Orthoperiodato Rhodium(III) Complex as a Possible Key to Catalytic Oxidation of Organic Dyes

Light yellow, air-sensitive single-crystals of the rhodium(III) orthoperiodato K8[Rh(IO6)2]OH ⋅ 3H2O were synthesized starting from Rh2O3 and KIO4. The reaction was carried out in a potassium hydroxide hydroflux with a molar water-base ratio of 1.8 at 200 °C. Single-crystal X-ray diffraction revealed a triclinic crystal structure (space group (Formula presented.)). The most striking feature of the structure is the [Rh(IO6)2]7− anion, a linear sequence of three face-sharing octahedra. It can be interpreted as a rhodium(III) cation coordinated by two orthoperiodato groups. A water molecule and a hydroxide ion form an associate (H3O2)−. Together with other water molecules, they connect the [Rh(IO6)2]7− anions via hydrogen bridges to form layers. Upon heating, the compound first loses its crystal water, then the iodine is gradually reduced before evaporating during the final decomposition step, which results in K0.63RhO2. In K8[Rh(IO6)2]OH ⋅ 3H2O, the unusually short RhIII−IVII distance of only 276.38(1) pm should allow direct charge transfer in the [Rh(IO6)2]7− anion. An electron-poor rhodium cation, accessible from the side, could be the active center in the rhodium-catalyzed oxidation of unsaturated organic molecules by periodate. © 2022 The Authors