Sodium 1-carboxycyclopropane-1-carboxylate cyclopropane-1,1-dicarboxylic acid monohydrate.

In the title type B(2) acid salt, Na(LH)(LH(2)).H(2)O [LH(2) = C(2)H(4)C(CO(2)H)(2)] or Na(+).C(5)H(5)O(4)(-).C(5)H(6)O(4).H(2)O, the vertices of a distorted octahedron centred on each Na(+) cation are defined by six O atoms, one from a water molecule, one from an internally hydrogen-bonded LH(-) anion and four from three neutral LH(2) acid molecules. Chains of edge-sharing O(6) octahedra are stabilized by hydrogen bonds, which interconnect the donor H(2)O and LH(2) molecules and LH(-) anions. In particular, the LH(2) molecule donates H atoms to LH(-) and H(2)O and forgoes the internal hydrogen bond which stabilizes the free acid and all of its characterized salts.