Gas-phase reactivity and bond energy determinations of metal cation complexes using Fourier transform mass spectrometry
Abstract
Gas-phase chemistry of metal cation-ligand complexes have been investigated using Fourier transform mass spectrometry (FTMS). Techniques used for the determination of metal ion-ligand bond energies include collision-induced dissociation, photodissociation, and the determination of equilibrium constants by both steady-state and kinetic methods. The reactions of CuFe$\sp+$ and YFe$\sp+$ with small hydrocarbons were investigated as part of an ongoing study of metal dimer ions in our laboratory. Both CuFe$\sp+$ and YFe$\sp+$ are unreactive with linear and cyclic alkanes up to C$\sb7$. However, reactions with alkenes are dominated by multiple dehydrogenations with C-C bond cleavage observed only in a couple of cases. Secondary reactions of CuFe(alkadiene)$\sp+$ with alkenes reveal an enhancement in reactivity towards further dehydrogenation. The bond energy of Cu$\sp+$-Fe was also determined to be 53 $\pm$ 7 kcal/mol. Bond energies were determined for twelve oxygenated compounds to Mg$\sp+$. Relative bond energies were assigned from the determination of equilibrium constants by both kinetic and steady-state methods. Competitive collision-induced dissociation was also used to determine ordering. Absolute bond energies were assigned from both photodissociation and relative bond energy results. Correlations are also made to several other metal cation bond energies. Thermochemical properties of gas-phase MgOH and MgO were determined by reactivity and photodissociation studies. Charge transfer reactions yielded IP(MgO) = 7.9 $\pm$ 0.1 eV, while photodissociation yielded D$\sp{\rm o}$(Mg$\sp+$-OH) = 75 $\pm$ 4 kcal/mol, D$\sp{\rm o}$(Mg$\sp+$-O) = 54 $\pm$ 5 kcal/mol, and IP(MgOH) = 7.48 $\pm$ 0.1 eV. These values were used to determine other thermochemical information for MgOH and MgO. Other techniques have yielded experimental values for the bond dissociation energy of Mg-O which appear high compared to this work, perhaps due to sample impurities. However, our results agree well with a recent theoretical value for D$\sp{\rm o}$(Mg-O).
Degree
Ph.D.
Advisors
Freiser, Purdue University.
Subject Area
Analytical chemistry
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