A NEUTRALIZATION-REIONIZATION (NR) CASE-STUDY FOR CATIONIC IRON COMPLEXES WITH SIMPLE LIGANDS - NR MASS-SPECTRA OF FE(C2H4)+ AND FE(CO)+

The cationic tron(I) complexes Fe(C2H4)+ and Fe(CO)+ were examined by neutralization-reionization mass spectrometry (NRMS). Whereas the NR m ass spectrum of the carbonyl complex exhibits a signal corresponding t o the reionized neutral molecule Fe(CO), for the neutral Fe(C2H4) comp lex no recovery signal is observed; rather, in the course of the exper iment the complex dissociates to Fe and C2H4. An explanation for this seemingly contradictory behaviour of structurally related metal comple xes in a NR process is provided by ab initio MO calculations, in which the geometries Of Fe(C2H4)+ (B-4(2)), Fe(C2H4) (B-5(2)), Fe(CO)+ (4SI GMA-), Fe(CO) (3SIGMA-), and Fe(CO) (5SIGMA-) have been fully optimize d at the QCISD(T) level of theory. From the theoretical results, a neu tralization-reionization scheme for organometallic ions MX+ emerges wh ich considers the effects caused by curve-crossing from a bound state to a repulsive ground-state asymptote of the neutral building blocks M and X. Thus, even for bound organometallic complexes MX, recovery sig nals in the NR mass spectrum can only be detected if the internal ener gy deposited in MX in the vertical electron-transfer reaction MX+ --> MX is too small to permit this curve-crossing. If dissociation occurs on the time scale of the NR experiments, the spectrum exhibits feature s of both the metal M and the ligand X, thus revealing the structural properties of the (organic) ligand X bound to the metal ion.