Electron impact ionization of dicyclopentadienyl-manganese and cyclopentadienyl-manganese-tricarbonyl compared with dimanganese-decacarbonyl: appearance energies, bond energies and enthalpies of formation

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Eur. J. Mass Spectrom. 7, 55 - 62 (2001)

Electron impact ionization of dicyclopentadienyl-manganese and cyclopentadienyl-manganese-tricarbonyl compared with dimanganese-decacarbonyl: appearance energies, bond energies and enthalpies of formation

Joachim Opitz
Universität Stuttgart, Institut für Organische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart,

ABSTRACT:

Electron impact (EI) ionization mass spectra, metastable-ion decays and appearance energies are reported for the title compounds. Gas-phase formation enthalpies (DH_f) and bond energies (as dissociation energies) are derived from these data. Obtained DH_f values for the parent compounds are (15.65 ñ 0.2) eV for Mn₂(CO)₁₀, (2.85 ñ 0.3) eV for Cp₂Mn (Cp = C₅H₅ = cyclopentadienyl ligand) and (3.91 ñ 0.3) eV for CpMn(CO)₃. The mean (Mn&150;CO) bond energy is 0.97 eV for Mn₂(CO)₁₀. In cations, the mean (MnCO)⁺ 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.

Keywords: enthalpies of formation, bond energies, dissociation energies, metastable ion decay, mass spectra

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