Ligand ionization

Innorta, Distefano et al. 53, 72) have reported first ionization potentials for a series of M(CO)jL complexes (L = various phosphines and RNC) and find a linear correlation between these values and the ligand ionization potentials and they report calculations of these ionization potentials using an equivalent orbital method. 

Ionizations are evident before ligand ionizations with early transition metals Ti(m), V(III), or Cr(III), not evident at all or masked under ligand ionization bands with late transition metals such as Cu(ll) or Zn(II), and highly intermixed with the first ligand ionizations for intermediate transition metal configurations such as d6 of Co(III) or d6 of Ni(H). (Fig. 11). This type of behavior is probably of general occurrence and is in fact found also in other classes of coordination compounds, especially with sulfur ligands. 

TABLE 1. Stability of Mg(L) + complexes in the gas phase as a function of ligand ionization energy (IE)... 

Figure 11 PE spectra of FeCp2, RuCp2, and OsCp2 measured with a photon energy of 27 eV. Assignment of the d and top ligand ionizations are given for an eclipsed Dg/, structure. Note the increased separation between the e and e/ bands for the second and third row transition metals as a consequence of increased covaient bonding. Adapted with permission of Tayior Francis from...

All shifts are to lower IE in comparison with the unsubstituted derivatives. The presence of two methyl groups in a metallocene (one on each ring) has a fairly uniform effect on the -ionizations, but decreases the ligand ionizations... 

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