Exploring ion-molecule reactions in a quadrupole ion trap as a tool to obtain coordination structure from transition metal complexes.

摘要

Metal complexes play fundamental roles in synthetic, biological, and catalytic processes, and when doing so they are often present at very low concentrations. Determining the coordination structure of complexes at trace levels or in complicated mixtures, however, is a very difficult task. This dissertation focuses on the investigation of a new methodology, based on ion-molecule (I-M) reactions and mass spectrometry (MS), to determine the coordination structure of metal complexes sensitively. This work describes the study of the gas-phase reactivity exhibited by a variety of model transition metal complexes with different reagent ligands in a quadrupole ion trap mass spectrometer.; A series of tetradentate and pentadentate ligands containing N, O, and/or S donor atoms were synthesized and complexed with late first-row transition metals. Noticeable differences in reactivity were found as the ligand field around the central metal ion was changed. The electronic structure of the metal center was also found to exert a remarkable effect on the gas-phase reactions of metal complexes, and in fact, complexes with different geometric structures could be distinguished. Angular overlap model (AOM) and density functional theory (DFT) calculations were used to explain the experimental observations. The analytical utility of the I-M reactions was also investigated. Fluctuations in reagent and buffer gas pressures and vacuum system temperature were examined as possible error sources affecting the conclusions drawn from the I-M reaction procedure. Reagent gas pressure and temperature were found to be the most important factors affecting the reproducibility of the experimental data. Because the analytical information derived from these I-M reactions relies on complexation of a reagent ligand, steric factors that might affect these reactions were also evaluated. In summary, I-M reactions can distinguish complexes with different coordinating functional groups and geometries, and these reactions have some potential for providing coordination structure information for complexes present at trace levels.