Chemical Bonding in the Perchromate Ion

The perchromate ion, CrO₈^3—, in K₃CrO₈ has D_2d($\text{4̄2m}$ ) symmetry and consists of a central pentavalent chromium ion surrounded by four peroxide groups. On the basis of a refinement of the previous structure determination, the chromium ion is nearer to one oxygen of each peroxide group than to the other and the peroxide oxygen—oxygen distance is shorter than normal. A ligand field calculation, based on the optical spectrum and the electron paramagnetic resonance spectrum, accounts for these structural features and leads to a description of the bonding in the perchromate ion.