Mo⁶⁺ Cation Enrichment of the Structure Chemistry of Iodates: Syntheses, Structures, and Calculations of Ba(MoO₂)₂(IO₃)₄O, Ba₃[(MoO₂)₂(IO₃)₄O(OH)₄]·2H₂O, and Sr[(MoO₂)₆(IO₄)₂O₄]·H₂O

The three metal iodates Ba­(MoO₂)₂(IO₃)₄O (1), Ba₃[(MoO₂)₂(IO₃)₄O­(OH)₄]·2H₂O (2), and Sr­[(MoO₂)₆(IO₄)₂O₄]·H₂O (3) have been successfully synthesized by introducing second-order Jahn–Teller distorted Mo⁶⁺ cations by a mild hydrothermal method. Single-crystal X-ray diffraction (XRD) was used to determine the structures of the three title compounds. In compound 1, the [Mo₂O₁₁]^10– dimers connect with the [IO₃]⁻ units by sharing oxygen atoms to form two-dimensional (2D) layers that are separated by the Ba²⁺ cations. For comparison, the [Mo₂O₁₁]^10– dimers and the [IO₃]⁻ units are isolated in compound 2, and they are connected by the [BaO₁₁]^20– polyhedra forming a 3D network. For compound 3, the [MoO₆]^6– polyhedra link with each other by corner and edge sharing to build 2D corrugated layers with tunnels containing isolated [IO₄]^3– units. The [SrO₉]^16‑ polyhedra link the 2D corrugated layers to form a 3D network. The infrared (IR) spectra, the ultraviolet–visible–near-infrared (UV–vis–NIR) diffuse reflectance spectra, and thermal stabilities of compounds 1 and 2 are presented. In addition, the theoretical calculations are also carried out to evaluate their band gaps and density of states.