Single crystal structure, vibrational study, and thermal behavior of a new rare earth diphosphate HYbP₂O₇·4H₂O

A new ytterbium diphosphate: HYbP₂O₇·4H₂O was prepared via soft chemistry route from evaporation of aqueous solution. It was investigated by single crystal X-ray diffraction, vibrational spectroscopy, and thermal analysis.

The framework of the title compound consists in an assemblage of HP₂O₇ groups and [YbO₅(H₂O)₂] polyhedra, giving rise to corrugated layers stacked along the b axis at y = 1/4 and y = 3/4. Between these layers are located two uncoordinated water molecules. The cohesion of this arrangement is well ensured by a three-dimensional network of water-layer and inter-layer hydrogen bonds of different strengths. Non-coincidences are observed between the majority of the IR and Raman bands and confirm a centrosymetric structure for this compound. Thermal analysis reveals the elimination of 4.5 water molecules per formula unit in three stages between 310 K and 1100 K, which correspond to the departure of the four crystallization water molecules and the OH group. A comparative study among hydrated lanthanide monohydrogendiphosphates known in the literature is presented.