• Homburg, T.; Tschense, C.B.L.; Wolkersdoerfer, K.; Reinsch, H.; Wark, M.; Többens, D.; Zander, S.; Senker, J.; Stock, N.: Magnesium doped Gallium Phophonates Ga1-xMgx[H3+x(O3PCH2)3N] (x = 0, 0.20) and the influence on proton conductivity. Zeitschrift für Anorganische und Allgemeine Chemie 644 (2018), p. 86-91


In our contribution to the development of new proton conductive coordination polymers (CPs) we focus on the impact of a partial replacement of Ga3+ by Mg2+. 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 AlH3P3N [H6P3N = nitrilotris(methylene)triphosphonic acid], where Al3+ is replaced by Ga3+, since all attempts to incorporate Mg2+ ions directly into AlH3P3N were not successful. The relative amount of Mg2+ and Ga3+ was established by EDX analysis. Rietveld refinement of the synchrotron data located the Ga3+ and Mg2+ ions on a split position, proving the disordered incorporation of the Mg2+ 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[H3(O3PCH2)3N], denoted GaH3P3N as well as Ga0.80Mg0.20[H3.20(O3PCH2)3N], denoted GaMgH3.20P3N, 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 Ea = 0.15 eV for GaH3P3N and 0.17 eV for GaMgH3.20P3N). The GaMgH3.20P3N sample shows a reduced proton mobility (σ = 1.2 × 10–4 S·cm–1) of about one order of magnitude in comparison to GaH3P3N (σ = 1.0 × 10–3 S·cm–1).