COMPARATIVE CHEMICAL-IONIZATION AND ELECTRON-IONIZATION MASS-SPECTRA OF SALEN COMPLEXES WITH METALS OF THE FIRST TRANSITION SERIES

Positive-ion methane chemical-ionization (CI) mass spectra and 70 and 18 eV electron-ionization (EI) mass spectra are obtained for N,N'-bis(salicylidene)ethylenediamine, H(2)salen, and for Met(salen) where Met = TiO, VO, CrCl, Mn, FeCl, Co, Ni, Cu, and Zn. Comparison of the relative abundances of the ions from the various compounds under these modes of ionization elucidates the gaseous ion chemistry. This is understood by considering the preferred oxidation states of the metals and whether the molecular ion results from electron loss at a metal or a ligand site. For Met = VO, Mn, Co, Ni, and Cu, the complexes ionize at the metal and, except for Cu(salen), undergo little Fl fragmentation at 70 eV. For Met = TiO, CrCl, FeCI, and Zn, the complexes ionize at the ligand and undergo more extensive EI fragmentation. Many of the CI and Fl processes involve loss or transfer of H-2 from the ethylene bridge of the ligand. Cyclized ionic or neutral fragments account for some of the low-energy processes observed. Conclusions are supported by collision-induced-dissociation mass spectra. Under 70 eV;EI, elimination of CuH from [CuC8H7NO](.+) has been invoked to account for the abundant [C8H6NO](+) from Cu-(salen), but the latter fragment is now found to be significant also for Mn(salen) and Zn(salen).