The Flexibility of P2O7 Dimers in Soft Structures: M2CdP2O7 (M = Rb Cs)

Abstract

Two new congruent-melting alkali metal diphosphates, Rb₂CdP₂O₇ and Cs₂CdP₂O₇, were synthesized by conventional solid-state reactions. Single-crystal X-ray structural analyses showed that M₂CdP₂O₇ (M = Rb, Cs) feature two-dimensional [CdP₂O₇]^2– layers that are composed of CdO₅ pyramids and P₂O₇ dimers. The Rb⁺ and Cs⁺ cations ions fill the interlayers. The flexible P₂O₇ dimers could be bent and distorted if the Cs⁺ ion was substituted by the Rb⁺ ion, which led to crystallization of the Rb₂CdP₂O₇ compound in the lower symmetry monoclinic space group P2₁/c (No. 14) and crystallization of the Cs₂CdP₂O₇ compound in the high-symmetry orthorhombic space group Pnma (No. 53). Thermal analyses showed that the two compounds melt congruently and that the melting point of Rb₂CdP₂O₇ compound is lower than that of the Cs₂CdP₂O₇ compound owing to distortion of the P₂O₇ dimers. IR spectroscopy and UV/Vis–near-IR diffuse reflectance spectroscopy were performed on the reported compounds.

Distortion of the P₂O₇ dimer in the Rb₂CdP₂O₇ compound leads to a lower melting point than that of the Cs₂CdP₂O₇ compound. It is found that the soft structures of Rb and Cs compounds can crystallize in different space groups.

from #MedicinebyAlexandrosSfakianakis via xlomafota13 on Inoreader http://ift.tt/1TiAQHN
via IFTTT