Hydrated metal-oxide versus dihydroxide structures of [MO2H2]+ cations with MFe, Co, and Ni

The formal metal(III) cations [CoO2H2]+ and [NiO2H2]+ can be generated by electrospray ionization of aqueous solutions of the corresponding metal(II) nitrates. In contrast to MFe, the fragmentations of [CoO2H2]+ and [NiO2H2]+ imply that the hydrated metal-oxide cations, (H2O)MO+, are more favorable compared to the dihydroxo isomers M ( OH ) 2 + than for MFe. The experimental data are corroborated by density functional calculations of the [ MO 2 H 2 ] + surfaces for MFe–Ni, which predict Fe ( OH ) 2 + to be more stable than (H2O)FeO+, whereas the opposite applies for MNi and both isomers are energetically close for MCo.