How Far Can We Go? Quantum‐Chemical Investigations of Oxidation State +IX

The highest known oxidation state of any element is +VIII. After the recent discovery of Ir VIII O 4 under cryogenic conditions, we have investigated the stability of cationic species [MO 4 ] + (M=Rh,Ir,Mt). Such compounds would formally represent the new oxidation state +IX, which is experimentally unknown so far for the whole periodic table. [IrO 4 ] + is predicted to be the most promising candidate. The calculated spin–orbit (SO) coupling shows only minor effects on the stability of the iridium species, whereas SO‐coupling increases enormously for the corresponding Eka‐Iridium (Meitnerium) complexes and destabilizes these.