A STUDY OF HETEROTETRANUCLEAR TRANSMETALATION PRODUCTS BY FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

Transmetalation is the stoichiometric replacement of the metals in a p olymetallic target with other metals from reagents called transmetalat ors. The family of heteropolymetallic complexes (mu4-O)L4Cu4-xMxCl6 (M = Ni and x = 0-4 in I-V, respectively) was obtained by transmetalatin g the parent (x = 0) with x mol of Ni(NS)2, where L is N,N-diethylnico tinamide and NS is S-methyl isopropylidenehydrazinecarbodithioate. The se and other neutral polymetallic complexes VI-XI containing different combinations of Co, Ni, Cu, and Zn were evaluated by fast atom bombar dment mass spectrometry (FAB/MS). Ionization of I-XI by FAB/MS produce d no molecular ions under the analysis conditions employed, but the pr oduction of characteristic fragments as well as the formation of sever al metal-ligand complexes was observed. No heteropolymetallic fragment s were observed in this study. The spectral patterns of the mixed meta l complexes II-IV and VI-X indicate that metal exchange occurs in the matrix as a result of exposure to the FAB beam. (Mu4-O)L4CuNi3Cl6 prod uces a fragmentation pattern indistinguishable from that of (mu4-O)L4C u4Cl6 in the mass range from m/z 650 and above, yet produces ions at m /z 419 and 449 (CuL2+ and [NiCl]L2+, respectively) in ratios expected from the stoichiometric metal content of the original complex. It appe ars that the m/z 419 and 449 peaks do not result from an ionically ind uced fragmentation of the parent complex but rather from decomposition of the complex and recombination of neutral ligand and metal species in the nitrobenzyl alcohol matrix. Isotopic abundance calculations wer e used to determine fragmentation pathways and fragment compositions. A mixture of (mu4-O)L4Cu4Cl6(I) and (mu4-O)L4Ni4Cl6(V) in 3-nitrobenzy l alcohol produced a spectrum whose major fragments were remarkably di fferent from those of the heteropolymetallic copper/nickel complexes ( II-IV).