EXPERIMENTAL ELECTRON-DENSITY OF THE OZONIDE ION (O3-) IN POTASSIUM OZONIDE, KO3

The deformation electron density in potassium ozonide has been determi ned by multipole refinement with the Hirshfeld formalism using single- crystal X-ray data collected at 170 K. No electron excess is observed in the oxygen-oxygen bond region of the ozonide ion, a feature that is at first sight surprising, but it is not unusual for bonds between el ectronegative atoms, The explanation is that oxygen has a degenerate g round state with an open p shell, and therefore the total deformation density results from both chemical bonding effects and the superpositi on of nonspherical ground states. The former effect, if small, cannot compensate for the latter, and a net charge depletion results. The oxy gen lone-pair regions exhibit well-distinguished maxima, while a charg e depletion is found near O(2) in the direction of the shortest interm olecular O-O distances. This can be taken as an indication for a small electrostatic interaction between the paramagnetic ozonide anions, al though the roles of ''donor'' and ''acceptor'' seem to be interchanged compared to the expectation from the relative polarities. On the basi s of the refinement results, the terminal oxygen atoms carry more nega tive partial charge compared to the central atom, which is in agreemen t with quantum chemical calculations.