G.A. Grieves

NOVEL MIXED LIGAND SANDWICH COMPLEXES : COMPETITIVE BINDING OF IRON WITH BENZENE, CORONENE, AND C60

Abstract Organometallic complexes of iron with benzene, coronene and C60 are produced in a molecular beam and studied with time-of-flight mass spectrometry and laser photodissociation. The cation complexes are produced in a pulsed nozzle laser vaporization source using an iron rod coated with a sublimed film of coronene and/or C60. Benzene is seeded in the expansion gas. Masses of the form [Ax–Fe–By]+ are observed when A and B are benzene, coronene, or C60, taken any two at a time. Masses are observed for all combinations where x + y = 1 or 2, indicating the formation of monoligand and sandwich complexes. Mixed-ligand sandwiches form with comparable abundance to homoligand sandwiches. Mass-selected photodissociation probes the relative bonding strengths in these new species.

Generation of "unstable" doubly charged metal ion complexes in a laser vaporization cluster source

Doubly charged metal ion complexes of the form M 2+ (L)n are generated using a laser vaporization cluster source in conjunction with a time-of-flight mass spectrometer. Contrary to expectations, a variety of doubly charged species are produced with this source, including many so-called “unstable” or “metastable” ions in which the metal has a second ionization potential greater than the first ionization potential of the ligand or solvent. The species identified include Mg 2+ (CO2)n ,M g 2+ (H2O), Mg 2+ (Ar)n ,C o 2+ (Ar)n ,C o 2+ (H2O), Si 2+ (Ar)n and Ti 2+ (CO2)n. This is apparently the first observation by any means of Co 2+ (Ar)n ,T i 2+ (CO2)n and Si 2+ (Ar)n. Of the complexes studied, only the “stable” species Mg 2+ (Ar)n have been generated previously by laser vaporization. The conditions necessary for the production of these ions are investigated and possible mechanisms for their growth are suggested. Charge-transfer photodissociation is observed for Co 2+ (Ar) complexes.

Growth dynamics and intracluster reactions in Ni+(CO2)n complexes via infrared spectroscopy

Ni(+)(CO(2))(n), Ni(+)(CO(2))(n)Ar, Ni(+)(CO(2))(n)Ne, and Ni(+)(O(2))(CO(2))(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO(2) molecules from Ni(+)(CO(2))(n) and Ni(+)(O(2))(CO(2))(n) complexes, and by elimination of the noble gas atom from Ni(+)(CO(2))(n)Ar and Ni(+)(CO(2))(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO(2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO(2), consistent with structures having linear Ni(+)-O=C=O configurations. Fragmentation of larger Ni(+)(CO(2))(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for n> or =5. These combined observations indicate that the coordination number for CO(2) molecules around Ni(+) is exactly four. Trends in the loss channels and spectra of Ni(+)(O(2))(CO(2))(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni(+)(CO(2))(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product.

Photodissociation of exohedral transition metal–C60 complexes

Abstract Laser ablation/vaporization of solid metal samples coated with thin films of C60 is employed in a pulsed-nozzle cluster source to produce various transition metal–C60 complexes. Mass spectra contain species of the form Mx(C60)y, where x = 1–5 and y = 1,2. Mass-selected photodissociation studies investigate the structural and bonding properties of these complexes. Photodissociation shows primarily the elimination of metal in all complexes, demonstrating that the complexes are exohedral. Atomic and molecular desorption of metal are observed in different situations, suggesting that these complexes have metal dispersed to some degree as “films” on the fullerene surface. Some clusters fragment by loss of metal carbides (e.g. C59Fe+, V3C4+), indicating insertion of metal into the fullerene cage wall. Keywords: Clusters; Metallo-fullerenes; Photodissociation

Photodissociation of silver–coronene cluster cations

Abstract Gas phase complexes of coronene and silver are produced in a molecular beam and studied with time-of-flight mass spectrometry and laser photodissociation. The cation complexes are produced in a pulsed nozzle laser vaporization cluster source using a silver rod coated with a sublimed film of coronene. Cluster masses of the form Agx–(cor)y+ are observed for x = 0, 1, 2 and y = 1–3. Mass-selected photodissociation experiments probe the structure and bonding in these new cluster species. These studies demonstrate that silver binds weakly to coronene and that cation clusters of pure coronene have substantial stability.

Growth dynamics and intracluster reactions in Ni{sup +}(CO{sub 2}){sub n} complexes via infrared spectroscopy

Ni(+)(CO(2))(n), Ni(+)(CO(2))(n)Ar, Ni(+)(CO(2))(n)Ne, and Ni(+)(O(2))(CO(2))(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO(2) molecules from Ni(+)(CO(2))(n) and Ni(+)(O(2))(CO(2))(n) complexes, and by elimination of the noble gas atom from Ni(+)(CO(2))(n)Ar and Ni(+)(CO(2))(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO(2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO(2), consistent with structures having linear Ni(+)-O=C=O configurations. Fragmentation of larger Ni(+)(CO(2))(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for n> or =5. These combined observations indicate that the coordination number for CO(2) molecules around Ni(+) is exactly four. Trends in the loss channels and spectra of Ni(+)(O(2))(CO(2))(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni(+)(CO(2))(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product.

Growth Dynamics and Intracluster Reactions in Ni + (CO 2 ) n via infrared spectroscopy

Ni(+)(CO(2))(n), Ni(+)(CO(2))(n)Ar, Ni(+)(CO(2))(n)Ne, and Ni(+)(O(2))(CO(2))(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO(2) molecules from Ni(+)(CO(2))(n) and Ni(+)(O(2))(CO(2))(n) complexes, and by elimination of the noble gas atom from Ni(+)(CO(2))(n)Ar and Ni(+)(CO(2))(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO(2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO(2), consistent with structures having linear Ni(+)-O=C=O configurations. Fragmentation of larger Ni(+)(CO(2))(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for n> or =5. These combined observations indicate that the coordination number for CO(2) molecules around Ni(+) is exactly four. Trends in the loss channels and spectra of Ni(+)(O(2))(CO(2))(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni(+)(CO(2))(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product.