γ-HIO3 — A Metastable, Centrosymmetric Polymorph of Iodic Acid

From solutions of chromium(III) perchlorate and periodic acid, single crystals of gamma-HIO3 were obtained and characterized by single-crystal X-ray diffraction, Raman spectroscopy and thermal analysis. The compound crystallizes in the orthorhombic crystal system, space group Pbca (a = 563.92, b = 611.10, c = 1507.16 pm). The structure is built up by dimers (HIO3)(2), which are formed by hydrogen bonds. The crystals are metastable and transform into the stable modification, alpha-HIO3, within a couple of weeks.