Chemistry and photochemistry of gas phase ionic transition metal complexes and clusters studied using Fourier transform mass spectrometry: Structural studies and bond energy determinations
Abstract
Differences between a variety of metal ion-ligand isomers have been probed using Fourier transform mass spectrometry (FTMS). A variety of gas phase techniques such as collision-induced dissociation (CID), ion-molecule reactions, and photodissociation have successfully been implemented in uncovering differences in the reactivity and the structure of some Sc$\sp{+}$-ligand isomers. After studying Sc$\sp{+}$ chemistry, the heteronuclear diatomic metal cluster ScFe$\sp{+}$ was investigated. This dimer, being a combination of an early and a late transition metal exhibited chemistry that reflected a weak metal to metal dimer bond relative to various Sc$\sp{+}$-ligand bonds as well as to other metal dimer bonds. First attempts at obtaining values for Sc$\sp{+}$-ligand bond energies were made by using a new experiment that made it possible to generate endothermic reaction products. These endothermic products were used to bracket the Sc$\sp{+}$-benzene bond strength. This new "excitation" experiment is the first demonstration that endothermic metal ion reaction products can be generated and studied by FTMS. In order to support the bracketed value of Sc$\sp{+}$-benzene, photodissociation experiments were performed. In addition, a variety of M$\sp{+}$-benzene and M$\sp{+}$-benzene$\sb2$ bond strengths were determined by photodissociation. These results, which were well supported by ion-molecule reactions, suggested that photodissociation is a good technique for obtaining absolute metal ion-ligand bond strengths. Also, by determining the second benzene to metal bond strength, the effect of ligands on subsequent bonding by metal ions was found to be an interesting topic. The presence of the benzene ligand either had no effect on, or served to weaken, the bond between the metal ion and the second benzene ring. In order to elaborate on this, the effects of a benzene ligand on metal dimer bonding was studied next. The determination of various dimer ion-benzene bond strengths was made possible by the design and implementation of a dual pulsed valve system. As was the case for some of the metal benzene species studied, the presence of a benzene ligand on a metal dimer seems to slightly weaken the dimer bond. This may be due to charge delocalization by the benzene ring. Finally, the reactions of metal ions with a variety of polymers were studied. These preliminary experiments were the first reported reactions of transition metal ions with polymers and takes advantage of the utility of metal ions as chemical ionization reagents. These reactions yield a series of peaks that can be used to determine the repeating unit of the polymer, thus making these metal ions very important analytical tools.
Degree
Ph.D.
Advisors
Freiser, Purdue University.
Subject Area
Analytical chemistry
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