Structural and vibrational study of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO4-KH2PO4 system, aimed at developing novel proton conducting solids, resulted in the new compound K2(HSeO4)1.5(H2P04)0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals have been prepared by slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by X-ray single analysis (performed at room temperature), which revealed that K2 (HSeO4)1.5 (H2PO4)0.5 (KHSeP) crystallizes in space group P1 with lattice parameters: a = 7.417(3) A, b=7.668(2) A, c=7.744(5) A, a=71.59(3)DG, ,8=87.71(4)DG and y=86.04(6)DG. The compound has a unit cell volume 416.8(3) A3 and two formula units per cell, giving a calculated density of 2.732. The structure was solved from 3210 independent reflections and refined with 112 parameters yielded weighted residuals of 0.1113 and 0.0594 based on F2 and F values, respectively. This structure is characterized by HSeO4- and disordered (HxSe/P)04- tetrahedra connected to dimmer via hydrogen bridges. These dimmers are linked and stabilized by an additional hydrogen bonds (O-H-O) and hydrogen bonds (O-H..0) to built a chains of dimmers, which are parallel to the [0 10] direction at the position x = 0.5. The potassium atoms have an eight-fold coordination. The infrared spectrum at room temperature is investigated in the frequency range 4000-400 cm-1 and confirm a structural disorder in this material and the coexistence of two different anions (H2PO4- and HSeO4-) in the same crystal structure.