Symmetric hydrogen bonding in dimethylammonium hydrogen diphenyldiphosphonate.

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) A]. 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) A.