Ionic Ozonides

Ionic Ozonides [1] were mentioned for the first time during the second half of the nineteenth century. However, fundamental aspects of their chemistry and physics remained obscure until more recently procedures had been provided that allow for their syntheses in gram‐amounts, and in high purity. Respective preparative approaches start by reacting the alkali metal superoxides KO 2 , RbO 2 , or CsO 2 with O 2 /O 3 mixtures, at punctilious temperature control. Subsequently, the raw product is extracted with liquid ammonia. From the solution obtained, solid ozonides are harvested and purified by recrystallization. As rather versatile and efficient accesses to ozonides of further cations, metathesis reactions or cation exchange in liquid ammonia have been developed. The samples obtained have allowed for full structural and basic physical characterizations. All ionic ozonides known are metastable with respect to release of dioxygen, [NMe 4 ]O 3 being the most stable one (onset of rapid decomposition at 348 K). Depending on the respective crystal field, the bond lengths and angles of the ozonide anion vary significantly, and consistently, from 135 to 129 pm, and 113 to 120°, respectively. The magnetic moments of the paramagnetic O 3 − determined by susceptibility measurements (1.70–1.80 μ B ) deviate but slightly from the spin‐only value for one unpaired electron. This finding complies well with the small anisotropy of the g ‐factors. As an achievement of possibly far reaching consequences, stable solutions of ionic ozonides in organic solvents have become available, opening the way to the use of O 3 − as a ligand, or synthon, in coordination and molecular chemistry.