Author(s)

Dylan K. Smith¹, Daniel K. Unruh², Michelle L. Pantoya¹

¹Department of Mechanical Engineering, Texas Tech University, Lubbock, USA.
²Department of Chemistry, Texas Tech University, Lubbock, USA.

The β-HIO₃ polymorph, previously difficult to detect and whose existence was questioned, has been structurally characterized. The crystal structure of β-HIO₃ was solved in the same space group as α-HIO₃ (P212121); however, it was found that the unit cell axes were all different by about 1 Å. Similar to that of α and γ phases, the unit cell contains only a single HIO₃ molecule in the asymmetric unit with I-O bond lengths ranging from 1.786(5) to 1.903(7) Å. The I(V) atom is further coordinated by three oxygen atoms of neighboring acid molecules forming a distorted octahedral with a range of I-O distances (2.498(6) - 2.795(7) Å). The one structural difference that separates the β phase from the α and γ phases is that the hydroxyl group is bridging between two I(V) atoms, resulting in a smaller hydrogen bonding distance (O-O distance: 2.559 Å (β), 2.665 Å (γ) and 2.696 Å (α)) and presumably a different crystalline energy. Similar to γ-HIO₃, β-HIO₃ is metastable and slowly converts to α-HIO₃. It is hypothesized that β-HIO₃ is a transition step in the formation of α-HIO₃ and β-HIO₃ is a result of trapped water inside particles during crystallization.

X-Ray Diffraction, Iodates, Acids, Crystal Structure, Oxides

Smith, D. , Unruh, D. and Pantoya, M. (2018) Discovery of β-HIO₃: A Metastable Polymorph of HIO₃. Advances in Materials Physics and Chemistry, 8, 246-256. doi: 10.4236/ampc.2018.85016.