Synthesis, crystal structure and characterization of Na3H(SO4)1.78(SeO4)0.22

Synthesis, crystal structure, Raman, IR and TG/DTA characterization are given for Trisodium hydrogen bisulfate selenite Na3H(SO4)1.78(SeO4)0.22. This compound crystallizes in the monoclinic system with space group P21/c and cell parameters: a = 8.6787 (4) Å, b = 9.6631 (6) Å, c = 9.2070 (5) Å, ß = 108.825 (4)°, Z = 4 and V = 730.83 (7) Å3. The refinement of 2492 observed reflections (I > 2σ(I)) leads to R1 = 0.045 and wR2 = 0.125. ructure is characterized by S/SeO4 tetrahedra which are linked into isolated pairs by hydrogen bonds which form dimers of composition [ H ( SO 4 ) 2 ] 3 - . The existence of O–H and (S/Se)–O bonds in the structure at room temperature has been confirmed by IR and Raman spectroscopy in the frequency ranges 50–1300 and 500–4000 cm−1, respectively. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) measurements have been carried out on Na3H(SO4)1.78(SeO4)0.22 crystal in the temperature range between 50 and 600 °C. Water evolution and major thermal decomposition take place with onset temperatures of approximately 282 °C and 395 °C, respectively. A Raman study of the decomposition of Na3H(SO4)1.78(SeO4)0.22 as a function of temperature supports a reaction sequence and possible intermediates during the process.