Spectroscopy and photochemistry of novel organometallic complexes

by 1978- Jaeger, Todd Dougals

Metal-benzene complexes of the form M+(benzene)n (M=Ti, V, Fe, Co, Ni) are produced in the gas phase using laser vaporization in a pulsed nozzle cluster source. Several different laser photodissociation techniques are used to elucidate structures, examine fragmentation patterns, and obtain vibrational spectra for investigation of trends in shifts of the ligand based vibrational modes. First, fixed frequency photodissociation at 532 nm and 355 nm is used to probe the photochemistry of several transition metal ion-benzene and cyclooctatetraene systems. Complexes with different metals follow different fragmentation pathways including simple ligand elimination, ligand decomposition, and photo-induced charge-transfer. Next, the vibrational spectra of several transition metal-ion benzene complexes are obtained in the 600 to 1700 cm -1 region via Infrared Resonance Enhanced Multiple-photon Photodissociation (IR- REMPD) spectroscopy with a free electron laser. Photodissociation of all complexes occurs by the elimination of intact neutral benzene molecules, and this process is enhanced on resonances in the vibrational spectrum, making it possible to measure vibrational spectra for size-selected complexes by monitoring fragment yield versus IR excitation wavelength. Finally, vibrational spectra for metal ion-benzene and metal ion-benzene-argon complexes are obtained by employing infrared photodissociation spectroscopy in the C-H stretch region (2700-3300 cm-1) using an Optical Parametric Oscillator/Amplifier (OPO/OPA). Density functional theory calculations are employed to investigate the structures, energetics and vibrational frequencies of these complexes. The comparison between experiment and theory provides fascinating new insight into the bonding in these prototypical organometallic complexes.