Crystal structure of Rb2Mn3(H2O)2[P2O7]2, a new representative of the family of hydrated diphosphates

The crystal structure of Rb2Mn3(H2O)2[P2O7]2, a new phase obtained in the form of single crystals under hydrothermal conditions in the MnCl2–Rb3PO4–H2O system, is determined by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.0270): a = 9.374(2), b = 8.367(2), c = 9.437(2) Å, ß = 99.12(2)°, space group P21/c, Z = 2, Dx = 3.27 g/cm3. A correlation between the unit-cell parameters and the size of cations forming the crystal structures of isostructural A2M3(H2O)2[P2O7]2 diphosphates (A = K, NH4, Rb, or Na; M = Mn, Fe, Co, or Ni) is revealed. It is shown that, due to the topological similarity, the structures of diphosphates and orthophosphates of the farringtonite structural type can undergo mutual transformations.