Chaoxian Chi

Infrared Photodissociation Spectroscopy of Mononuclear Iron Carbonyl Anions

The infrared photodissociation spectroscopy of mass-selected mononuclear iron carbonyl anions Fe(CO)(n)(-) (n = 2-8) were studied in the carbonyl stretching frequency region. The FeCO(-) anion does not fragment when excited with infrared light. Only a single IR active band was observed for the Fe(CO)(2)(-) and Fe(CO)(3)(-) anions, consistent with theoretical predictions that these complexes have linear D(∞h) and planar D(3h) symmetry, respectively. The Fe(CO)(4)(-) anion is the most intense peak in the mass spectra and was characterized to have a completed coordination sphere with high stability. Anion clusters larger than n = 4 were determined to involve a Fe(CO)(4)(-) core anion that is progressively solvated by external CO molecules. Three CO stretching vibrational fundamentals were observed for the Fe(CO)(4)(-) core anion, indicating that the Fe(CO)(4)(-) anion has a C(3v) structure. All the carbonyl stretching frequencies of the Fe(CO)(n)(-) anion complexes are red-shifted with respect to those of the corresponding neutrals.

Infrared photodissociation spectra of mass selected homoleptic dinuclear iron carbonyl cluster anions in the gas phase

Infrared spectra of mass-selected homoleptic dinuclear iron carbonyl cluster anions Fe2(CO)n− (n = 4–9) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The cluster anions are produced via a laser vaporization supersonic cluster source. Density functional calculations have been performed and the calculated vibrational spectra are compared to the experimental data to identify the gas-phase structures of the cluster anions. The experimentally observed Fe2(CO)n− (n = 4–7) cluster anions are characterized to have unusual asymmetric (OC)4Fe–Fe(CO)n−4 structures, which also correspond to the computed lowest energy structures. The experimentally observed Fe2(CO)8− cluster anion is determined to have an unbridged structure instead of the previously reported dibridged structure. The Fe2(CO)9− cluster anion is determined to involve a Fe2(CO)8− core anion that is solvated by an external CO molecule. Bonding analysis indicates that these anions each have a Fe–Fe single bond to satisfy the 18-electron configuration of one iron center. The results provide important new insight into the structure and bonding mechanisms of transition-metal carbonyl clusters.

Bonding in homoleptic iron carbonyl cluster cations: a combined infrared photodissociation spectroscopic and theoretical study

Infrared spectra of mass-selected homoleptic iron carbonyl cluster cations including mononuclear Fe(CO)5+ and Fe(CO)6+, dinuclear Fe2(CO)8+ and Fe2(CO)9+, and trinuclear Fe3(CO)12+ are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. Only one IR band is observed for the Fe(CO)5+ cation, which is predicted to have a C4v structure. The Fe(CO)6+ cation is determined to be a weakly bound complex involving a Fe(CO)5+ core ion. In contrast to neutral clusters which have symmetric structures with two and three bridging carbonyl ligands, the dinuclear Fe2(CO)8+ and Fe2(CO)9+ cations are characterized to have unbridged asymmetric (OC)5Fe–Fe(CO)n+ (n = 3 and 4) structures. The trinuclear Fe3(CO)12+ cluster cation is determined to have an open chain like (OC)5Fe–Fe(CO)2–Fe(CO)5 structure instead of the triangular structure with two bridging CO groups for the Fe3(CO)12 neutral. The di- and trinuclear cluster cations all involve a square pyramid like Fe(CO)5 building block that satisfies the 18-electron configuration of this iron center. The Fe(CO)5 building block is isolobal to the CH3 fragment in hydrocarbon chemistry, the Fe2(CO)9+ and Fe3(CO)12+ cluster cations may be considered through isolobality to be metal carbonyl analogues of the ethyl and isopropyl cations.

Infrared photodissociation spectroscopy of mass-selected heteronuclear iron-copper carbonyl cluster anions in the gas phase.

Mass-selected heteronuclear iron-copper carbonyl cluster anions CuFe(CO)n(-) (n = 4-7) are studied by infrared photodissociation spectroscopy in the carbonyl stretching frequency region in the gas phase. The cluster anions are produced via a laser vaporization supersonic cluster ion source. Their geometric structures are determined by comparison of the experimental spectra with those calculated by density functional theory. The experimentally observed CuFe(CO)n(-) (n = 4-7) cluster anions are characterized to have (OC)4Fe-Cu(CO)n-4 structures, each involving a C3v symmetry Fe(CO)4(-) building block. Bonding analysis indicates that the Fe-Cu bond in the CuFe(CO)n(-) (n = 4-7) cluster anions is a σ type single bond with the iron center possessing the most favored 18-electron configuration. The results provide important new insight into the structure and bonding of hetronuclear transition metal carbonyl cluster anions.

Infrared Photodissociation Spectroscopy of Mass-Selected Homoleptic Cobalt Carbonyl Cluster Cations in the Gas Phase

Infrared spectra of mass-selected homoleptic cobalt carbonyl cluster cations including dinuclear Co2(CO)8(+) and Co2(CO)9(+), trinuclear Co3(CO)10(+) and Co3(CO)11(+), as well as tetranuclear Co4(CO)12(+) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The geometric structures of these complexes are determined by comparison of the experimental spectra with those calculated by density functional theory. The Co2(CO)8(+) cation is characterized to have a Co-Co bonded structure with Cs symmetry involving a bridging CO ligand. The Co2(CO)9(+) cation is determined to be a mixture of the CO-tagged Co2(CO)8(+)-CO complex and the Co(CO)5(+)-Co(CO)4 ion-molecular complex. The Co3(CO)10(+) cation is the coordination-saturated trinuclear cluster, which is characterized to have a triangle Co3 core with C2 symmetry involving two edge-bridging and eight terminal CO ligands. The Co3(CO)11(+) cation is a weakly bound complex involving a Co3(CO)10(+) core ion. The Co4(CO)12(+) cluster cation is deduced to have a tetrahedral Co4(+) core structure with three edge-bridging and nine terminal carbonyls.

Electron Affinities of the Early Lanthanide Monoxide Molecules

The photoelectron imagings of LaO−, CeO−, PrO−, and NdO− at 1064 nm are reported. The well resolved photoelectron spectra allow the electron affinities to be determined as 0.99(1) eV for LaO, 1.00(1) eV for CeO, 1.00(1) eV for PrO, and 1.01(1) eV for NdO, respectively. Density functional calculations and natural atomic orbital analyses show that the 4f electrons tend to be localized and suffer little from the charge states of the molecules. The photodetached electron mainly originates from the 6s orbital of the metals. The ligand field theory with the δ=2 assumption is still an effective method to analyze the ground states of the neutral and anionic lanthanide monoxides.

Photoelectron Spectroscopy of C60Fn− and C60Fm2− (n = 17, 33, 35, 43, 45, 47; m = 34, 46) in the Gas Phase and the Generation and Characterization of C1-C60F47− and D2-C60F44 in Solution

A photoelectron spectroscopy investigation of the fluorofullerene anions C(60)F(n)(-) (n = 17, 33, 35, 43, 45, 47) and the doubly charged anions C(60)F(34)(2-) and C(60)F(46)(2-) is reported. The first electron affinities for the corresponding neutral molecules, C(60)F(n), were directly measured and were found to increase as n increased, reaching the extremely high value of 5.66 +/- 0.10 eV for C(60)F(47). Density functional calculations suggest that the experimentally observed species C(60)F(17)(-), C(60)F(35)(-), and C(60)F(47)(-) were each formed by reductive defluorination of the parent fluorofullerene, C(3v)-C(60)F(18), C(60)F(36) (a mixture of isomers), and D(3)-C(60)F(48), respectively, without rearrangement of the remaining fluorine atoms. The DFT-predicted stability of C(60)F(47)(-) was verified by its generation by chemical reduction from D(3)-C(60)F(48) in chloroform solution at 25 degrees C and its characterization by mass spectrometry and (19)F NMR spectroscopy. Further reductive defluorination of C(60)F(47)(-) in solution resulted in the selective generation of a new fluorofullerene, D(2)-C(60)F(44), which was also characterized by mass spectrometry and (19)F NMR spectroscopy.

Photoelectron Imaging of Ag―(H2O)x and AgOH―(H2O)y (x = 1,2, y = 0―4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.

Photoelectron Imaging of AgOCH3- and Ag-(CH3OH)(x) (x=1, 2)

The AgOCH3− and Ag−(CH3OH)x (x = 1, 2) anions are studied by photoelectron imaging as well as ab initio calculations. The adiabatic and vertical detachment energies (ADE and VDE) of AgOCH3− are determined as 1.29(2) and 1.34(2) eV, respectively, from the vibrational resolved photoelectron spectrum. The Ag−(CH3OH)1,2 anionic complexes are characterized as metal atomic anion solvated by the CH3OH molecules with the electron mainly localized on the metal. The photoelectron spectra of Ag−(CH3OH)x(x = 0, 1, 2) show a gradual increase in VDE with increasing x, due to the solvent stabilization. Evidence for the methanol-methanol hydrogen bonding interactions appears when the Ag− is solvated by two methanol molecules.