Mg(H2O)6[(IO2(OH))2(IO3)]2: a new iodate with a very large band gap and optical anisotropy

Abstract

Centimeter-sized large crystals of a new magnesium iodate, Mg(H₂O)₆[(IO₂(OH))₂(IO₃)]₂, have been successfully grown by a facile aqua-solution method. The title compound exhibits an interesting structural feature, namely, [(IO₂(OH))₂(IO₃)]⁻ pseudo-chains interacting with [Mg(H₂O)₆]²⁺ octahedra via the hydrogen bonds. Mg(H₂O)₆[(IO₂(OH))₂(IO₃)]₂ possessing a large band gap of 4.10 eV exhibits the largest birefringence (0.230 @1064 nm) among the iodate systems containing alkali, alkaline earth, or rare earth metal cations, indicating that the compound is a promising birefringent material that could be applied in the ultraviolet region. The electron density difference map indicates that the great birefringence of the material is attributed to the synergistic effect of the iodate groups and the coordinated water molecules. This work also successfully provides a new method for functional crystals with large birefringence via a facile aqua-solution method.