Crystal Structure of a Tetrapoly‐Dipolyphosphate: CaNb2O(P4O13)(P2O7)

Chemical preparation and crystal structure of CaNb2O(P4O13)(P2O7) are described. The monoclinic unit cell has the following dimensions: a = 13.264(9), b = 10.577(8), c = 12.393(9) Å, β = 96.09(1)°. Space group is C2/m with Z = 4. The crystal structure has been solved by using 1204 unique reflexions with a final R value 0.049. The main outstanding feature of this compound rests on the coexistence in its atomic arrangement of two kinds of phosphate anions with different degrees of condensation: a tetrameric linear one: (P4O13)6− and dimeric linear one: (P2O7)4−. The atomic arrangement can be schematically described as a stacking of alternating rows of P4O13 and P2O7 groups, parallel to the ā axis. The P4O13 groups have a twofold symmetry while the P2O7 groups have a non usual mirror symmetry. One of the oxygen atoms does not belong to the phosphoric groups.