Hetpacoordination. Synthesis and characterization of the IOF52- dianion, an XOF5E species

The new IOF52- dianion was prepared in the form of its cesium salt by heati ng stoichiometric amounts of CsF, I2O5, and IFS to 162 degrees C for 14 day s. The white stable solid was characterized by vibrational spectroscopy. A normal coordinate analysis was carried out with the help of ab initio calcu lations at the HF/ECP/DZP level of theory and resulted in an excellent agre ement between observed and calculated frequencies. The structure of IOF52- iS that of a pentagonal bipyramid with five equatorial fluorine ligands, an d an oxygen atom and one sterically active free valence electron pair occup ying the two axial positions. The structure is very similar to that previou sly established by vibrational spectroscopy and X-ray diffraction for isoel ectronic XeOF5- and represents only the second example of a heptacoordinate d XOF5E (E = free valence electron pair) main group species. The possible e xistence of the IOF63- trianion is briefly discussed.