Electron Impact Ionization of Dicyclopentadienyl-Manganese and Cyclopentadienyl-Manganese-Tricarbonyl Compared with Dimanganese-Decacarbonyl: Appearance Energies, Bond Energies and Enthalpies of Formation

Abstract

Electron impact (EI) ionization mass spectra, metastable-ion decays and appearance energies are reported for the title compounds. Gas-phase formation enthalpies (Δ Hf) and bond energies (as dissociation energies) are derived from these data. Obtained Δ Hf values for the parent compounds are (–15.65 ± 0.2) eV for Mn2(CO)10, (2.85 ± 0.3) eV for Cp2Mn (Cp = C5H5 = cyclopentadienyl ligand) and (–3.91 ± 0.3) eV for CpMn(CO)3. The mean (Mn–CO) bond energy is 0.97 eV for Mn2(CO)10. In cations, the mean (Mn–CO)+ bond energy ranges from 0.75 to 0.80 eV for Mn2(CO)10 and CpMn(CO)3, respectively. In Cp2Mn+ the dissociation energies are 2.14 eV for the first Cp ligand and 3.21 eV for the second. In the neutral Cp2Mn, 2.12 eV is needed for the detachment of a first Cp ligand and 3.00 eV for the second. The results for the second ligand are valid for the elimination of Cp from CpMn(CO)3 as well.