The caesium phosphates Cs3(H1.5PO4)2(H2O)2, Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3

The caesium phosphates Cs-3(H1.5PO4)(2)(H2O)(2) and Cs-3(H1.5PO4)(2) were obtained from aqueous solutions, and Cs4P2O7(H2O)(4) and CsPO3 from solid state reactions, respectively. Cs-3(H1.5PO4)(2), Cs4P2O7(H2O)(4), and CsPO3 were fully structurally characterized for the first time on basis of single-crystal X-ray diffraction data recorded at - 173 degrees C. Monoclinic Cs-3(H1.5PO4)(2) (Z = 2,C2/m) represents a new structure type and comprises hydrogen phosphate groups involved in the formation of a strong non-symmetrical hydrogen bond (accompanied by a disordered H atom over a twofold rotation axis) and a very strong symmetric hydrogen bond (with the H atom situated on an inversion centre) with symmetry-related neighbouring anions. Triclinic Cs4P2O7(H2O)(4) (Z = 2, P (1) over bar) crystallizes also in a new structure type and is represented by a diphosphate group with a P-O-P bridging angle of 128.5 degrees. Although H atoms of the water molecules were not modelled, O center dot center dot center dot O distances point to hydrogen bonds of medium strengths in the crystal structure. CsPO3 is monoclinic (Z = 4, P2(1)/n) and belongs to the family ofcatena-polyphosphates (MPO3)(n) with a repetition period of 2. It is isotypic with the room-temperature modification of RbPO3. The crystal structure of Cs-3(H1.5PO4)(2)(H2O)(2) was re-evaluated on the basis of single-crystal X-ray diffraction data at - 173 degrees C, revealing that two adjacent hydrogen phosphate anions are connected by a very strong and non-symmetrical hydrogen bond, in contrast to the previously described symmetrical bonding situation derived from room temperature X-ray diffraction data. In the four title crystal structures, coordination numbers of the caesium cations range from 7 to 12.