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

Abstract

New diphosphates AErP2O7, A = Rb (1), Cs (2), and HEuP2O7·3H2O (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 P21/c with the following unit cell dimensions: (1) a = 7.7248(4) A, b = 10.9342(6) A, c = 8.6716(3) A, β = 105.434(4)° and Z = 4; (2) a = 7.9192(4) A, b = 10.8606(4) A, c = 8.7684(5) A, β = 104.317(5)° and Z = 4. Compound (3) crystallises in the triclinic space group P − 1, with the unit cell parameters: a = 6.4036(5) A, b = 6.8753(6) A, c = 9.7964(8) A, α = 81.706(7)°, β = 80.218(7)°, γ = 88.381(7)°. 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···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. Edge-sharing [LnO8] polyhedra (here Ln is Eu) lead to ladder channels in the crystal structure of HEuP2O7·3H2O. These channels are linked through O–P–O bridges from the diphsophates groups and an intricate H-bonds network to build a lamellar structure. Crystal structure of AErP2O7, A is Rb or Cs consists of a three dimensional open framework, built from octa-coordinated Er which share corners with diphosphates groups. These channels run through the monoclinic cell along c, in which the nonovalent cations are located.