of E<jats:sub>a</jats:sub> = 0.15 eV for GaH<jats:sub>3</jats:sub>P3N and 0.17 eV for GaMgH<jats:sub>3.20</jats:sub>P3N). The GaMgH<jats:sub>3.20</jats:sub>P3N sample shows a reduced proton mobility (<jats:italic>σ</jats:italic> = 1.2 × 10<jats:sup>–4</jats:sup> S<jats:bold>·</jats:bold>cm<jats:sup>–1</jats:sup>) of about one order of magnitude in comparison to GaH<jats:sub>3</jats:sub>P3N (<jats:italic>σ</jats:italic> = 1.0 × 10<jats:sup>–3</jats:sup> S<jats:bold>·</jats:bold>cm<jats:sup>–1</jats:sup>).</jats:p>