Structural, IR and thermal study of a new inorganic solid acid: Rb3(HSeO4)2.5(H2PO4)0.5

Abstract

The structure of a new inorganic solid acid Rb3(HSeO4)2.5(H2PO4)0.5 trirubidium hydrogenselenate dihydrogenphosphate: (RbHSeP) has been examined by X-ray single analysis performed at room temperature.This compound crystallizes in triclinic space group P1¯ with lattice parameters a=7.637Å; b=7.825Å; c=12.320Å; α=106.85°; β=106.49° and γ=91.10°. It has a unit cell volume 671.5Å3 and two formula units per cell, giving a calculated density of 2.732gcm−3. The structure was solved from 2458 independent reflections and refined with 166 yielded parameters, weighted residuals of R1=0.0558 and WR2=0.1384 based on F2 and F values, respectively. The main feature of the structure of (RbHSeP) is the coexistence of three ordered and disordered anions on the one hand, and of rubidium cations Rb+ in the same crystal on the other hand. Rubidium cations and hydrogen-selenate and phosphate anions are linked with ionic bands whereas hydrogen-selenate and phosphate anions are linked each other with hydrogen bands leading, thus, to a three-dimensional aspect structure.The infrared spectrum performed at room temperature in the frequency range 4000–500cm−1 confirms the presence of structural disorder in this material and the coexistence of two different anions (H2PO4− and HSeO4−) in the same crystal structure. The thermogravimetry (TGA) analysis and the differential scanning calorimetric (DSC) show the presence of a structural phase transition of the title compounds at 374K.