Synthesis and Crystal Structure of Anhydrous Di-iodyl Carbonate (IO ₂ ) ₂ [CO ₃ ], Hosting I ⁵⁺ -Cations

The anhydrous di-iodyl carbonate (IO₂)₂[CO₃] has been synthesized in a laser-heated diamond anvil cell at 30(2) GPa and 1600(200) K by a reaction of I₂O₅ with CO₂. Its monoclinic crystal structure (<i>C</i>2/<i>c</i> with <i>Z</i> = 4) was determined from synchrotron single crystal X-ray diffraction data. The experimental structural model was confirmed by density functional theory based calculations in combination with experimental Raman spectroscopy. (IO₂)₂[CO₃]-<i>C</i>2/<i>c</i> belongs to the family of sp²-carbonates, and its crystal structure is characterized by the presence of nearly trigonal-planar [CO₃]^2- groups. In contrast to other iodide-containing carbonates, in this structure the iodine atoms are present as small and highly oxidized I⁵⁺-cations and not as large I^--anions. The I⁵⁺-cations are coordinated by seven oxygen atoms. The successful synthesis of (IO₂)₂[CO₃]-<i>C</i>2/<i>c</i> represents a significant enlargement of the crystal chemistry of carbonates, as this chemically simple carbonate demonstrates that anhydrous carbonates with highly charged cations can be formed and that sp²-carbonates hosting a positively charged halogen atom as the only cation can be synthesized.