Potassium magnesium hydrogendiphosphate dihydrate

The title compound, KMg(HP₂O₇)·2H₂O, is isotypic with other members of the series KM(HP₂O₇)·2H₂O, where M = Mn, Co and Zn. The structure consists of a three-dimensional framework of [MgHP₂O₇]^- layers parallel to (100) linked by K⁺ cations and hydrogen-bonding inter­actions. The metal ions and water O atoms lie on mirror planes, as does the bridging O atom of the eclipsed (HP₂O₇)^3- anion. The acid H atom of the diphosphate anion is split into two half-occupied positions around a center of inversion.