AErP2O7 (A = Rb, Cs) and HEuP2O7•3H2O: Crystal Structures, Vibrational Studies and Thermal Behaviours

New diphosphates AErP(2)O(7), A = Rb (1), Cs (2), and HEuP2O7 center dot 3H(2)O (3) have been prepared via soft chemistry route from evaporation of aqueous solution. Their crystal structures have been solved by single crystal diffraction data. The compounds (1) and (2) crystallize in the monoclinic space group P2(1)/c with the following unit cell dimensions: (1) a = 7.7248(4) , b = 10.9342(6) , c = 8.6716(3) , beta = 105.434(4)A degrees and Z = 4; (2) a = 7.9192(4) , b = 10.8606(4) , c = 8.7684(5) , beta = 104.317(5)A degrees and Z = 4. Compound (3) crystallises in the triclinic space group P - 1, with the unit cell parameters: a = 6.4036(5) , b = 6.8753(6) , c = 9.7964(8) , alpha = 81.706(7)A degrees, beta A = 80.218(7)A degrees, gamma A = 88.381(7)A degrees. Crystal structure of (1) and (2) consists of 3D open framework built from [ErO6] octahedra sharing corners with [P2O7] units, leading to the formation of channels running along c direction in which A(+) [A = Rb(1), Cs(2)] ions are located. The compound (3), on the other hand, exhibits a lamellar structure, in which edge-sharing polyhedra of eightfold coordinated europium form chains along [010]. These chains are joined in turn to each others using diphosphates bridges. A network of O-H center dot center dot center dot O hydrogen bonds reinforces the cohesion of the structure of (3). The diphosphate groups in (1), (2) and (3) adopts an eclipsed configuration. IR and Raman spectra of the three new phosphates show usual signals related to the P2O7 diphosphate group and the water molecule. TG and DTA studies were carried out on crystals of (3). The data are correlated to the crystal structures ones.