A SINGLE-CRYSTAL NEUTRON-DIFFRACTION STUDY OF HIO3 AT 295-K AND 30-K AND DIO3 AT 295-K

The crystal structures of hydrogen iodate, HIO3, and its deuterated form, DIO3, have been refined from single-crystal neutron data, lambda = 1.215(1) angstrom, P2(1)2(1)2(1), Z = 4, HIO3: 295 K; a = 5.5400 (2), b = 5.8768(3), c = 7.7370(4) angstrom, R(F) = 0.022 from 377 unique reflections and at 30 K; a = 5.492(3), b = 5.841(3), c = 7.660(8) angstrom, R(F) = 0.021 from 375 unique reflections and DIO3: a = 5.5402(3), b = 5.8746(4), c = 7.7351(5) angstrom, R(F) = 0.024 from 375 unique reflections. The iodate group forms a pyramid with iodine as one apex. Including oxygens at distances shorter than the sum of van der Waals radii the I-O coordination can be described as a distorted bicapped trigonal prism and the structure as of the anti-cementite type. The iodate groups are connected through hydrogen bonding, forming chains along the b-axis, H...O, 1.725(3) angstrom and O-H...O 173.5(2)-degrees. The only significant difference between HIO3 and DIO3 is a longer [1.747(2) angstrom] D...O distance. At 30 K, HIO3 shows decreased intermolecular distances and O-I-O angles.