Single crystal structure, vibrational study, and thermal behavior of a new rare earth diphosphate HYbP<sub>2</sub>O<sub>7</sub>·4H<sub>2</sub>O

<p>A new ytterbium diphosphate: HYbP<sub>2</sub>O<sub>7</sub>·4H<sub>2</sub>O 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.</p> <p>The framework of the title compound consists in an assemblage of HP<sub>2</sub>O<sub>7</sub> groups and [YbO<sub>5</sub>(H<sub>2</sub>O)<sub>2</sub>] polyhedra, giving rise to corrugated layers stacked along the <i>b</i> axis at <i>y</i> = 1/4 and <i>y</i> = 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.</p>