GAS PHASE CHEMISTRY AND PHOTOCHEMISTRY OF IONIC TRANSITION METAL COMPLEXES AND CLUSTERS BY FTMS: BOND ENERGY AND STRUCTURE DETERMINATIONS (PHOTODISSOCIATION, SPECTROSCOPY, FOURIER)

ROBERT LLOYD HETTICH, Purdue University

Abstract

Metal-ion ligand bond energies and reactivities have been investigated using Fourier transform mass spectrometry (FTMS). Specifically, photodissociation has been shown to provide both spectroscopic and thermodynamic information for organometallic ions. Collision-induced dissociation and ion-molecule reactions were also used to probe ionic structure. The reactions of Fe('+) and Co('+) with organoboron compounds were examined in an effort to investigate the nature of electropositive heteroatoms in organometallic reactions. Reaction mechanisms were explained on the basis of facile (beta)-hydrocarbon shifts from boron onto the metal ion. The effect that an alkene ligand has on the reactivity of Co('+) and Ni('+) was also examined. Co(alkene)('+) is very reactive in its secondary reactions whereas Ni(alkene)('+) is very unreactive. The photodissociation of MCH(,2)('+) for M = Fe, Co, Rh, La, and Nb, which yielded different fragmentation than that observed for the collision-induced dissociation of these ions, gave spectroscopic information and provided bond energies for M('+)-CH(,2), M('+)-CH, and M('+)-C. In general, photodissociation of organometallic ions and metal cluster ions (MFe('+)) was found to provide bond energies and thermodynamic information. Evidently these complexes have a large number of low-lying excited states, providing for thermodynamic, and not spectroscopic cutoffs. Isomer differentiation of organometallic ions by photodissociation was demonstrated by examining differences in cross sections, fragmentation products, and spectral band positions. Photodissociation was often observed to exhibit different dissociation than either ion-molecule reactions or collision-induced dissociation, thus providing complementary structural information. This report is one of the first comprehensive examinations of the photochemistry of gas phase organometallic ions. The studies have produced information which allow predictions to be made for the nature of the bonding in metal-ion ligand complexes.

Degree

Ph.D.

Subject Area

Analytical chemistry

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