Preparation, Crystal Structure, Vibrational Spectra, and Thermal Behavior of Rb 2 H 2 P 2 O 6 ·2H 2 O

Single crystals of Rb 2 H 2 P 2 O 6 · 2H 2 O could be obtained from aqueous solutions of hypodiphosphoric acid and rubidium carbonate. Its crystal structure was determined by X‐ray diffraction and it crystallizes in the monoclinic space group P 2 1 / c with Z = 4. The salt‐like title compound consists of [H 2 P 2 O 6 ] 2– units in staggered P 2 O 6 ‐skeleton conformation, Rb + cations, and H 2 O molecules, held together by intermolecular hydrogen bonds of the type O ··· O. The vibrational spectra (IR/FIR and Raman) of the rubidium salt were recorded and an assignment of the vibrational modes is proposed based on the point group C 2 h for the P 2 O 6 ‐skeleton of the anion. The thermal behavior of Rb 2 H 2 P 2 O 6 · 2H 2 O is dominated by a complex TG decay indicating a simultaneous H 2 O delivery coupled with a disproportionation of [H 2 P 2 O 6 ] 2– , what is also supported by Raman spectra of heated samples.