Binding of O2 and CO to Metal Porphyrin Anions in the Gas Phase

The binding energies of O2 and CO to iron(II) and manganese(II) porphyrin anions has been determined in the gas phase. Low-pressure ion–molecule equilibria have been measured in a cryogenically cooled trap of an FT-ICR mass spectrometer, and binding energies of (40.8±1.3) kJ mol−1 and (66.3±2.6) kJ mol−1 have been obtained for oxygen and carbon monoxide, respectively, with a heme-analogue FeII porphyrin complex.