How Far Can We Go? Quantum-Chemical Investigations of Oxidation State plus IX

The highest known oxidation state of any element is +VIII. After the recent discovery of (IrO4)-O-VIII under cryogenic conditions, we have investigated the stability of cationic species [MO4](+) (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. [IrO4](+) 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.