The crucial role of CO as a ligand in the formation of long-lived neutral iron complexes in the gas phase

Neutralization reionization (NR) mass spectra of mono- and bis-ligated iron cations Fe(L)n+ (n=1, 2) are reported for the simple ligands L=H2O, CO, C2H4, C4H6, C6H6, and NH3. Most of these iron complexes do not survive the NR process, and dissociation of the neutrals into Fe+nL prevails. Interestingly, those complexes containing CO ligands exhibit much more pronounced recovery signals in the NR spectra. Electronic arguments imply that the carbonyl ligand favors the generation of low-spin complexes of neutral iron which are less prone to dissociate and are not accessed with the other ligands.