A new metal iodate, BaI3O9H, has been successfully synthesized by the hydrothermal method. It crystallizes in the monoclinic space group P21/c with the lattice parameters: a = 7.777(3) Å, b = 8.000(3) Å, c = 13.7905(5) Å, β = 92.803(4)°, Z = 4. The structure contains both isolated [IO3] group and [I2O6H] dimer, which is obtained by introducing hydroxyl groups into the iodate. We investigated the crystal structure, optical properties and thermal stability of the title compound, which indicates that BaI3O9H is a good candidate as a UV birefringence material. In addition, the relationship between structure and property is analyzed by first-principles calculations.
