Zwitterionic pyrrolidine-2,2-diylbis(phosphonic acid) at 100, 150 and 293 K

The title compound, C₄H₁₁NO₆P₂, reveals a two-dimensional network of P—O—H⋯O=P and N—H⋯O=P hydrogen-bond interactions, forming molecular slabs parallel with the (010) plane. One O—H⋯O interaction is distinct within these sets: whilst forming the shortest intermolecular hydrogen bond, it possesses a short P—O(H) bond of 1.5291 (10) Å. Weak C—H⋯O contacts link individual stacks to produce a three-dimensional array. The compound is zwitterionic: one H atom from a P—O—H group has transferred to the pyrrolidine ring N atom.