In our contribution to the development of new proton conductive coordination polymers (CPs) we focus on the impact of a partial replacement of Ga 3+ by Mg 2+ . 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 3 P3N [H 6 P3N = nitrilotris(methylene)triphosphonic acid], where Al 3+ is replaced by Ga 3+ , since all attempts to incorporate Mg 2+ ions directly into AlH 3 P3N were not successful. The relative amount of Mg 2+ and Ga 3+ was established by EDX analysis. Rietveld refinement of the synchrotron data located the Ga 3+ and Mg 2+ ions on a split position, proving the disordered incorporation of the Mg 2+ ions. Solid-state NMR spec-