Solid State Reaction of MO 2 (M = Zr and Hf) with K 2 S 2 O 7 : Evidence of Noncentrosymmetric K 10 M 2 (SO 4 ) 9

The reaction of ZrO 2 with K 2 S 2 O 7 has been performed at different temperatures between 400 and 450 °C in order to identify the formation of potential products and investigate their reactivity and their thermal and dissolution behavior. The products formed during the reaction were fully characterized by chemical and thermal analyses as well as X-ray diffraction. The solid state reaction with a 2 ZrO 2: 5 K 2 S 2 O 7 molar ratio at 440 °C leads to new compound K 10 Zr 2 (SO 4 ) 9, never identified before, which further decomposed into K 2 SO 4 and ZrO 2 at 950 °C. The crystal structure of K 10 Zr 2 (SO 4 ) 9 was refined from single-crystal XRD data in noncentrosymmetric monoclinic space group Cc and characterized by infrared and Raman spectroscopies and SHG analysis. Finally, it was found to be soluble in water with a minimal solubility of 11.8 g/L at 18 °C. Because of the chemical similarities between Zr and Hf, isotype phase K 10 Hf 2 (SO 4 ) 9 was also identified and synthesized as a pure phase.