Abstract: | In the title compound, C2H8N+·C12H11O5P2?, pairs of hydrogen diphenyldiphosphonate anions form dimers across a twofold axis, with two symmetric O?H?O hydrogen bonds O?O = 2.406 (3) and 2.418 (3) Å]. The 12‐membered ring thus formed has crystallographic 2 and quasi‐222 symmetry. Cations on either side of the ring form N—H?O hydrogen bonds to the four extraannular O atoms, with N?O distances of 2.765 (2) and 2.748 (3) Å. |