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The tris(acety1acetonate) (LJ and tris( l,l,l-trifluoromethyl-2,4-pentanedionate) (Li) complexes of transition metals V, Cr, Mn, Fe, Co, Ru and 0 s in their +3 oxidation states were studied under fast-atom bombardment (FAB) conditions using 3-nitrobenzyl alcohol as a matrix. All complexes showed the formation of molecular ion and protonated molecules [ML2]+ and [ML;]' are the most abundant ions in the spectra of all the metal acetylacetonates (L) and trifluoroacetylacetonates (L') studied. Interaction of matrix with metal complexes and polynuclear metal complexes led to the formation of polynuclear species with significant abundance especially for manganese and iron complexes. Formation of these metal ions was observed with relative intensities from 3-30%. Ions corresponding to ligand-exchange reactions were observed with moderate to high abundance in all metal complexes studied except those of ruthenium and osmium. Experiments carried out with a split FAB probe tip suggested ligand-ligand exchange reactions were not due to gas-phase reactions but only due to solutionphase exchanges. Osmium and ruthenium complexes do not yield polynuclear species or ions due to matrix clustering. Instead they show neutral ligand losses and formation of acetyl ion.Due to their high solubility in organic solvents and their volatile nature, metal P-diketonates have been the focus of attention of various groups.'-3 Metal acetylacetonates are used in industries such as ceramic,2 rubber4 and polymer.'^^ These compounds can also, due to their unsaturation, quench triplet states of benzophenone.' The volatile nature of these compounds attracted mass spectrometrists to study the gas-phase properties of these metal acetyla~etonates.~. '-19 A number of reports on electron ionization of metal complexes in the gas phase due to their thermal stability and ease of preparation.' These studies are useful for structure elucidation and also allow us to compare the effect of metals of different oxidation states and different electronegativities on the stability of the metal complexes towards fragmentation of the molecular ion, and on the formation of polynuclear ions. A few reports are available on the soft ionization mass spectrometry of these metal c o m p l e~e s .~~-~~ High pressure mass spectra of 16 bis-and tris-acetylacetonates and hexafluoroacetylacetonates of transition metals showed the formation of positive ions containing two or more metal atoms with significant abundance which could be produced from an iodneutral molecule reaction.20 The formation of bimetallic polymer ions was also reported for chromium acetylacetonate under electron ionization due either to the vaporization of a neutral dimer or to the high pressure which caused ion/molecule reactions in the electron ionization (EI) source itself." The polynuclear ion concentration was sample dependent, but this work was never followed up.Similar formation of polynuclear ions (two or more metal ions) was observed in the ammonia and methane chemical ionization mass spectra of Cu(II), ...

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Fast-atom bombardment (FAB) mass spectrometry was used to investigate the interaction of proton and alkali metal ions with dinucleotide analogs such as T-n-T (T = thymine moiety, n = polyether chain, e.g., triethylene, tetraethylene, pentaethylene, and hexaethylene ether 1-4), A-n-T (A = adenine unit 5-8), and T-n-OMe (9-12) in 3-nitrobenzyl alcohol matrix. The [M + H](+) ion is the most abundant ion for the A-n-T series, whereas in 1-4 and 9-12 the (TC2H4)(+) ion is the most abundant. Formation of [M + H -C2H4O](+) ions, a characteristic fragmentation of crown ethers under electron ionization, is observed for compounds 1-12 and is more pronounced in 6 and 7. An abundant [M - H](-) ion is observed for all the compounds studied under negative ion FAB due to the presence of the (-CO-NH-CO-) group of thymine, an indication of existence of intramolecular H bonding. The FAB mass spectra of 1-12 with alkali metal ions (Li(+), Na(+), K(+), Rb(+), and Cs(+)) showed formation of abundant metal-coordinated ions ([M + Met](+) and [TC2H4 + Met](+)). Compounds 3, 4, 6, 7, and 10-12 showed ions due to the substitution of the thymine moiety by a hydroxyl group ([M + Met - 108](+), Met = metal ion). For compound 3 alone, substitution of two thymine groups ([M + Met - 216](+)) was observed. Metastable ion studies were used to elucidate the structures of these potentially significant ions, and the ion formule were confirmed with high resolution measurements. Selectivity toward metal complexation with ligand size was seen in the T-n-T and A-n-T series and was even more pronounced in A-n-T series. These dinucleotide analogs fall in the following order of chelation of alkali metal ions, acyclic glymes < dinucleotide analogs (acyclic glymes substituted with nitrogen bases) < crown ethers, which places them in perspective as receptor models.

The site of the metal-ion interaction is mostly at the amide nitrogens.