Crystal structure of dicalcium potassium trihydrogen bis(pyrophosphate) trihydrate

The crystal structure of Ca₂KH₃(P₂O₇)₂·3H₂O has been determined by single crystal X-ray diffraction. Crystals are monoclinic, space groupP2₁/n witha=10.518(3),b=19.253(9),c=7.340(3)Å,=90.07(2)°, andZ=4. The structure was refined toR=0.048 andR _w=0.044 for 1839 reflections withI3(I). The structure consists of a compact assembly of Ca, K, HP₂O₇, and H₂P₂O₇ ions and three water molecules arranged in layers perpendicular to theb-axis. The two independent Ca ions and the HP₂O₇ ion comprise one layer; K and H₂P₂O₇ ions and the three water molecules form an interstitial layer. Coordinations of the two independent Ca ions are quite similar, but the environments of HP₂O₇ and H₂P₂O₇ ions are quite different, probably due to their locations in different layers. The general structural features are quite similar to those of Ca(NH₄)HP₂O₇.Certain commercial materials and equipments are identified in this paper to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Institute of Standards and Technology or the ADA Health Foundation or that the material or equipment identified is necessarily the best available for the purpose.