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

<p>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.</p> <p>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 <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

Étude qualitative de la croissance cristalline de HLnP2_2O7_7·3H2_2O ; (Ln = La, Gd)

The effect of reagents concentration, pH, and temperature on the crystallization of HLnP$_2$O$_7$·3H$_2$O (Ln=La, Gd) has been determined separately. The results show that the crystallization is enhanced at ambient temperature, by reducing reagents concentrations and using an optimal value of pH. Monocrystals of HLaP$_2$O$_7$·3H$_2$O and HGdP$_2$O$_7$·3H$_2$O have been obtained respectively with a length of 150 µm and 700 µm. The observation of HGdP$_2$O$_7$·3H$_2$O crystal state at different times of synthesis using optical microcopy indicates that the growth follows a bi-dimensional nucleation mechanism.L’influence de la concentration des réactifs, du pH et de la température, ont été étudiées séparément pour déterminer les conditions d’obtention des cristaux HLnP$_2$O$_7$·3H$_2$O (Ln = La, Gd). Les résultats ont montré que la cristallisation est favorisée, à température ambiante, pour des concentrations de réactifs relativement basses et dans un mélange dont le pH est optimum. Des monocristaux de HLaP$_2$O$_7$·3H$_2$O et HGdP$_2$O$_7$·3H$_2$O ont été obtenus de longueur respectives 150 µm et 700 µm. L'observation de l’évolution de la croissance de l'hydrate au gadolinium, par microscopie optique, a permis de conclure qu’elle se fait selon le mécanisme de nucléation bidimensionnell

Synthesis, Crystal Structure and Thermal Decomposition of [HGdP₂O₇ · 2 H₂O] · NH₃ Electric properties of HGdP₂O₇ and Gd₂P₄O₁₃

<p>A new gadolinium diphosphate [HGdP₂O₇ · 2 H₂O] · NH₃ was synthesized <i>via</i> a soft chemistry route from evaporation of aqueous solution. It crystallizes in the space group Pī with Z = 2 and the following unit cell dimensions: a = 6.4609(2), b = 6.9810(2), c = 9.813(4) Ǻ, α = 81.345(3), β = 80.547(3), γ = 88.430(3)°. IR spectroscopy confirmed the presence of P-OH group, and both ammonia and water molecule in the studied material.</p> <p>The thermal decomposition of [HGdP₂O₇ · 2 H₂O] · NH₃, as investigated by Controlled Rate Thermal Analysis, took place in three stages between -23 and 600 °C leading to the anhydrous salt HGdP₂O₇. The calcination of the synthesized product at 850 °C in a static air furnace allowed us to obtain the tetraphosphate Gd₂P₄O₁₃. X-ray powder diffraction and infrared spectroscopy were used to identify these materials.</p> <p>The electrical properties of HGdP₂O₇ and Gd₂P₄O₁₃ were investigated through impedance complex analysis. Modest conductivity has been observed in both materials at relatively medium temperature range. Activation energies of 0.62 and 1.21 eV, were deduced from the Arrhenius plots for HGdP₂O₇ and Gd₂P₄O₁₃, respectively.</p