Yuxiu Lei

Electronic states of neutral and cationic bis(benzene) titanium and vanadium sandwich complexes studied by pulsed field ionization electron spectroscopy

Ti- and V-bz2 (bz=C6H6) sandwich complexes have been prepared in a laser-ablation cluster beam source and studied by pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy and theoretical calculations. The ground electronic states of the neutral Ti- and V-bz2 complexes are determined to be 1A1g and 2A1g, and their ionization energies are measured to be 5.732+/-0.001 and 5.784+/-0.002 eV, respectively. These neutral complexes have eta6 binding and are in an eclipsed D6h configuration with flat benzene rings. Ionization of the 1A1g and 2A1g neutral states of Ti- and V-bz2 yields the 2B1g and 3B1g ion states, respectively, in a D2h point group with slightly puckered benzene rings. In addition, the binding and structures of these two complexes are compared with other first-row transition metal bis(benzene) sandwiches.

Metal coordination converts the tub-shaped cyclo-octatetraene into an aromatic molecule: Electronic states and half-sandwich structures of group III metal-cyclo-octatetraene complexes

Group III (Sc, Y, and La) metal-(1,3,5,7-cyclo-octatetraene) (COT) complexes were produced in a laser-vaporization molecular beam source and studied by pulsed-field-ionization zero-electron-kinetic-energy (ZEKE) spectroscopy. Adiabatic ionization energies and metal-ligand stretching frequencies were measured from the ZEKE spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the spectroscopic measurements with the molecular orbital treatment and density functional theory calculations. The ionization energies and metal-ligand stretching frequencies of these complexes are in the order of Sc>Y>La. The ground electronic state of the neutral complexes is A21, whereas the ground state of the ions is A11. The molecular symmetry is C8v in both neutral and ionic ground states. Although free COT is a nonaromatic molecule with a tublike structure, coordination of the group III metal atoms converts the tub-shaped molecule into a planar, aromatic ...

Pulsed-field ionization photoelectron and IR-UV resonant photoionization spectroscopy of Al-thymine

Al-thymine (Al-C(4)H(3)N(2)O(2)CH(3)) is produced by laser vaporization of a rod made of Al and thymine powders in a molecular beam and studied by single-photon pulsed-field ionization-zero electron kinetic energy (ZEKE) photoelectron and IR-UV resonant two-photon ionization spectroscopy and density functional theory calculations. The ZEKE experiment determines the adiabatic ionization energy of the neutral complex and 22 vibrational modes for the corresponding ion with frequencies below 2000 cm(-1). The IR-UV photoionization experiment measures two N-H and three C-H stretches for the neutral species. The theoretical calculations predict a number of low-energy isomers with Al binding to single oxygen or adjacent oxygen and nitrogen atoms of thymine. Among these isomers, the structure with Al binding to the O4 atom of the diketo tautomer is predicted to be the most stable one by the theory and is probed by both ZEKE and IR-UV measurements. This work presents the first application of the IR-UV resonant ionization to metal-organic molecule systems. Like ZEKE spectroscopy, the IR-UV photoionization technique is sensitive for identifying isomeric structures of metal association complexes.

Ring Deformation and π-Electron Redistribution of Methylbenzenes Induced by Metal Coordination

Scandium (Sc) complexes of p-xylene, mesitylene, and hexamethylbenzene were produced in a laser-vaporization molecular beam source and studied with pulsed-field-ionization zero-electron-kinetic-energy spectroscopy, and density functional theory. In addition, infrared-ultraviolet resonant two-photon ionization spectra were recorded for Sc(hexamethylbenzene) in the C-H stretching region. Adiabatic ionization energies and several vibrational frequencies of these complexes were obtained from the spectroscopic measurements, and electronic transitions were determined by combining the spectra with the theoretical data. The ionization energies of the three complexes decrease with increasing number of the methyl groups, whereas the metal-ligand stretching frequencies of the p-xylene and mesitylene complexes are essentially the same and slightly smaller than that of the hexamethylbenzene species. Unlike benzene, the arene ring of the methylbenzene molecules is bent and the pi-electrons are localized in a 1,4-diene fashion upon Sc coordination. The distortion of the aromatic ring is due to differential metal binding with the ring carbon atoms in the low-spin ground electronic state.

Electron Spin Multiplicities of Transition-Metal Aromatic Radicals and Ions: M[C6(CH3)6] and M+[(C6(CH3)6] (M = Ti, V, and Co)

Determination of electron spin multiplicities of transition-metal radicals and ions challenges both experimentalists and theoreticians. In this work, we report preferred electron spin states of M[C(6)(CH(3))(6)] and M(+)(C(6)(CH(3))(6)], where M = Ti, V, and Co. The neutral radicals were formed in a supersonic metal cluster beam source, and their masses were measured with time-of-flight mass spectrometry. Precise ionization energies of the radicals and metal-ligand stretching frequencies of the ions were measured by pulsed field ionization zero electron kinetic energy spectroscopy. C-H stretching frequencies of the methyl group in the radicals were obtained by infrared-ultraviolet two-photon ionization. Electron spin multiplicities of the radicals and ions were investigated by combining the spectroscopic measurements, density functional theory, and Franck-Condon factor calculations. The preferred spin states are quintet, sextet, and quartet for the neutral Ti, V, and Co radicals, respectively; for the corresponding singly charged cations, they are quartet, quintet, and triplet. In these high-spin states, the aromatic ring remains nearly planar. This finding contrasts to the previous study of Sc(hmbz), for which low-spin states are favored, and the aromatic ring is severely bent.