Formation of a Spin-Forbidden Product, (1)[MnO4](-), from Gas-Phase Decomposition of (6)[Mn(NO3)3](.)

The manganese nitrate complex, [Mn(NO3)3](-), was generated via electrospray ionization and studied by tandem quadrupole mass spectrometry. The complex is assumed to decompose into [MnO(NO3)2](-) by elimination of NO2(•). The [MnO(NO3)2](-) product undergoes elimination of NO2(•) to yield [MnO2(NO3)](-), or elimination of NO(•) to yield [MnO3(NO3)](-). Both [MnO2(NO3)](-) and [MnO3(NO3)](-) yield [MnO4](-) via the transfer of oxygen atoms from the remaining nitrate ligand. The mechanism of permanganate formation is interesting because it can be generated through two competing pathways, and because the singlet ground state is spin-forbidden from the high-spin sextet [Mn(NO3)3](-) precursor. Theory and experiment suggest [MnO2(NO3)](-) is the major intermediate leading to formation of [MnO4](-). Theoretical studies show crossing from the high-spin to low-spin surface upon neutral oxygen atom transfer from the nitrate ligand in [MnO2(NO3)](-) allows formation of (1)[MnO4](-). Relative energy differences for the formation of (1)[MnO4](-) and (1)[MnO3](-) predicted by theory agree with experiment.